Using Oyster shell for production of greener building mortars: exploring mechanical and microscale characteristics

In the pursuit of greener and sustainable materials for developimg cementitious composites, several agricultural and undustrial wastes are continually explored for use in the process. The current study focused on the use of 20%, 25% and 30% Oyster shell powder (OSP) as a partial substitute for Ordinary Portland cement, and 100% Oyster shell aggregate (OSA) and 100% recycled concrete aggregate (RCA) (OPC) as total replacement for fine aggregate in mortar production. The mechanical properties of the mortars such as compressive strength, flexural stremntgh and water abosprion were determined. Also, microscale analysis using SEM-EDX was conducted on selected mortars. The results showed that the control mortar demonstrated the maximum compressive strength, however, OSP is adequate as binder at upto 25% replacement level, producing strength somewhat close to that of the control mortar. Results obviously showed that the replacement amounts of OSP, RCA and OSA greatly influence the hydration process of the mortar matrix, and the overall performance.


Introduction
Mortar, consisting of cement, sand, and water, is crucial in construction as it binds building materials like bricks together, ensuring structures are durable, stable, and strong.Its characteristics, such as strength and workability, are affected by factors like the proportions of ingredients, the type of cement used, and the type of sand utilized.These factors can be adjusted on-site to tailor the mortar mix to the specific needs of each construction project.However, a significant environmental issue linked with the use of conventional mortar stems from the emission of carbon dioxide (CO 2 ) during its production process.This is primarily due to the inclusion of cement, which is an energy-intensive ingredient essential to mortar formulation (Santos et al 2021).With an 8% global contribution, the cement manufacturing industry poises as one of the major industrial contributors to CO 2 emissions (Andrew 2018, Adesina ), second second to the energy production and transportation sector (Rissman et al 2020, Ahmed et al 2021 ).Further to its environmental implication, the production of mortar entails potential consequences for various types of pollution, including air and water pollution.The production of cement, a vital element of mortar, releases various pollutants into the environment such as particulate matter (PM), sulfur dioxide (SO2), nitrogen oxides (NOx), carbon monoxide (CO), volatile organic compounds (VOCs), and heavy metals like mercury (Hg) and lead (Pb) (Mikulčić et al 2016).These pollutants pose risks to human health, including respiratory problems and other serious medical conditions, while also contributing to environmental degradation.Therefore, it is crucial for civil engineering projects to carefully consider the environmental impact of cement manufacturing (Sivaguru 2019).
Moreover, the generation of mortar waste during structural demolition contribute to the overall volume of waste directed towards landfills (Akhtar andSarmah 2018, Islam et al 2019).This is due to the inherent durability of mortar, a result of its microstructural composition and physiochemical properties, which significantly extends its degradation lifespan (Abora et al 2014).Consequently, the slow degradation kinetics of the mortar promotes waste accumulation, potentially leading to a sustained severe environmental and ecological impacts.This waste accumulation necessitates effective waste management strategies within the context of civil engineering projects, aiming to minimize the environmental ramification and promote sustainable practices (Duan et al 2015).
Recycled aggregate concrete (RAC), incorporating recycled aggregates from demolished concrete instead of natural aggregates, offers a promising solution to mitigate the environmental impacts of concrete production (Makul et al 2021, Wang et al 2021, Courland 2022, Xing et al 2022).However, it's essential to note that RAC generally exhibits lower strength and durability compared to conventional concrete (Guo et al 2018).These shortcomings stem from its high-water absorption rate, which compromises its water repellency and structural integrity.Moreover, contaminants in recycled aggregates and weaker bonding between recycled aggregate and cement paste further diminish its effectiveness relative to traditional concrete (Ouyang et al 2020).Nevertheless, integrating RAC into civil engineering projects can promote sustainable practices and mitigate environmental impacts (Buyle-Bodin & Hadjieva-Zaharieva 2002, Carneiro et al 2014).To address the shortcomings associated with the use of RAC, researchers have explored various admixtures in its production.
Numerous investigations have examined the effectiveness of additives like fly ash (FA), silica fume (SF), metakaolin (MK), and ground granulated blast furnace slag (GGBFS) in enhancing the properties of RAC, particularly its workability and strength.Henry et al (2011) demonstrated that incorporating FA into low-grade RCA yielded comparable performance to conventional concrete, with the added benefits of reduced CO2 footprint and material volume.Additionally, Kou et al (2011) conducted a comprehensive study assessing the impact of various mineral admixtures, including FA, SF, MK, and GGBFS, on the performance of both natural aggregate concrete (NAC) and RAC.Their findings indicated that replacing 10% and 15% of SF and MK improved compressive strength and durability, while substituting 35% and 55% of FA and GGBSS led to decreased compressive strength but enhanced durability performance.
