Long-term carbonation resistance of concrete under initial high-temperature curing

To evaluate the influences of initial high-temperature curing on concrete long-term carbonation resistance, four mixtures of concrete specimens were designed and fabricated. After a certain degree of pre-curing, specimens were cured in 40, 60, or 80 °C water until they attained the designed strength. Accelerated carbonation, mercury intrusion porosimetry, and scanning electron microscopy experiments were then conducted at different ages. Results indicate that the carbonation resistance of concrete changes nonlinearly as the curing temperature rises because of the activity stimulation and hydration degree promotion of binder materials; porosity increases at the same time. Concrete carbonation resistance gradually improves with rising curing temperature until the upper limit of 60 °C and then declines sharply. Pre-curing can improve the microscopic pore structures of concrete by increasing the proportion of harmless pores, thereby improving concrete carbonation resistance. Whether under normal-temperature curing or high-temperature curing, concrete carbonation resistance improves with growing age because of successive hydration of binder materials. By contrast, replacement of pozzolanic materials, such as fly ash, slag, or silica fume, decreases concrete carbonation resistance.