Optimum mix design for quarry waste-based masonry blocks with alkali-activated rice husk ash and eggshell ash as a binder

: Using suitable waste materials as a replacement for cement and natural sand presents a viable and pragmatic approach to tackle the challenges associated with the construction sector's scarcity of building materials and environmental issues. Additionally, this approach aids in conserving a substantial quantity of waste. This study explored the possibility of geopolymer technology in manufacturing masonry blocks by utilizing eggshell ash, rice husk ash, quarry waste, and caustic soda. Various permutations of the mixture were evaluated to ascertain the components' optimal blending ratios. The ideal composition for block manufacturing was determined by studying many factors, including compressive strength, water absorption rate, energy demand, and carbon dioxide emissions during production. It was found that a geopolymer mortar comprising 2.5% eggshell ash, 7.5% rice husk ash, and 4% caustic soda mixed with quarry waste yielded the most favourable results. The findings indicate that the geopolymer blocks could meet the strength requirements of 1.2 MPa outlined in the SriLankan standard SLS 855 for non-load-bearing masonry when combined in specific ways. Yet, it should be noted that the geopolymer mortar's compressive strengths were relatively lower than those of the cement-quarry waste mortar. The geopolymer mortar with the optimum mix showed 14.1% less energy embodied per unit strength and 15.4% less CO 2 emission per unit strength, respectively, compared to the control mortar.


Introduction
Masonry is a prevalent building material utilized extensively in forming residential dwellings around the globe (Yogananth, Thanushan et al. 2019).Sandcrete blocks are extensively used in Sri Lanka because of their favourable mechanical and durability properties.The primary constituents of sandcrete blocks are cement and natural sand, constituting around 10-15% and 85-90%, respectively (Sathiparan, Anusari et al. 2014).The construction sector has seen a rising concern over the environmental difficulties related to manufacturing raw materials used in cement sand blocks.The excessive extraction of river sand has notable ecological consequences, including deepening river beds, intensified soil erosion, reduced water table levels, and the depletion of aquatic biodiversity within water bodies.Cement manufacturing is depicted by a substantial demand for energy and is associated with considerable carbon dioxide (CO2) emissions.Reducing the rate of use of construction materials is a long-term strategy to lessen their detrimental effects on the environment.However, because infrastructure is developing at a rapid pace, it is challenging for developing nations to cut back on consumption.Consequently, industrial ecology can be practiced in the short term.This technique uses recycled trash from one business to replace raw materials in another (Sathiparan 2023).
In light of these concerns, several research studies have been conducted to identify potential alternatives to cement and natural sand.Considerable advancements have been made in using quarry waste as a viable alternative to river sand in producing cementitious materials.Quarry waste is a residual material generated during rock crushing, which exacerbates environmental concerns and poses potential risks to human health.The utilization of quarry waste in cementitious materials has the potential to mitigate or perhaps eradicate these issues significantly.The substitution of quarry waste for natural sand in concrete and cement mortar offers a potential solution to address the waste accumulation issue while enhancing the sustainability of these materials.
Using suitable waste materials as substitutes for cement is a viable and pragmatic approach to tackle the challenges associated with the shortage of building materials and the environmental implications linked to their extraction and manufacturing processes.The use of biomass ashes yields economic advantages (Zhang 2013).The integration of biomass ashes, such as rice husk ash (Oyetola and Abdullahi 2006, Mayooran, Ragavan et al. 2017, Seevaratnam, Uthayakumar et al. 2020), eggshell ash (Sathiparan 2021), groundnut shell ash (Sathiparan, Anburuvel et al. 2023, Sathiparan, Anburuvel et al. 2023), waste wood ash (Tamanna, Raman et al. 2020), bamboo leaf ash (Rithuparna, Jittin et al. 2021) and sugarcane bagasse ash (Jahanzaib Khalil, Aslam et al. 2021), offers a possible solution for reducing the quantity of cement in construction materials.Biomass ashes are being extensively utilized in the manufacturing of cement-based products.They are classified as additional cementitious materials and can substitute a portion of the cement in concrete formulations.Its high silica concentration makes it suitable for use as supplemental cementitious materials (Danish, Karadag et al. 2023).Utilizing biomass ashes as a partial substitute for cement in concrete has several environmental advantages, including the preservation of resources and the management of agricultural waste.Additionally, it promotes the concept of a circular economy within the building sector.Rice husk ash (RHA) is a by-product derived from agriculture and is considered waste.The pozzolanic property of RHA is determined by its amorphous silica content, specific surface area, and particle fineness.For use in concrete, controlled combustion and grinding can improve these properties (Jamil, Kaish et al. 2013, Subramaniam andSathiparan 2022).Jittin et al. (2020) assessed the pozzolanic activity of RHA and examined the impact of incorporating RHA as a cementitious material in various types of concrete, alkali-activated binder, pavement construction, and brick production.The pozzolanic reactivity of RHA is affected by many factors, including fineness, incineration time and temperature, the amount of alkaline media that is available, the mix proportion, and the concentration of amorphous silica.Siddika et al. (2021) and Amran et al. (2021) did in-depth studies on these topics.In addition, they have provided information on the mechanical properties, hardening conditions, microstructure, and durability of concrete blended with RHA.Christopher et al.
(2017) and Thomas (2018) have conducted a thorough examination of concrete that incorporates RHA as a substitute for a portion of OPC.They discuss in detail the various processing factors and attributes associated with this approach.These published studies suggest that RHA can be used as a substitute for cement in concrete, up to a maximum of 10% to 20%, without negatively affecting its performance.This is because RHA possesses strong pozzolanic qualities.Nevertheless, it is crucial to consider that the appropriateness of locally accessible RHA must be assessed based on its micro-texture, chemical composition, and mineralogical composition.Furthermore, the incorporation of RHA in concrete at 15% and 20% weight replacement levels demonstrated reduced workability.
Using waste materials as a partial replacement for cement in manufacturing masonry units provides a cost-effective and manageable approach.Furthermore, it offers a more efficient structure in terms of resource use compared to traditional conventional materials.
Manufacturing masonry units using several alternatives for cement has a similar pattern.
Increasing the proportion of replacement materials in the mixture manufactures blocks with reduced weight.The materials' compressive strength (fc) exhibits a drop while the water absorption rate increases, particularly at elevated levels.Despite the potential viability of using waste materials in constructing masonry blocks as a substitute for cement, the consequential decrease in strength and increased water absorption seen at higher replacement levels impose limitations on the maximum feasible replacement percentage, estimated to be around 30%.

