Next Article in Journal
Hyperparameter Optimization of Neural Networks Using Grid Search for Predicting HVAC Heating Coil Performance
Previous Article in Journal
Resilience Assessment for Corroded Reinforced Concrete Bridge Piers Against Vessel Impact
Previous Article in Special Issue
Performance Limits of Hydraulic-Binder Stabilization for Dredged Sediments: Comparative Case Studies
 
 
Search for Articles:
Title / Keyword
Author / Affiliation / Email
Journal
Article Type
 
 
Advanced Search
 
Section
Special Issue
Volume
Issue
Number
Page
 
Journals
Buildings
Volume 15
Issue 15
10.3390/buildings15152751
buildings-logo
Submit to this Journal Review for this Journal Propose a Special Issue
► Article Menu

Article Menu

share Share announcement Help format_quote Cite question_answer Discuss in SciProfiles
first_page
settings
Order Article Reprints
Font Type:
Arial Georgia Verdana
Font Size:
Aa Aa Aa
Line Spacing:
Column Width:
Background:
Article

Effects of Natural Seashell Presence on the Engineering Performance of Sea Sand Concrete

by
Anuradha Koswaththa
1,
Pasindu Abeyaratne
1,
Samith Buddika
1,*,
Hiran Yapa
1 and
Satheeskumar Navaratnam
2
1
Department of Civil Engineering, Faculty of Engineering, University of Peradeniya, Peradeniya 20400, Sri Lanka
2
Institute of Innovation, Science and Sustainability, Federation University, Ballarat, VIC 3350, Australia
*
Author to whom correspondence should be addressed.
Buildings 2025, 15(15), 2751; https://doi.org/10.3390/buildings15152751
Submission received: 26 June 2025 / Revised: 31 July 2025 / Accepted: 1 August 2025 / Published: 4 August 2025
(This article belongs to the Collection Advanced Concrete Materials in Construction)
Browse Figures
Versions Notes

Abstract

Processed sea sand has emerged as a viable alternative to traditional fine aggregates in the Sri Lankan construction industry. Despite its economic and environmental advantages, concerns over residual seashell content have limited its widespread adoption by local contractors. Residual seashell content, typically ranging from 1% to 3% after processing, has raised concerns about its impact on the performance of concrete. This study systematically investigates the influence of seashell fragments, with a content of up to 5%, on the fresh, mechanical, and durability properties of sea sand concrete and mortar. Experimental results indicate that workability remains stable, with minor variations across the tested range of shell content. Compressive strength remains relatively consistent from 0% to 5% seashells, indicating that seashell content does not significantly impact the strength within this range. Durability tests reveal minimal effects of shell content on concrete performance within the tested shell range, as indicated by results for water absorption, rapid chloride penetration, and acid exposure testing. Accelerated corrosion indicates that the typical shell content does not increase corrosion risk; however, high shell content (>3%) can compromise corrosion durability. Overall, these findings demonstrate that the mechanical and durability performance of sea sand concrete remains uncompromised at typical seashell content levels (1–3%), supporting the use of processed sea sand as a sustainable and viable alternative to traditional fine aggregates in Sri Lankan construction.

Graphical Abstract

1. Introduction

The construction industry is a major consumer of natural resources, with concrete production accounting for a significant portion of this consumption [1,2,3]. The increasing demand for concrete, coupled with the depletion of natural resources like river sand, has led to the exploration of alternative materials. One such alternative is sea sand, a readily available resource in coastal regions [3,4,5]. The use of sea sand in concrete construction has garnered worldwide concern and increasing attention from researchers [5,6]. In a global context, the utilization of sea sand has increased, especially in developed countries such as Japan, China, and the UK [6,7,8]. In Sri Lanka, the adoption of sea sand in concrete production dates back to the 1990s [9] and it has been incorporated into major infrastructure projects, including the Colombo Port City Project, the Colombo South Harbour Expansion Project, and the Colombo–Katunayake Expressway. Given its widespread availability and lower cost compared to river sand, sea sand presents an economically feasible alternative.
When sea sand is used in concrete without being treated to remove chloride and other impurities, it significantly compromises the structure’s durability, primarily through corrosion of steel reinforcement [4,5,6,10,11]. Normally, steel reinforcement in concrete is protected by an alkaline environment that forms a passive film. However, chloride ions (Cl−), abundant in untreated sea sand and seawater, can damage or break down this protective film [1,12]. This breakdown can result in a potential difference across the steel surface, which serves as the initiation point for corrosion, a process widely recognized as electrochemical in nature. As illustrated in Figure 1, at the anodic regions, iron is oxidized, forming rust (iron oxides) and releasing electrons. These electrons flow through the steel to the cathodic regions, where they participate in oxygen reduction, leading to the formation of hydroxide ions (OH−) [13,14]. This ongoing reaction increases internal pressures due to rust expansion, resulting in cracking, delamination, and ultimately spalling of the concrete, thus significantly reducing the structure’s service life [12,15].
To address these concerns, sea sand undergoes a treatment process involving washing with fresh water to reduce chloride levels and sieving to remove coarser particles [10,16]. In Sri Lanka, this process is primarily carried out at the Muthurajawela sea sand washing plant. While these methods effectively remove large shells, smaller shell fragments (typically less than 4 mm) often remain in the processed sand, as presented in Figure 2. The potential impact of these residual fragments on the mechanical and durability properties of concrete remains a key concern, raising questions about its long-term performance and structural reliability.
The chemical composition of seashells was determined using X-ray Fluorescence (XRF) analysis, as summarized in Table 1. Additionally, a Loss on Ignition (LOI) test was conducted to quantify the volatile content, primarily carbon dioxide (CO2), released during the thermal decomposition of calcium carbonate. The combined XRF and LOI results confirm that the primary constituent of the seashells is calcium carbonate (CaCO3), aligning them chemically with limestone, a standard fine aggregate material in concrete production [17]. Minor amounts of other trace elements were also detected. Notably, no chloride was identified in the tested samples, indicating that its concentration is below the minimum detection limit of the XRF analytical microscope (<0.01% by mass). Consequently, the influence of trace chloride content in the seashells is considered negligible.
The physical characteristics of seashells, such as their porous nature, irregular shape, and higher water absorption compared to conventional aggregates, can also affect concrete properties. These characteristics can lead to increased void content, reduced density, and weaker bonding between the seashells and cement paste [17,18,19]. These impacts of seashells highly depend on the size distribution and the percentage of shell content in the sand.
The impact of seashells on concrete’s mechanical properties appears complex and dependent on several factors. A high shell content in sea sand generally leads to reduced workability of the concrete [3]. This decrease in workability is attributed to the elongated shape of shell particles, which hinders the smooth flow and compaction of the concrete mix [20]. Previous studies indicate that shrinkage increases as the shell content in sea sand increases [3]. Studies like [17,21] suggest minimal-to-slight reductions in compressive strength with moderate seashell content (10–29%). However, others report significant decreases at higher replacement levels (50% or more) [2,22]. Interestingly, Safi et al. [23] observed an initial increase in strength with small seashell additions, followed by a drop with more significant amounts. This suggests an optimal content range for strength. The angular shape and size variations of seashells compared to traditional aggregates can negatively affect strength [23]. Seashells seem like a viable partial replacement for aggregates, but careful consideration of content, processing, and mix design is crucial to maintaining acceptable mechanical properties in concrete [17,21].
Furthermore, the irregular shapes of seashells can negatively impact the workability of sea sand concrete [3]. This can lead to difficulties in mixing, placing, and compacting the concrete, potentially resulting in an inconsistent final product with compromised strength and durability. The elongated nature of shell particles can hinder the smooth flow and proper compaction of the concrete mix, making it challenging to achieve the desired consistency and uniformity [24,25].
Seashells appear to offer both positive and negative effects on durability. Their low porosity can significantly enhance water resistance and permeability [23]. This aligns with the observation that seashell content can improve resistance to freeze–thaw cycles in some cases [17]. However, the presence of organic matter and the inherent fragility of some seashells can weaken this resistance.
Some studies have investigated the use of seashells as an aggregate replacement in concrete, offering a sustainable alternative to quarried aggregates. Seashell aggregate concrete generally has more porosity and a slightly lower bulk density than normal concrete [17]. This can affect durability properties such as water permeability, air content, and freeze–thaw resistance. The effect of seashell content on these properties can vary depending on the type of seashell, the size of the aggregate, and the mix proportions. However, concrete made with seashells may have improved sound absorption and thermal insulation properties [17,21].
Table 2 shows the limits of shell content in different regions and standards. This reveals significant variations in shell content limits for construction aggregates across regions, reflecting local material properties and practices. The British standards set limits based on size, while the British/EU standard considers application type. Sri Lanka allows up to 15% for specific sand sizes by mass of the sand, so it has a higher limit for shell content than other standards.
Based on the data provided by the Sri Lanka Land Reclamation and Development Corporation (SLLRDC), processed sea sand from the Muthurajawela main sea sand yard typically contains between 1% and 3% seashells. Despite the widespread use of sea sand in construction, limited research has been conducted on the influence of residual seashell content on the engineering performance of sea sand concrete. This has been a significant concern among local contractors in Sri Lanka, hindering its broader adoption. Additionally, previous studies present conflicting conclusions regarding the influence of seashells on sea sand. This study aims to bridge the knowledge gap by systematically evaluating the impact of varying residual seashell content, based on its natural distribution, on the fresh, mechanical, and durability properties of sea sand concrete. This research directly addresses the concerns raised by local contractors in Sri Lanka regarding the impact of residual seashell content on concrete performance, aiming to provide evidence-based recommendations for the wider adoption of sea sand. Experimental investigations with shell contents ranged from 0% to 5% in 1% increments by mass of the sand, reflecting the maximum level observed in historical data. By analyzing the influence of seashells on concrete performance, this study provides critical insights into optimizing the use of sea sand as a fine aggregate, ensuring its suitability for structural applications.

