Application of micro-crystalline cellulose as additive in Portland cement-based and alkali activated slag-fly ash mortar: Comparison of compressive strength, hydration and shrinkage

The research aims to examine the effects of micro-crystalline cellulose (MCC) as additive in Portland cement -based (OPC) and sodium hydroxide slag-fly ash blend (AAM) with the objective of mitigating shrinkage and improve mechanical and durability properties of constructions. MCC was dispersed using ultrasonication and added at dosages of 0.25%, 0.50% and 1% by weight of binder. The mentioned engineering properties of OPC-mortar and AAM-mortars were examined under three exposure conditions - sealed curing (SC), dry curing (DC, 30 degrees C/65% RH) and steam curing (STC, only for AAM). The experimental outcome suggests that addition of 1% MCC mitigates loss in strength and hydration of OPC-mortar when curing condition is changed from SC to DC, and offers similar strength as control at 28-day age. In comparison, 0.25% MCC dosage is found to be optimal for AAM, offering lower porosity and slight improvement (7 - 10%) in compressive strength at 28-day mark. In-crease in MCC dosage to 1% drastically reduces compressive strength, which is attributed to noticeable retar-dation in fly ash dissolution in the presence of MCC and alkaline environment based on isothermal calorimetry. Addition of MCC has a substantial effect on shrinkage of OPC-mortar, evident from reduction in 7-day sealed shrinkage by 67%, 31% and 66% than control due to addition of 0.25%, 0.50% and 1% MCC respectively. In comparison, MCC eliminates shrinkage of AAM under sealed condition until 3-day and reduces total shrinkage by 8 - 36% at 7-day and 50-day age. Combination of STC and 1% MCC dosage is found to offer a substantial reduction in total shrinkage by 68% at 7-day and 23% at 50-day mark compared to control. The findings from the study suggest a promising potential of using MCC, which can be extracted from locally generated biomass wastes and textile wastes, as curing additive for OPC and alkali-activated based construction materials.