The effect of coarse aggregate content and size on the age at cracking of bonded concrete overlays subjected to restrained deformation

• Coarse aggregate content has a near-linear relationship with cracking age in overlays.
• Coarse aggregate size has a significant effect on overlay cracking.
• An analytical model for overlay cracking, depending on aggregate content is proposed.

The influence of coarse aggregate content and size on cracking of bonded concrete overlays was investigated using the ring test. Specimen parameters included 4 different coarse aggregate contents, 2 aggregate sizes and 3 strength grades. Test results for relevant time-dependent material properties such as drying shrinkage, tensile strength, tensile relaxation and elastic modulus were used to predict the time to first cracking using previously established analytical models. Increases in both coarse aggregate volume content and size were shown to significantly prolong the time to first cracking in the ring test, while an inverse relationship was observed for crack intensity. The analytical model was found to be ineffective in detecting the influence of coarse aggregate content and size on the cracking behavior of bonded overlays. This was ascribed to the model’s inability to account for aggregate-related differences in strain softening and fracture mechanisms on a micro scale.