2. Materials and Methods

2.1. Materials

Ordinary Portland Cement, classified under CEM 1 42.5 R according to EN 197-1 [29], was used as the primary binder for this study. The cement type was selected due to its widespread usage in the country and compliance with national standards. A poly-naphthalene-based admixture was incorporated as the superplasticizer to enhance the workability of the mortar mixture. Crushed stone with a particle size range of 5~19 mm was utilized as the coarse aggregate. Washed sea sand from the Muthurajawela sea sand yard was used as the fine aggregate, and the key physical and mechanical properties of the sea sand employed in this study are summarized in Table 3.

2.2. Mix Design

The concrete mix design was developed following the British method of concrete mix design (DOE) [34]. The quantities of both fine and coarse aggregates were calculated based on the surface saturated dry (SSD) condition. For concrete mix design, grade 20/25 concrete was selected as it represents the minimum grade for structural applications according to Eurocode 2 [35] and contains the highest fine aggregate content.
For the mortar mix design, a binder content of 555 kg/m3 and a water-to-cement ratio of 0.45 were utilized. A lower water/cement ratio was selected to achieve a balance between workability and strength for proper comparison of the effect of different shell contents [36,37]. The cement-to-sand ratio was considered to be 2.75, as suggested by ASTM C109 [38]. Additionally, a superplasticizer, at a dose of 1% of cement content, was incorporated into the mix to enhance the workability of the mortar mixture. Table 4 shows the detailed mixture proportions of the concrete and mortar mixtures.

2.3. Test Specimen Preparation

Both concrete and mortar specimens were prepared for different experimental purposes. Cement mortar samples were utilized to minimize the material requirement, and investigations focused on the compressive strength and chemical exposure. Mortar cubes with dimensions of 50 × 50 × 50 mm were prepared using a Hobart mixing machine. Specimens were kept in the molds for 24 h and water-cured until the tests. Concrete specimens were utilized mainly for durability assessments, including accelerated corrosion, water absorption, and rapid chloride penetration tests. For water absorption and rapid chloride permeability tests (RCPTs), cylindrical specimens with a diameter of 100 mm and a height of 200 mm were cast. For the accelerated corrosion test, a 100 mm diameter, 200 mm height cylinder with a 16 mm steel bar embedded was utilized. These specimens were cured under similar conditions to those described above and prepared according to ASTM C31/C31M [39].
Six concrete mix types were prepared, corresponding to seashell content (SSH) levels of 0%, 1%, 2%, 3%, 4%, and 5% by mass of fine aggregate. For each mix, three specimens were tested for compressive strength, workability, chemical resistance, and water absorption. Two replicate specimens per mix were tested for both accelerated corrosion and rapid chloride permeability, ensuring consistent evaluation across all SSH levels. This testing scheme allowed for comparative assessment of the mechanical and durability properties of concrete incorporating varying seashell content.

2.4. Analysis of Shell Content in Sea Sand

To assess the shell content distribution in processed sea sand, samples were sieved into different particle size fractions using standard sieve sizes of 4.00 mm, 2.36 mm, 1.18 mm, 0.6 mm, and 0.3 mm. At least five samples from each sieve fraction were tested to determine the shell content. The procedure for shell content determination was conducted in accordance with SLS 1397:2010 [28] Appendix B. The process is schematically illustrated in Figure 3. A representative sample of around 50 g was separated from each sieve fraction, followed by drying at a temperature of 105 ± 5 °C until a constant mass was achieved, and the weight was recorded (M1). This test portion was then treated with hydrochloric acid to dissolve the shell material, which is primarily composed of calcium carbonate. A dilute hydrochloric acid solution (approximately 4 mol/L) was prepared by diluting concentrated hydrochloric acid with distilled water. The test portion was placed in a beaker or conical flask, and an initial volume of 25 mL of hydrochloric acid was added. The mixture was agitated and allowed to stand for five minutes, observing for any effervescence, which indicates the reaction between the acid and calcium carbonate. Additional acid portions were added until no further effervescence occurred, confirming the complete dissolution of shell content. Following this reaction, the mixture was heated gently to maintain a temperature between 65 °C and 90 °C until boiling to ensure full dissolution of any remaining shell material. After ensuring no further effervescence, the solution was decanted through a pre-weighed filter paper (M3) to separate undissolved residue from the dissolved shell content. The residue was washed multiple times with hot distilled water to ensure the complete transfer of any remaining particles. The final step involved drying the residue and filter paper at 105 ± 5 °C until constant mass was achieved. Once cooled in a desiccator, their combined mass (M2) was recorded. The percentage of acid-soluble shell content in the sea sand was calculated using the following formula:
Percentage of acid-soluble shell content = [(M1 + M3) − M2]/M1 × 100%

2.5. Sea Sand Preparation with Different Shell Content

A systematic approach was employed to prepare sand samples with precisely defined shell contents to investigate the effect of varying shell content in sea sand concrete/mortar. The preparation consisted of two main phases, including the preparation of cleaned sea sand, as illustrated in Figure 4, and the preparation of seashells, as illustrated in Figure 5.
The first step involves the dissolution of seashells present in the sea sand. A controlled quantity of sea sand was treated with hydrochloric acid to dissolve the calcium carbonate shells effectively. This process removes the shell content and ensures that any residual chloride ions are eliminated in subsequent washing steps. After the acid treatment, the sand is thoroughly washed with fresh water to remove any remaining acid and chloride residues, ensuring that the cleaned sand is suitable for further use. Once washed, the sand was dried at a controlled temperature to eliminate moisture content and stored in a clean, dry environment to prevent contamination. This preparation yields a clean base material devoid of shell content, ready to blend with processed shells to achieve the desired proportions.
The next phase involves processing the shells to obtain specific sizes that will be incorporated into the sand. Initially, the seashells collected from Muthurajawela were sieved using a 4 mm sieve to separate larger particles and finer materials. This step isolates small seashell particles containing other debris, such as stones and dust. Following this separation, the shells were carefully collected and subjected to washing to remove any contaminants or residues from their surfaces. Once cleaned and dried, the shell mixture was further processed through a series of sieves with apertures of 2.36 mm, 1.18 mm, 0.6 mm, and 0.3 mm. Seashells from each retained amount were then separated by hand-picking to remove other debris. To achieve precise shell content, particularly for smaller sizes, larger shells may need to be crushed and re-sieved to obtain particles that meet the required size specifications. Figure 6 shows the final seashell fragments prepared in different size ranges. With both the cleaned sand and processed shells ready, sea sand samples with known shell content were prepared by blending specific proportions of cleaned sand with classified shells.

