RETRACTED: Investigating the potential of the limestone calcined clay cement with cement content below 50 wt%: Hydration properties and environmental impact analysis

Abstract

Limestone calcined clay cement (LC3) is a promising strategy and technology to mitigate the climate change in the field of cement-based materials. The purpose of this work was to systematically investigate the properties of the LC3 system with cement content below 50 wt%, in which two clays with kaolinite content of 33.2% (MK30) and 50% (MK50) were used for comparison. Cement pastes and mortars were prepared with four coupled replacement levels of 50 wt%, 65 wt%, 75 wt% and 85 wt% by calcined clay and limestone. The compressive strength of the mortars was tested for up to 90 days. The hydration process was monitored in detail by isothermal calorimetry, phase assemblages calculated by quantitative XRD-Rietveld refinement and the reaction of metakaolin in calcined clay calculated by mass balance approach. Finally, an environmental performance indicator with consideration of CO2 emission and compressive strength was also introduced to evaluate the application feasibility of these different low-cement LC3 systems. From the observation of the experiment, cement hydration dominated the compressive strength of LC3 system before 3 days, while the pozzolanic reaction between metakaolin and CH as well as the synergistic reaction between metakaolin and limestone supported the late-strength development regardless of the calcined clay types. Compared to MK30, MK50 was more conducive to hydrates precipitation and microstructure densification, resulting in a higher compressive strength. The environmental performance indicator showed that LC3-50 and LC3-35 prepared by MK30, and LC3-50, LC3-35 and LC3-25 prepared by MK50 can be treated as ideal systems, as they presented much lower environmental impact and also maintained the desired compressive strength. The results of this work present a promising contribution to realizing the environmental sustainability of cement production.