Eco-Friendly Activating Solutions from Cocoa Pod Ash and Rice Husk Ash for Geopolymerization

Eco-Friendly Activating Solutions from Cocoa Pod Ash and Rice Husk Ash for Geopolymerization | 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 Eco-Friendly Activating Solutions from Cocoa Pod Ash and Rice Husk Ash for Geopolymerization Cyprien Joël Ekani, Paul Venyite, Jean Marie Kepdieu, Chantale Njiomou Djangang, and 2 more This is a preprint; it has not been peer reviewed by a journal. https://doi.org/ 10.21203/rs.3.rs-6396121/v1 This work is licensed under a CC BY 4.0 License Status: Published Journal Publication published 08 Dec, 2025 Read the published version in Silicon → Version 1 posted 9 You are reading this latest preprint version Abstract This study investigated the potential of Cocoa Pod Ash (CPA) and Rice Husk Ash (RHA), respectively, as sustainable sources of potassium and amorphous silica, in the preparation of activating solutions for geopolymerization. CPA was successfully used to extract K-salt that was found to be a carbonate salt using FTIR analysis. The K-salt was used as substitute of NaOH, together with RHA as silica source to prepare activating solutions via hydrothermal dissolution. The obtained activating solutions were successfully used in the geopolymerization of both calcined kaolinitic and lateritic clays. The synthesized geopolymers were characterized using X-ray Diffraction (XRD), Fourier transformed infra-red (FTIR) and the measurement of some physico-mechanical parameters. including setting time, compressive strength, density, porosity and water absorption. The results indicate an improved response of the geopolymer products withing K-salt addition of 15–20% (w/w), with respect to total alkali. Beyond 20%, there was a lowering of the various responds that was associated to matrix weakening brought by carbonatation. The alkalinity of all the activating solutions was sufficient for geopolymerization without retention of excess alkali ions in the binder system, as indicated by the absence of efflorescence on the geopolymer surfaces. This study demonstrates the potential of using locally sourced agro-wastes materials to produce sustainable activating solution. Geopolymerization Agro-waste Mechanical response Metakaolin Figures Figure 1 Figure 2 Figure 3 Figure 4 Figure 5 Figure 6 Figure 7 Figure 8 Figure 9 Figure 10 Figure 11 1 Introduction The widespread adoption of geopolymer technology has been hindered by several factors, including high production costs, limited availability of raw materials, and environmental concerns associated with traditional activators[ 1 – 3 ]. Additionally, lack of standardization and regulations, public perception and awareness, competition with established materials, specialized labor and training have all contributed to the timid adoption of geopolymers [ 4 – 7 ]. Furthermore, the high cost of conventional activators, such as potassium silicate (K 2 SiO 3 ) and potassium hydroxide (KOH), poses a significant barrier to adoption in developing countries, particularly in Africa. Since the total production cost of geopolymers primarily depends on the cost of these activators [ 8 , 9 ], it becomes difficult for countries with limited financial resources to adopt the innovative technology. To address these challenges and make geopolymer technology more accessible, this study aims to develop a sustainable and cost-effective activating solution using two abundantly available agro-waste materials: Cocoa Pod Ash (CPA) and Rice Husk Ash (RHA). Recent studies have explored the use of agro-wastes as sustainable alternatives for the preparation of activated solutions in geopolymers. For example, Rice Husk Ash (RHA) has been utilized due to its high silica content [ 10 , 11 ]. Similarly, Cocoa Pod Ash (CPA) has been investigated for its high potassium content [ 12 – 15 ]. However, the combined use of RHA and CPA for the production of Na/K silicates has not been extensively explored. Cameroon is the fourth largest cocoa producer in the world, accounting for 280,000 to 290,000 metric tons per year [ 16 ]. The production is also large in terms of paddy, eg. 332, 000 tons in 2018 [ 17 ]. The important quantities of waste generated by these two crops after extracting cocoa bean or rice are often discarded and burnt or left to rot in opened fields. The practice of improper waste deposition has in most cases resulted in the transformation of large useful surfaces into wastelands. In other situations, typical of the tropical climate, the accumulation of the ashes along river bangs in dry seasons leads to blockage of water way, resulting in flooding upstream in the rainy season. Additionally, the lack of proper waste management and disposal practices exacerbates these issues, posing a significant threat to the environment and public health[ 18 ]. The innovative character of this work lies in the preparation of geopolymer activating solutions based on the extraction of target precursor from locally available agro-wastes (CPA and RHA) and their adaptable application in geopolymer synthesis using calcined clay from locally available clay materials. This unique combination will potentially lead to a more sustainable alternative for building binders. 2 Materials and experimental procedures 2.1 Materials Two kaolinitic clay materials from Ntouessong II a locality of the Mefou and Akono Division in the Centre Region of Cameroon were used. One of the samples coded OWC, is sedimentary clay with a whitish appearance (The Munsell color code 2.5Y 8/1) and the other one coded ORC, is a lateritic clay having a yellowish color (Munsell color code 10YR8/6). The respective geographical coordinates of the sampling are 11°14'30'' and 11°26'30'' East longitude and between 3°36'15'' and 3°47'45'' North latitude, respectively for ORC and OWC. The clay materials were wet sieved through a 120µm mesh, dried at ambient conditions (24 ± 5⁰C and 70 ± 5% RH), crushed, then sieved at 100 µm before being stored in polyethylene bags for further uses. The calcined clays were obtained by heating the raw powdered material in an electric furnace (Nabertherm Model LH 60/14) from ambient temperature of 25⁰C to 700°C. The heating rate was 5°C/min and the samples were left for 4 hours at the final temperature before cooling to room temperature. The calcined powders were coded OWC7 and ORC7 respectively for OWC and ORC. Cocoa pods and rice husk were respectively, collected from Ntouessong II, locality in the Centre Region of Cameroon and from the Upper Nun Valley Development Association (UNVDA), a rice factory in Ndop, Northwest Region of Cameroon. The biomass ashes were collected from open-air burnt dumps, then sieved at 100 µm to obtain the ashes coded CPA and RHA, respectively for cocoa pod ash and rice husk ash. 2.2 Experimental procedures 2.2.1 Extraction of Potassium Salts For the extraction of the K-salt, CPA were dispersed in distilled water in a solid/liquid ratio of 1:5 then boiled under constant stirring for 10 min, then filtered over a Whatman 5 filter. The procedure was repeated using the collected solid residue until the filtrate pH is in the range 7 to 8. The collected filtrate was left for evaporation under ambient and the K-salt was collected and stored in polyethylene bags prior to its use for activation solution preparation. 2.2.2 Preparation of Activating Solutions The sodium silicate solution was prepared with a Na 2 O/SiO 2 ratio of 0.7[ 19 , 20 ]. The alkali content of the solution was then modified by adding varying percentages of K-salt with respect to total alkali (Na + K), to obtain six activating solutions. Each mixture was reflux heated at 80°C for 4 hours. Thereafter, the gel phase was collected, its pH was recorded and the solution stored for 48h in closed glass vessel prior to its use as activating solution. The activating solutions were coded S0, S8, S14, S20, S25, and S30 with respective K-salt percentages of 0%, 8%, 14%, 20%, 25% and 30%. 2.2.3 Preparation of Geopolymer binders The calcined clay was mixed with the various activating solutions, S0, S1, S2, S3, S4, and S5 at solid/liquid mass ratios of 1.3 and 1.4, respectively for OWC7 and ORC7. The obtained mixtures were homogenized for 5 minutes using a BOMANN mixer (model D-479086) to obtain two series of geopolymer binders. The obtained geopolymers were labelled GB-x and GR-x, respectively for OWC7 and ORC7. The “x” in the label is related to the activating solution used. The pastes were then poured into cylindrical PVC molds having dimensions, diameter × height of 20mm×40mm. The resulting specimens were immediately sealed in a thin polyethylene film and then placed in ambient condition of the laboratory (27 ± 3°C). Specimens were demolded 48 hours after casting and left in the open air for physical and mechanical characterization at 28 days. 2.3 Characterization techniques The mineralogical analysis of the raw clays and geopolymer products was carried out using a Bruker-AXS D8 Advanced X-ray Powder Diffractometer. The diffraction patterns are recorded using a Cu-Kα (λ = 1.5406 Å) radiation operating under a voltage of 40 kV and a current of 40 mA in a 2θ range of 5 to 70° and a scanning step of 0.03 °/s. The FTIR analysis was carried out in total reflectance mode in a wavenumber range of 4000 and 400 cm − 1 using a Bruker Alpha-p spectrometer. The thermo gravimetric analysis (TGA) was performed using a thermo gravimetric device NETZSCH STA 409PC/PG The amorphous phase content of the calcined clays OWC7 and ORC7 was determined through chemical treatment with sodium hydroxide (NaOH) and hydrochloric acid (HCl) solutions. In this process, 3g of the calcined clay is mixed with 30 mL of 8 M NaOH solution then warmed for 30 minutes at 30°C before washing and centrifuging until neutral pH is measured in the supernatant. The residue is further dissolve in 0.5 M HCl solution and submitted to the same cycle of warming, washing and centrifuging to neutral pH in the supernatant. The resulting residue was dried at 110°C for 24 hours and weighed to calculate the amorphous phase content using the Eq. 1. % amorphous phase = \(\:\frac{{M}_{1}-{M}_{2}}{{M}_{1}}\) x 100 (1) where M 1 is the mass of sample and M 2 , the mass of residue The specific surface area (SSA) by nitrogen absorption of the clay materials was determined using Brunauer-Emmet-Teller (B.E.T) method. The chemical analysis of extracted salts was carried out using Inductive Coupled Plasma by Optical Emission Spectroscopy (ICP-OES) using a Thermo Scientific iCAP 7400 duo ICP-OES apparatus. The initial and final setting time of the various geopolymers was evaluated according to EN 1963 standard using the Vicat apparatus, measuring the time taken for a needle to penetrate a cement paste or mortar held in a frustoconical mold. Apparent density, water absorption rate, and open porosity were assessed from the Archimedes test (ISO 5017/1985). Compressive strength of geopolymer samples aged for 28 days was obtained by the average of three samples tested on an Automatic Compression Testing Machine (AIMIL COMPTEST 2000, India). 3 Results and discussion 3.1 Characteristics of starting materials 3.1.1 Mineralogical Composition of raw materials The XRD analysis of the two raw clay materials OWC and ORC (Fig. 1 (a)), reveals a similar mineralogical assemblage due to the sampling environment. The presence of Muscovite, Kaolinite, Anatase and Quartz in both samples indicates a common silicate-rich provenance. However, the ORC is iron oxy/hydroxyl richer than the OWC. The hematite diffraction peaks are less intense in OWC, which accounts for its whitish color. Both clays are kaolinite rich materials, with main associate minerals being muscovite and quartz. After calcination at 700°C (OWC7 and ORC7) in Fig. 1 (b), the Kaolinite mineral completely transformed into metakaolinite, while the goethite totally disappeared in ORC7 (Fig. 1 (b)), suggesting the conversion of goethite into hemathite (α-Fe 2 O 3 ), which accounts for the intensification of the reddish brown color of the ORC7 [ 10 ]. The relative intensity of 7.18 Å diffraction peak in both samples indicates a higher kaolinite content in OWC, compared to ORC. 3.1.2 Thermal Behavior (ATD/TG) of the raw materials The thermal analysis curve of the clayey materials is presented in Fig. 2 . Both curves corroborate the mineral composition of the sample from XRD. In Fig. 2 (a) and 2 (b), the adsorbed water departure onsets at 66°C and 77°C, respectively for OWC and ORC. The difference is attributed to the presence of goethite in ORC that induces increase adsorbed water [ 21 ]. Both samples exhibit kaolinite dehydroxylation at 480°C for OWC and 490°C for ORC. The dehydroxylation temperatures agree with the kaolinitic nature of the clayey materials. Additionally, the ORC curves (Fig. 2 (b)) exhibit a pronounced peak at 298°C, corresponding to the transformation of goethite into hematite, whereas a similar but less intense peak appears in OWC at 288°C (Fig. 2 (a)). 