The global construction industry consumes huge amounts of mined materials that are considered unsustainable for earth resources. In addition, Portland cement which is a key element in concrete and most construction materials is considered one of the main contributors to worldwide CO2 emissions. On the other hand, natural cemented soil deposits are examples of sustainable structures that have survived decades of severe environmental conditions. Mimicking these natural biological systems provide an alternative to the current practices of construction materials production. Enzyme-induced carbonate precipitation (EICP) is a bio-inspired technique based on the precipitation of calcium carbonate for enhancing the geo-mechanical properties of soils. In this technique, calcium carbonate acts as a cementitious agent that binds the soil particles together at the points of contact, hence, increasing the strength and stiffness of treated soils, while relatively reducing the soil permeability and porosity. The achieved enhancements make EICP useful for applications such as ground improvement, construction materials, and erosion control over traditional binders. This paper presents a state-of-the-art review of EICP for ground improvement including the fundamental basics of EICP treatment. The paper also discusses the chemical and physical factors affecting the performance of EICP such as enzyme source, enzyme activity and solution constitutes. Moreover, the paper reviews the different methods and testing techniques used in the application of EICP for soil treatment. Furthermore, the paper compares EICP with other biomineralization techniques in terms of performance and applicability on ground improvement. Finally, the paper discusses the research gaps and existing challenges concerning the commercialization and large-scale implementation of the technology.

Testing using a dynamic shear rheometer (DSR) and rheological analysis were conducted to analyse the detachment behaviour of bio-cemented soil at a microstructural level. Preventing detachment of soil particles from the ground surface is the key to mitigating the generation of fugitive dust due to wind-blown soil, a significant environmental problem in arid and semi-arid regions. Bio-cementation by way of enzyme-induced carbonate precipitation (EICP) has shown potential for mitigating soil particle detachment and the associated fugitive dust emissions. A strong correlation between particle detachment rate measured in wind tunnel tests and amplitude sweep test results using the DSR demonstrates the ability of the device to capture the detachment potential of soil bio-cemented using EICP. In addition to facilitating optimisation of bio-cementation for dust control, the rheometer tests also give an insight into the efficacy of rheometry for assessing soil microstructure strength for other geotechnical applications.

Enzyme induced carbonate precipitation (EICP) is a biogeotechnical ground improvement technique that enhance the mechanical properties of the soil by binding the soil particles together through precipitating calcium carbonate at the particles contact points. Taguchi design of experiment technique was implemented to optimize the EICP cementing solution. The analysis suggests that a solution of 3 M Urea, 1.5 M CaCl2, 3 g/L Urease and 4 g/L of milk is optimum for maximum carbonate precipitation. To verify the efficiency of the obtained solution, silica sand was treated with the optimized solution to confirm the effectiveness of the proposed solution. An average compressive strength of 1.22 MPa was achieved using this cementing solution.