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1 University of Maiduguri Faculty of Engineering Seminar Series Volume 9, Number 2, November 2018 Determination of Infiltration Capacity of Rice Husk Ash (RHA) Treated Black A. N. Alkali 1 *, I.S. Muhammad 1, A. K. Gazali 2 and Y. B. Magu 1 1 Department of Civil and Water Resources Engineering, University of Maiduguri, Maiduguri - Nigeria 2 Department of Geology, Faculty of Science, University of Maiduguri - Nigeria *abdulhamidalkali.aa@gmail.com; Abstract The use of agro-wastes for use as pozzolanic material has been at the center of researchers interest in recent times. Their use as sanitary landfill liners have been of great importance due to their high contents of Silicon, Aluminium and Zinc Oxides. This practice has brought about the protection of our scarce groundwater sources as well as the environment as a whole by putting these wastes to alternative use. For the purpose of this study, Black Cotton Soil (BCS) was used due to its high cohesive properties. The oxide composition of Rice Husk Ash was tested and was used to treat Black Cotton soil at different percentages of 0%, 4%, 8% and 12%. Compaction test was carried out using BS Light standard compactive effort. The values of the Optimum Moisture Contents for each of the replacements were used to subject the soil samples to Hydraulic Conductivity tests. The combined Oxides of Silicon, Aluminium and Iron gave an 86.9% composition which has satisfied the standard minimum requirement of 70%. The index properties showed an improvement in the properties of BCS mixed with RHA. The MDD obtained from the compaction test decreased with increase in RHA while the OMC increased from 15% to 21%. The hydraulic conductivity decreased from 6.1 x 10-9 m/s of the natural BCS to 2.7 x m/s with 12% replacement of RHA. The research has shown that the Black Cotton soil stabilized with RHA could be used as a hydraulic barrier for sanitary landfill sites. Further tests such as Unconfined Compressive Strength and Volumetric Shrinkage can be carried out to further assess the properties of the soil. Keywords: Hydraulic Conductivity, Pozzolana, soil, compaction 1.0 Introduction The quality of the earth s available water resources is of crucial importance in terms of conservation. Groundwater sources although constitutes about 0.6% of the world s water resources is more appealing as it does not provide a suitable environment for disease causing bacteria. However, if the sources are shallow, this may be inevitable. The depth of these water sources is not immune against leachates that may contain heavy metals such as Chromium, Cadmium, Arsenic, Zinc, Mercury etc. The infiltration capacity of a soil is considered to be the tendency of the soil material to permit the flow of water through its surface into a porous profile under the action of gravity and pressure effects. The expansive characteristics of clayey soils are attributable to the presence of Montmorillonite mineral content. Montmorillonite is the most common of all the clay minerals in expansive clay soils made up of sheet like units sandwiched between two Seminar Series Volume 9(2), 2018 Page 34

