Impact Strength and Physical Properties of Geopolymer Composites Reinforced with Bagasse Cellulose Fibers

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1 Impact Strength and Physical Properties of Geopolymer Composites Reinforced with Bagasse Cellulose Fibers *Darunee Wattanasiriwech 1), Tawanporn Munmueangkham 2), and Suthee Wattanasiriwech 3) 1), 2), 3) Materials for Energy and Environment (MEE) Research Group, School of Science, Mae Fah Luang University, Thailand ) ABSTRACT Geopolymer is a new type of construction materials with promising mechanical properties, thermal stability, and chemical resistance. On the other hand, geopolymer exhibits brittle behavior similar to ceramics. This study attempted to improve the brittle behavior by reinforcement the geopolymer matrix with bagasse cellulose fibers. The effects of the bagasse cellulose fiber contents, ranging from 0.5, 1.0, 2.0, 5.0 wt%, on impact strength and physical properties were investigated. Addition of bagasse cellulose fibers up to 1-2% could improve impact strength of the geopolymers. Further addition of the fibers resulted in a decrease of the impact strength according to agglomeration of fibers and thus less degree of intact with the matrix. Hydrophillicity of these fibers, however, led to an increase of water absorption, but a decrease of density of the composites. Keywords: Impact strength, fly ash, geopolymer composite, bagasse cellulose fiber 1. INTRODUCTION Geopolymer is an innovative material with a great potential to replace traditional Portland cement [1]. Geopolymer could be obtained from a reaction between solid aluminosilicate with alkaline activators [2]. It was estimated that the production of geopolymeric cement emited about 80% less carbon dioxide (CO 2 ) than the production of ordinary Portland cement [1,3,4]. Moreover, geopolymer displayed low creep and low shrinkage, great compressive strength and excellent chemical resistance [3,5]. Despite these desirable characteristics, geopolymer exhibited poor flexural properties and failure behavior similar to brittle solids [4, 6]. A propose to overcome this drawback of geopolymer was by reinforcement with fibers which could improve flexural strength, toughness and energy absorption capacities of the matrix by retarding crack propagation [4]. Common inorganic fibers used are such as carbon, basalt, and glass fibers. With the mindset on environmental impact, the use of natural fibers has recently become of interest.

2 Plant fibers were less expensive, have low density and display good mechanical properties when compared with industrial fibers [7 10]. Investigations on natural fibers such as bamboo, sisal, jute and cellulose have revealed desirable effects on the mechanical and physical properties of brittle organicand inorganic matrices. Both compressive and Impact strength of the geopolymer composited with 0.5% cotton fibers was increased to about 2 folds while further increasing to greater than this amount was harmful to the properties [5]. Metakaolin-based geopolymers reinforced by bamboo 63 fibers showed excellent qualities in sustainable structural applications [11]. Factors which could affect final properties of the composites were fiber content, fiber orientation, fiber length, and adhesion between the fiber and the matrix [6]. Bagasse is the fibrous matter obtained as the by-product of the sugar or alcohol production. Presently some refine bagasse can be used to produce food packaging so its fibers became more available in the ready to use form. The objective of this research was to prepare geopolymer reinforced with bagasse cellulose fibers. Impact strength and physical properties were determined. Morphology of the samples were examined using an optical microscope (OM). 2. MATERIALS AND METHODS 2.1 Sample Preparation Bagasse papers obtained from the Biodegradable Packaging for Environment Public Co., Ltd (BPE), Thailand was used as a source of cellulose fibers. The bagasse papers were cut into small pieces and soaked in water for 1 day as shown in Figure 1(a). The soaked bagasse papers were then treated with 10 wt% sodium hydroxide (NaOH) solution for 2 h at a fiber to solution ratio of 1:20 by weight. The system was constantly stirred using a magnetic stirrer. The extracted fibers were rinsed with water, dried in an oven at 100 C for 8 h, to obtained fiber as shown in Figure 1(b). (a) (b) Figure 1. The figure shows (a) cut bagasse papers which is soaked in water and (b) the obtained fibers after drying The liquid activator was prepared by mixing liquid sodium silicate with 10 M NaOH solution in a beaker. Fly ash powder, obtained from Mae Moh Power Plant, Lampang

