Effect of microcrystalline cellulose on rheology, hydration kinetics and early-age properties of Portland cement-based and alkali-activated slag-fly ash blend

The research examines the influence of microcrystalline cellulose (MCC) on the evolution of rheological behaviour, micro-structural build-up, hydration kinetics and early-age strength (up to seven days) of OPC and AAM matrices subject to dry and sealed curing. Rheological measurements show that the addition of MCC improves recoverability of viscosity and thixotropy of OPCbased matrices. While viscosities of MCC-OPC matrices increase with relatively low change in yield stress, MCC- AAM shows drastic increase in yield stress, up to 2.2 folds within 15 min, due to an increase in MCC content from 0.25% to 1%. This is attributed to gelation and swelling of MCC in NaOH. Hydration kinetics of MCC-OPC in the first 24 h is severely retarded with increase in MCC dosage (about 5.3 h for 1% MCC), while that of AAM is less sensitive to MCC dosage, attributed to rupture of hydrogen bonds in MCC after exposure to NaOH. The findings also show that addition of MCC reduces the heat evolution of AAM after seven days of hydration, due to its suppressing effect on fly ash dissolution. Early-age compressive strength of MCC-OPC reduces with increase in MCC content, registering a maximum reduction of 21% at 1% MCC dosage. Compressive strength of MCC-based AAM is less sensitive to curing conditions and the dosage of MCC than OPC-based matrices. The findings suggest that MCC can be a potential admixture for modifying rheology and hardening of OPC and AAM matrices, while providing an avenue for upcycling cotton textile and biomass wastes.