Promoting internal curing in concrete by replacing sand with sustainable biochar

Using biochar as a replacement for sand in concrete provides a sustainable solution to the ecological degradation and environmental pollution. This study investigates the use of biochar for internal curing when substituting sand in concrete. Various properties, including slump, mechanical strength , and hydration products , were assessed. The results show that prewetted biochar effectively preserves the slump of fresh concrete. The prewetted biochar provides internal curing by extending the hydration process , resulting in a 56 % increase in the duration between the first and third hydration peaks at the 100 % replacement level. This extended hydration process reduced the amount of unhydrated cement clinkers and enhanced the development of Calcium Silicate Hydrate (C-S-H) and CaCO₃, indicating a more complete degree of hydration of cement. Furthermore, the addition of biochar effectively reduces the total shrinkage of concrete by 65 % at a 100 vol% replacement level at 28 days and guarantees later strength development of concrete.