The Influence Mechanism of Ettringite Crystals and Microstructure Characteristics on the Strength of Calcium-Based Stabilized Soil.

Youmin Han,Hongfei Chang,Junwu Xia,Jun Xu

doi:10.3390/ma14061359

Abstract

To reveal the influence mechanism of ettringite (AFt) crystals and microstructure characteristics on the strength of calcium-based stabilized soil, the strengths and microscopic properties of seven groups of stabilized soil samples were studied systematically through unconfined compressive strength, scanning electron microscope (SEM), X-ray diffraction (XRD), thermogravimetry (TG), and Fourier transform infrared spectroscopy (FTIR) testing methods. The results indicate that the strength of the cement-stabilized soil is relatively high because abundant calcium silicate hydrate (CSH) gels coat the outer surface of soil particles to cement together. For the cement–gypsum-stabilized soil, superabundant thick and long AFt crystals make the pores in soil particles larger, and the sample becomes looser, resulting in lower strength than that of the cement-stabilized soil. However, the strength of the cement–gypsum–lime-stabilized soil is slightly stronger than that of the cement-stabilized soil, for the reason that the appropriate amount of fine AFt crystals fill the macropores between soil particles to form a network space structure and sufficient CSH gels cement the soil particles and the AFt crystals network space structure tightly together. It could be suggested that the components of calcium-based stabilizer should consider the optimal production balance between CSH gels and fine AFt crystals.

Highlights

With the implementation of the development strategy for coastal, riverside, and lakeside areas in various countries, many large-scale infrastructure construction projects need to be launched in these areas
Superabundant thick and long amount of ettringite (AFt) crystals make the pores in soil particles larger, while calcium silicate hydrate (CSH) gels cannot cement the soil particles and the AFt crystals together, and the stabilized soil becomes looser (Figure 3b)
The strengths and microscopic properties of seven calcium-based stabilized soils were systematically studied through unconfined compressive strength (UCS), scanning electron microscope (SEM), X-ray diffraction (XRD), TG, and Fourier transform infrared spectroscopy (FTIR) testing methods

Summary

Introduction

With the implementation of the development strategy for coastal, riverside, and lakeside areas in various countries, many large-scale infrastructure construction projects need to be launched in these areas. The most conventional soft soil stabilizers in engineering are calcium-based stabilizers, which are rich in calcium minerals such as ordinary Portland cement, lime, and part of industrial wastes. The stabilization mechanism of the cement-stabilized soil mainly comes from the hydrolysis and hydration reaction of cement, followed by the ion-exchange reaction and agglomeration, pozzolanic reaction, and carbonation reaction between soil particles and cement hydrate [2]. When lime [2] or carbide slag [3,4] is used as a soft soil stabilizer, its stabilization mechanism originates from the ion-exchange reaction, pozzolanic reaction, and carbonation reaction between calcium hydroxide and soil particles. According to the microstructural analysis such as scanning electron microscope (SEM) and X-ray diffraction (XRD), the main hydration products of calcium-based stabilized soil include calcium silicate hydrate (CSH)

Methods

Discussion

Conclusion