Development of superpave binder performance grade selection guide for Liberia

The Superpave binder grading system ensures that appropriate binder grades are selected to meet the climatic and traffic conditions of a project site. Liberia still selects asphalt binders based on a penetration grading system, despite its significant limitations. Premature asphalt pavement failures are common, and there is a need to improve asphalt mixture performance. To facilitate the adoption of the Superpave binder performance grade (PG) system in Liberia, a selection guide was developed in this study. Temperature data spanning 1979 to 2014 were gathered from 29 weather stations in Liberia and incorporated in the Long-Term Pavement Performance Program (LTPP) and the Strategic Highway Research Program (SHRP)- based models to determine PG binder grades at 50 %, 85% and 98 % reliability levels. While the SHRP model produced higher binder grades at 50 % reliability compared to the LTPP model, at 85% and 98% reliability levels, the LTPP model produced higher binder grades. However, the highest variance in the PG produced by the two models was one standard grade (6 °C) at all reliability levels. At 98 % reliability, recommended for high traffic volume roads, the LTPP model produced high standard grades of PG 64-YY and PG 70-YY, compared with PG 58-YY and PG 64-YY, for the SHRP model. The study resulted in the development of a PG binder grade selection guide for Liberia to facilitate asphalt mixture design, construction and research. The study recommends field performance monitoring to improve effectiveness of the recommended binder grades, and further research to develop local pavement temperature prediction models.