Implementation of the Hydraulic Fracture Test at MnDOT · 2008. 12. 9. · Preparation and testing...

Implementation of theHydraulic Fracture Test at MnDOT

-Final Report-

by

Mark B. Snyder, Engineering Consultant

prepared for

The Minnesota Department of TransportationTransportation Building, Mail Stop 680

395 John Ireland BoulevardSt. Paul, Minnesota 55155

June 23, 2005

ACKNOWLEDGMENTS

The author would like to express his appreciation to the Minnesota Department ofTransportation (MnDOT) for its financial and technical support of the implementation effortdescribed herein.

Special thanks are offered to Rebecca Embacher, Bernard Izevbekhai and Douglas Schwartz fortheir technical support and guidance in the conduct of this effort.

The author also thanks Daniel Squires for his enthusiastic assistance in preparing the lab for (andhelping with) the apparatus set up, and Kevin Rosaasen for his help in fabricating a test stand andmaking several minor modifications to the test equipment to improve their function.

The author also acknowledges the contributions of Dr. Donald Janssen of the University ofWashington Department of Civil Engineering, the original developer of the hydraulic fracturetest concept for assessing concrete aggregate freeze-thaw durability.

TABLE OF CONTENTSPage

Background and Summary of Previous Work............................................................................1Expected Users and Benefits of the HFT .....................................................................................1Project Work Task Descriptions and Products...........................................................................1

Task 1: Develop a Specification for Using the HFT............................................................2Task 2: Assemble and Set Up HFT Test Apparatus ............................................................2Task 3: Program MnDOT’s Equipment for Determining HFT Release Rates....................2Task 4: Calibrate the Small and Large HFT Apparatus.......................................................4Task 5: Develop Test Protocol Documents .........................................................................4Task 6: Create a Framework for a Database of HFT Test Results ......................................4Task 7: Document Procedures for

Developing a Large Chamber Dilation Prediction Model .......................................7Task 8: Train MnDOT Personnel ........................................................................................7Task 9: Final Report.............................................................................................................8

Conclusions and Recommendations .............................................................................................8

References ..................................................................................................................................8

APPENDICIES

Appendix A – Standard Test Method for Hydraulic Fracture of Coarse Aggregatefor Portland Cement Concrete

Appendix B – Hydraulic Fracture Test Protocol

Appendix C – Procedures for Developing Dilation Prediction Modelsfor Alternate Pressure Chambers or Alternate Freeze-Thaw Tests

LIST OF FIGURES

Figure 1. Photo of large chamber set up in MnDOT concrete lab. ............................................3

Figure 2. Photo of small chamber set up in MnDOT concrete lab.............................................3

Figure 3. HFT data collection form............................................................................................5

Figure 4. Example screen print from HFT data entry and analysis spreadsheet. .......................6

Figure A1. HFT apparatus calibration target pressure release rate curve. ............................. A-10

Figure A2. Example plot of pressure release rate profiles

for various actuator pressure settings................................................................... A-11

Figure B1. Photos of large chamber cylinder assembly............................................................B-1

Figure B2. Photos of chamber pressure regulator and gages (left) and actuator pressure

regulator and gages (right). .....................................................................................B-2

Figure B3. Photo of large chamber with drain line attached to quick connect fitting. .............B-3

Figure B4. Large chamber fill valve assembly. ........................................................................B-3

Figure B5. Photos of small chamber cylinder assembly (top plate removed) and stand. .........B-5

Figure B6. Small chamber fill valve assembly. ........................................................................B-7

Figure B7. Photo of small chamber pressurization and drain assemblies.................................B-7

Figure B8. Photo of drain valve assembly, including drain tube on inside of chamber. ..........B-8

Figure B9. Aggregate washer and oven in MnDOT concrete lab.............................................B-9

Figure B10. Photos of double boiler and silane under MnDOT fume hood and treated sample

draining in double boiler. ......................................................................................B-10

Figure B11. Photos of typical aggregate tumbler with sample in drum (left) and large tumbler in

MnDOT lab (right)................................................................................................B-10

Figure B12. Assembly of large chamber bottom plate and fill with aggregate sample, including

strike-off. ...............................................................................................................B-12

Figure B13. Removal of large chamber assembly pins and tightening of assembly bolts. ......B-13

Figure B14. Small chamber, ready to be filled with aggregate sample. ...................................B-14

Figure B15. Tightening of small chamber assembly bolts........................................................B-15

Figure B16. Connecting the drain/overflow line (left) and opening the fill valve (right). .......B-16

Figure B17. Removing trapped air bubbles using rubber mallet. .............................................B-16

Figure B18. Pressurization of chamber (left) and installation of muffler (right)......................B-17

Figure B19. Pressure release operation: close pressure isolation valve,

then flip electric switch. ........................................................................................B-18

Figure B20. Opening the large chamber drain valve. ...............................................................B-18

Figure B21. Attaching the fill overflow line (left) and opening the fill valve (right). ..............B-20

Figure B22. Dislodging attached air bubbles from the inside of the small chamber. ...............B-21

Figure B23. Closing the pressure release valve and fill valve (left) and removing the fill

overflow line (right). .............................................................................................B-21

Figure B24. Closing the pressure release valve and fill valve (left) and removing the fill

overflow line (right). .............................................................................................B-22

Figure B25. Release of pressure from small chamber by closing pressure isolation valve, then

flipping electric switch. .........................................................................................B-23

Figure B26. Removing water from small chamber by closing pressure release valve and nitrogen

bottle valve, opening drain valve and slowly opening pressure isolation valve. ..B-23

Figure B27. HFT data collection form......................................................................................B-26

Figure B28. HFT apparatus calibration target pressure release rate curve. ..............................B-28

Figure B29. Connecting pressure transducer to dynamic signal analyzer. ...............................B-29

Figure B30. Example plot of pressure release rate profiles

for various actuator pressure settings....................................................................B-30

LIST OF TABLES

Table A1. HFT Apparatus Calibration Target Pressure Release Rate Data. ........................ A-10

Table B1. HFT Apparatus Calibration Target Pressure Release Rate Data Table . ..............B-27

Table C1. Summary of aggregate sources used in U of Mn study (including their locations and

freeze-thaw durability factors) . ..............................................................................C-3

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Background and Summary of Previous Work“D”-cracking and other forms of aggregate-related freeze-thaw damage have often beenassociated with concrete pavements in Minnesota. The best approach for preventing these typesof distress is to avoid using aggregate sources that are known to be susceptible to freeze-thawdamage in concrete applications.

The most widely accepted methods of evaluating aggregate freeze-thaw durabilityinvolve the preparation and freeze-thaw testing of concrete beams that contain the aggregate inquestion. These tests are generally time-consuming, sometimes requiring months to complete,and often require the use of expensive equipment and/or highly skilled operators. Furthermore,the variable nature of many aggregate sources necessitates frequent testing to ensure theadequate freeze-thaw resistance of material being produced at any given point in time.

A more rapid test of aggregate freeze-thaw durability was developed under the StrategicHighway Research Program in 1994. This test, called the Washington Hydraulic Fracture test(WHFT), was relatively inexpensive and allowed a single laboratory technician to assess thefreeze-thaw durability of several samples of aggregate in as few as seven working days. Broaderevaluations of the WHFT revealed several deficiencies, however.

Subsequent research studies were performed between 1996 and 2002 at Michigan StateUniversity and the University of Minnesota for the Michigan Department of Transportation(MDOT) and Mn/DOT, respectively. These efforts resulted in the refinement and validation ofthe test procedures and apparatus using Minnesota aggregates. The most significantimprovements included the modification of the test apparatus and procedures, and thereplacement of the “hydraulic fracture index” with a model that predicts ASTM C 666 freeze-thaw test dilation as a function of the distribution of particle mass retained on various sieves afterhydraulic fracture testing. These changes greatly improved the efficiency and accuracy of thetest. In addition, a large test chamber was developed to allow the testing of aggregate samplesfive times larger than those tested in the original small chamber, thereby allowing aggregatedurability characterization of one representative sample with a single test run.

It is believed that the hydraulic fracture test is now ready for implementation inMinnesota as an accurate screening tool for concrete aggregate freeze-thaw durability.

Expected Benefits and Users of the HFTThe implementation effort performed under this contract provides Mn/DOT with the abilityto rapidly and accurately evaluate the freeze-thaw durability of coarse aggregate sourcesintended for use in Portland cement concrete applications. This will aid in increasing theutilization of existing aggregate sources that are not currently accepted for concreteaggregate production, while ensuring acceptable freeze-thaw durability and performancepotential. In the context of the decreasing availability of suitable concrete aggregatesources, the ability to make better use of existing local aggregate sources will forestallexpected increases in aggregate costs that will result from transportation over increasinglygreat distances.

Project Work Task Descriptions and ProductsThis project included nine work tasks. Descriptions of these task activities and the resultingdeliverables are provided below.

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Task 1: Develop a Specification for Using the HFTThe original goal of this task was to document standard sampling and testing procedures andacceptance/rejection criteria for use by Contractors and Mn/DOT, thereby helping to ensureconsistent test results among operators and between test apparatus. The specification was toprovide a detailed description of the required test equipment and procedures, including (but notlimited to):

Sampling of coarse aggregate (e.g., details concerning the requirements for test samplenumbers, sizes, retrieval locations and handling).

Sample submittal details (e.g., sample handling and labeling, lead time required prior topaving for source approval).

Preparation and testing of the aggregate sample (including sample size reduction, pre-testtreatments and all test procedural details).

Acceptance / Rejection criteria based on percent dilation per 100 cycles. Number of test results upon which the acceptance / rejection criteria are to be based.As the project progressed, it became clear that there was potential overlap between the

content of this proposed specification and the test protocol being developed under Task 5. It wasdecided that MnDOT would be better served by developing the Task 1 specification with acontent and format that closely matched that of a standard ASTM or AASHTO specification.The resulting specification, provided in Appendix A, defines appropriate parameters for testequipment and operations in a general sense that should allow the development and use ofimproved or modified equipment. In other words, the specification is intended to ensure thatvarious users of generic hydraulic fracture test equipment produce comparable test results.

Step-by-step instructions specific to the use of the current MnDOT test apparatus areprovided in the Appendix B Test Protocol.

Task 2: Assemble and Set Up HFT Test ApparatusThe scope of this task was to assemble and set up one small chamber (2-in inside height, 10-ininside diameter) and one large chamber (10-in inside height, 10-in inside diameter) hydraulicfracture test apparatus using equipment available Minnesota Department of TransportationOffice of Materials laboratory.

This task was accomplished with the help and assistance of MnDOT staff. Figures 1 and2 are photos of the assembled apparatus in the MnDOT Concrete Testing Lab.

Task 3: Program MnDOT’s Equipment for Determining HFT Release RatesThe goal of this task was to program MnDOT’s existing dynamic signal analyzer (a Hewlett-Packard model 35565) and computer equipment for use in determining HFT chamber pressurerelease rates (for test chamber calibration and monitoring procedures). This was necessarybecause MnDOT’s signal analyzer is of a different brand and requires different softwareprogramming than those used under previous research efforts.

This goal was accomplished with the development of two tools: 1) a file containing thecorrect settings for the signal analyzer (HFT.STA), and 2) a spreadsheet (CALIBRATE.XLS)that automatically produces a calibration comparison plot when the user enters pressure releasedata obtained from signal analyzer.

These software tools were provided (on a CD) to the MnDOT project technical liaison.

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Figure 1. Photo of large chamber set up in MnDOT concrete lab.

Figure 2. Photo of small chamber set up in MnDOT concrete lab.

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Task 4: Calibrate the Small and Large HFT ApparatusThe goal of this task was to calibrate the small and large chambers by determining anddocumenting actuator and chamber pressures that consistently produce pressure release rates thatmatch those of the target data.

This was accomplished with the following results:Small chamber settings: Chamber pressure = 1150 psi, Actuator pressure = 155 psiLarge chamber settings: Chamber pressure = 1300 psi, Actuator pressure = 240 psi

Task 5: Develop Test Protocol DocumentsThe goal of this task was to develop test protocol documents to provide MnDOT personnel withcomplete “plain language” details (to supplement the specifications developed in Task 1)describing how tests and calibrations should be performed.

This was accomplished and the resulting document is presented in Appendix B.A data collection/reporting form was developed using Excel and is shown in figure 3.

The file used to produce this form is called “HFT Data Collection Form.xls” and is contained onthe project CD that was provided to the MnDOT Technical Liaison.

A spreadsheet was also developed to allow operators to enter data collected using theabove form and automatically calculate predicted dilation per 100 cycles of freezing and thawing(using ASTM C 666 Procedure B modified with cloth wraps). A screen print of this spreadsheetis provided in figure 4 and the file (called “HFT Data Entry and Analysis.xls”) is contained onthe project CD that was provided to the MnDOT Technical Liaison.

