s stated in the House Bill 62 Transportation Budget in Brief, roughly 5 billion dollars is spent yearly on road pavement construction in the state of Ohio, with a significant chunk for maintenance. Moreover, maintenance activities and their associated costs are increased in the colder regions of the US where damages and distress on roadways are associated to the Low Temperature Cracking (LTC) phenomena or at least in combination with other distress like rutting and fatigue cracking. Thermally induced internal cracking is a mechanism that occurs under low temperature conditions. Akentuna et al. (2017) postulated that the differential in Coefficient of Thermal Contraction (CTC) values in asphalt binder and aggregate gives rise to thermally induced internal cracking at low temperatures. Owing to its potential significance and effect on LTC modeling, this study investigated the thermally induced thermal cracking phenomena using the Indirect Tensile (IDT) test. The IDT test was selected since it is the test procedure used in fracture property investigation in the AASHTOWare Pavement Mechanistic Empirical (ME) Design program for low temperature cracking modeling. In addition, a study on the effect of loading rate and temperature on asphalt mixtures during the ITS test was also investigated. Although thermally induced internal cracking was observed by Li et al. (2007) using the acoustic emissions test and Behnia et al. (2014) using the Disc-shaped Compact Test (DCT), its quantified effect has not been studied. The results garnered from this study validated the occurrence of thermally induced internal cracking, evidenced by significant reduction in IDT peak strengths and energy at peak stress to averaged magnitudes of 4% and 12% respectively. The second objective of this study on varying loading rate and temperature during the IDT strength tests proved that the standard test loading rate of 12.5mm/min rate was too fast and not representative of field loading rate. In addition, knowing that LTC could occur even at lower stress compared to the IDT strengths, ‘Creep to fail’ tests were performed to analyze the behavior of mixtures in such circumstances. Results showed that creep loads at extremely lower percentages of IDT strengths still fractured asphalt samples with output parameters offering valuable information on crack behavior under low temperature conditions. Time to fracture and crack speed parameters were shown to decrease 62% and increase 46% in thermally induced internal cracking samples.

Introduction and Research Approach -- Findings -- Interpretation, Appraisal, and Applications -- Conclusions and Recommendations -- References -- Appendixes.

Rutting, fatigue, moisture susceptibility, and thermal cracking are the primary distresses of asphalt pavement. Currently several test methods are used to predict the rutting and fatigue behavior of asphalt concrete. This study uses the indirect tensile (IDT) test to evaluate both the rutting and fatigue behavior of asphalt. Recycled concrete aggregate (RCA) and virgin aggregate are blended at different percentages (0 %, 20 %, 40 %, 60 %, 80 %, and 100 %) to produce mixes with a variety of fatigue and rutting performance. The IDT rutting test was performed by running high temperature IDT flow time and strength tests. In addition, flow number tests were performed using an asphalt mixture performance tester (AMPT). A strong correlation is observed between the high temperature IDT flow time/strength and flow number from AMPT. The test results show that IDT tests can be used to predict the rutting behavior of asphalt concrete at high temperatures. To characterize fatigue, cyclic IDT and monotonic fracture energy tests were performed at intermediate temperatures. At intermediate temperatures, good correlation is found between the fatigue life obtained from cyclic IDT test results and the fracture energy obtained from monotonic fracture test results. Based on the laboratory test results, the IDT test can be used to evaluate both the fatigue and rutting behavior of asphalt concrete. Considering that IDT testing has been used to characterize thermal cracking and moisture susceptibility, the IDT test has the potential to serve as a single performance test for fatigue, rutting, thermal cracking and moisture damage. Validation of the findings with more materials and field performance are recommended.

This report describes the thermal stress restrained specimen test (TSRST), which was selected to evaluate the low-temperature cracking resistance of asphalt concrete mixtures. The TSRST system includes a load frame, step-motor-driven load ram, data acquisition hardware and software, temperature controller, and specimen alignment stand. An experiment design that considered a range of mixture and test condition variables was developed to evaluate the suitability of TSRST for characterizing low-temperature cracking resistance of asphalt concrete mixtures. Four asphalts and two aggregates were selected for the experiment. The mixture variables included asphalt type, aggregate type, and air voids content; the test condition variables included specimen size, stress relaxation, aging, and cooling rate.

The purpose of the field validation program was to evaluate the thermal stress restrained specimen test (TSRST) as the accelerated performance test to predict low-temperature cracking of asphalt concrete mixtures. Construction histories, cracking observations, and temperature data were collected for five test roads. In addition, a validation program was conducted at the United States Army Cold Regions Research and Engineering Laboratory. The laboratory test program consisted of performing the TSRST on specimens fabricated in the laboratory with original materials from the test roads and asphalt concrete pavement specimens cut from the actual test sections. In addition, the field pavements were monitored for crack history and, where possible, crack initiation. TSRST fracture temperature correlated with field cracking temperature and crack frequency. TSRST results can be used to predict field low-temperature cracking of asphalt-aggregate mixtures. Preliminary models to predict cracking frequency and temperature for the test roads were developed.

The current means of evaluating the low temperature cracking resistance of HMA relies on extensive test methods that require assumptions about material behaviors and the use of complicated loading equipment. The purpose of this study was to develop and validate a simple test method to directly measure the cracking resistance of hot mix asphalt under field-like conditions. A ring shape asphalt concrete cracking device (ACCD) was developed. ACCD utilizes the low thermal expansion coefficient of Invar steel to induce tensile stresses in a HMA sample as temperature is lowered. The results of the tests of the notched ring shaped specimens compacted around an ACCD Invar ring showed good repeatability with less than 1.0°C (1.8°F) standard deviation in cracking temperature. A laboratory validation indicated that ACCD results of five mixes correlate well with thermal stress restrained specimen test (TSRST) results with the coefficient of determination , r2 = 0.86. To prepare a sample and complete TSRST measurement, it takes minimum 2-3 days. For ACCD, two samples can be easily prepared and tested in a single day with a small test set-up. The capacity of ACCD can be increased easily with minimal cost to accommodate a larger number of samples. Among factors affecting the low temperature performance of HMA, the coefficient of thermal expansion (CTE) of aggregate has been overlooked for years. A composite model of HMA is proposed to describe the low temperature cracking phenomenon. Due to the orthotropic and composite nature of asphalt pavement contraction during cooling, the effects of aggregate CTE is amplified up to 18 times for a typical HMA. Of 14 Ohio aggregates studied, the maximum and the minimum CTEs are 11.4 and 4.0 x 10-6/°C, respectively. During cooling, the contraction of Ohio aggregate with high CTE can double the thermal strain of asphalt binders in the asphalt mix and may cause asphalt pavement thermal cracking at warmer temperature.