Utilization of Common Shell Wastes as a Limestone Alternative in Cementitious Materials

Utilization of Common Shell Wastes as a Limestone Alternative in Cementitious Materials | Research Square window.SnipcartSettings = { analytics: { enabled: false } }; (function() { var accessVector = localStorage.getItem('access_vector') || ''; window.dataLayer = window.dataLayer || []; if (accessVector) { window.dataLayer.push({ user: { profile: { profileInfo: { snid: accessVector } } } }); } })(); (function(w,d,s,l,i){w[l]=w[l]||[];w[l].push({'gtm.start':new Date().getTime(),event:'gtm.js'});var f=d.getElementsByTagName(s)[0],j=d.createElement(s),dl=l!='dataLayer'?'&l='+l:'';j.async=true;j.src='https://www.googletagmanager.com/gtm.js?id='+i+dl;f.parentNode.insertBefore(j,f);})(window,document,'script','dataLayer','GTM-K279D39R'); Browse Preprints In Review Journals COVID-19 Preprints AJE Video Bytes Research Tools Research Promotion AJE Professional Editing AJE Rubriq About Preprint Platform In Review Editorial Policies Our Team Advisory Board Help Center Sign In Submit a Preprint Cite Share Download PDF Research Article Utilization of Common Shell Wastes as a Limestone Alternative in Cementitious Materials Kylee Rux, Montale Tuen, Prannoy Suraneni This is a preprint; it has not been peer reviewed by a journal. https://doi.org/ 10.21203/rs.3.rs-5278623/v1 This work is licensed under a CC BY 4.0 License Status: Published Journal Publication published 24 Oct, 2025 Read the published version in Materials and Structures → Version 1 posted 5 You are reading this latest preprint version Abstract Efforts to decarbonize the concrete industry have motivated the use of alternative sustainable materials. While limestone fillers are promising, reducing reliance on virgin materials and natural resources remains essential. Shell waste from seafood and egg production are available in large quantities and their disposal poses several environmental challenges. Utilizing these CaCO 3 -containing waste shells as an alternative to conventional limestone can divert shell waste from landfills while lessening cement demand. To test this hypothesis, five types of waste shells were ground into powder, including oyster shells, mussel shells, crab shells, shrimp shells, and eggshells. The raw shell powders were first characterized, followed by testing of hydration kinetics and mechanical properties. Results indicated that shell powders were analogous to limestone filler, consisting primarily of calcite, with the exception of shrimp shells. Small amounts of organics were also present in the shell materials. Incorporation of eggshell or oyster shell at a 20% cement replacement yielded compressive strengths similar to limestone after 28 days of curing, but other materials reduced strength. The mortar flow and compressive strength were likely influenced by morphology, size, chemical composition, and organics of the shell powders. The findings of this study indicate that substituting limestone filler in cementitious materials with recycled shell materials is feasible. Cement mortar sustainable concrete shell waste limestone filler Figures Figure 1 Figure 2 Figure 3 Figure 4 Figure 5 Figure 6 Figure 7 Figure 8 Figure 9 Figure 10 Figure 11 Figure 12 1 Introduction Approximately 4.1 billion metric tons of cement are produced globally every year, accounting for over 7% of global anthropogenic greenhouse gas emissions [ 1 ]. Cement demand is expected to increase as a result of rapid urbanization and economic development [ 2 ]. Efforts to reduce the environmental impact of the cement industry have motivated the use of fillers. Limestone filler—composed of calcium carbonate (CaCO 3 )—has been widely studied as a partial replacement for cement, offering technical, economic, and environmental advantages [ 3 ]. While this technique mitigates carbon emissions, the mining and processing of raw limestone continues to present environmental challenges [ 4 ]. Researchers have begun exploring alternative materials analogous to limestone, including waste food shells. Aquaculture is a sustainable food source, with bivalve production in particular having more than tripled in the past thirty years [ 5 ]. Every year, approximately 7 million tons of oyster, clam, scallop, and mussel shells are generated globally [ 6 ]. Additionally, 8 million tons of waste crab, shrimp, and lobster shells are produced. Poultry eggs are also a major industry due to their high-quality protein content, with nearly 8.6 million tons of eggshells discarded annually [ 7 , 8 ]. Increased reliance on aquaculture, poultry, and other shell waste producing industries is essential to achieve global food security [ 9 ]. However, higher waste production has presented the difficulties of managing shell waste that has detrimental environmental impacts, Waste shells are often discarded in landfills or at sea where they cause soil and water pollution, including the release of stored carbon into the environment [ 5 , 6 ]. The disposal of eggshells also contributes to environmental concerns with their waste ranked as the fifteenth major food industry pollution problem by the Environmental Protection Agency [ 7 ]. As landfills approach capacity, exploring other disposal methods, such as reuse, becomes increasingly crucial. Utilizing these CaCO 3 -rich waste shells as an alternative to limestone can divert shell waste from landfills and the natural environment, lessen global raw limestone extraction, and reduce cement demand. Various shell wastes have been employed in cementitious materials as fine or coarse aggregate replacement [ 2 , 10 , 11 ]. Previous studies have also investigated their potential as substitutes for limestone. Lertwattanaruk et al. [ 12 ] evaluated the effect of various waste seashells, oyster, mussel, clam, and cockle, as binder replacements in cement plastering applications. Mortar containing ground mussel shell led to lower compressive strength than the other shells tested. This reduction in strength was attributed to the relatively larger particle size of mussel shells compared to Portland cement, resulting in a lower particle packing density. Han et al. [ 13 ] reported that partially replacing cement with oyster shell powder accelerated the rate of cement hydration due to dilution and nucleation effects. However, these early-age acceleration effects combined with low initial reactivity of the powder, resulted in a reduction in the hydration products, negatively impacting the development of compressive strength. Other researchers have utilized eggshell powder as a partial substitute for cement. Several studies recommend the incorporation of eggshell powder at lower replacements (5–15%) to achieve better mechanical performance [ 14 – 16 ]. Factors affecting reduction in strengths at higher proportions include dilution of cement, higher matrix porosity, and eggshell powder size [ 17 ]. While previous studies have explored the effects of waste shells as cement replacement, critical gaps remain regarding their use in civil engineering applications. First, there are limited studies examining the impact of uncalcined shell powder as cement replacement. In particular, the performance of mortar containing crab shell and shrimp shell powder has not been extensively researched. Further investigations are also necessary to better interpret the effect of shell powder materials on paste microstructure. Ultimately, a thorough comparison of various CaCO 3 -rich materials that could serve as substitutes for traditional limestone filler in cementitious composites is needed. This study aims to assess the feasibility of using waste shell powders as alternatives to limestone filler in cementitious materials. Five shell types—oyster, mussel, crab, shrimp, and eggshells—were collected and pulverized. Shell powders were characterized using thermogravimetric analysis (TGA), Fourier transform infrared spectroscopy (FTIR), X-ray diffraction (XRD), scanning electron microscopy (SEM), and the modified R 3 test. Early-age hydration kinetics were analyzed via isothermal calorimetry. Furthermore, mortar flow, compressive strength development, and bulk resistivity were investigated. 2 Materials and Methods 2.1 Materials Waste shells utilized in this study were obtained from various Miami-area restaurants. Shells included oyster shells ( Crassostrea viginica ), mussel shells ( Mytilus edulis ), stone crab shells ( Menippe mercenaria , Menippe adina ), shrimp shells ( Litopenaeus vannamei ), and poultry eggshells. While crab shell is primarily composed of shell and legs, this study specifically used the legs of the stone crab. The entire shell was used for all other materials. Shells were cleaned using water and a nylon brush to remove any surface residue. Subsequently, shells were dried in an oven at 105 ± 5°C for 24 h to remove moisture. Shells were ground into powder and passed through a 45 µm sieve. Microna 10 limestone from Columbia River Carbonates was used as a traditional inert filler. A commercially available Portland limestone cement (PLC) was used containing 12% limestone. The particle size distributions and median particle sizes of the shell powders, limestone, and PLC are shown in Fig. 1 and Table 1 , respectively. Particle size distribution was measured on dry powders using particle refractive index of 1.60 and absorption coefficient 0.1. Each PSD measurement was performed four times and averaged values are reported. For the preparation of mortar, silica sand was used as fine aggregate. Table 1 Median particle size of shell powders, limestone, and PLC. Powder PLC Limestone Oyster Shell Mussel Shell Crab Shell Shrimp Shell Eggshell d 50 (µm) 8.6 14.1 5.2 25.6 23.5 40.7 28.2 2.2 Characterization of shell waste The powders were characterized using TGA, FTIR, XRD, SEM, and the modified R 3 test. A total of 35 ± 5 mg powder was placed in a platinum pan. The thermal analysis system was heated from room temperature to 1000°C at a rate of 10°C/min within an inert nitrogen atmosphere. The mass loss corresponding to water, organics/other, and CaCO 3 was quantified. FTIR spectra was measured for the powders using an FTIR spectrometer. Powders were placed on the top-plate of the instrument, covering the sensor entirely. The gauged pressure arm was adjusted tightly atop the powder. Spectra were collected from 4000 to 500 cm − 1 . The analysis range was reduced to 1800 to 600 cm − 1 to minimize noise. The transmittance strength and wavenumber location of each sample was recorded. The crystalline phases in the powder were identified via XRD analysis. Powder was filled into the sample holder and the surface was manually flattened. Scans were performed in the 2θ range of 8–65° using a copper x-ray source producing CuKα radiation (λ = 1.5418 Å). Peaks were identified using X’pert HighScore Plus. High resolution images of the powder were obtained using field emission scanning electron microscopy. A thin layer of powder was fixed onto carbon fiber tape. A layer of carbon was sputtered on the surface to aid in electron conduction. An acceleration voltage of 2-10kV was applied with a working distance of 9.3–9.8 mm. The reactivity of the powders was assessed using the modified R 3 test. Six grams of laboratory grade calcium hydroxide was combined with two grams of shell powder and dry mixed by hand for 4 min. A 0.5 M potassium hydroxide solution was then added to achieve a final liquid-to-solid ratio of 0.9. After an additional 4 min of mixing, approximately 6–7 g of the mixture was inserted into a glass ampoule and sealed. The ampoule was placed in the preconditioned 50°C isothermal calorimeter. The heat flow and heat release were measured for 72 hours. 2.3 Tests on cementitious pastes The hydration heat evolution was investigated via isothermal calorimetry. Shell powder was mixed with PLC at a 20% replacement, resulting in a mixture of 2 g shell powder and 8 g PLC. A paste was prepared using a water-to-cementitious material (w/cm) ratio of 0.40. The paste was mixed for 4 min, after which, about 6–7 g was inserted into a glass ampoule and sealed. The ampoule was lowered into an isothermal calorimeter preconditioned at 23°C. Heat flow and heat release data were obtained for 7 days. TGA was performed immediately following the removal of the cement paste samples from the calorimeter to quantify calcium hydroxide and calcium carbonate content at 7 days. Half of the cement paste sample was ground into a fine powder using a mortar and pestle. Approximately 35 mg of powder was placed in a platinum pan, loaded into the TGA, and heated to 1000°C. The calcium hydroxide (CH) and CaCO 3 contents were determined based on the mass loss between approximately 350–500°C and 500–750°C, respectively [ 18 , 19 ]. The remaining half of the sample was stored in an air-tight container and subjected to TGA at 28 days. 2.4 Tests on mortar Seven mortar mixtures were cast to compare the five different shell powders, traditional limestone filler, and a control. Mortar specimens were prepared using a fixed w/cm ratio of 0.40 and a sand-to-cementitious material ratio of 2.75. Shell powder or limestone filler replaced PLC at a 20% mass replacement. PLC and shell powder were premixed by-hand for 60s to achieve homogenous blending. The components were then mixed in a mechanical mixer for four minutes per ASTM 305, and the mixed mortar was cast into 2x2 in plastic cube molds [ 20 ]. The specimens were demolded after 24 h and cured in a moist room (> 95% humidity, 23°C) until the test age. Flow table tests were also performed in accordance with ASTM C1437 [ 21 ]. The mold was filled with mortar and compacted. After the mold was removed, the table was dropped 25 times over a span of 15 s. Three measurements of the mortar base diameter were recorded. Mass, dimensions, bulk resistivity, and compressive strength measurements were recorded after 7 and 28 days. Mortar cubes were removed from the moist room, surface-dried, and subjected to bulk resistivity tests using a resistivity meter at a frequency of 1 kHz. A total of three replicates were tested per mix at each testing age. Corrections for sample size and dimensions were accounted for. Specimens were then subjected to compression until failure using a mechanical testing machine. Three replicate samples were tested for each mixture. 