ARID ZONE JOURNAL OF ENGINEERING, TECHNOLOGY & ENVIRONMENT AZOJETE December 2021. Vol. 17(4):527-534 Published by the Faculty of Engineering, University of Maiduguri, Maiduguri, Nigeria. Print ISSN: 1596-2490, Electronic ISSN: 2545-5818 www.azojete.com.ng Corresponding author’s e-mail address: ibnibrohim88@gmail.com 527 ORIGINAL RESEARCH ARTICLE OPTIMISATION OF COVER THICKNESS IN TYRE-FIBRE CONCRETE UNDER ELEVATED TEMPERATURE O. A. Ibrahim1, M. M. Afodun2, F. G. Mije3 and T. Ako4 1,2Department of Civil Engineering, Faculty of Engineering and Technology, University of Ilorin University of Ilorin, Ilorin, Nigeria 3,4Department of Civil Engineering, University of Jos, Nigeria *Corresponding author’s email address: ibnibrohim88@gmail.com 1.0 Introduction Environmental pollution is in existence from the earliest days of life, but now it is a serious issue which poses a threat to human survival Ajello et al., (2005a). Ajello et al., (2005b) and Pacheco, (2012) explained that many problems arise in the waste management system, especially for tyres and coals. Growing volumes of used tyres at landfills around the world have created a major environmental problem. Stergios and Atalia, (2016) considered means of recycling these solid wastes (scrap tyres) or renewed interest in developing alternatives to its disposal in the construction industry is needed to be devised in order to curtail the negative environmental hazards caused by it. Gideon (2012), Failure of structural elements after fire outbreak is mostly attributed to spalling action. Spalling of concrete is an occurrence which results to decrease in the cross sectional area of the concrete elements, thus decreases the resistances to fire loads. Concrete as a common material used in construction and it competes directly with all other major construction materials such as timber, steel, asphalt, and stone, because of its versatility in applications. The concrete cover required to protect the reinforcement against corrosion depends on the exposure conditions and the quality of the concrete as placed and cured immediately surrounding the reinforcement. There may be cases where extra precautions are needed beyond those given in order to ensure protection of the reinforcement (BS 8110-1:1997). ARTICLE INFORMATION ABSTRACT Failure of structural elements after fire outbreak is mostly attributed to spalling action. Spalling of concrete is an occurrence which results to decrease in the cross sectional area of the concrete elements, thus decreases the resistances to fire loads. This study, optimized the concrete cover thickness in tyre fibre concrete (TFC), which was subjected to single temperature load according to ISO 834 using graphical method. Three (3) samples were prepared from each series of mix containing tyre fibers of 10 mm width and varying length viz; 0%, 2.5%, 5.0% and 7.5%, using water cement ratio of 0.55. The samples were produced in 100 x 100 x 100mm cubes and tested for compressive strength. However, the cubes were structural modeled using TEDDS 2.0.01 and STAADPro v8i to under temperature load to determine optimum cover thickness through the deflection mode. The cover thickness for tyre-fibre concrete reduced from 25mm to 17.5mm under the same condition with the conventional concrete mixture. This shows that inclusion of tyre-fibre in concrete increases the fire resistance and reduces the cover thickness. It is recommended that tyre-fibre concrete should be used in our daily construction work