2.6. Fresh and Hardened Properties

The workability of each mix was tested using the flow table test, following the ASTM C1437 [40]. Compressive strength testing was performed using a universal testing machine as per ASTM C109/C109M-20 [38]. The machine applies a controlled and measurable load to the specimen. Each cured cube was placed centrally on the machine’s lower plate, and a compressive load was applied at a constant rate until failure.

2.7. Durability of Sea Sand Concrete

2.7.1. Accelerated Corrosion Testing

The accelerated corrosion test (ACT) methodology described by Güneyisi et al. [15] was followed in this study. Concrete cylinders with a diameter of 100 mm and a height of 200 mm were cast, each containing a centrally embedded 16 mm diameter steel reinforcement bar. After casting, the specimens were water-cured for 28 days prior to testing. The test setup employed a DC power source (12 V) to accelerate the electrochemical corrosion process. The positive terminal of the DC power supply was connected to the steel bar (anode), and the negative terminal was connected to a stainless-steel plate, which served as the cathode. A 5% sodium chloride (NaCl) solution was used as the electrolyte, ensuring that the liquid level reached mid-height of the specimens. A data logger was utilized to record corrosion current variation over time. A sudden increase in the corrosion current was considered indicative of specimen failure, signifying the onset of active corrosion. The experimental setup in the laboratory is shown in Figure 7.
After the accelerated corrosion test, the concrete specimens were crushed to retrieve the embedded steel bars. The corroded bars were then meticulously cleaned to remove all rust and adhering concrete. This cleaning was performed using a wire brush, following the dissolution of the corrosion product using a specific chemical solution (hydrochloric acid (HCl) in water with hexamethylenetetramine). The cleaned steel bar was then weighed (W1) and compared to its initial weight (W0) before the test. The percentage weight loss is calculated using the following formula.
Percentage Weight Loss = (W0 − W1)/W0 × 100
To assess corrosion severity, the current efficiency (η) was determined by relating the mass loss to the total electric charge passed during the test (Q, in coulombs), calculated from the recorded corrosion current over time. Current efficiency was computed as follows.
Current Efficiency (η) = Mass Loss (%)/Charge Passed (C)

2.7.2. Rapid Chloride Penetration (RCPT)

The RCPT was performed following ASTM C1202 [41] to evaluate the chloride penetration resistance of concrete. Concrete cylinders with dimensions of 100 mm × 200 mm were cast, from which two disk-shaped specimens with a thickness of 50 mm and a diameter of 95–100 mm were extracted. All specimens were water-cured for a minimum of 28 days under controlled conditions before testing. Prior to testing, all specimens underwent vacuum saturation to ensure complete saturation of internal voids with water. Saturated specimens were then mounted in the RCPT apparatus, where one end was immersed in a 3.0% sodium chloride solution and the other in a 0.3 N sodium hydroxide solution. A constant voltage of 60 V DC was applied across the specimen ends, and the instant current was recorded at 30 min regular intervals over a 6 h period. The total current charge (Q) passed through each specimen, measured in coulombs, was calculated for each specimen to assess chloride ion penetration resistance. The laboratory test setup of the RCPT is shown in Figure 8.

2.7.3. Chemical Resistance

The chemical resistance of cement mortar containing varying shell contents was evaluated by exposing it to sulfuric acid (H2SO4). A 1.5% sulfuric acid solution was prepared by diluting concentrated sulfuric acid (98%) with distilled water as the testing medium. After the 28-day curing period, the mortar cubes were submerged in this acid solution at a constant temperature of 22 ± 1 °C for 7, 14, and 28-day periods. To maintain the integrity of the testing environment, the acid solution was completely renewed every week. Upon completion of each exposure period, mortar cubes were visually inspected to identify any signs of deterioration, such as cracking, crazing, or color changes that may have indicated chemical degradation. For quantitative analysis, mass measurements were taken periodically, removing specimens from the acid solution, washing them, and brushing off any adhered material from the surface, followed by drying in an oven before weighing. The percentage of mass loss was then calculated relative to the initial mass of the specimen. Compressive strength tests were also conducted on the cubes after varying exposure periods to evaluate how acid exposure affects their mechanical properties.

2.7.4. Water Absorption Rate

A water absorption test was conducted on concrete samples at 28 days of water curing, following ASTM C 642-97 [42]. For each set, three cylindrical samples, each with a diameter of 100 mm and a depth of 50 mm, were prepared using 200 mm diameter cylinders. The samples were then dried in an oven at 100 °C for 24 h. After drying, the samples were cooled in air to room temperature, and their dry weights, denoted as M1, were recorded. The samples were subsequently immersed in water, and the mass of the surface-dry samples, denoted as M2, was measured at intervals of 5 min, 10 min, 15 min, 30 min, and 24 h. This process continued until two consecutive measurements, taken 24 h apart, showed an increase in mass of less than 0.5% of the larger value. The water absorption percentage was calculated using the formula:
Absorption after immersion = ((M2 − M1)/M1) × 100

3. Results and Discussion

3.1. Sea Sand Particle Size Distribution and Seashell Distribution

The shell content of each sieve-retained sample was tested to determine the shell content distribution in the sea sand. Analysis revealed that the highest shell content was present in the sample for the 4.00–2.36 mm range, which was 30.7%. Visual inspection of sea sand also confirmed this high shell content in the large size range. Overall, the distribution indicates a lower percentage of shells in the mid-size range and a higher percentage of shells at smaller and larger sizes, as illustrated in Figure 9. The source location and the effectiveness of the processing methods may influence the overall distribution and the composition of the shell content.
The particle size distribution of sea sand was performed in accordance with the ASTM D422 standard, and the percentage mass retained on each sieve was determined. These retention percentages and the shell content distribution previously calculated were subsequently utilized to estimate the shell content proportion across different particle size ranges for various total shell contents, as summarized in Table 5.
As illustrated in Figure 10, shell content is more concentrated in the finer range. However, shell particles with a size less than 0.3 mm were not considered for the experiments due to the potential presence of other fine impurities, which may not solely consist of seashell fragments.
The technical relationship between seashell size fraction and concrete performance is critical, as larger seashell particles tend to act as weak inclusions, increasing microcracking propensity due to poor stress transfer and higher stress concentrations at a lower specific surface area, resulting in weaker interface bonding behavior and increased ITZ porosity that ultimately reduces mechanical and durability properties [22,43]. Conversely, finer seashell particles distribute more uniformly, acting as micro-fillers that reduce stress concentrations and improve crack resistance, promoting better adhesion and a denser ITZ due to their higher specific surface area, thereby enhancing mechanical strength and improving overall durability, particularly at moderate replacement levels [43].

