Microbially induced carbonate precipitation (MICP) for stabilisation of road foundation

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Road foundation, typically made of unbound granular materials, is a vital component of road structure, functioning to support the overlying pavement under traffic loading and drain any intruded water. Deficiencies in the engineering properties of road foundation, such as low strength and stiffness, will cause accumulation of large deformation, which will propagate upwards and eventually result in road distress (e.g., cracks, ruts and potholes). This is particularly the case in developed countries such as the UK where the majority of road stock was built decades ago to lower standards than are currently in use and is suffering greatly from distress. Repair to distressed roads with problematic foundation is a puzzle. Surface treatment, while cheap and causes low disruption, has limited efficacy as it does not address the root cause of distress. Reconstruction of the road structure down to the foundation is required for complete retrofit, but the associated high costs and prolonged road closure are of concern.Microbially induced carbonate precipitation (MICP) is a novel technique for soil stabilisation developed in the recent two decades. It is essentially a bio-mineralisation process that harnesses microbial metabolic activities to induce precipitation of calcium carbonate. When implemented into a granular material, the precipitated calcium carbonate crystals can form cementation between within the granular matrix, improving its mechanical performance. Compared with conventional soil stabilisation techniques such as cement grouting, MICP has much lower environmental impacts and energy consumption. Further, its simple implementation by injection or percolation enables the material in question to be stabilised in place. Within this context, it is of great interest to apply MICP to road foundation to improve its performance and mitigate road distress. This, if realised, would bring enormous benefits to road maintenance and repair.To facilitate this application, a prerequisite is a sound understanding of the mechanical behaviour of of MICP-treated road foundation materials, and this study represents a step towards this end. A series of multi-scale experimental programmes will be conducted to thoroughly investigate the effects of MICP treatment on the mechanical behaviour of road foundation materials.