Influence of pore structures on the frost resistance of concrete

The effects of air content, mineral admixtures and strength on the freeze–thaw resistance of concrete were studied from the perspective of pore structure. With respect to different size ranges, the pore structures of concrete were analysed at multiple scales and across multiple dimensions by mercury intrusion porosimetry, gas physical adsorption method, linear traverse method and X-ray computerised tomography, respectively. The experimental results indicate that the size and quantitative characteristics of pores which are greater than 0·35 nm in diameter can be obtained by combining these four methods. As simply improving the strength grade tends to decrease the porosity, which further increases the air-void volume and number of harmful pores at a macro-scale, it is not necessarily conducive to improving the frost resistance of concrete. Moreover, when the air content varies from 2% to 6%, the proportion of tiny closed pores in concrete increases significantly, the spacing factor and average diameter decrease in turn, and the frost resistance improves with increasing air content.