BIBECHANA ISSN 2091-0762 (Print), 2382-5340 (Online) Journal homepage: http://nepjol.info/index.php/BIBECHANA Publisher: Department of Physics, Mahendra Morang A.M. Campus, TU, Biratnagar, Nepal BIBECHANA 19 (1-2) (2022) 119-126 Development of construction materials from the geopolymerization of red clay and coal fly ash Arvind Pathak*, Arpana Ranjit and Bijaya Dhakal Department of Chemistry, Tri-Chandra Multiple Campus, Tribhuvan University, Kathmandu-44600, Nepal *Email: apathak2070@gmail.com Article Information: Received: November 29, 2021 Accepted: December 4, 2021 Keywords: Alkaline activator, Compressive strength, Construction material, Geopolymer ABSTRACT Red clay contains solid aluminosilicate has been shown to be reactive in the presence of an alkaline activator. The addition of coal fly ash and lime has shown improvements in their mechanical and physical properties of the geopolymer products. FTIR analysis and SEM images of the product have shown the formation of aluminosilicate gel in the geopolymeric product. The maximum compressive strength of the geopolymer products GP-RFL was achieved to be 15.92 N/mm2 having water absorption of 10.47 % and bulk density 2.81 g/cm3. These results indicated that geopolymer mortars made from red clay, coal fly ash and lime could be used as an alternative construction material. DOI: https://doi.org/10.3126/bibechana.v19i1-2.46403 This work is licensed under the Creative Commons CCBY-NC License. https://creativecommons.org/licenses/by-nc/4.0/ 1. Introduction Red clay is found in Banepa, Beltar, Chidika, Gaighat, Gultar, Guttu, Lamasure, Manna Buddhuk, Panchkhal, Salghari and Sunkada areas of Nepal. Red clay is widely used in house painting in the rural areas of Nepal. The presence of high alumina and iron content in red clay has been proved suitable as an additive material to produce cement. 10300.1 m3 of red clay in the fiscal year 2015/16 have been utilized in the cement industries [1]. In the construction industry, Portland cement is the leading material for concrete. The cement industry contributes about 8 % of the global CO2 gas emissions and it also produces about 5 % of greenhouse gas emissions [2]. This causes several environmental issues due to the high carbon foot print during cement production. Due to environmental concerns, readily available commercial byproducts as a source of aluminosilicate such as fly ash, blast furnace slag and red mud have been used rather than 119 http://nepjol.info/index.php/BIBECHANA mailto:apathak2070@gmail.com https://doi.org/10.3126/bibechana.v19i1-2.46403 https://creativecommons.org/licenses/by-nc/4.0/ Pathak et al. / BIBECHANA 19 (1-2) (2022) 119-126 120 naturally available materials such as metakaolin, red soil to meet these demands. Geopolymer concrete is one of the building materials that have become popular since it is environmentally friendly [3, 4]. The formation of geopolymer at low temperature generally below than 100 ºC, consists of chains of mineral molecules joined with covalently with a three dimensional polymeric chain consisting of Si-O-Al-O bonds [5, 6]. The high strength development is considered due to the presence of chemical charge-balancing species located in the tetrahedral sites, i.e. the part of the structural network. Mössbauer spectroscopy demonstrates that Fe3+ is included in the geopolymer structure, i.e., Fe3+ is the equivalent of Al3+ in the alumino-silicate network, yielding a ferro-silico-aluminate sequence (-Fe-O-Si-O-Al-O-), i.e, ferro- sialate[7]. The tetrahedrons of silicon and aluminum are connected by oxygen bridges to form the high- connectivity chain or ring network structures. Such high-connectivity molecular structures of the products perform excellent in terms of strength and durability [8]. Geopolymers are characterized by higher durability and greenness relative to conventional OPC. These products have distinct cementitious and ceramic like formulation with good mechanical strength and