Air Entrainment, Carbonation, and Shrinkage in Concrete Containing Reclaimed Water-Based Paint

Incorporating postconsumer reclaimed water-based paint (RWBP) into concrete provides a sustainable alternative to landfill disposal. However, the application of RWBP-incorporating concrete has remained limited mostly to sidewalks, because critical parameters for practical use remain unclear, such as air-entrained stability, slump loss, and drying shrinkage of formed concrete over time. Additionally, the effect of RWBP on the carbonation resistance of concrete has not been explored, which is critical for concrete containing supplementary cementitious materials. This study systematically investigated these aspects in concrete with fly ash. Due to its liquid phase and fine particles, RWBP partially replaced fine sand and water at different dosages. The air bubble stability and slump loss of fresh concrete were tested, along with compressive strength at 3, 7, and 28 days. Moreover, the carbonation resistance of RWBP-incorporating concrete was evaluated by measuring the pH value of the pore solution. Finally, the sorptivity and drying shrinkage of concrete were tested. The results show that incorporating RWBP adds significant value, particularly by slowing alkalinity loss in carbonated areas and improving carbonation resistance. The presence of RWBP increased air bubbles in concrete, leading to reduced strength. However, sorptivity and drying shrinkage improved with increasing RWBP dosage. Notably, these air bubbles were unstable, which accelerated slump loss and increased drying shrinkage.