Problem statement
Consequently, a significant quantity of cement is still necessary to manufacture masonry blocks.Therefore, it is imperative to develop a method for producing masonry blocks that require no cement and minimize the use of river sand.An imperative is the development of a technology that can produce environmentally friendly blocks by completely substituting cement in blocks with industrial or agricultural byproducts.This technology should have a minimal carbon footprint, decrease embodied energy, and be both environmentally friendly and sustainable.
The mixing ratios of geopolymer mortars exhibit a wide range of variations and are difficult to forecast accurately.Consequently, multiple iterative experiments are necessary to determine the mechanical properties of the resulting mixtures.These trial studies necessitate a significant allocation of laboratory resources, natural resources, energy, labour, and time.
Hence, the utilization of a computational model is imperative in order to forecast mechanical characteristics, such as compressive strength.

Past studies
Using quarry waste in building materials has several benefits, including reduced cement consumption, which enhances the strength of cementitious materials, and its environmentally benign nature (Sundaralingam, Peiris et al. 2022).According to Shen et al. (Shen, Yang et al. 2016) and Goncalves et al. (Gonçalves, Tavares et al. 2007), it has been observed that the water needed for achieving consistent workability of fresh mortar is more significant when using quarry dust as opposed to river sand.However, compared to concrete produced using an equivalent quantity of river sand, concrete constructed using quarry waste has enhanced strength (Donza, Cabrera et al. 2002).Such a pattern was documented in the existing scholarly literature about self-compacting concrete (Nanthagopalan and Santhanam 2011, Benabed, Kadri et al. 2012, Mahakavi, Chithra et al. 2019).According to Sundaralingam et al. (Sundaralingam, Peiris et al. 2022), it has been said that a greater water-to-cement ratio is necessary to maintain the appropriate workability of the cement-sand mortar.The setting time and water retention capacity of new cement-sand mortar were found to increase with the inclusion of quarry waste material, as indicated by a specific slump value (Sundaralingam, Peiris et al. 2021).Furthermore, it has been shown that the incorporation of quarry waste in hardened mortar leads to an increase in water absorption, sorption, and drying.Nevertheless, It is noteworthy to mention that the incorporation of quarry waste in the mortar enhanced both compressive and flexural strength.
Scholars have investigated the use of geopolymer technology in manufacturing masonry units to complete the elimination of cement.In this context, using geopolymer gel serves as a replacement for cement.Geopolymer gel is created by the alkali activation process, which involves the interaction among aluminate and silicate-rich fly ash with alkaline activator solutions.During the 1980s, Davidovits and Sawyer (Davidovits and Sawyer 1985) made significant advancements in cement technology by introducing the first geopolymer cement.This breakthrough subsequently paved the way for the developing pyrament cement or slagbased geopolymer cement (Davidovits and Sawyer 1985).1997 Silverstrim et al. (Silverstrim, Rostami et al. 1997) and Van Jaarsveld et al. (Van Jaarsveld, Van Deventer et al. 1997) successfully formulated a geopolymer cement using fly ash as a primary component.In recent years, fly ash-based geopolymer technology has increasingly been used to manufacture diverse structural components and construction materials.These include concrete (Naskar and Chakraborty 2016, Talakokula, Vaibhav et al. 2016, Chithambaram, Kumar et al. 2018), concrete blocks (Amran, Al-Fakih et al. 2021), earth walls (Cristelo, Glendinning et al. 2012), walling materials (Komnitsas 2011, Lemougna, Madi et al. 2014, Petrillo, Cioffi et al. 2016), recycled concrete (Posi, Teerachanwit et al. 2013), and ceramics (Assaedi, Shaikh et al. 2016).
