MECHANICAL PROPERTIES OF CONCRETE CONTAINING RECYCLED STEEL FIBRES (BM-036)

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1 MECHANICAL PROPERTIES OF CONCRETE CONTAINING RECYCLED STEEL FIBRES (BM-036) Noralwani Modtrifi 1*, Izni Syahrizal bin Ibrahim 2, and Ahmad Baharuddin Abd. Rahman 3 1 Researcher, Precast Concrete Research Group (PCRG), Faculty of Civil Engineering, Universiti Teknologi Malaysia, UTM Johor Bahru, Johor, Malaysia 2 Senior Lecturer, Precast Concrete Research Group (PCRG), Faculty of Civil Engineering, Universiti Teknologi Malaysia, UTM Johor Bahru, Johor, Malaysia 3 Associate Professor, Precast Concrete Research Group (PCRG), Faculty of Civil Engineering, Universiti Teknologi Malaysia, UTM Johor Bahru, Johor, Malaysia * of corresponding author: kzedz@yahoo.com ABSTRACT Lack of knowledge to properly dispose or to turn used tyres into useful recycled materials may become hazardous to the environment. A study by Economic Planning Unit (EPU) and Danish International Development Agency (Danida) in 2003 reported 19.7 millions or 157,000 tonnes tyres were junk by us annually. Two years later, it has been reported an increasing to 180,000 tonnes tyres are tossed per year or 500 tonnes per day. Therefore, innovative and creative technique to properly dispose used tyres is very important and also to encourage public on the development of new market for used tyres. Initiative has been taken by researchers at Universiti Teknologi Malaysia to use steel fibres recovered by tyre recycling process in concrete mixtures. The mechanical properties of recycled steel fibres (RSFs) was determined which include its diameter, and tensile strength while the length is fixed to 60±5 mm. Furthermore, these RSFs were added in the concrete mixture and tested for cube compressive strength (f cu), tensile splitting strength (f ct), and flexural strength (f cf). The volume of RSFs were 0% (as control batch), 0.3%, and 0.7%. The aim of this research is to investigate the effect of recycled steel fibre on the properties of concrete in comparison with plain concrete. The usage of recycled steel fibre in concrete has shown satisfactory results on the improvement of its mechanical properties. Besides, the successful on using recycled steel fibre in concrete later not only develop new market on used tyres but also contribute to the sustainable development of building construction. Keywords: Concrete properties, recycled steel fibres, volume fractions. 1. INTRODUCTION The problem associated with the huge amount of waste tyres dumped at the landfills is not new. However, the problems still been ignored and we also forget the consequences of the problems in the future. The issue to properly dispose the waste tyres has been raised for few years, not only to reduce the burden that has been carry by the landfills but to save the environment. Nowadays, it has become serious problem to the country when illegal dumping area created by irresponsible people, which end up as pest-breeding areas, and increase in dengue cases. Therefore, without serious actions taken by all parties, the problems associated with disposal of waste tyres could not be solved. In fact, the resulting of huge heaps of waste tyres would not only lead to uneven settlement at landfills but also resulted in major health problems for the public and environment. In the last few years, many researchers have taken into consideration to develop new method to use waste tyres in construction industry. Modern technology and brilliant mind of researchers has resulted the use of recycled tyre products in Civil Engineering materials. One of the invention created is the used of steel fibre recovered from tire recycling process in concrete mixture. The use of recycled steel fibre (RSF) in concrete has started to get a lot of attention from all over the world. Some of the research that has shown satisfactorily results with the use of RSFs recovered from waste tyres by mechanical process (Aiello et.al, 2009). The authors studied the mechanical behaviour by conducting pull-out tests, compressive strength, and flexural tests. At the end of the study, the authors found the addition of RSFs in concrete shown promising applications but further study also needed to have more understanding on the materials itself. Besides, study conducted by researchers at University of Massachusetts Dartmouth used steel beads, another product produced by tire shredding process and tested at the fresh and hardened stage of concrete (Papakonstantinou et.al, 2006). Hence, one of the behaviour which shown good result is toughness since the role of randomly distributed steel beads to bridge the crack, and the specimen are impossible to be separated.