for more durability. © 2021 Faculty of Engineering, University of Maiduguri, Nigeria. All rights reserved. Submitted 17 August, 2021 Revised 2 Oct., 2021 Accepted 7 Oct., 2021 Keywords: Spalling tyre-fibre concrete cover thickness deflection temperature load http://www.azojete.com.ng/ file:///C:/Users/USER/Desktop/azojete/AZOJETE%20ARCHIVE/UPLOAD/USER/Desktop/azojete/AZOJETE%20ARCHIVE/UPLOAD/VOL%2017%20NO%204/ibnibrohim88@gmail.com file:///C:/Users/USER/Desktop/azojete/AZOJETE%20ARCHIVE/UPLOAD/VOL%2017%20NO%204/New%20folder/ibnibrohim88@gmail.com Arid Zone Journal of Engineering, Technology and Environment, December, 2021; Vol. 17(4):527-534. ISSN 1596-2490; e-ISSN 2545- 5818; www.azojete.com.ng Corresponding author’s e-mail address: ibnibrohim88@gmail.com 528 Muhammed (2014) said, increasing the concrete cover of structural elements such as beams, columns or slabs in the conventional concrete to prevent the reinforcement’s exposure, reduces the effective depths of these elements which may eventually leads to increase in structural member thickness in cases where deflections are not satisfied. For this reason, design for fire resistance has become a necessity. It ensures that the structure has sufficient capacity to support its loads for a period of fire exposure that guarantees safety during the evacuation and fire extinguishing processes. Robert (2013) explained that modern applications have led to the development and use of new types of concrete (tyre-fibre concrete). The disadvantages caused by increasing concrete cover of structural elements can be avoided by the presence of tyre-fibres in the concrete hence, paving way for effective materials utilization. Wasiu and Raji (2015) defined optimization of the concrete design as an act of searching for a design for which the sum of the costs of the ingredients is lowest, and satisfying the required performance of concrete, such as workability strength and durability. Therefore, this study determines the optimum cover thickness needed for a tyre-fibre concrete due to inclusion of tyre-fibre under temperature load. 2.0 Methodology 2.1 Material Used: Ordinary Portland cement (Dangote 3X) of 42.5R grade (BS 12:1991) was used for preparing the concrete mix. The Coarse aggregate (manually crushed) used was granite with maximum nominal size of 20mm and sourced locally from a completed project along Oko- Erin, Ilorin. The fine aggregate (Sharp sand) used in the concrete mixture was obtained from Gaa Akanbi, Ilorin, Kwara State. The sand was sieved in accordance with BS 933 Part 1 (1997) to remove bigger aggregate sizes and organic impurities. The square tyre-fibres (10mm) used were pre- treated with Sodium Hydroxide solution (NaOH) of 20g/dm3 before used in order to enhance the adhesion with concrete matrix and increase transfer rate of water and hydration. 2.2 Mixing Proportion: The mix proportion, 1:2:4 (M25 grade) with water cement ratio (w/c) of 0.55 as shown in Table 1 was designed according to BS 5328: part 1. Tyre-fibers were added to the mix in various proportions namely; 0%, 2.5%, 5% and 7.5%, respectively. The maximum of 7.5% was adopted for this study. This was used for all the samples for consistency in the comparison. Table 1: Mix Design for cube 100 x100 x 100 mm CRA Content (%) Cement (𝒌𝒈/𝒎𝟑) Sand (𝒌𝒈/𝒎𝟑) Granite (𝒌𝒈/𝒎𝟑) Coarse Rubber Aggregate (𝒌𝒈/𝒎𝟑) Water (𝒌𝒈/𝒎𝟑) W/C 0 33.70 67.32 134.64 0.00 18.54 0.55 2.5 33.70 67.32 131.27 3.37 18.54 0.55 5.0 33.70 67.32 127.90 6.74 18.54 0.55 7.5 33.70 