Application of microbially induced carbonate precipitation to form bio-cemented artificial sandstone

Abstract

It is difficult to collect and characterise well-preserved samples of weakly cemented granular rocks as conventional sampling techniques often result in destruction of the cementation. An alternative approach is to prepare synthetic geomaterials to match required specifications. This paper introduces microbially induced carbonate precipitation (MICP) as a method to reliably deliver artificially cemented specimens with customised properties, closely resembling those of soft carbonate sandstones. The specimens are generated from materials with two very different particle size distributions to access a range of achievable combinations of strengths and porosities. The MICP parameters are kept constant across all samples to obtain similar calcium carbonate characteristics (size of individual crystals, type etc.), while injected volume is varied to achieve different cementation levels. Although uniform cementation of very coarse sands has been considered very difficult to achieve, the results show that both the fine and coarse sand specimens present high degrees of uniformity and a good degree of repeatability. The strengths (UCS values less than 3000 kPa) and porosities (0.25-0.4) of the artificial specimens fall in the same range of values reported for natural rocks. The strength gain was greater in the fine sand than in the coarse sand, as the void size in the latter was significantly larger compared to the calcium carbonate crystals’ size, resulting in precipitation on less effective locations, away from contacts between particles. The strengths and porosities obtained for the two sands in this work fall within ranges reported in the literature for natural soft rocks, demonstrating the MICP technique is able to achieve realistic properties and may be used to produce a full range of properties by varying the grain sizes, and possibly the width of the particle size distribution.