Task 6: Create a Framework for a Database of HFT Test ResultsThe creation of a well-designed database is essential for monitoring aggregate source durabilityover time. Database trends can also be used to identify possible systematic problems withconsistency between operators or equipment calibration, so a functional database will beessential to the successful implementation of the HFT at MnDOT.

With this in mind, the original goal of this task was to create a framework for establishinga database of hydraulic fracture test results (e.g., field names), and the engineering consultantwas to assist Mn/DOT personnel in developing suitable data reporting forms and an ORACLEtable for storing HFT test data.

As the project progressed, MnDOT’s Technical Liaison determined that MnDOT’sdatabase needs might be better served in the short term with an Excel spreadsheet rather than anOracle database. A file called “HFT Database.xls” was created and is contained on the projectCD that was provided to the MnDOT Technical Liaison. Data entry columns in this spreadsheetinclude:

MnDOT Source DesignationSource Common NameArea or Ledge

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HFT Data Collection Sheet

Replicate Number 1 2 3 4 5Silane Treatment DateInitial Mass, g

Test Date: Test Date:M3/4" (ret), g M3/4" (ret), gM5/8" (ret), g M5/8" (ret), g

M1/2" (ret), g M1/2" (ret), gM3/8" (ret), g M3/8" (ret), g


M#4 (ret), g M#4 (ret), gMpan, g Mpan, gMass Check: Mass Check:Test Date: Test Date:M3/4" (ret), g M3/4" (ret), g



M1/4" (ret), g M1/4" (ret), gM#4 (ret), g M#4 (ret), gMpan, g Mpan, g

Mass Check: Mass Check:Test Date:

M3/4" (ret), g Source: Submitted by:M5/8" (ret), g

M1/2" (ret), g Date Rec'd: Carbonate Content (%):M3/8" (ret), g

M5/16" (ret), g Test Technician: Equip No:M1/4" (ret), g

M#4 (ret), g Chamber Pressure (psi): Solonoid Press. (psi):Mpan, g

Mass Check: Comments:

10 Cycles

20 Cycles

30 Cycles

40 Cycles

50 Cycles

Figure 3. HFT data collection form.

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HFT Data Entry and Analysis Sheet

Replicate Number 1 2 3 4 5 CombinedSilane Treatment Date 06/10/05 06/13/05 06/14/05 06/15/05 06/16/05Initial Mass, g 3059.2 3067.6 2668.4 2907.2 3019.9 14722.3

Test Date: 06/13/05 06/14/05 06/15/05 06/16/05 06/17/05 Comb M RetM3/4" (ret), g 2691.7 2835.7 2448.4 2617.1 2554.2 13147.1M5/8" (ret), g 203.8 89.4 170.2 228.8 416.8 1109.0M1/2" (ret), g 46.0 43.2 7.6 5.1 0.0 101.9

M3/8" (ret), g 32.9 34.1 6.9 9.6 3.5 87.0M5/16" (ret), g 11.5 5.9 0.0 1.2 0.0 18.6M1/4" (ret), g 11.0 8.3 2.1 3.5 0.5 25.4M#4 (ret), g 6.1 6.2 1.3 1.2 0.6 15.4Mpan, g 33.9 29.8 20.1 21.7 23.9 129.4Mass Check: 3036.9 3052.6 2656.6 2888.2 2975.6 14633.8Test Date: 06/14/05 06/15/05 06/16/05 06/17/05 06/20/05 Comb M RetM3/4" (ret), g 2691.7 2835.7 2448.4 2617.1 2554.2 13147.1M5/8" (ret), g 203.8 89.4 170.2 228.8 416.8 1109.0M1/2" (ret), g 46.0 43.2 7.6 5.1 0.0 101.9M3/8" (ret), g 32.9 34.1 6.9 9.6 3.5 87.0M5/16" (ret), g 11.5 5.9 0.0 1.2 0.0 18.6

M1/4" (ret), g 11.0 8.3 2.1 3.5 0.5 25.4M#4 (ret), g 6.1 6.2 1.3 1.2 0.6 15.4Mpan, g 33.9 29.8 20.1 21.7 23.9 129.4Mass Check: 3036.9 3052.6 2656.6 2888.2 2975.6 14633.8Test Date: 06/15/05 06/16/05 06/17/05 06/20/05 06/21/05 Comb M RetM3/4" (ret), g 2691.7 2835.7 2448.4 2617.1 2554.2 13147.1M5/8" (ret), g 203.8 89.4 170.2 228.8 416.8 1109.0M1/2" (ret), g 46.0 43.2 7.6 5.1 0.0 101.9

M3/8" (ret), g 32.9 34.1 6.9 9.6 3.5 87.0M5/16" (ret), g 11.5 5.9 0.0 1.2 0.0 18.6M1/4" (ret), g 11.0 8.3 2.1 3.5 0.5 25.4M#4 (ret), g 6.1 6.2 1.3 1.2 0.6 15.4Mpan, g 33.9 29.8 20.1 21.7 23.9 129.4Mass Check: 3036.9 3052.6 2656.6 2888.2 2975.6 14633.8Test Date: 06/16/05 06/17/05 06/20/05 06/21/05 06/22/05 Comb M RetM3/4" (ret), g 2691.7 2835.7 2448.4 2617.1 2554.2 13147.1

M5/8" (ret), g 203.8 89.4 170.2 228.8 416.8 1109.0M1/2" (ret), g 46.0 43.2 7.6 5.1 0.0 101.9M3/8" (ret), g 32.9 34.1 6.9 9.6 3.5 87.0M5/16" (ret), g 11.5 5.9 0.0 1.2 0.0 18.6M1/4" (ret), g 11.0 8.3 2.1 3.5 0.5 25.4M#4 (ret), g 6.1 6.2 1.3 1.2 0.6 15.4Mpan, g 33.9 29.8 20.1 21.7 23.9 129.4Mass Check: 3036.9 3052.6 2656.6 2888.2 2975.6 14633.8Test Date: 06/17/05 06/20/05 06/21/05 06/22/05 06/23/05 Comb M RetM3/4" (ret), g 2691.7 2835.7 2448.4 2617.1 2554.2 13147.1M5/8" (ret), g 203.8 89.4 170.2 228.8 416.8 1109.0M1/2" (ret), g 46.0 43.2 7.6 5.1 0.0 101.9M3/8" (ret), g 32.9 34.1 6.9 9.6 3.5 87.0M5/16" (ret), g 11.5 5.9 0.0 1.2 0.0 18.6M1/4" (ret), g 11.0 8.3 2.1 3.5 0.5 25.4

M#4 (ret), g 6.1 6.2 1.3 1.2 0.6 15.4Mpan, g 33.9 29.8 20.1 21.7 23.9 129.4Mass Check: 3036.9 3052.6 2656.6 2888.2 2975.6 14633.8

Predicted Dilation/100 cycles 0.009 0.008 0.008 0.009 0.008 0.008

Source: Submitted by: Date Rec'd:

Carbonate Content (%): 100

Test Technician: Equip No:

Chamber Pressure (psi): Solonoid Press. (psi):

10 Cycles

20 Cycles

16-Jun-05

Tech 1

30 Cycles

40 Cycles

50 Cycles

1150

Small 1

155

Example 1 Quarry A

Figure 4. Example screen print from HFT data entry and analysis spreadsheet.

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HFT Test DataTest Start DateTest OperatorPredicted Dilation/100 cycles (%)

Absorption CapacityTest DateAbsorption Capacity (%)

Petrographic ExaminationExamination DateCarbonate Content (%)

ASTM C 88 (Magnesium Sulfate) Test DataTest DateMass Loss

ASTM C 666 (Rapid Freezing and Thawing) Test DataTest Start DateTest Procedure (A, B, etc.)Testing LabNumber of Specimens TestedAverage Durability FactorAverage Dilation/100 cycles (%)Average Mass Loss (%)14-day Compressive Strength (psi)14-day Elastic Modulus (ksi)

Task 7: Document Procedures for Developing a Large Chamber Dilation Prediction ModelOnly a few aggregate sources have been tested using the modified large HFT chamber4. Whilethe dilation prediction model should be good for any properly calibrated test chamber, it wouldbe good practice to verify this fact and, if necessary, modify the dilation prediction model so thatit provides the highest possible accuracy when using data obtained from the large chamber.

Furthermore, it was determined that it would be most useful if guidance was provided toallow for the development of durability prediction models for other test chamber configurationsand other durability test results (e.g., durability factor or dilation performed in accordance withASTM C 666 Procedure A or B).

Therefore, while the original goal of this task was to document procedures for developinga large chamber dilation prediction model, the final goal became to document procedures fordeveloping durability prediction models for situations where either the durability measure isdifferent from the one currently used and/or when any chamber other than the original smallchamber is used or modified.

This was accomplished and the resulting procedures are documented in Appendix C ofthis report.

Task 8: Train MnDOT PersonnelThe goal of this task was to train Mn/DOT personnel to use the small and large HF chambers.This was accomplished through the delivery of a 2-hour presentation on the test development andconduct (made to more than 30 MnDOT staff engineers and technicians, along with several

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interested industry representatives), followed by a half week of hands-on training for a group of4 engineers and technicians to ensure the proper and consistent implementation of the HFT test.

Training included all aspects of test apparatus management, operation and repair, as wellas evaluation of test results and completion of test reporting and data storage documents.

The powerpoint files used for the presentations to MnDOT staff are titled “MnDOT HFTOrientation” and “MnDOT HFT Training” and they are included on the CD that was provided tothe MnDOT technical liaison.

In addition, a full day was spent filming a DVD video of both the presentations andactual operation of the test equipment in the lab. Copies of the DVD video should be availablefrom MnDOT’s Office of Communication and Workforce Development.

Task 9: Final ReportThe goal of this task was to assemble and organize all of the documents prepared under tasks 1through 8 into a single document that describes the entire implementation effort. This report isthat document.

Conclusions and RecommendationsThe Hydraulic Fracture Test equipment (both large and small chambers) were successfullyinstalled in the MnDOT Concrete Laboratory, MnDOT staff have been trained in the use of theequipment, and supporting documents and software have been developed. Everything is in placeto initiate a full implementation of the test using the small chamber, and procedures are availableto validate the large chamber or develop a new model for the large chamber.

It is recommended that MnDOT begin to collect and test aggregate samples using the HFapparatus and freeze-thaw tests (at the same time as standard sulfate soundness tests areperformed). It will be necessary to either adopt the same freeze-thaw test procedure that wasused during the University of Minnesota study, or to adopt an existing standard (e.g., AASHTOT161 Procedure A or B) for all future tests.

When sufficient HF and freeze-thaw data have been collected to validate the existingmodel (or develop a new model) for the large chamber, the HF test should be fully implementedwith periodic checks of continued model accuracy when compared to the results of freeze-thawtests.

References

1. D. J. Janssen and M. B. Snyder, SHRP C-391: Resistance of Concrete to Freezing andThawing (Washington, DC: Transportation Research Board, 1994).2. M. B. Snyder, D. J. Janssen and W. Hansen, Adoption of a Rapid Test for DeterminingAggregate Durability in Portland Cement Concrete (Ann Arbor, MI: University of MichiganDepartment of Civil Engineering, 1996).3. J. J. Hietpas, Refinement and Validation of the Washington Hydraulic Fracture Test(Minneapolis, MN: University of Minnesota Department of Civil Engineering, 1998).4. R. A. Embacher and M. B. Snyder, Refinement and Validation of the Hydraulic FractureTest (St. Paul, MN: Minnesota Department of Transportation, 2003).

APPENDIX A

Standard Test Method forHydraulic Fracture of Coarse Aggregate for Portland Cement Concrete

A-1

Standard Test Method forHydraulic Fracture of Coarse Aggregate for Portland Cement Concrete(draft prepared for MnDOT by Mark B. Snyder, Engineering Consultant – rev 6/24/2005)

1. Scope

1.1 This test method covers the resistance of aggregates to fracture under the effect ofinternal pressure expelling water from aggregate pores. The procedure is intended to assist in theidentification of aggregates that cause deterioration in concrete when exposed to repeated cyclesof freezing and thawing (D-cracking).

1.2 The values state in either inch-pound or SI units shall be regarded separately as standard.The SI units are shown in brackets. The values stated may not be exact equivalents; thereforeeach system must be used independently of the other. Combining values from the two units mayresult in nonconformance.

1.3 This procedure may involve hazardous materials, operations and equipment. Thisprocedure does not purport to address all the safety concerns, if any, associated with its use. Itis the responsibility of the user of this standard to establish appropriate safety and healthpractices and determine the applicability of regulatory limitations prior to use.