3.1.3 Infra-Red analysis of clay materials The infrared spectroscopy results for the two clay materials, OWC and ORC (Fig. 3 ) reveal significant changes in their vibration frequencies upon calcination at 700°C. The strong and broad bands observed between 3695 cm − 1 and 3620 cm − 1 in both samples (Fig. 3 (a)), are characteristic of external and internal –OH stretching vibrations of kaolinite [ 22 , 23 ]. The inner surface stretching is observed at about 3655 cm − 1 . A distinct band at 1635 cm − 1 in ORC, which is less marked in OWC, is attributed to the group vibration of H–O–H in free water adsorbed within the kaolinite interlayer [ 24 ]. The sharp peak at 1004 cm⁻¹ corresponds to asymmetric stretching vibrations of Si–O characteristic of the tetrahedral silicate framework [ 25 ]. The band at 909 cm⁻¹ is characteristic of the stretching vibration of M–OH bonds, where M is a metal ion (e.g., Fe³⁺ or Al³⁺) [ 19 , 26 ]. The doublet observed at 753–791 cm⁻¹ corresponds to Si–O–Si inter-tetrahedral bridging bonds [ 27 ]. The bands at 678 cm⁻¹ and 451 cm⁻¹ correspond to the bending vibrations of Si-O bond, indicating silicate network contributions commonly observed in quartz [ 28 , 29 ]. The band at 524 cm⁻¹ is attributed to the bending of Si-O-Al in clay minerals [ 30 ]. The vibration frequency at 407 cm⁻¹ is attributed to Ti-O bonds of anatase [ 31 ]. After calcination at 700°C (Fig. 3 (b)), O-H vibration bands disappear, which is indicative of the dehydroxylation of the kaolinite and goethite to form metakaolinite and hematite, respectively. The band at 1022 cm⁻¹ in both calcined clays corresponds to the asymmetric stretching vibration of Si–O bond. The shift of the band to higher wave number, in comparison to raw clays is related to the modification of the interaction environment due to dehydroxylation [ 27 ].This modification of the bonding environment also results in the modification of the Si-O-Si bending vibration that appears in calcined samples at around 777 cm − ¹. The overall observations are coherent with the dehydroxylation of kaolinite, resulting in amorphous metakaolin, which is of interest for improving geopolymerization. 3.1.4 Amorphous phase content of solid precursors The result of the amorphous phase content of OWC7 and ORC7 (Table 1 ) indicates that OWC7 has a higher amorphous phase content (46.7%) than ORC7 (19.96%). This is coherent with the relative highest content of kaolinite in OWC when compared to ORC from their XRD (see section 3.1.1). Also, contribution of amorphous free silica by both samples may be higher for OWC. These results imply that OWC7 might exhibit higher reactivity in geopolymerization processes, while the relatively higher proportion of insoluble minerals in ORC will result in a high amount of aggregate after polymerization that may affect the mechanical response of binders based on ORC. Table 1 Amorphous Phase Content (%) of OWC7 and ORC7 Samples OWC7 ORC7 Amorphous Phase Content (%) 46.7% 19.96% 3.2 FTIR analysis of K-salt The infrared spectrum of K-salt (Fig. 4 ) shows the broad vibration band around 3121 cm − 1 which is attributed to the stretching vibrations of the OH groups of water molecules [ 32 – 34 ]. The vibration around 1344 cm − 1 is attributed to the asymmetric stretching vibration of the C-O bond in carbonates. The peak at 1059 cm − 1 corresponds to the symmetric stretching vibration of C-O, indicating the presence of carbonate ions (CO 3 2− ) or bicarbonate ions (HCO 3 − ) [ 35 , 36 ]. The peak at 878 cm − 1 indicates the bending vibration of C-O bonds of the CO 3 2− groups [ 37 ]. The peak at 698 cm − 1 is attributed to the stretching vibration of K-O [ 32 – 34 ]. These frequencies suggest that most of the potassium contained in the extracted salt from cocoa pod ash is in the form of potassium carbonate (K 2 CO 3 ) or potassium bicarbonate (KHCO 3 ). Potassium carbonate (K 2 CO 3 ) or potassium bicarbonate (KHCO 3 ) present in K-salt can contribute to the alkalinity of the system due to their buffering capacity, helping to dissolve amorphous silica from RHA (Eq. 2 ) and form activating solution of potassium silicate which can enhance geopolymerization. $$\:{{SiO}_{3}^{2-}}_{aq}+{{K}_{2}{CO}_{3}}_{aq}+\:{nH}_{2}O\to\:{K}_{2}{SiO}_{3}.{nH}_{2}O+{{CO}_{3}^{2-}}_{aq}\:\:\:\:$$ 2 3.3 Chemical compositions of biomass-based precursors: K-salt and RHA Table 2 presents the percentages of the major oxides in the biomasses (K-salt and RHA), quantified by ICP-OES and XRF, respectively. K 2 O (90.7%) is the major oxide in the K-salt, which confirms it as an important source for K + , which is one of the target alkali for water glass synthesis, required in geopolymerization [ 38 , 39 ]. This observation is in line with the FTIR observation (Fig. 4 ), from which potassium carbonate is the dominant constituent. Associated oxides are Na 2 O (1.4%), SO 3 (5.8%) and SiO 2 (2.0%). Regarding the major oxides of RHA, silicium oxide is dominant about 93.2% (Table 2 ). Associated oxide is K 2 O in a relatively low amount of 3.1%. These compositions highlight the potential of an alkali-silicate activating solution made from the combination of the two biomasses, via hydrothermal dissolution. Table 2 Percentage oxides composition of the K-salt and RHA Oxides CaO K 2 O Na 2 O SO 3 SiO 2 LOI nd K-salt (%) - 90.7 1.4 5.8 2.0 - - RHA (%) - 3.10 - - 93.20 1.20 3.40 3.4 Characteristics of activating solutions from partial substitution by K-salt 3.4.1 Effects of K-salt addition on pH of the activating solution All the activating solutions have pH > 13 (Fig. 5 ), indicating good alkalinity of solutions for geopolymer binder synthesis. The pH values show an approximate linear growth with K-salt addition (Fig. 5 ). This is linked to the alkalinity of the carbonate of the salt. 3.4.2 FTIR analysis of activating solutions The FTIR spectra of these solutions (Fig. 6 ) evidence the complete dissolution of the K-salts, as well as the formation of silicate as shown by the band at 980 cm − 1 [ 40 , 41 ]. The presence of free waters molecules is obvious from weakly H-bonded O-H bands at 3272 cm − 1 associated to the group vibration of the water molecule at 1637 cm − 1 [ 32 – 34 ]. As the amount of K-salt increases, a band related to the carbonatation of the solution appears at 1383 cm − 1 , which was associated to the stretching of C-O bonds [ 35 , 36 ]. This carbonatation will probably induce increase porosity of the products[ 42 ]. The increased intensities of C-O bonds suggest that K-salt addition enhances the alkalinity of the solutions, which potentially promote the geopolymerization. The band at 980 cm-1corresponds to the Si-O stretching vibration of RHA, confirming its siliceous nature [ 41 , 42 ]. The bands around 400 cm-1 is attributed to the Na/K-O bending vibration [ 43 ], suggesting the presence of sodium ions (Na+) and potassium (K+) ions in the activating solution. 3.5 Characteristics of synthesized geopolymers 3.5.1 Effect of K-salt addition on Initial and Final setting time of geopolymer binders Figure 7 illustrates the effect of K-salt addition on the initial and final setting times of two sets of geopolymer binders, GB and GR, labeled as G0, G8, G14, G20, G25, and G30, based on respective K-salt addition of 0%, 8%, 14%, 20%, 25%, and 30% to activating solutions used. These times increase with the extracted salt addition, up to 20 wt.% addition, before decreasing for both samples sets. The first phase observation is possibly due to the slow dissolution of the reactive species at room temperature (26 ± 5⁰C). Although the prepared activating solution forms a highly alkaline environment, the dissolution of the solid aluminosilicate phases (mainly from metakaolin) is probably slowed by the presence of inert phases, including quartz, muscovite, and anatase. The early setting of the lateritic clay compared to the kaolinitic clay geopolymer, can be associated with high reactive iron content. It has been reported that hematite associates with free silica and alumina to form ferri-silicate or ferri-alluminosilicate binding phases in alkaline activated geopolymer systems [ 43 ]. The unreactive phases mostly act as filler and might hinder the reaction rate by blocking reactive sites. This will consequently result in delaying the setting. The decrease in setting time above 20 wt.% K-salt addition observed in the second phase is indicative of the rapid polycondensation of dissolved silicate and aluminate species, once sufficient gel has formed. The increasing solubility of aluminosilicate precursors after the initial dissolution phase is facilitated by the increased alkalinity of the medium, leading to rapid gelation [ 44 ]. The difference in initial and final setting times of the two formulation sets is directly linked to the variation in iron content within their solid precursors. However, while the reaction with iron phases shortens the setting time, the reaction product is mostly consolidated ferri/ferro hydroxides, which does not contribute much to strength development. 3.5.2 Physical appearance of the synthesized geopolymers The 28-day-aged geopolymers specimens are exhibited in Fig. 8 . Their color aspect is coherent with their respective starting product OWC7 (for GB serie) and ORC7(for GR serie). Both series (GB and GR) expose no efflorescence, which is indicative of reduce excess alkalinity of the activating solution. This observation indicates that the used activating solutions have sufficient alkalinity to allow setting and consolidation of the geopolymers 3.5.3 Effect of K-salt addition on the structural and mineralogical properties of the synthesized geopolymers The FT-IR spectra of the obtained geopolymers are given in Fig. 9 . In both GB (Fig. 9 (a)) and GR (Fig. 9 (b)) series, the stretching of O-H is observed at 3675 cm − 1 related to water molecules which are confirmed by the group vibration band at 1645 cm − 1 [ 25 ]. These bands are absent in the starting materials’ spectra (Fig. 3 (b)), indicating the conversion of metakaolin to aluminosilicate oligomers and subsequent polycondensation into three-dimensional solid network of geopolymer. In addition, the shift in the Si-O stretching bands to lower wave number at around 980 cm − 1 relative to the starting calcined clays at around 1050 cm − 1 (Fig. 3 (b)) further confirms this transformation [ 45 ]. The incorporation of carbonate from k-salt into the geopolymer matrices is evidenced by the presence of the asymmetric stretching vibration of C-O bond around 1400 cm − 1 . The bands around 780cm − 1 in both samples correspond to Si–O–Si inter-tetrahedral bridging bonds [ 27 ] and those around 691 cm⁻¹ and 437 cm⁻¹ correspond to the bending vibrations of Si-O bond, indicating silicate network contributions commonly observed in quartz [ 28 , 29 ]. The X-ray diffraction (XRD) patterns of the formulated geopolymers (Fig. 10 ) do not exhibit any newly formed crystalline phases. The observed peaks correspond only to the mineral phases of the calcined clays, such as muscovite, quartz, anatase, and hematite, which remain approximately unchanged. The potential new mineral phases are poorly crystalized, which justifies the absence of distinct diffraction peaks characteristic of new crystalline structures. 3.5.4 Effect of K-salt addition on Physical and mechanical properties of geopolymers Figure 11 elucidates the effect of K-salt addition on physical and mechanical properties of the formulated geopolymers GB and GR series at 28th days age. The apparent density (Fig. 11 (a)) increases while open porosity (Fig. 11 (b)) and water absorption (Fig. 11 (c)) decreases with the addition of K-salt up to 20% in both series. This behavior is consistent with the increase in compressive strength (Fig. 11 (d)), with maximum values of 27.2 MPa and 17.9 MPa, respectively for GB and GR, at K-salt addition of 20 wt.%. This reveals that the slow dissolution and gelation results in a gradual strength gain over time. The higher compressive strengths of GB, compared to GR is due to the higher amorphous content (46.7%) of their precursor (Table 1 ). The more amorphous phase content of the aluminosilicate source materials, the higher the densification of the geopolymer matrix and vice versa. Hence, the optimal K-salt dosage recommended for best matrix strength is 20 wt.% of total alkaline. Beyond 20 wt.% addition, a decrease in apparent density as well as compressive strength is observed, while water uptake and porosity are almost constant. These pessimal tendencies with above 20 wt.