Optimizing the Performance of Blended Refractory Bricks from Amagu and Amokwe Clays Through Composition and Thermal Treatment

575 Nigerian Research Journal of Engineering and Environmental Sciences 10(2) 2025 pp. 575-581 p ISSN: 2635-3342; e ISSN: 2635-3350 Original Research Article Optimizing the Performance of Blended Refractory Bricks from Amagu and Amokwe Clays Through Composition and Thermal Treatment 1Nweke-Ogah, J.A., *2Chima, O.M., 1Ikele, S.U., 1Ndukwe, A. I., 2Ozurumba, E., 2Achalla, O.J. and 2Amajoh, N.N. 1Department of Materials & Metallurgical Engineering, Federal University of Technology, Owerri. Nigeria. 2Department of Mechanical Engineering, Michael Okpara University of Agriculture Umudike, Umudike, Nigeria. *chimamelf[email protected] http://doi.org/10.5281/zenodo.18061961 ARTICLE INFORMATION ABSTRACT Article history: Received 04 Nov. 2025 Revised 19 Nov. 2025 Accepted 20 Nov. 2025 Available online 30 Dec. 2025 The performance of blended clay bricks was studied under varied firing temperatures and composition using samples from Amagu and Amokwe clay deposits. The chemical composition of the clays was evaluated using X-ray fluorescence technique. The clay materials were blended at ratios of 90:10, 80:20, 70:30, 60:40, 50:50 to produce refractory bricks fired at different temperatures of 900 oC, 1100 oC, and 1200 oC and thereafter tested for linear shrinkage, apparent porosity, bulk density, water absorption, and modulus of rupture using standard methods. The results obtained show that Amagu and Amaokwe clays have the respective compositions of 23% and 21.9% for alumina and 36.1% and 35.1% for silica which classifies them as alumino-silicate refractories suitable for intermediate duty applications. The linear shrinkage increased with firing temperature for the blend of 50:50, indicating optimum material stability in all the fired temperatures. The apparent porosity decreased while bulk density and modulus of rupture increased with increase in firing temperature. Ratio 90:10 gave the optimum value of 42.1 MPa for modulus of rupture. The optimum performance of the blended clay material was observed at a 1200 oC temperature value. This suggests that firing temperature is a key factor to regulate properties of clay bricks. It was concluded that through strategic blending and controlled thermal treatment, optimum performance of locally blended clays could be achieved. © 2025 RJEES. All rights reserved. Keywords: Firing temperature Composition Refractory brick Physiomechanical properties Optimum performance 1. INTRODUCTION Refractory materials are indispensable in high-temperature industrial processes such as metal smelting, heat treatment, glass manufacturing, and ceramic production (Saidu, 2025; Horckmans, et al., 2019). Their primary function is to withstand extreme thermal, mechanical, and chemical stresses without 576 J.A. Nweke-Ogah et al. / Nigerian Research Journal of Engineering and Environmental Sciences 10(2) 2025 pp. 575-581 significant degradation, thereby ensuring operational efficiency, safety, and longevity of industrial furnaces (Aragaw, 2025). The growing industrialization in developing nations has spurred a consistent demand for cost-effective and locally sourced refractory products to reduce reliance on expensive imports and bolster economic sustainability (Priyajit and Biswajit, (2024). Naturally occurring clay deposits remain a primary raw material for the production of aluminosilicate refractories, prized for their availability, workability, and refractory properties (Anthony et al., 2013). The suitability of a clay for refractory application is largely determined by its chemical composition, particularly the ratio of alumina (Al₂O₃) to silica (SiO₂), as this directly influences the refractoriness, mechanical strength, and thermal stability of the final product (Ana Rosa, 2021; Bello et al, 2016). The development of refractory bricks from locally sourced clay deposits has been a significant focus of materials science research, driven by the economic need to reduce dependence on expensive imports. The literature establishes that the performance of clay-based refractories is predominantly governed by their chemical composition and the processing conditions, particularly the firing temperature. Extensive research confirms that the alumina (Al₂O₃) and silica (SiO₂) content in clay is the primary determinant of its refractory potential (Bello et al., 2016). Clays are generally classified as refractory when the Al₂O₃ content is above 25%, though those with contents above 20% can still be suitable for many medium-duty applications (Bello et al., 2016). Studies on various Nigerian clay deposits, such as those from Amaokwe, have shown promising alumina content but often fall just short of the ideal benchmark, necessitating blending or additive incorporation to enhance their properties (Bello et al., 2016) The silica content, while