Bio-modification of sand for cement grouting

• Main Author: Ng, Samuel Joel Rui Ming
• Other Authors: Chu Jian
• Format: Final Year Project
• Language: English
• Published: Nanyang Technological University 2018
• Subjects: Engineering::Civil engineering
• Online Access: http://hdl.handle.net/10356/74925
• Institution: Nanyang Technological University

Sand and aggregates used for concrete and grouting in Singapore are mainly imported from overseas. They are expensive and yet, the supplies are not sustainable. There is a need to look for ways to use less sand, less aggregates or substitutes for concrete and grouting, or use the same amount of sand or aggregates to produce higher strength concrete and grouting materials. Recently, new soil improvement methods based on the Microbial Induced Calcite Precipitation (MICP) process have been developed. The same approach may be used to improve the properties or gain surface of the sand or aggregates used for concrete and grouting and thus improve the strength of concrete and cement grout. The MICP based method may also heal cracks in concrete. The main objective of this project is to verify whether by treating the sand surface using a MICP approach will lead to an increase in bonding between the sand and cement, thus improving the strength of lean concrete or grout. The second objective is to explore whether the MICP based method can also be used to treat sea sand for lean concrete or grout. The first objective was investigated by comparing the compressive strength of 5 batches of lean concrete cubes made with MICP treated river sand, each batch being treated 1 to 5 times respectively, with a control sample of untreated cubes. Scanning Electron Microscope (SEM) analysis of the 5 batches was also done to examine the amount of calcium carbonate precipitated on the river sand. These two experiments help to verify if there is a correlation between the amount of calcium carbonate precipitated on the sand surface using MICP and the strength of lean concrete. The second objective was evaluated using two criteria, the comparability of strength between using treated sea sand versus untreated river sand and the cost-effectiveness. This was answered by comparing the compressive strength of lean concrete cubes made with MICP treated sea sand to lean concrete made with untreated river sand. Research was done to find its economic cost. From the results obtained, it was found that as the amount of calcium carbonate increased, the strength of the lean concrete, in other words, grout, also increased with an optimum treatment run of 2 times. This strength could be due to the calcium carbonate coating the sand particles, making them rougher and thus promoting stronger interlocking. The strength of lean concrete cubes made with MICP treated sea sand was also found to be higher than lean concrete cubes made with untreated river sand despite chloride supposedly weakening lean concrete. From the research conducted, sea sand was found to be cost effective due to it being S$10.86/tonne cheaper than river sand and the savings generated being greater than the cost of nutrients for the MICP based method, which is S$3.28/tonne. With the MICP based method being verified to increase the strength of grout and sea sand being cost-effective, the combination of the two could lead to a more sustainable and cost- effective method to produce cement grout, making Singapore less reliant on sand imports.