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

道路基础通常由松散的颗粒材料制成，是道路结构的重要组成部分，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。道路基础工程特性的不足，如强度和刚度较低，会造成较大变形的积累，并向上传播，最终造成道路的破坏（如裂缝、车辙、坑洞等）。在英国等发达国家，情况尤其如此。在这些国家，大多数道路是在几十年前建造的，当时的标准低于目前的使用标准，因此严重受损。修复地基有问题的破旧道路是一个难题。表面处理虽然成本低，造成的破坏也小，但效果有限，因为它不能解决困扰的根本原因。彻底改造需要重建道路结构直至地基，但相关的高费用和长时间的道路封闭令人担忧。微生物诱导碳酸盐降水（MICP）是近二十年来发展起来的一种土壤稳定新技术。它本质上是一个利用微生物代谢活动诱导碳酸钙沉淀的生物矿化过程。当注入到颗粒材料中时，沉淀的碳酸钙晶体可以在颗粒基体内部之间形成胶结，提高其力学性能。与水泥灌浆等传统的土体稳定技术相比，MICP对环境的影响和能耗明显降低。此外，它通过注入或渗透的简单实现使所讨论的材料能够稳定在适当的位置。在这种背景下，将MICP应用于道路基础以提高其性能和减轻道路损伤是非常有意义的。如果实现这一点，将为道路维护和维修带来巨大的好处。为了促进这一应用，一个先决条件是对micp处理的道路基础材料的力学行为有充分的了解，而这项研究代表了朝着这一目标迈出的一步。将进行一系列多尺度试验项目，以彻底研究MICP处理对道路基础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.