% K-salt addition can be linked to carbonation, which may render the structure fragile by inducing disruption in the continuous spreading of geopolymer gel prior to geopolymer network formation. This result is in line with the findings by Yip et al. (2008) [ 46 ]. The slight changes in porosity or water uptake are associated with the disruption induced by carbonates, which mainly affects the mechanical response (Fig. 11 (d)) 4 Conclusion The main objective of this work was to examine the potentiality of two agro wastes as source materials for ecofriendly activating solutions to be used for geopolymerization. Ashes form cocoa pod and rice husk were respectively used in the extraction of amorphous silica and K-salt for the activating solution preparation. The aluminosilicate precursors used were obtained by firing two clay materials, one kaolinitic and the other lateritic, from Ntuissong II. The infra-red analyses of both raw and calcined clays confirmed the formation of metakaolin. The activating solutions were prepared hydrothermally by adding varying percentages of K-salt from cocoa pod to a mixture of amorphous silica from RHA and sodium hydroxide. The synthesized geopolymers indicate improving mechanical and physical responses with K-salt addition between 15 wt.% and 20 wt.% with respect to total alkali, to activating solution. In this same interval the initial and final setting times were relatively high. The use of activating solution with the least K-salt of 8 wt.% induces geopolymerization with improved physical (increase density, reduce water porosity and water uptake) and mechanical responses, compared to the use of activating solution without K-salt. Based on these findings, the study agro waste ashes can be conveniently used in ecofriendly biding materials via hydrothermal dissolution. Declarations Funding: The authors declare that no specific funding was received for this research. Conflict of Interest/Competing Interests: The authors declare no conflicts of interest or competing interests related to this work. Ethics Approval and Consent to Participate: This study complies with ethical standards. Consent for Publication: All authors have reviewed and approved the final manuscript for publication. Data Availability: The authors declare that the data supporting the findings of this study are available within the paper. Should any raw data file be needed in another format, they are available from the corresponding author upon reasonable request. Materials Availability: Not applicable Code Availability: Not applicable Author Contributions: Cyprien Joël Ekani : Conceptualization, Methodology, Investigation, Writing - original draft & Project administration. Paul Venyite: Investigation, Visualization, Writing - review & editing. Jean Marie Kepdieu: Visualization, Writing - review & editing, Chantale Njiomou Djangang: Conceptualization, Validation, Supervision & Resources. Phillipe Blanchart: Conceptualization & Supervision. Jean Aimé MBEY : writing - review & editing. References Van Deventer JS, Provis JL, Duxson P (2012) Technical and commercial progress in the adoption of geopolymer cement. Miner Eng 29:89–104 Van Deventer JS, Provis JL, Duxson P, Brice DG (2010) Chemical research and climate change as drivers in the commercial adoption of alkali activated materials. Waste Biomass Valorization 1:145–155 Shamsaei E, Bolt O, Basquiroto de Souza F, et al (2021) Pathways to commercialisation for brown coal fly ash-based geopolymer concrete in Australia. Sustainability 13:4350 Danish A, Ozbakkaloglu T, Mosaberpanah MA, et al (2022) Sustainability benefits and commercialization challenges and strategies of geopolymer concrete: A review. J Build Eng 58:105005 Revathi T, Vanitha N, Jeyalakshmi R, et al (2022) Adoption of alkali-activated cement-based binders (geopolymers) from industrial by-products for sustainable construction of utility buildings-A field demonstration. J Build Eng 52:104450 Matsimbe J, Dinka M, Olukanni D, Musonda I (2022) Geopolymer: A systematic review of methodologies. Materials 15:6852 Kadhim A, Mankhi BS, Al-Bujasim M (2024) Review of Geopolymer Technology, Barriers and Limitations. Al-Mustaqbal J Sustain Eng Sci 2:4 You S, Ho SW, Li T, et al (2019) Techno-economic analysis of geopolymer production from the coal fly ash with high iron oxide and calcium oxide contents. J Hazard Mater 361:237–244 Segura IP, Ranjbar N, Damø AJ, et al (2023) A review: Alkali-activated cement and concrete production technologies available in the industry. Heliyon 9: Venyite P, Makone EC, Kaze RC, et al (2021) Effect of combined metakaolin and basalt powder additions to laterite-based geopolymers activated by rice husk ash (RHA)/NaOH solution. Silicon 1–20 Kamseu E, à Moungam LB, Cannio M, et al (2017) Substitution of sodium silicate with rice husk ash-NaOH solution in metakaolin based geopolymer cement concerning reduction in global warming. J Clean Prod 142:3050–3060 Rhein-Knudsen N, Ale MT, Rasmussen S, et al (2018) Alkaline extraction of seaweed carrageenan hydrocolloids using cocoa pod husk ash. Biomass Convers Biorefinery 8:577–583 Vriesmann LC, Amboni RD de MC, de Oliveira Petkowicz CL (2011) Cacao pod husks (Theobroma cacao L.): Composition and hot-water-soluble pectins. Ind Crops Prod 34:1173–1181 Cruz G, Pirilä M, Huuhtanen M, et al (2012) Production of activated carbon from cocoa (Theobroma cacao) pod husk. J Civ Env Eng 2:1–6 Zawawi Daud ZD, Angzzas Sari M, Ashuvila Mohd Aripin AMA, et al (2013) Chemical composition and morphological of cocoa pod husks and cassava peels for pulp and paper production. FAO (2024). online https://www.fao.org/faostat/en/#country FAO (2018) Cameroon production. online Abubakar IR, Maniruzzaman KM, Dano UL, et al (2022) Environmental sustainability impacts of solid waste management practices in the global South. Int J Environ Res Public Health 19:12717 Dehnavi A, Rajabi M, Bavarsiha F (2021) The effect of temperature, time of curing and Na2O/SiO2 molar ratio on mechanical and chemical properties of geopolymer cement. Metall Mater Eng 27:213–226 Alves L, Leklou N, De Barros S (2020) A comparative study on the effect of different activating solutions and formulations on the early stage geopolymerization process. p 01039 Koudia LM, Lebouachera SEI, Blanc S, et al (2022) Characterization of Clay Materials from Ivory Coast for Their Use as Adsorbents for Wastewater Treatment. J Miner Mater Charact Eng 10:319–337 Madejová J (2003) FTIR techniques in clay mineral studies. Vib Spectrosc 31:1–10 Black L (2009) Raman spectroscopy of cementitious materials. Spectrosc Prop Inorg Organomet Compd 40:72–127 Jirásek J, Cejka J, Vrtiska L, et al (2017) Molecular structure of the phosphate mineral koninckite-a vibrational spectroscopic study. J Geosci 62:271–279 Madejová J (2003) FTIR techniques in clay mineral studies. Vib Spectrosc 31:1–10 José Fripiat (1960) Application de la spectroscopie infrarouge à l’étude des minéraux argileux. Bull. Groupe Fr. Argiles 25–41 Zawrah M, Gado R, Khattab R (2018) Optimization of slag content and properties improvement of metakaolin-slag geopolymer mixes. Open Mater Sci J 12: Belmokhtar N, Ammari M, Brigui J (2017) Comparison of the microstructure and the compressive strength of two geopolymers derived from Metakaolin and an industrial sludge. Constr Build Mater 146:621–629 Saikia BJ, Parthasarathy G (2010) Fourier transform infrared spectroscopic characterization of kaolinite from Assam and Meghalaya, Northeastern India. J Mod Phys 1:206–210 AZIZI K, MAISSARA J, CHBIHI ME, NAIMI Y Thermal Transformation of Kaolinite Clays: Analyzing Dehydroxylation and Amorphization for Improved Pozzolanic Performance Sui R, Rizkalla AS, Charpentier PA (2006) FTIR study on the formation of TiO2 nanostructures in supercritical CO2. J Phys Chem B 110:16212–16218 Etim AO, Betiku E, Ajala SO, et al (2018) Potential of ripe plantain fruit peels as an ecofriendly catalyst for biodiesel synthesis: optimization by artificial neural network integrated with genetic algorithm. Sustainability 10:707 Nath B, Das B, Kalita P, Basumatary S (2019) Waste to value addition: Utilization of waste Brassica nigra plant derived novel green heterogeneous base catalyst for effective synthesis of biodiesel. J Clean Prod 239:118112 Betiku E, Okeleye AA, Ishola NB, et al (2019) Development of a novel mesoporous biocatalyst derived from kola nut pod husk for conversion of kariya seed oil to methyl esters: A case of synthesis, modeling and optimization studies. Catal Lett 149:1772–1787 Kalinkin A, Kalinkina E, Zalkind O, Makarova T (2005) Chemical Interaction of Calcium Oxide and Calcium Hydroxide with CO2 during Mechanical Activation. Inorg Mater 41:1073–1079. https://doi.org/10.1007/s10789-005-0263-1 Zhao C, Lv P, Yang L, et al (2018) Biodiesel synthesis over biochar-based catalyst from biomass waste pomelo peel. Energy Convers Manag 160:477–485 Li H, Liu F, Ma X, et al (2019) Catalytic performance of strontium oxide supported by MIL–100 (Fe) derivate as transesterification catalyst for biodiesel production. Energy Convers Manag 180:401–410 da Silva Rocha T, Dias DP, França FCC, et al (2018) Metakaolin-based geopolymer mortars with different alkaline activators (Na+ and K+). Constr Build Mater 178:453–461 Duxson P, Mallicoat SW, Lukey GC, et al (2007) The effect of alkali and Si/Al ratio on the development of mechanical properties of metakaolin-based geopolymers. Colloids Surf Physicochem Eng Asp 292:8–20 Liu C, Yao X, Zhang W (2020) Controlling the setting times of one-part alkali-activated slag by using honeycomb ceramics as carrier of sodium silicate activator. Constr Build Mater 235:117091 Handke M, Mozgawa W (1993) Vibrational spectroscopy of the amorphous silicates. Vib Spectrosc 5:75–84 Pasupathy K, Sanjayan J, Rajeev P (2021) Evaluation of alkalinity changes and carbonation of geopolymer concrete exposed to wetting and drying. J Build Eng 35:102029 Kamseu E, Kaze CR, Fekoua JNN, et al (2020) Ferrisilicates formation during the geopolymerization of natural Fe-rich aluminosilicate precursors. Mater Chem Phys 240:122062 Duxson P, Fernández-Jiménez A, Provis JL, et al (2007) Geopolymer technology: the current state of the art. J Mater Sci 42:2917–2933 Samadhi TW, Purbasari A, Wulandari W (2020) Geopolymer Preparation from Bamboo Ash Containing Kaolin as Ash Fusion Control Agent. Trans Tech Publ, pp 189–194 Yip CK, Provis JL, Lukey GC, van Deventer JS (2008) Carbonate mineral addition to metakaolin-based geopolymers. Cem Concr Compos 30:979–985 Additional Declarations No competing interests reported. Cite Share Download PDF Status: Published Journal Publication published 08 Dec, 2025 Read the published version in Silicon → Version 1 posted Editorial decision: Revision requested 01 Jul, 2025 Reviews received at journal 16 Jun, 2025 Reviews received at journal 14 Jun, 2025 Reviewers agreed at journal 13 Jun, 2025 Reviewers agreed at journal 17 May, 2025 Reviewers invited by journal 15 May, 2025 Editor assigned by journal 11 Apr, 2025 Submission checks completed at journal 11 Apr, 2025 First submitted to journal 07 Apr, 2025 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-6396121","acceptedTermsAndConditions":true,"allowDirectSubmit":false,"archivedVersions":[],"articleType":"Research Article","associatedPublications":[],"authors":[{"id":457995974,"identity":"7da96af5-68ec-411d-ba80-26ce4dd58756","order_by":0,"name":"Cyprien Joël Ekani","email":"","orcid":"","institution":"University of Yaounde I","correspondingAuthor":false,"prefix":"","firstName":"Cyprien","middleName":"Joël","lastName":"Ekani","suffix":""},{"id":457995975,"identity":"7c9d1f6d-27d5-4a92-8cd3-03181af70c63","order_by":1,"name":"Paul Venyite","email":"","orcid":"","institution":"University of Yaounde I","correspondingAuthor":false,"prefix":"","firstName":"Paul","middleName":"","lastName":"Venyite","suffix":""},{"id":457995976,"identity":"76b69fce-4327-4969-842f-753bf6ecfbd9","order_by":2,"name":"Jean Marie Kepdieu","email":"","orcid":"","institution":"University of Yaounde I","correspondingAuthor":false,"prefix":"","firstName":"Jean","middleName":"Marie","lastName":"Kepdieu","suffix":""},{"id":457995977,"identity":"ca9f4e08-3a63-4cb2-a82d-9d287c95db12","order_by":3,"name":"Chantale Njiomou Djangang","email":"data:image/png;base64,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","orcid":"","institution":"University of Yaounde I","correspondingAuthor":true,"prefix":"","firstName":"Chantale","middleName":"Njiomou","lastName":"Djangang","suffix":""},{"id":457995978,"identity":"fb978b1a-a772-4d03-98db-89d563c15d6c","order_by":4,"name":"Phillipe Blanchart","email":"","orcid":"","institution":"University of Limoges","correspondingAuthor":false,"prefix":"","firstName":"Phillipe","middleName":"","lastName":"Blanchart","suffix":""},{"id":457995979,"identity":"b00549a3-6e79-4dc9-8200-f75e35e27cb4","order_by":5,"name":"Jean Aimé","email":"","orcid":"","institution":"University of Yaounde I","correspondingAuthor":false,"prefix":"","firstName":"Jean","middleName":"","lastName":"Aimé","suffix":""}],"badges":[],"createdAt":"2025-04-07 