Similarly, Jindal and Ransinchung (2018) showcased the utilization of both industrial waste (FA) and agricultural waste (rice husk ash and bagasse ash) to enhance the mechanical and durability characteristics of recycled aggregate concrete (RAC).Their research highlighted a significant improvement in strength, with FAinfluenced RAC exhibiting a 15% increase in compressive strength and a 25% increase in flexural strength.Moreover, RAC enhanced with rice husk ash and bagasse ash demonstrated strength gains of 12% and 25%, and 13% and 20%, respectively, compared to RCA without any additives.In another study, Xu and Sun (2011) illustrated the development of high-performance RAC through the combination of mineral admixture, ultrafine FA, and a chemical admixture, superplasticizer.Additionally, Limbachiya et al (2012) conducted notable research indicating that substituting 30% of natural aggregates with coarse RAC in concrete compositions containing either Portland cement or FA did not adversely affect the performance of the concrete.In addition to the aforementioned studies, research conducted by Zhu et al (2013), Awoyera et al (2018) Bui et al (2018), Guo et al (2020), Ju et al (2020), Alyousef et al (2021), Rais and Khan (2021), Dosho (2021), Gao et al (2022), Kashini and Brindha (2024) provides evidence supporting the utilization of mineral admixtures in RAC.These findings contribute significantly to enhancing the overall performance and sustainability of RAC, thus playing a crucial role in advancing ongoing sustainability development initiatives.
Mineral admixtures play a role in indirectly enhancing the water repellent properties of RAC by improving its microstructure, consequently reducing permeability (Tam et al 2021).Conversely, chemical admixtures such as water reducers, air-entraining agents, and set retarders are specifically designed to directly enhance the water repellency of RAC (Aıẗcin 2000).This category of admixtures offers significant advantages in RAC production by improving workability, reducing the water-cement ratio, and increasing durability.Barbudo et al (2013) investigated the effectiveness of two water-repellent admixtures, traditional and high-performance plasticizer, in enhancing the properties of RCA, with encouraging results favoring the use of plasticizers.Similarly, Matar and Barhoun (2020) observed improved properties of RAC due to the influence of waterproofing admixture, resulting in reduced permeability and increased compressive strength.Kannan et al (2021) provided supporting evidence that the incorporation of chemical admixtures effectively counters water loss by reducing porosity, thus restoring a slump comparable to that of control concrete.Furthermore, recent studies by Seralin et al (2022) and Yoon and Lee (2020) underscore the ongoing exploration of water repellent properties through admixtures as a promising area for further investigation, complementing early innovative water repellency approaches.
In this context, this study investigates the feasibility of using oyster shell particles as a binder in waterrepellent recycled aggregate mortar.It is worthy of note that Oyster shell particles has been utilized as a concrete constituent in numerous research works, as aggregates (Liao et al 2023, Her et al 2024), and the performance of such concretes were found somewhat valuable.Overall, oyster shell particles are an appealing option for usage in a variety of research projects and applications due to their unique combination of abundance, renewability, biocompatibility, structural characteristics, mineral composition, pH buffering capability, and waste utilisation.However, in this study, key objectives include assessing the water absorption rate, mechanical properties, and microstructure of oyster shell mortars through scanning electron microscopy (SEM) analysis.By optimizing mortar composition and properties, the research aims to address limitations of recycled materials, enhancing their performance and expanding their potential applications.Moreover, by repurposing waste from the landfills, the study contributes to environmental sustainability by reducing reliance on new resources and diverting waste from landfills.Due to its large volume and potential effects on the environment, oyster shell waste has been shown in the literature to be a good candidate for sustainable waste management techniques (Hassoun et al 2023).The seafood industry can reduce its environmental impact and promote a more circular economy by putting recycling programmes and composting initiatives into place and by looking into creative applications for oyster shells.This research direction aligns with Sustainable Development Goals (SDGs) 9, 11, and 13, emphasizing the importance of continued development and improvement to achieve sustainability objectives.

