Cement-Bentonite Fillings Mixing Sodium Carbonate for Holes Formed by Pulling-Out Piles

Abstract

In a series of studies, it is aimed to develop fillings for holes formed by pulling-out piles. Cement-bentonite is used as a filling in general. Although cement-bentonite has an advantage of being able to perform blending according to circumstance of work on site, cement and water cause segregation, so uniform filling is difficult. In addition, there is a disadvantage that cement-bentonite cannot perform a predetermined strength when diluted by penetration of groundwater and so on. Sodium carbonate (Na₂CO₃) is a substance expected to suppress the segregation of cement-bentonite and to speed up the development of strength. In this study, we conducted an indoor mixing test on fillings mixed with Na₂CO₃ into cement-bentonite which is a mixture consisting of water, cement and bentonite, and examined various characteristics from the viewpoint of physical and chemical aspects. The following two points were clarified; (i) by mixing Na₂CO₃, bleeding of cement-bentonite is suppressed and (ii) by mixing Na₂CO₃, the strength development time of the cement-bentonite becomes faster and the long-term strength also increases. These two points are considered to be due to the improvement of the swelling property of bentonite, the early strength development of cement and the formation of calcium carbonate (CaCO₃).