16:23:10","currentVersionCode":1,"declarations":"","doi":"10.21203/rs.3.rs-6396121/v1","doiUrl":"https://doi.org/10.21203/rs.3.rs-6396121/v1","draftVersion":[],"editorialEvents":[{"content":"https://doi.org/10.1007/s12633-025-03472-8","type":"published","date":"2025-12-08T15:58:12+00:00"}],"editorialNote":"","failedWorkflow":false,"files":[{"id":83068577,"identity":"4a54b2d1-ccec-4e6a-91fe-a1bdadbdf0d8","added_by":"auto","created_at":"2025-05-19 16:10:34","extension":"png","order_by":1,"title":"Figure 1","display":"","copyAsset":false,"role":"figure","size":150764,"visible":true,"origin":"","legend":"\u003cp\u003eXRD patterns (a) raw OWC and ORC and (b) calcined OWC7 and ORC7\u003c/p\u003e","description":"","filename":"floatimage1.png","url":"https://assets-eu.researchsquare.com/files/rs-6396121/v1/684bca1495d6aee39852e4b2.png"},{"id":83068626,"identity":"9ce4864c-5c0d-407a-a9b3-545034d15fac","added_by":"auto","created_at":"2025-05-19 16:10:40","extension":"png","order_by":2,"title":"Figure 2","display":"","copyAsset":false,"role":"figure","size":109234,"visible":true,"origin":"","legend":"\u003cp\u003eThermal behaviour (a) OWC and (b) ORC\u003c/p\u003e","description":"","filename":"floatimage2.png","url":"https://assets-eu.researchsquare.com/files/rs-6396121/v1/df44429b49d46a415ae34234.png"},{"id":83068506,"identity":"f44794f7-8306-4855-8d82-11c34f7d9f02","added_by":"auto","created_at":"2025-05-19 16:10:28","extension":"png","order_by":3,"title":"Figure 3","display":"","copyAsset":false,"role":"figure","size":116148,"visible":true,"origin":"","legend":"\u003cp\u003eFTIR spectra of (a) raw clays (OWC and ORC); (b) calcined products at 700°C (OWC7 and ORC7)\u003c/p\u003e","description":"","filename":"floatimage3.png","url":"https://assets-eu.researchsquare.com/files/rs-6396121/v1/10fc7bee1fc1ff8fa372b49d.png"},{"id":83068601,"identity":"ff190e66-55ba-4419-89d3-fe1265bb2d33","added_by":"auto","created_at":"2025-05-19 16:10:37","extension":"png","order_by":4,"title":"Figure 4","display":"","copyAsset":false,"role":"figure","size":105932,"visible":true,"origin":"","legend":"\u003cp\u003eFTIR spectrum of K-salt\u003c/p\u003e","description":"","filename":"floatimage4.png","url":"https://assets-eu.researchsquare.com/files/rs-6396121/v1/ebbcb73fa5515721e00190da.png"},{"id":83068575,"identity":"aaa4985d-3b18-4048-b99b-997f08632325","added_by":"auto","created_at":"2025-05-19 16:10:34","extension":"png","order_by":5,"title":"Figure 5","display":"","copyAsset":false,"role":"figure","size":112837,"visible":true,"origin":"","legend":"\u003cp\u003eEffect of K-salt addition on the pH of activating solutions\u003c/p\u003e","description":"","filename":"floatimage5.png","url":"https://assets-eu.researchsquare.com/files/rs-6396121/v1/d10faaac2a004593c0cc12ab.png"},{"id":83068455,"identity":"4afb33a0-aa29-46f1-b91e-8c8bd4a1759b","added_by":"auto","created_at":"2025-05-19 16:10:24","extension":"png","order_by":6,"title":"Figure 6","display":"","copyAsset":false,"role":"figure","size":234103,"visible":true,"origin":"","legend":"\u003cp\u003eEffect of K-salt addition on the chemical structures of activating solutions\u003c/p\u003e","description":"","filename":"floatimage6.png","url":"https://assets-eu.researchsquare.com/files/rs-6396121/v1/1d4fa3b24f35d78b561abe6d.png"},{"id":83069349,"identity":"d924f03a-ceb2-447d-9562-f7f3f7a3e6b5","added_by":"auto","created_at":"2025-05-19 16:18:31","extension":"png","order_by":7,"title":"Figure 7","display":"","copyAsset":false,"role":"figure","size":674453,"visible":true,"origin":"","legend":"\u003cp\u003eEffect of K-salt addition on the initial and final setting times of the synthesized geopolymers specimens\u003c/p\u003e","description":"","filename":"floatimage7.png","url":"https://assets-eu.researchsquare.com/files/rs-6396121/v1/caa7a4f58ca3226cf7e6fa20.png"},{"id":83068605,"identity":"6abd63bd-489c-41f3-bd2a-b8ffd5b3d345","added_by":"auto","created_at":"2025-05-19 16:10:38","extension":"png","order_by":8,"title":"Figure 8","display":"","copyAsset":false,"role":"figure","size":149866,"visible":true,"origin":"","legend":"\u003cp\u003eImages of 28 days old geopolymers specimens\u003c/p\u003e","description":"","filename":"floatimage8.png","url":"https://assets-eu.researchsquare.com/files/rs-6396121/v1/13e9f7c62c29db55bb48f256.png"},{"id":83068636,"identity":"90d6a870-4da8-450f-836b-6e4405872440","added_by":"auto","created_at":"2025-05-19 16:10:42","extension":"png","order_by":9,"title":"Figure 9","display":"","copyAsset":false,"role":"figure","size":163468,"visible":true,"origin":"","legend":"\u003cp\u003eEffect of the K-salt addition on the structural framework of geopolymers (a) made from OWC7 and (b) made from ORC7\u003c/p\u003e","description":"","filename":"floatimage9.png","url":"https://assets-eu.researchsquare.com/files/rs-6396121/v1/2a72d6a955055047f7346d28.png"},{"id":83068572,"identity":"cfde613a-b5b8-4537-927d-58a968cc3645","added_by":"auto","created_at":"2025-05-19 16:10:34","extension":"png","order_by":10,"title":"Figure 10","display":"","copyAsset":false,"role":"figure","size":234636,"visible":true,"origin":"","legend":"\u003cp\u003eXRD patterns of the geopolymers (a) made from OWC7and (b) made from ORC7\u003c/p\u003e","description":"","filename":"floatimage10.png","url":"https://assets-eu.researchsquare.com/files/rs-6396121/v1/ce266db2f187a862dc4284ef.png"},{"id":83068579,"identity":"e2b2995c-15f5-4d20-908d-2e8db70c8a3b","added_by":"auto","created_at":"2025-05-19 16:10:34","extension":"png","order_by":11,"title":"Figure 11","display":"","copyAsset":false,"role":"figure","size":144964,"visible":true,"origin":"","legend":"\u003cp\u003eEffect of K-salt addition on: a) apparent density; b) open porosity; c) water absorption; d) compressive strength, of GB and GR\u003c/p\u003e","description":"","filename":"floatimage11.png","url":"https://assets-eu.researchsquare.com/files/rs-6396121/v1/27a01f9e1b840200a99b3738.png"},{"id":98245282,"identity":"0a8189d8-ee89-4e9f-a813-3cf52f5a1671","added_by":"auto","created_at":"2025-12-15 16:17:33","extension":"pdf","order_by":0,"title":"","display":"","copyAsset":false,"role":"manuscript-pdf","size":3316457,"visible":true,"origin":"","legend":"","description":"","filename":"manuscript.pdf","url":"https://assets-eu.researchsquare.com/files/rs-6396121/v1/b9478de6-2ddb-400d-b9e5-5912e27c9bbb.pdf"}],"financialInterests":"No competing interests reported.","formattedTitle":"Eco-Friendly Activating Solutions from Cocoa Pod Ash and Rice Husk Ash for Geopolymerization","fulltext":[{"header":"1 Introduction","content":"\u003cp\u003eThe widespread adoption of geopolymer technology has been hindered by several factors, including high production costs, limited availability of raw materials, and environmental concerns associated with traditional activators[\u003cspan additionalcitationids=\"CR2\" citationid=\"CR1\" class=\"CitationRef\"\u003e1\u003c/span\u003e\u0026ndash;\u003cspan citationid=\"CR3\" class=\"CitationRef\"\u003e3\u003c/span\u003e]. Additionally, lack of standardization and regulations, public perception and awareness, competition with established materials, specialized labor and training have all contributed to the timid adoption of geopolymers [\u003cspan additionalcitationids=\"CR5 CR6\" citationid=\"CR4\" class=\"CitationRef\"\u003e4\u003c/span\u003e\u0026ndash;\u003cspan citationid=\"CR7\" class=\"CitationRef\"\u003e7\u003c/span\u003e].\u003c/p\u003e \u003cp\u003eFurthermore, the high cost of conventional activators, such as potassium silicate (K\u003csub\u003e2\u003c/sub\u003eSiO\u003csub\u003e3\u003c/sub\u003e) and potassium hydroxide (KOH), poses a significant barrier to adoption in developing countries, particularly in Africa. Since the total production cost of geopolymers primarily depends on the cost of these activators [\u003cspan citationid=\"CR8\" class=\"CitationRef\"\u003e8\u003c/span\u003e, \u003cspan citationid=\"CR9\" class=\"CitationRef\"\u003e9\u003c/span\u003e], it becomes difficult for countries with limited financial resources to adopt the innovative technology.\u003c/p\u003e \u003cp\u003eTo address these challenges and make geopolymer technology more accessible, this study aims to develop a sustainable and cost-effective activating solution using two abundantly available agro-waste materials: Cocoa Pod Ash (CPA) and Rice Husk Ash (RHA). Recent studies have explored the use of agro-wastes as sustainable alternatives for the preparation of activated solutions in geopolymers. For example, Rice Husk Ash (RHA) has been utilized due to its high silica content [\u003cspan citationid=\"CR10\" class=\"CitationRef\"\u003e10\u003c/span\u003e, \u003cspan citationid=\"CR11\" class=\"CitationRef\"\u003e11\u003c/span\u003e]. Similarly, Cocoa Pod Ash (CPA) has been investigated for its high potassium content [\u003cspan additionalcitationids=\"CR13 CR14\" citationid=\"CR12\" class=\"CitationRef\"\u003e12\u003c/span\u003e\u0026ndash;\u003cspan citationid=\"CR15\" class=\"CitationRef\"\u003e15\u003c/span\u003e]. However, the combined use of RHA and CPA for the production of Na/K silicates has not been extensively explored.\u003c/p\u003e \u003cp\u003eCameroon is the fourth largest cocoa producer in the world, accounting for 280,000 to 290,000 metric tons per year [\u003cspan citationid=\"CR16\" class=\"CitationRef\"\u003e16\u003c/span\u003e]. The production is also large in terms of paddy, eg. 332, 000 tons in 2018 [\u003cspan citationid=\"CR17\" class=\"CitationRef\"\u003e17\u003c/span\u003e]. The important quantities of waste generated by these two crops after extracting cocoa bean or rice are often discarded and burnt or left to rot in opened fields. The practice of improper waste deposition has in most cases resulted in the transformation of large useful surfaces into wastelands. In other situations, typical of the tropical climate, the accumulation of the ashes along river bangs in dry seasons leads to blockage of water way, resulting in flooding upstream in the rainy season. Additionally, the lack of proper waste management and disposal practices exacerbates these issues, posing a significant threat to the environment and public health[\u003cspan citationid=\"CR18\" class=\"CitationRef\"\u003e18\u003c/span\u003e].\u003c/p\u003e \u003cp\u003eThe innovative character of this work lies in the preparation of geopolymer activating solutions based on the extraction of target precursor from locally available agro-wastes (CPA and RHA) and their adaptable application in geopolymer synthesis using calcined clay from locally available clay materials. This unique combination will potentially lead to a more sustainable alternative for building binders.\u003c/p\u003e"},{"header":"2 Materials and experimental procedures","content":"\u003cdiv id=\"Sec3\" class=\"Section2\"\u003e \u003ch2\u003e2.1 Materials\u003c/h2\u003e \u003cp\u003eTwo kaolinitic clay materials from Ntouessong II a locality of the Mefou and Akono Division in the Centre Region of Cameroon were used. One of the samples coded OWC, is sedimentary clay with a whitish appearance (The Munsell color code 2.5Y 8/1) and the other one coded ORC, is a lateritic clay having a yellowish color (Munsell color code 10YR8/6). The respective geographical coordinates of the sampling are 11\u0026deg;14'30'' and 11\u0026deg;26'30'' East longitude and between 3\u0026deg;36'15'' and 3\u0026deg;47'45'' North latitude, respectively for ORC and OWC. The clay materials were wet sieved through a 120\u0026micro;m mesh, dried at ambient conditions (24\u0026thinsp;\u0026plusmn;\u0026thinsp;5⁰C and 70\u0026thinsp;\u0026plusmn;\u0026thinsp;5% RH), crushed, then sieved at 100 \u0026micro;m before being stored in polyethylene bags for further uses.\u003c/p\u003e \u003cp\u003eThe calcined clays were obtained by heating the raw powdered material in an electric furnace (Nabertherm Model LH 60/14) from ambient temperature of 25⁰C to 700\u0026deg;C. The heating rate was 5\u0026deg;C/min and the samples were left for 4 hours at the final temperature before cooling to room temperature. The calcined powders were coded OWC7 and ORC7 respectively for OWC and ORC.\u003c/p\u003e \u003cp\u003eCocoa pods and rice husk were respectively, collected from Ntouessong II, locality in the Centre Region of Cameroon and from the Upper Nun Valley Development Association (UNVDA), a rice factory in Ndop, Northwest Region of Cameroon. The biomass ashes were collected from open-air burnt dumps, then sieved at 100 \u0026micro;m to obtain the ashes coded CPA and RHA, respectively for cocoa pod ash and rice husk ash.\u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec4\" class=\"Section2\"\u003e \u003ch2\u003e2.2 Experimental procedures\u003c/h2\u003e \u003cdiv id=\"Sec5\" class=\"Section3\"\u003e \u003ch2\u003e2.2.1 Extraction of Potassium Salts\u003c/h2\u003e \u003cp\u003eFor the extraction of the K-salt, CPA were dispersed in distilled water in a solid/liquid ratio of 1:5 then boiled under constant stirring for 10 min, then filtered over a Whatman 5 filter. The procedure was repeated using the collected solid residue until the filtrate pH is in the range 7 to 8. The collected filtrate was left for evaporation under ambient and the K-salt was collected and stored in polyethylene bags prior to its use for activation solution preparation.