A Fresh View on Limestone Calcined Clay Cement (LC³) Pastes

• Main Authors: Hassan Ez-zaki, Joseph Mwiti Marangu, Maurizio Bellotto, Maria Chiara Dalconi, Gilberto Artioli, Luca Valentini
• Format: Article
• Language: English
• Published: MDPI AG 2021-06-01
• Series: Materials
• Subjects: limestone calcined clay cement; LC³; yield stress; plastic viscosity; rheology; plastic shrinkage
• Online Access: https://www.mdpi.com/1996-1944/14/11/3037

In this work, the factors controlling the fresh state properties of limestone calcined clay cement (LC³) are assessed and compared to Portland and binary cements, extending the scope of previous research by combining rheological measurements with setting time determination and the evaluation of plastic shrinkage by a novel method. Yield stress and elastic modulus are considered indicators for the structural build-up/breakdown process when stress is applied to the system. On the other hand, plastic shrinkage occurs from the mixing to the setting of fresh paste and plays an important role in governing microstructural changes due to settlement and evaporation. Evaluation of the rheological properties with time was appropriate to give an overview of the influence and behavior of different added materials. The elastic modulus of all binders (clinker, LC³, clinker–limestone, and clinker–calcined clay) was increased from mixing to 60 min of curing as follows: 5.27 × 10³ to 9.50 × 10⁵ Pa, 5.94 × 10³ to 9.87 × 10⁵ Pa, 6.89 × 10³ to 5.62 × 10⁵ Pa and 7.85 × 10³ to 1.27 × 10⁶ Pa, respectively. Moreover, during the first three hours of curing, LC³ exhibited a reduction of plastic shrinkage by more than a factor of 2 compared to clinker cement. The use of calcined clay with clinker increases the elastic modulus of the system due to the flocculation effect and increased water absorption, while a dilution effect is contributed due to deflocculation and a free-water increase in the system when a high fraction of limestone is present in the binary cement. The combination of limestone and calcined clay with clinker can induce additional chemical reactions, which control the early age properties, such as plastic shrinkage. The obtained results can contribute to optimizing the fresh state properties of ternary blends of OPC, calcined clay, and limestone through a knowledge-based approach.