Decrease in Viscosity Caused by Agglomeration and Particle Dispersion in Cement-Fly Ash Suspensions

Incorporating fly ash in a concrete mix significantly improves its consistency, resulting in lower viscosity. It is believed that the spherical shape of the fly ash particles is the main cause of the low viscosity. However, the physicochemical causality of the fly ash effect has not been deeply studied and there have been only limited experiments on the particles' interactions. The use of laser backscattering measurement in this paper allowed the investigation of the agglomeration and dispersion of fly ash particles in an in situ paste. It was found that agglomerates composed of mixed particles develop in a fly ash-cement paste. Their dimensions are comparable to those in neat cement paste. More importantly, incorporating nano-scale spherical dispersed fly ash particles in the mix provides a ball-bearing effect between the micro-scale agglomerates. The viscosity of the mix consequently decreases.