chemical properties and have gained much attentions recently as a promising partial substitute to OPC [6, 9, 10]. Light weight geopolymer concretes are found as good insulators and fire-resistant and therefore applicable for high-rise buildings and in the areas of high earthquake risk [11]. Global Warming concerns will inevitably lead to the decrease of coal burning for the production of electricity and consequently to the exhaustion of this ultimate waste, which have been utilizing largely for the production of geopolymer and PPC cement [12]. The recent discovery of ancient red geopolymer sandstone monuments in South America (Tiwanaku/ Pumapunku, Bolivia) have shown the extraordinary long-term durability of this [Fe-O-Si-O-Al-O-] geopolymer molecule withstood at least 1400 years of archaeological burial. These artificial red sandstone megaliths contains in the form of ferro-sialate matrix [13]. The aim of this study was to optimize the condition of geopolymerisation behavior of red clay and coal fly ash in the presence of lime. 2. Material and methods Materials The red clay (RC) was collected from Banepa and coal fly ash (CFA) was collected from brick factory of Satungal, Kathmandu. It was then grounded into a powder and dried at 120 ºC for 2 hours to remove the moisture content. Calcium oxide was prepared by heating calcium hydroxide at 580 ºC for 2 hours. The powder form of sample was weight and mixing was done in different proportion. Activator Solution Laboratory grade of NaOH (97 %), liquid sodium silicate (Na2O: 8.6 %, SiO2: 28.0 % and H2O: 63.4 % Lobe Chemme, India) were used. 4 M NaOH was prepared 24 h before mixing with liquid sodium silicate to prepare 1:1 activator solution. The use of 4 M NaOH solution was found to develop higher compressive strength [14]. Synthesis of Geopolymer The red clay and coal fly ash (0 - 20 %) were dry mixed in different composition and then mixed with activator solution to prepare the geopolymer product. After the selection of CFA %, the amount of CaO was varied to prepare the geopolymer product. Finally two geopolymer products GP-RF (90 % red clay, 10 % coal fly ash and activator solution) and Pathak et al. / BIBECHANA 19 (1-2) (2022) 119-126 121 GP-RFL (mixture of 90 % red clay and 10 % coal fly ash was mixed with of 2 % of lime and activator solution) were considered for study. Thus prepared clay paste was then casted in a wooden mould (2.5 cm × 2.5 cm × 2.5 cm) and cured at 60 ºC in oven for 2 hours followed by curing at room temperature for 7 – 28 days, schematically represented as: Fig. 1. Schematic diagram of geopolymer synthesis. Curing at temperature at 60 ºC was found dominant compared to higher temperature and requires less energy consumption [15, 16]. Characterization of the raw materials and Geopolymer products Chemical composition of the raw materials was obtained by using EDX spectrophotometer (EDX-8000, shimadzu) available at Department of Custom, Tripureshwor, Kathmandu. Phase analysis of the powdered raw materials and the geopolymer products were carried out by X-Ray Diffractometer (D2 Phaser Diffractometer, Bruker, Germany) using CuKα radiation available at Nepal Academy of Science and Technology (NAST), Khumaltar, Lalitpur. Fourier transform infrared Spectrophotometer (IR Tracer 100, Shimadzu, Japan) was used for structural characterization Mechanical and Physical Properties Compressive strength values were taken as the average of three consecutive measurements of geopolymer products and were measured using SLF 9 Load frame machine at Central Material Testing Laboratory, Institute of Engineering Pulchowk Campus, Tribhuvan University. Physical properties: apparent specific gravity, and bulk density, porosity and water absorption were measured as per ASTM C373 [17]. 