Studying the Effect of Adding Natural Sand on the Mechanical Properties of Asphalt Mixture

Abstract

Asphalt mixture is the most widely used material in roads and highways construction. It is composed of mineral aggregates, asphalt binder and filler. Properties of these materials and their interactions determine the mechanical behavior of asphalt mixtures, and consequently the durability of resultant asphalt pavements over time. Thus, adequate selection of materials is required to obtain correct asphalt pavement performance. This study aims to determine the optimum ratio of natural sand to be introduced to the asphalt mixture while maintaining or improving the mechanical properties of the mixture, at the same or lower cost per unit. To this reason, several material properties must be assessed and compared to control specimens. Those parameters are Stability, Density, Flow, Voids Mineral Aggregate (VMA), Air Voids Content (Va) and Voids Filled with Bitumen (VFB) in asphalt mixtures. Before conducting the experimental works, the material properties for all aggregates to be used in the experimental program were evaluated, such as physical properties and sieve analysis for the aggregates and bitumen-related properties such as penetration, specific gravity, ductility, flash point and softening point tests. Additionally, an aggregate blending procedure was implemented to properly select the various ratios of each aggregate in the asphalt mixture. The experimental program consisted of three phases. Phase (A) to determine the optimum bitumen content (OBC) without adding natural sand. Results from Phase (A) were considered as control data to be compared with when adding the natural sand at various amounts. The Following phase is Phase (B) were natural sand replaced Trabia by various amounts, starting from 2.50% until 15%, which is the maximum Trabia content based on the aggregate blending procedure. Aggregate blends with various percentage of natural sand were blended as closely as possible to same gradation. While phase (C) aimed to re-evaluate the bitumen content after obtaining the optimum sand content. Results from Phase (A) indicated that a bitumen content of 5.00% would yield the most optimum results in terms of stability, bulk density and air voids. Based on this result, Phase (B) was implemented with bitumen content of 5.00%, in which, a natural sand content of 7.5% yielded the optimum results in terms of the same properties, i.e., stability, bulk density and air voids. Results from Phase (C) indicated that for asphalt mixture with natural sand content of 7.50%, the optimum bitumen content would be 4.60%. Based on the findings of this research, it is recommend to use asphalt mixture with embedded natural sand content (Optimum: 7.50%) in real-life application to assess its long term behavior.