Correlation of chloride diffusion coefficient and microstructure parameters in concrete: A comparative analysis using NM
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RESEARCH ARTICLE
Correlation of chloride diffusion coefficient and microstructure parameters in concrete: A comparative analysis using NMR, MIP, and X-CT Yurong ZHANGa,b, Shengxuan XUa, Yanhong GAOa, Jie GUOa, Yinghui CAOa, Junzhi ZHANGa,b* a
College of Civil Engineering, Zhejiang University of Technology, Hangzhou 310014, China Key Laboratory of Civil Engineering Structure & Disaster Prevention and Mitigation Technology of Zhejiang Province, Hangzhou 310014, China b
*
Corresponding author. E-mail: [email protected]
© Higher Education Press 2020
ABSTRACT Permeability is a major indicator of concrete durability, and depends primarily on the microstructure characteristics of concrete, including its porosity and pore size distribution. In this study, a variety of concrete samples were prepared to investigate their microstructure characteristics via nuclear magnetic resonance (NMR), mercury intrusion porosimetry (MIP), and X-ray computed tomography (X-CT). Furthermore, the chloride diffusion coefficient of concrete was measured to explore its correlation with the microstructure of the concrete samples. Results show that the proportion of pores with diameters < 1000 nm obtained by NMR exceeds that obtained by MIP, although the difference in the total porosity determined by both methods is minimal. X-CT measurements obtained a relatively small porosity; however, this likely reflects the distribution of large pores more accurately. A strong correlation is observed between the chloride diffusion coefficient and the porosity or contributive porosity of pores with sizes < 1000 nm. Moreover, microstructure parameters measured via NMR reveal a lower correlation coefficient R2 versus the chloride diffusion coefficient relative to the parameters determined via MIP, as NMR can measure non-connected as well as connected pores. In addition, when analyzing pores with sizes > 50 µm, X-CT obtains the maximal contributive porosity, followed by MIP and NMR. KEYWORDS
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permeability, microstructure, NMR, MIP, X-CT
Introduction
Permeability is a major factor influence on the durability of reinforced concrete (RC) structures [1]. Many studies have shown that in chloride-rich environments, concrete structures suffer damage in the form of steel corrosion, which was caused by chloride ions penetrating into the surface of RC structures and reaching a certain critical concentration [2–4]. The chloride transport performance of concrete is one of the important indicators used to evaluate concrete durability [5,6]. Therefore, the chloride transport performance of concrete represents a hotspot of durability analysis for concrete structures in chloride environments Article history: Received Jul 30, 2019; Accepted Jan 10, 2020
and studying the microstructure of concrete is the foundation of the chloride transport process [5,7]. As a heterogeneous porous material, concrete has many pores with diverse shapes and sizes [8]. The slow ingress of fluid media into the pores of concrete indicates a lower permeability. Thus, the microstructure of concrete
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