Expanded study on the effects of aggregate coating and films on concrete performance

Abstract

The WisDOT sponsored study entitled: "Effects of Aggregate Coatings and Films on Concrete Performance", ID: 0092-00-07, found that clay coatings showed a deleterious impact in concrete compared with other microfine mineralogy such as dust or carbonates. The principal aim of this research was to complement the previous project by identifying the primary variables that govern the effects of clay microfine coatings on concrete pavements and to use this knowledge to improve the present aggregate monitoring situation in Wisconsin. The materials selected for this research were two naturally-coated igneous aggregates located near Eau Claire and an igneous clean coarse aggregate from Black River Falls which was lab-coated with four different clay suspensions (kaolin, illite, sodium montmorillonite and calcium montmorillonite). A total of ten batches: a control, two containing natural coatings and 4 containing each one of the select clays as coarse aggregate coatings at a 0.45 w/c ratio were prepared along with 3 additional batches with extra water to maintain workability. The major findings are that the effects of microfines in concrete are not only dependent on the amount of microfines but also on their nature. The methylene blue test together with P200 to calculate the modified methylene blue value is the best predictor of the influence of coatings on concrete performance, but the methylene blue test presents practical difficulties for WisDOT implementation and a new test is needed.