Analysis of Thermohydraulic Spalling in Blended Cement Concrete

Abstract

Recently, the construction industry has increasingly focused on the development of more sustainable transport infrastructure, such as tunnels, driven by the growing use of clinker-reduced cements. One major challenge in this context is fire exposure, which can lead to severe structural damage through concrete spalling, thereby compromising the integrity of the structure. To date, the fire-induced spalling behavior of blended cement concrete remains insufficiently understood. This is particularly concerning, given the increasing adoption of blended cements with reduced clinker content, which are expected to see widespread use in the future. Consequently, a deeper understanding of how different cement types influence spalling susceptibility is of great importance. A comprehensive study was conducted to investigate spalling behavior and analyze the associated thermohydraulic effects in concretes made with CEM I, CEM II/A-LL, CEM III/A, and CEM II/B-Q. The findings revealed that the use of blended cements generally led to increased spalling susceptibility, even in normal-strength concrete. Additional analysis indicated that blended cement concretes exhibited lower permeability and higher moisture content, both of which are likely contributors to the elevated spalling risk. Furthermore, the study showed that moisture transport during heating closely follows the dehydration behavior of the cementitious matrix. Blended cement pastes were found to contain lower quantities of early-dehydrating AFt and AFm phases, as well as more thermally stable C-(A)-S-H phases. Moreover, the incorporation of polypropylene fibers into the concrete mix effectively mitigated spalling across all cement types. Therefore, demonstrating the continued effectiveness of polypropylene fibers as a spalling prevention strategy.