contributing to refractoriness, must be balanced, as excess free silica can lead to detrimental phase transformations during heating, reducing mechanical strength (Yunfeng et al, 2025). The firing or sintering temperature is a critical processing parameter that directly influences the microstructure and, consequently, the physiomechanical properties of the final brick. It is welldocumented that increasing firing temperature promotes vitrification—the formation of a glassy phase that bonds the particles together (Lee, & Moore, 2018). This process typically leads to increased linear shrinkage, bulk density, and modulus of rupture, while simultaneously decreasing apparent porosity and water absorption (Anthony et al., 2013). Research on similar clay systems has consistently shown that properties like cold crushing strength improve significantly as the temperature approaches the vitrification point, but excessive temperatures can lead over-firing and deformation (Ugwuoke and Amalu, 2017). To overcome the limitations of single-source clays, blending has emerged as a viable and cost-effective strategy. The literature contains numerous examples where two or more clay materials are combined to achieve a more favorable overall chemistry and particle size distribution (Chima, and Nwokeocha, 2018; Chima et al., 2017). For instance, a clay with high plasticity but low refractoriness can be blended with a less plastic, more refractory clay or with grog (pre-fired clay) to improve dimensional stability and thermal resistance. This synergistic approach allows for the tailoring of properties to meet specific industrial requirements (Egole, et al., 2024). While the individual effects of chemical composition and firing temperature are well-understood in a general sense, a critical gap exists in the systematic, combined investigation of these factors for specific local clay pairs. Previous studies on Nigerian clays, such as the work on Amokwe clay have largely focused on characterizing single deposits (Obialo et al., 2025; Avizovas et al., 2022). There is a scarcity of published research that deliberately explores the synergistic effects of blending Amagu and Amokwe clays in a progressive ratio series. Furthermore, there is limited or no study that quantifies how the interaction between blend composition and firing temperature simultaneously affects a comprehensive set of properties such as shrinkage, porosity, density, strength, thermal conductivity (El Wardi et al., 2025). Therefore, this study is designed to fill this gap by providing a detailed experimental analysis of the Amagu-Amokwe clay system, linking processing parameters directly to performance metrics to enable the optimized production of refractory bricks. By addressing these research problems, this work 577 J.A. Nweke-Ogah et al. / Nigerian Research Journal of Engineering and Environmental Sciences 10(2) 2025 pp. 575-581 provides a scientific and practical framework for valorizing local clay resources, reducing import dependency, and contributing to the growth of indigenous industrial capabilities. 2. MATERIALS AND METHODS 2.1. Materials and Equipment Sourcing The material used in the research work are two clay samples from the Amagu and Amokwe clay deposit both in Ishiagu, Ivo local government of Ebonyi State, Nigeria. The equipment and machines used in the work include computerized X-ray fluorescence (Thermodyne 46200), electric furnace and ceramic kiln, digital weighing machine, spiral balance, sieves, mortar, pestle, moulds, pair of tongs, strong thread, thermal conductivity testing machine, meter rule, and veneer caliper. 2.2. Raw Materials Chemical Oxide Analysis Samples of the two clay materials were analyzed to determine their chemical constituents using X-ray Fluorescence (XRF) analysis machine. 2.3. Raw Material Beneficiation/Preparation The raw clay samples were air-dried before processing. The raw dry clay samples were crushed in a mortar to small grain sizes. The samples were soaked in a container of water and allowed to soak for three days. The clay was dispersed in excess water in a pre-treated plastic container and stirred vigorously to ensure proper dissolution. Mineral constituents, alkalis and dead organic matters were removed by washing during the soaking. This treatment was done since the presence of alkalis (Na and K) tend to retard mullite formation which lowers refractoriness and strength of clay brick. The dissolved clay was then filtered through a 0.425 mm mesh sieve to get rid of unwanted particles and plant materials. The filtrate was filtered further by the use of a mesh sieve of size 0.18 mm in order to obtain finer particles. The filtrate was allowed to settle for three days after which excess water was decanted off. The clay slip obtained was sun dried for 2 days and then dried in an oven at 1000C. The processed dried clay was pulverized and then passed again through a 0.18mm mesh sieve. Each of the clay samples were mixed with water and moulded using different mould size that suits the respective tests they were to be used. Amagu and Amokwe clays were later blended at ratio: 90:10, 80:20, 70:30, 60:40 and 50:50 to produce five different formulations. 