Investigations on factors influencing physical properties of recycled cement and the related carbon emissions and energy consumptions

Abstract

Cement production emits large amounts of carbon dioxide and has long been considered a significant source of global atmospheric CO2 emissions. The production of recycled cement (RC) could be an effective and sustainable way for the cement industry. This work studied the effect of different factors, including burn temperature (450 °C, 650 °C, and 800 °C) for preparing RC, carbonation degree of precursor, particle size of RC and water-cement (w/c) ratio on the compressive strength, hydration products and microstructure of RC pastes through mechanical, XRD, TG-DTG and SEM tests. The results show that burn temperature is the most important parameter for RC, and 650 °C RC performed best and had the highest compressive strength of the paste. The higher carbonation degree of the precursor resulted in a slightly higher strength of the RC paste due to the finer particle size of the cement particles and more calcite in produced RC, which all contributed to accelerated cement hydration. Similar as OPC, smaller particle size and w/c produced a higher strength of RC paste. RC paste (w/c = 0.5) with a compressive strength of 35 MPa at the age of 28 days can be achieved by producing the RC under 650 °C and a particle size range of 0–300 μm. Noticeably, compared to the OPC production process, more than 70% CO2 emissions and 60% energy consumption could be reduced for RC production under 650 °C.