Impact of water retainers in the strength, drying and setting of lime hemp concrete

Abstract

Lime hemp concrete is a sustainable, carbon negative building material that can be used in certain applications lowering the environmental impact of construction. Hemp absorbs large quantities of mixing water (325% of its own weight at 24hours), and this may not leave sufficient moisture in the binder for hydration or carbonation to take place adversely affecting curing and strength development. This paper investigates the effect of using water retainers to ensure that sufficient water is available for proper curing. Hemp concrete including a lime: pozzolan (either GGBS or metakaolin) binder and three water retainers (methyl cellulose and two commercial water retainers one of which is methyl cellulose based) were investigated. This paper studies the impact of the water retainers on strength, drying, setting and microstructure. It was found that the three water retainers delayed setting and drying. The commercial binders did not significantly affect strength however the methyl cellulose improved the compressive strength of both lime:pozzolan pastes and hemp concrete at later ages (100 days). The increase in compressive strength is partially attributed to an enhanced binder water retention that improves hydration. This assumption is based on the increase in the amount of pozzolanic cements, evidenced with SEM at the hemp interface, in the composite with methyl cellulose.