Use of Bagasse as Natural Fiber for Soil Reinforcement

Transcription

1 Use of Bagasse as Natural Fiber for Soil Reinforcement Anees Raja * and Aneel Kumar Civil Engineering Department, Mehran University of Engineering & Technology, Jamshoro * Corresponding Author rajaanees14@gmail.com Abstract In the contemporary world, there is growing concern about environmental pollution, overflowing landfills and increased depletion of non-renewable resources. More than ever, there is the need for waste utilization and use of renewable materials that are friendly to the environment. The fibrous residue that remains after sugarcane is crushed in the mills is known as Bagasse. It is continuously being produced in very large quantities in tropical regions of the world including Pakistan. This huge amount of bagasse poses handling and disposal issues and leaves a significant environmental footprint. This study aims to assess the potential of bagasse fiber as a reinforcement material for soil. For this reason, the millrun bagasse obtained directly from the sugar mill was sieved to obtain coarse/long fibers. These fibers were then mixed with commercially available bentonite clay at varying contents of 0.25%, 0.5%, 0.75% and 1% of the dry unit weight of soil. Unconfined Compressive Strength (UCS) tests were conducted on the specimens prepared at their maximum dry unit weight and optimum moisture content under light compaction. The results show that the addition of bagasse fibers increases the UCS of the soil specimens significantly. Keywords: Bagasse Fiber; Soil Reinforcement; Environment; Unconfined Compressive Strength. 1. Introduction Sugarcane bagasse is continuously being produced in large quantities, especially in the tropical regions of the world. Pakistan being the fifth largest sugarcane producer in the world, produces about 15 million tons of sugarcane bagasse annually. Production of Bagasse comes with many problems. It is a light material occupying large volumes and as a result, requires sizeable storage facilities. This massive volume presents handling and disposal problems for the mill owners. In moist conditions, bagasse undergoes fermentation and decay, whereas in the dry state it easily catches fire. Also, the prolonged contact with dry bagasse may cause an interstitial lung disease known as Bagassosis [1]. To overcome these problems, sugar millers have historically been dumping bagasse into landfills, which has its adverse environmental footprints. Nowadays, Bagasse is used as captive fuel for running the mill, and the technology for making different products such as papers, boards, and chemicals from bagasse has also been introduced. However, despite being used as captive fuel and in other innovative applications, the sugar industry in Pakistan is producing surplus bagasse [2]. On the other hand, strength, cost, and ease of construction are major considerations in geotechnics. Developing new and innovative ways of improving the soil properties has, therefore, become a major focus of interest in recent years. Fiber reinforced soils have recently attracted a great deal of interest from researchers all over the world who are investigating the effects of adding fibers to soils. These fibers when randomly mixed with soil provide tension reinforcement to improve its strength characteristics. Fibers used for soil reinforcement are generally classified into two groups; natural fibers derived from plants (palm, bamboo, coir, sisal, sugarcane etc.) and synthetic fibers created in laboratories (polyethylene, polypropylene, polyester etc.). Natural fibers are reasonably strong, cost-effective, possess environmental friendly characteristics, and are available in bulk, but they have a practical drawback of biodegradability. However, the problem of biodegradability of natural fibers can be checked by alkali and other chemical treatments, physical and chemical coatings, and antimicrobial finishes with some additional cost. Therefore, these fibers may find application as alternative reinforcing materials for the improvement of weak soils in some of the geotechnical works such as pavements for rural and forest areas. They can also be ideally used for short-term applications where the durability of fibers is not required. Using natural fibers for soil reinforcement is both sustainable and environmentally friendly leading to cleaner and greener earth.

