Thermoactivated recycled cement waste: optimal dehydration temperature and binder properties insights

Cimento reciclado termoativado: insights sobre a melhor temperatura de desitratação e propriedades do ligante

Abstract

Thermoactivated recycled Portland cement (RC) is obtained by dehydrating cement paste waste, recovering the binder capacity. This research aims to determine the optimal dehydration temperature for achieving better mechanical and environmental performance for RC as a binder or if dehydration is necessary at all. A literature review was conducted using 23 papers. Physico-chemical characteristics of RC powders were analyzed and discussed during rehydration based on combined water, water demand, combined water fraction (cwf), and CO₂ intensity. In conclusion, RC dehydrated at 450-550 °C was optimal for a rapid reaction, showing the highest combined water at 1 and 7 days. At 28 days, combined water increased as treatment temperatures rose. Untreated recycled cement (i.e., ground-hardened cement paste) has low reactivity and requires 30٪ more water than ordinary Portland cement (OPC), leading to higher CO₂ emissions or lower performance. Recycled cement dehydrated at 450-550 °C, especially when blended with slags, pozzolans, and Portland clinker demonstrated optimal environmental and mechanical results. These findings support the development of blended RC formulations, promoting circular economy practices in the cement industry.

Keywords
Recycled cement; Dehydration; Rehydration; Combined water fraction (cwf); Carbon dioxide (CO₂); Blended cement