2. Referenced Documents

2.1 AASHTO StandardsT 2 Sampling AggregatesT 161 Resistance of Concrete to Rapid Freezing and ThawingM 92 Wire Cloth Sieves for Testing PurposesM 231 Weights and Balances Used in the Testing of Highway Materials

2.2 ASTM StandardsC 666 Resistance of Concrete to Rapid Freezing and ThawingC 702 Method for Reducing Field Samples of Aggregate to Testing SizeD 3665 Practice for Random Sampling of Construction Materials

3. Significance and Use

3.1 As noted in the scope, the procedure described in this method is intended to aid in theidentification of coarse aggregate sources that may be susceptible to D-cracking. Aggregateparticles that exhibit a high rate of fracturing under repeated pressurization cycles are consideredto be more susceptible to D-cracking when critically saturated and subjected to cycles of freezingand thawing in field applications.

3.2 The relatively short time required for completion of this procedure (approximately eightworking days) makes it suitable for use as a screening test to identify aggregate sources thatshould be subjected to more traditional (and more time-consuming) testing prior to approval.

3.3 The results of this test, like D-cracking susceptibility, are sensitive to the size of theaggregate particles tested. Therefore, this test may be appropriate for identifying aggregatesources that should be reduced in size to avoid D-cracking in field applications.

3.4 The results of this test are also sensitive to the number of soft or nondurable particles(e.g., sandstone, clay ironstone, etc.) in the test sample. Therefore, this test may be appropriate

A-2

for determining the amount of durable aggregate that must be blended with nondurable aggregateto produce a blend with sufficiently low D-cracking potential to provide acceptable performance.

3.5 This test is not considered useful in identifying the potential for coarse aggregate popoutscaused by the freezing and thawing of saturated particles of chert in concrete.

4. Apparatus

4.1 Tumbling Apparatus4.1.1 The tumbling apparatus (hereafter referred to as the tumbler) shall consist of a rubber

drum (for holding the sample) and a motorized drive unit.4.1.2 The rubber drum shall have inside dimensions appropriate for tumbling the test sample.

The inside shall be faceted to facilitate tumbling of the aggregate particles. The drum shall havea removable cover (so that the sample can be placed in the drum), and the cover should notinterfere with the rotation of the drum when it is mounted in or on the motorized drive unit.

Note 1 - Suitable tumblers of various sizes are available commercially for polishing rocks. Internal dimensionsof approximately 6.75 in (171 mm) in diameter by 8 in (200 mm) deep have been used successfully, but largerdrums may be more useful and efficient for samples weighing more than about 6 lbs (3 kg).

4.2 Pressurization Apparatus4.2.1 The pressurization apparatus shall include a pressure chamber of sufficient volume for

testing aggregate samples of the desired size. The chamber must be certified for safe operationat pressures of up to 1500 psi (10,000 kPa).

Note 2 - Shop-built pressure chambers are not recommended for use in this test due to the difficulty in obtainingpressure-tight seals at the high pressures involved, as well as the hazards associated with their operation at highpressures. If a shop-built pressure chamber is used, it should be pressure -certified to provide a safety factor of atleast 5 to 1.

4.2.2 The inside surfaces of the pressure chamber shall be suitably treated to prevent thephysical fracture of aggregates by the expansion and recovery of the chamber duringpressurization/de-pressurization cycles.

Note 3 - For cylindrical steel chambers with 1-in (25-mm) thick walls and having inside dimensions of 10 in(250 mm) diameter, 0.0313 in (0.8 mm) thick neoprene rubber sheets, glued to the insides of the flat chamber ends,has proven sufficient to prevent aggregate crushing by chamber expansion and recovery. It is not necessary to coator otherwise treat the inside wall of this cylindrical chamber.

4.2.3 The pressure chamber shall be fitted with valves and fittings to permit the pressurizationof the chamber (pressurization valve), release of chamber pressure (ball-type pressure releasevalve), filling with water (fill valve), and draining (drain valve). Valve and fitting sizing andlocation must be selected to ensure proper function of the apparatus and to achieve the necessarypressure release rate. The apparatus must be capable of producing a pressure drop of at least 300psi (2,100 kPa) during the first 0.01 second of the opening of the pressure release valve.

4.2.4 A compressed nitrogen gas supply shall be provided to pressurize the test chamber. Theavailable nitrogen gas supply pressure must be greater than the specified test pressure.

4.2.5 A pressure gauge and regulator shall be provided to attach directly to the compressednitrogen gas cylinder and control the level of pressure induced in the chamber. The regulatorshall have an output capacity of at least 1500 psi (10,000 kPa). The regulator outlet pressure

A-3

gauge shall have a precision of 0.25 percent of full scale and shall be properly calibrated andcertified at least once every 12 months.

4.2.6 An electrically triggered pneumatic actuator shall be provided to open and close the testchamber pressure release valve at a speed that provides consistent pressure release rates.

4.2.7 A second compressed nitrogen gas supply shall be provided to provide a source ofpressure for the pneumatic actuator.

4.2.8 A second pressure gauge and regulator shall be provided to attach directly to the secondcompressed nitrogen gas cylinder and control the level of pressure used to operate the pneumaticactuator. The regulator shall have an output capacity of at least 250 psi (1500 kPa). Theregulator outlet pressure gauge shall have a precision of 0.25 percent of full scale and shall beproperly calibrated and certified at least once every 12 months.

4.2.9 The test chamber assembly shall be mounted on a stand that permits rotation of thepressurization apparatus through all positions necessary for proper operation.

4.3 Drying Oven - The drying oven should allow free circulation of air through the oven andshould be capable of maintaining a temperature of 230oF + 9oF (110oC + 5oC).

4.4 Balance - The balance should conform to the requirements of AASHTO M 231 for theclass of general purpose balance required for determining the principal mass of the sample beingtested.

5. Special Solutions Required

5.1 A solution of alkylakoxysilane in water (referred to as silane solution) is used inpreparing aggregate test samples, as described in section 7.3.

Note 4 - Some aggregates absorb water at a very rapid rate, which may prevent them from being fractured bythis test. The silane treatment described in section 7.3 reduces the absorption rate by making the aggregates morehydrophobic. This treatment has been demonstrated to have no effect on the hydraulic fracture performance ofaggregates with slower absorption rates.

Note 5 - An appropriate silane solution is available commercially as Enviroseal 40 from Hydrozo, Inc. Othersources may provide suitable results as well.

5.2 Appropriate precautions should be observed in handling the silane solution.

6. Pressurization Cycle

6.1 Each pressurization cycle consists of pressurizing the water-filled chamber containing thetest sample, holding the specified pressure for the specified time (see sections 9.10 and 9.14),and releasing the pressure.

6.2 The pressure release rate must closely match the standard pressure release rate curvepresented in Appendix A. It is especially important to achieve a chamber pressure drop of atleast 300 psi (2100 kPa) during the first 0.01 second of depressurization.

Note 6 – Calibration of the test apparatus consists of identifying a pneumatic actuator pressure that results in thedesired pressure release rate. A procedure for measuring pressure release rate is described in Appendix A. It maybe necessary to modify outlet and valve sizes to achieve the desired release rate curve.

Note 7 – Each successive pressurization cycle increases the degree of saturation of the aggregate particles.When the particles are saturated, pressurization cycles do not produce significant internal stresses and particle

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practures. For this reason, a maximum of 10 pressurization cycles can be performed on a given sample on a givenday.

7. Test Specimens

7.1 Representative samples of aggregate sources should be obtained by appropriate means and in accordancewith accepted procedures such as AASHTO T 2 and ASTM C 702 and D 3665.

7.2 Each aggregate sample to be tested should be screened and split to produce one or moretest samples consisting of the desired particle sizes (see section 7.1). The size fractionrecommended for indicating D-cracking potential contains only particles retained on the ¾-in(19-mm) sieve.

7.3 Replicate specimens may be run to determine test variability, and sufficient materialshould be collected in the initial sampling to provide the necessary number of particles in eachparticle size range being evaluated.

Note 8 – Research indicates that 600 to 800 coarse aggregate particles must be tested to provide a reasonablyaccurate estimate of D-cracking potential for a given source.

8. Preparation of Test Specimens

8.1 Obtain a sample of the desired particle size distribution (e.g., ¾-in (19-mm) plus) bysieving to refusal using appropriate wire screens (AASHTO M 92). Individual test samplesshould contain sufficient quantities of aggregate to fill the pressure chamber.

8.2 The aggregate sample should be washed thoroughly, dried to a constant mass at atemperature of 230oF + 9oF (110oC + 5oC), and allowed to cool to room temperature.

Note 9 - Adequate ventilation should be supplied for the following three steps. The use of a fume hood may beappropriate.

8.3 Place the aggregate sample in the silane solution, making sure that all aggregate particlesare submerged. Allow the specimen to remain in the silane solution for 30 + 5 seconds.

8.4 Remove the specimen from the silane solution and allow excess solution to drain.

Note 10 - Strainers or double boilers suitable for immersing the aggregate in the silane solution and draining arereadily obtainable from restaurant supply sources.

Note 11 - The silane solution may be re-used if it is placed in a sealed container between uses. The solutionshould be discarded if it begins to thicken.

8.5 Dry the specimens to a constant mass at a temperature of 230oF + 9oF (110oC + 5oC), andallow to cool to room temperature.

9. Procedure

9.1 Place enough aggregate in the tumbler to fill it approximately half full. Tumble theaggregate for 30 + 5 revolutions of the tumbler. Remove the aggregate from the tumbler anddiscard any pieces whose size is not within the selected size range (e.g., ¾” – 1.5” [19-38 mm]).Repeat until the entire aggregate test sample has been tumbled.

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9.2 A qualified petrographer should examine the sample to estimate the carbonate content (bypercent mass) of the aggregate sample.

9.3 Fill the test chamber with aggregate particles, being careful not to overfill the chamber(which may result in particle fracture due to closure of the chamber rather than due to thehydraulic fracture mechanism). Remove the aggregate from the test chamber and determine themass of the test sample. Record this number as the initial specimen mass.

9.4 Place the specimen in the pressure chamber; then close and seal the chamber.9.5 Rotate the apparatus from the filling position (typically horizontal) to the testing (typically

vertical) position.9.6 Close the pressure valve and open the main valve on the nitrogen tank that is used to

pressurize the chamber. The pressure regulator for this tank should be set to the pressureindicated on the most recent calibration sheet for the equipment.

Note 12 - A chamber test pressure of 1150 psi (7,930 kPa.) is currently recommended.

9.7 Open the main valve on the nitrogen tank that is used to operate the pneumatically-actuated pressure release valve. The pressure regulator for this tank should be set to the pressureindicated on the most recent calibration sheet for the equipment.

9.8 Connect the fill overflow line to the pressure release line. Open the fill and pressurerelease valves and fill the pressure chamber with water using the procedures described in themanufacturer’s instructions. After the chamber is full and as water is flowing through thechamber and drain line, remove air bubbles from the chamber walls by pivoting the chamber toapproximately 45degrees on either side of the testing position and tapping the exterior of thechamber smartly with a rubber mallet.

9.9 After the chamber has been filled and the air bubbles removed, close the pressure releasevalve and close the fill valve. Remove the fill overflow line from the end of the pressure releasevalve. This process should be completed in 2 minutes (+ 5 seconds).

9.10 Ensure that all chamber valves are initially closed. Pressurize the chamber for 5 minutes(+ 5 seconds) by opening the pressure valve. Adjust the pressure regulator as necessary tomaintain the required pressure. After about 4.75 minutes, close the pressure valve.

9.11 After about 4.9 minutes of pressurization, close the pressure valve; after 5 minutes (+ 5seconds) of pressurization, operate the electropnuematically actuated pressure release valve toproduce the prescribed pressure release.

Note 13 – A muffler may be attached to the pressure release line to reduce the noise associated with theexplosive decompression of the pressure vessel, provided that it does not prevent the achievement of the targetpressure release rate. Appropriate hearing protection should be used during pressure release, especially if a muffleris not used.

9.12 Re-attach the drain line to the pressure release line (which is now open), open the fillvalve, and turn on the water supply to refill the chamber with water as before. Allow water tofill for approximately 30 seconds, rotating the chamber to 45 degrees either side of the testposition and using the rubber mallet to remove any gas bubbles from the sides of the chamber.Close the pressure release valve, then the fill valve, and remove the drain line.

9.13 Re-pressurize the chamber after a total elapsed time of 1 minute (+ 5 seconds) withoutpressure. Adjust the regulator as necessary to maintain the desired pressure.

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9.14 After about 1.9 minutes of pressurization, close the pressure valve; after 2 minutes (+ 5seconds) of pressurization, operate the electropnuematically actuated pressure release valve toproduce the prescribed pressure release.

9.15 Repeat steps 9.12 through 9.14 eight additional times for a total of ten pressurization-depressurization cycles.

9.16 Rotate the pressure chamber back to the aggregate fill position to drain the chamber andremove the aggregate test sample.

