Investigation on the Environmental Impact of Soil Improvement Techniques: Comparison of Cement Grouting and Biocement

Abstract

Soil improvement techniques – including both mechanical and chemical stabilization methods such as dynamic compression and grouting – have potential drawbacks such as high cost, high energy consumption and sometimes negative environmental impacts. An alternative approach is to use biocement to improve the engineering properties of soil. Microbially induced calcite precipitation (MICP) has been introduced as a technique for modification of geotechnical properties of sand. Among many studies concerning biocementation of sand, there are few studies considering the comparison of cost and environmental impacts of cement grouting and microbial methods. The environmental concerns in the present study was focused on the produced CO₂ and calcite usage in Portland cement. The primary component of cement is limestone which is a natural resource. Cement manufacturing is highly energy and emissions intensive because of the extreme heat required to produce it. Producing a ton of cement requires 4.7 million BTU of energy and generates nearly a ton of CO₂. Given its high emissions and critical importance to society, cement is an obvious place to work on reducing greenhouse gas emissions. On the other hand, calcium chloride was also used as a crucial reagent in MICP treated samples. Therefore, the present study discussed the environmental aspects of conventional and innovative methods of soil improvement. In the cement grouting method, Portland cement was used as a chemical substance. Portland cement were applied by surface percolation and mechanical mixing to the samples. Then, the results of cement grouting were compared with the results of biocement samples which were gathered from literature. The results for treated samples were discussed and compared based on one cubic meter of soil and final target of 700 kPa. The results show that the amount of calcium usage in the cement grouting was 2.5 times more than bio-treated samples and therefore higher energy and gas emissions.