Influence of drying-induced microcracking and related size effects on mass transport properties of concrete

Microcracking has been suspected of influencing the transport properties and durability of concrete structures, but the nature and extent of this influence is unclear. This paper focuses on the influence of drying-induced microcracking. Samples were prepared with sample thickness/maximum aggregate size (t/MSA) ratios ranging from 2 to 20 and dried to equilibrium at 105 °C or 50 °C/7% RH or 21 °C (stepwise: 93% RH → 55% RH) prior to characterisation of microcracks and transport tests. Results show for the first time that there is a significant size effect on microcracks and transport properties. Samples with smaller t/MSA had more severe microcracking and higher gas permeability. Gas permeability decreased with increasing t/MSA (for a decreasing MSA), and remained constant beyond t/MSA of 10. However, this size effect was not seen on gas diffusivity and sorptivity. The implications of these findings particularly regarding the influence of drying-induced microcracks on the durability of concrete structures are discussed.