2.5 Data analysis All statistical analyses were completed in Minitab. The criteria for statistical significance was set a priori to 0.05. One-factor ANOVA was performed to evaluate the bulk resistivity and mortar test results among the various mixture types. Regression analysis tested the effects of density and shell powder composition on the resulting compressive strength of the specimens. 3 Results and Discussion 3.1 Characterization of shell waste 3.1.1 Thermogravimetric analysis TGA-DTG analysis of the raw shell powders revealed three distinct mass loss events, as shown in Fig. 2. The initial weight loss, from 23 to about 120 °C corresponds to the vaporization of water. In all materials except the shrimp shell, this value was less than 2%. Over a wide range of temperatures, from about 150 to 500 °C, the weight loss is attributed to the decomposition of organic matter. Trace amounts of other inorganics could also have contributed to this mass loss, but other tests performed did not find any evidence for such phases. The main weight loss for most of the powders is due to the decomposition of calcium carbonate to calcium oxide. The decomposition temperature range and quantification of H 2 O, organics, and CaCO 3 in limestone and shell powders is shown in Table 2 . Oyster shell, mussel shell, and eggshell had similar amounts of CaCO 3 to that of the limestone filler (> 94%); these materials have less than 5% mass loss due to organics or other phases. The CaCO 3 content and mass loss due to organics in crab shell was 86% and 12%, respectively. The difference in initial CaCO 3 decomposition temperature in the shell powders compared to limestone is likely due to the presence of inorganics in the shells, variations in crystallinity, changes in particle size, and differences in amounts of powder tested [ 22 ]. Unlike other materials, the primary weight loss for shrimp shell powder is associated with the degradation of chitin—a linear amino polysaccharide—and animal or vegetable protein [ 23 ]. Chitin and protein degradation accounted for 69% of the mass loss, while 16% was associated with CaCO 3 content. Pérez et al. [ 23 ] reported similar mass loss values for raw, dried shrimp shell that included vaporization of water (14%), chitin and protein degradation (60%), and CaCO 3 content (12%). Table 2 Decomposition temperatures and amounts of H 2 O and CaCO 3 of limestone and shell powders. For organics/other, the mass loss is given, but amounts are not computed, as the exact phase is not known. Material Decomposition Range (°C) Weight (%) H 2 O Organics/ other CaCO 3 H 2 O Organics/ other CaCO 3 Limestone 23–105 - 535–800 0.0 0.9 99.1 Oyster Shell 23–105 190–500 520–775 0.4 2.7 97.0 Mussel Shell 23–120 185–490 550–740 0.5 3.5 96.0 Crab Shell 23–105 155–520 550–725 1.8 12.1 86.1 Shrimp Shell 23–140 145–555 580–735 14.0 69.4 16.5 Eggshell 23–110 200–490 580–795 0.8 4.3 94.9 3.1.2 Fourier transform infrared spectroscopy The FTIR spectra of limestone filler and waste shell powders are shown in Fig. 3 . The patterns of oyster shell, mussel shell, crab shell, eggshell, and limestone are characteristic of CaCO 3 , particularly calcite [ 24 , 25 ], consistent with TGA results. The peak at ~ 1410 cm − 1 is due to C-O stretching. The band at ~ 875 cm − 1 corresponds to in-plane bending of CO 3 2− . The peak at ~ 712 cm − 1 is associated with Ca-O stretching. Mussel shell also exhibits peaks of aragonite. Carbonate out-of-bend vibration at 860 cm − 1 and the peak at 1445 cm − 1 both correspond to aragonite [ 26 ]. The FTIR spectrum for shrimp shell powder shows the presence of various functional groups, aligning with previous literature analyzing untreated shrimp shell that underwent a similar processing procedure [ 27 , 28 ]. The characteristic peaks of chitin at 1633 cm − 1 and 1031 cm − 1 corresponds to C = O amide stretching (amide I) and CO stretching, respectively. The absorption band at 1403 cm − 1 identifies as CH 3 bending and CH 2 deformation. The absorption peak at 1531 cm − 1 confirms the stretching vibration of protein [ 29 ]. Furthermore, the stretching and bending vibrations of calcite are apparent at 1410 cm − 1 and 874 cm − 1 [ 27 ]. 3.1.3 X-Ray diffraction analysis XRD patterns of limestone filler and waste shell powders are shown in Fig. 4 . The major diffraction peaks of CaCO 3 and chitin are identified. All waste shell powders, except for shrimp shell, were nearly analogous to limestone filler, consistent with TGA and FTIR results. The oyster shell, mussel shell, crab shell, and eggshell powders were predominantly composed of calcite. The main calcite peaks observed in the spectra occur at 24.3, 29.3, 36.0, 39.4, 43.1, 47.5, and 48.5 2θ. The results revealed that aragonite was also present in mussel shells. Recorded reflections were at 2θ positions 26.3, 27.3, 33.2, 38.0, 38.7, 45.9, 50.3, 52.5, and 53.0. As expected, chitin is the main component found in shrimp shells. Two main diffraction peaks at 9.7, 19.6, and weak diffraction peaks at 12.0, 23.4, and 26.9 2θ were observed. These diffraction peaks align with previous studies, indicating the crystalline structure of α-chitin, the most common and stable form of chitin [ 27 , 30 , 31 ]. Calcite peaks were also detected in the shrimp shell, appearing at the same positions on the spectra as the other shell powders. 3.1.4 Scanning electron microscopy The micrographs of the limestone and waste shell powders are shown in Fig. 5 . The morphologies of the waste shells exhibited irregularly shaped, multi-angular, and various sized particles. The prismatic and foliate morphology resembles that of calcite. At magnification 750x, the morphology of the eggshell powder was comparable to limestone filler. Eggshell powder also contains porous fibril structures that make up the eggshell membrane [ 32 ]. Mussel shell powder exhibited primarily flaky, needle-like structures. The rough surface of the shrimp shell is associated with chitin, likely attributed to proteins, minerals, and the highly packed structured with inter or intramolecular hydrogen bonds [ 33 ]. The particle sizes of the shell powders shown in the images validate the results of the particle size distribution measurements. 3.1.5 Modified R 3 test The heat release curves of limestone and waste shell powders are shown in Fig. 6 . Crab shells exhibited the highest heat release throughout the experiment. At the end of 3 days, crab shell measured the highest heat release at 36.5 J/g, nearly 2.65-fold greater than limestone (14.9 J/g). Shrimp shell, eggshell, and mussel shell followed with final heat release values of 39.0 J/g, 24.3 J/g, and 21.9 J/g, respectively. The heat release curve of oyster shell was similar to limestone with 13.2 J/g heat release. As expected, the materials exhibited low heat release values throughout the duration of the test. All materials are characterized as inert due to low heat release values, < 100 J/g SCM [ 34 ]. The coefficient of variability of these values from testing in the lab is less than 3% [ 35 ]. 3.2 Tests on cementitious pastes 3.2.1 Isothermal calorimetry The heat flow results for the pastes containing 20% limestone and waste shell powders are shown in Fig. 7 a. Of the five shell materials, oyster shell, mussel shell, and eggshell exhibited hydration reactions most similar to the limestone filler. As expected, the incorporation of limestone, eggshell, mussel shell, and crab shell decreased the peak heat flow of the paste relative to the control by 13.7% (3.0 mW/g), 19.6% (2.8 mW/g), 20.7% (2.7 mW/g), and 23.7% (2.6 mW/g), respectively. However, the peak heat flow of the paste containing oyster shell demonstrated a 4.0% decrease (3.3 mW/g), and an increased rate of hydration was observed. This is likely attributed to the nucleation effect of the finer oyster shell particles (d 50 = 5.2 µm). Finer particles promote the precipitation of hydration products and increase the hydration degree of cement, resulting in more hydration heat released [ 36 , 37 ]. Her et al. [ 22 ] reported a similar effect as the cementitious pastes containing fine oyster shell powder exhibited an accelerated dissolution of C 3 S due to the increased specific surface area of the particles, compared to pastes containing traditional limestone filler. There is an initial spike followed by a large retardation of paste containing shrimp shell powder. Žižlavský et al. [ 38 ] also observed a pronounced initial reaction upon introducing water cement pastes containing biopolymers, followed by a less intense main hydration peak. The rapid increase may be linked to heat of wetting [ 39 ]. The retardation effect of the main cement hydration peak is attributed to the polysaccharidic structure, a result also common among other biopolymers [ 38 , 40 ]. Several mechanisms have been proposed to explain the effect, including the complex interactions between sugars and calcium ions. Furthermore, the retardation may be due to dispersion kinetics and electrostatic interactions cement of shrimp shell powder with cement particles [ 41 , 42 ]. Chitin, one of the primary components of the shell, may adhere to cement particles due to their high negative zeta potentials (less than − 30 mV) in DI water or pore solution pH levels [ 43 ]. As a result, the reaction surface area between cement and water is reduced, thereby delaying the rate of hydration. In addition, the free hydroxyl groups of chitin may form hydrogen bonds with water and cement, reducing the formation of hydration products [ 41 ]. Cumulative heat release results of the cementitious pastes are shown in Fig. 7 b. The pastes containing limestone, oyster shell, mussel shell, and eggshell powder had similar cumulative heat throughout the 7 days. Heat release values of these pastes ranged from 149–160, 214–224, and 257–264 J/g cementitious material at 1 d, 3 d, and 7 d, respectively. A decrease in cumulative heat was observed for crab shell paste at early ages, showing a 15.4% decrease in heat compared to limestone at 24 h. However, this difference decreased with time. Heat release of paste containing shrimp shell resulted in a reduction in heat release at all ages. After 7 days, the cumulative heat was measured as 192 J/g, exhibiting a 27% decrease relative to limestone filler. 3.2.2 Thermogravimetric analysis The amount of CH after curing for 7 and 28 days is shown in Fig. 8 . The amount was quantified using the mass loss determined via TGA. Dehydroxylation of CH occurs between 350 and 500°C. Due to the simultaneous degradation of chitin within this temperature range, the CH content of the shrimp shell paste was excluded from this analysis. At 7 days, CH content ranges from 13.0 g/100 g cementitious paste (crab shell) to 15.1 g/100 g cementitious paste (oyster shell). As shown in the figure, control paste had the greatest increase in CH content over the testing duration. At 28 days, CH content ranges from 14.4 g/100 g cementitious paste (limestone) to 16.1 g/100 g cementitious paste (control). From 7 to 28 days, the paste experienced a 17.8% increase in CH, whereas paste containing 20% limestone filler or shell powder exhibited a 7.5% increase, on average. This result aligns with other studies demonstrating an increase in CH content over time for control and limestone-containing specimens [ 44 ]. While the filler effect has some impacts on the hydration products of cementitious materials, the dilution effects is more evident [ 36 ] and the CH content is reduced with a higher replacement of cement. The CaCO 3 content at 7 and 28 days is shown in Figure S1 (Supplementary Material). As expected, a greater amount of CaCO 3 was evident at both testing ages in pastes containing 20% limestone or shell powders, relative to the control. At 28 days, the control paste had a CaCO 3 content of 10.4 g/100 g cementitious paste. Whereas the CaCO 3 content of the pastes containing CaCO 3 filler at 28 days varied from 17.6 g/100 g cementitious paste (shrimp shell) to 22.7 g/1000 g cementitious paste (eggshell). Over the curing period, the CaCO 3 content decreased on average by 3.7% in all samples, except for pastes containing limestone and oyster shell powder, which exhibited an average 0.5% increase. 3.3 Tests on mortar The reduced workability of the mortar mix containing shrimp shells required the use of a high range water reducing admixture (Sika® ViscoCrete®-2100). Due to the lack of workability even after significant amounts of admixture added (10% by weight of cementitious material), the mortar results are not presented for shrimp shells. Shrimp shells are not a feasible replacement for limestone filler or for cement based on the massive workability reduction. However, our findings suggest their potential as an alternative retarder, or other admixture in cementitious materials. 