\u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec6\" class=\"Section3\"\u003e \u003ch2\u003e2.2.2 Preparation of Activating Solutions\u003c/h2\u003e \u003cp\u003eThe sodium silicate solution was prepared with a Na\u003csub\u003e2\u003c/sub\u003eO/SiO\u003csub\u003e2\u003c/sub\u003e ratio of 0.7[\u003cspan citationid=\"CR19\" class=\"CitationRef\"\u003e19\u003c/span\u003e, \u003cspan citationid=\"CR20\" class=\"CitationRef\"\u003e20\u003c/span\u003e]. The alkali content of the solution was then modified by adding varying percentages of K-salt with respect to total alkali (Na\u0026thinsp;+\u0026thinsp;K), to obtain six activating solutions. Each mixture was reflux heated at 80\u0026deg;C for 4 hours. Thereafter, the gel phase was collected, its pH was recorded and the solution stored for 48h in closed glass vessel prior to its use as activating solution. The activating solutions were coded S0, S8, S14, S20, S25, and S30 with respective K-salt percentages of 0%, 8%, 14%, 20%, 25% and 30%.\u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec7\" class=\"Section3\"\u003e \u003ch2\u003e2.2.3 Preparation of Geopolymer binders\u003c/h2\u003e \u003cp\u003eThe calcined clay was mixed with the various activating solutions, S0, S1, S2, S3, S4, and S5 at solid/liquid mass ratios of 1.3 and 1.4, respectively for OWC7 and ORC7. The obtained mixtures were homogenized for 5 minutes using a BOMANN mixer (model D-479086) to obtain two series of geopolymer binders. The obtained geopolymers were labelled GB-x and GR-x, respectively for OWC7 and ORC7. The \u0026ldquo;x\u0026rdquo; in the label is related to the activating solution used. The pastes were then poured into cylindrical PVC molds having dimensions, diameter \u0026times; height of 20mm\u0026times;40mm. The resulting specimens were immediately sealed in a thin polyethylene film and then placed in ambient condition of the laboratory (27\u0026thinsp;\u0026plusmn;\u0026thinsp;3\u0026deg;C). Specimens were demolded 48 hours after casting and left in the open air for physical and mechanical characterization at 28 days.\u003c/p\u003e \u003c/div\u003e \u003c/div\u003e \u003cdiv id=\"Sec8\" class=\"Section2\"\u003e \u003ch2\u003e2.3 Characterization techniques\u003c/h2\u003e \u003cp\u003eThe mineralogical analysis of the raw clays and geopolymer products was carried out using a Bruker-AXS D8 Advanced X-ray Powder Diffractometer. The diffraction patterns are recorded using a Cu-Kα (λ\u0026thinsp;=\u0026thinsp;1.5406 \u0026Aring;) radiation operating under a voltage of 40 kV and a current of 40 mA in a 2θ range of 5 to 70\u0026deg; and a scanning step of 0.03 \u0026deg;/s.\u003c/p\u003e \u003cp\u003eThe FTIR analysis was carried out in total reflectance mode in a wavenumber range of 4000 and 400 cm\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e using a Bruker Alpha-p spectrometer.\u003c/p\u003e \u003cp\u003eThe thermo gravimetric analysis (TGA) was performed using a thermo gravimetric device NETZSCH STA 409PC/PG\u003c/p\u003e \u003cp\u003eThe amorphous phase content of the calcined clays OWC7 and ORC7 was determined through chemical treatment with sodium hydroxide (NaOH) and hydrochloric acid (HCl) solutions. In this process, 3g of the calcined clay is mixed with 30 mL of 8 M NaOH solution then warmed for 30 minutes at 30\u0026deg;C before washing and centrifuging until neutral pH is measured in the supernatant. The residue is further dissolve in 0.5 M HCl solution and submitted to the same cycle of warming, washing and centrifuging to neutral pH in the supernatant. The resulting residue was dried at 110\u0026deg;C for 24 hours and weighed to calculate the amorphous phase content using the Eq.\u0026nbsp;1.\u003c/p\u003e \u003cp\u003e% amorphous phase = \u003cspan class=\"InlineEquation\"\u003e\u003cspan class=\"mathinline\"\u003e\\(\\:\\frac{{M}_{1}-{M}_{2}}{{M}_{1}}\\)\u003c/span\u003e\u003c/span\u003e x 100 (1)\u003c/p\u003e \u003cp\u003ewhere \u003cem\u003eM\u003c/em\u003e\u003csub\u003e\u003cem\u003e1\u003c/em\u003e\u003c/sub\u003e is the mass of sample and \u003cem\u003eM\u003c/em\u003e\u003csub\u003e\u003cem\u003e2\u003c/em\u003e\u003c/sub\u003e, the mass of residue\u003c/p\u003e \u003cp\u003eThe specific surface area (SSA) by nitrogen absorption of the clay materials was determined using Brunauer-Emmet-Teller (B.E.T) method.\u003c/p\u003e \u003cp\u003eThe chemical analysis of extracted salts was carried out using Inductive Coupled Plasma by Optical Emission Spectroscopy (ICP-OES) using a Thermo Scientific iCAP 7400 duo ICP-OES apparatus.\u003c/p\u003e \u003cp\u003eThe initial and final setting time of the various geopolymers was evaluated according to EN 1963 standard using the Vicat apparatus, measuring the time taken for a needle to penetrate a cement paste or mortar held in a frustoconical mold.\u003c/p\u003e \u003cp\u003eApparent density, water absorption rate, and open porosity were assessed from the Archimedes test (ISO 5017/1985).\u003c/p\u003e \u003cp\u003eCompressive strength of geopolymer samples aged for 28 days was obtained by the average of three samples tested on an Automatic Compression Testing Machine (AIMIL COMPTEST 2000, India).\u003c/p\u003e \u003c/div\u003e"},{"header":"3 Results and discussion","content":"\u003cdiv id=\"Sec10\" class=\"Section2\"\u003e \u003ch2\u003e3.1 Characteristics of starting materials\u003c/h2\u003e \u003cdiv id=\"Sec11\" class=\"Section3\"\u003e \u003ch2\u003e3.1.1 Mineralogical Composition of raw materials\u003c/h2\u003e \u003cp\u003eThe XRD analysis of the two raw clay materials OWC and ORC (Fig.\u0026nbsp;\u003cspan refid=\"Fig1\" class=\"InternalRef\"\u003e1\u003c/span\u003e (a)), reveals a similar mineralogical assemblage due to the sampling environment. The presence of Muscovite, Kaolinite, Anatase and Quartz in both samples indicates a common silicate-rich provenance. However, the ORC is iron oxy/hydroxyl richer than the OWC. The hematite diffraction peaks are less intense in OWC, which accounts for its whitish color. Both clays are kaolinite rich materials, with main associate minerals being muscovite and quartz. After calcination at 700\u0026deg;C (OWC7 and ORC7) in Fig.\u0026nbsp;\u003cspan refid=\"Fig1\" class=\"InternalRef\"\u003e1\u003c/span\u003e (b), the Kaolinite mineral completely transformed into metakaolinite, while the goethite totally disappeared in ORC7 (Fig.\u0026nbsp;\u003cspan refid=\"Fig1\" class=\"InternalRef\"\u003e1\u003c/span\u003e (b)), suggesting the conversion of goethite into hemathite (α-Fe\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e3\u003c/sub\u003e), which accounts for the intensification of the reddish brown color of the ORC7 [\u003cspan citationid=\"CR10\" class=\"CitationRef\"\u003e10\u003c/span\u003e]. The relative intensity of 7.18 \u0026Aring; diffraction peak in both samples indicates a higher kaolinite content in OWC, compared to ORC.\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec12\" class=\"Section3\"\u003e \u003ch2\u003e3.1.2 Thermal Behavior (ATD/TG) of the raw materials\u003c/h2\u003e \u003cp\u003eThe thermal analysis curve of the clayey materials is presented in Fig.\u0026nbsp;\u003cspan refid=\"Fig2\" class=\"InternalRef\"\u003e2\u003c/span\u003e. Both curves corroborate the mineral composition of the sample from XRD. In Fig.\u0026nbsp;\u003cspan refid=\"Fig2\" class=\"InternalRef\"\u003e2\u003c/span\u003e (a) and 2 (b), the adsorbed water departure onsets at 66\u0026deg;C and 77\u0026deg;C, respectively for OWC and ORC. The difference is attributed to the presence of goethite in ORC that induces increase adsorbed water [\u003cspan citationid=\"CR21\" class=\"CitationRef\"\u003e21\u003c/span\u003e]. Both samples exhibit kaolinite dehydroxylation at 480\u0026deg;C for OWC and 490\u0026deg;C for ORC. The dehydroxylation temperatures agree with the kaolinitic nature of the clayey materials. Additionally, the ORC curves (Fig.\u0026nbsp;\u003cspan refid=\"Fig2\" class=\"InternalRef\"\u003e2\u003c/span\u003e (b)) exhibit a pronounced peak at 298\u0026deg;C, corresponding to the transformation of goethite into hematite, whereas a similar but less intense peak appears in OWC at 288\u0026deg;C (Fig.\u0026nbsp;\u003cspan refid=\"Fig2\" class=\"InternalRef\"\u003e2\u003c/span\u003e (a)).\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec13\" class=\"Section3\"\u003e \u003ch2\u003e3.1.3 Infra-Red analysis of clay materials\u003c/h2\u003e \u003cp\u003eThe infrared spectroscopy results for the two clay materials, OWC and ORC (Fig.\u0026nbsp;\u003cspan refid=\"Fig3\" class=\"InternalRef\"\u003e3\u003c/span\u003e) reveal significant changes in their vibration frequencies upon calcination at 700\u0026deg;C. The strong and broad bands observed between 3695 cm\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e and 3620 cm\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e in both samples (Fig.\u0026nbsp;\u003cspan refid=\"Fig3\" class=\"InternalRef\"\u003e3\u003c/span\u003e (a)), are characteristic of external and internal \u0026ndash;OH stretching vibrations of kaolinite [\u003cspan citationid=\"CR22\" class=\"CitationRef\"\u003e22\u003c/span\u003e, \u003cspan citationid=\"CR23\" class=\"CitationRef\"\u003e23\u003c/span\u003e]. The inner surface stretching is observed at about 3655 cm\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e. A distinct band at 1635 cm\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e in ORC, which is less marked in OWC, is attributed to the group vibration of H\u0026ndash;O\u0026ndash;H in free water adsorbed within the kaolinite interlayer [\u003cspan citationid=\"CR24\" class=\"CitationRef\"\u003e24\u003c/span\u003e]. The sharp peak at 1004 cm⁻\u0026sup1; corresponds to asymmetric stretching vibrations of Si\u0026ndash;O characteristic of the tetrahedral silicate framework [\u003cspan citationid=\"CR25\" class=\"CitationRef\"\u003e25\u003c/span\u003e]. The band at 909 cm⁻\u0026sup1; is characteristic of the stretching vibration of M\u0026ndash;OH bonds, where M is a metal ion (e.g., Fe\u0026sup3;⁺ or Al\u0026sup3;⁺) [\u003cspan citationid=\"CR19\" class=\"CitationRef\"\u003e19\u003c/span\u003e, \u003cspan citationid=\"CR26\" class=\"CitationRef\"\u003e26\u003c/span\u003e]. The doublet observed at 753\u0026ndash;791 cm⁻\u0026sup1; corresponds to Si\u0026ndash;O\u0026ndash;Si inter-tetrahedral bridging bonds [\u003cspan citationid=\"CR27\" class=\"CitationRef\"\u003e27\u003c/span\u003e]. The bands at 678 cm⁻\u0026sup1; and 451 cm⁻\u0026sup1; correspond to the bending vibrations of Si-O bond, indicating silicate network contributions commonly observed in quartz [\u003cspan citationid=\"CR28\" class=\"CitationRef\"\u003e28\u003c/span\u003e, \u003cspan citationid=\"CR29\" class=\"CitationRef\"\u003e29\u003c/span\u003e]. The band at 524 cm⁻\u0026sup1; is attributed to the bending of Si-O-Al in clay minerals [\u003cspan citationid=\"CR30\" class=\"CitationRef\"\u003e30\u003c/span\u003e]. The vibration frequency at 407 cm⁻\u0026sup1; is attributed to Ti-O bonds of anatase [\u003cspan citationid=\"CR31\" class=\"CitationRef\"\u003e31\u003c/span\u003e].\u003c/p\u003e \u003cp\u003eAfter calcination at 700\u0026deg;C (Fig.\u0026nbsp;\u003cspan refid=\"Fig3\" class=\"InternalRef\"\u003e3\u003c/span\u003e (b)), O-H vibration bands disappear, which is indicative of the dehydroxylation of the kaolinite and goethite to form metakaolinite and hematite, respectively. The band at 1022 cm⁻\u0026sup1; in both calcined clays corresponds to the asymmetric stretching vibration of Si\u0026ndash;O bond. The shift of the band to higher wave number, in comparison to raw clays is related to the modification of the interaction environment due to dehydroxylation [\u003cspan citationid=\"CR27\" class=\"CitationRef\"\u003e27\u003c/span\u003e].This modification of the bonding environment also results in the modification of the Si-O-Si bending vibration that appears in calcined samples at around 777 cm\u003csup\u003e\u0026minus;\u003c/sup\u003e\u0026sup1;. The overall observations are coherent with the dehydroxylation of kaolinite, resulting in amorphous metakaolin, which is of interest for improving geopolymerization.\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec14\" class=\"Section3\"\u003e \u003ch2\u003e3.1.4 Amorphous phase content of solid precursors\u003c/h2\u003e \u003cp\u003eThe result of the amorphous phase content of OWC7 and ORC7 (Table\u0026nbsp;\u003cspan refid=\"Tab1\" class=\"InternalRef\"\u003e1\u003c/span\u003e) indicates that OWC7 has a higher amorphous phase content (46.7%) than ORC7 (19.96%). This is coherent with the relative highest content of kaolinite in OWC when compared to ORC from their XRD (see section 3.1.1). Also, contribution of amorphous free silica by both samples may be higher for OWC. These results imply that OWC7 might exhibit higher reactivity in geopolymerization processes, while the relatively higher proportion of insoluble minerals in ORC will result in a high amount of aggregate after polymerization that may affect the mechanical response of binders based on ORC.