“Thermally Induced Internal Cracking in Asphalt Mixtures – Validation with Indirect Tensile (IDT) Test”

CEE Seminar by Sang Soo Kim, Ph.D., founder of EZ Asphalt Technology and creator of Asphalt Binder Cracking Device

Abstract

The transition phenomenon has been observed during thermo-volumetric measurement of asphalt mixtures at low temperatures. This transition occurring near -30°C was believed to be caused by thermally induced internal cracking driven by the large differential contractions of asphalt binder and aggregates . The objectives of this paper were (1) to validate the thermally induced internal cracking using indirect tensile (IDT) strength test and (2) to determine how the thermo-volumetric transition temperature was related to the low temperature performance.

IDT strength tests were performed at -20°C, -10°C and 0°C with several loading rates on three groups of samples: control, internally cracked, and healed groups. The control group was tested as-is while the internally cracked group was first subjected to -60°C to induce internal cracking prior to IDT test. The healed group was subjected to -60°C and then to 25°C for minimum 2 hours to heal prior to IDT test.

The energy input to reach the peak stress for the internally cracked group was up to 30% lower than the control group. The thermally induced internal cracks appeared to be completely healed by exposing to 25°C for 2 hours. The thermo-volumetric transition temperatures were highly correlated with predicted cracking temperatures with r-square values greater than 0.95.