Sustainable road bases with microbial precipitation

The Australian road network is nearly a million kilometres long, of which 83% can be classified as rural roads. The size and remote nature of Australia's road network pose unique challenges in terms of asset monitoring and maintenance costs. Cement stabilisation is a practice commonly used to improve durability and reduce inspection and repair costs. However, due to the sheer length of the road network, a huge quantity of cement is consumed in stabilisation work, making this practice unsustainable. This paper explores a sustainable alternative through augmentation of the traditional cement-based stabilisation with microbial carbonate precipitation. The calcium carbonate crystals formed within the samples were investigated by scanning electron microscopy and X-ray diffraction. Bulk mechanical properties were characterised through unconfined compressive strength (UCS) testing and the digital image correlation technique was utilised during UCS testing to extract more refined information such as local deformation and strain build-up. The mechanical properties at the microscopic scale were characterised through nanoindentation testing. The results show that microbial precipitation is able to increase the strength of cement-stabilised and road base materials significantly and can considerably improve the technological, economic and social sustainability of Australian road bases.