\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\u003eAmorphous Phase Content (%) of OWC7 and ORC7\u003c/p\u003e \u003c/div\u003e \u003c/caption\u003e \u003ccolgroup cols=\"3\"\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 \u003cthead\u003e \u003ctr\u003e \u003cth align=\"left\" colname=\"c1\"\u003e \u003cp\u003eSamples\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c2\"\u003e \u003cp\u003eOWC7\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c3\"\u003e \u003cp\u003eORC7\u003c/p\u003e \u003c/th\u003e \u003c/tr\u003e \u003c/thead\u003e \u003ctbody\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eAmorphous Phase Content (%)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e46.7%\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e19.96%\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 \u003c/div\u003e \u003cdiv id=\"Sec15\" class=\"Section2\"\u003e \u003ch2\u003e3.2 FTIR analysis of K-salt\u003c/h2\u003e \u003cp\u003eThe infrared spectrum of K-salt (Fig.\u0026nbsp;\u003cspan refid=\"Fig4\" class=\"InternalRef\"\u003e4\u003c/span\u003e) shows the broad vibration band around 3121 cm\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e which is attributed to the stretching vibrations of the OH groups of water molecules [\u003cspan additionalcitationids=\"CR33\" citationid=\"CR32\" class=\"CitationRef\"\u003e32\u003c/span\u003e\u0026ndash;\u003cspan citationid=\"CR34\" class=\"CitationRef\"\u003e34\u003c/span\u003e]. The vibration around 1344 cm\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e is attributed to the asymmetric stretching vibration of the C-O bond in carbonates. The peak at 1059 cm\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e corresponds to the symmetric stretching vibration of C-O, indicating the presence of carbonate ions (CO\u003csub\u003e3\u003c/sub\u003e\u003csup\u003e2\u0026minus;\u003c/sup\u003e) or bicarbonate ions (HCO\u003csub\u003e3\u003c/sub\u003e\u003csup\u003e\u0026minus;\u003c/sup\u003e) [\u003cspan citationid=\"CR35\" class=\"CitationRef\"\u003e35\u003c/span\u003e, \u003cspan citationid=\"CR36\" class=\"CitationRef\"\u003e36\u003c/span\u003e]. The peak at 878 cm\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e indicates the bending vibration of C-O bonds of the CO\u003csub\u003e3\u003c/sub\u003e\u003csup\u003e2\u0026minus;\u003c/sup\u003e groups [\u003cspan citationid=\"CR37\" class=\"CitationRef\"\u003e37\u003c/span\u003e]. The peak at 698 cm\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e is attributed to the stretching vibration of K-O [\u003cspan additionalcitationids=\"CR33\" citationid=\"CR32\" class=\"CitationRef\"\u003e32\u003c/span\u003e\u0026ndash;\u003cspan citationid=\"CR34\" class=\"CitationRef\"\u003e34\u003c/span\u003e]. These frequencies suggest that most of the potassium contained in the extracted salt from cocoa pod ash is in the form of potassium carbonate (K\u003csub\u003e2\u003c/sub\u003eCO\u003csub\u003e3\u003c/sub\u003e) or potassium bicarbonate (KHCO\u003csub\u003e3\u003c/sub\u003e).\u003c/p\u003e \u003cp\u003ePotassium carbonate (K\u003csub\u003e2\u003c/sub\u003eCO\u003csub\u003e3\u003c/sub\u003e) or potassium bicarbonate (KHCO\u003csub\u003e3\u003c/sub\u003e) present in K-salt can contribute to the alkalinity of the system due to their buffering capacity, helping to dissolve amorphous silica from RHA (Eq.\u0026nbsp;\u003cspan refid=\"Equ1\" class=\"InternalRef\"\u003e2\u003c/span\u003e) and form activating solution of potassium silicate which can enhance geopolymerization.\u003cdiv id=\"Equ1\" class=\"Equation\"\u003e\u003cdiv format=\"TEX\" class=\"mathdisplay\" id=\"FileID_Equ1\" name=\"EquationSource\"\u003e\n$$\\:{{SiO}_{3}^{2-}}_{aq}+{{K}_{2}{CO}_{3}}_{aq}+\\:{nH}_{2}O\\to\\:{K}_{2}{SiO}_{3}.{nH}_{2}O+{{CO}_{3}^{2-}}_{aq}\\:\\:\\:\\:$$\u003c/div\u003e\u003cdiv class=\"EquationNumber\"\u003e2\u003c/div\u003e\u003c/div\u003e\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec16\" class=\"Section2\"\u003e \u003ch2\u003e3.3 Chemical compositions of biomass-based precursors: K-salt and RHA\u003c/h2\u003e \u003cp\u003eTable\u0026nbsp;\u003cspan refid=\"Tab2\" class=\"InternalRef\"\u003e2\u003c/span\u003e presents the percentages of the major oxides in the biomasses (K-salt and RHA), quantified by ICP-OES and XRF, respectively. K\u003csub\u003e2\u003c/sub\u003eO (90.7%) is the major oxide in the K-salt, which confirms it as an important source for K\u003csup\u003e+\u003c/sup\u003e, which is one of the target alkali for water glass synthesis, required in geopolymerization [\u003cspan citationid=\"CR38\" class=\"CitationRef\"\u003e38\u003c/span\u003e, \u003cspan citationid=\"CR39\" class=\"CitationRef\"\u003e39\u003c/span\u003e]. This observation is in line with the FTIR observation (Fig.\u0026nbsp;\u003cspan refid=\"Fig4\" class=\"InternalRef\"\u003e4\u003c/span\u003e), from which potassium carbonate is the dominant constituent. Associated oxides are Na\u003csub\u003e2\u003c/sub\u003eO (1.4%), SO\u003csub\u003e3\u003c/sub\u003e (5.8%) and SiO\u003csub\u003e2\u003c/sub\u003e (2.0%). Regarding the major oxides of RHA, silicium oxide is dominant about 93.2% (Table\u0026nbsp;\u003cspan refid=\"Tab2\" class=\"InternalRef\"\u003e2\u003c/span\u003e). Associated oxide is K\u003csub\u003e2\u003c/sub\u003eO in a relatively low amount of 3.1%. These compositions highlight the potential of an alkali-silicate activating solution made from the combination of the two biomasses, via hydrothermal dissolution.\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\u003ePercentage oxides composition of the K-salt and RHA\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=\"char\" char=\".\" 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=\"char\" char=\".\" 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\u003eOxides\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c2\"\u003e \u003cp\u003eCaO\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c3\"\u003e \u003cp\u003eK\u003csub\u003e2\u003c/sub\u003eO\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c4\"\u003e \u003cp\u003eNa\u003csub\u003e2\u003c/sub\u003eO\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c5\"\u003e \u003cp\u003eSO\u003csub\u003e3\u003c/sub\u003e\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c6\"\u003e \u003cp\u003eSiO\u003csub\u003e2\u003c/sub\u003e\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c7\"\u003e \u003cp\u003eLOI\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c8\"\u003e \u003cp\u003end\u003c/p\u003e \u003c/th\u003e \u003c/tr\u003e \u003c/thead\u003e \u003ctbody\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eK-salt (%)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e-\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e \u003cp\u003e90.7\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e1.4\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e \u003cp\u003e5.8\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c6\"\u003e \u003cp\u003e2.0\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c7\"\u003e \u003cp\u003e-\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c8\"\u003e \u003cp\u003e-\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eRHA (%)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e-\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e \u003cp\u003e3.10\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e-\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e \u003cp\u003e-\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c6\"\u003e \u003cp\u003e93.20\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c7\"\u003e \u003cp\u003e1.20\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c8\"\u003e \u003cp\u003e3.40\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=\"Sec17\" class=\"Section2\"\u003e \u003ch2\u003e3.4 Characteristics of activating solutions from partial substitution by K-salt\u003c/h2\u003e \u003cdiv id=\"Sec18\" class=\"Section3\"\u003e \u003ch2\u003e3.4.1 Effects of K-salt addition on pH of the activating solution\u003c/h2\u003e \u003cp\u003eAll the activating solutions have pH\u0026thinsp;\u0026gt;\u0026thinsp;13 (Fig.\u0026nbsp;\u003cspan refid=\"Fig5\" class=\"InternalRef\"\u003e5\u003c/span\u003e), indicating good alkalinity of solutions for geopolymer binder synthesis. The pH values show an approximate linear growth with K-salt addition (Fig.\u0026nbsp;\u003cspan refid=\"Fig5\" class=\"InternalRef\"\u003e5\u003c/span\u003e). This is linked to the alkalinity of the carbonate of the salt.\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec19\" class=\"Section3\"\u003e \u003ch2\u003e3.4.2 FTIR analysis of activating solutions\u003c/h2\u003e \u003cp\u003eThe FTIR spectra of these solutions (Fig.\u0026nbsp;\u003cspan refid=\"Fig6\" class=\"InternalRef\"\u003e6\u003c/span\u003e) evidence the complete dissolution of the K-salts, as well as the formation of silicate as shown by the band at 980 cm\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e[\u003cspan citationid=\"CR40\" class=\"CitationRef\"\u003e40\u003c/span\u003e, \u003cspan citationid=\"CR41\" class=\"CitationRef\"\u003e41\u003c/span\u003e]. The presence of free waters molecules is obvious from weakly H-bonded O-H bands at 3272 cm\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e associated to the group vibration of the water molecule at 1637 cm\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e[\u003cspan additionalcitationids=\"CR33\" citationid=\"CR32\" class=\"CitationRef\"\u003e32\u003c/span\u003e\u0026ndash;\u003cspan citationid=\"CR34\" class=\"CitationRef\"\u003e34\u003c/span\u003e]. As the amount of K-salt increases, a band related to the carbonatation of the solution appears at 1383 cm\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e, which was associated to the stretching of C-O bonds [\u003cspan citationid=\"CR35\" class=\"CitationRef\"\u003e35\u003c/span\u003e, \u003cspan citationid=\"CR36\" class=\"CitationRef\"\u003e36\u003c/span\u003e]. This carbonatation will probably induce increase porosity of the products[\u003cspan citationid=\"CR42\" class=\"CitationRef\"\u003e42\u003c/span\u003e]. The increased intensities of C-O bonds suggest that K-salt addition enhances the alkalinity of the solutions, which potentially promote the geopolymerization. The band at 980 cm-1corresponds to the Si-O stretching vibration of RHA, confirming its siliceous nature [\u003cspan citationid=\"CR41\" class=\"CitationRef\"\u003e41\u003c/span\u003e, \u003cspan citationid=\"CR42\" class=\"CitationRef\"\u003e42\u003c/span\u003e]. The bands around 400 cm-1 is attributed to the Na/K-O bending vibration [\u003cspan citationid=\"CR43\" class=\"CitationRef\"\u003e43\u003c/span\u003e], suggesting the presence of sodium ions (Na+) and potassium (K+) ions in the activating solution.\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003c/div\u003e \u003c/div\u003e \u003cdiv id=\"Sec20\" class=\"Section2\"\u003e \u003ch2\u003e3.5 Characteristics of synthesized geopolymers\u003c/h2\u003e \u003cdiv id=\"Sec21\" class=\"Section3\"\u003e \u003ch2\u003e3.5.1 Effect of K-salt addition on Initial and Final setting time of geopolymer binders\u003c/h2\u003e \u003cp\u003eFigure\u0026nbsp;\u003cspan refid=\"Fig7\" class=\"InternalRef\"\u003e7\u003c/span\u003e illustrates the effect of K-salt addition on the initial and final setting times of two sets of geopolymer binders, GB and GR, labeled as G0, G8, G14, G20, G25, and G30, based on respective K-salt addition of 0%, 8%, 14%, 20%, 25%, and 30% to activating solutions used. These times increase with the extracted salt addition, up to 20 wt.% addition, before decreasing for both samples sets. The first phase observation is possibly due to the slow dissolution of the reactive species at room temperature (26\u0026thinsp;\u0026plusmn;\u0026thinsp;5⁰C). Although the prepared activating solution forms a highly alkaline environment, the dissolution of the solid aluminosilicate phases (mainly from metakaolin) is probably slowed by the presence of inert phases, including quartz, muscovite, and anatase. The early setting of the lateritic clay compared to the kaolinitic clay geopolymer, can be associated with high reactive iron content. It has been reported that hematite associates with free silica and alumina to form ferri-silicate or ferri-alluminosilicate binding phases in alkaline activated geopolymer systems [\u003cspan citationid=\"CR43\" class=\"CitationRef\"\u003e43\u003c/span\u003e]. The unreactive phases mostly act as filler and might hinder the reaction rate by blocking reactive sites. This will consequently result in delaying the setting. The decrease in setting time above 20 wt.