Principles of Resolving Test Result Differences · Principles of Resolving Test Result Differences...

Presented by Cindy RutkoskiRocky Mountain Asphalt Education Center

Instructor

Principles of Resolving Test Result Differences

Friday, January 31, 14

Summary of Presentation

Prevent test result differences before they happen

What can contribute to causing test result differences

Having a procedure in place to resolve test result differences


• Take steps to prevent test result difference should be taken.

• More time, confusion and money is involved later, if prevention steps not taken seriously to begin with.

• Not doing so, can affect pavement quality & cause additional cost to contractor and/or owner.


Measures that can be taken to help prevent test result differences before they

happen.

Calibrate & maintain equipment. Adequate training & certified technicians. Use proper sampling procedures, resulting in similar field

samples between labs. Use same splitting procedure between labs, especaily if

problems persist. Follow standard test procedures.


Check testing – purpose is to compare testing equipment & personnel & test procedures before project begins to indentify & correct potential problems.

Process can be used any time confidence in test result differences occur.

Dispute resolution – Established process to address questions over acceptance test result differences in the properties & pay for asphalt mixtures and placement.


Basic Principles of Asphalt Testing

Representative Samples.Consistency in processes.

Accurate test results completed in a reasonable amount of time .

Good Communication.


Failing to accomplish this will result in differing test results

Representative Samples

Field samples – taken properly to represent material being produced and placed.

Good split samples (similar in gradation) for testing between labs.


Avoiding Test Result Differences

•Follow established sampling procedures and in approved locations.

•Sample in such a way and in a location where aggregates or asphalt mixtures are in a well mixed state. (not from the back of a truck or the paver hopper).

•Fill containers simultaneously, (ex. one scoop per container back and forth till full)

•Use Quarter Master – properly, to mix one or more field samples together, to then distribute between


Avoiding Test Result Differences

Many test result differences are caused by improper splitting.

Proper splitting is important, the resulting test sized specimen should result in a sample that is representative of the larger mass of material being produced or placed.

Follow established procedures, using proper equipment correctly.

Splitting method determined at Pre Pave meeting. Sample must be kept well mixed during splitting

process.


Typical Splitting Methods Method A-Selection by scoop

Method B-Quartering

Method C- Riffle type splitter

Method D-Selection by cross section


Win Win Situation

Accuracy

Test results that are accurate, result in comparable test results between labs.

Result in a Quality Product. Supplier/Contractor receives deserved Incentives Owner/Agency gets quality. Can’t get accurate results from bad samples or

un-calibrated equipment, you will end up with


COMMUNICATION

Perform tests & Communicate test results as soon as possible

The earlier problems or test result differences can be identified the easier it is to resolve them.

Changes that might need to be made at the plant or on the road can be made.

The whole idea is about quality and fair payment! Results being withheld or no urgency with

completing tests and reporting results is counter productive in test result disputes and resolution.


Resolution Process & steps to be taken should be discussed & understood at the Pre-Con &/or Pre–Pave meetings.

All personnel including the Project Engineer must be familiar with procedures and when to use them.

Project Engineer must be informed in writing of issues as they come up.

Proper steps must be followed in order to employ procedures.


Resolution when there are differences between test

results

Differences should be resolved at the lowest level possible.

Best when addressed on the project by project people involved in the project.

Inform those concerned.

CDOT procedure as example


Issues settled at lowest level as possible.

Issues settled on the project level are most effective.1. Initial check testing performed satisfactorily must be complete.2. No challenges can are allowed unless:• Check testing is complete.• Differences must be larger than allowable differences.• Documented split sample submitted by the Project Engineer. 3. Levels of resolution followed, dates & personnel involved

documented and completed within stated time constraints.4. Last level – blind samples submitted confidentially. These

results become the results used in the pay factor calculation in place of the results are in question. (No picking and choosing)


Basic test where differences may occur & then cause other test result differences as a result.

