Can calcined waste materials and low-grade clays be part of the limestone calcined clay cement binder system? An Australian case study

Calcined kaolinitic clay is one of the major supplementary cementitious materials (SCMs) utilized for reducing the clinker factor in cementitious composites and forms a substantial part of limestone calcined clay cement (LC3) composites. However, the availability of kaolinitic clay is limited to specific geographical locations globally. Thus, understanding the performance of LC3 composites with low-grade and nonkaolinitic clay is crucial for technological deployment in different regions of the world. This study explores the influence of different types of calcined clays along with varying alternatives of limestone (LS) and their influence on the fresh, hardened, and microstructural properties of 28-day cured LC3-70 composites. The calcined clays used include metakaolin (MK), bentonite, local mixed clay [LC(R)], brick waste (BW), and terracotta waste (TW). An alternative to limestone, such as garden lime (GL) and brick waste, was introduced to understand the impact on the workability and resulting mechanical properties of LC3-70 mixes at 7 and 28 days. The results demonstrate that LC3-70 with limestone obtained the highest 28-day strength of 48.12 MPa with metakaolin and 39.28 MPa as the lowest with terracotta waste. However, interestingly, identical or higher compressive strength was achieved with garden lime and brick waste as limestone replacements. The X-ray diffraction (XRD) analysis showed no new hydration products with the adoption of brick waste and terracotta waste as calcined clay or garden lime and brick waste as limestone substitutes. Based on the 28-day cured specimens, the portlandite (CH) consumption of the LC3 specimens with garden lime was lower than limestone. The current research provides positive insights into the integration of calcined waste materials and low-grade clays, although as a part of the LC3-70 binder system.