Although the primary focus of research in geopolymerization has been on aluminosilicate gel as the principal binder, numerous studies have explored the use of eggshell powder (ESP) or rice husk ash (RHA) as a precursor.Table 1 provides an overview of the research on using ESP or RHA as potential precursors for producing high-strength mortar, geopolymer composites and geopolymer concrete.

Research gap
The predominant body of research has primarily concentrated on the utilization of supplementary cementitious materials such as RHA or ESP in conjunction with metakaolin, fly ash, and ground granulated blast furnace slag as a principal constituent in the manufacturing of high-strength concrete and cement mortar.Nevertheless, there is a scarcity of literature that has discussed the incorporation of ESP and RHA as a precursor in the production of masonry blocks.Additionally, the existing literature demonstrates that geopolymerization is mostly employed in the production of masonry blocks using river sand or lateritic soil.However, the utilization of geopolymerization on quarry waste-based mortar is uncommon.Hence, the main aim of this work is to explore the impact of utilizing eggshell ash (ESA) in conjunction with RHA as an alkali-activated binder in quarry waste-based masonry blocks.ESP -eggshell powder, FA -fly ash, GBFS -Ground granulated blast furnace slag, MK -Metakaolin, POFA -palm oil fuel ash, RHA -rice husk ash

Objective of the study
The main objective of this research is to explore the feasibility of producing geopolymer blocks using ESA, RHA, and caustic soda with quarry waste as a complete substitution for river sand.
Additionally, the study seeks to identify the optimal composition for ESA-RHA geopolymer blocks that meet the minimum fc and acceptable water absorption rate requirements specified by local standards and consider eco-benefit production.The outcome of the study contributes to the construction industries in the following aspects: • Reduce the usage of unrenewable materials such as cement and river sand in the construction sector.
• Using ESA, RHA and quarry waste in the construction sector can enhance their value as viable building materials, mitigating their status as just waste products.

Material used
Figure 1 provides an overview of the raw materials used in the formulation of the mortar mix.
The cement used in this investigation is Ordinary Portland cement (OPC), following the guidance provided by the Sri Lankan standard SLS855 (SLS-855 1989).Eggshell ash was collected from several restaurants in Kilinochchi, a Northern Province of Sri Lanka region.
The eggshells that were gathered were washed using water and dried under sunlight.The eggshells that had been thoroughly dried were pulverized using a hammer mill and filtered through a screen with a mesh size of 1 mm.The eggshell powder was next subjected to calcination at a temperature of 700°C for three hours inside a furnace, resulting in eggshell The RHA used in this investigation was acquired from a kiln near Paranthan, a region in the Northern Province of Sri Lanka.The kiln used a heightened temperature of 650 °C to incinerate rice husk, which served as the only fuel source for the combustion process.The RHA obtained from the kiln was devoid of extraneous matter and included varying-sized particles.The obtained RHA was then subjected to sieving using a 2.36 mm screen, and the portion that passed through the sieve was collected to conduct tests.The quarry debris used in this study was sourced from a manufacturing facility in Divulapitiya, Western region, Sri Lanka.River sand is sourced from the local market and mined from the central area of Sri Lanka.This investigation used commercially available caustic soda as sodium hydroxide (NaOH).

