Evaluating Injection Strategies for Microbially Induced Calcite Precipitation and Implications for Applications to Road Structures

The objective of this study is to conduct a laboratory-based assessment of microbially induced calcium carbonate precipitation (MICP) as a viable approach to improving substructures beneath existing asphalt and concrete roadways. This was evaluated through unconfined compressive strength (UCS) testing, which can be correlated with the resilient modulus for subsurface samples to assess the degree of strength improvement achievable by the treatment. The calcium carbonate (CaCO3) distribution is a critical component of this study. Three different injection methods were adopted to investigate the effect of injection method on (1) the treatment efficiency of soil specimens and (2) UCS and failure mechanism of bio-cemented sand, using Sakrete medium commercial sand. The efficiency of the different injection strategies was tested using an acid digestion method, used to determine the CaCO3 content at different locations of the treated samples. Results concluded that samples injected in a top-to-bottom direction had better efficacy in terms of strength and uniformity over the alternatives.