Tolerable Strains for HMA Overlays over Concrete Pavements

Abstract

Materials from two Kansas Department of Transportation (KDOT) projects', namely 089 C-4318-01 (Mix 1) and 56-29 KA-1087-01 (Mix 2), were used for the laboratory study. Considering typical overlay thicknesses used in Kansas, samples of thickness 1.5in and 2in were chosen. Direct shear box tests and semi-circular bend tests were conducted on these chosen HMA mixtures to characterize their shear and tensile properties respectively. Crack width was simulated in lab by steel bars having thickness 0.25in, 0.375in, and 0.5in in direct shear tests. Measured relative movements of these HMA mixtures at failure varied from 4.5 percent to 9.4 percent of the sample thickness depending upon the simulated crack width. Tolerable tensile strain of Mix 1 under fatigue loading in semi-circular bend tests was 3.5 percent and that of Mix 2 was 1.4 percent for 2in thick samples. Two inch thick samples gave more consistent results than 1.5 in. thick samples hence the results obtained from 2in thick samples should be used.