Proposed Evaluation of Base Materials for Drainability

Base materials are normally selected to achieve maximum density and possess sufficient stiffness and strength to carry traffic loads. Long-time concerns about the poor drainability of these materials have recently prompted the highway materials community to address this problem. The main objectives of the research reported here were to evaluate the drainability of base materials used in Texas and to propose and evaluate modified materials that could improve drainability while maintaining stiffness and strength levels. Drainability is evaluated on the basis of the permeability coefficient and water retention tests. The water retention test was found to be a much easier test to perform than the permeability test and is believed to be much more directly related to the drainability of the compacted base than the permeability coefficient. Alternative materials evaluated consisted of open-graded bases and cement-stabilized gravel. The results of the present study indicate that cement-stabilized gravel is the best alternative to achieve high stiffness and strength and at the same time minimize water retention capacity.