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This paper studies the use of cockle shell as supplementary cementitious materials SCMs as substitute for cement. The cockle shells generally have a high CaO content which can alter the behavior and the properties of mortars and concrete. Cockle shell is used with weight ratios of 5, 10, 15 and 20% to formulate a mortar with cockle shell and a control mortar CM with 0% of cockle shell. The properties in the fresh state, the mechanical strength and the weight loss test as well as the depth of penetration of each mixture were carried out through the conducted experiments. Consistency and density of fresh mortars were determined, the results obtained showed that cockle shell have a significant influence on the properties of mortars in the fresh state. The different results of hardened mortars show that the introduction of cockle shell tends to accelerate the development kinetics of strength at the young age but its ratio cannot be above of 5%. Mortar with 10% presented the lower depth penetration, the loss weight increased proportionally with the increasing of cockle shell amount.

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The introduction of treated plant fibres into sand concretes leads to a reduction in density, improved ductility and thermal conductivity, and makes sand concrete an environmentally friendly and ecological material. The recovery of waste in this type of material allows the production of new ecological and sustainable materials used either in the new construction or in the rehabilitation of old buildings. In this context, a comparative study was based on the valorisation of marble and ceramic waste as sand in sand concrete made from straw fibres. To carry out this study, we introduced these wastes at substitution rates of 10% and 20%, separated and mixed, and studied the development of the properties of these concretes (density, workability, air content, compressive strength and bending tensile strength) and their behaviour with respect to durability (capillary and immersion absorption and chloride penetration). The study shows that the recovery of this waste as sand in sand concrete based on straw fibres gives satisfactory results. The chemical resistance, thermal conductivity and microstructure are under study, the results of which will be the subject of another publication.

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The aim of this research is to assess the mechanical performance of self-compacting concrete containing different percentages of fine aggregates, produced from the wastes generated by the cement plant industry and construction sites. Eight mixes, incorporating cement kiln dust (CKD) and hardened cement waste with partial fine aggregate replacement of 5%, 10%, 15%, and 20%, were produced and compared with a control mix made with 100% of crushed sand. The workability properties (e.g., flowability, passing ability, and resistance to segregation) and mechanical properties (e.g., compressive, flexural, and splitting tensile strengths) of all mixes were evaluated. The results showed that concretes containing recycled fine aggregates proved to have the best mechanical properties, compared to one made with crushed calcareous sand. However, self-compacting concrete with high mechanical strength could be produced with up to 15% wt. CKD replacement and with 10% wt. hardened cement waste replacement.

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