Steam-cured recycled aggregate concrete incorporating moderately high early strength cement: effect of binder content and curing conditions

Steam curing employed for faster strength gain due to higher hydration rate may lead to shrinkage issues, and hence the use of moderately high early strength cement (MESC) is proposed instead of typically used high early strength cement (HESC) which has a high C3S content. This paper evaluates the suitability of MESC for use in precast concrete. The objective was to (i) determine the feasibility of MESC in recycled aggregate concrete (RAC), (ii) determine the optimum steam curing conditions (curing duration, maximum temperature, and duration of holding maximum temperature), and (iii) evaluating the beneficial use of reduced binder content to compensate for steam curing. Four series of RAC were developed which were subjected to nine different steam curing condition, and the resulting strength properties were determined. Though all the developed concrete specimens achieved the design strength of 30 MPa, those cured at 50 °C with 1 h duration of exposure to maximum temperature exhibited the best performance. Further, it was found that even though reducing the binder content reduces the ultimate strength at 28-day age, curing at 70 °C with 2 h exposure to maximum temperature duration (for 7% reduction in binder volume) leads to merely 11.8% strength decline. It is concluded that MESC can be effectively used in steam cured RAC instead of OPC and HESC with meagre strength loss when cured at maximum temperature of 50 °C maintained for 1 h while the total curing time being 4.5 h. Thus, utilizing MESC in RAC shall not only help combat the persistently declining natural resources but also reduced the associated carbon dioxide emissions, thereby promoting sustainable development.