Use of accelerated loading equipment for determination of long term moisture susceptibility of hot mix asphalt

Stripping of HMA with moisture susceptible aggregates, under high temperature and aircraft loading has been a persistent problem in some areas of the Logan International Airport in Boston, Massachusetts. These problem mixes generally meet the retained tensile strength criteria, after freeze–thaw conditioning. This study was conducted to evaluate the use of accelerated loading equipment for identifying moisture susceptible mixes, and also to evaluate the effect of lime. Mixes with three different aggregates were prepared with PG 76-28 asphalt binder according to specifications. Specimens were conditioned by three different methods: (1) multiple cycles of freeze–thaw, (2) wet trafficking with the model mobile load simulator (MMLS3) and (3) cycles of stress with the moisture induced stress tester, (MIST). Thereafter, the respective indirect tensile strengths were determined. The results showed that accelerated loading can provide useful information for evaluating resistance of HMA to moisture damage under traffic at high temperature. For mixes to have adequate resistance to moisture damage by volumetric expansion–contraction, acceptable tensile strength tests were needed after at least six freeze–thaw conditioning cycles. The evaluation of resistance to moisture damage under traffic at high temperature using moisture stress conditioning proved to be highly promising. The methods should be investigated further. The use of hydrated lime, improved the resistance of HMA against moisture induced stress damage at high temperatures. On the basis of these conclusions, it is recommended that testing protocols, consisting of both freeze–thaw and accelerated loading/moisture induced stress testing at high temperature, be used for evaluating the most cost-effective anti-stripping agent (liquid or solid).