Laboratory evaluation of moisture damage in asphalt

Traditionally, moisture damage in asphalt is determined by laboratory testing of liquid asphalt binder, loose mix, and (or) solid asphalt concrete samples under wet and dry conditions. Yet some asphalt mixes pass such laboratory moisture damage tests but show poor moisture damage potential in the field. To this end, this study presents asphalt constituents such as mastic and matrix testing for true evaluation of field moisture damage in asphalt concrete. Three mixes included in this study have almost identical laboratory moisture damage potential, but coarse mix (SP-III) has higher field moisture damage potential than two fine mixes (SP-B, SP-C). Related to these mixes, three mastics namely natural fines (NF), crushed fines (CF), and combined natural and crushed fines (NF+CF) are tested using a dynamic shear rheometer (DSR) at varying temperature and frequency. Also, matrix materials passing #4 sieve is tested in DSR, tension, pull-off, and direct shear loadings. It is shown that mastic and matrix test results can better identify field moisture damage of asphalt concrete. Fine mastic and matrix have low moisture damage potential than the coarse matrix and mastic. At high temperature (above 25 degrees C), shear modulus converges to a small number irrespective of mastic type. Due to moisture conditioning, matrix ultimate stress decreases in tension and pull-off tests but not in shear test.