In the design of double chip seals, perhaps the most important factor to be computed is the amount of bituminous material required to fill the voids betweenthe aggregate to an optimum depth. A design method developed by the national institute for transport and road research was evaluated by texas transportation institute (tti). This method includes a simple test procedure for measuring the void content and effective layer thickness of the stone layers. It also provides for a way of estimating the loss of voids in the seal over its expected life due to embedment in the underlying surface and wear and degradation of the stone. This method also considers the fact that voids within the aggregate layers vary nonlinearly with depth. This design approach is quite different from anything currently used in the united states. Tti evaluated this method by using chip seal aggregates graded to texas state department of highways and public transportation specifications. Two double chip seal test roads built in texas according to the design methods discussed are performing well. This paper appears in transportation research record no. 1259, Chip seals, friction courses, and asphalt pavement rutting 1990.
Abstract