Asphalt Test Relationships The Devil s In The Details

Asphalt Test Relationships The Devil s In The Details Jayson Jordan, PE Technical Director jjordan@scasphalt.org

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Asphalt Test Relationships The Devil s In The Details!

Details Matter!

Details Matter Jayson R. Jordan Jason G. Jordan

Test Results Relationships What do we mean by Test Result Relationships? What are they? Why is it important to be able to identify trends in test results? What types of things can affect test results?

Test Results Relationships Accurate, Repeatable, and Comparable Consistency SCDOT has Percent Within Limits specification Pay Factors 30%: Percent Asphalt Content 25%: Percent Air Voids 10%: Percent VMA 35%: In-Place Density

Test Results Relationships Aggregates Binder or Asphalt Content VMA Rice Values Maximum Specific Gravity Compaction Temperatures Air Voids

Other Key Factors Specific Gravity of aggregates individual/combined Short Term Aging Gradation of mix (samples)

Asphalt Tests

Asphalt Content Measure weight of basket and sample prior to test Basket is placed in oven at a temperature of 1000º F + 18 ºF Oven prints ticket with percent loss The asphalt burned off during the test represents the asphalt content (in percentage of total weight)

Gradation Main reason why we are sampling our aggregates. Sieve analysis gives us our gradation. Typically we are interested in the percent passing any given sieve. We compare gradation to Job Mix Formula

Rice Test or Maximum Specific Gravity Take 1500-2000 g of loose sample and spread on non absorptive paper. Break up any clumps of asphalt by hand. Allow sample to cool to room temperature Measure weights of sample and bowls dry. Place 77 F ± 1.8 F water in bowl, submerge sample, apply vacuum (min 27 Hg) for 15 minutes After vacuuming, place sample in 77 F ± 1.8 F water bath for 10 minutes. Measure the underwater weight. MSG DryWeight DryWeight WetWeight

HMA Test Result Relationships Binder Content and Rice Value (Theoretical Maximum Specific Gravity)

Binder and Rice Relationship

Binder Content vs MSG 2.460 2.455 2.450 y = -0.0085x + 2.4937 R² = 0.05 2.445 2.440 2.435 2.430 2.425 2.420 5.10 5.20 5.30 5.40 5.50 5.60 5.70 5.80 5.90 6.00 Measured Predicted Linear (Measured) Linear (Measured) Linear (Predicted)

Binder Content & Rice Summary of Test Relationships: As the asphalt content increases, the rice value will decrease. As the asphalt content decreases, the rice value will increase. Discuss!

Binder Content, Rice Value (MSG) Does the GRADATION of a sample affect the results for Asphalt Binder Content or Rice? Affects AC content. Affects Rice value results.

How does Gradation affect Test Coarse sample will result in a lower AC content. Fine sample will result in a higher AC content. **Remember the trend of AC versus Rice (MSG).** Due to splitting (sampling)? A too coarse or too fine gradation will also affect the rice results. If the gradation is unrepresentative, then the rice result on that sample is not going to be correct to be used on the roadway!

HMA Test Result Relationships High Asphalt Binder Content Low Asphalt Binder Content

Low Binder Contents Dryness / raveling Impermeability Oxidation Fatigue Cracking Lack of compaction Flexibility Durability

High Binder Contents Durability Stability Rutting Flushing Bleeding

High and Low Asphalt Content Test Result Relationships Low asphalt content = high air voids Low asphalt content = higher maximum specific gravity (rice) High asphalt content = low air voids High asphalt content = lower maximum specific gravity (rice) Discuss, Explain

Summary Low %AC Higher % AirVoids Higher Ricevalue High %AC Lower % AirVoids Lower Ricevalue

HMA Test Result Relationships Rice (Theoretical Maximum Specific Gravity)/Maximum Density and Roadway Density

Rice Value and Density

Rice Value and Density Percent compaction is actually telling us the percent of air voids in the mat. In order to have a durable long lasting pavement, there needs to be between 8 & 4% air voids (92% - 96% compaction). Hence, the need for accurate rice values to monitor the compactive effort. AND AIR VOIDS! AND VMA!

