Water susceptibility of asphalt mixtures as influenced by hydraulically active fillers

Water affects asphalt pavements in a detrimental way and it is common knowledge that certain combinations of binder and aggregate can trigger premature failures. Asphalt manufacturing relies mainly on experience and continuous empirical testing. To reduce water sensitivity, adhesion promoters are frequently used. In this investigation, focus was on using portland cement and a by-product from cement manufacturing, cement kiln dust (CKD). The hypothesis was that water susceptibility is influenced by the grading of the hydraulically active fillers: a finer grading will give a stronger improvement. The experimental plan comprised, besides a reference material, 3 different cements and 2 CKDs. Water susceptibility was assessed with the tumbler abrasion test using mastic specimens. Potentially negative effects: decreased workability and degraded low temperature properties were investigated by measuring viscosity of filler/bitumen mixes and low temperature cracking properties, respectively. Admixing of hydraulic filler was made by partly replacing the base material filler with hydraulic filler, thus keeping the overall filler content unchanged. Results show that resistance to moisture damage is improved by adding hydraulically active fillers. However, the hypothesis of finer gradings giving stronger response was not supported; all three portland cements gave very similar results. Furthermore, it seems that fractions of added hydraulic filler above 1–1.5 % (mass of total aggregate) do not further increase abrasion resistance. Essentially, no potential drawbacks, decreased workability or increased low temperature cracking, were noted.