Mix design
Table 3 provides the mix ID, mixing ratios, and components used for the various mixes.
According to the literature cited (Sathiparan, Jaasim et al. 2022, Sundaralingam, Peiris et al. 2022), the water-to-binder ratio was consistently set at 1.5 for the control mixture, and an equivalent amount of water was used for the remaining combinations.The quantities of ESA, RHA, and NaOH included in the mix were determined on a per-kilogram basis of quarry waste.In this study, three distinct proportions of materials were used, with varying amounts of ESA and RHA ranging from 25g to 75g, increasing in increments of 25g.Similarly, NaOH varied between 20g and 40g, rising in increments of 10g.
During the block preparation process, the necessary amount of water was used to dissolve the caustic soda flakes.Subsequently, a comprehensive blending of the precursor materials, namely ESA and RHA, and quarry waste in the dry stage was conducted.Then, the liquid form of the caustic soda solution was combined with a pre-prepared dry mixture.The precursors, quarry waste, and an acidic soda solution were manually mixed until a uniform variety was attained.The test cubes were fabricated by sequentially pouring the wet mixture into the molds in three layers.The compaction process was done manually to each layer using a short tamping rod, with ten strokes administered for each layer.The cube's dimensions were 50 mm × 50 mm × 50 mm, and it was cast per the ASTM C109 standard (ASTM-C109 2020).
Twenty-one cubes were cast for each mix ID, with seven cubes allocated for dry compression testing, seven for wet compression testing, and seven for water absorption testing.The cubes underwent a curing process at ambient temperature for 28 days before conducting the tests.

Compression test
Seven cubes were subjected to compression testing at 28 days for each mix.The testing was conducted utilizing a computer-controlled Universal Testing Machine (UTM) with a displacement rate of 1 mm/min.Furthermore, the fc under moist conditions was also assessed after 28 days.To assess the fc under wet conditions, the cubes were submerged in water at ambient temperature for 24 hours.Subsequently, the cubes were extracted and allowed to drain any excess moisture at room temperature before testing.The mean fc of each set of cubes was determined by computing the average of the corresponding strength measurements.
Determining fc involved the calculation of the ratio between the ultimate load applied and the area of the bed face.

Water absorption test
The water absorption test was conducted to examine the saturated water absorption rate.
Initially, the specimens were placed within a controlled heating environment, specifically an oven, for 24 hours.Subsequently, the mass of the blocks in their dry state (Wdry) was measured.
Then, the blocks underwent immersion in water for 24 hours and measurement of the blocks' weight in their wet state (Wwet) was ascertained.The saturated water absorption rate (SAR) was determined using Eq. ( 1).

Experimental results
Figure 3 illustrates the visual characteristics of the blocks after a 28-day curing period.The cement blocks, identified explicitly as Q-C100, had a light grey hue.In contrast to cement blocks, geopolymer blocks had a significantly darker appearance.When the content of RHA in the mix is increased, the resulting colour gets darker.(ASTM-C140 2022), the volumes and weights of the blocks were measured after a 28-day curing period for each case.The densities were subsequently calculated based on these measurements.The results demonstrated that the density of control blocks (cement quarry waste block, Q-C100) was par with cement-sand blocks (S-C100).For all combinations, the density of the geopolymer blocks is less than that of the control blocks.The primary reason for this phenomenon can be attributed to the substitution of cement by ESA and RHA, which possess a lower density than cement.An increase in the caustic soda content leads to a rise in the density of the geopolymer blocks, whereas an increase in the RHA concentration results in a decrease in density.The increase in density can be due to the substitution of low-density RHA with relatively high-density ESA in the mixture.
The fc of control blocks and geopolymer blocks is depicted in Figure 4 The reaction occurring during this operation is represented by Eq. ( 3) (Boateng andSkeete 1990, DoIage, Mylvaganam et al. 2011).

