Utilization of limestone powder as an activator for early-age strength improvement of slag concrete

Using mineral slags to replace a portion of cement is a promising way to reduce carbon emissions from concrete production. However, slag concrete suffers from low early-age strength and large dry shrinkage. To address this issue, limestone powder was utilized as an activator for slag concrete in the present study. The effects of limestone addition on compressive strength, fluidity, carbonation resistance and drying shrinkage were evaluated. The results suggest that adding limestone significantly increases the early strength due to nucleation and filling effects. Remarkable decreases in the slump loss, carbonation depth and drying shrinkage are also achieved. Scanning electron microscope (SEM) and mercury intrusion porosimetry (MIP) analyses indicate that limestone powder contributes to densification of concrete microstructure by reducing the volume fraction of large capillary pores. Thermogravimetric analysis (TGA) suggests that limestone appreciably promotes early-age hydration. This work is the first attempt to quantify the net contribution of limestone addition to carbon footprint reduction and concrete production cost on an equal-strength basis. With 10 wt% limestone addition, approximately 60% reduction in CO2 emission and 21% in production cost can be achieved without compromising concrete strength.