Strain and crack distribution in concrete during drying

Uneven shrinkage behavior between cement paste and rock aggregate takes place when concrete is subjected to drying. Possible consequences including internal damage and strain distribution need to be researched to understand the changes in concrete properties over time. In this study, strain distributions over the cross section of sliced concrete specimens with age were determined using a digital image correlation method (DICM). After shrinkage had developed, crack distributions were visually observed using a fluorescent epoxy impregnation method (FEIM). High correlation was found between expansive strain at the maximum principal strain distribution obtained with DICM and positions of cracks obtained with FEIM, suggesting that DICM can be applied to the damage evaluation of a concrete cross section over time. Even the present DICM and FEIM studies are results of surface cracking of specimens, which is strongly affected by the water transfer process and resultant three dimensional stress distribution, the following findings were obtained: the area of internal fine cracks increased with increase in aggregate size, correlation was confirmed between the area of fine cracks and macroscopic strain of concrete, and two types of fine cracks were confirmed—cracks restrained by aggregate and interfacial cracks between aggregate and mortar as a result of stress arch formation.