2.4. Moulding and Firing of the Test Samples Each of the samples was mixed with an appropriate amount of water to make it plastic for moulding. The plastic clay was then moulded into two different moulds measuring 8cm (length), 4cm (width) and 1.5cm (height), and 9.5cm (length), 2 cm (width) and 1.5cm (height). An improvised wooded materials was prepared which was used for transmitting the necessary moulding pressure to the mould when the required quantity of plastic moulding mass was put into the mould. After pressing, a suitable wooden plunger was used to extrude out the green brick from the mould. The extruded green bricks were given a 50 mm mark using caliper and thereafter weighed to take the individual green weight. The test samples were sundried, oven dried to 1100C and finally fired to different temperatures of 900, 0C 11000C, 12000C respectively before testing for the properties. 2.5. Determination of the Refractory Properties of the Materials 2.5.1. Linear shrinkage The green test sample which was given a 50 mm mark (Lo) on the surface and thereafter dried in the kiln to a temperature of 1000C. The identified mark was measured to get the new lengths of the points after drying (Ld) and firing. (Lf). The dry-fired shrinkage was calculated using Equation 1. (𝐿𝑑−𝐿𝑓 𝐿𝑑) x 100 (1) 578 J.A. Nweke-Ogah et al. / Nigerian Research Journal of Engineering and Environmental Sciences 10(2) 2025 pp. 575-581 2.5.2. Bulk density, water of absorption and apparent porosity The dry weight (Wa) of the sample in air was taken using digital weighing balance. They were transferred to into a vessel of boiling water for 30 minutes after which the boiling was discontinued. The specimens were allowed to cool to room temperature in the vessel of water for four hours. After being left for 30 minutes in cold water, the specimen were tied in a string into a spiral balance suspended in a beaker of water to get the suspended weight in the water (Wsp). The specimens were removed from the water and gently cleaned before weighing it again to get the soaked weight (Wso). The bulk density, apparent porosity and water of absorption were calculated using equations 2, 3 and 4 respectively. Bulk density=( Weight in Air (Wa) Soaked Weight(Wso)−Suspended Weight (Wsp)) (2) Apparent porosity=( Soaked Weight(Wso)−Weight in Air (Wa) Soaked Weight(Wso)−Suspended Weight (Wsp))x 100 (3) Water of absorption=(Soaked Weight(Wso)−Weight in Air (Wa) Weight in Air (Wa)) x100 1 (4) 2.5.3. Modulus of rupture The electrical transversal strength machine was used to determine the breaking load, P (kg). A veneer caliper was used to determine the distance between support L (cm) of the transversal machine. The height H (cm) and the width B (cm) of the broken pieces were determined. The modulus of rupture was then calculated as: Modulus of rupture Kg/cm2 = 3PL 2BH2 (5) Where P = Load applied when the specimen failed L = Distance between the centre line of the lower bearing edges of the equipment. B = the width of the broken specimen H = Height of specimen (cm). 3. RESULTS AND DISCUSSION 3.1. Chemical Composition and Refractory Suitability The chemical oxide composition of Amagu and Amaokwe clays are presented in Table 1 and 2, respectively while physiomechanical properties of the single clays and the composite blended clay bricks are shown in Tables 3 and 4. From the results shown in Tables 1 and 2, it was observed that Amagu clay contains 23% Al₂O₃ and Amokwe clay 21.9% Al₂O₃, with silica contents of 36.1% and 35.1%, respectively. This composition classifies them as alumino-silicate refractories suitable for intermediate duty applications. This aligns with studies on other Nigerian clays, such as the characterization of Amokwe clay by Obialo, et al., (2025), which reported similar alumina content, confirming its inherent refractory potential. The combined alumina and silica content of over 55% in both clays is consistent with the established criterion for clays capable of forming a stable Mullite (3Al₂O₃·2SiO₂) phase upon high-temperature firing, which is essential for strength and thermal stability in refractories (Anthony et al., 2013). Table 1: Chemical oxide composition of Amagu clay Table 2: Chemical oxide composition of Amaokwe clay 579 J.A. Nweke-Ogah et al. / Nigerian Research Journal of Engineering and Environmental Sciences 10(2) 2025 pp. 575-581 Table 3: Physiomechanical properties of the single clay bricks fired at 1200 oC Clay sample Linear shrinkage (%) Apparent Porosity (%) Bulk density (g/cm3) Water absorption (%) Modulus of rupture (MPa) Amagu clay 4.5 10.15 1.5 2.10 28.02 Amaokwe clay 9.4 4.02 2.15 1.70 35.5 Table 4: Physiomechanical