3.2. Flowability of Mortar

Regarding workability, flow table results show that the flow percentages remain relatively consistent across different mixes, ranging from 100% to 114%, as shown in Figure 11. This indicates that the presence of seashells (SSH), at lower percentages up to 5%, does not significantly hinder the workability of the sea sand concrete. The morphology and surface texture of seashell particles can influence workability, as angular, flaky, or elongated particles tend to increase internal friction, thereby reducing flowability. However, with fragments smaller than 4 mm, the impact might be less pronounced than with larger or higher percentages of such shapes. Previous research by Eziefula et al. [17] on seashell aggregate concrete reported that partially substituting fine aggregate with crushed seashells at replacement levels of 5–25% resulted in a slight improvement in workability for certain mixtures. This supports the observed consistency in flow percentages up to 5% seashell content in the present study. The stability of workability across mixes suggests that the seashell content in processed sea sand does not negatively impact the mixing or placement processes, which is a critical consideration for practical construction applications.

3.3. Compressive Strength

When examining compressive strength, referring to Figure 12, the data reveal a nuanced relationship with seashell content. At 7 days, compressive strengths range from 33.3 MPa to 37.7 MPa, with a notable peak at 37.7 MPa for a 3% SSH mix. This suggests that moderate seashell content may enhance early strength development, possibly due to improved particle packing and cohesion within the mix. However, as the seashell content increases beyond this point, strengths tend to stabilize or slightly decrease, as observed in the 4% and 5% SSH mixes. By 28 days, compressive strength values range from 47.6 MPa to 52.9 MPa, with the highest strength again observed in the mix containing 0% SSH. This trend indicates that while some seashell content can benefit early strength gains, shells in smaller percentages may slightly reduce the long-term strength. However, variation remains in the acceptable range, aligned with previous studies [25], which suggest that typical shell content has a negligible impact on the overall compressive strength of sea sand concrete.

3.4. Accelerated Corrosion Testing

An accelerated corrosion test was conducted on specimens with varying shell content, and the corrosion current variation was monitored until the specimen failed. Figure 13 shows the time taken for specimen failure, and Figure 14 shows the current variation of specimens throughout the testing period. Results indicate that a relatively longer time was taken for the failure of low-shell-content specimens, and the time for failure was lower when the shell content increased. Specimens with 0% SSH exhibited the highest time to failure, indicating high resistance to corrosion in the absence of seashell content. The results suggest that higher seashell content (4–5%) may slightly accelerate corrosion, leading to earlier specimen failure. This could be attributed to the porous and heterogeneous nature of shells, which may weaken the concrete matrix and increase pathways for chloride penetration.
The current efficiency results illustrated in Figure 15 further support this trend. As shell content increases, the current efficiency also rises, peaking at 3.98 for 4% SSH. This indicates that more mass loss occurred per unit of charge passed, signifying higher corrosion severity. The elevated current efficiency in high-shell mixes suggests that the porous structure and weak interfacial bonding introduced by seashells likely facilitate more aggressive electrochemical reactions. Therefore, higher seashell content not only shortens the time to failure but also intensifies corrosion damage, confirming its detrimental effect on long-term durability.
Further analysis of the cracked specimens at failure, shown in Figure 16, reveals notable differences in crack distribution across varying shell content. The 0% SSH, 1% SSH, and 2% SSH specimens exhibit complex and multi-directional crack networks. In the 0% SSH specimen, the cracks appear more branched and interconnected, suggesting a more isotropic concrete matrix where corrosion-induced expansive stresses distribute relatively uniformly. This leads to a wider spread of damage and multiple intersecting crack paths, indicative of a diffuse stress distribution under corrosion. Similarly, the 1%, 2%, and 3% SSH specimens also show multi-directional cracking, though perhaps with slightly less branching than the 0% specimen. This suggests that at lower shell contents, the disruption to the concrete matrix’s homogeneity is minimal, allowing for a somewhat uniform propagation of corrosion-induced internal stresses. The cracks often appear to follow tortuous paths, indicative of the material’s inherent resistance to direct fracture and a tendency for the cracks to navigate around aggregate particles.
In stark contrast, the 4% SSH and 5% SSH specimens display predominantly unidirectional and often more rectilinear cracks. This distinct crack morphology suggests a significant alteration in the stress distribution and fracture paths. The cracks in the specimens with higher shell content appear to be more focused along specific planes, often forming a single dominant crack or a few parallel cracks. This unidirectional propagation suggests the presence of localized structural weaknesses and preferential pathways for crack initiation and propagation. Several mechanisms could explain these altered crack morphologies and localized stress concentrations due to shell inclusions.

3.4.1. Increased Porosity and Interfacial Transition Zone (ITZ) Weakness

Seashell fragments, by their very nature, are porous and have different physical and chemical properties from traditional aggregates. Their inclusion, even in small quantities, can introduce increased overall porosity within the concrete matrix, particularly at higher concentrations. More critically, the interfacial transition zone (ITZ) between the seashell fragments and the cement paste is likely to be weaker than that between conventional aggregates and cement paste. This weaker bond acts as a natural discontinuity, making these interfaces susceptible to early crack initiation under the expansive forces generated by rebar corrosion. These zones can become stress concentration points, acting as pre-existing micro-cracks or low-strength paths.

3.4.2. Heterogeneity and Anisotropy

The incorporation of shell fragments introduces a higher degree of heterogeneity and potentially anisotropy into the concrete. The irregular shapes and orientations of the shells, even when added according to natural distribution, can create preferred planes of weakness. When corrosion-induced expansive forces act within the concrete, these pre-existing planes of weakness, often aligned with the larger dimensions of the shells or the shell-matrix interfaces, can dictate the direction of crack propagation. This leads to the observed unidirectional cracking as cracks preferentially follow these paths of least resistance.

3.4.3. Preferential Chloride Penetration Pathways

The porous and potentially more permeable nature of seashell fragments, coupled with potentially weaker ITZs, can facilitate accelerated chloride ingress. These areas act as conduits for chloride ions to reach the rebar more rapidly. Once chlorides reach the rebar, localized corrosion is initiated and accelerated at these specific points. The localized nature of the corrosion then translates into highly concentrated expansive stresses at these specific sites, leading to the formation of localized, unidirectional cracks directly originating from and propagating along these areas of accelerated corrosion.
To address the increased corrosion susceptibility observed at seashell contents above 3%, future use of sea sand with higher shell content in practice should be accompanied by appropriate engineering measures such as incorporating corrosion inhibitors, using supplementary cementitious materials (SCMs), or applying protective surface treatments to enhance durability and mitigate corrosion risks.

3.5. Rapid Chloride Permeability Testing (RCPT)

The rapid chloride penetration test was conducted to measure the resistivity of concrete to chloride penetration at different shell content levels. As presented in Figure 17, all specimens exhibited relatively low resistance to chloride penetration, likely due to the high water-to-cement ratio in the mix design. Among them, the 0% SSH specimens demonstrated the lowest total charge passed, indicating the highest resistance and serving as a control reference. Interestingly, increasing shell content revealed a non-linear trend. Up to 2% SSH, the total charge passed slightly increased, suggesting a minor rise in permeability, possibly due to subtle interfacial defects or reduced packing efficiency caused by irregular shell fragments. However, from 3% to 5% SSH, the total charge passed decreased slightly and stabilized, implying that further additions did not significantly affect permeability and may even have marginally improved it. This counterintuitive behavior can be attributed to improved particle packing, where fine shell fragments may densify the matrix by filling voids and reducing pore connectivity. Additionally, the irregular shape and distribution of shells could increase the tortuosity of chloride diffusion paths, slowing ion migration despite unchanged pore volume. Moreover, at higher contents, shell particles might act as inert fillers that refine the pore structure without creating permeable interfaces. Thus, the RCPT findings indicate that seashell content has a limited and non-linear impact on bulk chloride ingress. While low contents may slightly increase permeability, higher contents may enhance the matrix structure and offset this effect, although localized corrosion risks may still exist due to microstructural defects not captured by RCPT.

