ASTM-Specific Gravity and Absorption of Aggregate by...
Transcript of ASTM-Specific Gravity and Absorption of Aggregate by...
9/23/2016
1
Specific Gravity and Absorption of Aggregate by Volumetric Immersion
Method(Phunque Test)
ASTM June 2015 Meeting
by Bryce Simons, P.E.
Eliminating the Guesswork – A New Absorption/Specific Gravity Test for
Aggregate
9/23/2016
2
Frustrated and Confused
Problems with ASTM C 128/AASHTO T‐84
• Test is • subjective;• profoundly influenced by operator;• Impossible to repeat the same result;
• Seriously different between different labs;• Unable to predict slumps in concrete;
• Variability creates construction and payment conflicts with HMA.
9/23/2016
3
Desired Characteristics
• Easy to perform;
• Easy to understand;
• Easily re‐produced;
• Operator and laboratory independent
Basic Physics
• Physically and visually measure total amount of water absorbed into the sample;
• Physically and visually measure Volume displacement of dry sample;
• Physically and visually measure Volume displacement of saturated sample.
9/23/2016
4
New Test Requirements
• Normal absorptions are relatively small, so large amount of aggregate needs to be tested to allow accurate measurement of total absorbed water;• Large waterproof bottom;
• Narrow, calibrated neck;• Ability to add materials quickly without loss.
Finding Equipment
• Checked existing glassware manufacturers and suppliers without success;
• Worked with specialty glass‐blowing company to construct a container meeting these requirements.
9/23/2016
5
Develop Procedure
• How to add material
• When to take readings
• How to calculate results
• How to interpret results
Characteristics Needed
• Absorption
• Bulk Dry Specific Gravity
• Bulk SSD Specific Gravity
• Apparent Specific Gravity
9/23/2016
6
Lab Procedure
• Flask
• Aggregate
• Introduction of Water
• Observations & Measurements
• Calculations & Corrections
Specialty Flask
9/23/2016
7
Lab Procedure
Documentation
• Initially, procedure was reviewed and evaluated by:• FHWA Research Laboratory in Washington, D.C.;
• Heidelberg Technology Center in Atlanta, Georgia;• Kansas Department of Transportation;
• New Mexico Department of Transportation (Allowed as alternative test method for all aggregates tested after July 1, 2006).
9/23/2016
8
T-84 AbsorptionPhunque Absorption
0.00
0.20
0.40
0.60
0.80
1.00
1.20
1.40
1.60
1.80
2.00
MaterialsBureau
(Santa Fe)
NMDOTDistrict 6
NMDOTDistrict 2
Billingsley AMEC Turner-Fairbanks
HeidelburgTech
Center
KansasDOT
Placitas Fine Aggregate Absorption Comparison
T-84 Absorption
Phunque Absorption
9/23/2016
9
2.480
2.500
2.520
2.540
2.560
2.580
2.600
2.620
2.640
MaterialsBureau
(Santa Fe)
NMDOTDistrict 6
NMDOTDistrict 2
Billingsley AMEC Turner-Fairbanks
HeidelburgTech
Center
KansasDOT
Bulk SSD Specific Gravity for Placitas Fine Aggregate
T-84 Bulk SSD Sp Gr
Phunque Bulk SSD Sp GR
2.460
2.480
2.500
2.520
2.540
2.560
2.580
2.600
2.620
T-84 Bulk Dry Sp Gr
Phunque Bulk Dry Sp GR
Bulk Dry Specific Gravity for Placitas Fine Aggregate
9/23/2016
10
2.620
2.625
2.630
2.635
2.640
2.645
2.650
2.655
T-84 Apparent Sp Gr
Phunque Apparent Sp GR
Apparent Specific Gravity for Placitas Fine Aggregate
The benefit of consistency in SuperpaveAsphalt Mixes was also considered:
• Volume determinations • QC/QA Pay Factor Calculations
9/23/2016
11
Specific Gravity & absorption by Volumetric Immersion Method
• Originally approved by AASHTO as TP‐77 in 2009
• This method was studied as a part of NCHRP 4‐35 “Testing of Specific Gravity and Absorption of Aggregates” This study found that:
• This method applies to coarse aggregate, fine aggregate and combined aggregate
• This was the only method suitable for measuring combined aggregates;
• It is a relatively simple operation;
• This method is the most repeatable and reproducible of all the methods studied;
• This method is not affected by P200 or particle shape/angularity;
• The Initial Reading at 30 seconds is questionable.
