Saturated And Unsaturated Ground Improvement With Induced Calcium Carbonate Precipitation

The raising demand for cement worldwide and its huge environmental impact from the cement production point of view are pushing researchers around the globe towards coming up with an alternative way to bond soil particles for construction purposes. Clearly, humanity is not close to figuring out a way to highly reduce the use of cement because of its great versatility. Nevertheless, reducing even a small part of the cement demand of the world would mean a huge break for the environment regarding carbon emissions. Success in this field would translate into an overall reduction in the consumption of cement for construction purposes. For this specific research, an interesting and novel alternative to cement will be studied in detail.Microbially Induced Carbonate Precipitation(MICP) is a soil stabilization method that has been gaining popularity in the recent years amongst researchers due to it?s environmental compatibility. Unfortunately, the method is not applicable in some countries since it uses live micro-organisms to treat and cement the soil. Said micro-organisms stay dorment in the soil-calcium carbonate matrix once the nutrients are depleted. There have been discussions on whether the bacterium is actually necessary for the treatment to work, as some stipulate that the bacterium provide a necessary nucleation site in the sand particles to which the calcium carbonate can attach. This document will be divided mainly into three parts.The first part of this thesis is an intensive and comprehensive literature review exploring the state of the art for MICP technology and an introduction to Enzymatic Carbonate Precipitation(ECP), a method for which micro-organisms are not necessary for the cementation to occur, instead urease enzymes from different sources, such as plants, funghi, or bacteria, are the catalyzers for the calcium carbonate cementation to occur. This last technique is highly attractive for places in which the use of external bacteria is forbidden by the country's legistalion.The second refers to the experimental part of this project, and it investigates the possibility to achieve cementation without the use of bacterial cells. The effectiveness of each of the sources was assessed and compared amongst the different possible sources, average UCS strengths of 14,84±8,68 MPa, 4,08±4,13 MPa and 8,88±3,76 MPa were achieved for the bacterial cell, supernatant and plant urease treated samples respectively. This part also compares the effectiveness of two widely used methods for treatment, the reverse injection saturated method and the surface percolation method. The surface percolation method, performed in unsaturated conditions, has been found to be effective in creating menisc-like bonds in efficient locations which translates into higher strength samples, this assertion was put to test. Average UCS strengths of 19,71±5,86 MPa and 15,07±5,73 MPa were obtained for the percolation method and reverse saturated method treated samples respectively.The technologies discussed in this document are still in the developmental stage, that is why costs might still seem prohibitive for the whole industry to adopt them; limiting their use to only highly environmentally concerned clients that are not necessarily looking te reduce costs, but rather to preserve nature. As the technologies become more widely available and optimized, the costs will drop, making it a serious alternative to cement, at least in the field of soil mechanics and foundations.This thesis proposes and discusses different applications for the induced carbonate cementation technology, as well as a brief introduction to the economical aspects of each technology.