Ca(OH)2 + SiO2 + H2O → C-S-H (3)
The pozzolanic processes will effectively envelop and unite the fine aggregate particles, resulting in a notable enhancement of the strength of the geopolymer blocks (Nguyen, Nguyen et al. 2020).To produce Ca(OH)2, the hydroxylation of CaO is a necessary step, as seen in Eq. ( 4) (Lin, Kiga et al. 2011).The procedure above necessitates thermal energy, which is anticipated to be provided by the solution of water and NaOH flakes.
CaO + H2O → Ca(OH)2 (4) The results demonstrate that the fc of geopolymer mortar is always less than control mortar.
The mortar with less caustic soda (EXXRXXN20) showed poor fc compared with the control mortar and all these mortars showed less than 45% fc of the control mortar.Out of all the geopolymer mortar, E50R50N30 and E75R25N40 showed the highest strength of 2.89 MPa, which is 82% of the control mortar.
Figure 4(c) shows the fc of both control and geopolymer blocks when subjected to wet conditions.The cubes, subjected to various combinations of geopolymer mixtures, exhibited damage when immersed in water, as seen in Fig. 5.The mortar that experienced damage was produced using a reduced quantity of sodium hydroxide (NaOH).Six out of 27 geopolymer mortars were damaged and compression tests for the mix were not conducted.Like dry fc, the wet fc of geopolymer mortar cubes was less than that of control blocks.Wet to dry fc ratio for the control mortar was 0.74 and the same ratio for geopolymer mortar varied between 0.48 to 0.80.The maximum ratio was observed for E75R50N40 mortar and the minimum ratio was observed for E75R25N20 mortar.shown to increase due to the bigger particle size and lower specific surface area of both ESA and RHA, compared to cement (Ferraz, Gamelas et al. 2018).The increased water absorption seen in the polymer blocks may be due to the hydrophilic character of the RHA, which is reflected in its inherent water absorption properties.
According to the ASTM C129 (ASTM-C129 2017) standard, it is recommended that non-loadbearing masonry units have a minimum fc of 3.45 MPa for each unit and an average of 4.14 MPa for three units.As per the specifications outlined in ASTM C55 (ASTM-C55 2011), the permissible water absorption rates for masonry blocks of normal weight, medium weight, and lightweight are 208, 240, and 288 kg/m 3 , respectively.However, the minimum fc requirement for load-bearing masonry units was much lower in developing countries.SriLankan standard SLS 855 (SLS-855 1989) recommended an average of 1.2 Mpa and a minimum of 0.9 Mpa for fc for non-load bearing blocks in wet conditions.Also, the requirement for water absorption rate is specified as a maximum limit of 240kg/m 3 .While geopolymer blocks exhibit a higher level of water absorption than cement blocks, their water absorption values remain within the acceptable range as specified by the ASTM and SLS standards, except for three specific mortar mixes.However, fc is the major issue and only the following eleven mixes are satisfied the minimum fc recommended by SLS 855 (SLS-855 1989): control, E25R24N30, E25R50N30, E50R50N30, E75R50N30, E25R25N40, E75R25N40, E25R50N40, E75R25N40, E25R75N40, and E50R75N40.Only these eleven mortars are considered for eco-benefit analysis and optimum mix design analysis.
Table 4 provides an overview of the findings from the present study and published literature, where ESA or RHA are used as potential precursors for mortar used for masonry block production.It is noteworthy to mention that the use of ESA or RHA as a precursor in quarry waste mortar is hardly found in the published literature.Therefore, mortar contained river sand or soil, as fine aggregate was used for comparison.The compressive strength of geopolymer mortar was relatively high in the studies conducted by Mashri et al. (Mashri, Johari et al. 2020) and Vivek and Mangai (Vivek and Alamelu Mangai 2023).However, in both cases, they used a high content of precursor in the geopolymer mix.For the other studies, the strength of the geopolymer is closer to that of the present study.ESA: eggshell ash, RHA: rice husk ash, and FA: fly ash