Materials
The investigation utilised both natural fine aggregates in the form of sharp sand passing through a 4.75mm screen and recycled fine aggregate derived from crushed concrete curbs and oyster shells.The gradation and specific gravity of the sharp sand were assessed according to British Standards to ensure suitability for mortar use, while the recycled aggregates were produced through a meticulous crushing process to achieve the desired size distribution and quality.Figure 1 shows the image of the materials (Oyster Shell aggregate, RCA, River Sand and Ordinary Portland Cement) used in the experimental program.The oyster shells, sourced from Badagry, underwent thorough preparation at Covenant University, including rinsing to remove impurities and sundrying to facilitate moisture evaporation, ensuring their suitability for construction purposes.Such attention to detail aligns with civil engineering standards, guaranteeing the integrity and quality of the materials employed in the project.Potable water for mixing and curing was sourced from Covenant University's Civil Engineering Facility in Ota, Ogun State, Nigeria, and was pure, colourless, freshwater, and odourless in accordance with specifications from ASTM C160.
The mortar's constituent elements, Oyster Shell Powder (OSP), River sand, and RCA, were subjected to extensive testing to determine their physical qualities.This research comprised sieve analysis to determine their gradation, specific gravity, and water absorption characteristics.Sieve analysis holds significance as it assesses the particle size distribution within fine aggregates, which significantly influences their mechanical properties.It is widely recognized that a higher proportion of fine particles in sand necessitates increased amounts of cement and water to adequately cover and bind these particles.Consequently, this leads to a higher water-to-cement ratio, resulting in less durable and more permeable concrete components.Therefore, evaluating the particle size distribution of the aggregates used in mortar was crucial for understanding their gradation and implications for mortar performance (Awoyera et al 2021).Figure 2 illustrates the particle gradation of the aggregates, while table 1 presents selected physical properties of these aggregates.
Figure 3 illustrates a schematic depicting the production process of OSP (Oyster Shell Powder).The first step involves sourcing oyster shells from a reliable supplier, followed by a meticulous rinsing process to remove any accumulated debris or dirt.Once cleaned, the oyster shells undergo crushing using a specialized abrasion machine.This machinery employs friction to break the shells into smaller fragments, with the crushing procedure repeated until the desired particle size is attained.Next, the crushed oyster shells were passed through a sieve shaker, a specialised equipment that utilizes vibration to separate the oyster shell powder from any remaining large particles.Through this process, only portion of the Oyster shell particles passing 4.75mm sieve was used as fine aggregates.For replacing OSP for cement, the particles should be passing 90 microns.
Figure 4 illustrates the step-by-step process for producing high-quality recycled fine aggregate.Initially, concrete curbs were collected and then fragmented into smaller segments before being introduced into an   abrasion machine.This machine employs abrasion and impact forces to break down the concrete into finer particles.Operating at specific speeds and durations ensures optimal particle size reduction.Subsequently, the fragmented material undergoes sieving, a critical phase aimed at isolating the fine aggregate.A sieve shaker is utilized to separate the fine aggregate from the coarse aggregate, with the choice of sieve size tailored to the desired fine aggregate dimensions, typically ranging from 4.75 mm to 0.15 mm.Following the completion of the sieving process, the fine aggregate is gathered and ready for utilization in mortar preparation.

Mortar mix design and production
The mix ratio adopted for this study was 1 part cement to 2 parts fine aggregate.However, it's crucial to highlight that the water-cement ratio varied among the different mixes to ensure optimal workability, a fundamental attribute of mortar.The mixing of constituent matrials was conducted manually using a trowel.Initially, the dry components were blended until a uniform distribution was achieved.Subsequently, potable water was added to create a thorough and workable mix.In-situ tests were conducted on the fresh mortar after mixing completion.
The homogenous mix was placed in a thoroughly greased 40 × 40 × 160 mm mold, facilitating easy removal after 24 h of drying.The mixed mortar was poured into the mold and compacted to ensure adequate compaction and eliminate air bubbles.A total of 10 mixes were prepared for each of the different replacement levels, as shown in table 2.   2.3.Testing procedures 2.3.1.Flexural strength test Flexural strength, also known as the modulus of rupture, is crucial in assessing a material's ability to withstand tensile stresses under bending forces.In this study, mortar specimens were subjected to flexural strength testing using the three-point loading technique, following standardized parameters.The test setup, illustrated in figure 5(a), involved applying incremental loads at a regulated rate using a specialized three-point flexural strength testing machine with a maximum capacity of 200 kN.Flexural strength values were quantified in N/ mm2 using a specific mathematical expression, allowing for insights into the material's structural performance in resisting bending stresses.