3.3.1 Flow table tests The flow table test results of the mortar mixes are presented in Table 3 , normalized to the PLC mortar values. Mortar containing 20% oyster shell and crab shell exhibited a flow value comparable to the control, measuring 100% of PLC for both. Limestone mortar demonstrated a small increase in flow relative to the control, 103%. Mussel shell mortar exhibited a significant increase in flow, 113%. In contrast, the flow of eggshell mortar was measured as 92%, indicating a significant decrease in flow. Differences in the rheological properties between the mortars containing various shell wastes may be associated with hydrophobicity of their components as well as particle size and morphology. Eggshell membrane—separating the mineralized eggshell from the egg white—is composed primarily of fibrous proteins, along with lipids and sugars [ 45 ]. The flow is likely reduced due to the hydrophobicity of the membrane protein, which leads to fewer interactions between particles and a less cohesive mix [ 46 ]. The high flow value attained for the mussel shell mortar may be attributed to morphology and particle size of mussel shell powder. SEM and laser diffraction of mussel shell powder revealed primarily large (d 50 = 25.6 µm), slender particles. Ballester et al. [ 47 ] reported a similar finding when substituting quarried limestone as fine aggregate with limestone derived from ground mussel shells. Mortars containing mussel shell limestone demonstrated improved workability, likely attributable to differences in particle morphology. The finer particles of quarried limestone promoted greater water adsorption, which in turn reduced workability. Table 3 Flow of the mortar mixtures. Mix Limestone Oyster Shell Mussel Shell Crab Shell Eggshell Flow (% PLC) 102.7 99.8 112.5 99.8 92.2 3.3.2 Bulk resistivity The bulk resistivity of the mortar specimens at 7 and 28 days of curing are shown in Fig. 9 . The bulk resistivity of all specimens increased with curing age. Resistivity increases as hydration products are formed and the pore structure of the composite becomes denser [ 48 ]. Mortar containing eggshell powder had the greatest bulk resistivity at both testing ages. At 28 days, the resistivity of eggshell and oyster shell specimens was significantly greater than the other samples ( p < 0.05), with mean values of 98.1 Ω-m and 82.1 Ω-m, respectively. The remaining specimens exhibited similar bulk resistivity measurements. Bulk resistivity is an indicator of transport properties and durability of a concrete mixture [ 49 , 50 ]. Unlike commonly utilized supplementary cementitious materials that achieve higher bulk resistivities with higher replacement levels, findings from previous studies have shown that addition of limestone filler does not increase bulk resistivity, even with changes to particle fineness [ 18 , 51 , 52 ]. Han et al.[ 13 ] found that mortar cylinders replacing 30% of cement with oyster shell powder had a slightly higher increase in surface resistivity over 28 days of curing, relative to the control. 3.3.3 Compressive strength The compressive strengths of the mortar specimens after 7 and 28 days of curing are presented in Fig. 10 . Replacing 20% cement in mortar with limestone or shell powder resulted in reduced strengths at both testing ages, relative to the control. The strength development of the samples varied depending on the raw material. The compressive strength development of the crab shell specimens was the lowest among all mortars, with only a 3% increase in strength between testing ages (7 day = 12.0 MPa, 28 day = 12.4 MPa). Incorporating 20% eggshell or oyster shell yielded compressive strengths similar to limestone after 28 days of curing ( p < 0.05). Mussel shell and crab shell are less effective as fillers. At 28 days, the mortar containing mussel shells and crab shells exhibited strength reductions of 35% and 56%, respectively, compared to the limestone specimens. Correlations between the properties of the shell powders and mortar with the 28-day compressive strength results were explored. The correlation between density and 28-day compressive strengths is shown in Fig. 11 . While there is limited data, there is a strong, positive relationship (R 2 = 0.86), indicating that strength increased with mortar density. These differences in density among the mortar specimens are likely due to morphology, size, and organic content of the various shell materials. Previous researchers have demonstrated that entrapped air caused by irregularly shaped shell waste, organic content, and poor packing density caused a reduction in composite density [ 11 , 12 , 53 ]. Moreover, these factors also contribute to strength reductions. Lertwattanaruk et al. [ 12 ] reported that larger-sized mussel shell powder resulted in a lower particle packing density and a considerably lower strength, relative to the control mortar. Figure 12 a shows a strong, positive correlation (R 2 = 0.77) between CaCO 3 content in the shell powder and the compressive strength. In contrast, a strong, inverse correlation (R 2 = 0.78) was evident among organic/other mass loss on the compressive strength, as shown in Fig. 12 b. These findings indicate that the composition of the shell powders may impact the compressive strength of the mortar. However, further testing is necessary to validate the specific mechanisms behind these effects. It is also worth noting that the relationship between shell composition and strength may be underpowered due to the limited number of data points. Moreover, one data point, that is the crab shell, with the lowest value, likely has a large impact on the correlations. These correlations demonstrate the feasibility of measuring CaCO 3 and organics/other content in other shell materials to evaluate their effect in cementitious materials. Similar correlations regarding compressive strength reductions due to the presence of organic matter are evident in literature [ 11 , 53 ]. Other factors that negatively impact strength are the higher absorption of the shell materials and the flaky or elongated shape, resulting in poor bonds with the cement paste. Additional specimens are recommended to validate these conclusions. When considering individual shells, the shrimp shells are not feasible due to their massive workability reduction, presumably as they are largely chitin and proteins. The organic phase in the crab shells is not evident, however, it seems to cause a substantial strength reduction. The mussel shells, while having a comparable amount of CaCO 3 to limestone, show a strength reduction, which may be due to the particle shape and size. Finally, the oyster shells and eggshells, show strength comparable to limestone, although the oyster shells are much finer than the eggshells. The eggshells could show even higher strengths if ground similar to limestone. 3.4 Limitations Several limitations are present in this study. In particular, shell composition is influenced by various factors. Individual shells may fluctuate in mineral/organic content based on species, gender, age, and environmental conditions. Furthermore, the shell waste received from the restaurants may have undergone different processing and cooking methods, potentially affecting shell properties. To gain a better understanding of how varying the replacement level of the waste shell materials affects the composite, further testing is recommended, such as testing at a similar particle size distribution/fineness. 4 Conclusions This study explored the feasibility of utilizing waste shell powders as alternatives to limestone filler in cementitious materials. Five different types of waste shell powders were compared to conventional limestone filler through a series of characterization and mechanical tests. The key findings of this study can be summarized as follows: The waste shell materials, including oyster shell, crab shell, mussel shell, eggshell, and shrimp shell, had median particles sizes of 5, 23, 26, 28, and 41 µm, respectively, as compared to 14 µm of the conventional limestone filler. The primary composition of the shells was calcium carbonate—exceeding 86% CaCO 3 content—except for shrimp shell, which contained 16% CaCO 3 . Characterization tests revealed that oyster shell, mussel shell, crab shell, and eggshell were nearly analogous to limestone filler. These materials were predominantly composed of calcite, while aragonite was also present in mussel shells. In contrast, chitin was the dominant component in shrimp shells. As expected, all materials were classified as inert due to low heat release values. Of the five shell materials, oyster shell, mussel shell, and eggshell exhibited hydration reactions most similar to limestone filler. Replacing 20% cement in mortar with limestone or shell powder resulted in reduced strengths at both testing ages, relative to the control. Incorporating eggshell or oyster shell powder yielded compressive strengths similar to limestone after 28 days of curing. Differences among compressive strength values were likely attributed to morphology, size, and chemical composition of the shell powders. These factors negatively impacted the composite density, leading to a reduction in strength. Moreover, higher CaCO 3 content improved the strength, whereas the presence of organic materials potentially contributed to a decrease. Declarations Prannoy Suraneni is Associate Editor of Materials and Structures. The authors declare no competing interests in this publication. Acknowledgements The authors acknowledge Nima Hosseinzadeh at Titan America for performing PSD and XRD measurements. The authors thank Sivakumar Ramanathan for providing additional guidance. The authors also thank The Lazy Oyster, Flanigan’s, and Joe’s Stone Crab for supplying waste shells. The Department of Defense National Defense Science and Engineering Graduate Fellowship (NDSEG) is thanked for partial salary support for Kylee Rux. References Tkachenko N, Tang K, McCarten M, Reece S, Kampmann D, Hickey C et al Global database of cement production assets and upstream suppliers. Sci Data 2023;10. https://doi.org/10.1038/s41597-023-02599-w Ruslan HN, Muthusamy K, Syed Mohsin SM, Jose R, Omar R (2021) Oyster shell waste as a concrete ingredient: A review. Mater Today Proc 48:713–719. https://doi.org/10.1016/j.matpr.2021.02.208 Bonavetti V, Donza H, Menéndez G, Cabrera O, Irassar EF (2003) Limestone filler cement in low w/c concrete: A rational use of energy. 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Constr Build Mater 162:751–764. https://doi.org/10.1016/j.conbuildmat.2017.12.009 Supplementary Files SupplementaryMaterial.docx Cite Share Download PDF Status: Published Journal Publication published 24 Oct, 2025 Read the published version in Materials and Structures → Version 1 posted Reviewers agreed at journal 10 Nov, 2024 Reviewers invited by journal 10 Nov, 2024 Editor invited by journal 22 Oct, 2024 Editor assigned by journal 19 Oct, 2024 First submitted to journal 16 Oct, 2024 You are reading this latest preprint version Research Square lets you share your work early, gain feedback from the community, and start making changes to your manuscript prior to peer review in a journal. As a division of Research Square Company, we’re committed to making research communication faster, fairer, and more useful. We do this by developing innovative software and high quality services for the global research community. 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Also discoverable on Platform About Our Team In Review Editorial Policies Advisory Board Help Center Resources Author Services Accessibility API Access RSS feed Manage Cookie Preferences © Research Square 2026 | ISSN 2693-5015 (online) Privacy Policy Terms of Service Do Not Sell My Personal Information {"props":{"pageProps":{"initialData":{"identity":"rs-5278623","acceptedTermsAndConditions":true,"allowDirectSubmit":false,"archivedVersions":[],"articleType":"Research Article","associatedPublications":[],"authors":[{"id":376242810,"identity":"817f15c3-2501-4bc2-a22f-e90bf42d3b87","order_by":0,"name":"Kylee Rux","email":"","orcid":"","institution":"University of Miami","correspondingAuthor":false,"prefix":"","firstName":"Kylee","middleName":"","lastName":"Rux","suffix":""},{"id":376242811,"identity":"68e0c364-62d8-401f-a880-3460edfadf35","order_by":1,"name":"Montale Tuen","email":"","orcid":"","institution":"University of Miami","correspondingAuthor":false,"prefix":"","firstName":"Montale","middleName":"","lastName":"Tuen","suffix":""},{"id":376242812,"identity":"b0595c3b-2388-414c-ba73-3dbb451f2388","order_by":2,"name":"Prannoy Suraneni","email":"data:image/png;base64,iVBORw0KGgoAAAANSUhEUgAAAZAAAAAyAQMAAABI0h/eAAAABlBMVEX///8AAABVwtN+AAAACXBIWXMAAA7EAAAOxAGVKw4bAAAA2klEQVRIiWNgGAWjYBADHgb2BoYDDAwSQHYCsVp4DpCoBagYrpKAFvkZuQ8/F1TckTGXfJ144GeOBQM/e44BXi0GN9KNpWececZjOTt3w8HebRIMkj1vCGiRSGOQ5m07zGNwO3fDAV6gFoMbBGyRn5HG/Jv3H1DLzbMbDv4FarEnpIXhRhqbNG8DUMsN3g2HwbZIEPLLmWds1jzHDvNY9uRuOCy7TYJH4syzAvwOa09jvs1Tc9jenP3s5o9vt9XJ8bcnb8DvMLh1UJqHOOXIWkbBKBgFo2AUYAAAEHlFd1HaFRkAAAAASUVORK5CYII=","orcid":"","institution":"University of Miami","correspondingAuthor":true,"prefix":"","firstName":"Prannoy","middleName":"","lastName":"Suraneni","suffix":""}],"badges":[],"createdAt":"2024-10-16 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11:14:09","extension":"png","order_by":2,"title":"Figure 2","display":"","copyAsset":false,"role":"figure","size":87251,"visible":true,"origin":"","legend":"\u003cp\u003eTGA-DTG curves of limestone and waste shell powders.\u003c/p\u003e","description":"","filename":"floatimage2.png","url":"https://assets-eu.researchsquare.com/files/rs-5278623/v1/4ca131e848d0e8c1586ba6f4.png"},{"id":70104881,"identity":"6926cd1d-07fb-48db-b076-234ee6451e37","added_by":"auto","created_at":"2024-11-28 11:14:09","extension":"png","order_by":3,"title":"Figure 3","display":"","copyAsset":false,"role":"figure","size":76585,"visible":true,"origin":"","legend":"\u003cp\u003eFTIR spectra results of limestone and waste shell powders.