properties of blended Amagu-Amaokwe clay bricks This study successfully investigated the synergistic effects of blend composition and firing temperature on the physiomechanical properties of refractory bricks produced from blended Amagu and Amokwe clays. The results demonstrate that these parameters are critical levers for tailoring brick performance for specific industrial uses. 3.2. The Pivotal Role of Firing Temperature The observed trends in the results presented in Table 3 which showed increased linear shrinkage, bulk density, and modulus of rupture alongside decreased apparent porosity with rising firing temperature are directly linked to the sintering phenomenon. As temperature increased from 900°C to 1200°C, the vitrification process intensified. The formation of a continuous glassy phase filled the inter-particle pores, drawing the particles closer together. This explains the increase in linear shrinkage and bulk density, and the corresponding decrease in apparent porosity. The increased modulus of rupture is a direct consequence of this denser, more coherent microstructure. This behavior is a classic finding in ceramic technology and strongly agrees with the principles outlined in standard texts like Anthony et al., (2013), where enhanced particle bonding and pore closure at elevated temperatures are well-documented. The general observation that the best overall physiomechanical properties were achieved at 1200°C underscores that a sufficient thermal energy input is necessary to activate the full potential of the clay blend, regardless of the ratio. 3.3. The Effect of Blend Composition The different optimal performances from different blend ratios highlight the power of compositional control. The 50:50 blend displayed the lowest value of linear shrinkage which indicates dimensional stability. It was also noted that in this blend of 50:50, the optimum dimensional stability exhibited (lowest linear shrinkage) across all temperatures. This suggests a complementary particle size distribution and chemical composition between the two clays at this ratio, which minimizes the net shrinkage stresses during firing. A blend can often result in more efficient particle packing, reducing the overall void space that needs to be eliminated during sintering, thereby reducing total shrinkage. This property is critical for applications requiring precise dimensional tolerances, such as in the construction of kiln ladles and soaking pits, where uneven shrinkage can lead to crack formation and structural failure. The 90:10 blend, yielding the optimum value of modulus of rupture indicates a different synergy. This blend likely maximizes the content of a specific clay (Amagu, based on its slightly higher alumina) that contributes most to the formation of a strong, well-bonded crystalline network (e.g., Mullite). The higher porosity suggests a less dense, less porous microstructure with better particle-to-particle contact. This reduces thermal 580 J.A. Nweke-Ogah et al. / Nigerian Research Journal of Engineering and Environmental Sciences 10(2) 2025 pp. 575-581 conduction pathway that could improve its thermal insulating capacity. Bricks with high mechanical strength and good thermal conductivity are ideal for the linings of crucible furnaces for non-ferrous metal production and heat treatment furnaces. High strength withstands mechanical abuse and metallostatic pressure, while good thermal conductivity ensures efficient thermal insulation that conserve heat energy that facilitate charge melting. Generally, it was observed in this study that while the trend of improvement with temperature is universal, the specific optimal ratios (50:50 for stability, 90:10 for strength) identified in this study are novel for the Amagu-Amokwe clay system. Many previous studies, such as those focusing on single clays could not reveal this kind of property trade-off (Obialo et al., (2025). This finding provides a good understanding that disagrees with a one-size-fits-all approach and emphasizes the need for targeted formulation. The novelties of this study lie on the synergistic blending of the two clay materials which explored the blending of Amagu and Amokwe clays in a systematic series of ratios (90:10, 80:20, 70:30, 60:40, 50:50) for refractory brick production. It also extends into multi-variable optimization where the study concurrently investigates the dual influence of blend composition and firing temperature (900°C, 1100°C, 1200°C), providing a holistic view of the processing-structure-property relationships. It also handled property tradeoff analysis thereby identifies optimal formulations for specific application needs, revealing, for instance, which blend offers the best dimensional stability versus which provides the highest mechanical strength, thus moving beyond a one-size-fits-all approach. 