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.