9/23/2016
12
Benefits related to this method
• Simplicity of test method;
• Not effected by which technician or laboratory performs the test;
• Not affected by fineness or coarseness of gradation;
• Not affected by particle shape;
• Can provide actual measurement of blended aggregates instead of requiring mathematical calculations;
• Method is sufficiently sensitive to quickly recognize changes in aggregate or pit characteristics.
Concerns related to use of this method
• Test vessel made of glass is breakable and somewhat fragile (This issue has been mitigated by constructing flasks from “Vacuum Grade” heavy duty glass which is very difficult to break);
• Significant difference between direct result from this method and the result from T85 or T84;
• Initial reading at 0.5 minutes (30 seconds) felt to be too late;
• Existing specifications as well as HMA and PCC mix designs currently based on results from T85 and T84 would be seriously impacted if these results are directly substituted.
9/23/2016
13
Evolutionary needs for this test
• Initial Reading must reflect true beginning water displacement before any water has been absorbed by any aggregate;
• Must be able to provide results that can be directly used in lieu of T84 or T85;
Initial reading
• Not realistically possible to obtain initial reading more quickly than 30 seconds;
• Initial reading at 30 seconds allows air introduced by pouring dry aggregate sample into flask to escape before it can affect the reading;
• Water is being absorbed by initial dry particles immediately upon entering the water bath even though initial reading is not taken until after all particles have been submerged in water and 30 seconds has elapsed since the pouring of aggregate started.
9/23/2016
14
Adjusted initial reading
• When actual readings are plotted on semi‐log graph with volume on the vertical scale and time on the logarithmic horizontal scale, the result is a virtual straight line.
• Logarithmic regression analysis provides a correlation coefficient typically significantly better than 0.9 confirming a very strong reliability.
• To calculate an adjusted Initial Reading, simply enter the desired Initial Time as the “x” variable and calculate the resulting displacement.
9/23/2016
15
Calculation of adjusted initial reading
• From previous slide for Trial #1, the equation for the line is:y = ‐3.265 * Ln(x) + 4527.7
• Substitute the desired time at which the Adjusted Initial Volume is desired (in this case assume it is desired to determine the Initial Reading at 0.01 minutes)
y = ‐3.265 * Ln(0.01) + 4527.7y = ‐3.265 * (‐4.6052) + 4527.7y = 15.04 + 4527.7y = 4542.74
• (Initial Volume read at 30 seconds = 4528.4)
Test results for this example
AASHTO T85 Direct Result Adjusted Result
Absorption: 1.52% 1.00% 1.55%
Sp Gravity (Dry): 2.588 2.651 2.586
Sp Gravity (SSD): 2.627 2.651 2.627
Apparent Gravity: 2.694 2.695 2.695
9/23/2016
16
All aggregate sources in new Mexico were tested and summarized in the following table
9/23/2016
17
Typical aggregate types
• Gneiss
• Monzonite
• Quartzite
• Rhyolite
• Shale
• Igneous
• Limestone
• Sandstone
• Andesite
• Basalt
• Caliche
• Granite
• Feldspar
9/23/2016
18
This data was plotted against a 1:1 line and the relationship determined
Absorption
T85 vs. Direct Results T85 vs. Adjusted to 0.10 minutes
9/23/2016
19
AbsorptionT85 vs. Adjusted to 0.05 minutes
T85 vs. Adjusted to 0.01 minutes
Bulk specific gravity (dry)
T85 vs. Direct Results T85 vs. Adjusted to 0.10 minutes
9/23/2016
20
Bulk specific gravity (dry)
T85 vs. Adjusted to 0.05 minutes T85 vs. Adjusted to 0.01 minutes
Bulk specific gravity (ssd)
T85 vs. Direct Results T85 vs. Adjusted to 0.10 minutes
9/23/2016
21
Bulk specific gravity (ssd)T85 vs. Adjusted to 0.05 minutes
T85 vs. Adjusted to 0.01 minutes
Conclusions• By using Initial Readings adjusted to 0.01 minutes, the relationship between T85 and the results using the Adjusted Initial Readings for all properties is approximately equal to or better than for the direct results determined from the procedure;
• Results calculated from Initial Readings adjusted to 0.01 minutes can be used directly in existing specifications and in the development of HMA and PCC mix designs.
• The correlation coefficient for the Absorption is lower because the inherent subjectivity of the test procedure profoundly effects accuracy, consistency and repeatability of T85.
9/23/2016
22
Conclusions (Pg 2)
• Fine aggregates were not included in this evaluation due to the flawed assumptions and biased effects from this procedure on the resulting properties.
• Since the basic physics for this test remain the same regardless of particle size, the conclusions from the evaluation of the coarse aggregate can be applied to fine aggregate and to combined aggregates.
• TP 77 has been balloted and approved as a full Test: T??.