Academic Journal of Science and Technology ISSN: 2771-3032 | Vol. 13, No. 1, 2024 31 Acoustic Enhancement of Sustainable Concrete Mixture Through Integration of Recycled Tyre Waste Zhiheng Zhang Universiti Sains Malaysia, Penang, 14300, Malaysia Abstract: This research examines the impact of rubber content on the acoustic and mechanical properties of concrete, using a mix ratio of 1:1.8:2.24 and replacing fine aggregate with 0%, 5%, 10%, and 15% rubber. From the result obtained for the compressive strength, the concrete with 0% wt reaches its highest strength which is 55.36 N/mm2 at 28 days. For split strength test, the concrete with 15% wt reaches its highest strength 3.50 N/mm2 at 14 days and for the flexural strength, it is observed that the concrete with 15% wt reaches its highest strength 5.01 N/mm2 at 14 days. Results indicate that higher rubber content decreases compressive, tensile, and flexural strengths, particularly with longer curing times, due to the elasticity and low density of rubber. However, the sound absorption coefficient improves with increased rubber, peaking at 15% after 7 days of curing. While waste tyre rubber enhances acoustic properties, it negatively affects mechanical strength, making rubber concrete suitable for applications prioritizing sound performance over structural integrity, such as soundproof walls. Future research should focus on optimizing rubber concrete mix designs and improving mechanical properties. Keywords: Rubber concrete, noise pollution, physical changes, sound absorption. 1. Introduction The rapid urbanization and growth of the automobile industry have significantly increased waste tyre quantities, leading to serious environmental issues. This study investigates the use of waste tyre rubber particles as a replacement for fine aggregate in concrete, aiming to address waste disposal and reduce reliance on natural resources,to investgate the effects of replacing fine aggregate with tyre rubber on compressive strength,spilt tensile strength,flexural strength and sound absorption. 2. Background As of the latest available information, noise pollution continues to be a significant concern in many parts of the world, affecting urban, industrial, and natural environments. In recent times, there is an increasing need for the design and development of mortar and concrete with an eco- friendly value. A simple and efficient method to prevent the rapid depletion of natural quarries (like sand, gravel, and crushed stone) and to maintain ecological balance is to use recycled materials, such as demolition waste or industrial by- products, instead of natural aggregates. The environmental aspects are not the only reason for the use of alternative aggregates. Indeed, a lot of waste products, including waste glass powder (Singh Shekhawat & Aggarwal, n.d.), plastics (Sharma & Bansal, 2016), ground granulated blast furnace slag(Özbay et al., 2016) wood ash (Cheah & Ramli, 2011) and crumb rubber from waste tyres (Zhang et al., 2022) properties suitable for being incorporated into cementitious matrices, bringing potential engineering functionalization in concrete materials, such as lightweight, higher durability, better shock absorption, and improved thermo-acoustic insulation properties. Each year 2–3 billion tyres are scrapped in the US with similar quantities in Europe. It is estimated that approximately 40 million tyres are discarded per year in the UK. Ireland produces over 35,000 tonnes of waste tyres which are banned from many landfill sites and may not be burned. With decreasing disposal options and increasing production, the volume of used tyres is becoming a major waste management issue. The use of crumb rubber concrete (CRC) produced from broken down waste tyres to replace a portion of natural aggregates in concrete mixes has been the subject of much research, CRC is a durable composite material capable of absorbing and reflecting sound and if used on the exterior of a structure can shield the occupants from ambient street noise. High rise apartment occupiers for example are often overlooking busy streets with high noise levels, often uncomfortably high, passing into dwelling spaces. 