Laboratory Study on Improvement of Expansive Soil by Chemically Induced Calcium Carbonate Precipitation

Yijiang Zhang,Shaoyang Han,Marte Gutierrez,Yibo Shan,Baotian Wang

doi:10.3390/ma14123372

Abstract

This paper proposes the use of calcium carbonate (CaCO3) precipitation induced by the addition of calcium chloride (CaCl2) and sodium carbonate (Na2CO3) solutions as a procedure to stabilize and improve expansive soil. A set of laboratory tests, including the free swell test, unloaded swelling ratio test, unconfined compression test, direct shear test, scanning electron microscopy (SEM) test, cyclic wetting–drying test and laboratory-scale precipitation model test, were performed under various curing periods to evaluate the performance of the CaCO3 stabilization. It is concluded from the free swell tests and unloaded swelling ratio tests that the addition of CaCl2 and Na2CO3 can profoundly decrease soil expansion potential. The reduction in expansion parameters is primarily attributed to the strong short-term reactions between clay and stabilizers. In addition, the formed cementation precipitation can decrease the water adsorption capacity of the clay surface and then consequently reduce the expansion potential. The results of unconfined compression tests and direct shear strength tests indicated that the addition of CaCl2 and Na2CO3 has a major effect on geotechnical behavior of expansive soils. Based on the SEM analyses, new cementing crystalline phases formatted by sequentially mixing CaCl2 and Na2CO3 solutions into expansive soil were found to appear in the pore space, which results in a much denser microstructure. A laboratory-scale model test was conducted, and results demonstrate the effectiveness of the CaCO3 precipitation technique in stabilizing the expansive soil procedure. The test results indicated that the concentration of CaCl2 higher than 22.0% and Na2CO3 higher than 21.2% are needed to satisfactorily stabilize expansive soil. It is proposed to implement the precipitation technique in the field by the sequential permeation of CaCl2 and Na2CO3 solutions into soils in situ.

Highlights

Expansive soils are known to exhibit large volume changes due to moisture fluctuations [1,2]
Chemical stabilization is one of the effective techniques to overcome the undesirable behavior of expansive soils
Among the chemical stabilization methods, traditional treatments such as physical mixing of lime, cement, fibers and fly-ashes with soils have been commonly used for the soil treatment [10,11,12,13,14,15]

Summary

Introduction

Expansive soils are known to exhibit large volume changes due to moisture fluctuations [1,2]. Among the chemical stabilization methods, traditional treatments such as physical mixing of lime, cement, fibers and fly-ashes with soils have been commonly used for the soil treatment [10,11,12,13,14,15]. These traditional methods show some limitations in engineering applications. Due to high plastic nature of expansive soils, working with and achieving appropriate pulverization in the field are difficult tasks [18]

Objectives

Methods

Conclusion