Binder Content/MoistureAggregate Gradation/Specific Gravity &

AbsorptionTheoretical Maximum Specific Gravity –

commonly called the Rice TestCompaction/Density/Air Voids – Final step 1. Nuclear Method / Corr F 2. Bulk Specific Gravity of Cores Air Void & VMA analysis


Asphalt Content Determination

Two Methods AC Content Nuclear Gauge - Quick results (once calibrated) - Quick way to check on aggregate source changes - New calibrations with any source changes

Ignition Oven / Aggregate gradation - Direct correlation between AC content & gradation is good

information - No need for belt cut

- Must use accurate Correction Factors


Possible Causes for Test Result differences with % binder

Nuclear AC content gauge:•Unrepresentative samples (gradation) (splitting)•Inaccurate or no moisture determination.•Pan packed when sample is to cool.•Switch pans if same base weight is used, way to check.

Ignition Oven Method:•Not applying CF or moisture determination.•CF not accurate.•Using wrong CF for mix.•CF are not inter-changeable between ovens. CF does not “go” with a particular mix.•Unrepresentative samples (gradation) (splitting)


Nuclear Content Gauge NCAT Ignition


Moisture Corrections

Must be done, either method

Moisture issues may be more prevalent when:

1. High RAP/RAS mixtures (they are prone to moisture) 2. Rainy weather 3. Using “Warm Mix” (lower temperatures @ plant) 4. Fluctuating volumetrics or AC contentsNot applying a moisture correction results in an in-accurate

binder content.


Asphalt Content Determination

Both Methods are affected by aggregate gradation of sample – if issues arise, could be result of poor splitting techniques.

How improper sampling & splitting can affect results

Gradation of sample must be representative. - Too fine = higher AC Content - Too coarse = lower AC Content


Test Result Differences between field and mix design

If an aggregate source has changed several things can happen.

New mix design may be needed New calibration for Nuc Gauge Correction Factors no longer accurate for Ignition Oven Volumetric calculations will be off for air voids & VMA

Reason is that the Bulk Specific Gravity/Absorption of aggregates may have

significantly changed. Need for consistency in materials


Aggregate Gradation

A Mix Design is based on using the proposed aggregates in prescribed

percentages within allowable deviations.

Percent AC is based on using this “recipe” to obtain specified % air voids and meet the specified minimum VMA requirement.

Changes in gradation can cause compaction problems, result in under-coated or over-coated aggregate.

Rice value is directly correlated to the % AC and gradation of mix being placed.


Maximum Specific Gravity TestThings that can affect results.

Short term aging of the samples before running the RICE test is very important. The absorption process of the binder must be allowed to take

place. Density test results will vary & be in-accurate when using

unrepresentative rice values. Errors in this test procedure arise from improper splitting

techniques. Calibration weights on flasks/lids need to be accurate. Pressure gauge pulling correct vacuum. Water temperature monitered.


Rice test


Determining %Compaction & % Air Voids

Two methods commonly used: Moisture Density Nuclear Gauge 1. Quick, non destructive. 2. Gauge set on correct mode (MA). 3. In-put correct numbers in gauge (max. density, corr. factor). 4. Calibrated & maintained. 5. Correlate gauge to pavement using Correction Factors. Bulk Specific Gravity on cores 1. Smaller quantity projects. 2. Correction Factors for MD gauge. 3. Check on gauge readings when in question. 4. Used for lab compacted specimens as well as roadway


Preventing & Resolving test result differences in the determination of

roadway densities

Nuclear Gauge Method•Gauge set in right mode.•Correct Maximum Density for mix being placed.•Correct CF used for mix type, lift and gauge.•Gauge calibrated and maintained.Bulk Specific Gravity using SSD Method of Roadway Cores•Water temperature correct.•Towel not to wet or dry for SSD measurement.•Not shaking or rolling specimen before SSD determination.CoreDry Apparatus – newer method – CDOT approved

Use CorLok Device – newer method - FHWA


Nuclear Gauges


Bulk Specific Gravity on Cores


CoreLok / CoreDryFriday, January 31, 14

No one test result stands aloneOne test result will affect others

Once again, to achieve proper compaction, we need accurate rice values.

To achieve accurate rice values we need to have samples that are representative of the mix being placed.

We also need to have an accurate determination of the asphalt cement


Rice value needs to be Accurate

Using an incorrect rice value that is too high will result in a calculated density that is actually lower than what the density of the roadway really is. This could result in over compaction of the mat.