2 silica sheets. Black Cotton soil is a clayey soil greyish to blackish in colour and is one of the most problematic soils in the civil engineering field due to its shrinking and swelling tendencies from exposure to varying weather conditions (Patel, 2014). Efforts have been made in developing countries to utilize waste materials in construction. In addition to getting rid of these waste materials, their use in construction has been found to go a long way in protecting the environment from contamination. Recent investigations have explored the use of agro-industrial waste as stabilizing material for soil. This has been established by different researches and has increased the utilization of these wastes. Some of these waste materials include Millet Husk Ash (MHA), Bagasse Ash (BA), Groundnut Husk Ash (GHA), and Rice Husk Ash (RHA), These materials, which will normally litter our environment are eliminated by incineration and are found to be environmentally friendly (Jimoh et al., 2013). This idea of exploiting local materials especially those regarded as waste, for construction purposes, could save the country from continuous economic decline. Rice Husk Ash (RHA) is one of the most suitable among these artificial pozzolanas due to its higher content of siliceous-aluminous constituents (Prasad et al., 2012). Stabilization of black cotton soil with pozzolanic material such as RHA is considered to change the physical characteristics of the soil notably its infiltration capacity. The stabilized soil is found to be ideal for sanitary landfill liners and top capping due to its low permeability rate. The bottom liner prevents deeper soil layers and ground water from contamination from soluble substrate while the top liner is to reduce infiltration rate of rain water and migration of odor from biogas to the atmosphere. The effects of infiltration of leachate resulting from waste in sanitary landfills are Chronic Kidney Disease, Leukemia, Skin cancer, Gangrene, Arsenicosis etc. It is therefore imperative to investigate the capacity of RHA to enhance the capacity of Black Cotton Soil as a hydraulic barrier. 2.0 Methodology 2.1 Materials Black Cotton Soil The soil sample used is black cotton soil, dark grey in color obtained from Numan local government area of Adamawa State, Nigeria. The location lies along 9.47N, 12.03E with elevation of 137m above mean sea level Rice Husk Ash The Rice Husk used for this project was sourced from Coplad Mills along Bama Road Maiduguri, Borno state. The ash was air dried and completely burnt openly. The ash was left to burn at a high temperature for twenty-four hours to obtain a certain degree of fineness. While adopting this method, the husk was completely converted into ash. The ash was then sieved using British Standard (BS) sieve size 425 µm. Seminar Series, Volume 9(2), 2018 Page 35

3 2.2 Methods All tests were carried out according to BS 1377: The tests conducted on the sample include; X-Ray Fluorescence (XRF), Specific gravity, Particle size distribution (sieve analysis), Atterberg limits, Compaction test, and Hydraulic conductivity (permeability) X-Ray Fluorescence Oxide composition of RHA was determined using X-ray fluorescence (XRF) analysis at the Department of Chemistry, Ahmadu Bello University Zaria, Kaduna. The XRF machine has a very sensitive and accurate power of determining trace and major elements in both geologic and biological samples. X-rays produced by the source irradiate sample and the element present in the sample emits fluorescent X-ray radiation with discrete energies that are characteristic of the elements in the sample. By measuring the energies of the radiation emitted by the sample it is possible to determine which elements are present. So one gram of well homogenized RHA was taken into the machine produced the oxide composition Index properties determination The index properties (Liquid limit, plastic limit, shrinkage limit and plasticity index, Particle size distribution analysis and Specific Gravity) of the natural soil and soil stabilised with rice husk ash (RHA) were determined by conducting laboratory tests according to British Standard BS 1377: 1990 (Oriola and Moses, 2011) Compaction Test The soil samples were prepared by pounding to break down large chunks and then sieved through 425um (4.25mm) sieve to get a fine sample for testing. An appropriate amount of soil sample of about 3kg was used. The compaction mould which consists of a base plate, the standard proctor mould (27 blows using a 2.5 kg rammer for 3 layers) and an extension collar, was assembled on a firm surface while the soil sample was mixed with an incremental amount. The moisture content was increased by 3% of the weight of the soil over the course of the test. The guide tube of the rammer was placed gently on the soil and held firmly in the mould while the required number of blows was applied on each layer The mould containing the soils sample was weighed and recorded whereas samples of the compacted soil was taken at the top and the bottom to determine the moisture content of the soil. The procedure was repeated for cumulative moisture content until a drop-in weight of compacted soil plus mould was observed (Osinubi et. al., 2011) Hydraulic conductivity The soil samples were collected and the lumps were broken using mortar and pestle. The soil samples were then mixed with the earlier obtained moisture contents (OMC) and the various proportion of Rice Husk Ash (RHA). Filter papers were placed on the bottom Seminar Series, Volume 9(2), 2018 Page 36