Statistical analysis
The Pearson correlation coefficient calculation is employed to ascertain the link between the mix parameters, density, fc and physical, mechanical and water absorption rate, as depicted in Fig. 6.An excellent positive correlation exists between the dry and wet fc with a correlation coefficient 0.96.Also, a positive correlation was found between both fc and NaOH content.
The RHA has a negative correlation with density and a positive correlation with water absorption rate.However, ESA content doesn't have any correlation with other parameters.utilized resource in Europe and developing nations (Hugo, Stoffberg et al. 2012), as well as from published research (Pode 2016, Seddik Meddah 2017, Poorveekan, Ath et al. 2021).The production of raw materials for a mass of 1 kg is presented in Table 5.The transportation phase encompasses the evaluation of embodied energy and CO2 emissions associated with transporting raw materials to the production facility.According to the Bath Inventory of Carbon and Energy (ICE) (2011), road transport is advised to have an embodied energy of 2.4 MJ/ton.km and a CO2 emission of 0.15 kg/ton.km.During the manufacturing phase, it was anticipated that the energy embodied and CO2 emissions would be consumed or released due to the electricity or other materials utilized in the production facility for masonry blocks.The energy consumption for preparing mortar using an on-site mixer is documented to be 0.002 MJ/kg (Gonzalez Stumpf, Kulakowski et al. 2014).Typically, electricity is employed as the primary energy source for this process.According to the cited source, it has been determined that for every kilowatt-hour (equivalent to 3.6 megajoules) of power supplied, approximately 0.59 kilograms of CO2 are emitted.
The total embodied energy and CO2 emission per unit production is modelled mathematically as in Eqs. ( 5) and ( 6) (Moncaster and Symons 2013). where: • k is the raw materials used for the production of the blocks; •   and   2 are embodied energy and CO2 emission during block production with units in MJ/m 3 and kg.CO2/m 3 , respectively; •   is the wastage percentage of the raw material k; • Qk is the raw material required per unit production (m 3 ).
• Pk is the embodied energy or CO2 emission for the one kg production of raw material k; • Tk is the embodied energy or CO2 emission for the one kg transportation of raw material k; • Em and Cm are embodied energy and CO2 emissions for manufacturing one unit (m 3 ).
In the present investigation, the wastage percentage was considered zero due to a lack of information about the wastage of raw materials.The data indicates that the overall energy demand for the manufacturing of geopolymer mortar was significantly lower in contrast to the control mortar.The primary factor contributing to this outcome was decreased cement quantity and the transportation of raw materials for the manufacturing facility.The transportation of the raw materials to the production site has a higher contribution to the total embodied energy of mortar production and it varied between 52-70% of total embodied energy.In the case of energy embodied for raw material production, the cement contributes 94% for control blocks and the combination of ESA and caustic soda contributes between 85 to 92% for geopolymer mortar.Mortar mix E50R50N30 has the least embodied energy of 1165 MJ/m 3 , which is 34% less than control mortar.
Figure 8 depicts the CO2 emissions that occur during a unit volume of mortar manufacturing.
Like embodied energy, it was shown that the CO2 emissions related to geopolymer mortar production were comparatively lower when compared to conventional control mortar.The transportation of the raw materials to the production site contributes around 30% of the total CO2 emission for control mortar and between 35-44% for geopolymer mortar.Regarding CO2 emission for raw material production, the cement contributes 95% for control blocks and the combination of ESA and caustic soda contributes 90 to 93% for geopolymer mortar.Mortar mix E50R50N30 has the least CO2 emission of kgCO2/m 3 , which is 40% less than control mortar.

Optimum mix design
To evaluate the embodied energy and CO2 emission efficiency of geopolymer blocks, the parameters Ef and Cf are calculated using Eqs.( 7) and (8).For this calculation, embodied energy and CO2 emission for the manufacture of blocks with dimensions 300×150×150 m 3 were considered.
Ef and Cf are parameters concerning embodied energy in MJ/MPa and CO2 emission in kgCO2/MPa, respectively.Eenergy and ECO2 are embodied energy and CO2 emissions during the production stage for one unit of blocks.fc denotes the compressive strength of mortar.
Table 6 summarizes the embodied energy per unit strength and CO2 emission per unit strength for the selected mortar mix.When comparing the embodied energy per unit strength (Ef), mortar mix E25R75N40 was the greatest energy-efficient and compared to control mortar, it required 14.1% and 5.3% less energy for unit strength in dry and wet conditions, respectively.In addition, mortar mixes E25R50N40 and E50R50N30 also performed better than control blocks regarding embodied energy per strength.When comparing the CO2 emission per unit strength (Ef), Mortar mix E50R50N30 has a lesser CO2 emission and compared to control mortar, it emitted 24.2% and 6.9% less CO2 for unit strength in dry and wet conditions, respectively.In addition, mortar mixes E25R75N40, E25R50N30 and E75R25N40 also performed better than control blocks regarding CO2 emission per strength.When both embodied energy and CO2 emission per unit strength were considered and given the same weightage, E25R75N40 can be recommended as the optimum mortar mix and, followed by E25R50N40 and E50R50N30.

