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CONCRETE TECHNOLOGY18 CPI %u2013 Concrete Plant International %u2013 6 | 2025 www.cpi-worldwide.comIn Africa, one of the most promising options for lowering costs and environmental impact of concrete is the use of limestone calcined clay cement (LC3) systems. However, improper use of the constituent materials may result in a concrete with substandard properties. The results reported here concern compressive strength, elastic modulus and drying shrinkage, and are part of a larger study on the properties of LC3 concrete made with African raw materials. Concrete with three different clinker levels and four different clays from South Africa and Tanzania were produced, which are compared with two reference mixes; one with 100% CEM II/A-L 52.5 N and the other with 50% of cement replaced by ground granulated blast-furnace slag. This paper concerns mechanical properties obtained on the various mix compositions. A second part to this publication, published in the following issue of CPI, will discuss relevant durability properties. Plain Portland cement (PC), which conventionally contains more than 90% clinker, is made from raw materials that are available in many places around the world. Currently, the manufacture of PC contributes about 8% of global anthropogenic CO2 emissions. In 2016, the UNEP report on eco-efficient cements identified two key areas with the greatest potential for reducing CO2 emission over the next few decades [1]. One area is replacing clinker in cement by the combined addition of calcined clay (CC) and LS. This ternary system, which is also called Limestone Calcined Clay Cement (LC3), has been shown to give good mechanical and durability performance at clinker contents of only 50% [2-4] and can help to reduce CO2 emissions by almost 30% compared to a reference PC [5, 6]. Moreover, industrial trials have already been carried out successfully in Cuba and India [7, 8]. Although supplementary cementitious materials (SCMs) offer several advantages such as the filler effect and pozzolanic reaction, they may also cause adverse effects on concrete properties, especially during the first few days after casting [9], such as compressive strength development and early-age cracking. These problems can be minimised by understanding the influence of the SCMs on the strength gain, shrinkage, elastic modulus and creep of concrete made with these materials. In this study, the free shrinkage and elastic modulus of LC3 concrete with three different clinker levels and four different clays were studied and compared with two reference mixes; one with 100% cement (CEM II/A-L 52.5 N) and the other with 50% of cement replaced by ground granulated blast-furnace slag (GGBS). Materials and methods MaterialsA total of four samples of kaolinite clay from South Africa (SA) and Tanzania (TZ) were considered in this study, Bronkhorstspruit (B-Clay) and Hopefield (H-Clay) deposits in SA, Pugu deposit (PH-Clay) in TZ, and sample from Heidelberg Cement plant area (HC-Clay) in Dar es Salaam, TZ. The composition of the associated cementitious binders was optimized based on compressive strength of mortars, and associated hydration aspects, as discussed in detail in [10]. Overall, the results indicated that, with these LC3 mixes, compressive strength is generally similar to a mix with 100% Portland cement and better compared to a mix with 50% cement replaced by GGBS [10]. Further, concerning durability parameters, permeability is generally reduced, resistivity is generally significantly increased, chloride ingress is reduced, while carbonation is generally increased [10]. Concrete mix compositionTwo water/binder (w/b) ratios of 0.4 and 0.55 were selected, 0.4 to represent a high-performance concrete for marine exposure, and 0.55 on selected mixes to represent medium quality concrete common in construction projects. Table 1 present the proportions decided for the concrete, superplasticizer (SP) dosage, and the slump obtained for all the selected concrete mixes.Mechanical properties of limestone calcined clay cement concrete Sustainable concrete technology, LC3 %u2013 Part 1n Emmanuel Safari Leo, Department of Structural and Construction Engineering, University of Dar es Salaam, TanzaniaMark G. Alexander and Hans Beushausen, Department of Civil Engineering, University of Cape Town, South Africa