9.17 Close the pressure release valve. Turn off the valve on the nitrogen bottle and open thedrain valve. Drain the water from the pressure chamber by slowly opening the pressure valveand allowing the compressed gas in the line to force water out of the chamber. Close the drainvalve when draining is complete.

9.18 Open the chamber and remove the test sample. Dry the specimen to a constant mass at atemperature of 230oF + 9oF (110oC + 5oC), and allow it to cool at room temperature.

9.19 Place enough aggregate in the tumbler to fill it approximately half full. Tumble theaggregate for 30 (+ 5) revolutions. Remove the aggregate from the tumbler, retaining allparticles. Repeat until the entire aggregate test sample has been tumbled.

9.20 Sieve the sample and determine (to the nearest 0.1g) the masses retained on the ¾-in(19.0-mm), 5/8-in (16.0-mm), ½-in (12.5-mm), 3/8-in (9.5-mm), 5/16-in (8-mm), ¼-in (6.25-mm) and #4 (4.75-mm) sieves. Record these values. Remove all particles passing the #4 (4.75-mm) sieve from the testing procedure, determine their mass to the nearest tenth of a gram, andsave in a labeled container.

9.21 Repeat Steps 9.4 through 9.20 for a total of 50 pressurization cycles per test sample.9.22 If necessary, test replicate samples of the same aggregate source until a sufficient

quantity of material has been tested to provide a reasonably accurate estimate of coarse aggregateD-cracking potential (currently considered to be 600-800 aggregate particles, about 33 lbs of ¾-1.5-in coarse aggregate).

10. Calculation

10.1 Determine the combined mass of particles retained on the ¾-in (19.0-mm), 5/8-in (16.0-mm), ½-in (12.5-mm), 3/8-in (9.5-mm), 5/16-in (8-mm), ¼-in (6.25-mm) and #4 (4.75-mm)sieves along with the mass of all particles passing the #4 (4.75-mm) sieve after 50 cycles ofpressurization for all replicate test samples representing a given aggregate source.

10.2 Estimate the dilation that would occur in a concrete prism containing this aggregatesource and tested using AASHTO TP17 using the following equation:

% Dil/100 cycles = C3*(6.7147E-9 + 1.4935E-9*M3/4 in – 2.8248E-7*M5/8 in

+ 3.6484E-7*M1/2 in – 5.6316E-7*M3/8 in + 2.1020E-6*M5/16 in

– 1.6750E-6*M1/4 in + 1.1833E-7*M#4)

where:C = Carbonate content of source, percent;

M3/4 in = Cumulative percentage of mass passing the ¾-in (19.0-mm) screen= 100 – Percentage of original mass retained on the ¾-in (19.0-mm) screen;

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M5/8 in = Cumulative percentage of mass passing the 5/8-in (16.0-mm) screen= M3/4 in – Percentage of original mass retained on the 5/8-in (16.0-mm) screen;

M1/2 in = Cumulative percentage of mass passing the ½-in (12.50-mm) screen= M5/8 in – Percentage of original mass retained on the ½-in (12.50-mm) screen;



M1/4 in = Cumulative percentage of mass passing the ¼-in (6.35-mm) screen= M5/16 in – Percentage of original mass retained on the ¼-in (6.35-mm) screen;

M#4 = Cumulative percentage of mass passing the #4 (4.75-mm) screen= M1/4 in – Percentage of original mass retained on the #4 (4.75-mm) screen.

10.3 Apply appropriate acceptance or rejection criteria to the results of the analysis todetermine the suitability of the given aggregate source or to suggest the need for additional orsupplemental testing using this or other tests of concrete coarse aggregate freeze-thaw damagepotential (e.g., ASTM C 666/AASHTO T161 or TP17, etc.).

Note 14 – It is not uncommon to use 0.04 percent dilation per 100 cycles of freeze-thaw testing as the maximumacceptable value based on AASHTO T 161 and ASTM C 666 tests.

11. Report

11.1 Test reports shall include, as a minimum, the following information and data:11.2 Sample Identification:11.2.1 Report the person or agency submitting the sample for testing.11.2.2 List the source or identifying code for the aggregate sample.11.3 Initial Sample Parameters:11.3.1 Report the particle size range tested.11.3.2 Report the estimated carbonate content of the sample, as determined in section 9.2

above.11.3.3 Report the initial mass of the sample, as determined in section 9.3 above.11.4 Mass Retained11.4.1 Report the mass retained on each required sieve and pan after each series of ten

pressurization cycles.11.4.2 When multiple specimens are tested from the same source and particle size range,

report both individual and combined specimen values.11.5 Predicted Dilation/100 Cycles11.5.1 Report the predicted dilation per 100 cycles computed using the test data and the

model presented in section 10.2.11.5.2 When multiple specimens are tested from the same source and particle size range,

report both individual and combined specimen values.

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12. Precision and Bias

12.1 Sufficient data for precision and bias statements are not currently available.

13. Keywords

13.1 accelerated testing; concrete-weathering tests; conditioning; freezing and thawing;resistance-frost

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Appendix A. Calibration of the Hydraulic Fracture Test Apparatus

The Hydraulic Fracture Test (HFT) apparatus must be operated in a manner that producesaggregate fracture rates that are consistent with those that were used in the development of thedilation prediction model. Previous research1-3 has found that aggregate fracture rates useful indurability prediction can be obtained consistently by controlling the rate of release of pressurefrom the test chamber. Higher pressure release rates correspond with higher fracture rates.Therefore, the parameter used to calibrate the HFT apparatus is the maximum pressure releaserate, computed over and plotted against various time intervals.

Generation of a maximum pressure release rate vs. time interval graph or profile begins withmeasurement of chamber pressure vs. time during the pressure release event. Pressure releaserates can be monitored using an appropriate chamber-mounted pressure transducer with adynamic signal analyzer.

Chamber pressure during the release event should be sampled at a rate of approximately 500 Hz(i.e., one pressure measurement every 0.002 seconds). The data are then used to compute theaverage pressure release rate (psi/sec) during each 0.002 second time interval and the highest rateis selected and recorded as the maximum pressure release rate over a 0.002 second time interval.This analysis process is repeated for successively larger time intervals (e.g., 0.004 seconds, 0.006seconds, etc.), and the maximum pressure release rate for each time interval is plotted against therespective time intervals.

Figure A1 presents the plot of maximum pressure release rate vs. time interval that was used tocalibrate the test apparatus used in developing the current dilation prediction model. Table A1summarizes the data used to create Figure A1. Previous research1-3 indicates that it is mostimportant to match the target maximum pressure release rate profile at 0.01 seconds, althoughthe overall maximum pressure release profile should closely resemble that of the target.

Release rates can be varied most easily by modifying the pressure used to operate the actuatorthat opens the pressure release valve, with higher actuator pressure corresponding to fasterrelease rates. Release rates can also be accomplished by modifying the test chamber plumbing(i.e., modifying pressure release port sizes, pipe and valve sizes, etc.) and/or chamber operatingpressure (although pressures less than 1150 psi may not produce aggregate fractures andpressures significantly higher than 1150 psi may produce too much aggregate fracture).

Maximum pressure release rate profiles for each actuator pressure setting (or chambermodification) can then be compared with the target curve as shown in Figure A2. The pressuresettings and/or chamber configurations that produce the maximum release rate profile closest tothe target profile should be selected for test operation (actuator pressure of 145 psi in theexample shown in Figure A2).

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Target Pressure Release Rate Profile for Calibrating HFT Apparatus(from original University of Washington HFT Apparatus)

0

10000

20000

30000

40000

50000

60000

70000

0 0.01 0.02 0.03 0.04 0.05 0.06 0.07 0.08 0.09

Time Interval, sec

Rel

ease

Rate

,psi

/sec

Figure A1. HFT apparatus calibration target pressure release rate curve.

Table A1. HFT Apparatus Calibration Target Pressure Release Rate Data Table

TimeInterval

(sec)

MaxPressureRelease

Rate(psi/sec)

TimeInterval

(sec)

MaxPressureRelease

Rate(psi/sec)

TimeInterval

(sec)

MaxPressureRelease

Rate(psi/sec)

0.00203 61467 0.02804 33027 0.05402 206940.00402 58950 0.03004 31697 0.05601 200540.00602 56343 0.03203 30469 0.05805 194410.00801 53615 0.03402 29301 0.06003 188680.01004 51159 0.03601 28214 0.06203 183220.01203 48706 0.03804 27156 0.06403 177960.01402 46387 0.04004 26195 0.06601 172980.01602 44035 0.04203 25288 0.06805 168210.01801 41759 0.04402 24416 0.07004 163650.02004 39675 0.04602 23614 0.07203 159160.02203 37802 0.04805 22811 0.07403 154920.02402 36119 0.05004 22072 0.07602 150860.02601 34521 0.05203 21362 0.07801 14691

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0

10000

20000

30000

40000

50000

60000

70000

0 0.01 0.02 0.03 0.04 0.05 0.06 0.07

Time (sec)

Rel

ease

Rat

e(p

si/s

ec)

U Wash90 psi100 psi

120 psi140 psi145 psi150 psi

Figure A2. Example plot of pressure release rate profiles for various actuator pressure settings.

References1. M. B. Snyder, D. J. Janssen and W. Hansen, Adoption of a Rapid Test for Determining

Aggregate Durability in Portland Cement Concrete (Ann Arbor, MI: University of MichiganDepartment of Civil Engineering, 1996).

2. J. J. Hietpas, Refinement and Validation of the Washington Hydraulic Fracture Test(Minneapolis, MN: University of Minnesota Department of Civil Engineering, 1998).

3. R. A. Embacher and M. B. Snyder, Refinement and Validation of the Hydraulic FractureTest (St. Paul, MN: Minnesota Department of Transportation, 2003).

APPENDIX B

Hydraulic Fracture Test Protocol

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Assembling and Operating theMnDOT Hydraulic Fracture Test Apparatus:A Test Protocol for Operators

Description of Parts – Large ChamberThe large chamber apparatus for the Washington Hydraulic Fracture Test consists of anumber of individual pieces.

Cylinder Assembly -The cylinder assembly includes the cylinder portion of the pressurechamber containing the valves and fittings, along with the attached pivot collar and stand.The cylinder portion has a machined channel for the O-ring seal (called an O-ringchannel) on each end. The "bottom" of the cylinder is the end closest to the three sets ofvalves and fittings.

A handle is attached to the pivot shaft on one side of the stand. A locking bolt or rod onthe handle can be pushed in to engage one of three positioning holes in the stand whenrequired to prevent the cylinder assembly from rotating.

The large chamber cylinder assembly is shown in figure B1.

Figure B1. Photos of large chamber cylinder assembly.

O-Rings - Two O-rings are used to seal the pressure chamber when it is assembled andpressurized. The O-rings should be regularly inspected for cuts and embedded rockparticles. The O-rings should be replaced when necessary.

End Plates - Two interchangeable end plates (with or without handles) complete thepressure chamber portion of the apparatus.

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High-Strength Bolts - Sixteen high-strength bolts are used to hold the end plates to thecylinder. These bolts are tightened to approximately 60 to 80 inch-pounds (6.8 to 9.0newton-meters).

Assembly Rods - Two 3/4-in (19-mm) diameter threaded rods, 14 in (356 mm) long, areused to assemble the pressure chamber. Each rod has holes located approximately 5 in(125 mm) from each end through which ¼-in (6-mm) diameter rods or cotter pins areinserted during the assembly process.

Pressure Regulator No. 1 - A pressure regulator (0-1500 psi outlet pressure) with inletand outlet pressure gages attaches directly to a high-pressure compressed nitrogencylinder (user-supplied) and connects to the pressure chamber via a flexible pressure line,as shown in figure B2.

Pressure Regulator No. 2 - A pressure regulator (0-300 psi outlet pressure) with inlet andoutlet pressure gages attaches directly to a high-pressure compressed nitrogen cylinder(user-supplied) and connects to the pneumatic actuator (attached to the pressure chambervia a flexible pressure line, as shown in figure B2.

Figure B2. Photos of chamber pressure regulator and gages (left) and actuator pressureregulator and gages (right).

Drain Line - A flexible plastic water line connects to the pressure chamber (through aquick-connect fitting) and leads to a free end at a water drain, as shown in figure B3.

Water Fill Line - A flexible plastic water line connects the pressure chamber to a watersource. The water line connection should comply with local plumbing codes andregulations, as shown in figure B4.

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Figure B3. Photo of large chamber with drain line attached to quick connect fitting.

The specific valve and fitting assemblies are described below:

Fill Assembly - This assembly consists of a brass “T” connection. One leg of the “T”connects to the fill valve and the connection to the water line. The second leg attaches tothe pressure vessel. The third leg houses the pressure transducer that is used incalibrating the apparatus. The fill assembly is shown in figure B4.