Using an incorrect rice that is too low will result in a

calculated density that is actually higher than what the density of the roadway really is. This could result in under compaction of the mat


Correction Factors

Correction factors correlate the gauges to the mat, allowing for calculated density to be more accurate for the mix being placed.

Cores are taken - cores measure the actual density

Correction Factor (CF) is calculated off the difference between the average of the cores and the average of gauge wet densities.

CF is applied in the calculation of the density from the gauge readings – verify correct CF is being used for mix, lift and gauge.


Relationship between

Relationship that should be seen if values are accurate – Trend that should be seen

As the AC Content increases, the Rice Value should decrease

As the Rice Value increases, the AC Content should decrease.

Helps in test result analysis to determine if results are accurate.


If this trend is not seen, check AC determination test process, samples at compaction temperature long enough, to long, gyratory angle set properly.

Another Trend that should be seen:

There is also a direct relationship between the %AC and %Air Voids, that goes along with pavement durability and compaction.


Air Void Analysis & VMA

What is VMA & why is it important?

VMA = Voids in the Mineral AggregateThe space between the uncoated aggregate, that allows

room for the binder to coat the aggregate. When mix is compacted, VMA is made up of the effective

binder (portion left as a coating on the aggregates) and air voids.

Mix must meet minimum VMA specs. Affected by gradation of mix & %AC. It is desirable if the

aggregates remain fairly consistent with aggregate proposed for the mix design.


% Air Voids & VMA accuracy

Values used in determination of % air voids (Va):

Gmm – Maximum Specific Gravity (Rice)Gmb – Bulk Specific Gravity of Compacted Asphalt.

Values needed for calculating VMA are:•Gmb – bulk specific gravity of compacted specimen.•Gsb – bulk specific gravity of total aggregate (no significant agg source changes off mix design).•Pb –% binder.

•Need accurate measurements for an accurate calculation of % air voids and VMA


Another Important Element

Temperature

Another important part of preventing test result differences, is maintaining and calibrating all testing equipment, including thermometers and ovens.


Resolving Test Result Differences in Air Voids

The Temperatures used in lab testing must be accurate.

This is one of the main things that can cause differences between lab test results in

determining percent of air voids.

Ovens must be checked for temperature accuracy.•Each shelf and location on that shelf must be checked to determine if samples are getting to compaction temperature throughout the specimen.•Specimens must be at compaction temperature for at least 15 minutes prior to compaction and no longer than 4 hours.


Resolving Test Result Differences – Air Voids

Gyratory angles

•Another important factor that can affect the percent of air voids, is the accuracy of the angle that the gyratory is set at.•The angle must be checked periodically and anytime there are test result differences that seem to persist.•Check testing programs performed before production starts can indentify such problems before they happen.


Summary

Representative samples & test specimens along with standard test procedures performed consistently & accurately, will contribute to producing & placing a quality pavement.

Accuracy & good communication help monitor the mix production & placement.

No one test result stands alone, all mix properties work together & are affected by one another, hence, the importance of accurately & continually monitoring mix properties, compaction and placement throughout production.


Summary of Preventing & Resolving test result relationships

• •Following standard test procedures accurately.• Pay attention to test results and trends, do they make sense. Qualified technicians.• Open door policy for lab and procedures being used/ split samples when issues come up. • TEMPERATURES – Lottman, rice, oven temp. of samples at time of compaction on gyratory.• Check testing program – identify potential problems up front.• Lab equipment maintenance & calibrations kept up.• Establish a Dispute Resolution Process, be familiar with the steps to follow.• Address problems quickly at the lowest level and keep project people informed.• • •


Common problems that occur

•Gyratory - Check angle, sample temperatures, representative samples. •Rice tests – Calibration weights, water temperature, careful splitting, shake times, vibrating tables calibrated.•Ignition Oven – Correction Factors correct and applied, moisture corrections, aggregate break down accounted for if applicable, samples representative, gradation effects results , RAP (other additives) included in samples.•AC Content gauge – Corrected for moisture, representative samples, gradation effects results.•Air void analysis – Bulk Specific Gravity run properly, use Cordry or Better yet CoreLok apparatus.•Density gauge testing – using gauge properly, right settings, accurate max density, accurate CF.


Remember no test result stands alone

Questions?

EXAM


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