2 2. Literature Review Reinforcement of soil with short, discrete and randomly distributed fibers has attracted the interest of researchers all over the world. Prabakar and Sridhar (2002) have studied the compaction characteristics of cohesivefrictional soil reinforced with sisal fibers at fiber content of 0.25, 0.5, 0.75 and 1% of dry weight. The inclusion of natural sisal fiber reduced the dry unit weight of soil. The optimum water content (OMC) increased with the initial inclusion of fibers, but a further increase in fiber content reduced the OMC [3]. The compaction behavior of clayey soil reinforced with carpet waste was studied by Mirzababaei et al. (2013). They showed that an increase in fiber content reduces the maximum dry density and increases the optimum water content. This was justified by the fact that the reinforcement resulted in high-density soil solids (s.g. 2.68) being replaced with low-density fiber (s.g.1.14) [4]. Chauhan et al (2008) studied the effect of coir and PP fibers on the unconfined compressive strength (UCS) of silty sand. The results show an increase in UCS value of soil up to an optimum fiber amount of 0.75% of coir fibers and 1% of polypropylene fibers [5]. Kumar and Singh (2008) showed that UCS of fly ash, reinforced with polypropylene fibers of aspect ratio 100, increased by 102% at fiber content of 0.5% [6]. Tang et al. (2007) have shown that UCS of clayey soil reinforced with polypropylene fibers and ordinary Portland cement is enhanced with 0.05% fiber content, but on further addition of fibers, the increase in UCS is very small [7]. Butt et al (2016) have reported that the California Bearing Ratio (CBR) value of highly compressible clay increased from 4.70 to 7.75% when reinforced with 2% human hair fiber. However, the CBR value reduced when the fiber percentage was increased beyond 2% [8]. Rabindra Kumar Kar et al (2014) studied the strength characteristics of low plastic clay when reinforced with randomly distributed coir fibers in a proportion of 0 to 1.6% of dry weight of soil. The test results revealed that the inclusion of 0.8% fibers in soil increases peak and residual shear strength, UCS and CBR value of soil at the optimum fiber content of 0.8% and 1.4% respectively [9]. Very limited studies have been conducted on sugarcane bagasse for its use as a reinforcement material. Few studies have considered the use of bagasse in cement and polymer composites [10] [11]. Cao (2006) has observed an increase in flexural and tensile strength of biodegradable polyester blocks mixed with sugarcane bagasse fiber. He further observed that treating bagasse fiber with 1% sodium hydroxide caused 13% increase in tensile strength [12]. The use of bagasse ash for improvement of CBR in latric soils have been studied by Osinubi et al. (2009). They have reported that adding bagasse ash increases CBR value of soil, and suggested that bagasse ash can be used in subbase for light traffic pavements [13]. 3. Materials and Methodology 3.1. Soil Commercially available bentonite clay has been selected for this study as the base soil. Factory made Bentonite clay has uniform chemical and physical properties and is composed of extremely fine and pure clay particles. Due to these characteristics, the choice of using bentonite has been made to help prepare identical samples for better comparison. Index properties of soil have been determined as given in Table 1. According to unified soil classification system, the soil was classified as clay of high plasticity (CH) i.e. Fat Clay. Table 1. Index Properties of Base Soil Natural moisture content 6.27 % Specific Gravity 2.33 Liquid Limit 215% Plastic Limit 45% Plasticity Index (PI) 170% Mean grain size, D50 (mm) Optimum moisture content 27.95% Maximum dry density 1.44 Unconfined Compressive Strength kpa 3.2. Bagasse Fiber Sugarcane bagasse utilized for this study was obtained directly from the nearby sugar mill where it had been stockpiled for about 6 months in an open yard. The natural moisture content of bagasse sample was found to be 18%. It was also investigated for any residual sugars in the laboratory using Polarimeter. The sucrose content (also known as POL) of the bagasse sample was found to be Nil. Figure 1 (a). Millrun Bagasse 14

