Effect of the Portland Cement Quality on the Rheology of LC3 Binders Containing Superplasticizers

Due to the urgent push towards low-CO2 binders, the development and application of limestone calcined clay cement (LC3) has received significant attention and is gaining momentum. In the early phase of LC3 development, reactivity, mechanical strength and durability issues were intensely studied.[1] Recently, also the rheological properties of LC3 binders, especially in combination with admixtures, are receiving increasing attention.[2,3] By addressing the rheological behavior of cementitious materials, both the fresh and hardened properties of concrete can be improved significantly. As the LC3 mixture allows a high substitution of the clinker (up to 50 wt.%), the focus is generally directed towards the impact of the calcined clays and limestone on the rheological properties of LC3 mixes.[2-4] How the composition of the Portland cement source influences the rheology of LC3 mixes has, however, not been widely reported as of yet. Therefore, this study investigates the reactivity and rheology of LC3-50 mixes containing various ordinary Portland cements (OPC). The reactivity of the LC3 mixes was characterized using isothermal calorimetry and the rheological properties were studied with a rotational rheometer. Additionally, the influence of a polycarboxylate ether (PCE) dispersant on the OPC pastes and LC3 pastes is evaluated and compared. The results indicate that the chemical composition and fineness of the OPC plays an important role regarding reactivity and workability of the respective LC3-50 mix, similar as reported for plain OPC.[4] Furthermore, while PCE-type dispersants allow to reduce the water demand for the OPC as well as the LC3 system, the required PCE dosage is significantly increased for LC3 compared to OPC systems, as highlighted in recent work.[5] In conclusion, the types of OPC and PCE have to be taken into account to optimize the rheology of LC3 binders. [1] K. Scrivener, F. Martirena, S. Bishnoi, S. Maity, Cement and Concrete Research 2018, 114, 49-56. [2] T. R. Muzenda, P. Hou, S. Kawashima, T. Sui, X. Cheng, Cement and Concrete Composites 2020, 107, 103516. [3] M. A. B. Beigh, V. N. Nerella, C. Schröfl, V. Mechtcherine, in Calcined Clays for Sustainable Concrete (eds.: S. Bishnoi), RILEM Bookseries, Singapore, 2020, pp. 229-236. [4] F. Zunino, K. Scrivener, Cement and Concrete Research 2019, 126, 105918. [5] R. Li, L. Lei, T. Sui, J. Plank, Cement and Concrete Research 2021, 141, 106334.     «

Due to the urgent push towards low-CO2 binders, the development and application of limestone calcined clay cement (LC3) has received significant attention and is gaining momentum. In the early phase of LC3 development, reactivity, mechanical strength and durability issues were intensely studied.[1] Recently, also the rheological properties of LC3 binders, especially in combination with admixtures, are receiving increasing attention.[2,3] By addressing the rheological behavior of cementitious mat...     »