Unconfined Compressive Strength and Splitting Tensile Strength of Lime Soil Modified by Nano Clay and Polypropylene Fiber

Ping Jiang,Lin Zhou,Weiqing Zhang,Na Li,Wei Wang

doi:10.3390/cryst12020285

Abstract

Here we study the effects of nano clay and polypropylene fiber on the unconfined compression and splitting properties of lime soil. Through a series of unconfined compressive strength (UCS) tests and splitting strength (STS) tests, the mechanical properties of lime soil (LS), nano clay modified lime soil (NLS), fiber modified lime soil (FLS), nano clay and fiber composite modified lime soil (NFLS) are analyzed, and the volume calculation formula of each phase in NFLS is deduced. Nano clay content αn, porosity volume η and lime volume LVi as independent variables, and the prediction models of UCS and STS of NFLS were established. Furthermore, the microstructure of LS, NLS, FLS and NFLS was analyzed by scanning electron microscope (SEM). It can be concluded that (1) with the increase in nano clay content, the UCS and STS of LS and FLS gradually increase. With the increase in fiber content, the UCS of LS first increases and then decreases, while the UCS and STS of NLS and STS of LS increase with the increase in fiber content, and the optimal fiber content is 0.75%. (2) UCS and STS of NFLS and η/LVi meet the linear relationship. The empirical formulas of UCS and STS established in this paper have a prediction accuracy of less than 10%. The strength of NFLS can be predicted according to the dry density of the sample and the content of each component material. (3) Nano clay can fill the pores of LS and promote the pozzolanic reaction between lime and soil, while fiber mainly plays a reinforcing role in LS, so as to improve the UCS and STS of LS. In NFLS, nano clay can improve the interfacial properties between fiber and LS, so as to improve its UCS and STS. This study can provide a reference for the modification technology of lime soil.

Highlights

Lime can improve the compressive strength and shear strength of soil, so as to meet the needs of engineering construction
Compared with L6 without nano clay, the strength growth rate of nano clay modified lime soil (NLS) with 8% nano clay is 51%. This is because with the increase in nano clay, on the one hand, nano clay can fill the pores between lime soil particles and make its internal structure more dense
Because fiber can slow down the failure and crack development of lime soil, there is still a certain bearing capacity after NFLS failure

Summary

Introduction

Lime can improve the compressive strength and shear strength of soil, so as to meet the needs of engineering construction. It is found that the volcano ash reaction between lime and soil will lead to the formation of calcium silicate hydrate (C–S–H) and calcium aluminate hydrate (C–A–H). These two kinds of gel materials can make the structure of soil compact and pore size decrease. Zhou et al studied the deformation characteristics and failure mechanism of lime improved soil through unconfined uniaxial compression test. The test results show that under the condition of unconfined uniaxial compression test, the failure of lime soil is a typical brittle failure mode [7]. The research shows that lime can effectively improve the strength of soil, but the brittle failure mode of lime soil needs to be further improved

Methods

Results

Conclusion