Influence of subsequent curing on water sorptivity and pore structure of steam-cured concrete

Steam-cured condition is found to cause larger porosity and worse properties of concrete compared with normal curing condition. For the sake of seeking effective measurements to eliminate this bad effect of steam-cured condition on concrete, the water sorptivity and pore structure of steam-cured concretes exposed to different subsequent curing conditions were investigated after steam-curing treatment. The capillary absorption coefficient and porosity of the corresponding concretes were analyzed, and their mechanisms were also discussed. The results indicate that water sorptivity and pore structure of steam-cured concrete are greatly influenced by the curing condition used in subsequent ages. Exposure steam-cured concrete to air condition has an obviously bad effect on its properties and microstructures. Adopting subsequent curing of immersing steam-cured concrete into about 20℃ water after steam curing period can significantly decrease its capillary absorption coefficient and porosity. Steam-cured concrete with 7 d water curing has minimum capillary absorption coefficient and total porosity. Its water sorptivity is decreased by 23% compared with standard curing concrete and the porosity is 9.6% lower. Moreover, the corresponding gradient of water sorptivity and porosity of steam-cured concrete both decrease, thus mictostructure of concrete becomes more homogeneous.

Experimental investigation on dynamic mechanical characteristics and microstructure of steam-cured concrete

Steam-cured concrete is widely used to manufacture prefabricated units of high-speed railway foundation structure such as girder and track slab.The dynamic mechanical property of steam-cured concrete is one of the key properties affecting service performance of high-speed railway foundation structure.In the present paper,serial macro/micro-experiments were carried out to investigate the dynamic elastic modulus,shear modulus,damping ratio,and microstructure of steam-cured concrete.The relationships between compositions,curing regime,microstructure,and dynamic properties of steam-cured concrete as well as the corresponding mechanisms were discussed.The results indicate that steam-cured concrete in early age has a larger dynamic elastic modulus and shear modulus as well as a smaller damping ratio compared with standard-cured concrete.On the contrary,at a later age a slightly smaller dynamic elastic modulus and a larger damping ratio of steam-cured concrete are observed.Addition of mineral admixture results in a bit lower dynamic elastic modulus and damping ratio of concrete than that of the control specimen without mineral admixtures.The achievements can provide some fundamental suggestions for materials parameters selection during structural design of steam-cured concrete precast element.