67.32 124.53 10.11 18.54 0.55 2.3 Impact Test: Each series of freshly mixed tyre fibre concrete was placed in the cubic moulds of dimension 100 x 100mm for casting the specimens. Twenty four (24) specimens (100 x 100 x100 mm) were cast and cured according to BS 1881: part 111(1983) and tested for impact strength at 7 and 28 days after heating (ISO 834 fire curve) at an average temperature of 300°C) (Figure 1-2) which were recorded at 30 and 60 minutes respectively. Thereafter, the file:///C:/Users/USER/user/Downloads/azojete143/www.azojete.com.ng file:///C:/Users/USER/Desktop/azojete/AZOJETE%20ARCHIVE/UPLOAD/USER/Desktop/azojete/AZOJETE%20ARCHIVE/UPLOAD/VOL%2017%20NO%204/ibnibrohim88@gmail.com Ibrahim et al: Optimization of Cover Thickness in Tyre Fibre Concrete under Elevated Temperature. AZOJETE, 17(4):527-534. ISSN 1596-2490; e-ISSN 2545-5818, www.azojete.com.ng Corresponding author’s e-mail address: ibnibrohim88@gmail.com 529 specimens were left at room temperature to cool. The schematic diagram of heat test machine is shown in Figure 1. Figure 1: Schematic diagram of heat test machine Source: Geology department, University of Ilorin 2.4 Design Optimization for the Tyre Fibre Concrete The objective function of the optimization process is to minimize the weight of the fibre concrete weight per unit length, which is to a large extent a function of the concrete cover thickness. The BS8110 is focused on the limit state philosophy and the main aim of the design is to ensure an adequate margin of safety against the ultimate limit state being reached. In the case of vertically loaded (one-sided temperature load) cube, this is obtained by ensuring that the ultimate temperature load (G) does not exceed the design load resistance of the concrete (GR). The optimization is carried out using graphical method [Wasiu and Raji, 2015]. The optimal design problem formulation is carried out to minimize the weight of the concrete cover subject to stress constraints due to vertical loading (temperature load). Figure 2 shows the cross-section of the concrete cube and the possible applied load. The followings are the notations used in Figure 2. Figure 2: Typical Cross-Section of a Tyre Fibre Concrete Cube with Temperature Load Where: h = the height of the cube (100mm) Ct= Concrete cover thickness (25mm, BS8110) Wt = Width of the cube (100mm) b = is the length of the cube (100mm) Qt = temperature load on the cube dt = effective depth of the cube Wr = Wt-2(Ct) http://www.azojete.com.ng/ file:///C:/Users/USER/Desktop/azojete/AZOJETE%20ARCHIVE/UPLOAD/USER/Desktop/azojete/AZOJETE%20ARCHIVE/UPLOAD/VOL%2017%20NO%204/ibnibrohim88@gmail.com Arid Zone Journal of Engineering, Technology and Environment, December, 2021; Vol. 17(4):527-534. ISSN 1596-2490; e-ISSN 2545- 5818; www.azojete.com.ng Corresponding author’s e-mail address: ibnibrohim88@gmail.com 530 For tyre fibre concrete cube, stress constraints: at the maximum temperature load of 50 kN per meter length of the cube, the fibre concrete cube weight per unit length is optimized as shwn in Equation 1-10. W= 𝑀𝑖𝑛𝑖𝑚𝑖𝑧𝑒 ∶ 𝑊 = φ(ℎ, 𝐶𝑡) (1) Ajamu and Adedeji, (2013) 𝑊 = 2ρ 𝑐𝑡 Vct + ρ 𝑤𝑟 Vwr (2) Where: ρ 𝑐𝑡 = density of the concrete cover thickness ρ 𝑤𝑟 = density of the concrete below the bottom reinf. - cover thickness Vct = Volume of the concrete cover per unit length of the cube Vwr = Volume of the concrete remain (minus cover) per unit length of the cube 𝑊 = (2 × 23.17𝐶𝑡ℎ) + (23.17 × 2𝐶𝑡ℎ) (3) Neglecting the weight of