Experimental Investigation of MgAl-NO2 and MgAl-CO3 LDHs on Durability of Mortar and Concrete

Zhanguo Li,Yue Li,Caiyun Jin,Huan Du,Zigeng Wang

doi:10.1155/2021/5582150

Abstract

Two kinds of layered double hydroxides (LDHs), MgAl-NO2 (N-LDH) and MgAl-CO3 (C-LDH), were incorporated to study the durability of mortar and concrete. The LDH contents of mortar were 1%, 2%, and 4% by mass and the LDH contents of concrete were 0.5%, 1%, 2%, 4%, respectively. The effect of LDHs on sulfate resistance of mortar was studied through dry-wetting cycle test, compressive strength test, and flexural strength test. In addition, the effects of LDHs on pore structure, chloride resistance, carbonation resistance, shrinkage, and creep of concrete were investigated by SEM, mercury injection test, XRD, chloride ion diffusion coefficient test, chloride salt corrosion depth test, carbonation depth test, shrinkage test, and creep test. The results showed that LDHs can improve the ability of resisting ion corrosion, carbonization, shrinkage, and creep, reduce the pore content, and optimize the pore structure of mortar and concrete to some extent. Moreover, 4% LDHs had a better effect on improving the durability of mortar and concrete compared to 0.5%, 1%, and 2% LDHs, and the effect of C-LDH was better than N-LDH.

Highlights

We studied the influence of N-layered double hydroxides (LDHs) and C-LDH on the mechanical properties of concrete. e results showed that when the content of N-LDH and C-LDH in concrete was higher than 4%, the mechanical properties of concrete
It can be seen from this paper that with the gradual increase of N-LDH and C-LDH content, the durability indexes of the studied concrete are improved. erefore, we speculate that when the content of N-LDH and C-LDH is higher than 4%, the durability index will continue to improve
When the content of N-LDH and C-LDH is less than 4%, the following conclusions are drawn: (1) N-LDH and C-LDH can remove chloride ions in solution by anion exchange and adsorption, respectively. e diffusion coefficient of chloride ions in concrete decreased with the increase of the content of LDHs

Summary

Introduction

Due to the long-term penetration and corrosion, cement in concrete in marine environment and saline soil area reacted with aluminum, sulfate, and calcium to form expansion stress, which caused volume expansion and reduced the mechanical properties and durability of the concrete [1,2,3,4,5,6,7]. E research by Qu et al [28] showed that adding 1% Ca-Al-NO3 LDHs into concrete can reduce the chloride ion content by 17%–53%. Yoon [42] researched the adsorption of chloride in concrete by Mg-Al LDHs (CLDH) calcined at 450°C. e results showed that the chloride ions were adsorbed in the process of structural reconstruction. E research results of Geng [45] revealed that the influence of reaction temperature on the chloride binding capacity of CLDH was 38°C > 50°C ≈ 20°C > 3°C. There is a lack of systematic research on the effect and mechanism of LDHs on the durability of mortar and concrete with different strength grades. The influence of LDHs and their content on chloride ion permeability, carbonation, shrinkage, and creep on different strength grades of concrete (C30 and C50) were explored

Materials

Experimental Methods

Chloride Ion Corrosion Resistance of Concrete

Conclusions