3 Province, Thailand, was added to the activator and stirred until a uniform mixture was obtained. Extracted bagasse fibers were added to the mixture at weight contents of 0, 0.5, 1.0, 2.0, and 5.0 %. The mixture was then molded and cured at 90 for 24 hr in an oven under water saturated atmosphere. Curing for another 6 days at 40 in a dry condition was further performed prior to testing. 2.2 Property Assessment Impact strength was evaluated using Charpy impact technique according to ASTM D Rectangular samples were prepared in Teflon molds to have the dimension of 12.7 x 12.7 x mm. V-shaped notch were marked on samples prior to testing as shown in Fig 2a. Average was taken from five samples (Fig. 2b). Water absorption and porosity were evlauted in accordance with the ISO Morphology was investigated using an optical microscope (Axinotech, Carl Zeiss) equipped with a digital camera. (a) (b) Figure 2. (a) Sample preparation for the Charpy Impact testing and (b) testing performance. 3. RESULTS AND DISCUSSION The impact strength results for geopolymer composites containing different bagasse cellulose fiber contents are shown in Fig. 3. The impact strength of the geopolymer matrix was approximately kj/m 2. The addition of 0.5, 1.0 and 2.0 wt% of bagasse cellulose fibers resulted improvement of the impact strength of the composites to 1.725, and kj/m 2 respectively. Fibers have ability to absorb energy by forming tortuous pathways and resistance to crack propagation [5]. Besides, the improvement in impact strength may be due to the good dispersion of fibers in the matrix which helps to increase the interaction or adhesion between the matrix and fibre interface [5]. Nevertheless, further increasing fiber content to 5.0 wt% led to reduction of the impact strength of geopolymer composites to kj/m 2. At this content of fiber, viscosity of the mixture was found to increase greatly affecting workability of paste so casting became difficult.

4 Figure 3. Effects of bagasse fiber contents on impact strength of the geopolymer composites. Density and water absorption and of geopolymers reinforced with different cellulose fiber contents are shown in Table 1. Density was found to only slightly decrease in the 0.5% fiber composite. Progressive decrease of the density was obtained when the fiber content was further increase to 1, 2 and 5%. In good agreement with the density result, water absorption was found to only slightly in the 0.5% composite but dramatically increase with further increase of the fiber content. The increase in water absorption was owing to hydrophilic nature of natural fiber. Additionally, the hydrophilic characteristics of cellulosic fiber can cause poor interaction between fiber and matrix [12]. Thus, increasing of fiber content led to the larger interfacial space between the fiber and the matrix so the porosity was increased in the geopolymer composites [13, 14] Density (g/cm3) Water absorption (%) Fiber content (wt%) Density (g/cm3) Water absorption (%)

5 Figure 4. Water absorption and porosity of geopolymer composite samples measured in accordance with the ISO Microstructures of geopolymer composites are shown in Fig. 5a e. The sample without fiber showed some microcracks on the surface according to evaporation of water during curing process (Fig 5a). In the 0.5% composite sample, fiber-matrix was found to be intact suggesting good interfacial bonding according to the hydrophilic nature of both materials (Fig 5b). Further increasing the fiber content to 1%, integrity of the fibermatrix could still be observed (Fig 5c). Increasing fiber content to 2%, some of the pull out-fibers and agglomeration could be observed (Fig 5d). Large agglomeration of fibers and pull out- fibers observed in 5% was evident for the decrease of impact strength (Fig 5e). Figure 5. OM images of the fracture surface for geopolymer composites reinforced with bagasse cellulose fibres at various contents of (a) 0%, (b) 0.5 wt%, (c) 1.0 wt%, (d) 2.0 wt%, and (e) 5.0 wt%. 4. CONCLUSION The fly ash-based geopolymer reinforced with bagasse cellulose fibers in the range of 0.5-2% had better impact strength than the pure matrix due to the flexibility of the cellulose fibers. Increasing the reinforcement content to 5% resulted in the degradation of the impact strength due to agglomeration of fibers and the dramatic decrease of density due to void formation. Water absorption was found to increase with increasing finer contents due to hydrophobicity of the fibers so intact between matrix and fibers become less.

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7 6. ACKNOWLEDGEMENT The authors are grateful for the financial support from Mae Fah Luang University. The authors are also grateful for the kind support of sodium silicate solution from C. Thai Chemicals, Thailand and bagasse papers from the Biodegradable Packaging for Environment Public Co., Ltd.