Nowadays, the sustainable development of the construction industry has become a focus of attention. Crushing and grinding waste seashells originating from the fishery industry, such as oyster shells, cockle shells, mussel shells, and scallop shells, into different particle sizes for usage as aggregate and cement in concrete or mortar provides an effective and sustainable solution to environmental problems by reducing natural resource dependence. Numerous studies have attempted to analyze the suitability of waste seashell as a possible alternative to natural aggregates and cement in concrete or mortar. This paper presents an up-to-date review of the characteristics of different types of waste seashell, as well as the physical, mechanical, durability, and other notable functional properties of seashell concrete or mortar. From the outcome of the research, waste seashell could be an inert material, and it is important to conduct a series of proper treatment for a better-quality material. It is also seen from the results that although the mechanical properties of seashell concrete have been reduced, they all meet the required criteria set by various international standards and codes. Therefore, it is recommended that the replacement of seashells as aggregate and cement should not exceed 20% and 5%, respectively. Seashell concrete or mortar would then have sufficient workability and strength for non-structural purposes. However, there is still a lack of investigation concerning the different properties of reinforced concrete members using seashells as the replacement of aggregate or cement. Further innovative research can solidify its utilization towards sustainable development.

In order to solve the problem of lack of natural river sand, crushed waste oyster shells (WOS) were used to replace river sand. By replacing 20% river sand, WOS mortar with different particle sizes of WOS were made for the experiment. Through experimental observation, the initial slump and slump flow loss rate were studied. The effects of different particle sizes and curing times on the compressive strength, flexural strength, static elastic modulus, and dry shrinkage of WOS mortar were analyzed. The relationship formulas between the compressive strength, flexural strength, particle size, and curing age were proposed. The results showed that the setting time and slump flow decreased with a decrease in the particle size of WOS. It was also found that the mortar with fine crushed WOS had high compressive strength, flexural strength, and static elastic modulus at both early and long-term curing age. A formula was proposed to describe the development of the compressive strength with the particle size of WOS and curing time, and the relations among these mechanical properties were discussed. Furthermore, drying shrinkage increased when WOS was used and could not satisfy the standard requirement of 0.075%. In contrast, the addition of fine WOS and double-dose sulfonated naphthalene-formaldehyde superplasticizer (SNF SP) reduced the shrinkage rate of the mortar by 8.35% and provided better workability and mechanical properties for mortar.

Recently, much attention has been paid to the mechanical properties of cementitious materials containing recycled crushed waste oyster shells (WOSs) instead of river sand. However, few have focused on their transport behavior. The present study investigated the mechanical and transport properties, as well as cost efficiency, of hardened mortars containing crushed WOSs. Mortar mixtures containing different amounts of crushed WOSs (10%, 20%, and 30%) in place of river sand were prepared and compared with mortar containing only river sand (reference). Use of crushed WOSs lowered hardened densities and mechanical properties, but increased water absorption, water permeability, and chloride ion penetration compared with control mortars. Increasing the curing period, however, effectively improved the hardened densities, mechanical properties, and transport behavior of crushed WOS mortars. Furthermore, use of crushed WOSs improved the cost efficiency of mortar production. By better understanding the behavior of mortars containing crushed WOSs, acceptable crushed WOS: river sand replacement ratios can be selected to make mortars with different mechanical and durability-related properties for various uses.

Sulfate and chloride in the marine environment threaten the lifespan of concrete structures. Predicting the strength of concrete under different degrees of ion erosion is essential for marine structure design and maintenance. In this paper, a novel method was developed to predict the compressive strength evolution due to sulfate and chloride attack. The degradation and ion diffusion behavior of cement-based materials was investigated by analyzing the visual appearance, compressive strength, porosity, and ion distributions of mortar soaked in sulfate and chloride solutions with different concentrations. The damage degree was observed to increase with sulfate concentration and decrease with chloride concentration. Additionally, it was discovered that chloride and sulfate ions inhibited the diffusion of each other, and a higher concentration resulted in a more substantial inhibition effect. The total effective sulfate and chloride intrusions were proposed to describe the erosion degree of mortar based on the evaluation of the ion distributions with Fick’s second law. A compressive strength assessment method was established based on the analysis of the correlation between the strength contribution of sulfate reaction and the total effective chloride and sulfate intrusions. This method exhibits the potential for estimating the concrete strength of actual marine structures damaged by sulfate and chloride with accelerated laboratory tests.

Over-exploitation of natural river sand and waste oyster shells (WOS) dumped randomly will cause serious environmental issues. Thus, a drive to using crushed WOS as fine aggregates to substitute river sand in concrete production has been initiated. This paper conducted experimental research to study the possibility of employing the crushed WOS as 100% fine aggregates in concrete. The workability, compressive strength and its size-effect, and sustainability performance of the concrete mixtures were investigated. The results indicated that, under the same water-cement ratio, the WOS concrete showed a great improvement in strength properties while a decline was found in slump tests, compared to the control concrete. Besides, the use of the crushed WOS in concrete production resulted in a modification in both eco-efficiency and cost-efficiency.