Assessment and mitigation of early-age cracking for on-site concrete structures by a combined scheme using Temperature Stress Testing Machine (TSTM) and long-span restraining frame

Abstract

From the field survey, thermal cracking frequently occurs in substructural concrete walls, although a high dosage of Calcium Sulfoaluminate (CSA) expansive additive is widely utilized. Conventional assessment methods fail to characterize the failure of CSA expansion under coupled realistic conditions. Therefore, an assessment scheme is proposed in this study: Firstly, mix proportions, temperature, restraint and curing conditions are used as input for a developed Temperature Stress Testing Machine (TSTM). By testing, limited expansions of CSA additive under low water-to-binder ratio, high temperature or drying condition, is unfolded. Corresponding countermeasures are also proposed. Secondly, long-span restraining frames are constructed to validate, and upscale findings from TSTM. Eventually, normal and optimized mixtures are applied and compared in real substructural walls. This combined scheme newly reveals that the lack of free water is the mechanism for CSA's stagnant expansion and a combination of CSA and lightweight aggregates shows promising potential as a countermeasure.