2 Quantity (nos) 2. METHODOLOGY (MATERIALS AND METHODS) 2.1. Fibre Characterizations Steel fibres used in the research were recovered from tyre recycling process known as pyrolisis. A total of 100 samples of these RSFs were analyzed and characterized based on its diameter. The diameter was recorded by using digital vernier at three different points and an average value was taken. The fibre diameters range from 0.61 mm to 2.02 mm. The class with the largest number of diameter was 1.00 mm to 1.49 mm (74%) and followed by class 0.50 mm to 0.99 mm (22%). The distribution of the fibre diameter is shown in Figure Diameter (mm) Figure 1. Distribution of RSFs diameter Furthermore, tensile strength test was also carried out with both ends of the fibre were attached with tape and Super Glue for additional grip and anchorage. This is to avoid any slippage when the test was conducted (Figure 2). Figure 2. Specimen failure after test Single fibre were used for each test and the measured diameter was 0.33 mm. A total of 5 samples were taken and from the test, the RSFs obtained good tensile strength with an average value of 1033 MPa. However, based on the experimental results obtained by Aiello et.al. (2009), average tensile strength for steel fibres recovered by shredding process is more than 2000 MPa, slightly higher than the strength obtained in this current research. Besides, steel beads has tensile strength varies from 1500 to 1900 MPa since its originate from various vehicle. (Papakonstantinou et.al, 2006) Apart from that, 10 samples were tested for density. At 24 C, the samples were tested by using Mettler Toledo apparatus. The average density of RSF was found to be 7.34 g/cm Mixture Proportions The amount of fibres added in concrete is based on the volumetric percentage: 0%, 0.3%, and 0.7%. The composition of the concrete mixtures are shown in Table 1.

3 Table 1. Mix proportions of concrete mixtures Components Volumetric Percentage of RSF 0% 0.3% 0.7% Cement (kg/m 3 ) Water (kg/m 3 ) Recycled steel fibre (kg/m 3 ) Superpasticizers* (%) Fine aggregate (kg/m 3 ) Coarse aggregate (kg/m 3 ) *From weight of cement 2.3. Specimens Preparation For each volume percentage of RSFs, a total of 6 cubes, 3 cylinders and 3 beams were cast and cured. All cubes having a dimension of 150 mm 150 mm 150 mm, cylinders of 150 mm diameter 300 mm long, and beams of 150 mm 150 mm 500 mm long. Slump test were conducted while the concrete was in its fresh state. In the hardened state, the cubes were tested at 7 and 28 days for compressive strength test. Meanwhile, cylinders were tested for tensile splitting strength and beams were tested in flexural at 28 days. 3. RESULTS AND DISCUSSIONS As mentioned in section 2.3, the concrete were tested in two conditions: (i) freshly state, and (ii) hardened state. The effect of RSFs in the concrete are discussed below Properties of Fresh Mixtures Slump test was carried out to confirm the workability of the concrete for each volume percentage. The mixture was design to have a slump of between 30 mm to 60 mm. The result is shown in Table 2. The findings in this study were similar as reported by previous researchers, such as Papakonstantinou et.al in 2006 (using steel beads), Aiello et.al in 2009 (using RSFs), and Ramli et.al in 2010 and Yazici et.al in 2007 (using steel fibres). Besides, concrete with higher concentrations of fibres cause the decrease in the slump value. The presence of RSFs in the concrete mixes slightly affected the workability of concrete Properties of Hardened Concrete After 28 days curing time, the following tests were conducted in the hardened state: i. Compressive strength test (BS EN ) ii. Flexural strength test (ASTM C78) iii. Tensile splitting strength test (BS EN ) The results are shown in Table 2. Table 2. Average mechanical properties of concrete with different RSF volumetric percentage Volume Fractions Slump (mm) Compressive Strength Test Flexural Strength Test Tensile Splitting Strength Test 7 days 28 days 28 days 28 days 0% % %

4 Tensile Splitting Strength, f ct Tensile Splitting Strength, f ct Strength Volume Fraction (%) 7 days comp. strength 28 days comp. strength Tensile splitting Flexural strength Figure 3. Relationship between volume fractions of RSFs with the strength of concrete f ct = f cu Days Compressive Strength, f cu Figure 4. Relationship between 28 days compressive strength and tensile splitting strength Flexural Strength, f cf f cf = f cu Compressive Strength, f cu Figure 5. Relationship between compressive strength and flexural strength f ct = 1.856f cf Flexural Strength, f cf Figure 6. Relationship between flexural strength and tensile splitting strength

