The enduring legacy of limestone: from an ancestral pillar of construction to a modern precursor in synergy with recycled concrete.

Facing the urgent need to reduce the environmental impact of Portland cement, this review explores the potential of limestone and pulverized recycled concrete (PRC) as pillars for sustainable binders. The historical and current role of limestone is analyzed, from its ancestral use to its application in modern cements, LC3, and, crucially, as a precursor in alkali-activated cements (AACs). PRC as a precursor in AACs is also examined, highlighting its contribution to the circular economy. The environmental and performance advantages of AACs based on these materials are discussed, as well as key challenges, including long-term durability, raw material variability, and the need for standardization. It is concluded that both resources are strategic, requiring focused research for their effective implementation.