Elaboration of alkali activated materials using a non-calcined red clay from phosphate mines amended with fly ash or slag: A structural study

This study aims to explore the feasibility of using waste red clay from a sedimentary, interlayered phosphate deposit to produce a geopolymer mortar without any pre-treatment. Alkali activated mortars were prepared by mixing fly ash or slag with red clay and sand, using different fly ash or slag/red clay ratios. The effects of sodium silicate to sodium hydroxide ratio (SS/SH) and curing time on the mortar's properties were studied. The results showed that compared to fly ash-based alkali activated materials, an increase of the slag content resulted in the formation of dense mortars while in the case of fly ash based-samples more porous mortars were formed when the fly ash amount was increased. The mineralogical investigations indicated a partial contribution of montmorillonite and palygorskite from the clay to the alkali activation reaction. The mechanical properties of the materials were promising with a maximum compressive strength of up to 39 MPa obtained for the mixture of fly ash and red clay at a fly ash/red clay ratio of 2 and a SS/SH of 1.