Thesis title: Ground Improvement Using Enzyme Induced Carbonate Precipitation (EICP) Derived from Plant Source.
Biocementation is recognized as a promising technique for strengthening loose and weak soils, offering a sustainable alternative to ordinary Portland cement (OPC) in geotechnical applications. This is particularly significant given OPC's high carbon footprint and energy-intensive production. The technique has demonstrated excellent efficiency across various soil types through both laboratory tests and large-scale models. Enzyme-Induced Carbonate Precipitation (EICP), an emerging ground improvement technology, cements soil by precipitating calcium carbonate, thereby enhancing strength and stiffness. EICP biocementation offers significant environmental and technical advantages, but its commercial adoption faces challenges, primarily due to economic factors. One of the main hurdles is the high cost of materials, such as the enzyme (e.g., urease), which is often expensive to produce or purchase. These economic challenges must be addressed to make EICP a viable and widely adopted solution.
This dissertation explores the use of natural materials as eco-friendly substitutes, focusing on biocementation techniques, particularly EICP. An innovative approach was introduced by extracting enzymes from expired plants (i.e., soybeans), repurposing waste materials to improve soil mechanical properties and promote a circular economy. The research was conducted in two stages. The first stage, carried out in the Department of Chemical Engineering, Materials, and Environment (DICMA), focused on optimizing the chemical components of the biocementation solution. Small-scale samples (3 cm in diameter and 10 cm in height) were used to determine the optimal concentrations. The second stage, conducted at the geotechnical laboratory of Structural and Geotechnical Engineering Department (DISG), investigated the mechanical properties of biocemented samples using unconfined compressive strength, Brazilian tests, direct shear tests, and triaxial tests.
Experiments optimized the biocementation solution using urease enzymes extracted from expired soybeans and calcium chloride. The optimal concentrations were identified as 25 g/L for soybeans and 0.5 M for calcium and urea. Results indicated stable pH levels (8.5) and resilience to temperature variations (20–40°C), though a slight reduction in CaCO₃ precipitation was observed near 50°C. Mechanical tests revealed that biocemented sand achieved compressive strength comparable to OPC-stabilized sand, with tensile strength significantly improving as the number of injections increased. Samples subjected to 14 injections showed a two-fold increase in tensile strength compared to those with 7 injections. Shear strength parameters, evaluated through direct shear and triaxial tests, also improved with increased injections, driven by higher CaCO₃ precipitation. Enhanced dilatancy further indicated stronger interparticle bonding and improved sand matrix stability.
Finaly, a mesoscale model (30 cm in diameter and height) was used to study the distribution of CaCO₃ precipitation. Results showed that precipitation was concentrated near the injection zones, underscoring the need for optimized injection techniques to ensure uniform distribution and consistent mechanical improvements across the soil mass.