4 surface of the mold prior to compaction. The compacted soil and the mould was then put inside the basin and allowed to stand for 48 hours. The fittings of the moulds were then coupled to the stand pipe of the falling head permeameters. Water was used to fill the tube to a certain specific level. The time at the initial height was recorded using a stop clock. This procedure was for the mixed percentages of RHA (0%, 4%, 8% and 12%) at OMC (15%, 18%, 21% AND 27%) respectively as the water level drops, the height (head) was noted alongside the time for 28 consecutive days (Moses and Afolayan, 2011). 3.0 Result and Discussion 3.1 Oxide Composition The oxide composition of the ash was carried out to obtain the pozzolanic behavior of the ash. Table 1: Oxide Composition of Rice Husk Ash Chemical Oxides RHA Composition (%) SiO Al2O Fe2O CaO 1.84 K2O 2.36 MgO 1.88 Na2O 0.12 The result of the XRF shows that RHA has a very high percentage of Silicon Oxide followed by P2O5. According to this investigation, the amount of silicon oxide contained in RHA is %, Aluminum oxide is 1.740%, and Ferric oxide is 0.538%. The oxide composition of rice husk ash indicates a combined SiO2, Al2O3 and Fe2O3 content of which is equivalent to % which satisfies the minimum requirement specified by ASTM C618 for pozzolana (minimum requirement of 70%). 4.2 Index Properties The index properties of the natural Black Cotton Soil and that stabilized with RHA were presented in Table 2. Seminar Series, Volume 9(2), 2018 Page 37

5 Table 2: Summary of Index Properties of natural soil and that mixed with RHA Properties 0% RHA 4% RHA 8% RHA 12% RHA Specific gravity Liquid limit (%) Plastic limit (%) Plasticity index (%) Linear shrinkage AASHTO soil classification A-7-6 A-7-6 A-7-6 A-7-6 The soil was classified as clay in accordance with AASHTO Soil classification. The variation of specific gravity of the sample with the addition of different percentage of RHA is shown in figure 4.2. Gradual decrease in specific gravity was observed with increasing percentage of RHA up to 12%. Further addition of RHA led to decrease in specific gravity. This was as a result of reduction of the weight of the sample compared to the weight of water due to the lighter weight of the ash replacement. The index properties were improved with a decrease in liquid limit (LL), an increase in plastic limit (PL) that resulted in a decrease in plasticity index (PI) values and decrease in linear shrinkage (LS) for rice husk ash contents from 0% up to 12%. These changes are probably due to physic- chemical reaction (i.e. cat-ion exchange) that depends on particle surface ion hydration and inter particle attractive forces. These results are in agreement with the work of Osinubi et al., (2011). The increase in particle size with increase in rice husk ash treatment decreases in PI and LL show that the engineering properties of the soil were improved. 4.5 Moisture Density Relationship The results of the compaction using standard proctor are provided in Fig. 1. The natural soil had MDD of 1.64g/cm 3. Upon 4% replacement of RHA, the MDD had reduced to 1.46g/cm 3. A slight increase to 1.48g/cm 3 occurred upon 8% replacement and then finally to 1.37g/cm 3. The decrease in MDD is attributed to initial simultaneous flocculation of clay particles caused by cat-ion exchange leading to increase in volume and decrease in dry density. Seminar Series, Volume 9(2), 2018 Page 38

6 Hydraulic conductivity (m/s) Dry Density g/cm3 Alkali et al. Determination of Infiltration Capacity of Rice Husk Ash (Rha) Treated Black Moisture Content % Fig. 1: Variation of maximum dry density and optimum moisture content with rice husk ash for BS standard compaction The OMC increased from 15%, 18%, 18% and 21% for 0%, 4%, 8% and 12% RHA replacement respectively which may be attributed to the increase in fine material from the RHA with larger surface areas that would require more water to react. 4.6 Hydraulic Conductivity The hydraulic conductivity decreased with increasing RHA content under the BS Light standard compaction tests as shown in Figure 2. 0% 4% 8% 12% 7.00E E E E E E E E+00 0% 2% 4% 6% 8% 10% 12% 14% RHA (%) Fig. 2: Variation effect of percentage replacement of BCS using RHA on hydraulic conductivity This decrease in the hydraulic conductivity could be linked with pozzolanic reactions leading to the formation of cementitious products and filling of the pores spaces conducting flow. The natural soil had a permeability of 6.1 x 10-9 m/s and decreased with4% RHA replacement to 1.5 x 10-9 m/s. Upon increase of 8% RHA content, the value Seminar Series, Volume 9(2), 2018 Page 39

