2007 annual conference when to worry about test results danny gierhart, p.e. odot bituminous...

2007 ANNUAL CONFERENCE

WHEN TO WHEN TO WORRY ABOUT WORRY ABOUT TEST RESULTSTEST RESULTS

Danny Gierhart, P.E. ODOT Bituminous Engineer

ANSWER:

(However, you need to worry about some more than others)

• What is the test designed to tell you?

• For this test, how much could the degree out of specification affect pavement performance?

• Are the potential ramifications minor or major?

• What are the potential ramifications of a failing test result?

Test results are often used to document the degree out of specification so that a corresponding financial penalty can be assessed.

The very best use of test results is to track the ongoing quality of a project and make corrections as necessary to ensure a quality pavement.

• LIQUID ASPHALT

• HOT MIX ASPHALT

• AGGREGATE

ASPHALT BINDER TEST – DYNAMIC SHEAR RHEOMETER (DSR)

1.15

• What is the test designed to tell you?The purpose of the test is to address potential rutting due to binder stiffness.


Typical failing DSR tests reveal increased rutting and/or cracking potential. from negligible up to an average of 1/4”. They can also indicate whether or not the binder has sufficient polymer.


A typical failing DSR test indicates relatively minor problems. Large deviations can indicate significant problems.

DSR tests that are slightly low (running 0.90 to 0.99) are minor. Tests that are ½ the target indicate a lower grade of binder was sampled.



• How much does the degree out of spec affect pavement performance?

ASPHALT EMULSION TEST – SAYBOLT-FUROL VISCOSITY

1.1577 20 - 100 22

• What is the test designed to tell you?The purpose of the test is to show the as-delivered viscosity, or fluidity of the material.


Failing tack coat results will often be on the low side, indicating a deficiency of residual asphalt. This could cause slippage between lifts. For chip seal emulsions, a low value could mean that aggregate particles will not stick well. Results on the high side may be caused by an old sample.


Slippage between lifts as a result of insufficient adhesion.

Failing viscosity tests that are an accurate indicator of low residual asphalt content can, under the right circumstances, have serious ramifications.

Field application has a significant effect on performance. It is very difficult to establish how big the problem is based on test results alone.




Emulsion test results are only as good as the sample quality. Emulsion samples are particularly susceptible to compromise.

• Samples obtained after the emulsion is diluted onsite.

RED FLAG ALERT!

• Samples obtained, but not submitted for weeks.

• Samples allowed to sit in sun or roll around in truck.

• Samples placed in a contaminated container.

ASPHALT CUTBACK TEST – KINEMATIC VISCOSITY

30 - 60 45

• What is the test designed to tell you?This test also shows the as-delivered viscosity, or fluidity of the material. It tells the supplier about the uniformity of shipments.


Low test results indicate a higher ratio of diluent to asphalt cement. The prime may not provide the moisture barrier intended. High test results indicate a lower ratio of diluent to asphalt cement.


Failing viscosity tests have a minimal effect on the quality of prime. For example, both MC-30 and MC-70 are acceptable for use as prime coat. An out-of-spec high MC-30 may meet or be low for MC-70.

Out-of-spec on the high side should not have a major effect. Tests for MC-30 that are significantly low will likely result in an ineffective moisture barrier.




AGGREGATE TEST - GRADATION

Comparison

Comparison

• What is the test designed to tell you?The maximum aggregate size influences allowable pavement thickness, susceptibility to segregation, asphalt content, and volumetric requirements.


A gradation on the maximum sieve size that is less than 100% indicates the presence of over-sized particles. This could result in compaction difficulties, segregation, and asphalt content problems.

AGGREGATE TEST – GRADATION (Max. Agg. Size)

Gradations results showing less that 100% passing the maximum sieve size are rare and usually only slightly less than 100%. Potential ramifications are minimal.

Results deviating by 10% or more indicate that a different type of HMA was sampled than expected.



AGGREGATE TEST – GRADATION (Max. Agg. Size)

Comparison

• What is the test designed to tell you?The % passing the # 200 sieve influences compaction, asphalt content, and volumetric requirements.


A low % passing the # 200 may result in high air voids, permeability, and a lower AC demand. A high value may result in low air voids and VMA, a higher AC demand, and a tender mix.

AGGREGATE TEST – GRADATION (% Passing # 200)

Check cracking as a result of a high % passing the #200 sieve combined with a low binder content

High % passing the #200 gives the HMA a lighter appearance, indicating a lower film thickness and lower durability.

High dust portions can have major ramifications on the longevity of a roadway. They are typically accompanied by lower than necessary binder contents which reduce pavement durability.

Deviations inside the tolerance of 2% typically don’t have too much of an effect. Deviations greater than 2% should be addressed immediately.




Comparison

• What is the test designed to tell you?The % passing the # 8 sieve has a major influence on voids and permeability.


A low % passing the # 8 sieve may result in a permeable mix. A high value is not as worrisome as a low value.


Low % passing the # 8 indicates a mix that is subject to permeability, which in turn can lead to stripping.

