Recycling of seashell waste in concrete: A review

•Seashell waste such as oyster, mussel, scallop and cockle shells usage in concrete.•The characteristics of seashell waste in aggregate and powder forms are summarized.•Effects on the fresh and hardened properties of concrete are discussed. In order to reduce the dependency on virgin materials for construction, efforts have been made to incorporate by-products and wastes from different industries as alternatives in concrete. Originating from the fishery industry, seashell waste, such as oyster shells, mussel shells, and scallop shells, among others, is available in huge quantities in certain regions, and is usually dumped or landfilled without any re-use value. This paper summarizes previous research concerning the use of seashell waste as a partial replacement for conventional materials in concrete and other related cement-based products. The characteristics of different types of seashell waste, as well as the effects of incorporating the seashells on the fresh and hardened properties of concrete, are discussed. The material characteristics suggest that, similar to limestone, seashell waste could be an inert material due to the high calcium oxide content. However, proper treatment such as heating at high temperature and crushing to achieve appropriate fineness are desirable for a better quality material. It is shown in past research that while seashell waste has been used as a replacement for both cement and aggregate, there is still a lack of investigation concerning its durability, as well as the actual influence of seashell powder as a cement replacement material. Despite the reduction in the workability and strength, based on the review, it is suggested that seashell waste could still be utilized as a partial aggregate at a replacement level of up to 20% for adequate workability and strength of concrete for non-structural purposes.