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

路基是道路结构的重要组成部分，通常由非结合粒状材料制成，其功能是在交通荷载下支撑上覆路面并排出任何侵入的水。路基工程性质的缺陷，如强度和刚度低，将导致大变形的积累，并将向上传播，最终导致道路损坏（例如，裂缝、车辙和坑洞）。在英国等发达国家，情况尤其如此，这些国家的大部分道路都是几十年前建造的，标准低于目前使用的标准，而且正在遭受严重的困境。地基有问题的破损道路的修复是一个难题。表面处理虽然便宜，造成的破坏也小，但效果有限，因为它不能解决痛苦的根本原因。为了彻底改造，需要重建道路结构直至地基，但相关的高成本和长时间的道路封闭是令人关注的。微生物诱导碳酸盐沉淀（Microbially Induced Carbonate Precipitation，MICP）是近二十年发展起来的一种新型土壤稳定技术。它本质上是一种利用微生物代谢活动诱导碳酸钙沉淀的生物矿化过程。当实施成颗粒材料时，沉淀碳酸钙晶体可以在颗粒基质内形成胶结，从而改善其机械性能。与传统的土壤稳定技术（如水泥灌浆）相比，MICP对环境的影响和能源消耗要低得多。此外，其通过注射或渗滤的简单实施使得所讨论的材料能够稳定在适当位置。在此背景下，将MICP应用于道路基础以改善其性能并减轻道路损坏具有极大的意义。这一点，如果实现，将带来巨大的好处，道路养护和维修。为了促进这一应用，一个先决条件是一个良好的理解的机械行为的MICP处理的道路基础材料，这项研究是朝着这一目标迈出了一步。将进行一系列多尺度实验方案，以彻底调查MICP处理对路基材料力学行为的影响。

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.