Case Studies in Construction Materials (Jul 2024)
Using surface free energy and mechanical methods to investigate the effect of aging on the fatigue cracking potential of UHMWPE-modified HMA
Abstract
Aging due to environmental conditions significantly affects the occurrence of fatigue cracking in hot-mix asphalt (HMA). Previous analyses showed that aging reduces mastic resistance and bitumen-aggregate adhesion, but these experiments were usually performed on HMA samples, and failure mechanisms were not reflected in the results. Accordingly, via the surface free energy (SFE) theory, this study examined the impact of aging on the fatigue cracking mechanism of HMA. Dynamic methods, including indirect tensile fatigue test (ITFT) and Pull-Off tensile strength (POTS), were applied to HMA samples at 5 and 20 ˚C to study the association between the results of SFE tests. Two performance-graded bitumens (PG 58–22 and PG 64–16), two aggregates with different mineralogical properties (limestone and siliceous), and a polymeric additive (ultra-high-molecular-weight polyethylene-UHMWPE) as a bitumen modifier were also used. Based on the results, aging decreased and increased the polar (28.6%) and non-polar (15.14%) properties of bitumens, respectively. A decline in polar properties lowered the bitumen-aggregate adhesion (8.11%), which was generally because of polar bonds. The rise in cohesion free energy (CFE) by up to 9.5% and non-polar properties due to aging decreased the failure probability in the bitumen film of the aged specimens. UHMWPE improved the non-polar properties of the asphalt (by up to 15.09%), providing greater resistance against aging and reduced adhesion with mineral aggregates. According to the POTS test results at the state of cohesive failure, aging enhanced the POTS of cohesion, especially in UHMWPE-modified bitumen-aggregate by up to 12.12%. POTS in the state of cohesive failure was independent of adhesion free energy (AFE), yet CFE influenced POTS at the state of adhesive failure. Based on the fatigue life of HMA, even though aging increased the CFE and stiffness of HMA, the decline in the AFE parameters and flexibility reduced the fatigue life of the aged HMA in comparison to similar non-aged specimens (by up to 5.17%). The polymer additive significantly improved the resistance of asphalt mixtures to cohesion (by up to 23.16%), adhesion (by up to 16.78%), and fatigue life (by up to 12.8%). Additionally, in aged samples, there was a noticeable reduction in the parameters of cohesion, adhesion, and fatigue life in the modified samples compared to the base samples.
