Soil-based construction materials are of interest as structural building materials due to their green credentials, as well as being present in many historical structures. For effective conservation of the latter, and to motivate greater uptake for new construction, understanding of the mechanical and hydraulic properties of these materials is in need of improvement. Earthen construction materials can be considered to be manufactured unsaturated soils, and advances in understanding can be made by considering them from a geotechnical point of view. This paper presents initial results from a major programme of testing, seeking improved properties for earthen construction materials, where unusual organic compounds have been employed as stabilisers. Two gums (guar and xanthan) used as stabilisers for a soil mixture are shown to have significant effects on certain mechanical properties, some of which can be explained, and other aspects which are in need of further investigation.

Climate change and global warming have prompted a notable shift towards sustainable geotechnics and construction materials within the geotechnical engineer’s community. Earthen construction materials, in particular, are considered sustainable due to their inherent characteristics of having low embodied and operational energies, fire resistance, and ease of recyclability. Despite these attributes, they have not been part of the mainstream construction due to their susceptibility to water-induced deterioration. Conventional soil improvement techniques are generally expensive, energy-intensive, and environmentally harmful. Recently, biostabilization has emerged as a sustainable alternative that can overcome some of the limitations of existing soil improvement methods. Enzyme-induced carbonate precipitation (EICP) is a particularly promising technique due to its ease of application and compatibility with different soil types. EICP exploits the urease enzyme as a catalyst to promote the hydrolysis of urea inside the pore water, which, in the presence of calcium ions, results in the precipitation of calcium carbonate. The purpose of this paper is to provide a state-of-the-art review of EICP stabilization, highlighting the potential application of this technique to field problems and identifying current research gaps. The paper discusses recent progress, focusing on the most important factors that govern the efficiency of the chemical reactions and the precipitation of a spatially homogenous carbonate phase. The paper also discusses other aspects of EICP stabilization, including the degree of ground improvement, the prediction of the pore structure of the treated soil by numerical simulations, and the remediation of potentially toxic EICP by-products.

This paper investigates the recyclability, liquid water durability and water vapour adsorption of both unstabilised and stabilised compressed earth bricks. Stabilised bricks were manufactured by adding either cement or the biopolymer guar gum to the base earth. Unconfined compressive strength tests were then performed on both unstabilised and stabilised earth bricks manufactured with recycled material (i.e. material taken from the failed compressed earth bricks after the compressive strength tests). These tests enabled to assess the influence of recycling on the stiffness, strength and strain energy of all compressed earth bricks. Immersion and drip tests were subsequently performed to investigate the effect of cement and biopolymer stabilisation on the durability of the compressed earth bricks against the weathering action of water. An additional set of laboratory experiments was finally conducted by means of a Dynamic Vapour Sorption (DVS) system to study the effect of earth stabilisation on the capacity of adsorbing/releasing water vapour as the ambient humidity changes. Outcomes from this experimental campaign showed that both unstabilised and biopolymer stabilised earth bricks maintained a similar mechanical performance after recycling, while cement stabilised bricks showed a remarkable reduction of both stiffness and strength. Finally, both cement and biopolymer stabilised bricks improved the liquid water durability while reducing the water vapour adsorption compared with the unstabilised earth bricks. Results from this experimental work will be useful for life cycle assessments, especially for modelling the end-of-life of the material as well as its potential reuse.