Production of Low Cost Self Compacting Concrete Using Rice Husk Ash

Transcription

1 First International Conference on Construction In Developing Countries (ICCIDC I) Advancing and Integrating Construction Education, Research & Practice August 4-5, 2008, Karachi,, Pakistan Production of Low Cost Self Compacting Concrete Using Rice Husk Ash Shazim Ali Memon Lecturer, National Institute of Technology, National University of Sciences and Technology, Pakistan Muhammad Ali Shaikh Lecturer, Military College of Engineering, National University of Sciences and Technology, Pakistan Hassan Akbar Student, Military College of Engineering, National University of Sciences and Technology, Pakistan Abstract Self Compacting Concrete as the name implies is the concrete requiring a very little or no vibration to fill the form homogeneously. Self Compacting Concrete (SCC) is defined by two primary properties: Ability to flow or deform under its own weight (with or without obstructions) and the ability to remain homogeneous while doing so. Flowability is achieved by utilizing high range water reducing admixtures and segregation resistance is ensured by introducing a chemical viscosity modifying admixture (VMA) or increasing the amount of fines in the concrete. The study explores the use of Rice Husk Ash (RHA) to increase the amount of fines and hence achieve self-compactibility in an economical way, suitable for Pakistani construction industry. The study focuses on comparison of fresh properties of SCC containing varying amounts of RHA with that containing commercially available viscosity modifying admixture. The comparison is done at different dosages of superplasticizer keeping cement, water, coarse aggregate, and fine aggregate contents constant. Test results substantiate the feasibility to develop low cost SCC using RHA. Cost analysis showed that the cost of ingredients of specific SCC mix is percent less than that of control concrete. Keywords Self Compacting Concrete, Rice Husk Ash, Flowability, Segregation Resistance 1. Introduction Owing to all its properties, use of SCC is increasing all over the world. But the adoption has not been as fast as it should have been. The primary reason is its higher cost per cubic yard of concrete. In Pakistan, SCC is used very little owing to lack of awareness and the high costs associated with its production. SCC is defined by two primary properties: Deformability and Segregation resistance. Deformability or flowability is the ability of SCC to flow or deform under its own weight (with or without obstructions). Segregation resistance or stability is the ability to remain homogeneous while doing so. High range water reducing admixtures are utilized to develop sufficient deformability. At the same time, segregation resistance is ensured, which is accomplished either by introducing a chemical VMA or by increasing the 260

2 amount of fines in the concrete. These viscosity modifying admixtures are very expensive and the main cause of increase in the cost of SCC. About 600 million tonnes of rice paddy was produced all over the world out of which an estimated 5.5 million tonnes was grown in Pakistan in Rice husk is the outer covering of the rice grain (Figure 1) that is removed as a result of milling process on rice kernel. On average 20% of rice paddy is husk which places the global estimate of the rice husk at 120 million tonnes. This means that in Pakistan alone, about 1.1 million tonnes of rice husk was generated in year [Bronzeoak Ltd, 2002 and Statistics Division, Government of Pakistan]. Huge amounts of RHA, obtained after burning of rice husk, probably has no use at all and getting rid of it is also a problem. This paper presents the results of research aimed to investigate the suitability of RHA as a viscosity modifying agent in SCC. The utilization of RHA in SCC mix produced desired results, reduced cost, and also provided an environment friendly disposal of agro-industry waste product. Figure 1: Rice Plant Basics (Source: LAROUSSE, modified for explanation) 2. Experimental Investigation 2.1 Materials Through out the experimental work ordinary portland cement confirming to ASTM C 150 (ASTM, 2004) was used. The chemical and physical properties of cement are illustrated in Table 1. The sieve analysis of fine and coarse aggregate was performed in accordance with ASTM C (ASTM, 2004). The results of sieve analysis of fine and coarse aggregate as compared with the requirement of ASTM C33-03 (ASTM, 2004) are tabulated in Table 2 and 3. The physical properties of fine and coarse aggregate are summarized in Table 4. To achieve superior workability and placeability, high range water reducing concrete admixture, Sikament NN was used. The dosage of superplasticizer was varied from 3.5 to 4.5 percent by weight of binder content. The technical data of Sikament NN is illustrated in Table 5. For control concretes, Sika Viscocrete-1 was used as viscosity modifying agent. It is a third generation of superplasticizer and meets the requirements for superplasticizer according to SIA 162 (1989) and pren The dosage of superplasticizer was kept as 2 percent by weight of binder content. The technical data of Sika Viscocrete-1 is illustrated in Table 5. For mixes other than control concrete, RHA was used as viscosity modifying agent. The chemical and physical properties of RHA are tabulated in Table

