New Specification of Material for Surfacing Unpaved Roads

To develop a new specification of material for surfacing unpaved roads, an experiment was conducted on 41 unpaved road sections located in five different physiographical regions in the state of Rio Grande do Sul, Brazil. The behavior of the sections under observation was analyzed qualitatively to evaluate the performance of the applied surfacing material. Because the traditional soil classifications (Highway Research Board and Unified Soil Classification System) are not suitable for classifying tropical soils, a new classification, namely MCT (miniature, compacted, tropical), developed in Brazil in 1981 was adopted as a basis for material selection. The behavior parameters observed were support, frictional resistance, and durability. The results obtained led to the specifications presented here, which were tested during a doctorate research program developed between 1991 and 1996 conducted by the first author and supervised by the second. It was concluded that the proposed specification based on the MCT classification system is more adequate than the ones previously used based on traditional classifications. The “binder content” of soils, a measure similar to that used for bituminous materials (asphalt binder content) is introduced to evaluate the agglomerating capacity of the fine fraction and, therefore, the material durability.