Particle Size Effect of Acacia Modesta Gum Powder on the Properties of Self-Compacting Paste Systems

Abstract

Particle size of powdered Acacia Modesta (AM) gum affects the fresh and hardened properties of self-compacting paste (SCP) systems and this aspect has not been researched so far. This study focuses on the effect of particle size of botanical Acacia Modesta (AM) gum powder incorporated in self-compacting paste systems (SCPs). Powdered Acacia Modesta gum with an average particle size (D50) of 307 microns, 135 microns and 47.5 microns were used with variable Acacia Modesta (AM) gum dosages in the range of 0.25% to 1% by weight of the dry cement. The results show that with the decrease in the average particle size of AM gum powder, the water demand, viscosity, yield stress, Vicat setting times, water absorption capacity, air content and maximum shrinkage values of SCPs were reduced while super-plasticizer (SP) demand, compressive strength, fresh and harden cement paste densities got increased. Scanning Electron Microscopy (SEM) technique has been used for microstructural studies which complement the findings of the experimental work. The effect of both air and water curing has been studied and results shows about 12% and 13% improvement in compressive strength for average particle size of 47.5 microns for air cured and water cured samples respectively as compare to OPC. While in comparison to average particle size of 307 microns, this improvement goes up to 20% and 25 % for air cured and water cured samples respectively. Improvement in compressive strength at smaller sizes was due to improvement in fresh paste and hardens densities of SCPs containing smaller sizes of AM gum particles. It was also observed that retardation effect of AM gum powder in SCPs is independent of average particle size of AM gum at constant w/c ratio of 27%. About 25% maximum shrinkage of SCPs got reduced by with average particle size of 47.5 microns of AM gum powder as compare to OPC. This can be either due to internal curing property of AM gum powder or due to higher ettringite growth at smaller sizes of AM gum powder.