Abstract
Metakaolin (MK), which has a fine particle size and higher activity in high alkaline environments, has been widely used in the fields of soil treatment engineering to stabilize soils. MK is used to replace part of ordinary Portland cement (OPC) with 0 : 15, 2 :13, 4 : 11 and 6 : 9 mass ratios of MK to OPC in this study. The mechanical property (e.g. stress‐strain relationship, strength, and deformation performance) and microstructure characteristics of MK‐based geopolymer cemented silty clay are investigated using unconfined compressive strength (UCS), nuclear magnetic resonance (NMR), and scanning electronic microscopy (SEM) tests. In addition, strength increase coefficient (ζs) and elasticity modulus increase coefficient (ζe) are defined to evaluate the effects of curing time on the mechanical property of MK‐based geopolymer cemented silty clay. Moreover, the relationships among porosity, UCS, and E50 of MK‐cemented silty clay are studied. By incorporating 2% MK, the UCS and E50 of MK‐cemented silty clay at 28 d are 1.32 and 1.30 times compared with MK0 group, respectively. The increase rate of UCS and E50 from 1 d to 7 d is faster compared with that from 7 d to 28 d. Furthermore, the microstructure of the sample modified by 2% MK is most homogeneous and dense. Finally, the optimistic mass ratio between MK and cement is 2 : 13 for silty clay in this test condition.
Highlights
Cement soil reinforcement technique has been accepted worldwide in the areas of foundation engineering, slope reinforcement, road construction, and rammed earth wall engineering for many years [1,2,3,4,5]
In the cement production process, about 900 kg CO2 will be emitted into the atmosphere per tonner of cement which contributed to global warming and climate change [8,9,10,11]. erefore, some supplementary cementitious materials have been used for replacing part of cement to reduce CO2 emission associated with cement production [12,13,14]
As a typical pozzolanic material, metakaolin (MK) is an amorphous aluminosilicate compound produced by calcinations of pure kaolinite at 500°C to 550°C [15], which has high activity and has attracted increasing attention in recent years that could partly replace ordinary Portland cement [16]
Summary
Cement soil reinforcement technique has been accepted worldwide in the areas of foundation engineering, slope reinforcement, road construction, and rammed earth wall engineering for many years [1,2,3,4,5]. Wu et al. Advances in Materials Science and Engineering [15] studied the effect of MK contents on the strength performance of cement-modified soil, and test results reveal that both the unconfined compression and splitting tensile strengths are improved, and the suitable ratio of MK to cement ranges from 1/3 to 1/2. Wang et al [22] investigated the effects of curing time and coal-metakaolin content on the properties of cemented sandy soils, and test results indicate that the unconfined compression strength at 28 d was improved by 1.68–2.18 times by incorporating coalmetakaolin. The objective of this research is to investigate the effects of curing time on mechanical property (i.e., unconfined compressive strength, elasticity modulus, and stress-strain relationship) and microstructure characteristic of cement-stabilized soil incorporate with different MK contents. SEM and nuclear magnetic resonance (NMR) techniques are used to study the porosity and microstructure characteristic of MK cement silty clay with 26.5% water content, to analyze the internal microstructure change of MK-cemented silty clay under different MK contents (i.e., 0%, 2%, 4%, and 6%) and curing times (i.e., 1 d, 3 d, 7 d, 14 d, and 28 d)
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