3 Table 1: Chemical and Physical Properties of Cementitious Materials Constituents % by wt of sample (Cement) % by wt of sample (RHA) SiO TiO Al 2 O Fe 2 O MnO MgO CaO Na 2 O K 2 O P 2 O SO Cl SrO LOI (1000 o C) Physical Property Specific gravity ASTM Sieve No. Table 2: Grading of Fine Aggregate Percentage Retained Cumulative Percentage Retained Cumulative Percentage Passing ASTM Range (C 33) to to to to to 10 Pan Sieve Size Table 3: Grading of Coarse Aggregate Cumulative Cumulative Percentage Percentage Percentage Retained Retained Passing ASTM Range (C 33) to to to to 5 Pan

4 Table 4 Physical Properties of Fine and Coarse Aggregate Unit Weight (Kg/m 3 ) Bulk Specific Gravity (SSD) Absorption Fineness Modulus Fine aggregate Coarse aggregate Table 5 Technical Data of Sikament NN and Sika Viscocrete 1 Sikament NN Sika Viscocrete-1 Type Naphthalene formaldehyde sulphonate Modified polycarboxylate Appearance Dark brown Green liquid Density (kg/l) Mix Design and Mix Proportions For this study, nine different mixes were prepared. These were subdivided into three groups: Control Concrete, 5% RHA and 10% RHA. For each group, dosage of superplasticizer was varied from 3.5% to 4.5% with an increment of 0.5%. The mix proportions are given in Table 6 while designation of mixes by specific names is explained in the Figure 2. CC R 4.5 Denotes Concrete Control SP dosage Denotes mix with 10% RHA SP dosage Figure 2: Mix Designation 2.3 Testing of Specimens For each mix, slump flow, L-box and V-funnel test were carried out. Brief explanation and illustration of Slump flow, L-Box and V-funnel test is given below Slump flow test It is the most commonly used test and gives a good assessment of filling ability. The apparatus is shown in Figure 3. At first, the inside of slump cone and the smooth leveled surface of floor on which the slump cone is to be placed are moistened. The slump cone is held down firmly. The cone is then filled with concrete. No tamping is done. Any surplus concrete is removed from around the base of the concrete. After this, the cone is raised vertically and the concrete is allowed to flow out freely. The diameter of the concrete in two perpendicular directions is measured. The average of the two measured diameters is calculated. This is the slump flow in mm. The higher the slump flow value, the greater its ability to fill formwork under its own weight. As per EFNARC guide, the range is from 650 mm to 800 mm [6]. 263

5 Table 6: Experimental Matrix Mix name Water Cement RHA Fine Aggregate Coarse Aggregate Sikament NN (% by weight of binder) Viscocrete-1 (% by weight of binder) Water/Binder ratio (kg/m 3 ) (kg/m 3 ) (kg/m 3 ) (kg/m 3 ) (kg/m 3 ) CC CC CC R R R R R R L box test method It assesses filling and passing ability of SCC. The apparatus is shown in Figure 4. The vertical section is filled with concrete, and then gate lifted to let the concrete flow into the horizontal section. When the flow has stopped, the heights H 1 and H 2 are measured. Closer to unity value of ratio H 2 /H 1 indicates better flow of concrete [6] V-funnel test and V-funnel at T=5 min The test measures flowability and segregation resistance of concrete. The apparatus is shown in Figure 5. At first, the test assembly is set firmly on the ground and the inside surfaces are moistened. The trap door is closed and a bucket is placed underneath. Then the apparatus is completely filled with concrete without compacting. After filling the concrete, the trap door is opened and the time for the discharge is recorded. This is taken to be when light is seen from above through the funnel. To measure the flow time at T 5minutes, the trap door is closed and V-funnel is refilled immediately. The trap door is opened after 5 minutes and the time for the discharge is recorded. This is the flow time at T 5minutes. Shorter flow time indicate greater flowability [6]. 264

