Elaboration of a blended binder based on marls from phosphate mines waste rocks

Abstract

This paper investigates the properties of a mixture design of three tender marls as a binder. The used marls are by-products of open-pit phosphate mine. At first, ten mixtures with diverse combinations of calcined marl (CM) were blended with cement at a ratio of 1:1. The properties of those blends were tested including hydration kinetics, setting time, and unconfined compressive strength (UCS) at different ages of curing. The findings confirm the reactivity of those marls and their contribution to the developed strengths by hydraulic and pozzolanic activity. Despite the higher incorporation of CM (50 %), some of the blended binders reached a strength index activity (SAI) higher than 75 % at all the curing age. This qualifies those blends as supplementary cementitious materials (SCMs). The findings imply that whatever the proportioning mixture of the marls, in a mix of 1:1 with cement, the UCS could achieve 17–26 MPa, 23–36 MPa, and 34–50 MPa at 7, 28, and 91 days, respectively. After optimizing the mixture proportioning of marls, their incorporation rate was varied and studied. The results showed that the optimal CM with a substitution rate of 20 wt% had the highest strengths at all the curing age with a SAI to the reference of 153, 138, and 127 % at 7, 28, and 91 days respectively. The incorporation of 40 wt% of the optimal CM led to a slightly higher and comparable results to the reference without mitigating the UCS. Blends with 40–80 wt% of optimal CM substitution rate could be used as a binder for masonry mortar. Upper this incorporation rate, 100 % optimal CM revealed a good self-reactivity that achieved 10 MPa at 28-d can be used as a binder for repairing historical building.