Research on the Corrosion Damage Mechanism of Concrete in Two Freeze–Thaw Environments

Xianhua Yao,Weifeng Bai,Junfeng Guan,Min Zhang,Lielie Li,Zepeng Liu

doi:10.1155/2020/8839386

Abstract

This study aims to investigate the effects of two freeze–thaw environments (i.e., maintenance freeze-thaw (MFT) environment and immersion freeze-thaw (IFT) environment) on the durability performance, deterioration rules, and mechanisms of concrete. In MFT, the concrete specimens were firstly cured in the standard curing environment (temperature, 20 ± 3, humidity, not less than 95%, and ages, 28 d) and then were carried out in freeze–thaw environment, while in IFT, the concrete specimens were firstly cured in the salt (NaHCO3, NaCl, and Na2SO4) immersion environment for 90 d and then were carried out in freeze–thaw environment. In this study, the damage features, relative dynamic elastic modulus, mass changes, and erosion-resistance coefficient of concrete have been measured. Thereafter, using the scanning electron microscopy (SEM) and the mercury intrusion porosimetry (MIP), the air-void structure parameters and the microstructures have been measured, respectively. The results show that the relative dynamic elastic modulus and the erosion-resistance coefficient of the compressive strength of the concrete in the IFT environment are, respectively, 14.3% and 21.0% higher than those of the concrete in the MFT environment. In addition, the results of the microstructure analyses show that the corrosion damages of the concrete are mainly caused by the combined action of the corrosion products of ettringite and freeze–thaw environment. However, the damage to the concrete in the MFT environment is more serious than that in the IFT environment. The results of the MIP analysis show that the harmful pore value for the concrete in the MFT environment is almost two times larger than that for the concrete in the IFT environment.

Highlights

Many earlier studies investigated the damage to concrete caused by freeze-thaw cycles [1, 2]
Ma et al [3] showed that the frost resistance of high-performance concrete blended with 20 wt% fly ash (FA) and 0.1% polypropylene fiber was superior when subjected to rapid freeze-thaw cycles
Liu et al [5] found that the addition of FA in ordinary concrete reduced the formation of gypsum and prevented the decalcification of calcium silicate hydrate (C-S-H) when subjected to sodium sulfate attack

Summary

Introduction

Many earlier studies investigated the damage to concrete caused by freeze-thaw cycles [1, 2]. Even for the studies on the effects of different freeze–thaw environments on the mechanical properties and microstructures of concrete, the methods used in most of these studies were freezing and thawing concrete in water, or in a single salt (e.g., NaCl) solution. Erefore, in the cold and saline-alkali corrosive areas of Western China, a study on the effects of freeze-thaw cycles and multisalt erosion on concrete has important scientific research significance and practical engineering value. In view of the multisalt solution attack environment in the cold region in western China and the actual situation of Dexiang Expressway Project in Delingha City, Qinghai Province, the effects of two freeze-thaw environments (i.e., MFT and IFT) on the durability performance, deterioration rules, and mechanisms of concrete have been investigated using the concrete mix ratio provided by the site so as to develop theories for the actual project and experimental basis

Experimental Materials and Concrete Specimens

Experimental Results and Discussion

Analysis of Microstructure of Concrete Specimens