3 Dry Density (g/cc) January 2018, Volume 1, No. 1 mm/min and the tests were performed as per ASTM D2166. To ensure the test-retest reliability, most of the tests were repeated up to 3 times. The results were mostly similar and the mean values were adopted for consideration. 4. Results and Discussion Figure 1 (b). Coarse/Long Bagasse Fibers The millrun bagasse is typically a mix of various sizes of fibers and pith. The fibers are the hard and fibrous outer rind of sugarcane, while the pith is its softer middle portion. For the purpose of this study, the obtained millrun bagasse was sieved to obtain coarse/long fibers. It is understood that the fiber size classification through sieving would depend more on the orientation of fibers and less on their diameter sizes. Fibers that are parallel to the sieve surface would retain even on the sieves larger than their diameters. To obtain a more accurate classification, the sieving was first carried out mechanically for 30 minutes and then by hand shaking. The portion of bagasse retained on 4.75 mm sieve has been termed as coarse/long fibers as shown in Fig 1. Upon measurement, it was observed that the fiber length generally varied between 4 and 8 cm Experimental Study In this study, fiber content was chosen as a parameter. Bagasse fibers were randomly mixed with unreinforced bentonite clay in percentage by dry unit weight of 0.25%, 0.5%, 0.75% and 1%. The mixing was carefully done to obtain near uniform distribution of fibers in the soil. A series of standard proctor compaction tests were performed on the unreinforced and reinforced soil-fiber composite samples as per ASTM D698. The samples were compacted in a mold of an internal diameter of mm and height of mm. The compaction was done in three layers with 25 blows on each layer from a 25.5 N rammer dropped from a height of 305 mm, producing a compaction effort of 600 kn-m. The unconfined compressive strength tests were conducted on the specimens compacted at their maximum dry density and optimum moisture content. A strain controlled compression testing machine was used to assess the stress-strain behavior of the base soil as well as the fiber reinforced soil specimens. The strain rate was kept at Effect of on Compaction The moisture-density curves for bentonite clay reinforced with varying percentages of bagasse fiber are shown in Fig 2(a). These curves reveal that the maximum dry density of the soil has decreased with the addition of bagasse fiber. The decrease in dry unit weight of reinforced samples is primarily attributed to the replacement of highdensity soil solids (s.g. 2.33) with the low density-fiber (s.g. 1.25) as a result of reinforcement. Further the inclusion of fibers in soil results in disturbance of the actual soil fabric which leads to an increase in the void ratio of the mixture and consequently decreases the dry unit weight Water Content (%) 0% 0.25% 0.50% 0.75% 1% Figure 2(a). Compaction Curves of Soil Reinforced with Varying Contents of Bagasse Fiber The maximum dry unit weight has decreased from 1.46 g/cc for the unreinforced soil to 1.38 g/cc for the 1% reinforcement as shown in Fig. 2(b). The variation in the maximum dry unit weight is about 5% and may, therefore, be considered as insignificant. The study further reveals that there is no any significant impact on the optimum 15

4 Unconfined Compressive Stress (kpa) Optimum Moisture Content (%) Unconfined Compressive Strength (UCS) Maximum Dry Density (g/cc) January 2018, Volume 1, No. 1 moisture content of bentonite clay when reinforced with varying contents of bagasse fiber as shown in Fig. 2(c). Figure 2(b). Effect of Bagasse Fiber Reinforcement on Maximum Dry Density of Soil Figure 2(C). Effect of Bagasse Fiber Reinforcement on Optimum Moisture Content of Soil 4.2. Effect of on UCS The unconfined stress-strain curves for unreinforced and the bagasse fiber reinforced soil specimens as obtained from UCS tests are shown in Fig. 3(a). The strain was calculated as the ratio of axial deformation of the specimen to its initial length, and the stress was computed as the ratio of the axial load on the specimen to its cross-sectional area % 1% 2% 3% 4% 5% 6% 7% 8% 9% Axial Strain (%) 0% 0.25% 0.50% Figure 3(a). Stress-Strain Curves from Unconfined Compression Tests All the curves suggest a similar brittle behavior. The tangent modulus of stress-strain curves (i.e. the stiffness of soil) seems to be unaffected by the addition of fiber. However, there is a significant increase in the unconfined compressive strength of soil specimens with increasing fiber content as shown in Fig 3(b). The UCS of soil increased from 183 kpa to 292 kpa which is about 60% improvement from the base value. This enhancement in the compression strength of soil could be the result of bridge effect of fibers which preserves the strength isotropy of soil and as a result prevents the development of failure planes in the soil Figure 3(b). Effect of Bagasse Fiber Reinforcement on UCS of Soil 5. Conclusion The results of this study provide the following conclusions. The addition of bagasse fibers in soil tended to slightly decrease the maximum dry unit weight of soil whereas the optimum moisture content remained almost unaffected. The unconfined compression strength of soil increased significantly with the increasing content of randomly distributed fibers. Given that there was a sharp increase in UCS of soil between fiber contents of 0.75% and 1%, a further study involving higher ranges of fiber reinforcement is needed. ACKNOWLEDGMENT Authors are thankful to Mr. Muhammad Maroof Rizvi, General Manager Bawany Sugar Mills, for providing the required quantity of Bagasse fiber material for this study, and also for giving various insights about production, availability, and use of bagasse fiber in Pakistan. REFERENCES [1] LAURIANNE, S.A. (2004). Farmer s lungs htm/ [2] Pakistan Sugar Mill Association Annual Report (2016). 16

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