5 From Figure 3, it can be observed that all RSFs recorded higher strength compared to control specimen. The results from the compressive strength proved that the addition of steel fibres from waste tyres has improved the mechanical properties of concrete. The result shows that concrete with RSFs recorded higher compressive strength compared to control specimen; i.e % and 12.54% higher for 0.3% RSF and 0.7% RSF, respectively. Apart from that, visual inspection after testing found that the control specimen exhibit more cracks with the exposed surfaces cracked approximately equal. On the contrary, specimen with RSFs only shows little cracks and bulging on the exposed surfaces. The visual comparison is shown in Figure 7. Figure 7. From left to right: Control specimen and specimen with 0.3% RSFs after testing The relationship between tensile splitting strength and compressive strength is shown in Figure 4. The tensile splitting also shows an increment in strength from plain to specimens with RSFs. For specimen with 0.3% RSFs, the strength was 2.99 MPa, which is 7.55% higher than the control and further 15.83% increased was also observed for specimen with 0.7% RSFs. Based on the visual observation after testing, control specimen split into two parts while specimen with RSFs only shows cracking along the surface intact with the plate (Figure 8). Besides that, specimen with RSFs helps to bridge the crack and preventing them from splitting. Figure 8. From left to right: Control specimen and specimen with 0.3% RSFs after testing The relationship between flexural strength and compressive strength is shown in Figure 5. Test on flexural strength also shows the advantages in adding RSFs in the concrete mixture. Control specimen only reach an average load of kn at ultimate with the strength of 3.64 MPa, while 0.3% RSFs specimen have an average load of kn at ultimate with the strength of 4.79 MPa. Therefore, 0.3% RSFs specimen was 31.59% higher than plain concrete in terms of its flexural strength. Meanwhile, 0.7% RSFs specimen recorded an average load of kn at ultimate with the strength of 5.82 MPa; 59.89% higher than the control specimen. During the flexural test, the control specimen split into two pieces immediately after reaching the ultimate load. However, specimen with RSFs exhibit cracking but still intact together without disintegration. The effect of adding RSFs in concrete was able to control the cracking upon reaching its ultimate load. The specimens after test are shown in Figure 9. RSFs used in this study were able to bridge the cracks to avoid total separation of the specimens. The similar behaviour was also found when concrete was added with steel beads (Papakonstantinou et.al, 2006).

6 Figure 9. From left to right: Control specimen and specimen with 0.7% RSFs after testing The relationship tensile splitting strength and flexural strength is shown in Figure 6. In all cases, the tensile splitting strength increases as the flexural strength increases. 4. CONCLUSIONS The experimental work has remarks some important points in the addition of RSFs in concrete as follows: i. The addition of RSFs in concrete shows an improvement in the compressive, flexural and tensile splitting strength of concrete. ii. Workability of the concrete is highly concerned. Addition of RSFs up until 0.7% is not recommended since homogeneous mixtures is hard to achieve because the RSF tends to ball up during the mixing process. iii. Besides, higher volumetric percentage causes problem in compaction hence resulted in honeycomb with rough surfaces. iv. RSFs in concrete acts to bridge the concrete, hence improve the energy-absorption capacity. v. Further research is required to understand the behaviour of RSFs with various volumetric percentages in order to find the optimum value. 5. ACKNOWLEDGEMENT The author would like to acknowledge all staffs from Materials and Structure Laboratory, Faculty of Civil Engineering, Universiti Teknologi Malaysia for their help and guide throughout project. We also acknowledge Mr. James Ng from Hoi Hing Loong Sdn. Bhd. for supplying the recycled steel fibre and financial support from the Ministry of Higher Education of Malaysia (MoHE) under the VOT GUP (Q.J J82). 6. REFERENCES [1] Aiello, M.A., et.al. (2009). Use of Steel Fibres Recovered from Waste Tyres as Reinforcement in Concrete : Pull-out Behaviour, Compressive and Flexural Strength. Waste Management 29, pp [2] Papakonstantinou, C.G., et.al. (2006). Use of Waste Tire Steel Beads in Portland Cement Concrete. Cement and Concrete Research 36, pp [3] Ramli, M., et.al. (2007). Performance of High Srength Flowing Concrete Containing Steel Fibre. Malaysian Construction Research Journal, Volume 6, No. 1, pp [4] Yazici, S., et.al. (2007). Effect of Aspect Ratio and Volume Fraction of Steel Fiber on the Mechanical Properies of SFRC. Constructions and Building Materials 21, pp [5] British Standard Institution. (2009). Testing Hardened Concrete, Part 3 : Compressive Strength of Test Specimens. London, BS EN [6] ASTM International. (2010). Standard Test Method for Flexural Strength of Concrete (Using Simple Beam with Third-Point Loading. United States, ASTM C78/C78M-10 [7] British Standard Institution. (2009). Testing Hardened Concrete, Part 6 : Tensile Splitting Strength of Test Specimens. London, BS EN 12390