Preliminary studies of hemp and recycled aggregate concrete

Abstract

This paper reports on preliminary tests conducted on Hemp and Recycled Aggregate Concrete (HRAC), a sustainable concrete material prepared by partial replacement of natural coarse aggregates (NA) with recycled concrete aggregates (RCA) and incorporating hemp fibers in the concrete mix. The aim of this study was to evaluate the effect of such replacement on the hardened mechanical properties of concrete. For this purpose, six concrete mixes were prepared, where natural coarse aggregates were partially replaced by RCA or by hemp fibers or by both and where the hemp fiber length was varied between 20mm and 30mm. For each mix, specimens were prepared and tested for compressive strength, modulus of elasticity, flexural strength and splitting tensile strength. The results showed that a replacement of 50% of NA by RCA decreased the compression strength and the modulus of elasticity by around 10%, while the inclusion of hemp fibers decreased them by 25%. HRAC mixes had a compression strength 30% lower than the control mix. While the flexural strength and the splitting tensile strength also decreased by an average of 10% when 50% of NA was replaced by RCA, although the inclusion of hemp fibers had no significant negative effect on the modulus of rupture. As for fiber length, 30mm length fibers showed slightly better results for compression strength and modulus of elasticity, opposed to the flexural and tensile strengths which were higher with 20mm fibers.