Abstract

Lime hemp concrete is a sustainable building material made with hemp shiv and lime. In this research, pozzolans are added to the lime binder. Hemp shiv contains water soluble constituents including pectic polysaccharides which can dissolve in the mixing water. Sugars and pectins are known to retard clinker hydration in portland cement. This research studies whether the hemp soluble components impact lime-pozzolan paste reactions thus affecting the properties of hemp concrete with lime-pozzolan binder. Physical tests and microstructural analyses were undertaken to determine how the water soluble hemp constituents influence the hydration reactions responsible for setting and hardening of lime-pozzolan pastes. The effect of hemp particles on a lime-pozzolan binder was also investigated using microstructural analysis.

Physical testing evidenced that the hemp’s soluble constituents do not alter ultimate strength however, they delay pozzolanic reaction retarding setting and early strength development. The microstructural analysis of lime-pozzolan pastes agreed with the above, evidencing that the hemp delays the formation of hydrates, in particular calcium silica hydrates. The halt of the pozzolanic reaction by the hemp particles was clear at the hemp interface, where few hydrates were evident. This suggests that the properties of the hemp particles including their high suction (which removes water at the interface) and their high porosity (which assists CO₂ diffusion) contribute to the halt of the pozzolanic reaction.

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