reinforcement (∅ = 12𝑚𝑚) ∴ 𝑊 = 92.68𝐶𝑡ℎ (4) For the design constraints: (a) Vertical load due to compression This is expressed as: 𝜎𝑜 − 𝜎𝑎𝑙𝑙 ≤ 0 (5) Ajamu and Adedeji (2013) Where σall = allowable stress (17.6 N/mm2, from load-deformation test) and σo = design stress 𝜎𝑜 = 𝜇𝑁 𝑊𝑡𝑥ℎ = 1.4𝑁 4𝐶𝑡×ℎ = 1.4𝑁 16𝐶𝑡 (6) Where 𝜇= partial factor of safety, N= design load (kN), allowable load = 198kN (Compressive strength test), Therefore; 1.4𝑁𝑣𝑒𝑟𝑡𝑖𝑐𝑎𝑙 𝑙𝑜𝑎𝑑 16𝐶𝑡 − 198000 100×100 ≤ 0 (7) 𝑁𝑣𝑒𝑟𝑡𝑖𝑐𝑎𝑙 𝑙𝑜𝑎𝑑 − 226.29𝐶𝑡 ≤ 0 (8) Ajamu and Adedeji, (2013) (b) Temperature Load The rate at which heat is conducted across the specimens of diameter D =100mm is shown in Equation 9. 𝑸 = 𝑲 𝝅𝑫𝟐 𝟒 ( 𝜽𝟐−𝜽𝟏 𝒅 ) (9) Where: Q = rate of heat conduction (W) K = thermal conductivity of the material of the specimen (W/mK) θ 2 – θ1 = change in temperature (oC or K) from 30-60 minutes. For an area of concrete cube of thickness d, the rate of heat conduction per unit area q (W/m2) of the cube can be expressed as: 𝒒 = 𝑲 ( 𝜽2−𝜽𝟏 𝒅 ) (10) Nthermal 16𝐶𝑡 − 29.34 0.10x 0.10 ≤ 0 (11) Nthermal − 46944𝐶𝑡 ≤ 0 (12) Ajamu and Adedeji, (2013) file:///C:/Users/USER/user/Downloads/azojete143/www.azojete.com.ng file:///C:/Users/USER/Desktop/azojete/AZOJETE%20ARCHIVE/UPLOAD/USER/Desktop/azojete/AZOJETE%20ARCHIVE/UPLOAD/VOL%2017%20NO%204/ibnibrohim88@gmail.com Ibrahim et al: Optimization of Cover Thickness in Tyre Fibre Concrete under Elevated Temperature. AZOJETE, 17(4):527-534. ISSN 1596-2490; e-ISSN 2545-5818, www.azojete.com.ng Corresponding author’s e-mail address: ibnibrohim88@gmail.com 531 2.5 Modelling and Simulation The second aspect involves numerical simulation. Finite element modelling of concrete cube with and without tyre fibre for deflection curve was analysed using TEDDS 2.0.01. The primary objective is to obtain the curve which will be used for optimization computation. This is shown in Figure 3 and 4. Figure 3: Static Analysis Operation (TEDDS) Figure 4: Static Analysis Operation (StaadPro v8i) 3.0 Result and Discussion Table 2 and 3 show the combined temperature of the concrete (with and without tyre fibre) which was only considered for 0, 30 and 60 minutes respectively. The temperature of the samples increases with increase in time. The temperature in the fibre concrete was slightly lower because there was no free movement of heat within the concrete due to tyre fibre action. However these gains are functions of temperature differences and the time interval between temperature measurements. Table 2: Temperature (°C) of the Concrete (with and without tyre fibre) Time (min) Percentage of tyre fibre replaced 0 2.5 5 7.5 0 0 0 0 0 30 619 556 474 600 60 970 914 760 872 Table 3 shows the rate of heat gain at equal time interval for the specimen. The total heat gain per square meter through the concrete (Table 3) in one hour was found to be 2934 J/m2 http://www.azojete.com.ng/ file:///C:/Users/USER/Desktop/azojete/AZOJETE%20ARCHIVE/UPLOAD/USER/Desktop/azojete/AZOJETE%20ARCHIVE/UPLOAD/VOL%2017%20NO%204/ibnibrohim88@gmail.com Arid Zone Journal of Engineering, Technology and Environment, December, 2021; Vol. 17(4):527-534. ISSN 1596-2490; e-ISSN 2545- 5818; www.azojete.com.ng Corresponding author’s e-mail address: ibnibrohim88@gmail.com 532 (1.63J/s per sq. meter, (Ajamu and Adedeji 2013)) and the allowable thermal load per unit length is given as 29.34N. Table 3: Evaluation of Rate of Gain of Internal Temperature of the Concrete Cubes % T 𝜃1(℃) 𝜃2(℃) 𝜃2 − 𝜃1(℃) Gain Rate q(𝑤/𝑚2) Time Interval t(s) Heat