3. Scope of Study This study aims to determine the sound adsorption of crumb rubber concrete, in addition, the concrete mix with a ratio of 1:1.8:2.24 of cement, fine aggregate and coarse aggregate which then replaced the fine aggregate with the crumb rubber content of 0%, 5%, 10% and 15% was studied. he use of the concrete mix ratio of 1:1.8:2.24 for cement, fine aggregate, and coarse aggregate is beneficial for several reasons, especially when incorporating crumb rubber. This ratio ensures a good balance among the materials, allowing the concrete to maintain strength while taking advantage of crumb rubber's sound-absorbing properties. The higher amount of fine aggregate (1.8) helps integrate the crumb rubber better, filling gaps and enhancing acoustic performance. Crumb rubber is effective at reducing noise because its porous structure helps dissipate sound waves, making the concrete ideal for applications like sound barriers and soundproofing in buildings. Additionally, this mix ratio supports the concrete's durability and stability, ensuring that it remains strong while also providing good sound absorption. Overall, this ratio enhances both the acoustic and structural qualities of rubberized concrete. As well as physical changes after replacing rubber to fine aggregate which including compressive strength, split tensile strength, and flexural. 32 4. Experiment 4.1. Conversion factor In this test, the mixing conversion factor is using 1.54, as 1.54 is commonly used at the same time, the 1.54 factor is an empirical value often used in practical construction, including in many mix designs that follow ACI 211.1 guidelines. Aggregates, both fine (sand) and coarse, are made up of individual particles with small void spaces in between them. These void spaces are an inherent characteristic of the aggregates and cannot be eliminated completely, even when the aggregates are in a compacted state (Haque et al., 2012). The volume of these voids needs to be accounted for when determining the actual quantities of materials required for the concrete mix. 4.2. Compressive Strength Table 1. Concrete mix proportion with the tyre rubber in compressive strength Tyre rubber (%) Mix ratio Cement (kg/m3) Water (kg/m3) Fine aggregate (kg/m3) Coarse aggregate (kg/m3) Tyre rubber (kg/m3) 0 1:1.8:2.24 4 1.8 7.7 8.7 0 5 7.3 0.4 10 6.9 0.8 15 6.5 1.2 Table 2. The compressive strength test result Curing days Compressive strength by composition, N/mm2 0% 5% 10% 15% 7 days 47.06 38.35 22.09 14.71 14 days 55.11 39.20 23.39 15.11 28 days 55.36 42.34 26.22 16.18 The data from this test indicates that increasing the rubber replacement of sand aggregate results in a decrease in compressive strength. This is primarily because rubber particles, when added to concrete, make the material more flexible and less dense than traditional concrete, which relies on stiff aggregates like sand and gravel to achieve its compressive strength. Rubber is significantly less rigid than these aggregates and deforms more easily under load, which reduces the overall strength of the concrete. Additionally, the incorporation of rubber tends to increase the amount of air entrapped in the concrete mix, leading to greater porosity, further weakening the material's ability to withstand compressive forces. The extent of the compressive strength reduction is closely tied to the percentage of rubber used to replace traditional aggregates. The data shows that as the rubber content increases, the compressive strength decreases more significantly. For example, (Ganjian et al., 2009)found that replacing 10% of fine aggregate with crumb rubber led to a 20- 30% reduction in compressive strength. Despite this reduction in strength, rubberized concrete gains advantages in flexibility and ductility, which can be beneficial in applications requiring impact resistance and energy absorption, such as pavements, sidewalks, and structures subjected to dynamic loads. Rubberized concrete also exhibits improved resistance to cracking, especially under conditions where traditional concrete might become brittle. The data also shows that compressive strength increases with longer curing times. As cement undergoes hydration—a chemical reaction with water—over time, the concrete gains strength. Prolonged curing allows the hydration process to continue, resulting in higher compressive strength. Concrete does not achieve its full strength immediately but continues to strengthen, particularly when kept moist. This prolonged curing is essential for making the surface of the concrete harder and more resistant to abrasion and wear, which is especially important for areas subjected to heavy traffic or mechanical wear, such as pavements and industrial slabs. 4.3. Split Tensile Strength Table 3. The split tensile strength test result Curing days Split Tensile Strength by composition, N/mm2 0% 5% 10% 15% 14 days 3.28 2.91 2.70 1.18 28 days 3.50 3.40 2.44 1.83 The data from this test demonstrates that adding rubber to concrete tends to reduce split tensile strength, which is a critical measure of the concrete's ability to resist tension and prevent cracking, thereby affecting its overall durability. The highest can be found in 0% 28 days 3.50N/mm2.Several factors contribute to this decrease in tensile strength. First, rubber particles have lower bond strength with the cement matrix compared to traditional aggregates like sand and gravel, which weakens the concrete’s ability to resist tensile forces. Additionally, rubber is more deformable than standard aggregates, meaning that under tensile stress, rubber particles are more likely to deform, reducing the concrete’s overall tensile resistance. The inclusion of rubber can also introduce more air into the concrete mix, increasing its porosity and providing more voids where cracks can begin and propagate, further reducing tensile strength. Furthermore, rubber is less dense than traditional aggregates, resulting in a less compact concrete matrix, which also contributes to the decrease in tensile strength. 