4. CONCLUSION This study has successfully demonstrates that through strategic blending and controlled thermal treatment, locally sourced Amagu and Amokwe clays can be engineered into high-value refractory products. It is concluded that firing temperature is the primary driver for enhancing densification and strength, while the blend ratio allows for the optimization of specific properties. The industrial applications can be directly mapped to the findings: -For lining crucible furnaces and heat treatment furnaces: The 90:10 blend fired at 1200°C is recommended. Its high modulus of rupture ensures structural integrity under load, and which allows for efficient energy use. -For kiln Ladles, soaking pits, and ovens: The 50:50 blend fired at 1100-1200°C is highly suitable. Its superior dimensional stability ensures the construction retains its shape and seal over repeated thermal cycles, preventing leak paths and structural weaknesses. -General-purpose refractory linings: For applications where cost or a balance of properties is key, other intermediate blends like 70:30 or 80:20 fired at 1100°C could provide a satisfactory and cost-effective solution for applications like industrial ovens. 5. ACKNOWLEDGMENT The authors wish to acknowledge the assistance and contributions of the laboratory staff of the Department of Ceramics, Project Development Institute (PRODA), toward the success of this work. 6. CONFLICT OF INTEREST There is no conflict of interest associated with this work. REFERENCES Ana Rosa, S. A., Gricirene, S. C and Nazare do Socorro, L. S. V (2021). New Clayey Deposit and Their Potential as Raw Material for Red or Structured Ceramics: Technological Characterization. Materials 14(24):7672. Anthony, A., Joseph, A. and Simon, K. Y.G. (2013). Development of Fireclay Aluminosilicate Refractory from Lithomargic Clay Deposits. Ceramics International 39(1). pp 779–783. Aragaw, M. M. (2025). Multi-Objective Optimization and Performance Evaluation of Rotary Furnace Refractory Linings Using Locally Sourced Materials. Advances in Mechanical Engineering. 17(6), pp 1-16. Avizovas, R, Baskutis, S, Navickas, V and Tamanddi, L. (2022). Effect of Chemical Composition of Clay on Physical-Mechanical Properties of Clay Paving Blocks. Building. 12(7).pp 943. 581 J.A. Nweke-Ogah et al. / Nigerian Research Journal of Engineering and Environmental Sciences 10(2) 2025 pp. 575-581 Chima, O. M. and Nwokeocha, T. O. (2018). Performance Enhancement of Refractory Properties of Clay Material with Local Content Input. June 2018. Umudike Journal of Engineering and Technology (UJET) Vol 4(1). pp 107-114. Chima, O. M., Nwoye, C. O, and Nnuka E.E. (2017). Enhancement of Refractory Properties of Blended Clay with Groundnut Shell and Rice Husk Additives. (2017) American Journal Engineering Research (AJER). 6. (6) pp 218 – 226. Egole, C. P., Medupin, R. O., Nzebuka, G. C., Nnodum, N. A., Ochieze, U. P., Eterigho-Ikelegbe, O., Wilson, U. N and Yoro, K. O. (2024). Quartz and Feldspar-Blended Clay Composites for Thermal and Structural Applications. Results in Materials. 23(2024). 100584. El Wardi, F. Z., Annaba, K., Soumia Mounir, S., Maaloufa, Y., Belarouf, S., Khabbazi, A. and El Haddaji, B. (2025). Study of the Design Process and Thermomechanical Properties Of a Low Carbon Porous Fired Clay-Cork Composite for Building Insulation. Open Ceramics. 23(2025). 100833. Elakhame Z., Bello S. A., Agunsoye J. O., Patric I. and Otitoju O. (2016).Characterization of Ujogba Clay Deposits in Edo State, Nigeria for Refractory Applications. Kathmandu University Journal of Science, Engineering and Technology. 12(2). pp 71 – 82 Horckmans, L., Peter Nielsena, P., Dierckxa,P. and Antoine Ducastel, A. (2019). Recycling of refractory bricks used in basic steelmaking: A review. Resources, Conservation & Recycling. 140 (2019) pp 297 - 304 Obialo, T.O., Okolie P. C., Odeh, C. P., Okoye, C. N. and Uzodinma, M. A (2025). Firing Temperature Effect on the Thermo-structural Properties of Clay for Refractory Purposes: A Comparative Study on Nigerian Clay Deposits. Budapest International Research in Exact Sciences (BirEx) Journal. 7(2). pp. 92-105. Priyajit, K. G. and Biswajit, P. (2024). Influence of Industrialisation on Sustainable Development: Evidence from Asian and European Developing Countries. International Journal on Recent Trends in Business and Tourism. 8(4), pp 24-35 Saidu K. S. K. (2025). A Summarized Review of Refractory Materials and their Chemical Components. American Journal of Chemistry and Pharmacy (ASCP). 4(1). pp 37 - 47. Ugwuoke1, J. C. and Amalu, N. I. (2017). Characterization of Obe Clay Deposits for Refractory Production. American Journal of Engineering Research (AJER). 6(12). pp. 74 -77 Yunfeng, Q., Dingyi, Y, Yunxiao, Y., Guosheng, R.,and Miao, L. (2025). Synergistic effects of alkali content and silicate modulus optimization for enhanced properties in alkali-activated ultra-high performance concrete at ambient and high temperature. Case Studies in Construction Materials. 22(2025). .