\u003c/p\u003e","description":"","filename":"floatimage3.png","url":"https://assets-eu.researchsquare.com/files/rs-5278623/v1/faa9e1c7c17d01857de2079a.png"},{"id":70105069,"identity":"3e4befad-843b-4577-8ed8-72a1e4d94b19","added_by":"auto","created_at":"2024-11-28 11:22:09","extension":"png","order_by":4,"title":"Figure 4","display":"","copyAsset":false,"role":"figure","size":56821,"visible":true,"origin":"","legend":"\u003cp\u003eXRD patterns of limestone and waste shell powders.\u003c/p\u003e","description":"","filename":"floatimage4.png","url":"https://assets-eu.researchsquare.com/files/rs-5278623/v1/15f27723990aeb4a45e35251.png"},{"id":70104884,"identity":"228081cc-e916-4aca-8a85-c3c67cccd157","added_by":"auto","created_at":"2024-11-28 11:14:09","extension":"png","order_by":5,"title":"Figure 5","display":"","copyAsset":false,"role":"figure","size":232276,"visible":true,"origin":"","legend":"\u003cp\u003eScanning electron micrographs of limestone and waste shell powders at magnification of 750x and inset images at magnification of 5000x.\u003c/p\u003e","description":"","filename":"floatimage5.png","url":"https://assets-eu.researchsquare.com/files/rs-5278623/v1/aa6a456c4037d4d34a58395b.png"},{"id":70104890,"identity":"99433677-c5e1-46fc-8ecc-13ecaa6de0f9","added_by":"auto","created_at":"2024-11-28 11:14:09","extension":"png","order_by":6,"title":"Figure 6","display":"","copyAsset":false,"role":"figure","size":70087,"visible":true,"origin":"","legend":"\u003cp\u003eHeat release results of limestone and waste shell powders.\u003c/p\u003e","description":"","filename":"floatimage6.png","url":"https://assets-eu.researchsquare.com/files/rs-5278623/v1/840ff4d0e89129a13aed1084.png"},{"id":70105070,"identity":"18ee894d-ed85-41cb-bba4-fa927157ee91","added_by":"auto","created_at":"2024-11-28 11:22:09","extension":"jpeg","order_by":7,"title":"Figure 7","display":"","copyAsset":false,"role":"figure","size":591057,"visible":true,"origin":"","legend":"\u003cp\u003e(a) Heat flow and (b) heat release results of cement paste containing limestone and waste shell powder at a 20% cement replacement.\u003c/p\u003e","description":"","filename":"floatimage7.jpeg","url":"https://assets-eu.researchsquare.com/files/rs-5278623/v1/e3477a8d4cb25e7e4d13f708.jpeg"},{"id":70104891,"identity":"07e2e3c1-3d89-475f-a63f-0d8822c7f009","added_by":"auto","created_at":"2024-11-28 11:14:09","extension":"png","order_by":8,"title":"Figure 8","display":"","copyAsset":false,"role":"figure","size":65885,"visible":true,"origin":"","legend":"\u003cp\u003eAmounts of calcium hydroxide in cement paste containing 20% limestone and waste shell powder at 20% cement replacement. Error bars indicate two standard deviations of mean.\u003c/p\u003e","description":"","filename":"floatimage8.png","url":"https://assets-eu.researchsquare.com/files/rs-5278623/v1/6fe32804aac0322979e7a8bc.png"},{"id":70105072,"identity":"14944b0d-f5ae-40a0-97cc-ed0414c77e5a","added_by":"auto","created_at":"2024-11-28 11:22:09","extension":"png","order_by":9,"title":"Figure 9","display":"","copyAsset":false,"role":"figure","size":94334,"visible":true,"origin":"","legend":"\u003cp\u003eBulk resistivity of mortars containing limestone and waste shells at a 20% cement replacement. Error bars indicate two standard deviations of the mean.\u003c/p\u003e","description":"","filename":"floatimage9.png","url":"https://assets-eu.researchsquare.com/files/rs-5278623/v1/6511612bc533e45833a78e41.png"},{"id":70105073,"identity":"6db21484-d221-4c8c-9ddc-3175b3e880c1","added_by":"auto","created_at":"2024-11-28 11:22:09","extension":"png","order_by":10,"title":"Figure 10","display":"","copyAsset":false,"role":"figure","size":92863,"visible":true,"origin":"","legend":"\u003cp\u003eCompressive strengths of mortars containing limestone and waste shells at a 20% cement replacement. Error bars indicate two standard deviations of the mean.\u003c/p\u003e","description":"","filename":"floatimage10.png","url":"https://assets-eu.researchsquare.com/files/rs-5278623/v1/00d962d34bed2e4d9cd2f691.png"},{"id":70104883,"identity":"b6f905a1-9e8f-4c3e-ab03-18f70c760bba","added_by":"auto","created_at":"2024-11-28 11:14:09","extension":"png","order_by":11,"title":"Figure 11","display":"","copyAsset":false,"role":"figure","size":52884,"visible":true,"origin":"","legend":"\u003cp\u003eCorrelation between density and compressive strength.\u003c/p\u003e","description":"","filename":"floatimage11.png","url":"https://assets-eu.researchsquare.com/files/rs-5278623/v1/da1e94bc2ccaedccbf1ea3a3.png"},{"id":70104888,"identity":"89b56963-2ba1-41e8-a9a8-2d0c691ec955","added_by":"auto","created_at":"2024-11-28 11:14:09","extension":"jpeg","order_by":12,"title":"Figure 12","display":"","copyAsset":false,"role":"figure","size":193470,"visible":true,"origin":"","legend":"\u003cp\u003e(a) Correlations between compressive strength and (a) CaCO\u003csub\u003e3\u003c/sub\u003e content and (b) organics/other mass loss in waste shell powder.\u003c/p\u003e","description":"","filename":"floatimage12.jpeg","url":"https://assets-eu.researchsquare.com/files/rs-5278623/v1/7c1c0cd533a9324d9719cf1e.jpeg"},{"id":94490209,"identity":"454741e6-9805-463d-869d-c5c6d7a9d85e","added_by":"auto","created_at":"2025-10-27 17:08:11","extension":"pdf","order_by":0,"title":"","display":"","copyAsset":false,"role":"manuscript-pdf","size":2591792,"visible":true,"origin":"","legend":"","description":"","filename":"manuscript.pdf","url":"https://assets-eu.researchsquare.com/files/rs-5278623/v1/f6ad97de-a782-4c53-b9ec-e6f86c61e940.pdf"},{"id":70105071,"identity":"b2c282d1-d291-4306-a2b1-5ee326bae36b","added_by":"auto","created_at":"2024-11-28 11:22:09","extension":"docx","order_by":1,"title":"","display":"","copyAsset":false,"role":"supplement","size":297531,"visible":true,"origin":"","legend":"","description":"","filename":"SupplementaryMaterial.docx","url":"https://assets-eu.researchsquare.com/files/rs-5278623/v1/7452190f8c7be7be60eb32e2.docx"}],"financialInterests":"","formattedTitle":"Utilization of Common Shell Wastes as a Limestone Alternative in Cementitious Materials","fulltext":[{"header":"1 Introduction","content":"\u003cp\u003eApproximately 4.1\u0026nbsp;billion metric tons of cement are produced globally every year, accounting for over 7% of global anthropogenic greenhouse gas emissions [\u003cspan citationid=\"CR1\" class=\"CitationRef\"\u003e1\u003c/span\u003e]. Cement demand is expected to increase as a result of rapid urbanization and economic development [\u003cspan citationid=\"CR2\" class=\"CitationRef\"\u003e2\u003c/span\u003e]. Efforts to reduce the environmental impact of the cement industry have motivated the use of fillers. Limestone filler\u0026mdash;composed of calcium carbonate (CaCO\u003csub\u003e3\u003c/sub\u003e)\u0026mdash;has been widely studied as a partial replacement for cement, offering technical, economic, and environmental advantages [\u003cspan citationid=\"CR3\" class=\"CitationRef\"\u003e3\u003c/span\u003e]. While this technique mitigates carbon emissions, the mining and processing of raw limestone continues to present environmental challenges [\u003cspan citationid=\"CR4\" class=\"CitationRef\"\u003e4\u003c/span\u003e]. Researchers have begun exploring alternative materials analogous to limestone, including waste food shells.\u003c/p\u003e \u003cp\u003eAquaculture is a sustainable food source, with bivalve production in particular having more than tripled in the past thirty years [\u003cspan citationid=\"CR5\" class=\"CitationRef\"\u003e5\u003c/span\u003e]. Every year, approximately 7\u0026nbsp;million tons of oyster, clam, scallop, and mussel shells are generated globally [\u003cspan citationid=\"CR6\" class=\"CitationRef\"\u003e6\u003c/span\u003e]. Additionally, 8\u0026nbsp;million tons of waste crab, shrimp, and lobster shells are produced. Poultry eggs are also a major industry due to their high-quality protein content, with nearly 8.6\u0026nbsp;million tons of eggshells discarded annually [\u003cspan citationid=\"CR7\" class=\"CitationRef\"\u003e7\u003c/span\u003e, \u003cspan citationid=\"CR8\" class=\"CitationRef\"\u003e8\u003c/span\u003e]. Increased reliance on aquaculture, poultry, and other shell waste producing industries is essential to achieve global food security [\u003cspan citationid=\"CR9\" class=\"CitationRef\"\u003e9\u003c/span\u003e]. However, higher waste production has presented the difficulties of managing shell waste that has detrimental environmental impacts,\u003c/p\u003e \u003cp\u003eWaste shells are often discarded in landfills or at sea where they cause soil and water pollution, including the release of stored carbon into the environment [\u003cspan citationid=\"CR5\" class=\"CitationRef\"\u003e5\u003c/span\u003e, \u003cspan citationid=\"CR6\" class=\"CitationRef\"\u003e6\u003c/span\u003e]. The disposal of eggshells also contributes to environmental concerns with their waste ranked as the fifteenth major food industry pollution problem by the Environmental Protection Agency [\u003cspan citationid=\"CR7\" class=\"CitationRef\"\u003e7\u003c/span\u003e]. As landfills approach capacity, exploring other disposal methods, such as reuse, becomes increasingly crucial. Utilizing these CaCO\u003csub\u003e3\u003c/sub\u003e-rich waste shells as an alternative to limestone can divert shell waste from landfills and the natural environment, lessen global raw limestone extraction, and reduce cement demand.\u003c/p\u003e \u003cp\u003eVarious shell wastes have been employed in cementitious materials as fine or coarse aggregate replacement [\u003cspan citationid=\"CR2\" class=\"CitationRef\"\u003e2\u003c/span\u003e, \u003cspan citationid=\"CR10\" class=\"CitationRef\"\u003e10\u003c/span\u003e, \u003cspan citationid=\"CR11\" class=\"CitationRef\"\u003e11\u003c/span\u003e]. Previous studies have also investigated their potential as substitutes for limestone. Lertwattanaruk et al. [\u003cspan citationid=\"CR12\" class=\"CitationRef\"\u003e12\u003c/span\u003e] evaluated the effect of various waste seashells, oyster, mussel, clam, and cockle, as binder replacements in cement plastering applications. Mortar containing ground mussel shell led to lower compressive strength than the other shells tested. This reduction in strength was attributed to the relatively larger particle size of mussel shells compared to Portland cement, resulting in a lower particle packing density. Han et al. [\u003cspan citationid=\"CR13\" class=\"CitationRef\"\u003e13\u003c/span\u003e] reported that partially replacing cement with oyster shell powder accelerated the rate of cement hydration due to dilution and nucleation effects. However, these early-age acceleration effects combined with low initial reactivity of the powder, resulted in a reduction in the hydration products, negatively impacting the development of compressive strength. Other researchers have utilized eggshell powder as a partial substitute for cement. Several studies recommend the incorporation of eggshell powder at lower replacements (5\u0026ndash;15%) to achieve better mechanical performance [\u003cspan additionalcitationids=\"CR15\" citationid=\"CR14\" class=\"CitationRef\"\u003e14\u003c/span\u003e\u0026ndash;\u003cspan citationid=\"CR16\" class=\"CitationRef\"\u003e16\u003c/span\u003e]. Factors affecting reduction in strengths at higher proportions include dilution of cement, higher matrix porosity, and eggshell powder size [\u003cspan citationid=\"CR17\" class=\"CitationRef\"\u003e17\u003c/span\u003e].\u003c/p\u003e \u003cp\u003eWhile previous studies have explored the effects of waste shells as cement replacement, critical gaps remain regarding their use in civil engineering applications. First, there are limited studies examining the impact of uncalcined shell powder as cement replacement. In particular, the performance of mortar containing crab shell and shrimp shell powder has not been extensively researched. Further investigations are also necessary to better interpret the effect of shell powder materials on paste microstructure. Ultimately, a thorough comparison of various CaCO\u003csub\u003e3\u003c/sub\u003e-rich materials that could serve as substitutes for traditional limestone filler in cementitious composites is needed.\u003c/p\u003e \u003cp\u003eThis study aims to assess the feasibility of using waste shell powders as alternatives to limestone filler in cementitious materials. Five shell types\u0026mdash;oyster, mussel, crab, shrimp, and eggshells\u0026mdash;were collected and pulverized. Shell powders were characterized using thermogravimetric analysis (TGA), Fourier transform infrared spectroscopy (FTIR), X-ray diffraction (XRD), scanning electron microscopy (SEM), and the modified R\u003csup\u003e3\u003c/sup\u003e test. Early-age hydration kinetics were analyzed via isothermal calorimetry. Furthermore, mortar flow, compressive strength development, and bulk resistivity were investigated.\u003c/p\u003e"},{"header":"2 Materials and Methods","content":"\u003cdiv id=\"Sec3\" class=\"Section2\"\u003e \u003ch2\u003e2.1 Materials\u003c/h2\u003e \u003cp\u003eWaste shells utilized in this study were obtained from various Miami-area restaurants. Shells included oyster shells (\u003cem\u003eCrassostrea viginica\u003c/em\u003e), mussel shells (\u003cem\u003eMytilus edulis\u003c/em\u003e), stone crab shells (\u003cem\u003eMenippe mercenaria\u003c/em\u003e, \u003cem\u003eMenippe adina\u003c/em\u003e), shrimp shells (\u003cem\u003eLitopenaeus vannamei\u003c/em\u003e), and poultry eggshells. While crab shell is primarily composed of shell and legs, this study specifically used the legs of the stone crab. The entire shell was used for all other materials. Shells were cleaned using water and a nylon brush to remove any surface residue. Subsequently, shells were dried in an oven at 105\u0026thinsp;\u0026plusmn;\u0026thinsp;5\u0026deg;C for 24 h to remove moisture. Shells were ground into powder and passed through a 45 \u0026micro;m sieve. Microna 10 limestone from Columbia River Carbonates was used as a traditional inert filler. A commercially available Portland limestone cement (PLC) was used containing 12% limestone. The particle size distributions and median particle sizes of the shell powders, limestone, and PLC are shown in Fig.