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EVALUATION OF MOISTURE DAMAGE IN HOT-MIX ASPHALT WITH PENNDOT DISTRICT 1 LOCAL AGGREGATES
ABSTRACT
The sources delivering quality aggregate for use in hot-mix asphalt concrete have been depleting in PennDOT District 1, which has currently resulted in shortage of quality Type A aggregate in this district. The local aggregates don’t meet the required criteria on soundness or absorption level, or both. Furthermore, stripping and moisture damage in these gravel aggregates are of concern even though most of these aggregates exhibit excellent skid resistance and durability. As a result of this situation, research was conducted to evaluate resistance of moisture damage of hot-mix asphalt concrete using District 1-0 aggregates. Research included modifications that could be applied to asphalt mixtures to improve moisture resistance of such aggregates in hot-mix asphalt. Four Type C aggregates and one Type A aggregate, all sources located in District 1-0, were selected for evaluation. Mixes were prepared as control, with liquid anti-stripping agent, with lime, and with a gravel-limestone blend for the #8 material at equal proportions. The tests included PennDOT’s modified version of AASHTO test method T283 (Tensile Strength Ratio), one-third scale model mobile load simulator (MMLS3), and dynamic modulus test with repeated freeze-thaw cycles. Overall, it was concluded that two of the five aggregate sources without any treatment could pass the requirement on moisture damage resistance based on the PennDOT version of the AASHTO T283 test method. It was also found that the specific liquid anti-stripping agent used with these mixes improved the moisture damage resistance significantly. The study indicated improvement of moisture damage resistance using the limestone-gravel blend to a much lesser degree compared to the improvement gained through the usage of liquid anti-stripping agent. In testing with the MMLS3, only three control mixes were included, and testing was conducted under both dry and wet conditions. A higher rutting level was found in wet tested specimens compared to dry specimens. Only two of the five mixes were chosen for evaluation using dynamic modulus testing due to limited resources and time.
Each specimen was planned to be tested four times: unconditioned, after it was conditioned once, conditioned twice, and conditioned three times. However, a few specimens failed after second cycle of conditioning and therefore dynamic modulus could not be obtained for all conditions. Results indicate that the modulus decreases as the testing frequency decreases. Furthermore, the modulus dropped after being conditioned at all frequencies for all the mixes, especially after the second cycle of conditioning.
TABLE OF CONTENTS
LIST OF FIGURES……………………………………………………………………………………………………….vii
LIST OF TABLES…………………………………………………………………………………………………………xi
ACKNOWLEDGEMENTS……………………………………………………………………………………………xiii
Chapter 1 INTRODUCTION…………………………………………………………………………………………1
1.1 Problem Statement ……………………………………………………………………………………………1
1.2 Scope of Research …………………………………………………………………………………………….2
1.3 Research Objectives………………………………………………………………………………………….2
Chapter 2 REVIEW OF LITERATURE…………………………………………………………………………4
2.1 Moisture Damage in HMA………………………………………………………………………………..4
2.2 Additives to Minimize Moisture Damage …………………………………………………………..5
2.3 Moisture Sensitivity Tests …………………………………………………………………………………9
2.3.1 Modified Lottman Test (AASHTO T283) ………………………………………………..11
2.3.2 Dynamic Modulus…………………………………………………………………………………..12
2.4 MMLS3……………………………………………………………………………………………………………14
Chapter 3 MATERIAL, EXPERIMENT DESIGN, PROTOCOL, AND TESTING
EQUIPMENT ………………………………………………………………………………………………………..16
3.1 Materials ………………………………………………………………………………………………………….16
3.1.1 Aggregate Sources………………………………………………………………………………….16
3.1.2 Binder Source…………………………………………………………………………………………22
3.2 Mix Design ………………………………………………………………………………………………………223.3 Experiment Design……………………………………………………………………………………………25
3.4 Experiment Programs, Procedures and Test Equipment……………………………………….27
3.4.1 Indirect Tensile Testing…………………………………………………………………………..27
3.4.1.1 Testing Protocols ………………………………………………………………………….273.4.1.2 Lime Treatment…………………………………………………………………………….28
3.4.1.3 Testing Equipment………………………………………………………………………..29
3.4.2 One-Third Scale Model Mobile Load Simulator (MMLS3)……………………….30
3.4.2.1 Testing Equipment………………………………………………………………………..30
3.4.2.2 Specimen Preparation……………………………………………………………………36
3.4.2.3 Testing Protocol……………………………………………………………………………36
3.4.3 Dynamic Modulus Testing with Repeated Freeze-Thaw Cycles…………………38
3.4.3.1 Specimen Preparation……………………………………………………………………39
3.4.3.2 Testing Equipment………………………………………………………………………..39
3.4.3.3 Dynamic Modulus Test Protocol……………………………………………………41
Chapter 4 EXPERIMENTAL RESULT, ANALYSIS, AND DISCUSSION…………………….44