7 decreased to 7.1 x m/s and finally to 2.7 x m/s upon 12% RHA replacement. Similar results were obtained when other agricultural wastes were used as additives to different soils (Eberemu, 2013). There is increase in cat-ion exchange capacity with higher RHA content. This could be inferred that there was cat-ion exchange reaction between RHA and the soil (Kumar and Sharma, 2004). On the other hand, the subsequent increase in hydraulic conductivity could be due to the presence of excess RHA that would have changed the soil matrix, leading to increased flocculation (Eberemu, 2013). 5.0 Conclusion The basic purpose of the study was to evaluate the effect of RHA on the hydraulic conductivity of compacted black cotton soil using standard proctor compactive efforts and different moulding water contents with a view to ascertain its suitability in landfill application. The oxide composition of RHA indicates a combined SiO2, Al2O3 and Fe2O3 content of which is equivalent to % implying that it is a very good Pozzolana. Addition of RHA to the soil showed a significant improvement in the plasticity characteristics with all percentages of RHA contents, with the liquid limit and plasticity index values all within the acceptable values. The OMC had increased from 15% for natural soil to 21% for BCS with 12% RHA replacement. The lowest permissible hydraulic conductivity value of 2.7x m/s was obtained at 12% from the original 6.1 x 10-9 m/s of natural soil which is in conformity with standard. The study no doubt showed that the large quantity of waste produced by the rice milling industry has yet another geotechnical application as well as expanding the utilization of widely distributed black cotton soil. RHA should be used as stabilizer for black cotton soil for use as a hydraulic barrier as its benefits include greatly reducing the cost of stabilization and the adverse environmental impact of rice husk waste. Further research on the optimization of Rice Husk Ash as a stabilizing agent for black cotton soil should be made considering tests like volumetric shrinkage and unconfined compressive strength (UCS). Other compactive efforts such as British Standard heavy compaction, West Africa standard are recommended to ascertain the behavior of the soil Reference British Standard Institute (1990). Methods of test for soil for civil engineering purposes: BS British Standard Institute, London. Eberemu A. O. (2013). Hydraulic Conductivity of compacted lateritic soil treated with Bagasse ash. International Journal of Environment and Waste Management, 11 (1), Kumar P. And Sharma R. S. (2004). Effect of Fly Ash on Engineering Properties of Expansive soils. Journal of Geotechnical and Geo-environmental Engineering, 130(7). Seminar Series, Volume 9(2), 2018 Page 40

8 Moses G. And Afolayan J. O (2011). Compacted Foundry Sand Treated with Cement Kiln Dust as Hydraulic Barrier Material. EJGE, 16. Oriola F.O.P and Moses G. (2011). Compacted black cotton soil treated with cement kiln dust as hydraulic barrier material. Department of Civil Engineering, Nigerian Defense Academy, Kaduna, Nigeria. Osinubi K. J. and Eberemu A. O. (2013). Hydraulic Conductivity of compacted lateritic soil treated with Bagasse ash, International Journal of Environment and Waste Management, 11(1). Osinubi K. J., ASCE M. And Moses G. (2011), Compacted Foundry Sand treated with Bagasse Ash as Hydraulic Barrier Material. Geo-frontiers, American Society of Civil Engineers. Patel (2014). An Experimental Study of Black Cotton Soil, Stabilized with Rice Husk ash, Fly Ash and Lime. International Journal of Engineering Research & Technology, 3(11). Prasad T. (2012). Effect of Nanoscale Zinc Oxide on the germination, growth and yield of Peanut, Journal of Plant Nutrition, 35 (6). Seminar Series, Volume 9(2), 2018 Page 41