\u0026nbsp;\u003cspan refid=\"Fig1\" class=\"InternalRef\"\u003e1\u003c/span\u003e and Table\u0026nbsp;\u003cspan refid=\"Tab1\" class=\"InternalRef\"\u003e1\u003c/span\u003e, respectively. Particle size distribution was measured on dry powders using particle refractive index of 1.60 and absorption coefficient 0.1. Each PSD measurement was performed four times and averaged values are reported. For the preparation of mortar, silica sand was used as fine aggregate.\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003cp\u003e \u003cdiv class=\"gridtable\"\u003e\u003ctable float=\"Yes\" id=\"Tab1\" border=\"1\"\u003e \u003ccaption language=\"En\"\u003e \u003cdiv class=\"CaptionNumber\"\u003eTable 1\u003c/div\u003e \u003cdiv class=\"CaptionContent\"\u003e \u003cp\u003eMedian particle size of shell powders, limestone, and PLC.\u003c/p\u003e \u003c/div\u003e \u003c/caption\u003e \u003ccolgroup cols=\"8\"\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c1\" colnum=\"1\"\u003e\u003c/div\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c2\" colnum=\"2\"\u003e\u003c/div\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c3\" colnum=\"3\"\u003e\u003c/div\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c4\" colnum=\"4\"\u003e\u003c/div\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c5\" colnum=\"5\"\u003e\u003c/div\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c6\" colnum=\"6\"\u003e\u003c/div\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c7\" colnum=\"7\"\u003e\u003c/div\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c8\" colnum=\"8\"\u003e\u003c/div\u003e \u003cthead\u003e \u003ctr\u003e \u003cth align=\"left\" colname=\"c1\"\u003e \u003cp\u003ePowder\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c2\"\u003e \u003cp\u003ePLC\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c3\"\u003e \u003cp\u003eLimestone\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c4\"\u003e \u003cp\u003eOyster Shell\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c5\"\u003e \u003cp\u003eMussel Shell\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c6\"\u003e \u003cp\u003eCrab Shell\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c7\"\u003e \u003cp\u003eShrimp Shell\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c8\"\u003e \u003cp\u003eEggshell\u003c/p\u003e \u003c/th\u003e \u003c/tr\u003e \u003c/thead\u003e \u003ctbody\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003ed\u003csub\u003e50\u003c/sub\u003e (\u0026micro;m)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e8.6\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e14.1\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e5.2\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e \u003cp\u003e25.6\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c6\"\u003e \u003cp\u003e23.5\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c7\"\u003e \u003cp\u003e40.7\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c8\"\u003e \u003cp\u003e28.2\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003c/tbody\u003e \u003c/colgroup\u003e \u003c/table\u003e\u003c/div\u003e \u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec4\" class=\"Section2\"\u003e \u003ch2\u003e2.2 Characterization of shell waste\u003c/h2\u003e \u003cp\u003eThe powders were characterized using TGA, FTIR, XRD, SEM, and the modified R\u003csup\u003e3\u003c/sup\u003e test. A total of 35\u0026thinsp;\u0026plusmn;\u0026thinsp;5 mg powder was placed in a platinum pan. The thermal analysis system was heated from room temperature to 1000\u0026deg;C at a rate of 10\u0026deg;C/min within an inert nitrogen atmosphere. The mass loss corresponding to water, organics/other, and CaCO\u003csub\u003e3\u003c/sub\u003e was quantified.\u003c/p\u003e \u003cp\u003eFTIR spectra was measured for the powders using an FTIR spectrometer. Powders were placed on the top-plate of the instrument, covering the sensor entirely. The gauged pressure arm was adjusted tightly atop the powder. Spectra were collected from 4000 to 500 cm\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e. The analysis range was reduced to 1800 to 600 cm\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e to minimize noise. The transmittance strength and wavenumber location of each sample was recorded.\u003c/p\u003e \u003cp\u003eThe crystalline phases in the powder were identified via XRD analysis. Powder was filled into the sample holder and the surface was manually flattened. Scans were performed in the 2θ range of 8\u0026ndash;65\u0026deg; using a copper x-ray source producing CuKα radiation (λ\u0026thinsp;=\u0026thinsp;1.5418 \u0026Aring;). Peaks were identified using X\u0026rsquo;pert HighScore Plus.\u003c/p\u003e \u003cp\u003eHigh resolution images of the powder were obtained using field emission scanning electron microscopy. A thin layer of powder was fixed onto carbon fiber tape. A layer of carbon was sputtered on the surface to aid in electron conduction. An acceleration voltage of 2-10kV was applied with a working distance of 9.3\u0026ndash;9.8 mm.\u003c/p\u003e \u003cp\u003eThe reactivity of the powders was assessed using the modified R\u003csup\u003e3\u003c/sup\u003e test. Six grams of laboratory grade calcium hydroxide was combined with two grams of shell powder and dry mixed by hand for 4 min. A 0.5 M potassium hydroxide solution was then added to achieve a final liquid-to-solid ratio of 0.9. After an additional 4 min of mixing, approximately 6\u0026ndash;7 g of the mixture was inserted into a glass ampoule and sealed. The ampoule was placed in the preconditioned 50\u0026deg;C isothermal calorimeter. The heat flow and heat release were measured for 72 hours.\u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec5\" class=\"Section2\"\u003e \u003ch2\u003e2.3 Tests on cementitious pastes\u003c/h2\u003e \u003cp\u003eThe hydration heat evolution was investigated via isothermal calorimetry. Shell powder was mixed with PLC at a 20% replacement, resulting in a mixture of 2 g shell powder and 8 g PLC. A paste was prepared using a water-to-cementitious material (w/cm) ratio of 0.40. The paste was mixed for 4 min, after which, about 6\u0026ndash;7 g was inserted into a glass ampoule and sealed. The ampoule was lowered into an isothermal calorimeter preconditioned at 23\u0026deg;C. Heat flow and heat release data were obtained for 7 days.\u003c/p\u003e \u003cp\u003eTGA was performed immediately following the removal of the cement paste samples from the calorimeter to quantify calcium hydroxide and calcium carbonate content at 7 days. Half of the cement paste sample was ground into a fine powder using a mortar and pestle. Approximately 35 mg of powder was placed in a platinum pan, loaded into the TGA, and heated to 1000\u0026deg;C. The calcium hydroxide (CH) and CaCO\u003csub\u003e3\u003c/sub\u003e contents were determined based on the mass loss between approximately 350\u0026ndash;500\u0026deg;C and 500\u0026ndash;750\u0026deg;C, respectively [\u003cspan citationid=\"CR18\" class=\"CitationRef\"\u003e18\u003c/span\u003e, \u003cspan citationid=\"CR19\" class=\"CitationRef\"\u003e19\u003c/span\u003e]. The remaining half of the sample was stored in an air-tight container and subjected to TGA at 28 days.\u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec6\" class=\"Section2\"\u003e \u003ch2\u003e2.4 Tests on mortar\u003c/h2\u003e \u003cp\u003eSeven mortar mixtures were cast to compare the five different shell powders, traditional limestone filler, and a control. Mortar specimens were prepared using a fixed w/cm ratio of 0.40 and a sand-to-cementitious material ratio of 2.75. Shell powder or limestone filler replaced PLC at a 20% mass replacement. PLC and shell powder were premixed by-hand for 60s to achieve homogenous blending. The components were then mixed in a mechanical mixer for four minutes per ASTM 305, and the mixed mortar was cast into 2x2 in plastic cube molds [\u003cspan citationid=\"CR20\" class=\"CitationRef\"\u003e20\u003c/span\u003e]. The specimens were demolded after 24 h and cured in a moist room (\u0026gt;\u0026thinsp;95% humidity, 23\u0026deg;C) until the test age. Flow table tests were also performed in accordance with ASTM C1437 [\u003cspan citationid=\"CR21\" class=\"CitationRef\"\u003e21\u003c/span\u003e]. The mold was filled with mortar and compacted. After the mold was removed, the table was dropped 25 times over a span of 15 s. Three measurements of the mortar base diameter were recorded.\u003c/p\u003e \u003cp\u003eMass, dimensions, bulk resistivity, and compressive strength measurements were recorded after 7 and 28 days. Mortar cubes were removed from the moist room, surface-dried, and subjected to bulk resistivity tests using a resistivity meter at a frequency of 1 kHz. A total of three replicates were tested per mix at each testing age. Corrections for sample size and dimensions were accounted for. Specimens were then subjected to compression until failure using a mechanical testing machine. Three replicate samples were tested for each mixture.\u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec7\" class=\"Section2\"\u003e \u003ch2\u003e2.5 Data analysis\u003c/h2\u003e \u003cp\u003eAll statistical analyses were completed in Minitab. The criteria for statistical significance was set a priori to 0.05. One-factor ANOVA was performed to evaluate the bulk resistivity and mortar test results among the various mixture types. Regression analysis tested the effects of density and shell powder composition on the resulting compressive strength of the specimens.\u003c/p\u003e \u003c/div\u003e"},{"header":"3 Results and Discussion","content":"\u003cdiv id=\"Sec9\" class=\"Section2\"\u003e \u003ch2\u003e3.1 Characterization of shell waste\u003c/h2\u003e \u003cdiv id=\"Sec10\" class=\"Section3\"\u003e \u003ch2\u003e3.1.1 Thermogravimetric analysis\u003c/h2\u003e \u003cp\u003eTGA-DTG analysis of the raw shell powders revealed three distinct mass loss events, as shown in Fig.\u0026nbsp;2. The initial weight loss, from 23 to about 120 \u0026deg;C corresponds to the vaporization of water. In all materials except the shrimp shell, this value was less than 2%. Over a wide range of temperatures, from about 150 to 500 \u0026deg;C, the weight loss is attributed to the decomposition of organic matter. Trace amounts of other inorganics could also have contributed to this mass loss, but other tests performed did not find any evidence for such phases. The main weight loss for most of the powders is due to the decomposition of calcium carbonate to calcium oxide. The decomposition temperature range and quantification of H\u003csub\u003e2\u003c/sub\u003eO, organics, and CaCO\u003csub\u003e3\u003c/sub\u003e in limestone and shell powders is shown in Table\u0026nbsp;\u003cspan refid=\"Tab2\" class=\"InternalRef\"\u003e2\u003c/span\u003e. Oyster shell, mussel shell, and eggshell had similar amounts of CaCO\u003csub\u003e3\u003c/sub\u003e to that of the limestone filler (\u0026gt;\u0026thinsp;94%); these materials have less than 5% mass loss due to organics or other phases. The CaCO\u003csub\u003e3\u003c/sub\u003e content and mass loss due to organics in crab shell was 86% and 12%, respectively. The difference in initial CaCO\u003csub\u003e3\u003c/sub\u003e decomposition temperature in the shell powders compared to limestone is likely due to the presence of inorganics in the shells, variations in crystallinity, changes in particle size, and differences in amounts of powder tested [\u003cspan citationid=\"CR22\" class=\"CitationRef\"\u003e22\u003c/span\u003e]. Unlike other materials, the primary weight loss for shrimp shell powder is associated with the degradation of chitin\u0026mdash;a linear amino polysaccharide\u0026mdash;and animal or vegetable protein [\u003cspan citationid=\"CR23\" class=\"CitationRef\"\u003e23\u003c/span\u003e]. Chitin and protein degradation accounted for 69% of the mass loss, while 16% was associated with CaCO\u003csub\u003e3\u003c/sub\u003e content. P\u0026eacute;rez et al. [\u003cspan citationid=\"CR23\" class=\"CitationRef\"\u003e23\u003c/span\u003e] reported similar mass loss values for raw, dried shrimp shell that included vaporization of water (14%), chitin and protein degradation (60%), and CaCO\u003csub\u003e3\u003c/sub\u003e content (12%).\u003c/p\u003e \u003cp\u003e \u003cdiv class=\"gridtable\"\u003e\u003ctable float=\"Yes\" id=\"Tab2\" border=\"1\"\u003e \u003ccaption language=\"En\"\u003e \u003cdiv class=\"CaptionNumber\"\u003eTable 2\u003c/div\u003e \u003cdiv class=\"CaptionContent\"\u003e \u003cp\u003eDecomposition temperatures and amounts of H\u003csub\u003e2\u003c/sub\u003eO and CaCO\u003csub\u003e3\u003c/sub\u003e of limestone and shell powders. For organics/other, the mass loss is given, but amounts are not computed, as the exact phase is not known.\u003c/p\u003e \u003c/div\u003e \u003c/caption\u003e \u003ccolgroup cols=\"7\"\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c1\" colnum=\"1\"\u003e\u003c/div\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c2\" colnum=\"2\"\u003e\u003c/div\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c3\" colnum=\"3\"\u003e\u003c/div\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c4\" colnum=\"4\"\u003e\u003c/div\u003e \u003cdiv align=\"char\" char=\".\" class=\"colspec\" colname=\"c5\" colnum=\"5\"\u003e\u003c/div\u003e \u003cdiv align=\"char\" char=\".