Conclusions
The current investigation entails an assessment conducted to evaluate the optimal combination of ESA, RHA, and caustic soda in quarry waste-based geopolymer mortar for the manufacturing of masonry blocks.Based on the observed results, the subsequent conclusions have been made: • Although the geopolymer blocks exhibit a higher water absorption rate than cement blocks, it is noteworthy that the water absorption rate remained within the specified regulatory limits, specifically below 240 kg/m 3 for most of the geopolymer mortar.
• The fc of the various geopolymer mortar specimens satisfies the minimal criteria specified by the local standards for one-story housing units.Therefore, these blocks can be utilized in residential buildings that are one story tall, where wall construction may use lowstrength masonry blocks.When evaluating the energy consumption and CO2 emissions associated with the production of mortar, geopolymer blocks exhibit superior energy efficiency and lower CO2 emissions regardless of their mix ratios.
• After considering both the embodied energy and CO2 emissions per unit strength, it is recommended that E25R75N40 be used as the optimal mortar mix.This mix exhibited a 14.1% reduction in embodied energy and a 24.2% reduction in CO2 emissions compared to the mortar mix of cement-quarry waste.
The outcome of the study shows that incorporating environmentally sustainable alternatives such as ESA, RHA and quarry waste, alongside caustic soda as an alkaline activator, not only reduces the usage of unrenewable materials such as cement and river sand in the construction sector but also enhances their value as viable building materials, mitigating their status as just waste products.Also, this study provides extensive information, but there are still some limitations and some areas to explore for future studies.
• The characteristics of geopolymer mortar depend on many factors in addition to those considered in the present study.Therefore, further investigation is required to assess the complete potential of the geopolymer approach in comparison to standard cement blocks, with regards to other factors such as the content and concentration of NaOH, the additional use of Na2SiO3 as an activator, the ratio of Na2SiO3 to NaOH, and the curing temperature.
• The present only focuses on compressive strength and water absorption rate.So, it is advisable to perform additional studies to ascertain the long-term resilience of geopolymer earth blocks made from ESA, RHA, and quarry waste when subjected to various environmental conditions such as water, saltwater, alkaline and acidic environments, and wet/dry cycles.

Fig 1 .
Fig 1. Raw materials used in the experimental investigation

Fig 2 .
Fig 2. Particle size distribution of the raw materials

Fig 3 .
Fig 3.The visual appearance of the blocks after 28 days of curing (b).During the process of combining cement and quarry waste with water, the chemical compounds dicalcium silicate and tricalcium silicate undergo a reaction with water, resulting in the development of calcium silicate hydrate (C-S-H) gel, as represented by Eq. (2) (Gauffinet-Garrault 2012).This is the primary factor contributing to the strength of cement-based materials(Richardson 2008).Ca3SiO5/ Ca2SiO4 + H2O → C-S-H + Ca(OH)2(2)For geopolymer mixing, the combination of ESA and RHA leads to a chemical reaction between the calcium hydroxide in ESA and the silica in RHA.This reaction ultimately results in the development of a cementitious product known as calcium silicate hydrate, which plays a crucial role in determining the strength of the geopolymer (Al-Alwan,Al-Bazoon et al. 2022).

Fig 5 .
Fig 5. Damaged cubes during immersion in water

Fig 6 .
Fig 6.Pearson correlation analysis for mixed parameters and properties of mortars

Fig 7 .
Fig 7. Embodied energy for the production for unit volume of various mortar

Table 1 .
Application of ESP or RHA in the alkali-activated binder

Table 2 .
Physical properties and chemical composition of the raw materials

Table 3 .
Mix composition of control and geopolymer mortar

Table 4 :
Overview of the findings from the present study and published literature

Table 5 .
Energy embodied and CO2 emission for the raw material (per kg) 1 +   )

Table 6 .
Summary of fc, embodied energy per unit strength and CO2 emission per unit strength for selected mortar mix