6 3. Test Results and Discussions Properties of freshly mixed concrete were tested for qualifying within the specified EFNARC range of SCC [6]. 3.1 Slump Flow Test The slump flow for all mixes except 10R3.5 was within the EFNARC range of SCC. The results of slump flow show that the flow increased with the increase in the quantity of superplasticizer used for flowability. Proportionally, the flow decreased with the increased quantity of RHA. The experimental readings achieved in slump flow test were from 595 to 795 mm. Slump flow results are shown in Figures

7 3.2 L - Box Test While testing the concrete for passing ability, majority of the mixes passed through the bars very easily and without any blockage. The results of L-box test show that the ratio of L-box increased with the increase in the quantity of superplasticizer used for flowability. Proportionally, the ratio decreased with the increased quantity of RHA. The experimental readings achieved in the L - box test were from 0 to 1. L - Box test results are shown in Figures

8 3.2 V - Funnel Test As far as filling ability of the mixes was concerned, most of the results of V - funnel tests remained more towards the minimum range or even lesser. This showed more filling ability but less viscous mix. But as the quantity of RHA was increased, the viscosity of the mix started increasing. V - funnel test results are shown in Figures V - Funnel at T 5minutes Test V - Funnel at T 5minutes test shows the potential to segregation resistance. The results of this test remained very encouraging and within the EFNARC range. V - funnel at T 5minutes test results are shown in Figures Properties of freshly mixed concrete, which qualified all the four tests range limits, were four in numbers. Among them were CC3.5, 5R3.5, 10R4 and 10R4.5. The concrete mixes which remained very close to the EFNARC range were two in numbers. They were CC4 and 5R4. Mix 10R3.5 was totally out of the range for all four tests. 4. Cost Analysis Cost analysis of the materials used, has been analyzed as per the purchased price from the market (as of February 2008). The mixes selected for calculation and analysis were those which could pass maximum properties of freshly mixed concrete. Keeping these criteria, the mixes selected were CC3.5, among the control concrete mixes, and 10R4, among the mixes containing RHA. The detailed calculations are summarized in Table 7. It is clear that the cost of ingredients of specific SCC containing RHA is less than the control concrete. 267

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10 Table 7: Comparison of the Cost Analysis Control Concrete SCC with bagasse ash Rate Material per m 3 (CC3.5) (10R4) Quantity Amount Quantity Amount #(PKR) (kg) (PKR) (kg) (PKR) Cement (kg) Coarse aggregate (kg) Sand (kg) Superplasticizer (Sikament NN) (Lit) Superplasticizer (Sika viscocrete 1) (Lit) RHA Hauling Cost* Total Percent reduction in cost = #PKR stands for Pakistani Rupee * RHA Hauling Cost =Rs / metric tonne (assuming 10 km haul) 5. Conclusions Based on the study, following conclusions can be drawn. The possibility of developing low cost SCC using RHA is feasible. Low cost SCC can be made, by incorporating some percentage of RHA along with the main ingredients of concrete (cement, fine aggregate and coarse aggregate) and superplasticizer for flowability. In fresh state, some of the mix results values were out of the EFNARC range and therefore before casting the concrete, the properties of freshly mixed concrete must be checked for SCC. The utilization of RHA in SCC solves the problem of its disposal thus keeping the environment free from pollution. 6. References ASTM. (2004). Standard specification for Portland Cement, C Annual Book of ASTM Standards Cement; Lime; Gypsum, Section 4, Vol. 4.01, pp ASTM. (2004). Standard test method for sieve analysis of fine aggregates, C Annual Book of ASTM Standards Concrete and Aggregates, Section 4, Vol. 4.02, pp ASTM. (2004). Specifications for concrete aggregates, C Annual Book of ASTM Standards Concrete and Aggregates, Section 4, Vol. 4.02, pp Bronzeoak Ltd. (2003). Rice Husk Ash Market Study. Available online at: EFNARC. (2002). Specifications and Guidelines for Self Compacting Concrete. Available online at: Statistics Division, Government of Pakistan. Pakistan Statistics, Available online at: 269