Simplified novel approach for estimating HMA overlay thickness schedule using long-term performance indicators

Abstract

A simplified novel approach for estimating the HMA overlay thickness is proposed in this paper for flexible pavement resurfacing schedules. The overlay thickness is mainly estimated from the difference between the existing asphaltic thickness and reduced asphaltic thickness. The reduced asphaltic thickness is estimated as the sum of two components: a bottom component unaffected by pavement distresses and reduced thickness of a top component affected by pavement distresses. The reduced thickness of the top component is estimated from multiplying its thickness after subtracting the cold milling thickness by an asphaltic remaining strength factor. The remaining strength factor is defined as a ratio of average distress rating (DR) associated with the pavement remaining service life and average DR associated with the entire service life. This ratio is raised to the power (K) to be estimated from the minimisation of sum of squared errors. The two required DR averages are estimated from the performance curve for a particular pavement project. The remaining strength factor can also be defined as a ratio of the average surface deflection (D¯80) and tolerable deflection at the surface (TDS) as deployed by the Caltrans mechanistic-empirical design approach. The reduced asphaltic thickness is mainly used to estimate the overlay thickness required at a specified service time. The two case studies presented have indicated the effectiveness of the proposed approach in estimating overlay thickness schedules with relatively low errors.