Evaluation of Air Void Distributions of Cement Asphalt Emulsion Mixes Using an X-Ray Computed Tomography Scanner

Abstract

Abstract Air void distributions of cement asphalt emulsion mixes are different from those of ordinary asphalt mixes. In order to evaluate a relationship between air voids and aggregate gradations, or binders of the mixes, an x-ray computed tomography (CT) scanner was used to quantify air void ratio, air void area, and air void size in the mixes. A rheometer and scanning electron microscope (SEM) were adopted to analyze viscosity and microstructures of the asphalt emulsion composites. The results indicate that larger air voids are concentrated on the top and the bottom of the mixes. The middle part of the mixes, which constitutes about 60–70 % of its thickness, has a nearly uniform size of air voids. The demarcation of air void ratio between suspended dense structure and framework dense structure is 6.0 %; and that between framework dense structure and framework void structure is 9.0 %. Adoption of ordinary Portland cement and appropriate increase of asphalt emulsion dosages are beneficial to the decrease of the air void ratio. The binders exert little effect on the increase of the air void sizes than the aggregate gradation types do. Benefits of cement addition are to generate hydrates which are helpful to decrease the air void ratios of the mixes.