Figure B4. Large chamber fill valve assembly.

Fill Valve - This is a ball valve with a black lever handle and is the only valve onone side of the bottom of the pressure chamber. Opening and closing areaccomplished by 90-degree turns. Occasional maintenance includes replacingworn or damaged O-rings on the valve plug, and applying a thin film of siliconegrease when the valve is reassembled.

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Water Line Connection – A serrated brass nozzle fitting attaches to the fill valvethrough a standard threaded connection. The plastic water line slides over thenozzle and is secured with a worm clamp.

Pressure Transducer Assembly – A small pressure transducer is installed in astainless steel adapter, which is, in turn, installed in the bottom leg of the fillassembly “T” connector. Details concerning the pressure transducer are providedin the list of vendors at the end of this document.

Pressurization and Drainage Assembly - This assembly includes three valves andconnections for pressurization and depressurization as well as chamber drainage. Thisassembly can be seen in figure B3.

Pressure Isolation Valve - This is a ball valve with a black lever handle locatedbetween the chamber and the flexible nitrogen pressure line. Maintenance for thisvalve consists of periodically tightening the packing around the ball whenever aleak develops. This is accomplished by removing the lever handle (which isattached with a set-screw) and using a wrench to tighten the two-sided nutexposed under the handle. The nut should be tightened in 1/16th turns untilleaking stops.

Pressure Release Valve - This is a ball valve located beneath and operated by thepressure-driven actuator; there is no handle accessible to the operator.Maintenance is the same as for the pressure isolation valve described above.

Electrically-operated Pneumatic Actuator – The pneumatic actuator mounts onand operates the valve stem for the pressure release valve. The actuator turns thevalve stem 90 degrees in either direction through bursts of pressurized nitrogengas that are triggered by a standard two-pole electrical power switch.

Pressure Release Connector - This is the female half of a quick-connectassembly. The drain line is connected here (using the male half of a quick-connectassembly) while the pressure chamber is being filled with water. For pressurerelease, the drain line is disconnected and a muffler (optional) can be connected toreduce the noise of chamber decompression.

Drain Valve - This valve is located to the right of the pressure release assembly(when viewing the chamber from the top). It is identical to the fill valvedescribed previously.

Drain Line Connection – The large chamber drain line connects the drain valve tothe pressure release line at a point past the pressure release valve.

Description of Parts – Small ChamberThe small chamber apparatus for the Washington Hydraulic Fracture Test consists of anumber of individual pieces.

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Cylinder Assembly -The cylinder assembly includes the cylinder portion of the pressurechamber containing the valves and fittings. The cylinder has a machined channel for anO-ring seal (called an O-ring channel) on each end. The "bottom" of the cylinder is theend closest to the internal drain tube inlet (described below).

The small chamber cylinder assembly is shown in figure B5.

Figure B5. Photos of small chamber cylinder assembly (top plate removed) and stand.

O-Rings - Two O-rings are used to seal the pressure chamber when it is assembled andpressurized. The O-rings should be regularly inspected for cuts and embedded rockparticles. The O-rings should be replaced when necessary.

End Plates – There are two end plates, each with a replaceable neoprene pad centered onthe interior face. The bottom end plate is attached to a pivot assembly, which attaches tothe test stand through a pair of pivot shafts. A handle is attached to the pivot shaft on oneside of the stand. A locking bolt or rod on the handle can be pushed in to engage one ofthree positioning holes in the stand when required to prevent the cylinder assembly fromrotating.

The top end plate has a handle to facilitate chamber assembly.

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High-Strength Bolts - Sixteen high-strength bolts (approximately 5 inches [125 mm] inlength) are used to assemble the small chamber assembly. These bolts are tightened toapproximately 60 to 80 inch-pounds (6.8 to 9.0 newton-meters).

Pressure Regulator No. 1 - A pressure regulator (0-1500 psi outlet pressure) with inletand outlet pressure gages attaches directly to a high-pressure compressed nitrogencylinder (user-supplied) and connects to the pressure chamber via a flexible pressure line,as shown previously in figure B2.

Pressure Regulator No. 2 - A pressure regulator (0-300 psi outlet pressure) with inlet andoutlet pressure gages attaches directly to a high-pressure compressed nitrogen cylinder(user-supplied) and connects to the pneumatic actuator (attached to the pressure chambervia a flexible pressure line, as shown previously in figure B2.

Overflow Line - A flexible plastic water line connects to the pressure chamber (through aquick-connect fitting) and leads to a free end at a water drain, as shown previously infigure B3.

Drain Line - A flexible plastic water line fits over a serrated brass nozzle fitting that isattached to the drain valve through a standard threaded connection. One end of the waterline is secured to the nozzle with a worm clamp and the other end is placed near a waterdrain.

Water Fill Line - A flexible plastic water line connects the pressure chamber to a watersource. The water line connection should comply with local plumbing codes andregulations.

The specific valve and fitting assemblies are described below:

Fill Assembly - This assembly consists of a brass “T” connection. One leg of the “T”connects to the fill valve and the connection to the water line. The second leg attaches tothe pressure vessel. The third leg houses the pressure transducer that is used incalibrating the apparatus. The fill assembly is shown in figure B6.

Fill Valve - This is a plug valve with a small green lever handle and is the onlyvalve on one side of the pressure chamber. Opening and closing areaccomplished by 90-degree turns. Occasional maintenance includes replacingworn or damaged O-rings on the valve plug, and applying a thin film of siliconegrease when the valve is reassembled.

Water Line Connection – A serrated brass nozzle fitting attaches to the fill valvethrough a standard threaded connection. The plastic water line slides over thenozzle and is secured with a worm clamp.

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Figure B6. Small chamber fill valve assembly.

Pressure Transducer Assembly – A small pressure transducer is installed in astainless steel adapter, which is, in turn, installed in the bottom leg of the fillassembly “T” connector. Details concerning the pressure transducer are providedin the list of vendors at the end of this document.

Pressurization Assembly - This assembly includes two valves and connections forpressurization and depressurization. This assembly can be seen in figure B7.

Figure B7. Photo of small chamber pressurization and drain assemblies.

Pressure Isolation Valve - This is a ball valve with a black lever handle locatedbetween the chamber and the flexible nitrogen pressure line. Maintenance for thisvalve consists of periodically tightening the packing around the ball whenever aleak develops. This is accomplished by removing the lever handle (which isattached with a set-screw) and using a wrench to tighten the two-sided nutexposed under the handle. The nut should be tightened in 1/16th turns untilleaking stops.

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Pressure Release Valve - This is a ball valve located beneath and operated by thepressure-driven actuator; there is no handle accessible to the operator.Maintenance is the same as for the pressure isolation valve described above.

Electrically-operated Pneumatic Actuator – The pneumatic actuator mounts onand operates the valve stem for the pressure release valve. The actuator turns thevalve stem 90 degrees in either direction through bursts of pressurized nitrogengas that are triggered by a standard two-pole electrical power switch.

Pressure Release Connector - This is the female half of a quick-connectassembly. The drain line is connected here (using the male half of a quick-connectassembly) while the pressure chamber is being filled with water. For pressurerelease, the drain line is disconnected and a muffler (optional) can be connected toreduce the noise of chamber decompression.

Drain Valve Assembly - This assembly includes one valves and connection for chamberdrainage following testing. This assembly can also be seen in figure B7.

Drain Valve - This valve is located to the left of the pressure release assembly(when viewing the chamber from the top). It is identical to the fill valvedescribed previously.

Drain Tube – This is a small copper tube that is mounted over the drain outlet onthe inside of the pressure vessel, as shown in figure B8. This tube is bent so thatthe inlet end of the tube nearly touches the bottom end plate when the chamber isassembled. This assists in draining water to very near the bottom of the chamberprior to disassembly.

Drain Line Connection – The small chamber drain line connects the drain valve tothe drain line, which leads to an open end (to be placed near a water drain).

Figure B8. Photo of drain valve assembly, including drain tube on inside of chamber.

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Sample PreparationThe following steps describe procedures for obtaining and preparing aggregate samplesprior to testing them in the hydraulic fracture test apparatus.

1. Obtain a coarse aggregate sample using standard sampling techniques to ensurethat the sample is representative of material that will be used in concreteproduction. If various ledges of a particular quarry or various areas of a given pitwill be used, separate samples must be obtained and tested from each ledge orarea.

2. The sample size must be large enough to produce at least 40 lbs of ¾-in plusmaterial, plus whatever additional material is required for companion tests (forexample, sulfate soundness, absorption capacity, freeze-thaw beams, etc.).

3. The HFT test sample should be obtained by splitting the original sample asnecessary and sieving to refusal over a ¾-in (19-mm) sieve. The HFT sampleshould weigh at least 40 lbs before proceeding further.

4. The aggregate sample should be washed thoroughly (until water runs clear fromthe aggregate washer), dried to a constant mass (usually about 16-24 hours) at atemperature of 230oF + 9oF, and allowed to cool to room temperature (see figureB9).

Figure B9. Aggregate washer and oven in MnDOT concrete lab.

5. The water-based silane solution should be placed in a double boiler in an areawith good ventilation, such as under or within a fume hood (as shown in figureB10).

6. Place the aggregate sample in the strainer portion of the double boiler thatcontains the silane solution. Lower the strainer into the silane solution, makingsure that all aggregate particles are submerged. It may be necessary to split the

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sample into smaller portions for proper treatment coverage. Allow the specimento remain in the silane solution for 30 seconds.

7. Remove the specimen from the silane solution and allow excess solution to drain(as shown in figure B10).

Figure B10. Photos of double boiler and silane under MnDOT fume hood and treatedsample draining in double boiler.

8. The silane solution should be placed in a sealed container between uses andshould be discarded if it begins to thicken.

9. Dry the sample to a constant mass (usually 16-24 hours) at a temperature of 230oF+ 9oF, and allow it to cool to room temperature.

10. Place enough aggregate in an aggregate tumbler to fill it approximately half full.Tumble the aggregate for 30 + 5 revolutions of the tumbler. Remove theaggregate from the tumbler, screen the sample over the ¾-in sieve and discard anypieces passing the sieve. Repeat until the entire aggregate test sample has beentumbled.

Figure B11. Photos of typical aggregate tumbler with sample in drum (left) and largetumbler in MnDOT lab (right).

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11. A qualified petrographer should examine the sample to estimate the carbonatecontent (by percent mass) of the aggregate sample and to ensure that theaggregate does not contain significant quantities (e.g., more than 1% by weight)of chert.

12. Fill the test chamber with aggregate particles, being careful not to overfill thechamber (which may result in particle fracture due to closure of the chamberrather than due to the hydraulic fracture mechanism). Remove the aggregate fromthe test chamber and determine the mass of the test sample. Record this numberas the initial specimen mass.

13. The specimen is now ready for testing. Extreme care must be taken from thispoint forward to avoid losing aggregate particles due to mishandling or any otherprocess other than the hydraulic fracture mechanism.

Large Chamber Assembly

The pressure chamber is assembled by the following steps:

1. Rotate the pressure cylinder to the inverted position (bottom of cylinder up) andlock it in this position. Clean the bottom O-ring channel and remove and dirt,dust or rock chips. Place an O-ring in the channel.

2. Place an end plate on the bottom of the cylinder and visually align the holes in theend plate with the holes in the pivot collar surrounding the cylinder.

3. With a nut turned onto one end of an assembly rod, insert the assembly rodthrough one of the holes in the end plate and the corresponding hole in the pivotcollar. Insert an assembly or cotter pin into the hole in the assembly rod on side ofthe pivot collar furthest from the plate. Repeat this procedure with the secondassembly rod, using the hole in the end plate that is directly opposite the one usedfor the first assembly rod. Finger-tighten the nuts on each of the assembly rods asshown in figure B12.

4. Rotate the pressure cylinder right-side up and lock it in position. If a test ofaggregate durability is to be performed, place the aggregate specimen into thepressure cylinder. The large chamber will accommodate approximately 33 lbs (15kg) of typical aggregate. Use a strike-off bar to ensure than no aggregate particlesprotrude above the top of the chamber where they could be crushed duringassembly, as shown in figure B12. (If a chamber calibration is to be performed,there is no need to fill the chamber with aggregate. Assemble the chamber emptyand follow instructions for calibration.)

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Figure B12. Assembly of large chamber bottom plate and fill with aggregate sample,including strike-off.

5. Clean the top O-ring channel and install an O-ring. Place the remaining baseplate over the protruding ends of the assembly rods and onto the pressurecylinder.

6. (Optional) Place a nut on each of the protruding assembly rod ends and finger-tighten. Pivot the pressure chamber 90 degrees into the test position and continueassembly.

7. Insert 14 of the bolts into the holes in one of the base plates, through the pivotcollar, and through the other base plate. Place nuts on all of the bolts and finger-tighten them.

