A moisture treatment designed to simulate the condition that pavements are exposed to in the wet tropical climate of Singapore is described. A weathering chamber was specially fabricated to introduce simultaneous wetting-drying and thermal cycles. The experimental program subjected four different asphalt mixtures-an open-graded, a gap-graded, and two dense-graded mixes-to the moisture treatment. Results indicate that the treatment was able to induce bleeding, stripping, and softening (loss of strength) in test specimens. The extent and severity of the resultant moisture damage varied with the mixture type and with the length of the treatment cycle period and the number of~ re. at ment cycles. On the basis of the test results, a procedure cons1stmg of 150 4-hr cycles of simultaneous wetting-drying and thermal cycles was recommended. The treatment procedure shows~ ig nificant potential as a research and development tool for studymg the moisture damage resistance of new asphalt mixtures and the effect of modified binders in a wet tropical climate.

Aggregates of crushed natural rock and bituminous binder are the two principal constituents in asphalt paving mixtures. Although the proportion of binder in the mixtures, usually between 5 and 8 percent by weight, is very much less than that of the aggregates, the property of the bituminous binder has a marked influence on the performance of pavement mixtures. The common defects found on highway and airfield pavements, including cracks, rutting, surface distortion, and stripping, are closely related to binder behavior under weather and traffic loading.·