Early strength development in cement mortars containing high proportions of Jordanian natural Pozzolan

• High-volume (70%) pozzolan mortars activated by mechanical, thermal, and chemical methods. • Grinding significantly boosts early strength in cement-pozzolan blends. • Thermal curing at 120°C accelerates pozzolanic reaction and compressive strength. • Na₂SO₄ improves strength at low temperatures, with limited effect at elevated heat. • Combined mechanical and thermal activation achieves optimal early strength performance. In this study, three different methods were compared to activate Jordanian natural pozzolan: mechanical activation through grinding to increase the degree of fineness, thermal activation by curing mortars containing pozzolan at high temperatures, and chemical activation using activators such as Na 2 SO 4 . Additionally, combinations of two or more of these methods were tested to enhance the early strength of mortars containing high levels of natural pozzolan. Cement mortar cubes were prepared using a mixture of 70% natural pozzolan and 30% Portland cement (by weight), and their compressive strength was measured at ages of 1, 3, 7, and 28 days. The results demonstrated that all activation methods contributed to an increase in early-age strength to varying degrees. For instance, mechanical activation improved 3-day compressive strength by approximately 80% compared to the control mix. It was found that increasing fineness and curing temperature enhanced the reactivity of natural pozzolan, thus improving the early-age strength of cement mortars. The best results were achieved by combining mechanical grinding and heat treatment. Activating natural pozzolan and enhancing its early strength removes barriers to its use, thus providing an effective alternative to Portland cement, especially in countries rich in natural pozzolan, such as Jordan.