Reaction kinetics and microstructural characteristics of iron-rich-laterite-based phosphate binder

Due to their intriguing properties, phosphate cement, also known as chemically bonded phosphate cement, have been developed for the past decade. The need for sustainable building material with low cost and easy availability has prompted research into the use of laterites, which are abundant in Cameroon. The purpose of this research was to synthesize laterite-based phosphate cement (LPCs) with phosphoric acid as the sole activator. The parameters taken into consideration were the molar concentration of phosphoric acid, liquid to solid ratio and the type of solid precursors. Early reactivity of the LPCs was assessed using a semi-adiabatic calorimeter and the results showed an increase in the heat of reaction proportionally to the concentration of phosphoric acid, except for 10 M solutions where early reactivity was inhibited. The results of the 14-day compressive strengths of the studied LPCs were in the range of 23–98 MPa for LPE and 31–105 MPa for LPN, respectively depending on the specific formulation. For both laterite phosphate cement, molar concentrations of 6 and 8 M resulted in the optimum strength. The phase composition was determined using X-ray powder diffraction, and the amorphous and crystalline phases of the raw materials and phosphate cement were quantified using Rietveld measurement. The X-ray pattern of the laterite-phosphate cement revealed that the intensity peak of hematite decreases in the presence of phosphoric acid and led to the formation of an amorphous product, which is supported by phase analysis quantification using Rietveld refinement. The micrographs of LPCs revealed a dense matrix.