3. Results and Discussion Chemical composition of raw materials The chemical compositions of the raw materials red clay (RC) and coal fly ash (CFA) were analyzed and are shown in the following Table 1: Table 1. Chemical composition (mass %) of the raw materials Oxides (%) RC CFA SiO2 42.39 39.14 Fe2O3 28.72 24.95 Al2O3 17.85 1.27 K2O 7.34 0.80 CaO - 0.94 TiO2 - 1.11 SO3 - 28.54 Others 3.69 3.25 of geopolymers. FTIR spectra were obtained in the frequency range of 4000 to 400 cm-1 by mixing the samples with KBr, available at the Central Department of Chemistry, Tibhuvan University, Kirtipur. Morphological characterization of the fractured samples was carried out by SEM (S4800 10.0kV 7.9 mm × 2.5k SEM, LAO) at NIMS, Japan. Characterization of Raw Materials and the Geopolymer Products X- Ray Diffraction patterns Pathak et al. / BIBECHANA 19 (1-2) (2022) 119-126 122 X-ray diffraction patterns of red clay, coal fly ash and its geopolymer product are shown in the following Figure 2: Fig. 2. XRD Pattern of raw materials and the geopolymeric product Major peaks of the sample at 2θ values equal to 20.06, 26.85, 34.16, 36.72, 42.64, 45.63, 50.36 and 60.12 º mainly represents quartz (silica). These entire peaks are present in the both raw materials and its geopolymer products. FTIR analysis FTIR spectra of the raw materials red clay, coal fly ash and its geopolymer product GP-RFL are shown in the Figure 3. The main absorption bands in RC and CFA were observed at 2361.5, 1025.9, 1001.2, 908.9, 793.7, 747.7, 524.4 and 1047.4, 592.9 cm-1 whereas the spectra for GP-RFL: 1001.2, 910.7, 529.5 cm-1 wavenumbers. Absorption band at 2361 cm-1 could be attributed to bending vibration of H-O-H group associated with weakly bond water molecules [18]. The bands in the range of 950 to 1100 cm−1 assigned to the asymmetric stretching vibrations of Si–O–Si and/or Si–O–Al. The absorption bands at 910.7 cm-1 is due to Al- (OH) vibrations [19]. Fig. 3. FTIR spectra of red clay, coal fly ash and its geopolymeric product GP-RFL. The spectra in the frequencies between 800 cm- 1 and 480 cm-1 correspond to the symmetry of the Si-O-Si stretching vibration [20]. In the geoplymeric product the entire main characteristics band gets broadened shows the substitution of Si with Al forming the geopolymeric network. SEM analysis The scanning electron micrograph of the fractured surface of geopolymerization product GP-RFL is shown in the following Figure 4: Fig. 4. SEM image of GP-RFL (G-gel, P- porous site, A-aggregate) representing gel formation. The solid aluminosilicate material present in the powdered mixture are converted into a porous, hydrate gel and are bound through networking channel supported by the high Pathak et al. / BIBECHANA 19 (1-2) (2022) 119-126 123 compressive strength value of the geopolymerization product (GP-RFL). Variation of the Amount of RC and CFA The geopolymer products were prepared from the mixture of RC and CFA (5 – 20%) and mixing with the activator solution. The products were then cured at 60 °C for 2 hours followed by curing at room temperature for 7 days. The compressive strength values of the geopolymer products were found to be 0.60, 1.13, 1.75, 0.65 and 0.64 N/mm2 for 0, 5, 10, 15 and 20 % of CFA respectively and are shown in the following Figure 5: 2.0 1.5 1.0 0.5 0.0 0 5 10 15 20 Fly ash, % Fig. 5. Compressive strength of the geopolymer products with the variation of fly ash The compressive strength value increased with increasing with increase in amount of coal fly ash up to 10 %. The increase in compressive strength value may be due to the pozzolanic pozzo1anic activity of coal fly ash [21]. As the increases of % of coal fly ash some cracks was observed in the geopolymeric sample, thus compressive strength was decreased. Variation of the Amount of CaO 90 % red clay and 10 % coal fly ash was mixed and then the amounts of CaO were varied. At first these were dry mixed and then mixed with the activator solution. The geopolymer products were then cured at 60 °C for 2 hours followed by curing at room temperature for 7 days. The compressive strength of geopolymer products were found to be 5.78, 7.73, 5.66, and 4.64 N/mm2 for 