Rice Value and Density Example: Field Spec Grav. of 2.380 (nuclear gauge) / 2.507 (Mix Design)= 94.9% Field SG of 2.380 (nuclear gauge) / 2.482 (New Target Rice) = 95.9% Wet Density: (convert Spec. Grav to wet density- 62.4 x SG) 148.5 / 156.4 (Mix Design) = 94.9% 148.5 / 154.9 (adjusted New Target) = 95.9%

Rice Value & Density If Rice or MSG not representative of the mix being placed: Causes either an over or under compacted mat. Calculated percent compaction becomes just a number that is not accurate or a true reflection of the density of the mat. What happens to the Pavement Quality? Over compaction can lead to rutting, flushing or bleeding, resulting in a shortened pavement life and even dangerous driving conditions. Under compaction can lead to pavement susceptibility to moisture and air damage, shortening the life & durability of the road 70% of your Lot Pay Factor (In-Place Density, AV, VMA) hinges on accurate MSG results!

Rice Value & Density Summary of Test Relationship Using a 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 a 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 In Nuclear Gauges Correction Factors to correlate nuclear gauge to the mat result in more accurate density test results

Correction Factors In Nuclear Gauges Check the settings in the gauge MA for Asphalt Correct maximum density input into the gauge. Using the correct Correctiong Factor? Correction Factors correlate gauges to mat for accurate compaction.

HMA Test Result Relationships Air Voids and Gradation

Volumetric Calculations VMA & Air voids, most important mix properties being measured in process control testing (all based on physical tests) Complying with volumetric criteria is great assurance the mixture will be long lasting & well performing HMA pavement. SOON: PERFORMANCE TESTS! Also, along with quality comes incentive pay.

VMA Change in Rice value may indicate a change in the Bulk Specific Gravity of the Aggregate. When the Rice value changes, the VMA changes, but still has to meet the minimum specified requirements. VMA what is it and how does it affect the durability of the pavement? VFA what is it?

Air Voids and Gradations The durability of an asphalt pavement is a function of the air void content. Air voids = compaction = durability Aggregate gradation is what makes the strong stone skeleton to enhance resistance to permanent deformation and allows for sufficient void space to enhance mixture durability.

Voids and Gradation High % of 200 (esp. natural sands) = low % air voids in the compacted specimen. Addition of Crusher Fines (minus 3/8 angular shape) can increase VMA. Aggregate texture & shape also play into void content. Sampling, splitting & testing procedures.

Gradation and VMA VMA is affected by gradation Greater VMA values for smaller Nominal Max Aggregate size (greater intergranular void space) Leads to more about aggregate absorption and the importance of the aging process

Absorption of Binder Affected By: Viscosity of binder Aggregate type /pore size Time Temperatures

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HMA Test Result Relationships What Affects A Rice Value?

What Affects a Rice Value Sampling Splitting Temperatures Testing equipment Cure times for aggregate absorption

Cure Times of the Mix Standard practice for cure times or aging periods is 2 hours @ compaction temperature SC T 98: Determination of HMA Properties from HMA Contractor Plant Produced Mixtures Using Hot or Reheated Samples SC T 103: Field Procedure for Preparing Gyratory Specimens on Hot Mix Asphalt Mixtures Using the Gyratory Compactor

Mix Aging Aged Expected percent of asphalt binder has absorbed into the aggregate. Not aged At time of testing, asphalt binder still coating outside of aggregate, but will be lost due to absorption.

HMA Test Result Relationships The Importance of Monitoring Temperature During Compaction

Temperature & Compaction Even a good mix, if not compacted properly will not. result in a long lasting durable asphalt pavement

Temperature & Compaction As binder cools it becomes stiffer and bonds the aggregates to provide a durable structure.

Temperature & Compaction The temperature of a mix is perhaps the most important property in obtaining density Temperature Viscosity charts! Obtaining density is perhaps the most important process for a durable, long lasting asphalt pavement

Conclusion Even a good mix that meets all the mix design criteria in the lab has to be properly compacted to have an end result of a durable, long life pavement. BEST PRACTICES!

Longitudinal Joints Best Practices!

Thank You! jjordan@scasphalt.org