3.6. Acid Exposure Testing

Exposure to sulfuric acid is a significant cause of deterioration in cementitious materials used in aggressive environments such as wastewater systems and industrial settings [44]. The degradation results from chemical reactions between the acid and the components of the cement matrix. The acid reacts with the calcium hydroxide (Ca(OH)2) present in the cement paste, producing calcium sulfate (gypsum) and water. This reaction contributes to degradation, partly due to the formation of calcium sulfate, which can lead to subsequent sulfate attack. Following the consumption of calcium hydroxide, the acid attack proceeds to react with the calcium silicate hydrate (C-S-H), a primary binder in cement paste. The dissolution of C-S-H can cause severe structural damage in advanced cases of acid attack [45].
H2SO4 + Ca(OH)2 → CaSO4 + 2H2O
The degradation of the cementitious microstructure, including the increase in porosity (particularly larger pores) and the generation of cracks, directly impacts the mechanical properties of the material, leading to a reduction in compressive strength [46,47]. As evident from Figure 18, the compressive strength of all mortar specimens dramatically decreased with increasing exposure time to the sulfuric acid solution. The percentage reduction in compressive strength highlights the severity of the attack over time, as presented in Figure 19, calculated relative to the initial strength. Notably, all mixes exhibited similar initial strengths, while post-exposure residual strengths remained comparable across mixes, regardless of shell content.
Concurrently with the reduction in strength, the mortar samples exhibited significant mass loss upon exposure to the sulfuric acid. Figure 20 illustrates the percentage mass loss of mortar specimens relative to the initial mass (after curing) at 7, 14, and 28 days of acid exposure. Mass loss percentages are relatively low across all shell contents in the early stages, indicating minimal degradation during the early stage of acid exposure. After 7 days, mass loss varied from 1.6% (0% SSH) to 7.5% (2% SSH). By 14 days, mass loss increased across all samples, ranging from 7.2% (0% SSH) to 13.6% (2% SSH). After 28 days, substantial mass loss was recorded for all samples, ranging from 11.5% (0% SSH) to 23.5% (3% and 4% SSH). Mass loss in the context of sulfuric acid attack is a direct consequence of the physical removal of degraded material from the specimen surface. As the acid dissolves the cement matrix and forms reaction products, such as gypsum, the weakened surface layer may detach or erode. The higher mass loss observed with increasing exposure time reflects the progressive depth of acid penetration and the extent of material disintegration and removal.
The physical disintegration and loss of material from the surface, represented by mass loss, directly contributes to the reduction in the material’s ability to carry load, hence the decrease in compressive strength. The presence of seashells in fine aggregate likely introduces calcium carbonate (CaCO3) into the mix. Unlike the calcium silicates and hydroxides in the cement paste, CaCO3 directly reacts with sulfuric acid in a process known as acid dissolution.
CaCO3 +H2SO4 → CaSO4 + H2O + CO2
The dissolution of CaCO3 from the seashell particles directly contributes to the observed mass loss. As the shells, which constitute a portion of the aggregate, are consumed by the acid, their physical mass is removed from the specimen. This process is distinct from the degradation of the cement paste, although it occurs concurrently with it. The formation of gypsum from cement paste components leads to expansive stress and the physical disintegration of the cementitious binder. While the shells’ dissolution primarily impacts mass by aggregate removal, the strength of the concrete is more critically tied to the integrity of the cement matrix. Therefore, once a critical level of binder degradation by expansive gypsum formation is reached across all samples, regardless of the source of calcium for gypsum, the ability to resist load diminishes similarly, leading to comparable residual strengths despite varying rates of material detachment and mass loss [48].

3.7. Water Absorption Rate

Generally, seashells in concrete tend to increase water absorption, often attributed to the higher porosity and water absorption capacity of the seashells themselves compared to natural aggregates [17]. However, the cumulative water absorption results presented in Figure 21 indicate that concrete specimens with seashell content within the 0% to 5% range exhibit negligible differences in water absorption. While specimens containing 2% SSH display slightly elevated absorption values, the variation remains minor, suggesting that small-sized seashell fragments do not significantly alter the overall porosity or permeability of the concrete matrix. The minimal deviation in water absorption can be attributed to the relatively fine size of the incorporated seashell fragments, which are effectively embedded within the cementitious matrix. However, the accelerated corrosion test (ACT) test results indicate that increasing seashell content accelerates corrosion-induced failure. This apparent inconsistency is resolved by understanding that seashells, even at fine sizes, create more permeable Interfacial Transition Zones (ITZs) with the cement paste, acting as localized “hotspots” that facilitate rapid chloride ion penetration and accumulation directly at the steel reinforcement. These highly conductive pathways, rather than a general increase in porosity, lead to concentrated, accelerated corrosion and the formation of localized stress points, which in turn drive the observed unidirectional crack propagation and overall material degradation, disproportionate to what bulk water absorption alone would suggest [12].

4. Conclusions and Recommendations

The impact of varying residual seashell content on the fresh, mechanical, and durability properties of sea sand concrete was evaluated through experimental tests. Based on the findings from the experimental tests, the following conclusions can be made:
  • Shell content distribution in natural sea sand in Sri Lanka is size-dependent, with the highest concentration (6.49%) in the 0.3 mm to 0.6 mm range. The typical seashell content levels in sea sand in Sri Lanka are found to be in the range of 1–3%.
  • The presence of seashells up to 5% does not significantly hinder the workability of cement mortar, with flow percentages remaining stable between 100% and 114%. This indicates that seashells do not hinder mixing or placement processes.
  • Both 7-day and 28-day compressive strength remain relatively consistent from 0% to 5% seashells, indicating that seashell content does not significantly impact the strength within this range.
  • The differences in water absorption ratios among varying shell contents (0–5%) are minimal.
  • The rapid chloride penetration test results indicate that seashell content has a limited and non-linear influence on chloride ingress in concrete. Higher contents (3–5%) appear to improve particle packing and pore tortuosity, thereby stabilizing or marginally reducing chloride penetration.
  • Accelerated corrosion test results suggest that a high shell content (>3%) increases the risk of chloride-induced corrosion.
  • Exposure to sulfuric acid revealed similar mass loss and strength reduction across all mixes, regardless of the shell content, indicating that low shell contents (0–5%) do not promote chemical degradation in sea sand concrete.
Overall, it can be concluded that when seashell content is maintained at or below 3%, processed sea sand is a viable and sustainable alternative to conventional fine aggregates. However, the study findings are limited to laboratory-scale tests. Thus, it is essential to consider potential scale effects, such as compaction quality, curing conditions, and the distribution of shell particles, in larger structural elements. These factors significantly influence material behavior, underscoring the need for further large-scale validation studies to ensure the reliable use of seashell-containing sea sand in reinforced concrete applications. Furthermore, future research is needed to assess the bond-slip behavior of sea sand concrete, as seashell fragments influence corrosion behavior, which may affect bond strength and structural performance.
While the current SLS 1397:2010 allows a high 15% shell content, the findings suggest that this limit may be too generous for applications where chloride exposure and, consequently, corrosion of steel reinforcement are significant concerns. Therefore, the author(s) suggest that while the general limit in SLS 1397:2010 might remain broad, it would be beneficial to introduce more specific guidelines or sub-categories for sea sand concrete intended for structural applications in chloride-rich environments.
Within the range up to 3%, the presence of seashells was found to have no significant adverse impact on the mechanical or durability performance of sea sand concrete.

