Investigation on drying-induced microcracks distribution characteristic and its formation mechanism in concrete

Accurately capturing shrinkage-induced microcracks in concrete remains a challenging task. This study investigated the distribution and width of drying-induced microcracks in concrete with varying coarse aggregate sizes, using Digital Image Correlation (DIC). The reliability of DIC measurements was validated via a fluorescent epoxy impregnation method. A novel approach was developed to differentiate between radial and circumferential microcracks, and their distribution characteristics were analyzed. The results indicated that circumferential microcracks constituted approximately 60 % of the total radial microcrack area, while nearly all microcracks wider than 12 µm were radial. Initially, circumferential microcracks formed preferentially around mortar regions with larger major morphological axes, extending along aggregate edges. When these circumferential microcracks extend the angular corner of coarse aggregate, these cracks could propagate into radial microcracks along the same direction, depending on the surrounding mortar volume. The volume of mortar surrounding the aggregates and the spacing between aggregates were critical factors influencing the formation of radial microcracks. Excessive mortar in localized areas led to wider cracks. These findings highlight the crucial role of mortar distribution in microcrack formation and provide insights for designing concrete with enhanced volumetric stability. • Determine the distribution and width of drying-induced microcracks based on DIC. • Distinguish between radial and circumferential microcracks by minimum principal strain. • Distribution pattern of mortar affects the formation of drying-induced microcracks.