Fundamental mechanical properties and multi-scale microstructural characteristics of steam-cured concrete used in CRTS III slab ballastless track

In order to understand the fundamental mechanical properties and multi-scale microstructural characteristics of CRTS III slab ballastless track, the compressive/flexural strength, static elastic modulus, hydration products, water absorption, pore size distribution/porosity, air void and interface characteristics of four concrete groups were comprehensively investigated under both standard and steam curing conditions at 7 d, 28 d and 90 d, respectively. Results show that steam curing accelerates the formation of hydration products and increases the early-age mechanical properties of concrete, but the steam-curing damage still leads to some performance deteriorations of concrete including insufficient development of late-age mechanical properties, aggravated brittleness, unimproved surface damage, increased proportions of harmful pores and degraded interface characteristics. The incorporation of supplementary cementitious materials (SCMs) can alleviate the heat damage and mitigate performance degradation of concrete caused by steam curing, especially when FA and GGBS were both incorporated. The hybrid addition of 20% FA and 10% GGBS provides steam-cured concrete with equivalent or even better mechanical and microstructural performances compared with concrete without SCMs.