Author Contributions

Conceptualization, A.K. and S.B.; methodology, A.K., H.Y., and S.N.; formal analysis, A.K. and P.A.; investigation, A.K. and P.A.; resources, S.B. and H.Y.; writing—original draft preparation, A.K. and P.A.; writing—review and editing, A.K. and S.N.; visualization, A.K.; supervision, S.B., H.Y., and S.N.; project administration, S.B. and H.Y.; funding acquisition, S.B. and H.Y. All authors have read and agreed to the published version of the manuscript.

Funding

This research was funded by Sanken Construction (Pvt) Ltd.

Data Availability Statement

The data generated and analyzed during the current study are available from the corresponding author upon request.

Acknowledgments

The authors wish to acknowledge Anura Nanayakkara for his guidance in this study. The authors also wish to acknowledge the Sri Lanka Land Reclamation and Development Corporation (SLLRDC), Sanken Construction (Pvt) Ltd., for their information and support in this study, the Tahara Foundation for their financial support, and laboratory staff of the Material Laboratory, Department of Civil Engineering, Faculty of Engineering, University of Peradeniya for their support throughout this study.

Conflicts of Interest

The authors declare no conflicts of interest regarding the publication of this research article.

Abbreviations

The following abbreviations are used in this manuscript:
ACTAccelerated Corrosion Test
RCPTRapid Chloride Permeability Test
SCMSupplementary Cementitious Materials
SLLRDCSri Lanka Land Reclamation and Development Corporation
SLSSri Lanka Standard
SSHSeashell (content)