\" class=\"colspec\" colname=\"c6\" colnum=\"6\"\u003e\u003c/div\u003e \u003cdiv align=\"char\" char=\".\" class=\"colspec\" colname=\"c7\" colnum=\"7\"\u003e\u003c/div\u003e \u003cthead\u003e \u003ctr\u003e \u003cth align=\"left\" colname=\"c1\" morerows=\"1\" rowspan=\"2\"\u003e \u003cp\u003eMaterial\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colspan=\"3\" nameend=\"c4\" namest=\"c2\"\u003e \u003cp\u003eDecomposition Range (\u0026deg;C)\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colspan=\"3\" nameend=\"c7\" namest=\"c5\"\u003e \u003cp\u003eWeight (%)\u003c/p\u003e \u003c/th\u003e \u003c/tr\u003e \u003ctr\u003e \u003cth align=\"left\" colname=\"c2\"\u003e \u003cp\u003eH\u003csub\u003e2\u003c/sub\u003eO\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c3\"\u003e \u003cp\u003eOrganics/\u003c/p\u003e \u003cp\u003eother\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c4\"\u003e \u003cp\u003eCaCO\u003csub\u003e3\u003c/sub\u003e\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c5\"\u003e \u003cp\u003eH\u003csub\u003e2\u003c/sub\u003eO\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c6\"\u003e \u003cp\u003eOrganics/\u003c/p\u003e \u003cp\u003eother\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c7\"\u003e \u003cp\u003eCaCO\u003csub\u003e3\u003c/sub\u003e\u003c/p\u003e \u003c/th\u003e \u003c/tr\u003e \u003c/thead\u003e \u003ctbody\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eLimestone\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e23\u0026ndash;105\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e-\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e535\u0026ndash;800\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c5\"\u003e \u003cp\u003e0.0\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c6\"\u003e \u003cp\u003e0.9\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c7\"\u003e \u003cp\u003e99.1\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eOyster Shell\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e23\u0026ndash;105\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e190\u0026ndash;500\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e520\u0026ndash;775\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c5\"\u003e \u003cp\u003e0.4\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c6\"\u003e \u003cp\u003e2.7\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c7\"\u003e \u003cp\u003e97.0\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eMussel Shell\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e23\u0026ndash;120\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e185\u0026ndash;490\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e550\u0026ndash;740\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c5\"\u003e \u003cp\u003e0.5\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c6\"\u003e \u003cp\u003e3.5\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c7\"\u003e \u003cp\u003e96.0\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eCrab Shell\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e23\u0026ndash;105\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e155\u0026ndash;520\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e550\u0026ndash;725\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c5\"\u003e \u003cp\u003e1.8\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c6\"\u003e \u003cp\u003e12.1\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c7\"\u003e \u003cp\u003e86.1\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eShrimp Shell\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e23\u0026ndash;140\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e145\u0026ndash;555\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e580\u0026ndash;735\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c5\"\u003e \u003cp\u003e14.0\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c6\"\u003e \u003cp\u003e69.4\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c7\"\u003e \u003cp\u003e16.5\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eEggshell\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e23\u0026ndash;110\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e200\u0026ndash;490\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e580\u0026ndash;795\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c5\"\u003e \u003cp\u003e0.8\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c6\"\u003e \u003cp\u003e4.3\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c7\"\u003e \u003cp\u003e94.9\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003c/tbody\u003e \u003c/colgroup\u003e \u003c/table\u003e\u003c/div\u003e \u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec11\" class=\"Section3\"\u003e \u003ch2\u003e3.1.2 Fourier transform infrared spectroscopy\u003c/h2\u003e \u003cp\u003eThe FTIR spectra of limestone filler and waste shell powders are shown in Fig.\u0026nbsp;\u003cspan refid=\"Fig2\" class=\"InternalRef\"\u003e3\u003c/span\u003e. The patterns of oyster shell, mussel shell, crab shell, eggshell, and limestone are characteristic of CaCO\u003csub\u003e3\u003c/sub\u003e, particularly calcite [\u003cspan citationid=\"CR24\" class=\"CitationRef\"\u003e24\u003c/span\u003e, \u003cspan citationid=\"CR25\" class=\"CitationRef\"\u003e25\u003c/span\u003e], consistent with TGA results. The peak at ~\u0026thinsp;1410 cm\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e is due to C-O stretching. The band at ~\u0026thinsp;875 cm\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e corresponds to in-plane bending of CO\u003csub\u003e3\u003c/sub\u003e\u003csup\u003e2\u0026minus;\u003c/sup\u003e. The peak at ~\u0026thinsp;712 cm\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e is associated with Ca-O stretching. Mussel shell also exhibits peaks of aragonite. Carbonate out-of-bend vibration at 860 cm\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e and the peak at 1445 cm\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e both correspond to aragonite [\u003cspan citationid=\"CR26\" class=\"CitationRef\"\u003e26\u003c/span\u003e].\u003c/p\u003e \u003cp\u003eThe FTIR spectrum for shrimp shell powder shows the presence of various functional groups, aligning with previous literature analyzing untreated shrimp shell that underwent a similar processing procedure [\u003cspan citationid=\"CR27\" class=\"CitationRef\"\u003e27\u003c/span\u003e, \u003cspan citationid=\"CR28\" class=\"CitationRef\"\u003e28\u003c/span\u003e]. The characteristic peaks of chitin at 1633 cm\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e and 1031 cm\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e corresponds to C\u0026thinsp;=\u0026thinsp;O amide stretching (amide I) and CO stretching, respectively. The absorption band at 1403 cm\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e identifies as CH\u003csub\u003e3\u003c/sub\u003e bending and CH\u003csub\u003e2\u003c/sub\u003e deformation. The absorption peak at 1531 cm\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e confirms the stretching vibration of protein [\u003cspan citationid=\"CR29\" class=\"CitationRef\"\u003e29\u003c/span\u003e]. Furthermore, the stretching and bending vibrations of calcite are apparent at 1410 cm\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e and 874 cm\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e [\u003cspan citationid=\"CR27\" class=\"CitationRef\"\u003e27\u003c/span\u003e].\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec12\" class=\"Section3\"\u003e \u003ch2\u003e3.1.3 X-Ray diffraction analysis\u003c/h2\u003e \u003cp\u003eXRD patterns of limestone filler and waste shell powders are shown in Fig.\u0026nbsp;\u003cspan refid=\"Fig3\" class=\"InternalRef\"\u003e4\u003c/span\u003e. The major diffraction peaks of CaCO\u003csub\u003e3\u003c/sub\u003e and chitin are identified. All waste shell powders, except for shrimp shell, were nearly analogous to limestone filler, consistent with TGA and FTIR results. The oyster shell, mussel shell, crab shell, and eggshell powders were predominantly composed of calcite. The main calcite peaks observed in the spectra occur at 24.3, 29.3, 36.0, 39.4, 43.1, 47.5, and 48.5 2θ.\u003c/p\u003e \u003cp\u003eThe results revealed that aragonite was also present in mussel shells. Recorded reflections were at 2θ positions 26.3, 27.3, 33.2, 38.0, 38.7, 45.9, 50.3, 52.5, and 53.0. As expected, chitin is the main component found in shrimp shells. Two main diffraction peaks at 9.7, 19.6, and weak diffraction peaks at 12.0, 23.4, and 26.9 2θ were observed. These diffraction peaks align with previous studies, indicating the crystalline structure of α-chitin, the most common and stable form of chitin [\u003cspan citationid=\"CR27\" class=\"CitationRef\"\u003e27\u003c/span\u003e, \u003cspan citationid=\"CR30\" class=\"CitationRef\"\u003e30\u003c/span\u003e, \u003cspan citationid=\"CR31\" class=\"CitationRef\"\u003e31\u003c/span\u003e]. Calcite peaks were also detected in the shrimp shell, appearing at the same positions on the spectra as the other shell powders.\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec13\" class=\"Section3\"\u003e \u003ch2\u003e3.1.4 Scanning electron microscopy\u003c/h2\u003e \u003cp\u003eThe micrographs of the limestone and waste shell powders are shown in Fig.\u0026nbsp;\u003cspan refid=\"Fig4\" class=\"InternalRef\"\u003e5\u003c/span\u003e. The morphologies of the waste shells exhibited irregularly shaped, multi-angular, and various sized particles. The prismatic and foliate morphology resembles that of calcite. At magnification 750x, the morphology of the eggshell powder was comparable to limestone filler. Eggshell powder also contains porous fibril structures that make up the eggshell membrane [\u003cspan citationid=\"CR32\" class=\"CitationRef\"\u003e32\u003c/span\u003e]. Mussel shell powder exhibited primarily flaky, needle-like structures. The rough surface of the shrimp shell is associated with chitin, likely attributed to proteins, minerals, and the highly packed structured with inter or intramolecular hydrogen bonds [\u003cspan citationid=\"CR33\" class=\"CitationRef\"\u003e33\u003c/span\u003e]. The particle sizes of the shell powders shown in the images validate the results of the particle size distribution measurements.\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec14\" class=\"Section3\"\u003e \u003ch2\u003e3.1.5 Modified R\u003csup\u003e3\u003c/sup\u003e test\u003c/h2\u003e \u003cp\u003eThe heat release curves of limestone and waste shell powders are shown in Fig.\u0026nbsp;\u003cspan refid=\"Fig5\" class=\"InternalRef\"\u003e6\u003c/span\u003e. Crab shells exhibited the highest heat release throughout the experiment. At the end of 3 days, crab shell measured the highest heat release at 36.5 J/g, nearly 2.65-fold greater than limestone (14.9 J/g). Shrimp shell, eggshell, and mussel shell followed with final heat release values of 39.0 J/g, 24.3 J/g, and 21.9 J/g, respectively. The heat release curve of oyster shell was similar to limestone with 13.2 J/g heat release. As expected, the materials exhibited low heat release values throughout the duration of the test. All materials are characterized as inert due to low heat release values, \u0026lt; 100 J/g SCM [\u003cspan citationid=\"CR34\" class=\"CitationRef\"\u003e34\u003c/span\u003e]. The coefficient of variability of these values from testing in the lab is less than 3% [\u003cspan citationid=\"CR35\" class=\"CitationRef\"\u003e35\u003c/span\u003e].\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003c/div\u003e \u003c/div\u003e \u003cdiv id=\"Sec15\" class=\"Section2\"\u003e \u003ch2\u003e3.2 Tests on cementitious pastes\u003c/h2\u003e \u003cdiv id=\"Sec16\" class=\"Section3\"\u003e \u003ch2\u003e3.2.1 Isothermal calorimetry\u003c/h2\u003e \u003cp\u003eThe heat flow results for the pastes containing 20% limestone and waste shell powders are shown in Fig.\u0026nbsp;\u003cspan refid=\"Fig6\" class=\"InternalRef\"\u003e7\u003c/span\u003ea. Of the five shell materials, oyster shell, mussel shell, and eggshell exhibited hydration reactions most similar to the limestone filler. As expected, the incorporation of limestone, eggshell, mussel shell, and crab shell decreased the peak heat flow of the paste relative to the control by 13.7% (3.0 mW/g), 19.6% (2.8 mW/g), 20.7% (2.7 mW/g), and 23.7% (2.6 mW/g), respectively. However, the peak heat flow of the paste containing oyster shell demonstrated a 4.0% decrease (3.3 mW/g), and an increased rate of hydration was observed. This is likely attributed to the nucleation effect of the finer oyster shell particles (d\u003csub\u003e50\u003c/sub\u003e\u0026thinsp;=\u0026thinsp;5.2 \u0026micro;m). Finer particles promote the precipitation of hydration products and increase the hydration degree of cement, resulting in more hydration heat released [\u003cspan citationid=\"CR36\" class=\"CitationRef\"\u003e36\u003c/span\u003e, \u003cspan citationid=\"CR37\" class=\"CitationRef\"\u003e37\u003c/span\u003e]. Her et al. [\u003cspan citationid=\"CR22\" class=\"CitationRef\"\u003e22\u003c/span\u003e] reported a similar effect as the cementitious pastes containing fine oyster shell powder exhibited an accelerated dissolution of C\u003csub\u003e3\u003c/sub\u003eS due to the increased specific surface area of the particles, compared to pastes containing traditional limestone filler.