A low % passing the # 8 sieve can have major ramifications on the longevity of a roadway. They are often accompanied by permeability issues which can lead to stripping.

Gradations near the lower broad band are especially of concern when accompanied by a low % passing the # 200 sieve.




AGGREGATE TEST – SAND EQUIVALENT

• What is the test designed to tell you?The test is intended to show the relative proportions of fine dust or clay-like material in the aggregate.


A low sand equivalent result indicates a high percentage by volume of clay-like fines. These fines may cause the asphalt binder to debond from the aggregate in the presence of moisture.


Low sand equivalents indicate a high percentage of clay-like fines, which can cause a poor bond with the asphalt binder.

Although extremely rare, a failing sand equivalent test indicates a very poor aggregate quality, which can have major ramifications to the longevity of the pavement.

Sand equivalent results do not have to be much out of spec to be a cause for concern.




HOT MIX ASPHALT TEST – TENSILE STRENGTH RATIO

• What is the test designed to tell you?The test is intended to show the susceptibility of the HMA to moisture damage.


A failing TSR indicates the mix is inherently susceptible to stripping and raveling.


• Moisture Sensitivity– Prepare set of 6 specimens

• 6.5 to 7.5% voids– Represents anticipated in-service voids

– Use 3 specimens as controls– Remaining 3 specimens are vacuum saturated 70

to 80%– Min. 16 hour freezing at 0oF– 24 Hours in 140oF water bath – Bring all specimens to test temperature (77oF)

and determine indirect tensile strength

Tensile Strength Ratio AASHTO T 283

Tensile Strength Ratio AASHTO T 283

Saturating Specimens

Freezing Specimens

Specimens in Hot Water Bath

Calculate the Tensile Strength Ratio (TSR)

Minimum of 75% required for field tests

Determine the indirect tensile strengths of both sets of 3 specimens

TSR = Avg. wet tensile strength

Avg. dry tensile strength

Moisture SensitivityAASHTO T 283

The ramifications of a failing TSR can be severe.

Because the test procedure is not one of the most repeatable, results down to around 70% should be confirmed by further testing. TSR results less than 65% would be just cause for immediate work stoppage to investigate and fix the problem.




HOT MIX ASPHALT TEST – ASPHALT BINDER CONTENT

JMFResult Comparison

• What is the test designed to tell you?The test shows the percent of asphalt binder by weight of the total mix.


A low binder content can lead to premature aging of the pavement, stripping, or raveling. A high binder content can lead to flushing or bleeding in the pavement.


Low binder contents can lead to raveling, stripping, and premature aging.

High binder contents can lead to flushing or bleeding.

The ramifications would likely be different depending on the degree out of spec. Whether any of the potential pavement distresses occur also depend on other factors.

Binder content is one of several parameters that affect each other. However, binder contents very far out of spec should be a major cause for concern.




HOT MIX ASPHALT TEST – AIR VOID CONTENT

Specimen 2Specimen 1 Average

• What is the test designed to tell you?The test shows the percent air voids in lab-molded specimens. This test indicates a mix property, not in-place air voids.


With a low air void content, the pavement is susceptible to rutting, flushing, and bleeding. For high air void contents, the pavement is susceptible to premature aging, raveling, and stripping.


The ramifications can be severe depending on the degree out of specification. Whether any of the potential pavement distresses occur also depend on other factors.

All failing void contents need some type of action. Mixes that are 1% or more out of spec indicate a need for immediate shutdown for more trials.




HOT MIX ASPHALT TEST – VOIDS IN MINERAL AGGREGATE (VMA)

Specimen 2Specimen 1 Average

• What is the test designed to tell you?VMA is calculated from the binder content test and lab-molded specimens. It tells about the total volume of the voids created by aggregates.


Samples with low VMA do not have enough void space to provide the proper amount of binder and the proper amount of air. Low VMA, depending on the reason, could result in many distress types.


The ramifications can be severe depending on the degree out of specification. Whether any of the potential pavement distresses occur also depend on other factors.

Mixes that are 1% or more out of spec indicate a need for immediate shutdown for more trials.




HOT MIX ASPHALT TEST – ROADWAY DENSITY

Core 1 Core 2 Core 3

• What is the test designed to tell you?The test indicates the in-place density achieved by the compactive effort of the rolling operation.


Low density may result in permeability, stripping, raveling, cracking, premature aging, and premature failure. High density may result in rutting, flushing, or bleeding.


The ramifications of failure to achieve proper density are major. Proper density can in part make up for other shortcomings. Improper density can cause failure even if other parameters are good.

Any failing density report should cause the agency to closely examine the rolling operation. The further out of spec, the shorter the anticipated pavement life.




In summary, all failing test results should be followed up on.

Some test results may be received after all of the material is already in place.

Some test results will be received in time for corrective action, which should be immediate.

Remember that a few hours time addressing a problem may prolong the pavement life by several years.

QUESTIONS?

2007 annual conference when to worry about test results danny gierhart, p.e. odot bituminous...

Documents

failing test result

low test results

emulsion test results

high test results

aggregate test gradation

size slide

potential ramifications

best use of test results