References

  1. Hu, X.; Xiao, J.; Zhang, K.; Zhang, Q. The state-of-the-art study on durability of FRP reinforced concrete with seawater and sea sand. J. Build. Eng. 2022, 51, 104294. [Google Scholar] [CrossRef]
  2. Liu, T.; Ju, Y.; Lyu, H.; Zhuo, Q.; Qian, H.; Li, Y. Identification and analysis of seashells in sea sand using computer vision and machine learning. Case Stud. Constr. Mater. 2023, 18, e02121. [Google Scholar] [CrossRef]
  3. Yang, S.; Zang, C.; Xu, J.; Fan, G. Determination of fracture parameters of seawater sea sand concrete based on maximum fracture load. J. Mater. Civ. Eng. 2020, 32, 04019315. [Google Scholar] [CrossRef]
  4. Yin, H.; Li, Y.; Lv, H.; Gao, H. Durability of sea-sand containing concrete: Effects of chloride ion penetration. Min. Sci. Technol. 2011, 21, 123–127. [Google Scholar]
  5. Zhao, Y.; Hu, X.; Shi, C.; Zhang, Z.; Zhu, D. A review on seawater sea-sand concrete: Mixture proportion, hydration, microstructure and properties. Constr. Build. Mater. 2021, 295, 123602. [Google Scholar] [CrossRef]
  6. Guo, M.; Hu, B.; Xing, F.; Zhou, X.; Sun, M.; Sui, L.; Zhou, Y. Characterization of the mechanical properties of eco-friendly concrete made with untreated sea sand and seawater based on statistical analysis. Constr. Build. Mater. 2020, 234, 117339. [Google Scholar] [CrossRef]
  7. Lanka, M.S. Evaluation of the potential of sea sand as an alternative to river sand for concrete production in Sri Lanka. J. Geol. Soc. Sri Lanka 2014, 16, 109–117. [Google Scholar]
  8. Mahendran, R.; Godwin, K.; Gnana Selvan, T.; Murugan, M. Experimental study on concrete using sea sand as fine aggregate. Int. J. Sci. Eng. Res. 2016, 7, 48–52. [Google Scholar]
  9. Suraweera, A.; Fernando, P.; Muthurathna, S.; Guluwita, S. Analysis of the Waste Sludge Produced from the Offshore Sand Processing Plants in Sri Lanka. In Proceedings of the Innovation Geared Building Resilience—11th Annual Research Symposium, Battaramulla, Sri Lanka, 14–15 December 2021. [Google Scholar]
  10. Dolage, D.A.R.; Dias, M.G.S.; Ariyawansa, C.T. Offshore Sand as a Fine Aggregate for Concrete Production. Curr. J. Appl. Sci. Technol. 2013, 3, 813–825. [Google Scholar] [CrossRef]
  11. Pan, D.; Yaseen, S.A.; Chen, K.; Niu, D.; Leung, C.K.Y.; Li, Z. Study of the influence of seawater and sea sand on the mechanical and microstructural properties of concrete. J. Build. Eng. 2021, 42, 103006. [Google Scholar] [CrossRef]
  12. Li, H.; Liu, F.; Pan, Z.; Li, H.; Wu, Z.; Li, L.; Xiong, Z. Use of supplementary cementitious materials in seawater–sea sand concrete: State-of-the-art review. Constr. Build. Mater. 2024, 425, 136009. [Google Scholar] [CrossRef]
  13. Rodrigues, R.; Gaboreau, S.; Gance, J.; Ignatiadis, I.; Betelu, S. Reinforced concrete structures: A review of corrosion mechanisms and advances in electrical methods for corrosion monitoring. Constr. Build. Mater. 2021, 269, 121240. [Google Scholar] [CrossRef]
  14. Dhondy, T.; Remennikov, A.; Shiekh, M.N. Benefits of using sea sand and seawater in concrete: A comprehensive review. Aust. J. Struct. Eng. 2019, 20, 280–289. [Google Scholar] [CrossRef]
  15. Güneyisi, E.; Gesoğlu, M.; Karaboğa, F.; Mermerdaş, K. Corrosion behavior of reinforcing steel embedded in chloride contaminated concretes with and without metakaolin. Compos. Part B Eng. 2013, 45, 1288–1295. [Google Scholar] [CrossRef]
  16. Sampath, B.; Mohankuma, G. Preliminary study on the development of concrete with sea sandas fine aggregate. Indian J. Sci. Technol. 2016, 9, 1–5. [Google Scholar] [CrossRef]
  17. Eziefula, U.G.; Ezeh, J.C.; Eziefula, B.I. Properties of seashell aggregate concrete: A review. Constr. Build. Mater. 2018, 192, 287–300. [Google Scholar] [CrossRef]
  18. Boudjellal, K.; Bouabaz, M.; Bensebti, S.E. Formulation of a concrete based on grinded seashells as partial substitution for sand. Civ. Environ. Eng. Rep. 2020, 30, 56–71. [Google Scholar] [CrossRef]
  19. Nguyen, D.H.; Boutouil, M.; Sebaibi, N.; Baraud, F.; Leleyter, L. Durability of pervious concrete using crushed seashells. Constr. Build. Mater. 2017, 135, 137–150. [Google Scholar] [CrossRef]
  20. Arulmoly, B.; Konthesingha, C. Pertinence of alternative fine aggregates for concrete and mortar: A brief review on river sand substitutions. Aust. J. Civ. Eng. 2022, 20, 272–307. [Google Scholar] [CrossRef]
  21. Jiang, K.; Wang, X.; Chen, Z.; Ding, L.; Peng, Z.; Wu, Z. Effect of constituent content on mechanical behaviors of ultra-high performance seawater sea-sand concrete. Constr. Build. Mater. 2022, 351, 128952. [Google Scholar] [CrossRef]
  22. Elliott Richardson, A.; Fuller, T. Sea shells used as partial aggregate replacement in concrete. Struct. Surv. 2013, 31, 347–354. [Google Scholar] [CrossRef]
  23. Safi, B.; Saidi, M.; Daoui, A.; Bellal, A.; Mechekak, A.; Toumi, K. The use of seashells as a fine aggregate (by sand substitution) in self-compacting mortar (SCM). Constr. Build. Mater. 2015, 78, 430–438. [Google Scholar] [CrossRef]
  24. Ammari, M.Z.; Ghoraishi, M.; Abidou, A.; Al-Rousan, R.Z. Sand with crushed seashells and its effect on the strength of mortar and concrete used in the United Arab Emirates. Int. J. Civ. Eng. Technol. 2017, 8, 462–470. [Google Scholar]
  25. Xiao, J.; Qiang, C.; Nanni, A.; Zhang, K. Use of sea-sand and seawater in concrete construction: Current status and future opportunities. Constr. Build. Mater. 2017, 155, 1101–1111. [Google Scholar] [CrossRef]
  26. BS 882: 1992; Specification for Aggregates from Natural Sources for Concrete. British Standards Institution: London, UK, 1992.
  27. EN 12620:2013; Aggregates for Concrete. European Committee for Standardization: Brussels, Belgium, 2013.
  28. SLS1397:2010; Specification for Fine Agregates for Concrete and Mortar. Sri lanka Standards Institution: Colombo, Sri Lanka, 2010.
  29. EN 197-1:2011; Cement-Part 1: Composition, Specifications and Conformity Criteria for Common Cements. British Standards Institution: London, UK, 2000.
  30. EN 933-1:1997/A1:2005; Tests for Geometrical Properties of Aggregates—Part 1: Determination of Particle size Distribution—Sieving Method. European Committee for Standardization: Brussels, Belgium, 2005.
  31. BS EN 1097-6:2013; Tests for Mechanical and Physical Properties of Aggregates. Determination of Particle Density and Water Absorption. The British Standards Institution: London, UK, 2013. [CrossRef]
  32. EN 1744-1:1998; Tests for Chemical Properties of Aggregates—Part 1: Chemical Analysis. British Standards Institution: London, UK, 1998.
  33. BS EN 933-8; Tests for Geometrical Properties of Aggregates. Assessment of Fines. Sand Equivalent Test. British Standards Institution: London, UK, 2012. [CrossRef]
  34. Marsh, B.K. Design of Normal Concrete Mixes; Building Research Establishment: London, UK, 1988. [Google Scholar]
  35. EN 1992-1-1; Eurocode 2: Design of Concrete Structures—Part 1-1. European Committee for Standardization: Brussels, Belgium, 2004.
  36. Olubajo, O.; Osha, O.; El-Nafaty, U.; Adamu, H. Effect of water-cement ratio on the mechanical properties of blended cement containing bottom ash and limestone. Civ. Environ. Res. 2014, 6, 1–9. [Google Scholar]
  37. Sheikh Hassani, M.; Torki, A.; Asadollahfardi, G.; Saghravani, S.F.; Shafaei, J. The effect of water to cement ratio and age on the mechanical properties of cement mortar and concrete made of micro-nano bubbles without adding any admixtures. Struct. Concr. 2021, 22, E756-68. [Google Scholar] [CrossRef]
  38. ASTM C109/C109M-20; Standard Test Method for Compressive Strength of Hydraulic Cement Mortars. ASTM International: West Conshohocken, PA, USA, 2020. [CrossRef]
  39. ASTM C31/C31M-22; Standard Practice for Making and Curing Concrete Test Specimens in the Field. ASTM International: West Conshohocken, PA, USA, 2023.
  40. ASTM C1437-20; Standard Test Method for Flow of Hydraulic Cement Mortar. ASTM International: West Conshohocken, PA, USA, 2020.
  41. ASTM C1202-22e1; Standard Test Method for Electrical Indication of Concrete’s Ability to Resist Chloride Ion Penetration. ASTM International: West Conshohocken, PA, USA, 2022.
  42. ASTM C642-97; Standard Test Method for Density, Absorption, and Voids in Hardened Concrete. ASTM International: West Conshohocken, PA, USA, 1997.
  43. Hamada, H.M.; Abed, F.; Tayeh, B.; Al Jawahery, M.S.; Majdi, A.; Yousif, S.T. Effect of recycled seashells on concrete properties: A comprehensive review of the recent studies. Constr. Build. Mater. 2023, 376, 131036. [Google Scholar] [CrossRef]
  44. Khan, H.A.; Castel, A.; Khan, M.S.; Mahmood, A.H. Durability of calcium aluminate and sulphate resistant Portland cement based mortars in aggressive sewer environment and sulphuric acid. Cem. Concr. Res. 2019, 124, 105852. [Google Scholar] [CrossRef]
  45. Santos, B.S.; Machini, W.B.; Matias, G.; Moreira, N.F.; Portugal, P.M.; Torres, I.; Tadeu, A.; Almeida, J.A.S. Mortars with enhanced chemical resistance: Effects of sulphuric acid exposure. Dev. Built Environ. 2025, 21, 100592. [Google Scholar] [CrossRef]
  46. Gu, L.; Visintin, P.; Bennett, T. Sulphuric acid resistance of cementitious materials: Multiscale approach to assessing the degradation. J. Mater. Civ. Eng. 2020, 32, 04020171. [Google Scholar] [CrossRef]
  47. Ortega, J.M.; García-Vera, V.E.; Solak, A.M.; Tenza-Abril, A.J. Pore structure degradation of different cement mortars exposed to sulphuric acid. Appl. Sci. 2019, 9, 5297. [Google Scholar] [CrossRef]
  48. He, X.; Zhou, J. Mechanical characteristics of sea-sand concrete in simulated marine environment. Constr. Build. Mater. 2021, 274, 122098. [Google Scholar] [CrossRef]
Buildings 15 02751 g001
Figure 1. Mechanism of corrosion in sea sand concrete.
Figure 1. Mechanism of corrosion in sea sand concrete.
Buildings 15 02751 g001
Buildings 15 02751 g002
Figure 2. Processed sea sand contains seashell fragments.
Figure 2. Processed sea sand contains seashell fragments.
Buildings 15 02751 g002
Buildings 15 02751 g003
Figure 3. Shell content testing method schematic diagram.
Figure 3. Shell content testing method schematic diagram.
Buildings 15 02751 g003
Buildings 15 02751 g004
Figure 4. Cleaned sea sand preparation: (a) dissolve the seashells using hydrochloric acid, (b) wash the sand using fresh water to remove chloride, (c) dry and store the cleaned sand.
Figure 4. Cleaned sea sand preparation: (a) dissolve the seashells using hydrochloric acid, (b) wash the sand using fresh water to remove chloride, (c) dry and store the cleaned sand.
Buildings 15 02751 g004
Buildings 15 02751 g005
Figure 5. Seashell preparation: (a) sieve Sand with a 4 mm sieve (separate the passing), (b) separate shells and other materials, (c) wash and clean, (d) crush and sieve.
Figure 5. Seashell preparation: (a) sieve Sand with a 4 mm sieve (separate the passing), (b) separate shells and other materials, (c) wash and clean, (d) crush and sieve.
Buildings 15 02751 g005
Buildings 15 02751 g006
Figure 6. Seashells prepared according to the size distribution.
Figure 6. Seashells prepared according to the size distribution.
Buildings 15 02751 g006
Buildings 15 02751 g007
Figure 7. Accelerated corrosion test setup.
Figure 7. Accelerated corrosion test setup.
Buildings 15 02751 g007
Buildings 15 02751 g008
Figure 8. Laboratory test setup of the rapid chloride permeability test (RCPT).
Figure 8. Laboratory test setup of the rapid chloride permeability test (RCPT).
Buildings 15 02751 g008
Buildings 15 02751 g009
Figure 9. Shell content distribution across different particle size ranges.
Figure 9. Shell content distribution across different particle size ranges.
Buildings 15 02751 g009
Buildings 15 02751 g010
Figure 10. Variation of shell content per kilogram of sea sand across different particle size ranges.
Figure 10. Variation of shell content per kilogram of sea sand across different particle size ranges.
Buildings 15 02751 g010
Buildings 15 02751 g011
Figure 11. Flowability variation of sea sand mortar with different shell content.
Figure 11. Flowability variation of sea sand mortar with different shell content.
Buildings 15 02751 g011
Buildings 15 02751 g012
Figure 12. Compressive strength variation of sea sand mortar at 7 and 28 days for different seashell (SSH) levels.
Figure 12. Compressive strength variation of sea sand mortar at 7 and 28 days for different seashell (SSH) levels.
Buildings 15 02751 g012
Buildings 15 02751 g013
Figure 13. Time for failure under accelerated corrosion testing.
Figure 13. Time for failure under accelerated corrosion testing.
Buildings 15 02751 g013
Buildings 15 02751 g014
Figure 14. Corrosion current variation under accelerated corrosion testing.
Figure 14. Corrosion current variation under accelerated corrosion testing.
Buildings 15 02751 g014
Buildings 15 02751 g015
Figure 15. Variation of current efficiency in ACT with different seashell content levels.
Figure 15. Variation of current efficiency in ACT with different seashell content levels.
Buildings 15 02751 g015
Buildings 15 02751 g016
Figure 16. Cracked specimens after accelerated corrosion period; (a) 0% SSH, (b) 1% SSH, (c) 2% SSH, (d) 3% SSH, (e) 4% SSH, (f) 5% SSH.
Figure 16. Cracked specimens after accelerated corrosion period; (a) 0% SSH, (b) 1% SSH, (c) 2% SSH, (d) 3% SSH, (e) 4% SSH, (f) 5% SSH.
Buildings 15 02751 g016
Buildings 15 02751 g017
Figure 17. Total current passed through each specimen in the RCPT testing.
Figure 17. Total current passed through each specimen in the RCPT testing.
Buildings 15 02751 g017
Buildings 15 02751 g018
Figure 18. Compressive strength of cement mortar containing varying shell contents subjected to chemical exposure.
Figure 18. Compressive strength of cement mortar containing varying shell contents subjected to chemical exposure.
Buildings 15 02751 g018
Buildings 15 02751 g019
Figure 19. Percentage strength reduction of mortar cubes exposed to a sulfuric acid environment.
Figure 19. Percentage strength reduction of mortar cubes exposed to a sulfuric acid environment.
Buildings 15 02751 g019
Buildings 15 02751 g020
Figure 20. Mass loss percentage at 7 days, 14 days, and 28 days of chemical exposure.
Figure 20. Mass loss percentage at 7 days, 14 days, and 28 days of chemical exposure.
Buildings 15 02751 g020
Buildings 15 02751 g021
Figure 21. Water absorption rates of specimens with different seashell (SSH) contents.
Figure 21. Water absorption rates of specimens with different seashell (SSH) contents.
Buildings 15 02751 g021
Table 1. Chemical composition of seashell fragments.
Table 1. Chemical composition of seashell fragments.
Chemical
Component		SiO2Al2O3FeO3CaOSrOK2OZrO2TiO2Fe2O3SO3LOI
Seashells (%)6.670.692.5988.320.530.020.160.182.590.7643.8
Table 2. Limits for seashell content in different regions and standards.
Table 2. Limits for seashell content in different regions and standards.
RegionCodeApplicationLimit %Comment
BritishBS 882: 1983 5–10 mm20By aggregate
BS 882: 1992 [26]≥10 mm8By coarse aggregate
British/European UnionBSEN 12620-2013 [27]SC10<10
SCNRNo requirement
British/European UnionBSEN 12620-2013 [27]SC10≤10
SC Declared≥10
SCNRNo requirement
Sri LankaSLS 1397:2010 [28]0.5–8 mm≤15By sand
Note: SC10 denotes that the shell content in the coarse aggregate is 10% or less (≤10%), and SCNR stands for “No requirement”.
Table 3. Physical and mechanical characteristics of sea sand.
Table 3. Physical and mechanical characteristics of sea sand.
CharacteristicSea SandSeashellsStandard
Fineness modulus2.37-BS EN 933-1:1997 + A1:2005 [30]
Specific gravity (SSD)2.681.54BS EN 1097-6: 2013 [31]
Fines content < 0.075 mm (%)0.68-BS EN 933-1:1997 + A1:2005 [30]
Water absorption (%)0.20.3BS EN 1097-6: 2013 [31]
Water soluble chloride content (%) 0.0004-BS EN 1744-1: 1998 [32]
Shell content (%)1.9-SLS 1397: 2010 [28]
Silt content (%)4.2-BS EN 933-8 [33]
Table 4. Mixture proportions of concrete and mortar.
Table 4. Mixture proportions of concrete and mortar.
Mix IDSSH
Content		W/CWater
(kg/m3)		Cement (kg/m3)FA (Sand)
(kg/m3)		FA (SSH)
(kg/m3)		CA
(kg/m3)		SP
(kg/m3)
SSH0% C0%0.65200308725018830
SSH1% C1%0.65200308717.87.218830
SSH2% C2%0.65200308710.514.518830
SSH3% C3%0.65200308703.221.818830
SSH4% C4%0.652003086962918830
SSH5% C5%0.65200308688.736.218830
SSH0% M0%0.4524355515310153111.1
SSH1% M1%0.452435551515.715.3153111.1
SSH2% M2%0.452435551500.430.6153111.1
SSH3% M3%0.452435551485.045.9153111.1
SSH4% M4%0.452435551469.861.2153111.1
SSH5% M5%0.452435551454.576.6153111.1
Note: In the “Mix ID” column, “C” denotes concrete and “M” denotes mortar.
Table 5. Shell content distribution across different particle size ranges.
Table 5. Shell content distribution across different particle size ranges.
Sieve Size4–2.362.36–1.181.18–0.60.6–0.30.3–0.150.15–0.075
Retained sand percentage (%)0.353.4022.3239.6023.1110.71
Shell content per 1 kg of sea sand (g/kg)1.073.173.576.4912.7120.45
Disclaimer/Publisher’s Note: The statements, opinions and data contained in all publications are solely those of the individual author(s) and contributor(s) and not of MDPI and/or the editor(s). MDPI and/or the editor(s) disclaim responsibility for any injury to people or property resulting from any ideas, methods, instructions or products referred to in the content.

