Many unsealed roads require urgent upgrading to a sealed standard as a result of social issues, excessive traffic volumes, high maintenance requirements and a lack of suitable material for regravelling. The high cost of upgrading using conventional standards results in most of these roads remaining in an unacceptable condition. By using thinner pavement structures and marginal surfacing aggregates, the cost of upgrading can be made far more affordable. This report describes recent work to evaluate the minimum strength of stone necessary for satisfactory construction of surfacing seals. Laboratory simulation of seal construction with weak aggregates using steel drum and pneumatic tyred rollers as well as the effects of trafficking has allowed the identification of minimum strengths. It is suggested that the minimum 10 percent fines aggregate crushing test (FACT) value for surfacing aggregate should be related to traffic and values of 90, 120 and 150 kN are tentatively proposed for traffic of less than 3, from 3 to 6 and greater than 6 heavy vehicles per day respectively. This should be combined with excess binder to ensure structural integrity of the seal, even if some stone loss occurs. Timely maintenance is also essential. (a)
Abstract