Effects of steam curing on strength and porous structure of concrete with low water/binder ratio

A research program was carried out to investigate the effects of duration of initial steam curing at atmosphere pressure on compressive strength of concrete with low water/binder ratio. The results showed that the compressive strength of samples steam cured for 5, 10, 14 h increased, while it decreased distinctively for sample steam cured for 24 h. Mercury intrusion porosimetry (MIP) method and scanning electron microscope-backscattered electron (SEM-BSE) image analysis technique were adopted to measure the corresponding variation of porous characteristics caused by the increasing duration of steam curing. The changes in coarse porosity and total porosity calculated by SEM-BSE image analysis and MIP method respectively could indicate the relationship between porosity and mechanical properties of the concrete subjected to different duration of steam curing. Compared with total porosity obtained by MIP method, the coarse porosity by SEM-BSE image analysis was in better accord with the compressive strength because the coarse pores measured by SEM-BSE image analysis were larger than 0.5 μm and included not only the interconnected pores but also the closed ones. An empirical model was developed to evaluate the influence of duration of initial steam curing on the compressive strength of concrete. By comparison, the measured compressive strength was in great accordance with the compressive strength calculated by the proposed model.