8. Remove the assembly rods, place the remaining two bolts in the holes vacated bythe assembly rods, and place the remaining nuts on the remaining bolts.

9. Tighten all of the nuts to 60-80 in-lbs (6.8-9.0 N-m) using the following pattern toensure uniform compression of the O-rings:

Tighten two nuts on opposite sides of the pressure cylinder (nuts 1 and 9, if thenuts are numbered consecutively around the cylinder). Next, tighten the nuts oneach side and midway between the nuts already tightened (e.g., nuts 5 and 13).Next tighten the halfway between those already tightened (e.g., nuts 3, 7, 11, and15). Then tighten the remaining nuts. It will probably be necessary to completethis tightening pattern at least twice because the nuts tightened first will often

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develop some looseness as subsequent nuts are tightened and the O-rings arecompressed.

Figure B13. Removal of large chamber assembly pins and tightening of assembly bolts.

Small Chamber Assembly

The small pressure chamber is assembled by the following steps:

1. Rotate the bottom end plate to a vertical position (perpendicular to the floor).

2. Clean the O-ring channels of the pressure cylinder, removing all dirt, dust or rockchips. Place an O-ring in the bottom channel.

3. Place the pressure cylinder against the bottom end plate, making sure that the O-ring remains properly seated in the channel between the cylinder and end plate.

4. While holding the cylinder in place, rotate the cylinder-bottom plate assembly tothe horizontal position (parallel to the floor) and lock it in place. Verify that thecylinder and O-ring are properly seated against the bottom plate.

5. Rotate the cylinder on the end plate as needed to ensure that no valve assembliesblock the bolt holes.

6. If a test of aggregate durability is to be performed, place the aggregate specimeninto the pressure cylinder. The small chamber will accommodate approximately 7lbs (3 kg) of typical aggregate. Use a strike-off bar to ensure than no aggregateparticles protrude above the top of the chamber where they could be crushed

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during assembly. (If a chamber calibration is to be performed, there is no need tofill the chamber with aggregate. Assemble the chamber empty and followinstructions for calibration.)

Figure B14. Small chamber, ready to be filled with aggregate sample.

7. Clean the top O-ring channel and install an O-ring. Place the top end plate on thepressure cylinder and visually align the holes with those in the pivot assembliesand bottom base plate.

8. Insert the 16 high-strength through the holes in the bottom base plate, through thepivot assemblies (where necessary), and through the other base plate. Place nutson all of the bolts and finger-tighten them.

9. Tighten all of the nuts to 60-80 in-lbs (6.8-9.0 N-m) using the following pattern toensure uniform compression of the O-rings:

Tighten two nuts on opposite sides of the pressure cylinder (nuts 1 and 9, if thenuts are numbered consecutively around the cylinder). Next, tighten the nuts oneach side and midway between the nuts already tightened (e.g., nuts 5 and 13).Next tighten the halfway between those already tightened (e.g., nuts 3, 7, 11, and15). Then tighten the remaining nuts. It will probably be necessary to completethis tightening pattern at least twice because the nuts tightened first will oftendevelop some looseness as subsequent nuts are tightened and the O-rings arecompressed.

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Figure B15. Tightening of small chamber assembly bolts.

Large Chamber HFT Apparatus Operation

The following instructions assume that the chamber has already been charged withaggregate, completely assembled and is rotated into the horizontal testing position (i.e.,end plates are positioned on their edges, the pressure release assembly is on top and thefill line is on the bottom).

1. If the apparatus has not been used in the past 30 minutes, “warm up” the pressurerelease valve by turning the electrical switch on and off 20 times.

2. Attach the drain line to the pressure release connector.

3. Open the fill and pressure release valves and fill the chamber with water byturning on the water source (see figure B16).

4. After the chamber is full (overflow water is coming out of the drain line that isconnected to the pressure release valve), fill the copper drain pipe by brieflyopening the drain valve until a small amount of water comes out. Close the drainvalve.

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Figure B16. Connecting the drain/overflow line (left) and opening the fill valve (right).

5. Remove any air bubbles in the pressure chamber by pivoting the chamber backand forth, leaving the bottom end (the end closest to the valves and fittings)slightly higher than the top end. While pivoting the chamber, use a rubber malletto sharply rap the end plates to dislodge trapped air bubbles (see figure B17).

Figure B17. Removing trapped air bubbles using rubber mallet.

6. Close the pressure release valve, close the fill valve and disconnect the drain line.All valves on the chamber should be shut. The chamber is now ready forpressurization.

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7. If it has not already been done, open the valves on the top of the compressednitrogen cylinders. The pressure regulators for these tanks should be set to thepressures indicated on the most recent calibration sheet for the equipment.

8. Pressurize the chamber by fully opening the chamber pressure valve with a 90-degree turn and simultaneously start the timer or stop watch. The firstpressurization cycle for each sample on each day of testing lasts 5 minutes whilethe remaining 9 cycles each day last 2 minutes (see figure B18).

9. (Optional) Install the muffler (see figure B18).

Figure B18. Pressurization of chamber (left) and installation of muffler (right).

10. A few seconds before the end of the pressurization cycle, close the pressureisolation valve. At the end of the pressurization cycle, release the chamberpressure by flipping the electric switch that controls the pneumatic actuator (Seefigure B19). Note: it is advisable to wear hearing protection if a muffler is notused during depressurization.

11. Remove the muffler (if used) and repeat steps 2 through 10 until 10pressurization-depressurization cycles have been completed.

12. After 10 pressurization-depressurization cycles have been completed, remove themuffler (if used) and attach the drain/overflow line to the quick-release connector.

13. Pivot the pressure chamber back to the upright position (bottom plate parallel tothe floor) and lock the chamber in this position.

14. Use the electrically-operated pneumatic actuator to close the pressure releasevalve. Open the drain valve (see figure B20).

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Figure B19. Pressure release operation:close pressure isolation valve, then flip electric switch.

Figure B20. Opening the large chamber drain valve.

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15. Close the valve on the nitrogen cylinder. Slowly open the pressure isolation valveto allowing the gas pressure remaining in the line to force the water out of thepressure chamber.

16. If necessary, close the pressure isolation valve, open the valve on the nitrogencylinder to repressurize the pressure line, and then close the valve on the nitrogencylinder. Slowly open the pressure isolation valve. Repeat this process untilmostly gas (and little water) is passing through the drain/overflow line.

17. When all the water has been removed from the pressure chamber, close thepressure isolation valve.

18. (Optional) Pivot the chamber to the sideways position.

19. Remove two bolts on opposite sides of the pressure chamber and replace themwith assembly rods. Insert the assembly/cotter pins into the holes in the assemblyrods on the top side of the pivot flange.

20. Finger tighten nuts on the assembly rods (on both ends if the sideways position isbeing used).

21. Loosen the nuts on the remaining bolts and remove the bolts.

22. If necessary, rotate the chamber back to the upright position and remove the nutson the top ends of the assembly rods.

23. Remove the top end plate.

24. Take the O-ring out of the top O-ring channel.

25. Remove the aggregate specimen from the pressure chamber. Continue processingthe aggregate as described in “Specimen Testing – Summary” below.

26. Clean both the O-ring and the top O-ring channel.

27. Invert the pressure cylinder, loosen the remaining nuts on the assembly rods,remove the assembly pins, and remove the assembly rods.

28. Remove the bottom base plate and clean the inside faces of both base plates.

29. Remove the bottom O-ring from the O-ring channel, and clean the O-ring and theO-ring channel.

30. If no further testing is to be performed, thoroughly dry the chamber (inside andout, especially in the O-ring channels) and end plate surfaces. Store the parts in amanner that will permit further air-drying to minimize the formation of rust.

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Small Chamber HFT Apparatus Operation

The following instructions assume that the chamber has already been charged withaggregate, completely assembled and is rotated into the testing position (i.e., end platesare positioned on their edges, the pressure release assembly is on top and the fill line is onthe bottom).

1. If the apparatus has not been used in the past 30 minutes, “warm up” the pressurerelease valve by turning the electrical switch on and off 20 times.

2. Attach the fill overflow line to the pressure release connector (see figure B21).

Figure B21. Attaching the fill overflow line (left) and opening the fill valve (right).

3. Open the fill and pressure release valves and fill the chamber with water byturning on the water source.

4. After the chamber is full (overflow water is coming out of the line that isconnected to the pressure release valve), fill the drain valve assembly with waterby briefly opening the drain valve until a small amount of water comes out. Closethe drain valve.

5. Remove any air bubbles in the pressure chamber by pivoting the chamber backand forth. While pivoting the chamber, use a rubber mallet to sharply rap the endplates to dislodge trapped air bubbles, as shown in figure B22.

6. Close the pressure release valve, close the fill valve and disconnect the overflowline (see figure B23). All valves on the chamber should be shut. The chamber isnow ready for pressurization.

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Figure B22. Dislodging attached air bubbles from the inside of the small chamber.

Figure B23. Closing the pressure release valve and fill valve (left) and removing the filloverflow line (right).

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7. If it has not already been done, open the valves on the top of the compressednitrogen cylinders. The pressure regulators for these tanks should be set to thepressures indicated on the most recent calibration sheet for the equipment.

8. Pressurize the chamber by fully opening the chamber pressure valve with a 90-degree turn and simultaneously start the timer or stop watch. The firstpressurization cycle for each sample on each day of testing lasts 5 minutes whilethe remaining 9 cycles each day last 2 minutes (see figure B24).

9. (Optional) Install the muffler (see figure B24).

Figure B24. Closing the pressure release valve and fill valve (left) and removing the filloverflow line (right).

10. A few seconds before the end of the pressurization cycle, close the pressureisolation valve. At the end of the pressurization cycle, release the chamberpressure by flipping the electric switch that controls the pneumatic actuator (seefigure B25). Note: it is advisable to wear hearing protection if a muffler is notused during depressurization.

11. Remove the muffler (if used) and repeat steps 2 through 10 until 10pressurization-depressurization cycles have been completed.

12. After 10 pressurization-depressurization cycles have been completed, remove themuffler (if used) and attach the drain/overflow line to the quick-release connector.

13. Pivot the pressure chamber back to the upright position (bottom plate parallel tothe floor) and lock the chamber in this position.

14. Use the electrically-operated pneumatic actuator to close the pressure releasevalve. Open the drain valve.

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Figure B25. Release of pressure from small chamber by closing pressure isolation valve,then flipping electric switch.

15. Close the valve on the nitrogen cylinder. Slowly open the pressure isolation valveto allowing the gas pressure remaining in the line to force the water out of thepressure chamber (see figure B26).

Figure B26. Removing water from small chamber by closing pressure release valve andnitrogen bottle valve, opening drain valve and slowly opening pressure isolation valve.

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16. If necessary, close the pressure isolation valve, open the valve on the nitrogencylinder to repressurize the pressure line, and then close the valve on the nitrogencylinder. Slowly open the pressure isolation valve. Repeat this process untilmostly gas (and little water) is passing through the drain/overflow line.

17. When all the water has been removed from the pressure chamber, close thepressure isolation valve.

18. Loosen the nuts on the chamber assembly bolts and remove the bolts.

19. Remove the top end plate.

20. Take the O-ring out of the top O-ring channel.

21. Remove the aggregate specimen from the pressure chamber. Continue processingthe aggregate as described in “Specimen Testing – Summary” below.

22. Remove the pressure cylinder and clean both O-rings and O-ring channels.

23. If no further testing is to be performed, thoroughly dry the chamber (inside andout, especially in the O-ring channels) and end plate surfaces. Store the parts in amanner that will permit further air-drying to minimize the formation of rust.

Specimen Testing – SummarySampling and Specimen PreparationAggregate sampling and specimen preparation should be performed as described in“Sample Preparation” above. Key points include:

Good sampling techniques must be used to ensure that the sample obtained isrepresentative of material that will be used in concrete production.

The sample obtained must contain at least 33 lbs (600-800 particles) of ¾-in plusmaterial for hydraulic fracture testing, plus any additional material required forcompanion tests (such as magnesium sulfate testing, absorption capacity, freeze-thaw beams, etc.).

If various ledges of a particular quarry or various areas of a given pit will be used,separate samples must be obtained and tested from each ledge or area.

The aggregate sample should be washed thoroughly, then dried to a constantmass. The sample is then soaked in a water-based silane solution for 30 seconds,drained and again dried to a constant mass.

The sample is then placed in an aggregate tumbler, which is operated for 30revolutions. Upon removal, the aggregate is screened over the ¾-in sieve and theparticles that pass the sieve are discarded.

A qualified petrographer should examine the sample to estimate the carbonatecontent (by percent mass) of the aggregate sample and to ensure that the

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aggregate does not contain significant quantities (e.g., more than 1% by weight)of chert.

