Durability of compressed earth blocks stabilised with recycled cement from concrete waste and incorporating construction and demolition waste

Chemical stabilisation is essential to reduce the high water susceptibility of compressed earth blocks (CEB), the main shortcoming of earthen construction. However, alternative low-carbon stabilisers to Portland cement (PC) are needed to keep the low embodied energy of CEB, without significantly affecting their performance. This study explores the innovative use of recycled cement (RC), recovered from old cement waste, in the stabilisation of water-resistant CEB. The aim is to analyse the durability behaviour of CEB stabilised with RC and compare it with that of unstabilised CEB and reference CEB with PC. To this end, CEB with different stabiliser content (0, 4, 8 %), and partial to total replacement of PC with RC (20, 50, 100 %) were characterised in terms of their microstructure and main mechanical and durability properties, namely compressive strength, water absorption, drying rate, water erosion and water vapour permeability. In addition, soil was partly replaced with up to 25 % construction and demolition waste (CDW) to further improve the eco-efficiency of CEB. The CEB performance was essentially affected by the stabiliser amount and water content. CEB with PC had higher mechanical strength and lower water absorption than those with RC, due to their lower water demand. However, for the same water content, RC CEB performed similarly to PC CEB. Moreover, the water erosion and vapor permeability were not significantly affected by the type of binder. The CEB performance was affected by its microstructure, which tended to be more refined in RC CEB. In addition, the RC stabilisation almost triplicated the mechanical strength and significantly improved the water resistance of unstabilised CEB, remaining undamaged after immersion or severe water erosion. Durability was little affected by replacing up to 25 % of the soil with CDW. The simultaneous incorporation of just 4 % RC and up to 25 % CDW has made it possible to produce more eco-efficient CEB, while ensuring high water resistance.