\u003c/p\u003e \u003cp\u003eThere is an initial spike followed by a large retardation of paste containing shrimp shell powder. Žižlavsk\u0026yacute; et al. [\u003cspan citationid=\"CR38\" class=\"CitationRef\"\u003e38\u003c/span\u003e] also observed a pronounced initial reaction upon introducing water cement pastes containing biopolymers, followed by a less intense main hydration peak. The rapid increase may be linked to heat of wetting [\u003cspan citationid=\"CR39\" class=\"CitationRef\"\u003e39\u003c/span\u003e]. The retardation effect of the main cement hydration peak is attributed to the polysaccharidic structure, a result also common among other biopolymers [\u003cspan citationid=\"CR38\" class=\"CitationRef\"\u003e38\u003c/span\u003e, \u003cspan citationid=\"CR40\" class=\"CitationRef\"\u003e40\u003c/span\u003e]. Several mechanisms have been proposed to explain the effect, including the complex interactions between sugars and calcium ions. Furthermore, the retardation may be due to dispersion kinetics and electrostatic interactions cement of shrimp shell powder with cement particles [\u003cspan citationid=\"CR41\" class=\"CitationRef\"\u003e41\u003c/span\u003e, \u003cspan citationid=\"CR42\" class=\"CitationRef\"\u003e42\u003c/span\u003e]. Chitin, one of the primary components of the shell, may adhere to cement particles due to their high negative zeta potentials (less than \u0026minus;\u0026thinsp;30 mV) in DI water or pore solution pH levels [\u003cspan citationid=\"CR43\" class=\"CitationRef\"\u003e43\u003c/span\u003e]. As a result, the reaction surface area between cement and water is reduced, thereby delaying the rate of hydration. In addition, the free hydroxyl groups of chitin may form hydrogen bonds with water and cement, reducing the formation of hydration products [\u003cspan citationid=\"CR41\" class=\"CitationRef\"\u003e41\u003c/span\u003e].\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003cp\u003eCumulative heat release results of the cementitious pastes are shown in Fig.\u0026nbsp;\u003cspan refid=\"Fig6\" class=\"InternalRef\"\u003e7\u003c/span\u003eb. The pastes containing limestone, oyster shell, mussel shell, and eggshell powder had similar cumulative heat throughout the 7 days. Heat release values of these pastes ranged from 149\u0026ndash;160, 214\u0026ndash;224, and 257\u0026ndash;264 J/g cementitious material at 1 d, 3 d, and 7 d, respectively. A decrease in cumulative heat was observed for crab shell paste at early ages, showing a 15.4% decrease in heat compared to limestone at 24 h. However, this difference decreased with time. Heat release of paste containing shrimp shell resulted in a reduction in heat release at all ages. After 7 days, the cumulative heat was measured as 192 J/g, exhibiting a 27% decrease relative to limestone filler.\u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec17\" class=\"Section3\"\u003e \u003ch2\u003e3.2.2 Thermogravimetric analysis\u003c/h2\u003e \u003cp\u003eThe amount of CH after curing for 7 and 28 days is shown in Fig.\u0026nbsp;\u003cspan refid=\"Fig7\" class=\"InternalRef\"\u003e8\u003c/span\u003e. The amount was quantified using the mass loss determined via TGA. Dehydroxylation of CH occurs between 350 and 500\u0026deg;C. Due to the simultaneous degradation of chitin within this temperature range, the CH content of the shrimp shell paste was excluded from this analysis. At 7 days, CH content ranges from 13.0 g/100 g cementitious paste (crab shell) to 15.1 g/100 g cementitious paste (oyster shell). As shown in the figure, control paste had the greatest increase in CH content over the testing duration. At 28 days, CH content ranges from 14.4 g/100 g cementitious paste (limestone) to 16.1 g/100 g cementitious paste (control). From 7 to 28 days, the paste experienced a 17.8% increase in CH, whereas paste containing 20% limestone filler or shell powder exhibited a 7.5% increase, on average. This result aligns with other studies demonstrating an increase in CH content over time for control and limestone-containing specimens [\u003cspan citationid=\"CR44\" class=\"CitationRef\"\u003e44\u003c/span\u003e]. While the filler effect has some impacts on the hydration products of cementitious materials, the dilution effects is more evident [\u003cspan citationid=\"CR36\" class=\"CitationRef\"\u003e36\u003c/span\u003e] and the CH content is reduced with a higher replacement of cement.\u003c/p\u003e \u003cp\u003eThe CaCO\u003csub\u003e3\u003c/sub\u003e content at 7 and 28 days is shown in Figure S1 (Supplementary Material). As expected, a greater amount of CaCO\u003csub\u003e3\u003c/sub\u003e was evident at both testing ages in pastes containing 20% limestone or shell powders, relative to the control. At 28 days, the control paste had a CaCO\u003csub\u003e3\u003c/sub\u003e content of 10.4 g/100 g cementitious paste. Whereas the CaCO\u003csub\u003e3\u003c/sub\u003e content of the pastes containing CaCO\u003csub\u003e3\u003c/sub\u003e filler at 28 days varied from 17.6 g/100 g cementitious paste (shrimp shell) to 22.7 g/1000 g cementitious paste (eggshell). Over the curing period, the CaCO\u003csub\u003e3\u003c/sub\u003e content decreased on average by 3.7% in all samples, except for pastes containing limestone and oyster shell powder, which exhibited an average 0.5% increase.\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003c/div\u003e \u003c/div\u003e \u003cdiv id=\"Sec18\" class=\"Section2\"\u003e \u003ch2\u003e3.3 Tests on mortar\u003c/h2\u003e \u003cp\u003eThe reduced workability of the mortar mix containing shrimp shells required the use of a high range water reducing admixture (Sika\u0026reg; ViscoCrete\u0026reg;-2100). Due to the lack of workability even after significant amounts of admixture added (10% by weight of cementitious material), the mortar results are not presented for shrimp shells. Shrimp shells are not a feasible replacement for limestone filler or for cement based on the massive workability reduction. However, our findings suggest their potential as an alternative retarder, or other admixture in cementitious materials.\u003c/p\u003e \u003cdiv id=\"Sec19\" class=\"Section3\"\u003e \u003ch2\u003e3.3.1 Flow table tests\u003c/h2\u003e \u003cp\u003eThe flow table test results of the mortar mixes are presented in Table\u0026nbsp;\u003cspan refid=\"Tab3\" class=\"InternalRef\"\u003e3\u003c/span\u003e, normalized to the PLC mortar values. Mortar containing 20% oyster shell and crab shell exhibited a flow value comparable to the control, measuring 100% of PLC for both. Limestone mortar demonstrated a small increase in flow relative to the control, 103%. Mussel shell mortar exhibited a significant increase in flow, 113%. In contrast, the flow of eggshell mortar was measured as 92%, indicating a significant decrease in flow. Differences in the rheological properties between the mortars containing various shell wastes may be associated with hydrophobicity of their components as well as particle size and morphology. Eggshell membrane\u0026mdash;separating the mineralized eggshell from the egg white\u0026mdash;is composed primarily of fibrous proteins, along with lipids and sugars [\u003cspan citationid=\"CR45\" class=\"CitationRef\"\u003e45\u003c/span\u003e]. The flow is likely reduced due to the hydrophobicity of the membrane protein, which leads to fewer interactions between particles and a less cohesive mix [\u003cspan citationid=\"CR46\" class=\"CitationRef\"\u003e46\u003c/span\u003e]. The high flow value attained for the mussel shell mortar may be attributed to morphology and particle size of mussel shell powder. SEM and laser diffraction of mussel shell powder revealed primarily large (d\u003csub\u003e50\u003c/sub\u003e\u0026thinsp;=\u0026thinsp;25.6 \u0026micro;m), slender particles. Ballester et al. [\u003cspan citationid=\"CR47\" class=\"CitationRef\"\u003e47\u003c/span\u003e] reported a similar finding when substituting quarried limestone as fine aggregate with limestone derived from ground mussel shells. Mortars containing mussel shell limestone demonstrated improved workability, likely attributable to differences in particle morphology. The finer particles of quarried limestone promoted greater water adsorption, which in turn reduced workability.\u003c/p\u003e \u003cp\u003e \u003cdiv class=\"gridtable\"\u003e\u003ctable float=\"Yes\" id=\"Tab3\" border=\"1\"\u003e \u003ccaption language=\"En\"\u003e \u003cdiv class=\"CaptionNumber\"\u003eTable 3\u003c/div\u003e \u003cdiv class=\"CaptionContent\"\u003e \u003cp\u003eFlow of the mortar mixtures.\u003c/p\u003e \u003c/div\u003e \u003c/caption\u003e \u003ccolgroup cols=\"6\"\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c1\" colnum=\"1\"\u003e\u003c/div\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c2\" colnum=\"2\"\u003e\u003c/div\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c3\" colnum=\"3\"\u003e\u003c/div\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c4\" colnum=\"4\"\u003e\u003c/div\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c5\" colnum=\"5\"\u003e\u003c/div\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c6\" colnum=\"6\"\u003e\u003c/div\u003e \u003cthead\u003e \u003ctr\u003e \u003cth align=\"left\" colname=\"c1\"\u003e \u003cp\u003eMix\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c2\"\u003e \u003cp\u003eLimestone\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c3\"\u003e \u003cp\u003eOyster Shell\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c4\"\u003e \u003cp\u003eMussel Shell\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c5\"\u003e \u003cp\u003eCrab Shell\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c6\"\u003e \u003cp\u003eEggshell\u003c/p\u003e \u003c/th\u003e \u003c/tr\u003e \u003c/thead\u003e \u003ctbody\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eFlow (% PLC)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e102.7\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e99.8\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e112.5\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e \u003cp\u003e99.8\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c6\"\u003e \u003cp\u003e92.2\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003c/tbody\u003e \u003c/colgroup\u003e \u003c/table\u003e\u003c/div\u003e \u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec20\" class=\"Section3\"\u003e \u003ch2\u003e3.3.2 Bulk resistivity\u003c/h2\u003e \u003cp\u003eThe bulk resistivity of the mortar specimens at 7 and 28 days of curing are shown in Fig.\u0026nbsp;\u003cspan refid=\"Fig8\" class=\"InternalRef\"\u003e9\u003c/span\u003e. The bulk resistivity of all specimens increased with curing age. Resistivity increases as hydration products are formed and the pore structure of the composite becomes denser [\u003cspan citationid=\"CR48\" class=\"CitationRef\"\u003e48\u003c/span\u003e]. Mortar containing eggshell powder had the greatest bulk resistivity at both testing ages. At 28 days, the resistivity of eggshell and oyster shell specimens was significantly greater than the other samples (\u003cem\u003ep\u003c/em\u003e\u0026thinsp;\u0026lt;\u0026thinsp;0.05), with mean values of 98.1 Ω-m and 82.1 Ω-m, respectively. The remaining specimens exhibited similar bulk resistivity measurements. Bulk resistivity is an indicator of transport properties and durability of a concrete mixture [\u003cspan citationid=\"CR49\" class=\"CitationRef\"\u003e49\u003c/span\u003e, \u003cspan citationid=\"CR50\" class=\"CitationRef\"\u003e50\u003c/span\u003e]. Unlike commonly utilized supplementary cementitious materials that achieve higher bulk resistivities with higher replacement levels, findings from previous studies have shown that addition of limestone filler does not increase bulk resistivity, even with changes to particle fineness [\u003cspan citationid=\"CR18\" class=\"CitationRef\"\u003e18\u003c/span\u003e, \u003cspan citationid=\"CR51\" class=\"CitationRef\"\u003e51\u003c/span\u003e, \u003cspan citationid=\"CR52\" class=\"CitationRef\"\u003e52\u003c/span\u003e]. Han et al.[\u003cspan citationid=\"CR13\" class=\"CitationRef\"\u003e13\u003c/span\u003e] found that mortar cylinders replacing 30% of cement with oyster shell powder had a slightly higher increase in surface resistivity over 28 days of curing, relative to the control.\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec21\" class=\"Section3\"\u003e \u003ch2\u003e3.3.3 Compressive strength\u003c/h2\u003e \u003cp\u003eThe compressive strengths of the mortar specimens after 7 and 28 days of curing are presented in Fig.\u0026nbsp;\u003cspan refid=\"Fig9\" class=\"InternalRef\"\u003e10\u003c/span\u003e. Replacing 20% cement in mortar with limestone or shell powder resulted in reduced strengths at both testing ages, relative to the control. The strength development of the samples varied depending on the raw material. The compressive strength development of the crab shell specimens was the lowest among all mortars, with only a 3% increase in strength between testing ages (7 day\u0026thinsp;=\u0026thinsp;12.0 MPa, 28 day\u0026thinsp;=\u0026thinsp;12.4 MPa). Incorporating 20% eggshell or oyster shell yielded compressive strengths similar to limestone after 28 days of curing (\u003cem\u003ep\u003c/em\u003e\u0026thinsp;\u0026lt;\u0026thinsp;0.05). Mussel shell and crab shell are less effective as fillers. At 28 days, the mortar containing mussel shells and crab shells exhibited strength reductions of 35% and 56%, respectively, compared to the limestone specimens.\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003cp\u003eCorrelations between the properties of the shell powders and mortar with the 28-day compressive strength results were explored. The correlation between density and 28-day compressive strengths is shown in Fig.