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CONCRETE TECHNOLOGY20 CPI %u2013 Concrete Plant International | India Edition %u2013 1 | 2026 www.cpi-worldwide.comLimestone calcined clay cement (LC3) systems are considered one of the most promising options for lowering costs and environmental impact of concrete in the decades to come. Consequently, research and development worldwide aims at identifying and characterizing suitable mineral resources and deposits for fabricating LC3 cement, as well as developing concrete mix design guidelines and establishing the mechanical and durability performance of LC3 concrete. Concrete with three different clinker levels and four different clays from South Africa and Tanzania were produced and compared with two reference mixes. The first part of this publication concerned mechanical properties of LC3 concrete made with various African raw materials. This paper concerns durability properties obtained on the various mix compositions. Plain Portland cement (PC), with over 90% clinker, is widely produced but accounts for about 8% of global CO2 emissions. The 2016 UNEP report [1] highlighted clinker reduction as a major opportunity, notably through Limestone Calcined Clay Cement (LC3). This ternary system generally achieves good strength and durability at only 50% clinker [2-4], cutting CO2 emissions by nearly 30%. Successful industrial trials have already been conducted in various parts of the world, and LC3 is already available on the market in selected countries in Africa, Central America, and also in India. Some of the top ten countries contributing to population increase in Africa, including South Africa and Tanzania, are situated along the ocean, with major parts of the countries%u2019 infrastructure situated in marine exposure conditions. Due to the increase of economic activities and job opportunities, more infrastructure is likely to be built in these regions in the future. If the concrete usage related to this projected infrastructure development is to have minimal negative environmental impact, there is a need to develop low-clinker systems for structural applications with performance similar or better compared to conventional systems. Performance criteria to consider include mechanical concrete properties as well as durability characteristics, especially those related to marine exposure conditions. With regard to durability characteristics, studies have shown that a ternary LC3 system can produce mechanical properties, depending on age, similar to or better than the reference system and at the same time provide better resistance to chloride ingress than a system with plain cement, or a binary system with 30% of cement replaced by fly ash. The increased chloride penetration resistance is generally ascribed to a refinement in the pore structure as well as superior chloride-binding capacity of the LC3 system [5-8].Apart from construction processes and workmanship, the overall performance of concrete for a specific environment depends on the type, quality, and proportion of constituent materials in achieving the intended fresh and hardened concrete properties. For instance, the primary concern in the design and specification for concrete structures in marine environments is resistance against chloride-induced reinforcement corrosion, with concrete strength being a secondary concern [9]. Premature deterioration of concrete structures exposed to marine environments is typically a result of the penetration of chloride ions from the environment through the porous structure of the concrete cover, which eventually may cause steel reinforcement corrosion and hence cracking, delamination and spalling of the concrete. Carbonation can also induce corrosion, as it decreases the pH of the pore solution and destroys the stability of the passive oxide layer which is only stable at high pH values. In view of this, durability design largely addresses prevention of reinforcement corrosion for the intended service life of the structure, and penetrability and cover depth of concrete are considered the most important factors influencing time to rebar corrosion initiation and subsequent propagation. Concrete penetrability is mainly influenced by binder type, water/binder (w/b) ratio, compaction, and curing. The use of low w/b ratios together with suitable supplementary cementitious materials (SCM) can minimise chloride penetrability and has generally been adopted for the design of RC structures in Southern African marine environments [9]. The focus of this study is on the performance of selected low-clinker LC3 concrete mixes with kaolinite clays from selected deposits in east and southern Africa, compared with concrete mixes generally recommended for marine concrete structures in South Africa. The underlying aims were to create knowledge on the suitability of African clay resources for the production of LC3 concrete, and to aid industry in developing and manufacturing sustainable cementitious binders and Durability properties of limestone calcined clay cement concrete Sustainable concrete technology, LC3 %u2013 Part 2n 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