Booil Kim

Evaluation of Healing Property of Asphalt Mixtures

Although repeated traffic loading causes damage to accumulate in asphalt pavements, the damage heals during rest periods (time between traffic loadings). Consequently, this healing enhances the fatigue life of the pavement. A method was developed to determine the healing rate of asphalt mixtures in terms of recovered dissipated creep strain energy (DCSE) per unit time. The healing properties of four different asphalt mixtures were evaluated with this approach. The test procedure consists of a repeated loading test and periodic resilient modulus tests. A normalized healing rate in terms of DCSE/DCSEapplied was defined to evaluate the healing properties independent of the amount of damage incurred in the mixture. From the test results, it was determined that the healing rates of the asphalt mixtures tested increased dramatically above 10°C and were more affected by the aggregate structural characteristics (i.e., aggregate interlock, film thickness, voids in mineral aggregate) of the mixtures than by polymer...

Effect of styrene butadiene styrene modifier on cracking resistance of asphalt mixture

A laboratory investigation was conducted to evaluate the effects of styrene butadiene styrene (SBS) modification on the cracking resistance and healing characteristics of coarse-graded Superpave® mixtures. Four types of asphalt mixtures with 6.1% and 7.2% design asphalt contents using unmodified and SBS-modified asphalt cement were produced in the laboratory. Tests performed with the Superpave indirect tensile (IDT) test included repeated-load fracture and healing test, strength tests at two loading rates, and longer-term creep tests to failure. The test results showed that the benefit of SBS modifiers to mixture cracking resistance appeared to be primarily derived from a reduced rate of micro-damage accumulation. The reduced rate of damage accumulation was reflected in a lower m value without a reduction in fracture limit or healing rates. It was shown that the benefits of the SBS modifier were clearly identified by using the hot-mix asphalt fracture model, which accounts for the combined effects of m value and fracture energy limit on cracking resistance. It was also determined that the residual dissipated energy as determined from Superpave IDT strength tests appears to be uniquely associated with the presence and benefit of SBS modification and may provide a quick way to make relative comparisons of cracking performance. Longer-term creep test showed that time to crack initiation appeared to provide another parameter uniquely related to the effects of SBS modification. The key to characterizing the effects of SBS modifier on the cracking resistance of asphalt mixture is in the evaluation of the combined effects of creep and failure limits.

Cost Analysis for use of SBS Modifier in Asphalt Pavement using a Performance-based Fracture Criterion

ABSTRACT The effect of SBS modifier on cracking resistance of asphalt mixtures has been evaluated. The benefit of SBS modifiers appeared to be primarily derived from a reduced rate of micro-damage accumulation, which was reflected in a lower m-value without a reduction in fracture limit or healing rate. A cost analysis for use of SBS modifier in asphalt pavements was conducted using the performance-based fracture criterion, Energy Ratio. Cost analyses indicated that the construction cost of the AC layer would be reduced by up to 30% by SBS modification.

Laboratory and Field Toughening Characteristics of Fiber Reinforced Hot- Mix Asphalt Mixtures

This study investigated the enhanced toughening characteristics of plastic fiberreinforced hot-mix asphalt (HMA) mixtures in laboratory and field tests. The toughening effects of plastic fiber-reinforced HMA mixtures were characterized using direct tensile loading tests. Adding a small quantity of plastic fibers to HMA was found to significantly increase the mixture’s fracture energy, which was calculated using the tensile force-displacement curves. The fracture energy model appeared to be governed by the direct tensile toughening of fiber-reinforced HMA’s enhanced fiber bridging effects. The field measurement of the fiber reinforced mixture resulted in at least ten times lower tensile strains than those of the plain HMA at the bottom of HMA. This indicates that the fiber reinforced mixture has a superior field performance than the plain HMA does and can extend overall performance life of the mixtures if adding a small amount of fibers such as 0.4% by the mixture’s weight within the context of the fiber developed in this study.