4.1 Maximum Theoretical Specific Gravity (Gmm) with Different Mixture Curing
Times……………………………………………………………………………………………………………..44
4.1.1 Effect of Different Mixture Curing Durations on Maximum Theoretical
Specific Gravity (Gmm)……………………………………………………………………………..44
4.1.2 Statistical Analysis on the Relation of Water Absorptions of the
Aggregates and Gmm Values with Different Curing Duration………………………46
4.2 Indirect Tensile Strength Test…………………………………………………………………………….47
4.2.1 Results of PennDOT-Modified Version of AASHTO T283 Test………………..47
4.2.2 Statistical Comparison of Mean Tensile Strength of Dry and Conditioned
Specimens……………………………………………………………………………………………….50
4.3 MMLS3 Testing……………………………………………………………………………………………….53
4.3.1 Results of MMLS3 Testing in Wet Condition…………………………………………..54
4.3.2 Results of MMLS3 Testing in Dry Condition……………………………………………55
4.3.3 Comparison of Test Results …………………………………………………………………….56
4.4 Dynamic Modulus Tests with Repeated Freeze-Thaw Cycles………………………………61
4.4.1 Results of Dynamic Modulus Tests………………………………………………………….61
4.4.2 Analysis on Ratio of Moduli……………………………………………………………………64
Chapter 5 CONCLUSION AND RECOMMENDATION FOR FUTURE RESEARCH……66
5.1 Conclusion……………………………………………………………………………………………………….66
5.2 Recommendation for Future Research………………………………………………………………..68
BIBLIOGRAPHY………………………………………………………………………………………………………….70
Appendix A Regression Analysis of Gmm with Six-Hour Curing Duration versus Gmm with Two-Hour Curing Duration and Water Absorptions of the Aggregates……………….75 Appendix B Results of AASHTO T283 Tests………………………………………………………………..76
Appendix C Detailed Graphs from MMLS3 Testing……………………………………………………….81
Appendix D Dynamic Modulus Test Results ………………………………………………………………….95
Chapter 1
INTRODUCTION
1.1 Problem Statement
Aggregate plays a critical role in hot-mix asphalt (HMA) pavement. It affects performance of the pavement and its ability to resist distresses. To ensure better pavement performance and facilitate the selection of quality aggregates for highway construction industry, Superpave system incorporated aggregate criteria into the Superpave mix design procedures as quality requirements for aggregates used in HMA. These criteria apply to shape, angularity, clay content, toughness, soundness, deleterious materials, absorption, and gradation. However, in some areas, sources of good-quality aggregates for pavement may not be evenly spread, or may have already been depleted due to previous construction needs. For projects in those areas that are short of high-quality aggregates for HMA, the quality aggregates are often transported from sources outside the area.
Over the past few years, District 1 of Pennsylvania Department of Transportation (PennDOT) has begun facing depletion of high quality Type A aggregates. Most of the available local aggregates only fail to meet two requirements of Type A material, sodium sulfate soundness and water absorption. In addition, moisture induced damage in the area has drawn much attention. Therefore, studying moisture damage sensitivity in HMA pavement with these aggregates will provide a reference for agencies concerned with future usage of these local aggregates, and a guideline of what modification or additive should be adopted when incorporating these aggregates.
1.2 Scope of Research
The research was concentrated on moisture damage investigation of hot mix asphalt containing PennDOT District 1 local aggregates. Five different aggregates were procured from the district and were used to prepare lab-fabricated, Superpave Gyratory Compacted (SGC) specimens. Modifications to the asphalt mix and incorporation of additives such as liquid antistripping agent for asphalt, limestone, and hydrated lime were included in the experimental evaluation.
Three major experimental tracks were conducted separately to investigate different aspects of moisture damage:
- Modified AASHTO T283 method conducted on SGC specimens,
- Accelerated pavement testing using the 1/3rd scale model mobile load simulator (MMLS3) in both dry and wet environments performed on trimmed SGC specimens, and
- Dynamic modulus (DM) tests on laboratory specimens that underwent three cycles of conditioning according to AASHTO T283 method for vacuum saturation and freezethaw process.
1.3 Research Objectives
The research approach in this study consists of the following parts:
- To evaluate the moisture susceptibility of HMA with aggregates from PennDOT District
1 using the three preceding test methods.
- To evaluate results of PennDOT-modified AASHTO T283 method to determine the
feasibility of several proposed mixture treatments on improving the resistance to moisture damage in HMA with aggregates from PennDOT District 1.
To compare results from MMLS3 and from dynamic modulus testing including repeated freeze-thaw cycles with results from PennDOT-modified AASHTO T283 method.
