Estimation of Volumetric Parameters for Different Classes of Bituminous Mixtures Based on Compressible Packing Theory

Abstract

Bituminous mixture design follows volumetric based mix design, and the choice of the optimum binder content is linked to the required volumetric properties such as air voids (Va), and voids in mineral aggregates (VMA). The optimum binder content is selected by an iterative process by varying the binder content, and the one which satisfies the required volumetric criteria is chosen. It should be noted that the choice of a binder content satisfying the required volumetric criteria does not necessarily guarantee a closely packed aggregate skeleton. It will be useful if an analytical formulation is used to design the aggregate gradation and stipulate the required VMA and select an appropriate binder content. Such an approach is presented in this paper. Towards that end, a compressible particle packing model (CPM) is chosen to design and estimate the packing density (PD) for the aggregate blends. The binder content required to meet the required volumetrics is calculated from the estimated PD by linking VMA. It is observed that samples with higher packing density require less bituminous binders for a targeted Va. It is also observed that the binder requirement as determined here was less than what is normally used based on the air void requirement using Superpave mix design method. To quantify the mechanical performance of particle packed bituminous mixtures, the samples are subjected to repeated load haversine compression for a range of temperature and frequency so that their master curves can be constructed. The approach followed here focuses on a reverse mix design strategy by estimating packing density and then by computing the required binder content, and the large number of iterations required to design a bituminous mixture is reduced. From the analysis of master curve of all the samples, it is clearly seen all the mixtures exhibited identical modulus at higher reduced frequencies, and the bituminous mixtures designed with particle packing approach exhibited higher modulus at lower reduced frequencies.