Microbial-induced calcite precipitation (MICP) is a promising, sustainable, and environmentally friendly ground improvement technique. This study examined the effectiveness of molasses (MS) as a broth medium compared to nutrient broth (NB). Sporosarcina pasteurii was used in a 0.5 M cementation solution with pore volumes (PV) of 0.50, 0.75, and 1 PV in biotreatment cycles of 9 and 18 days. Mechanical properties of biotreated samples were assessed through unconfined compressive strength (UCS) and split tensile strength (STS) tests, while calcite content, scanning electron microscope (SEM), and energy dispersive X-ray spectroscopy (EDS) were used to interpret biocementation. NB-treated samples exhibited significantly higher strength and calcite content than MS-treated samples. The durability of biotreated samples under 6, 12, and 18 freeze-thaw (FT) cycles revealed that the FT cyclic process affects the mechanical and physical characteristics of biotreated samples. Samples treated with higher PV and for a longer duration exhibited higher strength and durability. The mass losses in NB and MS samples were 7-14.5% and 15-32%, respectively, after 18 FT cycles. Overall, NB samples exhibit higher strength and durability than MS samples. While MS proved less effective as a broth medium compared to NB for the MICP process, its cost-effectiveness and abundant availability make it a promising choice for the MICP process.

Coastal erosion is a global environmental concern, threatening infrastructure, human livelihoods and ecosystems. Recently, microbial-induced calcite precipitation (MICP) has emerged as a promising ground improvement technique. The present study examined the effects of adding three different fibre reinforcements, namely carbon, basalt and polypropylene, on the physical and mechanical properties of coastal soil through MICP. The fibre content used was 0.20%, 0.40% and 0.60% of soil weight. A comprehensive biotreatment investigation was conducted using Sporosarcina pasteurii (S. pasteurii) in a 0.5 molar cementation solution. The samples prepared for this study had aspect ratios of 2:1 and 1:1. These samples were subjected to biotreatment, consisting of a 24-h cycle for 9 and 18 days. Unconfined compressive strength (UCS), split tensile strength (STS) and ultrasonic pulse velocity (UPV) tests were conducted on the biotreated samples to evaluate the effect of fibre reinforcement on the mechanical properties of the biotreated samples. The amount of calcite precipitation, scanning electron microscope (SEM) and energy dispersive X-ray spectroscopy (EDS) were used to interpret biocementation. Results suggest that adding fibres to the MICP process enhances the mechanical properties of coastal soil. The optimum fibre content for carbon and basalt fibre was 0.40%, whereas, for polypropylene, it stood at 0.20%. The maximum UCS, STS, UPV and average CaCO3 were observed in a basalt fibre-reinforced biotreated sample with a fibre content of 0.40%, subjected to 18-day biotreatment. Conversely, the sample without fibre-reinforcement, biotreated for 9 days, exhibited the lowest values for these parameters. Samples subjected to 18 days of treatment have higher values of UCS, STS, UPV and CaCO3 content than 9-day-treated soil samples. SEM revealed the presence of CaCO3 precipitates on the surfaces of soil grains and their contact points, and the EDS spectrum corroborated this observation.