% K-salt addition observed in the second phase is indicative of the rapid polycondensation of dissolved silicate and aluminate species, once sufficient gel has formed. The increasing solubility of aluminosilicate precursors after the initial dissolution phase is facilitated by the increased alkalinity of the medium, leading to rapid gelation [\u003cspan citationid=\"CR44\" class=\"CitationRef\"\u003e44\u003c/span\u003e]. The difference in initial and final setting times of the two formulation sets is directly linked to the variation in iron content within their solid precursors. However, while the reaction with iron phases shortens the setting time, the reaction product is mostly consolidated ferri/ferro hydroxides, which does not contribute much to strength development.\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec22\" class=\"Section3\"\u003e \u003ch2\u003e3.5.2 Physical appearance of the synthesized geopolymers\u003c/h2\u003e \u003cp\u003eThe 28-day-aged geopolymers specimens are exhibited in Fig.\u0026nbsp;\u003cspan refid=\"Fig8\" class=\"InternalRef\"\u003e8\u003c/span\u003e. Their color aspect is coherent with their respective starting product OWC7 (for GB serie) and ORC7(for GR serie). Both series (GB and GR) expose no efflorescence, which is indicative of reduce excess alkalinity of the activating solution. This observation indicates that the used activating solutions have sufficient alkalinity to allow setting and consolidation of the geopolymers\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec23\" class=\"Section3\"\u003e \u003ch2\u003e3.5.3 Effect of K-salt addition on the structural and mineralogical properties of the synthesized geopolymers\u003c/h2\u003e \u003cp\u003eThe FT-IR spectra of the obtained geopolymers are given in Fig.\u0026nbsp;\u003cspan refid=\"Fig9\" class=\"InternalRef\"\u003e9\u003c/span\u003e. In both GB (Fig.\u0026nbsp;\u003cspan refid=\"Fig9\" class=\"InternalRef\"\u003e9\u003c/span\u003e (a)) and GR (Fig.\u0026nbsp;\u003cspan refid=\"Fig9\" class=\"InternalRef\"\u003e9\u003c/span\u003e (b)) series, the stretching of O-H is observed at 3675 cm\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e related to water molecules which are confirmed by the group vibration band at 1645 cm\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e[\u003cspan citationid=\"CR25\" class=\"CitationRef\"\u003e25\u003c/span\u003e]. These bands are absent in the starting materials\u0026rsquo; spectra (Fig.\u0026nbsp;\u003cspan refid=\"Fig3\" class=\"InternalRef\"\u003e3\u003c/span\u003e (b)), indicating the conversion of metakaolin to aluminosilicate oligomers and subsequent polycondensation into three-dimensional solid network of geopolymer. In addition, the shift in the Si-O stretching bands to lower wave number at around 980 cm\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e relative to the starting calcined clays at around 1050 cm\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e (Fig.\u0026nbsp;\u003cspan refid=\"Fig3\" class=\"InternalRef\"\u003e3\u003c/span\u003e (b)) further confirms this transformation [\u003cspan citationid=\"CR45\" class=\"CitationRef\"\u003e45\u003c/span\u003e]. The incorporation of carbonate from k-salt into the geopolymer matrices is evidenced by the presence of the asymmetric stretching vibration of C-O bond around 1400 cm\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e. The bands around 780cm\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e in both samples correspond to Si\u0026ndash;O\u0026ndash;Si inter-tetrahedral bridging bonds [\u003cspan citationid=\"CR27\" class=\"CitationRef\"\u003e27\u003c/span\u003e] and those around 691 cm⁻\u0026sup1; and 437 cm⁻\u0026sup1; correspond to the bending vibrations of Si-O bond, indicating silicate network contributions commonly observed in quartz [\u003cspan citationid=\"CR28\" class=\"CitationRef\"\u003e28\u003c/span\u003e, \u003cspan citationid=\"CR29\" class=\"CitationRef\"\u003e29\u003c/span\u003e].\u003c/p\u003e \u003cp\u003e \u003cdiv class=\"BlockQuote\"\u003e \u003cp\u003eThe X-ray diffraction (XRD) patterns of the formulated geopolymers (Fig.\u0026nbsp;\u003cspan refid=\"Fig10\" class=\"InternalRef\"\u003e10\u003c/span\u003e) do not exhibit any newly formed crystalline phases. The observed peaks correspond only to the mineral phases of the calcined clays, such as muscovite, quartz, anatase, and hematite, which remain approximately unchanged. The potential new mineral phases are poorly crystalized, which justifies the absence of distinct diffraction peaks characteristic of new crystalline structures.\u003c/p\u003e \u003c/div\u003e \u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec24\" class=\"Section3\"\u003e \u003ch2\u003e3.5.4 Effect of K-salt addition on Physical and mechanical properties of geopolymers\u003c/h2\u003e \u003cp\u003eFigure\u0026nbsp;\u003cspan refid=\"Fig11\" class=\"InternalRef\"\u003e11\u003c/span\u003e elucidates the effect of K-salt addition on physical and mechanical properties of the formulated geopolymers GB and GR series at 28th days age. The apparent density (Fig.\u0026nbsp;\u003cspan refid=\"Fig11\" class=\"InternalRef\"\u003e11\u003c/span\u003e (a)) increases while open porosity (Fig.\u0026nbsp;\u003cspan refid=\"Fig11\" class=\"InternalRef\"\u003e11\u003c/span\u003e (b)) and water absorption (Fig.\u0026nbsp;\u003cspan refid=\"Fig11\" class=\"InternalRef\"\u003e11\u003c/span\u003e (c)) decreases with the addition of K-salt up to 20% in both series. This behavior is consistent with the increase in compressive strength (Fig.\u0026nbsp;\u003cspan refid=\"Fig11\" class=\"InternalRef\"\u003e11\u003c/span\u003e (d)), with maximum values of 27.2 MPa and 17.9 MPa, respectively for GB and GR, at K-salt addition of 20 wt.%. This reveals that the slow dissolution and gelation results in a gradual strength gain over time. The higher compressive strengths of GB, compared to GR is due to the higher amorphous content (46.7%) of their precursor (Table\u0026nbsp;\u003cspan refid=\"Tab1\" class=\"InternalRef\"\u003e1\u003c/span\u003e). The more amorphous phase content of the aluminosilicate source materials, the higher the densification of the geopolymer matrix and vice versa. Hence, the optimal K-salt dosage recommended for best matrix strength is 20 wt.% of total alkaline. Beyond 20 wt.% addition, a decrease in apparent density as well as compressive strength is observed, while water uptake and porosity are almost constant. These pessimal tendencies with above 20 wt.% K-salt addition can be linked to carbonation, which may render the structure fragile by inducing disruption in the continuous spreading of geopolymer gel prior to geopolymer network formation. This result is in line with the findings by Yip et al. (2008) [\u003cspan citationid=\"CR46\" class=\"CitationRef\"\u003e46\u003c/span\u003e]. The slight changes in porosity or water uptake are associated with the disruption induced by carbonates, which mainly affects the mechanical response (Fig.\u0026nbsp;\u003cspan refid=\"Fig11\" class=\"InternalRef\"\u003e11\u003c/span\u003e (d))\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003c/div\u003e \u003c/div\u003e"},{"header":"4 Conclusion","content":"\u003cp\u003eThe main objective of this work was to examine the potentiality of two agro wastes as source materials for ecofriendly activating solutions to be used for geopolymerization. Ashes form cocoa pod and rice husk were respectively used in the extraction of amorphous silica and K-salt for the activating solution preparation. The aluminosilicate precursors used were obtained by firing two clay materials, one kaolinitic and the other lateritic, from Ntuissong II. The infra-red analyses of both raw and calcined clays confirmed the formation of metakaolin. The activating solutions were prepared hydrothermally by adding varying percentages of K-salt from cocoa pod to a mixture of amorphous silica from RHA and sodium hydroxide. The synthesized geopolymers indicate improving mechanical and physical responses with K-salt addition between 15 wt.% and 20 wt.% with respect to total alkali, to activating solution. In this same interval the initial and final setting times were relatively high. The use of activating solution with the least K-salt of 8 wt.% induces geopolymerization with improved physical (increase density, reduce water porosity and water uptake) and mechanical responses, compared to the use of activating solution without K-salt. Based on these findings, the study agro waste ashes can be conveniently used in ecofriendly biding materials via hydrothermal dissolution.\u003c/p\u003e"},{"header":"Declarations","content":"\u003cp\u003e\u003cstrong\u003eFunding:\u003c/strong\u003e The authors declare that no specific funding was received for this research.\u0026nbsp;\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eConflict of Interest/Competing Interests:\u003c/strong\u003e The authors declare no conflicts of interest or competing interests related to this work.\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eEthics Approval and Consent to Participate:\u003c/strong\u003e This study complies with ethical standards.\u0026nbsp;\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eConsent for Publication:\u003c/strong\u003e All authors have reviewed and approved the final manuscript for publication.\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eData Availability:\u003c/strong\u003e The authors declare that the data supporting the findings of this study are available within the paper. Should any raw data file be needed in another format, they are available from the corresponding author upon reasonable request.\u0026nbsp;\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eMaterials Availability:\u003c/strong\u003e Not applicable\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eCode Availability:\u003c/strong\u003e Not applicable\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eAuthor Contributions:\u003c/strong\u003e \u003cstrong\u003eCyprien Jo\u0026euml;l Ekani\u003c/strong\u003e: Conceptualization, Methodology, Investigation, Writing - original draft \u0026amp; Project administration.\u0026nbsp;\u003cstrong\u003ePaul Venyite:\u003csup\u003e\u0026nbsp;\u003c/sup\u003e\u003c/strong\u003eInvestigation, Visualization, Writing - review \u0026amp; editing.\u0026nbsp;\u003cstrong\u003eJean Marie Kepdieu:\u003c/strong\u003e Visualization, Writing - review \u0026amp; editing,\u0026nbsp;\u003cstrong\u003eChantale Njiomou Djangang:\u003c/strong\u003e Conceptualization, Validation, Supervision \u0026amp; Resources.\u003cstrong\u003e\u0026nbsp;\u003c/strong\u003e\u003cstrong\u003ePhillipe Blanchart:\u003c/strong\u003e Conceptualization \u0026amp; Supervision.\u003cstrong\u003e\u0026nbsp;\u003c/strong\u003e\u003cstrong\u003eJean Aim\u0026eacute; MBEY\u003c/strong\u003e: writing - review \u0026amp; editing.\u0026nbsp;\u003c/p\u003e\n"},{"header":"References","content":"\u003col\u003e\n\u003cli\u003eVan Deventer JS, Provis JL, Duxson P (2012) Technical and commercial progress in the adoption of geopolymer cement. Miner Eng 29:89\u0026ndash;104\u003c/li\u003e\n\u003cli\u003eVan Deventer JS, Provis JL, Duxson P, Brice DG (2010) Chemical research and climate change as drivers in the commercial adoption of alkali activated materials. Waste Biomass Valorization 1:145\u0026ndash;155\u003c/li\u003e\n\u003cli\u003eShamsaei E, Bolt O, Basquiroto de Souza F, et al (2021) Pathways to commercialisation for brown coal fly ash-based geopolymer concrete in Australia. Sustainability 13:4350\u003c/li\u003e\n\u003cli\u003eDanish A, Ozbakkaloglu T, Mosaberpanah MA, et al (2022) Sustainability benefits and commercialization challenges and strategies of geopolymer concrete: A review. J Build Eng 58:105005\u003c/li\u003e\n\u003cli\u003eRevathi T, Vanitha N, Jeyalakshmi R, et al (2022) Adoption of alkali-activated cement-based binders (geopolymers) from industrial by-products for sustainable construction of utility buildings-A field demonstration. J Build Eng 52:104450\u003c/li\u003e\n\u003cli\u003eMatsimbe J, Dinka M, Olukanni D, Musonda I (2022) Geopolymer: A systematic review of methodologies. Materials 15:6852\u003c/li\u003e\n\u003cli\u003eKadhim A, Mankhi BS, Al-Bujasim M (2024) Review of Geopolymer Technology, Barriers and Limitations. Al-Mustaqbal J Sustain Eng Sci 2:4\u003c/li\u003e\n\u003cli\u003eYou S, Ho SW, Li T, et al (2019) Techno-economic analysis of geopolymer production from the coal fly ash with high iron oxide and calcium oxide contents. J Hazard Mater 361:237\u0026ndash;244\u003c/li\u003e\n\u003cli\u003eSegura IP, Ranjbar N, Dam\u0026oslash; AJ, et al (2023) A review: Alkali-activated cement and concrete production technologies available in the industry. Heliyon 9:\u003c/li\u003e\n\u003cli\u003eVenyite P, Makone EC, Kaze RC, et al (2021) Effect of combined metakaolin and basalt powder additions to laterite-based geopolymers activated by rice husk ash (RHA)/NaOH solution. Silicon 1\u0026ndash;20\u003c/li\u003e\n\u003cli\u003eKamseu E, \u0026agrave; Moungam LB, Cannio M, et al (2017) Substitution of sodium silicate with rice husk ash-NaOH solution in metakaolin based geopolymer cement concerning reduction in global warming. J Clean Prod 142:3050\u0026ndash;3060\u003c/li\u003e\n\u003cli\u003eRhein-Knudsen N, Ale MT, Rasmussen S, et al (2018) Alkaline extraction of seaweed carrageenan hydrocolloids using cocoa pod husk ash. Biomass Convers Biorefinery 8:577\u0026ndash;583\u003c/li\u003e\n\u003cli\u003eVriesmann LC, Amboni RD de MC, de Oliveira Petkowicz CL (2011) Cacao pod husks (Theobroma cacao L.): Composition and hot-water-soluble pectins. Ind Crops Prod 34:1173\u0026ndash;1181\u003c/li\u003e\n\u003cli\u003eCruz G, Piril\u0026auml; M, Huuhtanen M, et al (2012) Production of activated carbon from cocoa (Theobroma cacao) pod husk. J Civ Env Eng 2:1\u0026ndash;6\u003c/li\u003e\n\u003cli\u003eZawawi Daud ZD, Angzzas Sari M, Ashuvila Mohd Aripin AMA, et al (2013) Chemical composition and morphological of cocoa pod husks and cassava peels for pulp and paper production.