1, 2, 3 and 4 % of CaO respectively and are shown in the following Figure 6: 10 8 6 4 2 0 0 1 2 3 4 5 CaO, % Fig. 6: Compressive strength of the geopolymer product with CaO % The compressive strength value of the geopolymer product was found maximum at 2 % of addition of CaO. In ceramics, mechanical strength usually increases with decreases in porosity. Similar trend of increase in strength was also observed in case of metakaolin based geoploymer on the addition of small amount of Ca(OH)2 [22]. Effect of Curing Time The geopolymer products GP-RF and GP-RFL were then cured at 60 °C for 2 hours followed by curing at room temperature up to 28 days. The compressive strength values of the geopolymer products were measured and are shown in the Figure 7. The compressive strength value of the geopolymer products were found increasing with curing time. C o m p r e s s iv e s tr e n g th , N /m m 2 C o m p r e ss iv e s tr e n g th , N /m m 2 Pathak et al. / BIBECHANA 19 (1-2) (2022) 119-126 124 20 16 12 8 4 0 0 7 14 21 28 Curing time, d Fig. 7. Compressive strength of the geopolymer products with curing time The curing for longer period of time at low temperature is preferable for the synthesis of geopolymer as the condensation and evaporation of water molecules takes place simultaneously preventing the formation of voids and cracks inside the materials thus increasing the compressive strength. The adequate curing time accelerates the extent of chemical reaction [23, 24]. Physical properties of the Geopolymer Products The lower the value of water absorption indicates good quality and has higher resistance to water infiltration and to environmental damage. The water absorption value less than the 17 % are applicable in masonry units. The physical properties of the geopolymeric product measured at 28 days as per ASTM C373 standards are mentioned in the following Table 2: Table 2. Physical properties of the geopolymer products measured at 28 days. Apparent specific gravity, bulk density, porosity and Water absorption and compressive strength value indicates these masonary unit can be used as an alternative construction material. Conclusions The geopolymerisation behavior of red clay and fly ash was studied. The compressive strength values of the geopolymer GP-RF using RC (90%) and CFA (10%) using 1:1 solution of 4M NaOH and liquid sodium silicate was found to be 8.80 N/mm2 at 28 days of curing. Use of 2 % lime as additives enhanced the compressive strength of 15.92 N/mm2 at 28 days of curing. Microstructural study of the geopolymeric product has shown the formation of aluminosilicate gel. The mechanical and physical properties of the geopolymer product were studies. These results indicated that geopolymer mortars made from red clay, coal fly ash and lime are suitable for construction activities and can be used as an alternative construction material. Acknowledgments The authors are thankful to University Grants Commission (UGC), Bhaktapur, Nepal, for providing Small RDI Grant (SRDIG-74- 75/S&T-05). We are grateful to the Central Material Testing Laboratory, Pulchowk, Lalitpur for compressive strength measurement, Department of Customs, Ministry of Finance, Tripureshor, Kathmandu for providing EDX of the samples, Nepal Academy of Science and Technology (NAST) for XRD measurements of the samples, Central GP-RF GP-RFL C o m p r e ss iv e s tr e n g th , N /m m 2 Physical properties GP-RFL Absorption of water (%) 10.47 Porosity (%) 27.56 Apparent specific gravity 3.63 Bulk density (g/cm3) 2.81 Compressive strength (N/mm2) 15.92 Pathak et al. / BIBECHANA 19 (1-2) (2022) 119-126 125 Department of Chemistry, Tribhuvan University, Kirtipur for FTIR spectra of the samples, Dr. Lok Kumar Shrestha, Scientist, MANA, NIMS, Japan for providing SEM Image of the sample. References [1] Ministry of Industry, Department of Mines and Geology, Kathmandu. Mineral Resources of Nepal. (2017) [2] Al. 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