Chemically Induced Calcium Carbonate Precipitation for Improving Strength of Sand

Chemically induced calcium carbonate precipitation (CCP) using calcium hydroxide (CH) and carbon dioxide (${\mathrm{CO}}_2$) was employed to clean sand for improving its strength. Joomunjin sand was mixed with 2% CH and 10% water, and then cured in a ${\mathrm{CO}}_2$ chamber under 100 or 200 kPa for 2 h. The treatments were repeated 1, 5, and 10 times. At the last treatment cycle, the treated sand was compacted into a mold for testing. A series of unconfined compression and direct shear tests were conducted on the treated sand to evaluate the effects of the CCP on the strength of the clean sand. Scanning electron microscopy (SEM) and X-ray powder diffraction (XRD) analysis were performed to evaluate the CCP and microstructure of the treated sand. The experimental results indicated that the effect of change in the ${\mathrm{CO}}_2$ chamber pressure on the calcium carbonate content (CCC) was insignificant due to the low pressures applied. As the number of treatments increased from 1 to 10, the CCC increased from 2% to 23%, resulting in increases of the unconfined compressive strength (UCS), and friction angle of treated sand. The efficiency of converting CH to ${\mathrm{CaCO}}_3$ reached 87% after 10 cycles. The UCS increased from 51 to 364 kPa as the number of treatments increased from 1 to 10. The friction angle and cohesion of clean sand also increased from 32° and 0 kPa to 49° and 53 kPa, respectively.