Share and Cite

MDPI and ACS Style

Koswaththa, A.; Abeyaratne, P.; Buddika, S.; Yapa, H.; Navaratnam, S. Effects of Natural Seashell Presence on the Engineering Performance of Sea Sand Concrete. Buildings 2025, 15, 2751. https://doi.org/10.3390/buildings15152751

AMA Style

Koswaththa A, Abeyaratne P, Buddika S, Yapa H, Navaratnam S. Effects of Natural Seashell Presence on the Engineering Performance of Sea Sand Concrete. Buildings. 2025; 15(15):2751. https://doi.org/10.3390/buildings15152751

Chicago/Turabian Style

Koswaththa, Anuradha, Pasindu Abeyaratne, Samith Buddika, Hiran Yapa, and Satheeskumar Navaratnam. 2025. "Effects of Natural Seashell Presence on the Engineering Performance of Sea Sand Concrete" Buildings 15, no. 15: 2751. https://doi.org/10.3390/buildings15152751

APA Style

Koswaththa, A., Abeyaratne, P., Buddika, S., Yapa, H., & Navaratnam, S. (2025). Effects of Natural Seashell Presence on the Engineering Performance of Sea Sand Concrete. Buildings, 15(15), 2751. https://doi.org/10.3390/buildings15152751

Note that from the first issue of 2016, this journal uses article numbers instead of page numbers. See further details here.

Article Metrics

Back to TopTop