Compressive strength test
Compressive strength measures a material's resistance to breaking under compressive forces.The compressive strength testing machine of UNIT TEST model was used in this study.The set-up for the mortars is shown in figure 5(b).
After failure, half-prisms of approximately 40 mm × 40 mm × 80 mm were formed from the prism sample, and these were tested for compressive strength.To ensure accurate results, the compression testing machine's bearing surfaces were thoroughly cleaned, and the half-prisms were positioned centrally on the base plate.A steadily increasing force is applied until the maximum load is reached and recorded.

Water absorption test
Assessing water absorption in mortars is crucial for understanding how moisture infiltrates the material through air condensation, capillary action, and precipitation.Split prisms measuring approximately 40 mm × 40 mm × 80 mm resulting from flexure tests were used for this assessment.After submerging the prisms in water for 12 h, any residual water was removed, and their masses were recorded.To determine water absorption, the prisms were oven-dried at 110 •C for 12 h to remove all moisture, and the change in mass was calculated.

ЅEM analyses
Microstructural investigations utilizing scanning electron microscopy (SEM) was conducted to delve into the inherent characteristics and compound composition of the selected mortars.In addition to the physical and mechanical property testing, eight distinct mortar mixes (MM) along with a control mortar (Mix 1) underwent supplementary examination.SEM analysis was performed on crushed mortar specimens at three curing stages: early (7 days), intermediate (14 days), and ultimate (28 days).By studying microstructure and compound composition over these intervals, valuable insights into the genesis and evolution of the mortars were obtained.SEM, or scanning electron microscopy, is a powerful tool used to examine the surface morphology and structure of materials at a microscopic level.By bombarding the surface of the sample with a focused beam of electrons, SEM generates high-resolution images that reveal fine details of the sample's topography and microstructure.In the context of this study, SEM analysis enabled the observation of the surface characteristics, particle size, shape, and distribution of the OSP particles.
SEM analysis facilitated examination of surface morphology and detection of microstructural alterations.This investigation were instrumental in understanding mortar behavior, estimating structural integrity, and assessing potential durability.

Compressive strength
Figure 6 shows the compressive strength of various mortar mixes, offering crucial insights into their performance in comparison to the control mortar mix.Evidently, the control mortar showcased the highest compressive strength, indicating its superior structural robustness.Mixes 1 and 2 demonstrated closely aligned compressive strength values, with mix 1 marginally surpassing mix 2. This similarity could be attributed to both mixes predominantly comprising conventional components like cement and fine aggregate, without substantial replacement or integration of unconventional materials.Consequently, they exhibited akin strength properties.
With the escalation in the replacement level of OSP (Oyster Shell Powder) in mixes 3 and 4, a gradual decline in compressive strength occurred.This decrement can be associated with OSP's unique characteristics, including particle morphology, size, and composition.The process of crushing and refining oyster shells into powder may introduce irregularities or inconsistencies that adversely influence bonding attributes and overall strength.Thus, as the OSP content increased, there was a proportional decrease in the mortar's compressive strength.
Mixes 5, 6, and 7, incorporating RCA, manifested the lowest compressive strength values among all mixes.The incorporation of RCA poses challenges to mortar performance owing to the presence of recycled concrete constituents, which may harbor inherent flaws such as diminished interfacial adhesion and reduced aggregate strength due to previous usage and recycling processes.Consequently, the mortar's structural integrity and strength are affected.Conversely, mixes 8, 9, and 10 exhibited improved compressive strength when contrasted with mixes 5, 6, and 7.This enhancement could be attributed to the incorporation of OSP.The use of OSP with cement likely bolstered the bond between the cementitious matrix and the aggregates, leading to heightened compressive strength.However, it's essential to acknowledge that despite this improvement, the compressive strength values of mixes 8, 9, and 10 still fell short of those in the first four mixes.
An exception was noted in mix 9, where its compressive strength value at the conclusion of the 14-day curing period was close to that of the control mortar.This indicates that the material combination in mix 9 yielded a compressive strength comparable to that of standard mortar.
The results portrayed the unique mechanical behaviour of mortar incorporating Osyter shell as binder or aggregate in addition to recycled aggregate.
From the strength results, it could be seen that strength increased with curing age for mixes 1 to 3.An indication that OSP is adequate as a binder at up to 25% replacement level and using natural sand as aggregate.However, beyond 25% replacement level, there was only appreciable performance of the mixes 4-10 up to 14 days of curing.This showed that OSP mixes are not fit for long-term strength performance.

