Thermal analysis of non-kaolinitic clays for low-cost mixed cement

Thermal analysis of non-kaolinitic clays for low-cost mixed cement

Abstrakt

For decades, research on clays and calcined clays has primarily centred on kaolinite and its calcined form. However, recent economic fluctuations have significantly increased the cost of these materials. Consequently, scientists and the industry have begun developing alternatives to reduce cement cost and CO2 emissions. The newly adopted EN 197-5 standard presents a solution, it permits up to 50% substitution of cement with supplementary cementitious materials (SCM), an increase from the previous 35% limit, which opens new, unexplored possibilities. This study explores the potential of locally sourced non-kaolinitic clays as SCM in blended cements. A comprehensive characterization of these clays was conducted using techniques such as isothermal and isoperibol calorimetry, thermogravimetric analysis (TGA) coupled with differential thermal analysis (DTA), and evolved gas analysis (EGA). These methods were employed to assess hydration kinetics, calcination behaviour, and CO₂ emissions during calcination. Based on these results, mixtures with different levels of cement replacement were prepared and evaluated for workability and compressive strength over time. Our results demonstrate that non-kaolinitic clays significantly reduce the total heat of hydration while accelerating the hydration process. TG-EGA revealed that CO2 emissions during calcination are approximately one-tenth of those produced during Portland clinker production. Cement replacement led to increase of compressive strength and reduction of workability. Furthermore, increasing the clay content i.e., the level of cement replacement, amplifies these effects. TG-DTA analysis confirmed that complete calcination is achieved at 800 °C after 2 hours. These findings confirm the suitability of non-kaolinitic clays as effective and sustainable supplementary cementitious materials for blended cements.

For decades, research on clays and calcined clays has primarily centred on kaolinite and its calcined form. However, recent economic fluctuations have significantly increased the cost of these materials. Consequently, scientists and the industry have begun developing alternatives to reduce cement cost and CO2 emissions. The newly adopted EN 197-5 standard presents a solution, it permits up to 50% substitution of cement with supplementary cementitious materials (SCM), an increase from the previous 35% limit, which opens new, unexplored possibilities. This study explores the potential of locally sourced non-kaolinitic clays as SCM in blended cements. A comprehensive characterization of these clays was conducted using techniques such as isothermal and isoperibol calorimetry, thermogravimetric analysis (TGA) coupled with differential thermal analysis (DTA), and evolved gas analysis (EGA). These methods were employed to assess hydration kinetics, calcination behaviour, and CO₂ emissions during calcination. Based on these results, mixtures with different levels of cement replacement were prepared and evaluated for workability and compressive strength over time. Our results demonstrate that non-kaolinitic clays significantly reduce the total heat of hydration while accelerating the hydration process. TG-EGA revealed that CO2 emissions during calcination are approximately one-tenth of those produced during Portland clinker production. Cement replacement led to increase of compressive strength and reduction of workability. Furthermore, increasing the clay content i.e., the level of cement replacement, amplifies these effects. TG-DTA analysis confirmed that complete calcination is achieved at 800 °C after 2 hours. These findings confirm the suitability of non-kaolinitic clays as effective and sustainable supplementary cementitious materials for blended cements.