Influence of biopolymeric water-retaining admixtures on hydration of Portland cement studied using isothermal calorimetry

摘要

Viscosity enhancing and water-retaining admixtures based on the cellulose ethers are widely used in the building industry to improve the properties of concrete and ready-mix mortars.The study focuses on the influence of the alternative natural viscosity enhancing admixtures(sodium salt of alginic acid, carrageenan, diutan gum, xanthan gum, and hydroxypropyl derivatives of guar gum and chitosan)in doses of 0.1%, 0.5%, and 1% of the binder weight on the cement hydration.The study is carried out using isothermal calorimetry studying the heat flow and the total heat evolved during the reaction from the very beginning-the water-introduction into system.All of the studied biopolymers showed the set retarding ability as they are all of polysaccharide origin.The dosage-dependency was significant for the hydroxypropyl guaran and diutan gum, while retarding effect of other admixtures varied only slightly with the amount of biopolymer in the studied range of doses.However the studied admixtures were less effective in the delay of accelerating period, as well as the reduction of total heat generated during the reaction, in comparison with cellulose ethers.Other admixture than hydroxypropyl guar gum or diutan gum should be chosen if the set-retarding ability is not appropriate for the mixture use, otherwise the advantage over cellulose ethers will not be significant.