A review on recycling seashells as aggregates and binders for mortar and concrete in China: Production, engineering properties and new applications

Abstract

The increasing amount of seashell waste have become a large burden on China's coastal cities. Recycling discarded seashells as binders and aggregates for mortar and concrete is a promising solution. Chinese institutions have conducted extensive research on the performance of mortar and concrete made with seashell aggregates and binders. However, there is currently no comprehensive review that summarizes findings reported by Chinese institutions. This may hinder the engineering application of seashell mortar and concrete. Due to a lack of systematic review, engineers and designers lack a reference for using seashell mortar and concrete in engineering projects. To fill these gaps, this article reviews the literature published by Chinese institutions in the past decade on the substitution of discarded seashells for cement, fine aggregates, and coarse aggregates. Reduced flowability and mechanical properties and increased drying shrinkage are critical issues for seashell mortar and concrete. Adding superplasticizers can alleviate the reduction in flowability. Incorporating fibers and surface treatment of seashell aggregates can increase mechanical properties and reduce drying shrinkage. In recent years, new seashell mortar and concrete have been proposed, increasing their potential engineering applications. Using seashell powder can increase resistance to biological adhesion in reef concrete and extend its service life. Coarse seashell aggregates filled with polyurethane foam can be used to produce lightweight concrete members. Surface treatment of seashell aggregates with polyvinyl alcohol and sodium silicate solutions can alleviate the shortcomings of seashell aggregates and improve mechanical properties and durability so that this surface-modified seashell mortar and concrete can be applied in most areas. Superhydrophobic seashell mortar and concrete have good chloride resistance and are suitable for use in coastal areas. The following research gaps should be addressed in future research. The influence of seashell content on environmental benefits remains scarce. The influence of calcined seashell powder on the setting time of concrete should be fully understood in future research. The influence of fiber type on the tensile strength of seashell mortar and concrete remains unknown. The influence of surface treatment of seashell aggregates with polyvinyl alcohol and sodium silicate solutions remains unclear and should be investigated in future studies.