Effect of Polyphosphates on Properties of Alkali-Activated Slag/Fly Ash Concrete

Polyphosphate materials such as sodium tripolyphosphate (STPP) and sodium hexametaphosphate (SHMP) are usually used as a dispersion agent for the ceramic industry, auxiliary materials in high-range water-reducing admixtures, and retarders in traditional cement systems. Until now, however, no comprehensive study has been performed on the effect of STPP or SHMP on the properties of alkali-activated materials (AAMs). Thus, in this paper, the effect of different concentrations (2 to 8 wt. %) of STPP and SHMP on the properties of alkali-activated slag/fly ash concrete was investi-gated. The variations in workability, compressive strength, water absorption, and total porosity with the incorporation of either STPP or SHMP at levels of 2, 4, 6, and 8%, by weight, were conducted. Modern techniques were employed to investigate the crystalline phases and microstructure morphologies. The primary results showed that both STPP and SHMP can increase workability. Each type of polyphosphate showed a positive effect on the compres-sive strength, but 4% was the optimum concentration. Both water absorption and total porosity were reduced with the incorporation of each type of polyphosphate, but 4% was the optimum. The incor-poration of a suitable concentration of each type of polyphosphate can enhance the dispersion and deagglomeration of the particles and refine the microstructure.