Flexural strength
The flexural strength of the mortars displayed a consistent decline as the concentration of OSP (oyster shell powder) increased.This reduction could be attributed to various factors, including OSP's influence on the overall composition and structure of the mortar.Furthermore, including RCA and OSA (oyster shell aggregate) notably contributed to the diminishing flexural strength.Notably, the absence of reinforcing elements, such as fibers, which are known to enhance flexural properties, likely exacerbated the observed decline in flexural strength in this study.Among the different mortar mixes, Mix 8, Mix 9, and Mix 10 exhibited the lowest flexural strengths, as indicated in figure 7.
The principal reason behind this trend can be attributed to the hygroscopic nature of OSA.Hygroscopic materials tend to absorb moisture from their surroundings, including excess water during the curing process.In the case of OSA, this increased water absorption could lead to an imbalance in the water-cement ratio, hindering the hydration process of cement.Consequently, the mortar may absorb more water than necessary, resulting in diminished strength properties, particularly in flexural strength.
In summary, the presence of OSP, RAC, and OSA and the absence of reinforcing elements contributed to the decrease in flexural strength observed in Mix 8, Mix 9, and Mix 10.The hygroscopic properties of OSA, in particular, significantly reduced flexural strength by altering the water-cement ratio and impacting the cement hydration process within the mortar.

Water absorption
The findings from water absorption tests on the mortars are depicted in figure 8.The control mix, devoid of any replacements, exhibits relatively lower water absorption values, albeit with a slight increase observed over time.Conversely, Mixes 2, 3, and 4, which incorporate OSP as a replacement for cement, display fluctuations in water absorption values.This variability could be attributed to the irregular particle shape and composition of OSP, potentially affecting bonding properties within the mortar and consequently influencing water absorption.To enhance water absorption performance, exploration of alternative cementitious materials or incorporation of OSP that enhance bonding and reduce porosity is warranted.
Mixes 5, 6, and 7, which combine OSP and RAC replacements, demonstrate diverse water absorption The presence of impurities in RAC may introduce flaws and diminish aggregate strength, thereby contributing to increased water absorption.The water absorption ratio increased from 7 to 14 days, most likely as a result of a confluence of factors including drying, curing, mixing ratios, and material quality as well as environmental influences.Generally, to improve water resistance, it is advisable to opt for high-quality RAC with enhanced interfacial bonding properties or consider integrating water-reducing admixtures to minimize porosity.
Mixes 8, 9, and 10 involve the replacement of sand with OSA alongside OSP substitution.OSA's hygroscopic nature and propensity for excessive water absorption can lead to an imbalanced water-cement ratio, thereby affecting the hydration process and amplifying water absorption.To mitigate this, selecting alternative aggregates with lower hygroscopicity or employing surface treatments to reduce water absorption could prove beneficial.
3.4.SEM analysis 3.4.1.SEM and elemental analysis of OSP The SEM results, as depicted in figure 9, alongside the elemental composition data presented in table 3, provide valuable insights into the microstructure and chemical composition of the examined OSP (oyster shell powder).
The reported elemental composition of the OSP, with high weight concentrations of Silicon (Si), Aluminum (Al), Oxygen (O), and Carbon (C), along with traces of other elements, offers valuable insights into the chemical makeup of the material.Silicon and aluminum are common elements found in minerals and rocks, suggesting  that the OSP may contain mineral components derived from the shells' natural environment.Oxygen and carbon are fundamental elements present in organic compounds, indicating the organic nature the oyster shells.The presence of these elements aligns with the expected composition of oyster shells, which are primarily composed of calcium carbonate (CaCO3), along with organic matter and trace minerals.

