Chloride Penetration into Concrete under the Coupling Effects of Internal and External Relative Humidity

Fangzhi Zhu,Mingmin Zhang,Zhiming Ma

doi:10.1155/2020/1468717

Abstract

Chloride penetration frequently happens in an unsaturated concrete; in this case, the chloride migration is under the coupling effects of internal moisture and external relative humidity (RH). Various chloride attack tests were designed in this paper to investigate the effects of internal moisture and external RH (50–100%) on the chloride penetration into an unsaturated concrete, and the chloride content was determined to quantify the chloride migration in concrete. The results highlighted that there was a good correlation between the chloride penetration into concrete and its internal RH. The chloride ion was difficult to penetrate into concrete when its internal RH was below 50%; however, the chloride penetration rate increased when the internal RH of concrete was above 75%, and the chloride migration increased with increasing RH and exposure duration. Water evaporation in concrete increased with decreasing external RH, and an obvious increase in the surface chloride content may be observed when external RH was 50%; however, when external RH was above 75%, the inner chloride content increased and surface chloride content decreased with increasing exposure duration. Simulating the chloride penetration under wet-dry cycling, the water migration resulted in an increase in the surface chloride content and a decrease in the inner chloride content, and the chloride crystal precipitated on the surface of concrete with a high w/c ratio.

Highlights

With rapid development of construction technology, concrete structure was inevitably exposed to various harsh environments, mainly including chloride attack, freezingthawing, and carbonation environments [1,2,3]
When the exposure duration was 12 months, some chloride ions migrated from the inner layer to the surface of the A specimen, and there was a slight increase in the surface chloride content of the B specimen; this may be due to that the low internal relative humidity (RH) hampered the chloride migrating from A specimen to B specimen, and a long time exposure was needed to achieve the chloride migration in concrete
Concrete was inevitably subjected to various environments, and this paper was developed to quantify the effects of internal moisture content and external RH on the chloride migration in an unsaturated concrete

Summary

Introduction

With rapid development of construction technology, concrete structure was inevitably exposed to various harsh environments, mainly including chloride attack, freezingthawing, and carbonation environments [1,2,3]. For simulating the chloride migration in an unsaturated concrete when exposed to marine tidal zone and spray zone, the chloride penetration was frequently determined by capillary absorption test and wet-dry cycling test, and the previous study reported that the chloride penetration was close to the wet-dry cycles, ion concentration and exposure duration [11,12,13]. Some scholars further investigated the influence of RH and moisture content on the chloride penetration into concrete; for example, Homan et al [21] reported that the increasing internal moisture content aggravated the chloride penetration, and the water convection had a significant impact on chloride migration in concrete [22]. A quantitative test for determining the influence of internal moisture and external RH on the chloride penetration was lacking, which was helpful to better understand the chloride migration in an unsaturated concrete. We hope the findings in this paper were helpful to the further investigation of chloride penetration into unsaturated concrete

Materials and Experimental Details

A Vacuum saturation meter

Chloride migration by concentration gradient

Experimental Results and Discussion

Conclusions

Conflicts of Interest