Effect of loading area on triaxial compression behavior of microcapsule-based self-healing concrete

Concrete is customarily subjected to a complex triaxial stress state in structures under service. True triaxial experiments using cubic specimens in laboratory settings often utilize shims marginally smaller than the specimen surface for loading purposes. However, the influence of shim dimensions on the triaxial mechanical characteristics of concrete remains obscure. Therefore, in this study, for urea-formaldehyde (UF)/epoxy microcapsule-based self-healing concrete, shims of varying sizes were designed to conduct true triaxial compression experiments, examining the effects of loading area size and microcapsule content on triaxial mechanical behavior. The crack damage morphology was observed using a scanning electron microscope (SEM), the rupture of microcapsules was analyzed through energy-dispersive X-ray spectroscopy (EDS), and the micropore structure was determined via nuclear magnetic resonance (NMR). The research findings reveal that reducing the loading area induces stress concentration near the shim edge, significantly decreasing the first peak strength with a maximum reduction of 37 %; while also increasing the second peak strength, with a maximum increase of 52 %. Notably, a “sleeve-like” delamination occurs when the loading area is below 95 % of the specimen surface area. Incorporating microcapsules into concrete enhances ductility and porosity, achieving a maximum 1.9 % increase in first peak strain and 1.98 % in porosity. This study may offer valuable insights and data for the optimization of concrete materials and structural design, thereby contributing to the safety and durability of engineering structures.