It has been known for many decades that the mixing moisture content (MMC)in a granular material can affect asphalt dispersion when treated with foamed asphalt. However in the literature this issue remained as a supposition only supported by subjective observations. This paper attempts to reveal the micromechanics of the effects of MMC on foamed asphalt dispersion by combining direct microstructure observations and conventional laboratorytesting. It was found that for a typical granular material in a recycledpavement, the agglomeration state evolves through a series of states as the MMC increases. If the MMC is high, the fine particles become saturatedand form a paste like substance that coats bigger aggregate particles, creating large agglomerations. Fracture face image analysis for tested ITS specimens revealed that moist granular materials with large agglomerationstend to yield inferior asphalt dispersion. Different conventional laboratory tests found that mixes with inferior asphalt dispersion yield lower strength and lower resilient modulus. The resilient modulus of these mixesis also more sensitive to the stress states but less sensitive to loadingrate. These effects are more significant for granular materials with higher fines content. The main engineering implication of the findings is that relatively dry (~75% of optimum moisture content) loose granular mixes are preferred for foamed asphalt dispersion, and a balance should be sought between asphalt dispersion and mix compactability. The postulation thathigh MMC aids foamed asphalt dispersion is dismissed.
Abstract