Gain/sq.m H(𝐽/𝑚2) 0 619 975 356 1.78 1800 3204 2.5 556 920 364 1.82 1800 3276 5.0 474 800 326 1.63 1800 2934 7.0 600 893 293 1.47 1800 2637 3.1 Optimization The loads applied to the specimen increases with increase in cover reinforcement at 5% fibre replacement under a single face temperature load. The deflection observed was approximately linear. Figure 5 shows the graphical representation. The curve intersected at 2.5mm which means the constraints are between 2.5mm and 25mm. Figure 5: Constraints Optimization 𝐶𝑡 = 2.5 + 2 3 × (25 − 2.5) = 17.5𝑚𝑚 𝑁 = 50 + 1 3 × (200 − 50) = 100𝑘𝑁/𝑚𝑚 (The centroid of the “shaded triangle”) (i) The minimum cover thickness: 𝐶𝑡 = 17.5𝑚𝑚 (ii) The optimal weight per unit length for a cube of 1m is: ∴ 𝑊 = 92.68𝐶𝑡ℎ (4.1) 𝑊 = 92.68 × 17.5 × 100 𝑊 = 162.19 𝑘𝑁 𝑝𝑒𝑟 𝑚𝑒𝑡𝑒𝑟 That is, 162.19 < 231.7 Ok. Table 4, 5 and 6 show the cover-load values and average blows on the produced samples. The ratio of the initial to final crack ratio for the sample increases with increase in percentage of tyre-fibre added. This shows that the tyre-fibre has a greater impact on the durability of the concrete. file:///C:/Users/USER/user/Downloads/azojete143/www.azojete.com.ng file:///C:/Users/USER/Desktop/azojete/AZOJETE%20ARCHIVE/UPLOAD/USER/Desktop/azojete/AZOJETE%20ARCHIVE/UPLOAD/VOL%2017%20NO%204/ibnibrohim88@gmail.com Ibrahim et al: Optimization of Cover Thickness in Tyre Fibre Concrete under Elevated Temperature. AZOJETE, 17(4):527-534. ISSN 1596-2490; e-ISSN 2545-5818, www.azojete.com.ng Corresponding author’s e-mail address: ibnibrohim88@gmail.com 533 Table 4: Values for Cover - Load at 5% Fibre Replacement Cover (mm) Load (kN) % Fibre replaced (%) 0 35 5 5 70 5 10 105 5 15 140 5 20 175 5 25 200 5 Table 5: Drop Weight Test Results for Heated and Non Heated Cubes (Average blows) 𝑁1 𝑁2 ⁄ Date Spec. No 𝐹0% 𝐹2.5% 𝐹5% 𝐹7.5% 18/9/19 A 14 20⁄ 15 22⁄ 15 23⁄ 15 25⁄ R 0.70 0.68 0.65 0.60 Table 6: Drop Weight Test Results for Cubes (Average blows) 𝑁1 𝑁2 ⁄ Date Spec. No 𝐹0% 𝐹2.5% 𝐹5% 𝐹7.5% NH H NH H NH H NH H 18/9/19 A 16 20⁄ 15 2⁄ 17 28⁄ 18 2⁄ 15 2⁄ 16 2⁄ 16 33⁄ 19 20⁄ R 0.80 0.77 0.62 0.88 0.59 0.76 0.48 0.96 R=ratio, A= Average; F=% of replaced Rubber 4.0 Conclusion Based on this study, the following conclusions are drawn out. a. By adding 2.5%, 5.0% and 7.5% volume fraction of tyre-fibre, the energy required causing the visibility of first crack and failure was increased by 8%, 15% and 4% respectively over plain concrete: b. The results show that 5% volume fraction of tyre fibre considerably increases the impact energy in case of Tyre-Fibre Concrete (TFC) when compared to plain concrete. c. Inclusion of rubber-tyre in concrete geometry under temperature load reduced the cover thickness by 30%. The study concluded that the rubber-tyre concrete had maximum resistance to fire and least probability of failure as likened to the conventional concrete. The study recommended that rubber-tyre inclusion in concrete should be preferred for improving its resistance ability to fire. References ACI Committee 544.2R-89, 1989. Measurement of Properties of Fibre Reinforced Concrete, Detroit: American Concrete Institute. Adedeji AA. and Ajamu S. 2013. 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Construction and Building Materials 169 (2018) 473–488 file:///C:/Users/USER/user/Downloads/azojete143/www.azojete.com.ng file:///C:/Users/USER/Desktop/azojete/AZOJETE%20ARCHIVE/UPLOAD/USER/Desktop/azojete/AZOJETE%20ARCHIVE/UPLOAD/VOL%2017%20NO%204/ibnibrohim88@gmail.com