The effects of different types of clay sources on the fresh and mechanical properties of limestone calcined clay cement (LC3) mortars

Limestone Calcined Clay (LC3) cements are promising primarily due to their lower CO2 emissions, accessible raw material sources, and lower energy consumption during calcination compared to clinker. This thesis focuses on developing LC3 cement/mortar mixtures with fresh and mechanical properties competitive with CEM I cement/mortar mixtures, using various low-quality clay sources from Türkiye. In this study, LC3 pastes and mortars were developed using various low-quality and waste-based clays from Türkiye. Within this scope, the properties of these clays were determined through individual X-ray diffraction (XRD) analysis and thermogravimetric analysis (TGA). Subsequently, the plasticity levels of the clays and their effects on grinding were identified. Based on the analyses, low-quality clays calcined at 750 °C were prepared with other raw material sources using a hybrid grinding system. Additionally, perforated bricks obtained as construction/demolition waste were used as the clay source in LC3 mortars. CEM I standard cement and LC3 mortars produced with refined kaolin with high kaolinite content were used as reference. The results showed that the developed LC3 mortars had an average spread diameter of 20 cm and 28-day compressive strengths ranging between 45-55 MPa. All LC3 mortars prepared with low-quality clays met the pozzolanic activity index, defined as a compressive strength threshold of 38 MPa. Furthermore, evaluations of the micro-morphologies of the samples using scanning electron microscopy (SEM) revealed that LC3 mortars with low-quality and waste-based clays contained less calcium hydroxide (CH) compared to the reference mortars. The consumption of CH by the calcined clays contributed to the mechanical properties, resulting in a more compact microstructure, with ettringite formations observed in some mortars. When the results were evaluated, it was seen that various low-quality clays, which had not undergone enrichment-filtration processes, were not selectively mined, were chemically untreated, could be calcined at low temperatures (450-900 °C), and had lower costs compared to bulk clinker, could be used as a binder that could replace clinker in terms of environmental and cost aspects.