The test chamber should then be filled (but not overfilled) with aggregate particlesto determine the size of the test sample. The aggregate is then removed andweighed to determine the initial mass of the test specimen.

Extreme care must be taken from this point forward to avoid losing aggregateparticles due to mishandling or any other process other than the hydraulic fracturemechanism.

Testing ProceduresThe hydraulic fracture test process consists of two parts: the pressurization-depressurization cycles, and the post-pressurization sieving and mass measurement. Thesteps involved in completing the test are described below:

1. A total of 50 pressurization-depressurization cycles are performed at a rate of 10per day over five days of testing. Detailed procedures for performing thepressurization cycles are described for each of the available pressure chambers insections titled “Large Chamber HFT Apparatus Operation” and “Small ChamberHFT Apparatus Operation.”

2. After the 10 th pressurization cycle for any particular test specimen on anyparticular day, the sample must be removed from the test chamber (taking care toremove all aggregate particles) and dried to a constant weight (typically 16-24hours in an oven operating at 230oF + 9oF).

3. After the aggregate has cooled, place enough aggregate in an aggregate tumbler tofill it approximately half full. Tumble the aggregate for 30 + 5 revolutions of thetumbler. Remove the aggregate from the tumbler being careful not to lose anyparticles or pieces. Repeat until the entire aggregate test sample has beentumbled.

4. Sieve the sample and determine (to the nearest 0.1g) the masses retained on the¾-in, 5/8-in, ½-in, 3/8-in, 5/16-in, ¼-in and #4 sieves. Record these values on thestandard data collection sheet provided (see figure B27). Determine and recordthe mass of all particles found in the pan and save these particles in a labeledbaggie or other container.

5. All particles retained on any of the sieves must be returned to the test apparatusfor 10 additional pressurization cycles (unless the sample has already beensubjected to 50 pressurization cycles; in this case, the testing is complete).

Data Reporting, Data Entry and Calculations (All Chambers and Devices)All data are initially recorded manually on a standard data collection form (see figureB27), which includes entry spaces for aggregate source and sample identification, samplesubmittal and testing dates, estimated carbonate content, initial test sample mass andmasses retained on each sieve after each 10 cycles of testing. Data can be recorded on asingle sheet for up to 5 samples from each aggregate source.

The data can be transferred to an Excel spreadsheet titled “HFT Data Entry andAnalysis.xls”. This spreadsheet automatically performs all calculations necessary to

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HFT Data Collection Sheet

Replicate Number 1 2 3 4 5Silane Treatment DateInitial Mass, g

Test Date: Test Date:M3/4" (ret) , g M 3/4" (ret), gM5/8" (ret) , g M 5/8" (ret), gM1/2" (ret) , g M 1/2" (ret), gM3/8" (ret) , g M 3/8" (ret), gM5/16" (ret), g M 5/16" (ret), gM1/4" (ret) , g M 1/4" (ret), gM#4 (ret), g M #4 (ret), gMpan, g M pan, g

Mass Check: Mass Check:Test Date: Test Date:M3/4" (ret) , g M 3/4" (ret), gM5/8" (ret) , g M 5/8" (ret), gM1/2" (ret) , g M 1/2" (ret), gM3/8" (ret) , g M 3/8" (ret), gM5/16" (ret), g M 5/16" (ret), gM1/4" (ret) , g M 1/4" (ret), gM#4 (ret), g M #4 (ret), gMpan, g M pan, gMass Check: Mass Check:Test Date:M3/4" (ret) , g Source: Submitted by:M5/8" (ret) , gM1/2" (ret) , g Date Rec'd: Carbonate Content (%):M3/8" (ret) , gM5/16" (ret), g Test Technician: Equip No:M1/4" (ret) , gM#4 (ret), g Chamber Pressure (psi): Solonoid Press. (psi):Mpan, gMass Check: Comments:

10 Cycles

20 Cycles

30 Cycles

40 Cycles

50 Cycles

Figure B27. HFT data collection form.

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predict freeze-thaw dilation (%/100 cycles) for each individual sample. It also estimates anoverall dilation value based on the combined values of all individual samples tested. NOTE: Itis important to use the “Save As …” function to store the data with a filename that will beassociated with the sample tested (for example, “Bryan Red Rock – Large Chamber – June2005.xls”)

When testing and calculations are complete, the aggregate source can be accepted or rejectedbased on the results obtained. A value of 0.4 percent dilation per 100 cycles of freeze-thawtesting is often used as the maximum acceptable value for freeze-thaw testing. NOTE: Ratherthan rejecting sources that exceed this value, it may be appropriate to recommend supplementaltesting (for example, actual freeze-thaw testing) to ultimately determine the suitability of aparticular aggregate source.

Calibrating the HFT ChambersThe Hydraulic Fracture Test (HFT) apparatus must be operated in a manner that producesaggregate fracture rates that are consistent with those that were used in the development of thedilation prediction model. This is done by matching a graph of the maximum rate of release ofpressure vs. time interval for the test chamber with a similar standard graph.

Generation of a maximum pressure release rate vs. time interval graph or profile begins withmeasurement of chamber pressure vs. time during the pressure release event. Pressure releaserates can be monitored using the chamber-mounted pressure transducer (installed in the bottomleg of the brass “T” that also connects to the fill valve) and the dynamic signal analyzer (a HP35565 in the MnDOT concrete lab). The signal analyzer can be programmed for this task byloading a “state” file called “HFT.STA” into the signal analyzer using a 3.5-in floppy disk.

Chamber pressure during the release event should be sampled at a rate of approximately 500 Hz(i.e., one pressure measurement every 0.002 seconds; the signal analyzer program “HFT.STA” isalready set for this sample rate). The collected data are then used to compute the averagepressure release rate (psi/sec) during each 0.002 second time interval and the highest rate isselected and recorded as the maximum pressure release rate over a 0.002 second time interval.This analysis process is repeated for successively larger time intervals (e.g., 0.004 seconds, 0.006seconds, etc.), and the maximum pressure release rate for each time interval is plotted against therespective time intervals. The computation process is done automatically by the spreadsheetprogram “CALIBRATE.XLS”, but the operator must enter the collected chamber pressure vs.time data into the spreadsheet manually.

Table 1 presents the standard maximum pressure release rate data that have been adopted forcalibrating the HFT apparatus. These data are summarized graphically in figure 28. It is mostimportant to match the target maximum pressure release rate profile at the 0.01-second timeinterval value, although the overall pressure release profile should closely resemble that of thetarget.

The steps involved in calibration are as follows:1. Turn on the signal analyzer. Insert the disk containing the file “HFT.STA” into the disk

drive.

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2. Press the “Save/Recall” button on the signal analyzer and look on the right of the displayscreen for the words “Recall State”. Push the button closest to these words and then usethe buttons on the front of the analyzer to enter the file name “HFT.STA”. Use thebackspace and erase keys to eliminate the file name that appeared by default.

3. Use the special cable to connect the pressure transducer to Channel 1 of the signalanalyzer (see figure 29).

Table 1. HFT Apparatus Calibration Target Pressure Release Rate Data Table

TimeInterval

(sec)

MaxPressureRelease

Rate(psi/sec)

TimeInterval

(sec)

MaxPressureRelease

Rate(psi/sec)

TimeInterval

(sec)

MaxPressureRelease

Rate(psi/sec)

0.00203 61467 0.02804 33027 0.05402 206940.00402 58950 0.03004 31697 0.05601 200540.00602 56343 0.03203 30469 0.05805 194410.00801 53615 0.03402 29301 0.06003 188680.01004 51159 0.03601 28214 0.06203 183220.01203 48706 0.03804 27156 0.06403 177960.01402 46387 0.04004 26195 0.06601 172980.01602 44035 0.04203 25288 0.06805 168210.01801 41759 0.04402 24416 0.07004 163650.02004 39675 0.04602 23614 0.07203 159160.02203 37802 0.04805 22811 0.07403 154920.02402 36119 0.05004 22072 0.07602 150860.02601 34521 0.05203 21362 0.07801 14691

4. Assemble the chamber (with or without aggregate), fill it with water, and perform astandard pressurization-depressurization cycle (without the 2-minute or 5-minute pressurehold).

5. When the pressure is released, the signal analyzer will automatically produce a trace ofpressure vs. time. The wheel on the front of the analyzer can be used to move a cursoralong the trace, displaying both pressure and time coordinates as it moves from data pointto data point.

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Target Pressure Release Rate Profile for Calibrating HFT Apparatus(from original University of Washington HFT Apparatus)

0

10000

20000

30000

40000

50000

60000

70000

0 0.01 0.02 0.03 0.04 0.05 0.06 0.07 0.08 0.09

Time Interval, sec

Rel

ease

Rate

,psi

/sec

Figure 28. HFT apparatus calibration target pressure release rate curve.

Figure 29. Connecting pressure transducer to dynamic signal analyzer.

6. Manually record pressure and time values for at least 50 data points that capture theinitial release of pressure from the chamber.

7. Open the excel spreadsheet called “CALIBRATE.XLS”. Click on the tab labeled“PRESSURE RELEASE DATA”. Enter the manually collected test data into one of theopen fields and enter the regulator settings (e.g., “1150 psi/150 psi) into the cell that lies

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directly above the data entered. NOTE: this spreadsheet can accommodate as many as 5different data sets (in addition to the standard data set) representing 5 differentcombinations of chamber/actuator regulator settings.

8. Click on the tab labeled “CALIBRATION CURVE AND DATA PLOT” to view a graphof both the standard curve and the data collected. If the regulator settings used do notresult in a pressure release curve that closely matches the standard curve, change thesettings and run the test again.

9. Release rates can be varied most easily by modifying the pressure used to operate theactuator that opens the pressure release valve, with higher actuator pressurecorresponding to faster release rates. Release rates can also be accomplished bymodifying the test chamber plumbing (i.e., modifying pressure release port sizes, pipeand valve sizes, etc.) and/or chamber operating pressure (although pressures less than1150 psi may not produce aggregate fractures and pressures significantly higher than1150 psi may produce too much aggregate fracture).

10. After several test runs, the calibration curve and data plot may resemble the one shown infigure 30. Identify the curve that lies closest to the standard curve, especially at time =0.01 seconds (in this figure, it would be for an actuator pressure of 145 psi [the chamberpressure was 1150 psi in all of the tests]).

11. Record the selected regulator settings and perform all future tests (until the nextcalibration) using these settings.

NOTE: Each test apparatus must be calibrated separately; regulator settings for one devicemay not be suitable for another.

0

10000

20000

30000

40000

50000

60000

70000

0 0.01 0.02 0.03 0.04 0.05 0.06 0.07

Time (sec)

Rel

ease

Rat

e(p

si/s

ec)

U Wash90 psi100 psi

120 psi140 psi145 psi150 psi

Figure 30. Example plot of pressure release rate profiles for various actuator pressure settings.

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Calibration should be performed: whenever the pressure release valve is adjusted, maintained or replaced; whenever significant chamber modifications are performed (e.g., modifications in the

length or shape of pressure release plumbing, etc.); whenever the equipment is prepared for use following storage; at least once per week when the equipment is in constant use (to monitor the effects of

wear in the valve assemblies); and whenever there is reason to believe that the pressure release rate has changed.

APPENDIX C

Guidelines for Developing Dilation Prediction Modelsfor Alternate Pressure Chambers or Alternate Freeze-Thaw Tests

C-1

Guidelines for Developing Dilation Prediction Modelsfor Alternate Pressure Chambers or Alternate Freeze-Thaw Tests

Introduction

Snyder and Embacher1 concluded that, based on limited test results, the use of a single

hydraulic fracture test using the modified large hydraulic fracture (HF) test chamber offered

good potential for use in lieu of replicate tests using the smaller chamber, but that additional

validation work is required. They recommended that additional hydraulic fracture testing should

be performed using the modified large hydraulic fracture test chamber using mass measurements

and particles in the 19 to 38 mm (0.75 to 1.5 in) range to further validate the large test chamber.

What this recommendation really means is that one of two tasks must be accomplished:

1) perform additional HF tests using the same aggregate sources that were used in the successful

development of the dilation prediction model for the small chamber and verify that the same

model accurately predicts the dilation values that were obtained from freeze-thaw testing in that

same study, or 2) perform additional HF and freeze-thaw durability tests using the same (or

different) aggregate sources and develop a new dilation prediction model for the large chamber

(a model that may or may not be similar to the one developed for the small chamber).

There are at least two reasons why the second option is the one that should be pursued:

1. There is no guarantee that aggregate samples obtained from the same sources used in the

development of the small chamber will have identical properties to the sample obtained

from the sources when the small chamber models were developed. The only way to

ensure the development of a model that is well-correlated with freeze-thaw test results is

to perform HFT tests and freeze-thaw tests on specimens obtained from the same

aggregate sample.

