Influence of Different Alkali Sulfates on the Shrinkage, Hydration, Pore Structure, Fractal Dimension and Microstructure of Low-Heat Portland Cement, Medium-Heat Portland Cement and Ordinary Portland Cement

Yang Li,Ke Jiang,Haibo Yin,Shengwen Tang,Minghui Huang,Hui Zhang,Kaitao Xiao

doi:10.3390/fractalfract5030079

Abstract

In cement-based materials, alkalis mainly exist in the form of different alkali sulfates. In this study, the impacts of different alkali sulfates on the shrinkage, hydration, pore structure, fractal dimension and microstructure of low-heat Portland cement (LHPC), medium-heat Portland cement (MHPC) and ordinary Portland cement (OPC) are investigated. The results indicate that alkali sulfates magnify the autogenous shrinkage and drying shrinkage of cement-based materials with different mineral compositions, which are mainly related to different pore structures and hydration processes. LHPC has the lowest shrinkage. Otherwise, the effect of alkali sulfates on the autogenous shrinkage is more profound than that of drying shrinkage. Compared with the pore size distribution, the fractal dimension can better characterize the shrinkage properties of cement-based materials. It is noted that the contribution of K2SO4 (K alkali) to the promotion effect of shrinkage on cement-based materials is more significant than that of Na2SO4 (Na alkali), which cannot be ignored. The microstructure investigation of different cement-based materials by means of nuclear magnetic resonance (NMR), mercury intrusion porosimetry (MIP) and scanning electron microscope (SEM) shows that this effect may be related to the different pore structures, crystal forms and morphologies of hydration products of cement-based materials.

Highlights

IntroductionWith the rapid development of human society and the economy, the service environment of modern buildings will become diversified and problematic, placing high requirements on the durability of modern cement-based materials [1,2]
Considering that the alkali sulfates in cement-based materials mainly exists in the form of alkali sulfates (R2 SO4, R is Na and K), this paper mainly studies the influence of different alkali sulfates (Na2 O and K2 O) on the drying shrinkage and autogenous shrinkage of cement-based materials of different mineral compositions by adding alkali sulfates
When the alkali content ranges from 0.8% to 1.2% at 28 d, the autogenous shrinkage of low-heat Portland cement (LHPC) mortars with Na alkali increases from 38% to 41%, but that with K alkali increases from 56% to 99% compared with L0

Summary

Introduction

With the rapid development of human society and the economy, the service environment of modern buildings will become diversified and problematic, placing high requirements on the durability of modern cement-based materials [1,2]. Based on a large number of experimental data, Burrows et al [8] considered that alkali sulfate content and tricalcium aluminate (C3 A) were the most important 4.0/). 2021, 5, 79 and the third most important factors affecting the shrinkage and cracking performance of cement-based materials, respectively. For modern cement-based materials, due to the promotion of new dry calcination technology, the reduction of high-quality cement raw materials and the service environment of ocean and saline alkali land, the alkali sulfate content of cement-based materials has become difficult to control [9].

Methods

Results

Conclusion