\u0026nbsp;\u003cspan refid=\"Fig10\" class=\"InternalRef\"\u003e11\u003c/span\u003e. While there is limited data, there is a strong, positive relationship (R\u003csup\u003e2\u003c/sup\u003e\u0026thinsp;=\u0026thinsp;0.86), indicating that strength increased with mortar density. These differences in density among the mortar specimens are likely due to morphology, size, and organic content of the various shell materials. Previous researchers have demonstrated that entrapped air caused by irregularly shaped shell waste, organic content, and poor packing density caused a reduction in composite density [\u003cspan citationid=\"CR11\" class=\"CitationRef\"\u003e11\u003c/span\u003e, \u003cspan citationid=\"CR12\" class=\"CitationRef\"\u003e12\u003c/span\u003e, \u003cspan citationid=\"CR53\" class=\"CitationRef\"\u003e53\u003c/span\u003e]. Moreover, these factors also contribute to strength reductions. Lertwattanaruk et al. [\u003cspan citationid=\"CR12\" class=\"CitationRef\"\u003e12\u003c/span\u003e] reported that larger-sized mussel shell powder resulted in a lower particle packing density and a considerably lower strength, relative to the control mortar.\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003cp\u003eFigure \u003cspan refid=\"Fig11\" class=\"InternalRef\"\u003e12\u003c/span\u003ea shows a strong, positive correlation (R\u003csup\u003e2\u003c/sup\u003e\u0026thinsp;=\u0026thinsp;0.77) between CaCO\u003csub\u003e3\u003c/sub\u003e content in the shell powder and the compressive strength. In contrast, a strong, inverse correlation (R\u003csup\u003e2\u003c/sup\u003e\u0026thinsp;=\u0026thinsp;0.78) was evident among organic/other mass loss on the compressive strength, as shown in Fig.\u0026nbsp;\u003cspan refid=\"Fig11\" class=\"InternalRef\"\u003e12\u003c/span\u003eb. These findings indicate that the composition of the shell powders may impact the compressive strength of the mortar. However, further testing is necessary to validate the specific mechanisms behind these effects. It is also worth noting that the relationship between shell composition and strength may be underpowered due to the limited number of data points. Moreover, one data point, that is the crab shell, with the lowest value, likely has a large impact on the correlations. These correlations demonstrate the feasibility of measuring CaCO\u003csub\u003e3\u003c/sub\u003e and organics/other content in other shell materials to evaluate their effect in cementitious materials. Similar correlations regarding compressive strength reductions due to the presence of organic matter are evident in literature [\u003cspan citationid=\"CR11\" class=\"CitationRef\"\u003e11\u003c/span\u003e, \u003cspan citationid=\"CR53\" class=\"CitationRef\"\u003e53\u003c/span\u003e]. Other factors that negatively impact strength are the higher absorption of the shell materials and the flaky or elongated shape, resulting in poor bonds with the cement paste. Additional specimens are recommended to validate these conclusions.\u003c/p\u003e \u003cp\u003eWhen considering individual shells, the shrimp shells are not feasible due to their massive workability reduction, presumably as they are largely chitin and proteins. The organic phase in the crab shells is not evident, however, it seems to cause a substantial strength reduction. The mussel shells, while having a comparable amount of CaCO\u003csub\u003e3\u003c/sub\u003e to limestone, show a strength reduction, which may be due to the particle shape and size. Finally, the oyster shells and eggshells, show strength comparable to limestone, although the oyster shells are much finer than the eggshells. The eggshells could show even higher strengths if ground similar to limestone.\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003c/div\u003e \u003c/div\u003e \u003cdiv id=\"Sec22\" class=\"Section2\"\u003e \u003ch2\u003e3.4 Limitations\u003c/h2\u003e \u003cp\u003eSeveral limitations are present in this study. In particular, shell composition is influenced by various factors. Individual shells may fluctuate in mineral/organic content based on species, gender, age, and environmental conditions. Furthermore, the shell waste received from the restaurants may have undergone different processing and cooking methods, potentially affecting shell properties. To gain a better understanding of how varying the replacement level of the waste shell materials affects the composite, further testing is recommended, such as testing at a similar particle size distribution/fineness.\u003c/p\u003e \u003c/div\u003e"},{"header":"4 Conclusions","content":"\u003cp\u003eThis study explored the feasibility of utilizing waste shell powders as alternatives to limestone filler in cementitious materials. Five different types of waste shell powders were compared to conventional limestone filler through a series of characterization and mechanical tests. The key findings of this study can be summarized as follows:\u003c/p\u003e \u003cp\u003e \u003cul\u003e \u003cli\u003e \u003cp\u003eThe waste shell materials, including oyster shell, crab shell, mussel shell, eggshell, and shrimp shell, had median particles sizes of 5, 23, 26, 28, and 41 \u0026micro;m, respectively, as compared to 14 \u0026micro;m of the conventional limestone filler. The primary composition of the shells was calcium carbonate\u0026mdash;exceeding 86% CaCO\u003csub\u003e3\u003c/sub\u003e content\u0026mdash;except for shrimp shell, which contained 16% CaCO\u003csub\u003e3\u003c/sub\u003e.\u003c/p\u003e \u003c/li\u003e \u003cli\u003e \u003cp\u003eCharacterization tests revealed that oyster shell, mussel shell, crab shell, and eggshell were nearly analogous to limestone filler. These materials were predominantly composed of calcite, while aragonite was also present in mussel shells. In contrast, chitin was the dominant component in shrimp shells.\u003c/p\u003e \u003c/li\u003e \u003cli\u003e \u003cp\u003eAs expected, all materials were classified as inert due to low heat release values. Of the five shell materials, oyster shell, mussel shell, and eggshell exhibited hydration reactions most similar to limestone filler.\u003c/p\u003e \u003c/li\u003e \u003cli\u003e \u003cp\u003eReplacing 20% cement in mortar with limestone or shell powder resulted in reduced strengths at both testing ages, relative to the control. Incorporating eggshell or oyster shell powder yielded compressive strengths similar to limestone after 28 days of curing.\u003c/p\u003e \u003c/li\u003e \u003cli\u003e \u003cp\u003eDifferences among compressive strength values were likely attributed to morphology, size, and chemical composition of the shell powders. These factors negatively impacted the composite density, leading to a reduction in strength. Moreover, higher CaCO\u003csub\u003e3\u003c/sub\u003e content improved the strength, whereas the presence of organic materials potentially contributed to a decrease.\u003c/p\u003e \u003c/li\u003e \u003c/ul\u003e \u003c/p\u003e"},{"header":"Declarations","content":" \u003cp\u003ePrannoy Suraneni is Associate Editor of Materials and Structures. The authors declare no competing interests in this publication.\u003c/p\u003e\u003ch2\u003eAcknowledgements\u003c/h2\u003e \u003cp\u003eThe authors acknowledge Nima Hosseinzadeh at Titan America for performing PSD and XRD measurements. The authors thank Sivakumar Ramanathan for providing additional guidance. The authors also thank The Lazy Oyster, Flanigan\u0026rsquo;s, and Joe\u0026rsquo;s Stone Crab for supplying waste shells. The Department of Defense National Defense Science and Engineering Graduate Fellowship (NDSEG) is thanked for partial salary support for Kylee Rux.\u003c/p\u003e"},{"header":"References","content":"\u003col\u003e\u003cli\u003e\u003cspan\u003eTkachenko N, Tang K, McCarten M, Reece S, Kampmann D, Hickey C et al Global database of cement production assets and upstream suppliers. Sci Data 2023;10. \u003cspan class=\"ExternalRef\"\u003e\u003cspan class=\"RefSource\"\u003ehttps://doi.org/10.1038/s41597-023-02599-w\u003c/span\u003e\u003cspan address=\"10.1038/s41597-023-02599-w\" targettype=\"DOI\" class=\"RefTarget\"\u003e\u003c/span\u003e\u003c/span\u003e\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eRuslan HN, Muthusamy K, Syed Mohsin SM, Jose R, Omar R (2021) Oyster shell waste as a concrete ingredient: A review. 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Constr Build Mater 162:751\u0026ndash;764. \u003cspan class=\"ExternalRef\"\u003e\u003cspan class=\"RefSource\"\u003ehttps://doi.org/10.1016/j.conbuildmat.2017.12.009\u003c/span\u003e\u003cspan address=\"10.1016/j.conbuildmat.2017.12.009\" targettype=\"DOI\" class=\"RefTarget\"\u003e\u003c/span\u003e\u003c/span\u003e\u003c/span\u003e\u003c/li\u003e\u003c/ol\u003e"}],"fulltextSource":"","fullText":"","funders":[],"hasAdminPriorityOnWorkflow":false,"hasManuscriptDocX":true,"hasOptedInToPreprint":true,"hasPassedJournalQc":"","hasAnyPriority":false,"hideJournal":false,"highlight":"","institution":"","isAcceptedByJournal":true,"isAuthorSuppliedPdf":false,"isDeskRejected":"","isHiddenFromSearch":false,"isInQc":false,"isInWorkflow":true,"isPdf":false,"isPdfUpToDate":true,"isWithdrawnOrRetracted":false,"journal":{"display":true,"email":"[email protected]","identity":"materials-and-structures","isNatureJournal":false,"hasQc":true,"allowDirectSubmit":false,"externalIdentity":"maas","sideBox":"Learn more about [Materials and Structures](http://link.springer.com/journal/11527)","snPcode":"11527","submissionUrl":"https://www.editorialmanager.com/maas/default2.aspx","title":"Materials and Structures","twitterHandle":"","acdcEnabled":true,"dfaEnabled":true,"editorialSystem":"em","reportingPortfolio":"Springer Hybrid","inReviewEnabled":true,"inReviewRevisionsEnabled":false},"keywords":"Cement mortar, sustainable concrete, shell waste, limestone filler","lastPublishedDoi":"10.21203/rs.3.rs-5278623/v1","lastPublishedDoiUrl":"https://doi.org/10.21203/rs.3.rs-5278623/v1","license":{"name":"CC BY 4.0","url":"https://creativecommons.org/licenses/by/4.0/"},"manuscriptAbstract":"\u003cp\u003eEfforts to decarbonize the concrete industry have motivated the use of alternative sustainable materials. While limestone fillers are promising, reducing reliance on virgin materials and natural resources remains essential. Shell waste from seafood and egg production are available in large quantities and their disposal poses several environmental challenges. Utilizing these CaCO\u003csub\u003e3\u003c/sub\u003e-containing waste shells as an alternative to conventional limestone can divert shell waste from landfills while lessening cement demand. To test this hypothesis, five types of waste shells were ground into powder, including oyster shells, mussel shells, crab shells, shrimp shells, and eggshells. The raw shell powders were first characterized, followed by testing of hydration kinetics and mechanical properties. Results indicated that shell powders were analogous to limestone filler, consisting primarily of calcite, with the exception of shrimp shells. Small amounts of organics were also present in the shell materials. Incorporation of eggshell or oyster shell at a 20% cement replacement yielded compressive strengths similar to limestone after 28 days of curing, but other materials reduced strength. The mortar flow and compressive strength were likely influenced by morphology, size, chemical composition, and organics of the shell powders. The findings of this study indicate that substituting limestone filler in cementitious materials with recycled shell materials is feasible.\u003c/p\u003e","manuscriptTitle":"Utilization of Common Shell Wastes as a Limestone Alternative in Cementitious Materials","msid":"","msnumber":"","nonDraftVersions":[{"code":1,"date":"2024-11-28 11:14:04","doi":"10.21203/rs.3.rs-5278623/v1","editorialEvents":[{"type":"communityComments","content":0},{"type":"reviewerAgreed","content":"","date":"2024-11-10T14:58:05+00:00","index":0,"fulltext":""},{"type":"reviewersInvited","content":"","date":"2024-11-10T13:13:34+00:00","index":"","fulltext":""},{"type":"editorInvited","content":"Materials and Structures","date":"2024-10-22T09:25:36+00:00","index":"","fulltext":""},{"type":"editorAssigned","content":"","date":"2024-10-19T04:49:20+00:00","index":"","fulltext":""},{"type":"submitted","content":"Materials and Structures","date":"2024-10-16T19:49:48+00:00","index":"","fulltext":""}],"status":"published","journal":{"display":true,"email":"[email protected]","identity":"materials-and-structures","isNatureJournal":false,"hasQc":true,"allowDirectSubmit":false,"externalIdentity":"maas","sideBox":"Learn more about [Materials and Structures](http://link.springer.com/journal/11527)","snPcode":"11527","submissionUrl":"https://www.editorialmanager.com/maas/default2.aspx","title":"Materials and Structures","twitterHandle":"","acdcEnabled":true,"dfaEnabled":true,"editorialSystem":"em","reportingPortfolio":"Springer Hybrid","inReviewEnabled":true,"inReviewRevisionsEnabled":false}}],"origin":"","ownerIdentity":"c9a61af9-ad47-4058-bd75-ca35ba37afef","owner":[],"postedDate":"November 28th, 2024","published":true,"recentEditorialEvents":[],"rejectedJournal":[],"revision":"","amendment":"","status":"published-in-journal","subjectAreas":[],"tags":[],"updatedAt":"2025-10-27T16:26:16+00:00","versionOfRecord":{"articleIdentity":"rs-5278623","link":"https://doi.org/10.1617/s11527-025-02832-5","journal":{"identity":"materials-and-structures","isVorOnly":false,"title":"Materials and Structures"},"publishedOn":"2025-10-24 16:17:22","publishedOnDateReadable":"October 24th, 2025"},"versionCreatedAt":"2024-11-28 11:14:04","video":"","vorDoi":"10.1617/s11527-025-02832-5","vorDoiUrl":"https://doi.org/10.1617/s11527-025-02832-5","workflowStages":[]},"version":"v1","identity":"rs-5278623","journalConfig":"researchsquare"},"__N_SSP":true},"page":"/article/[identity]/[[...version]]","query":{"redirect":"/article/rs-5278623","identity":"rs-5278623","version":["v1"]},"buildId":"qtupq5eGEP_6zYnWcrvyt","isFallback":false,"isExperimentalCompile":false,"dynamicIds":[84888],"gssp":true,"scriptLoader":[]}