SEM and EDX analysis of RAC
The SEM results displayed in figure 9(b), coupled with the elemental composition data provided in figure 9(c), offer a comprehensive understanding of the microstructure and chemical composition of the examined RCA.
The SEM image presented in figure 9(b) provides visual insights into the surface characteristics structure of the RAC particles.This image enables the observation of particle morphology, surface texture, and any potential aggregation or clustering behavior.Such information is crucial for understanding the physical properties and structural attributes of the RAC.
In addition to SEM imaging, the elemental composition data shown in figure 9(c) offer quantitative information regarding the chemical constituents present in the RAC sample.Elemental analysis, often conducted using techniques like Energy-Dispersive x-ray Spectroscopy (EDX) alongside SEM, provides data on the relative abundance of different elements within the sample.
The reported elemental composition of the RAC, indicating high-weight concentrations of Silicon (Si), Oxygen (O), and Phosphorus (P), suggests the presence of specific minerals and compounds within the concrete matrix.Silicon and oxygen are commonly found in silicate minerals, which are prevalent in aggregates used in concrete production.Phosphorus may originate from additives or contaminants present in the recycled concrete materials.Furthermore, the traces of other elements detected in the elemental composition analysis could stem from impurities in the raw materials or environmental influences during sample preparation and analysis.
3.4.3.SEM analysis of mortar samples at 7, 14 & 24 days of curing Scanning electron microscopy (SEM) analysis was conducted on Mix 1, Mix 2, and Mix 5 samples after 7 days of curing.Figures 10a to 10f display SEM images and elemental compositions, revealing calcium as the dominant element in all samples.
With the SEM-EDX analysis, it was confirmed that there was consistent crystalline phases across all mixes, including quartz, orthoclase, albite, calcite, muscovite, and lime.Calcium remained the dominant element throughout the curing process, underscoring its pivotal role in determining mortar properties and characteristics.Similarly, at the end of the 28-day curing period, SEM was conducted, yielding results consistent with the earlier assessments.Crystalline phases remained unchanged in Mixes 1, 2, and 5, highlighting the stability of mortar compositions over time.Notably, calcium continued to exert its dominant influence, emphasising its significance in determining mortar behavior.
Overall, the comprehensive analysis of mortar samples throughout the curing process provides valuable insights into their structural and chemical characteristics.The consistent presence of crystalline phases and dominance of calcium underscore the reliability and stability of the mortars, offering valuable information for material design and construction applications.

Conclusion and recommendation
This study extensively explored the potential of utilizing Oyster shell powder (OSP) as a partial substitute for cement and RCA or Shell Aggregate (OSA) as total replacements for sand in mortar production.The focus was on evaluating the mechanical properties of the mortars and conducting detailed microstructural investigations on selected specimens.The following conclusions were drawn from the • The control mortar (mix 1) and mix 2 containing 20% OSP exhibited increased strength with the increasing curing age.The outcomes demonstrated the distinct mechanical characteristics of mortar that uses Osyter shell as aggregate or binder in addition to recycled material.Also, for mixes 1 through 3, it was evident from the strength data that strength rose with curing age, a sign that OSP works well as a binder when natural sand is used as the aggregate, and the binder can be replaced up to 25%.Still, the mixes showed only moderate performance beyond the 25% replacement level, lasting up to 14 days for curing.This demonstrated that OSP mixes are unsuitable for long-term strength gains.• The increase in OSP concentration resulted in a continuous decrease in flexural strength, likely due its impact on the mortar's composition and structure.Furthermore, the presence of RAC and OSA contributed to a further decline in flexural strength, highlighting the negative influence of these alternate materials.
• The study of water absorption properties revealed that OSP, RAC, and OSA replacement levels significantly influenced mortar water absorption.The inclusion of these materials contributed to increased water absorption, affecting overall mortar performance.
Overall, utilizing Oyster shell particles, derived as by-products from the seafood industry, presents a promising alternative for sustainable construction practices.Using OSP in construction contributes to waste reduction and promotes recycling practices, aligning with sustainable principles in civil engineering.

Figure 1 .
Figure 1.The image of the materials (oyster shell aggregate, RCA, river sand and ordinary portland cement) used in the experimental program.

Figure 2 .
Figure 2. Particle size distribution of aggregates used.

Figure 3 .
Figure 3. Schematics for the production of OSP.

Figure 4 .
Figure 4. Schematics for the production of RCA.
level using OSP.B: Replacement level using RCA.C: Replacement level using OSA.

Figure 6 .
Figure 6.Compressive strength of the mortar mix.

Figure 7 .
Figure 7. Flexural strength of the mortar mix.

Figure 8 .
Figure 8. Water absorption of the mortar mix.

Figure 10 .
Figure 10.(a) SEM image of Mix 1 after 7 days of curing.(b) EDX analysis of Mix 1 after 7 days of curing.(c) SEM image of Mix 2 after 7 days of curing.(d) EDX analysis of Mix 2 after 7 days of curing.(e) SEM image of Mix 5 after 7 days of curing.(f) EDX analysis of Mix 5 after 7 days of curing.

Table 1 .
Physical properties of the aggregates.