2. The small chamber HFT model predicts freeze-thaw dilation that results from the use of a

modified version of AASHTO T 161 (Procedure B using a cloth wrap on the beams to

ensure that the beams are saturated during the freezing process). This procedure was

found to correlate best with field durability performance of concrete aggregate during

SHRP program research, and was proposed as a new AASHTO standard (T161

Procedure C), but was not adopted. If MnDOT wants to expand the database used to

develop the small chamber model by including tests of additional aggregate sources,

freeze-thaw testing will need to be performed using this procedure. There may be some

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difficulty in identifying a lab that will perform the test in this way because they will have

to change their freeze-thaw machine operating parameters to do so. Thus, it may be

necessary to develop a new model to use the HFT test to predict freeze-thaw dilation or

durability factor as measured using current standards for AASHTO T 161 Procedures A

or B.

The generalized procedures described below summarize the steps necessary to collect and

process data for the development of a new model from tests of new aggregate samples. The

principles contained can also be applied to validation of the existing model with additional HFT

tests. Most of these procedures are documented in more detail in Embacher and Snyder (2003).

Sampling and Testing

Selection of Aggregate Sources

Identify at least twenty aggregate sources representing the full range of aggregate freeze-thaw

durability should be selected for inclusion in the program. The selected sources should also

represent the range of source types that are believed to be susceptible to freeze-thaw durability

problems (i.e., quarried carbonates and gravels with various carbonate contents). Sources

selected should not include significant quantities of chert, which is known to produce freeze-

thaw damage (popouts) but does not fracture readily using the HFT. The selected sources could

be the same as those that were used in the University of Minnesota study (listed below in Table

C1.)

Sampling the Selected Sources

Sample quantities obtained from each source should be representative of materials that will be

used to produce concrete and should be obtained in sufficient quantity to prepare HFT test

samples (at least 600 particles in the ¾ - 1½-inch range for each test), prepare air-entrained

concrete mixtures for use in casting freeze-thaw and strength specimens and to determine any

desired fundamental aggregate properties such as absorption capacity, specific gravity and unit

weight. A representative sample of proper size must also be provided to the geology unit for

determining the carbonate content of the source (if it is not 100 percent carbonate). It may also

be desirable to prepare a sample for magnesium sulfate soundness testing (since MnDOT

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Table C1. Summary of aggregate sources used in U of Mn study (including their locations and freeze-thaw durability factors).

Location

Aggregate SourceMn/DOT PitDesignation

Freeze-Thaw

DurabilityFactor

County/State SEC TWN RNG

QUARRIEDAaland, Zumbrota 25083 80.5 Goodhue, MN 34 110 15Big Springs, Harmony 23096 18.0 Fillmore, MN 09 101 10Bryan Rock, Shakopee 70006 16.0 Scott, MN 29 115 23Coralville Concrete Ledge, Waterloo N/A 31.2 Waterloo, IAEarly Chapel 155011 36.1 Early Chapel, IAEdward Kramer & Sons, Burnsville 19106 78.6 Dakota, MN 33 027 24Goldberg, Rochester 55037 95.2 Olmsted, MN 36 108 14Michigan Limestone, Cedarville Plant 197001 99.3 Mackinac, MIOsmundson, Grand Meadow 50011 78.4 Mower, MN 09 103 14Shiely Grey Cloud (Larson) 182002 98.8 Washington, MN 26 27 22Southern MN Corp. (SMC) Mankato 74071 13.4 Steele, MN 33 108 20Swedberg 66084 26.2 Rice County, MN 04 109 20Ulland Northwood, Iowa 193018 97.0 Worth, IA 10 99 22

GRAVELAshwill, Kingston 47076 97.1 Meeker, MN 34 120 29Johnson, Henderson 72001 90.2 Sibley, MN 26 113 26Johnson Le Sueur 140002 88.3 Le Sueur, MN 15 111 26Loeffler, Halma 35002 93.9 Kittson, MN 17 160 46Mark, Underwood 56003 95.5 Otter Tail, MN 10 132 41Northern Con, Luverne 67001 83.8 Rock, MN 06 102 44North Star Kasota 140001 79.4 Le Sueur, MN 04 109 26

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currently performs that test routinely, even though evidence suggests that it does not accurately

predict field freeze-thaw durability performance and is not needed for the model building

described herein). Experience suggests that a 500-lb sample of material is usually sufficient to

produce all necessary specimens if the freeze-thaw beams can be prepared from the first batch of

concrete that is mixed. Seven hundred pounds of as-produced aggregate usually provides

enough material, even if multiple concrete batches must be prepared.

Split the Sample

Each aggregate sample must be split using standard ASTM or AASHTO splitting techniques to

produce specimens of the proper sizes for each test to be performed (i.e., HFT, absorption

capacity, specific gravity, freeze-thaw, concrete compressive strength, air content, unit weight,

etc.). In establishing split fractions, remember that over-sized splits must be obtained for the

HFT specimen because only the particles in the ¾ - 1½-inch size range will be used. If the as-

produced material contains little material in this size range, a very large sample may be required

to produce the approximately 35 lbs of material needed in the proper size range for the hydraulic

fracture test.

Prepare Test Specimens

As a minimum, specimens should be prepared for hydraulic fracture tests and freeze-thaw

durability tests. For the hydraulic fracture test, one 600-particle specimen is required; however,

it may be advisable to prepare up to three specimens for each source to provide data for the

preparation of precision and bias statements for the HFT test specification. In preparing the HFT

test specimen(s), it is suggested that a complete sieve analysis be performed for the source

because it may be useful in developing the model to know what proportion of the original as-

produced material is carbonate with particles in the ¾-in plus size range. For freeze-thaw

testing, sufficient concrete should be batched to prepare 4 to 6 test beams (3 to 5 for testing and

one for possible petrographic examination to verify proper entrained air content in the event of

freeze-thaw beam failure), an air content/unit weight specimen, and any strength cylinders or

beams desired. Note that freeze-thaw tests should be performed using concrete prepared using

the as-produced coarse aggregate together with a standard fine aggregate. Suggestions for the

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preparation of the concrete mix preparation are provided below. The freeze-thaw beams should

be cast with gage studs in the ends so that dilation tests can be performed using a comparator.

Perform Tests

All planned tests should be performed in accordance with applicable standards. Freeze-thaw

testing should include determination of relative dynamic modulus (calculated according to

ASTM C 215 “Fundamental Transverse, Longitudinal, and Torsional Resonant Frequencies of

Concrete Specimens”) and dilation (expansion) using a comparator. This will leave model

developers the flexibility to correlate with whichever criterion provides the best model.

In the event that the freeze-thaw test specimens for any particular aggregate source exhibit signs

of freeze-thaw damage, a slice of concrete should be cut from one of the freeze-thaw test

specimens, polished and examined microscopically to verify that any durability failures were due

to the coarse aggregate and not to the cement mortar matrix. The air void system of this same

specimen (or a different specimen obtained from an undamaged beam or cylinder) can be

measured using standard linear traverse technique. There is general agreement in the literature

that a spacing factor of 0.008 in or less and a specific surface equal to or exceeding 600 in2/in3

PCC Mix Preparation

A standard air-entrained PCC paving mixture should be prepared for each selected aggregate

source; Mn/DOT Mix 3A41 (meeting the requirements of specification 2461) was used as the

base mix design for the mix designs used in the University of Minnesota study and is

recommended for continued use here. It is suggested that the mixtures comprise natural river

sand, Type I cement, water and an air-entraining admixture (to ensure that any freeze-thaw

durability problems observed are due to the coarse aggregate and not the cement mortar

matrix). The coarse aggregate should be conditioned to be in a saturated, surface-dry (SSD)

condition at the time of batching to guarantee critical saturation when subjected to rapid

freezing and thawing; using oven-dry fine aggregate makes it easier to control overall water

content and facilitates batching. A water-cement ratio of 0.40, the maximum currently

allowed in Minnesota PCC paving mixtures, is recommended.

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should be observed for concrete intended to be resistant against repeated cycles of freezing and

thawing2,3,4.

Data Reduction and Modeling

Normalization of Hydraulic Fracture Test Results

The hydraulic fracture data must be normalized to account for variations in specimen size.

Normalization is achieved by expressing the mass of particles passing or retained on each sieve

after 50 cycles as a percentage of the total mass of particles contained in the specimen at test

initiation (0 pressurization cycles). This is done automatically in the spreadsheet “HFT DATA

ENTRY AND ANALYSIS.XLS” when the test operators or data entry specialists enter values

for initial specimen weight and particle masses retained on each sieve into the spreadsheet;

cumulative percentages of mass passing each sieve are automatically computed and are

contained in several hidden columns.

Regression Analysis

Model building is a very complex topic to which entire courses and books are devoted. While it

is entirely possible to develop models that are mathematically correct simply by operating a

statistical analysis package, such models often make little practical sense, suggesting impossible

relationships between variables and exhibiting improbable sensitivities outside of the inference

space over which they are developed. A thorough knowledge of both good model development

techniques and the mechanics of the process being modeled are essential in the development of a

useful statistical model.

It is impractical to attempt to provide instruction in model development in the context of this

document. Instead, references 5, 6 and 7 are recommended to those who wish to develop an

understanding of the principles of model building and Appendix E of Embacher and Snyder

(2003) presents a detailed description of the development of the University of Minnesota project

models. The tools and techniques described in that Appendix should be useful in subsequent

model development and refinement.

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The remainder of this section provides a brief introduction to the current HFT dilation prediction

model because it is believed to be a reasonably good template for future model development.

Suggestions for improvements to the University of Minnesota HFT small chamber model are

also included.

The University of Minnesota HFT-dilation Prediction Model (Small Chamber)

The University of Minnesota HFT-dilation model for the small chamber was developed using the

statistical analysis software package ARC , which was developed by Cook and Weisberg5 of the

University of Minnesota Department of Applied Statistics. However, any good statistical

analysis program that is capable of performing multiple linear and nonlinear regression analysis

can be used.

The following model was developed and selected for use in the University of Minnesota study:

% Dil/100 = C3*(6.714711E-9 + 1.493469E-9*M3/4 in

– 2.824751E-7*M5/8 in + 3.648412E-7*M1/2 in

– 5.631620E-7*M3/8 in + 2.102003E-6*M5/16 in

– 1.675012E-6*M#1/4 + 1.183342E-7*M#4)

where:

C = Carbonate content, percent

Mx = cumulative mass of particles passing the indicated sieve as a

percentage of the original sample mass

r2 = 0.978 (r2adj = 0.957), ̂= 0.009934, n = 18

The goodness of fit of this model suggests that future successful models might be developed with

a similar general form, such as:

% Dil/100 = Cn*(β0 + Σβi*Mi)

where:

C = Carbonate content, percent

or

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C = percentage (by weight) of ¾-in-plus carbonate in the as-produced sample (note that

this is different from what was used in the U of Mn model, but may produce better

correlations between the model and the observed freeze-thaw test performance)

β0,βi = regression constants

Mi = a function of the mass retained on or passing sieve “i” , expressed in percentage of

the original sample mass

For additional information on the development of the current small chamber dilation prediction

model, please see Appendix E of reference 1.

References

1. Embacher, R.A. and M. B. Snyder. “Refinement and Validation of the Hydraulic

Fracture Test.” Report No. MN-RC-2003-28. Minnesota Department of Transportation.

St. Paul, MN. 2003.

2. Powers, T. C. Research Department Bulletin RX033: The Air Void Requirements of

Frost-Resistant Concrete. Portland Cement Association. Skokie, IL. 1949.

3. Klieger, P. Research Department Bulletin RX040: Studies of the Effect of Entrained Air

on the Strength and Durability of Concretes Made with Various Maximum Sizes of

Aggregates. Portland Cement Association. Skokie, IL. 1952.

4. Mielenze, R.C., V. E. Wokodoff, J. E. Backstrom, and H. L. Flack. “Origin, Evolution,

and Effects of the Air-Void System in Concrete, Part 1 – Entrained Air in Unhardened

Concrete, Part 2 – Influence of Type and Amount of Air-Entraining Agent, Part 3 –

Influence of Water-Cement Ratio and Compaction, Part 4 – The Air-Void System in Job

Concrete.” Journal of American Concrete Institute, Jul. 1958, Aug. 1958, Sep. 1958,

Oct. 1958. American Concrete Institute. Farmington Hills, MI.

5. Cook, D. R. and S. Weisberg. Applied Regression Including Computing and Graphics.

John Wiley and Sons, Inc. New York, NY. 1999.

6. Agresti, A. An Introduction to Categorical Data Analysis. John Wiley and Sons, Inc.

New York, NY. 1996.

7. Devore, J. and R. Peck. Statistics: The Exploration and Analysis of Data, Second

Edition. Wadsworth, Inc. Belmont, CA. 1993.

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