\u003c/li\u003e\n\u003cli\u003eFAO (2024). online https://www.fao.org/faostat/en/#country\u003c/li\u003e\n\u003cli\u003eFAO (2018) Cameroon production. online\u003c/li\u003e\n\u003cli\u003eAbubakar IR, Maniruzzaman KM, Dano UL, et al (2022) Environmental sustainability impacts of solid waste management practices in the global South. Int J Environ Res Public Health 19:12717\u003c/li\u003e\n\u003cli\u003eDehnavi A, Rajabi M, Bavarsiha F (2021) The effect of temperature, time of curing and Na2O/SiO2 molar ratio on mechanical and chemical properties of geopolymer cement. Metall Mater Eng 27:213\u0026ndash;226\u003c/li\u003e\n\u003cli\u003eAlves L, Leklou N, De Barros S (2020) A comparative study on the effect of different activating solutions and formulations on the early stage geopolymerization process. p 01039\u003c/li\u003e\n\u003cli\u003eKoudia LM, Lebouachera SEI, Blanc S, et al (2022) Characterization of Clay Materials from Ivory Coast for Their Use as Adsorbents for Wastewater Treatment. J Miner Mater Charact Eng 10:319\u0026ndash;337\u003c/li\u003e\n\u003cli\u003eMadejov\u0026aacute; J (2003) FTIR techniques in clay mineral studies. Vib Spectrosc 31:1\u0026ndash;10\u003c/li\u003e\n\u003cli\u003eBlack L (2009) Raman spectroscopy of cementitious materials. Spectrosc Prop Inorg Organomet Compd 40:72\u0026ndash;127\u003c/li\u003e\n\u003cli\u003eJir\u0026aacute;sek J, Cejka J, Vrtiska L, et al (2017) Molecular structure of the phosphate mineral koninckite-a vibrational spectroscopic study. J Geosci 62:271\u0026ndash;279\u003c/li\u003e\n\u003cli\u003eMadejov\u0026aacute; J (2003) FTIR techniques in clay mineral studies. Vib Spectrosc 31:1\u0026ndash;10\u003c/li\u003e\n\u003cli\u003eJos\u0026eacute; Fripiat (1960) Application de la spectroscopie infrarouge \u0026agrave; l\u0026rsquo;\u0026eacute;tude des min\u0026eacute;raux argileux. Bull. Groupe Fr. Argiles 25\u0026ndash;41\u003c/li\u003e\n\u003cli\u003eZawrah M, Gado R, Khattab R (2018) Optimization of slag content and properties improvement of metakaolin-slag geopolymer mixes. Open Mater Sci J 12:\u003c/li\u003e\n\u003cli\u003eBelmokhtar N, Ammari M, Brigui J (2017) Comparison of the microstructure and the compressive strength of two geopolymers derived from Metakaolin and an industrial sludge. Constr Build Mater 146:621\u0026ndash;629\u003c/li\u003e\n\u003cli\u003eSaikia BJ, Parthasarathy G (2010) Fourier transform infrared spectroscopic characterization of kaolinite from Assam and Meghalaya, Northeastern India. J Mod Phys 1:206\u0026ndash;210\u003c/li\u003e\n\u003cli\u003eAZIZI K, MAISSARA J, CHBIHI ME, NAIMI Y Thermal Transformation of Kaolinite Clays: Analyzing Dehydroxylation and Amorphization for Improved Pozzolanic Performance\u003c/li\u003e\n\u003cli\u003eSui R, Rizkalla AS, Charpentier PA (2006) FTIR study on the formation of TiO2 nanostructures in supercritical CO2. J Phys Chem B 110:16212\u0026ndash;16218\u003c/li\u003e\n\u003cli\u003eEtim AO, Betiku E, Ajala SO, et al (2018) Potential of ripe plantain fruit peels as an ecofriendly catalyst for biodiesel synthesis: optimization by artificial neural network integrated with genetic algorithm. Sustainability 10:707\u003c/li\u003e\n\u003cli\u003eNath B, Das B, Kalita P, Basumatary S (2019) Waste to value addition: Utilization of waste Brassica nigra plant derived novel green heterogeneous base catalyst for effective synthesis of biodiesel. J Clean Prod 239:118112\u003c/li\u003e\n\u003cli\u003eBetiku E, Okeleye AA, Ishola NB, et al (2019) Development of a novel mesoporous biocatalyst derived from kola nut pod husk for conversion of kariya seed oil to methyl esters: A case of synthesis, modeling and optimization studies. Catal Lett 149:1772\u0026ndash;1787\u003c/li\u003e\n\u003cli\u003eKalinkin A, Kalinkina E, Zalkind O, Makarova T (2005) Chemical Interaction of Calcium Oxide and Calcium Hydroxide with CO2 during Mechanical Activation. Inorg Mater 41:1073\u0026ndash;1079. https://doi.org/10.1007/s10789-005-0263-1\u003c/li\u003e\n\u003cli\u003eZhao C, Lv P, Yang L, et al (2018) Biodiesel synthesis over biochar-based catalyst from biomass waste pomelo peel. Energy Convers Manag 160:477\u0026ndash;485\u003c/li\u003e\n\u003cli\u003eLi H, Liu F, Ma X, et al (2019) Catalytic performance of strontium oxide supported by MIL\u0026ndash;100 (Fe) derivate as transesterification catalyst for biodiesel production. Energy Convers Manag 180:401\u0026ndash;410\u003c/li\u003e\n\u003cli\u003eda Silva Rocha T, Dias DP, Fran\u0026ccedil;a FCC, et al (2018) Metakaolin-based geopolymer mortars with different alkaline activators (Na+ and K+). Constr Build Mater 178:453\u0026ndash;461\u003c/li\u003e\n\u003cli\u003eDuxson P, Mallicoat SW, Lukey GC, et al (2007) The effect of alkali and Si/Al ratio on the development of mechanical properties of metakaolin-based geopolymers. Colloids Surf Physicochem Eng Asp 292:8\u0026ndash;20\u003c/li\u003e\n\u003cli\u003eLiu C, Yao X, Zhang W (2020) Controlling the setting times of one-part alkali-activated slag by using honeycomb ceramics as carrier of sodium silicate activator. Constr Build Mater 235:117091\u003c/li\u003e\n\u003cli\u003eHandke M, Mozgawa W (1993) Vibrational spectroscopy of the amorphous silicates. Vib Spectrosc 5:75\u0026ndash;84\u003c/li\u003e\n\u003cli\u003ePasupathy K, Sanjayan J, Rajeev P (2021) Evaluation of alkalinity changes and carbonation of geopolymer concrete exposed to wetting and drying. J Build Eng 35:102029\u003c/li\u003e\n\u003cli\u003eKamseu E, Kaze CR, Fekoua JNN, et al (2020) Ferrisilicates formation during the geopolymerization of natural Fe-rich aluminosilicate precursors. Mater Chem Phys 240:122062\u003c/li\u003e\n\u003cli\u003eDuxson P, Fern\u0026aacute;ndez-Jim\u0026eacute;nez A, Provis JL, et al (2007) Geopolymer technology: the current state of the art. J Mater Sci 42:2917\u0026ndash;2933\u003c/li\u003e\n\u003cli\u003eSamadhi TW, Purbasari A, Wulandari W (2020) Geopolymer Preparation from Bamboo Ash Containing Kaolin as Ash Fusion Control Agent. Trans Tech Publ, pp 189\u0026ndash;194\u003c/li\u003e\n\u003cli\u003eYip CK, Provis JL, Lukey GC, van Deventer JS (2008) Carbonate mineral addition to metakaolin-based geopolymers. Cem Concr Compos 30:979\u0026ndash;985\u003c/li\u003e\n\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":false,"isPdf":false,"isPdfUpToDate":true,"isWithdrawnOrRetracted":false,"journal":{"display":true,"email":"[email protected]","identity":"silicon","isNatureJournal":false,"hasQc":true,"allowDirectSubmit":false,"externalIdentity":"scon","sideBox":"Learn more about [Silicon](https://www.springer.com/journal/12633)","snPcode":"12633","submissionUrl":"https://submission.nature.com/new-submission/12633/3","title":"Silicon","twitterHandle":"","acdcEnabled":true,"dfaEnabled":true,"editorialSystem":"em","reportingPortfolio":"Springer Hybrid","inReviewEnabled":true,"inReviewRevisionsEnabled":false},"keywords":"Geopolymerization, Agro-waste, Mechanical response, Metakaolin","lastPublishedDoi":"10.21203/rs.3.rs-6396121/v1","lastPublishedDoiUrl":"https://doi.org/10.21203/rs.3.rs-6396121/v1","license":{"name":"CC BY 4.0","url":"https://creativecommons.org/licenses/by/4.0/"},"manuscriptAbstract":"\u003cp\u003eThis study investigated the potential of Cocoa Pod Ash (CPA) and Rice Husk Ash (RHA), respectively, as sustainable sources of potassium and amorphous silica, in the preparation of activating solutions for geopolymerization. CPA was successfully used to extract K-salt that was found to be a carbonate salt using FTIR analysis. The K-salt was used as substitute of NaOH, together with RHA as silica source to prepare activating solutions via hydrothermal dissolution. The obtained activating solutions were successfully used in the geopolymerization of both calcined kaolinitic and lateritic clays. The synthesized geopolymers were characterized using X-ray Diffraction (XRD), Fourier transformed infra-red (FTIR) and the measurement of some physico-mechanical parameters. including setting time, compressive strength, density, porosity and water absorption. The results indicate an improved response of the geopolymer products withing K-salt addition of 15\u0026ndash;20% (w/w), with respect to total alkali. Beyond 20%, there was a lowering of the various responds that was associated to matrix weakening brought by carbonatation. The alkalinity of all the activating solutions was sufficient for geopolymerization without retention of excess alkali ions in the binder system, as indicated by the absence of efflorescence on the geopolymer surfaces. This study demonstrates the potential of using locally sourced agro-wastes materials to produce sustainable activating solution.\u003c/p\u003e","manuscriptTitle":"Eco-Friendly Activating Solutions from Cocoa Pod Ash and Rice Husk Ash for Geopolymerization","msid":"","msnumber":"","nonDraftVersions":[{"code":1,"date":"2025-05-19 16:05:05","doi":"10.21203/rs.3.rs-6396121/v1","editorialEvents":[{"type":"communityComments","content":0},{"type":"decision","content":"Revision requested","date":"2025-07-01T06:09:55+00:00","index":"","fulltext":""},{"type":"editorInvitedReview","content":"","date":"2025-06-16T08:39:20+00:00","index":"hide","fulltext":""},{"type":"editorInvitedReview","content":"","date":"2025-06-14T13:45:48+00:00","index":"hide","fulltext":""},{"type":"reviewerAgreed","content":"185925142341056155556621603258148536853","date":"2025-06-13T11:57:03+00:00","index":"hide","fulltext":""},{"type":"reviewerAgreed","content":"287850145730790106413727929741692832606","date":"2025-05-17T12:20:12+00:00","index":"hide","fulltext":""},{"type":"reviewersInvited","content":"","date":"2025-05-15T11:38:24+00:00","index":"","fulltext":""},{"type":"editorAssigned","content":"","date":"2025-04-11T23:37:23+00:00","index":"","fulltext":""},{"type":"checksComplete","content":"","date":"2025-04-11T23:36:29+00:00","index":"","fulltext":""},{"type":"submitted","content":"Silicon","date":"2025-04-07T16:09:10+00:00","index":"","fulltext":""}],"status":"published","journal":{"display":true,"email":"[email protected]","identity":"silicon","isNatureJournal":false,"hasQc":true,"allowDirectSubmit":false,"externalIdentity":"scon","sideBox":"Learn more about [Silicon](https://www.springer.com/journal/12633)","snPcode":"12633","submissionUrl":"https://submission.nature.com/new-submission/12633/3","title":"Silicon","twitterHandle":"","acdcEnabled":true,"dfaEnabled":true,"editorialSystem":"em","reportingPortfolio":"Springer Hybrid","inReviewEnabled":true,"inReviewRevisionsEnabled":false}}],"origin":"","ownerIdentity":"0c754778-58e4-4d68-909c-2f9d8870d796","owner":[],"postedDate":"May 19th, 2025","published":true,"recentEditorialEvents":[],"rejectedJournal":[],"revision":"","amendment":"","status":"published-in-journal","subjectAreas":[],"tags":[],"updatedAt":"2025-12-15T16:14:05+00:00","versionOfRecord":{"articleIdentity":"rs-6396121","link":"https://doi.org/10.1007/s12633-025-03472-8","journal":{"identity":"silicon","isVorOnly":false,"title":"Silicon"},"publishedOn":"2025-12-08 15:58:12","publishedOnDateReadable":"December 8th, 2025"},"versionCreatedAt":"2025-05-19 16:05:05","video":"","vorDoi":"10.1007/s12633-025-03472-8","vorDoiUrl":"https://doi.org/10.1007/s12633-025-03472-8","workflowStages":[]},"version":"v1","identity":"rs-6396121","journalConfig":"researchsquare"},"__N_SSP":true},"page":"/article/[identity]/[[...version]]","query":{"redirect":"/article/rs-6396121","identity":"rs-6396121","version":["v1"]},"buildId":"8U1c8b4HqxoKbykW_rLl7","isFallback":false,"isExperimentalCompile":false,"dynamicIds":[84888],"gssp":true,"scriptLoader":[]}