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The use of a high amount of calcined clays as cement replacement presents a great challenge in designing self-consolidating concrete. This current attempt evaluates the influence of cement replacement with up to 40 vol.% by a calcined common clay (CC), dominated by 2:1 phyllosilicates in combination with a fixed limestone powder (LP) content on fresh and hardened properties of self-consolidating mortar (SC-M). The fresh properties of SC-M were investigated by mini-slump flow, V-funnel and rotational viscometer measurements. Setting and hardening behavior were observed via dynamic modulus of elasticity and plastic shrinkage. Hydration mechanisms were determined by isothermal calorimetry and thermal analysis. Hardened properties of SC-M were evaluated using compressive strength tests and mercury intrusion porosimetry (MIP). The results revealed a decreased rate of deformability in SC-M when cement is substituted increasingly by CC and a rising superplasticizer (SP) demand, but indicated an improved stability of SC-M even at a higher dosage of SP and hardly any impact on the setting behavior. CC enhanced the precipitation of monocarboaluminate phases and thereby refined the pore size distribution of the binder matrix. SC-M can be produced with up to 40 vol.% CC as cement replacement without having effect on its 28 days mechanical properties.

One principal approach to achieve self-compacting properties is the increased amount of finer constituents of the mixture. This, in turn, increases cement consumption leading to higher greenhouse gas emissions. Pozzolanic materials, like rice husk ash or calcined highly kaolinitic clays, have gained increased attention as supplementary cementitious materials in self-compacting concrete production. These materials could be viable alternative supplementary cementitious materials for sub-Saharan Africa which already lacks fly ash, slag and silica fume. This current effort reviews the impact of rice husk ash and calcined clays for the production of self-compacting concrete. Special focus is on their impact on rheological, mechanical and durability properties of self-compacting concrete. Rice husk ash and, in particular, calcined highly kaolinitic clays are introduced as technical and cost-effective supplementary materials for use in self-compacting. The review disclosed a lack of knowledge when it comes to the use of low-kaolinitic calcined clays as sole SCM or together with rice husk ash, which could be a very promising combination for e.g., several countries in Africa. Further studies are needed on the rheological properties, shrinkage, creep, and durability of self-compacting concrete produced with other calcined common clays and their blend with rice husk ash.

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This study compares the pozzolanic activity of kaolinitic and illite clays after calcination as they are the most abundant types of clays worldwide. The impact of calcined clays on microstructure development is tested by determining the porosity of cement paste as well as by phase and optical analysis of cement matrix and interfacial transition zone of concrete. As water transportation with damaging carbonate or chloride ions is the main reason for reduced durability of reinforced concrete, the results are complemented with water absorption tests on blended concretes. At 28 days, system with calcined kaolinitic clay reveal a higher densification of its microstructure with lower water absorption rate compared to plain concrete and concrete with calcined illite clay, which is related to its higher pozzolanic reactivity. Nonetheless calcined illite clays can be considered as low-cost clinker replacement as a significant pozzolanic contribution is detectable and after 90 days, the water absorption behaviour is comparable with those of the other systems investigated.