33 4.4. Flexural Test Table 4. Concrete mix proportion with the tyre rubber in flexural Mix ratio Cement (kg/m3) Water (kg/m3) Fine aggregate (kg/m3) Coarse aggregate (kg/m3) Tyre rubber (kg/m3) 0 1:1.8:2.24 10.6 4.8 20.5 23.2 0 5 19.5 1.0 10 18.5 2.0 15 17.4 3.1 Table 5. The flexural test result Curing days Flexural Strength, N/mm2 by composition 0% 5% 10% 15% 14 days 4.97 4.53 3.54 3.30 28 days 5.01 3.74 3.47 3.12 This study reveals that increasing the rubber content in concrete results in a decrease in flexural strength, which measures a material's ability to resist bending forces. The highest can be found in 0% 28 days 5.01N/mm2.Several factors contribute to this reduction when rubber is incorporated into the concrete mix. Firstly, rubber, being a soft and flexible material, is significantly less stiff than traditional aggregates like sand or gravel. This lower stiffness reduces the concrete's overall ability to resistbending forces. Additionally, rubber's deformability under load further diminishes the concrete's capacity to withstand flexural stresses, as the material becomes more prone to deformation. Another factor contributing to the reduction in flexural strength is the weaker bond between the rubber particles and the cement matrix. The bond between traditional aggregates and cement is typically stronger, allowing the concrete to carry more load under flexural stress. However, rubber particles form a weaker bond with the cement paste, leading to a reduction in the concrete's load-carrying capacity. Furthermore, the inclusion of rubber increases the air voids within the concrete, raising its porosity. Higher porosity makes the material less resistant to bending forces, as the voids provide areas where cracks can form and propagate. Additionally, rubber is less dense than traditional aggregates, resulting in a lower overall density of the concrete, which often correlates with decreased strength. 4.5. Sound Absorption Test Table 6. Concrete mix proportion with the tyre rubber in sound absorption Tyre Rubber (%) Mix ratio Cement (kg/m3) Water (kg/m3) Fine aggregate (kg/m3) Coarse aggregate (kg/m3) Tyre rubber (kg/m3) 0 1:1.8:2.2 4 0.2 0.1 0.3 0.4 0 5 0.28 0.02 10 0.27 0.03 15 0.25 0.05 This study reveals that increasing the rubber content in concrete improves sound absorption, particularly in the mid to high-frequency range (500-2000 Hz). Rubber particles enhance the porosity of the concrete, creating voids that trap and dissipate sound energy, making the material more effective at absorbing sound in this frequency range. Additionally, the elasticity of rubber compared to traditional concrete aggregates contributes to better sound absorption, as it allows the material to more efficiently dissipate the energy of sound waves. However, the data also shows that as the curing time increases, the sound absorption coefficient (SAC) tends to decrease. This is because, as the concrete cures, the matrix hardens and the rubber particles become more integrated into the structure. As the material stabilizes and the concrete continues to hydrate and set, its porosity decreases slightly, leading to a reduction in sound absorption. While the SAC may still remain relatively high, the decreased porosity and increased stiffness of the material contribute to a slight decline in sound absorption performance over time. The findings of this study are consistent with previous research, such as the work by (Flores Medina et al., 2016), which also found that the sound absorption coefficient of rubberized concrete increases with higher rubber content, particularly in the medium and high-frequency ranges. This improvement is likely due to the formation of pores in the concrete by the rubber particles, which increase its porosity and enhance its sound absorption performance. Additionally, the lower elastic modulus of rubber compared to traditional aggregates results in reduced stiffness, making the concrete more capable of absorbing mid to high-frequency sound waves. 34 Table 7. The sound absorption test result Air gap Sound Absorption Coefficient (SAC) 250Hz 500Hz 750Hz 1000Hz 2000Hz 3000Hz 4000Hz 5000Hz 5600HZ 0% 7D 10mm 0.209 0.163 0.109 0.095 0.117 0.236 0.137 0.179 0.279 20mm 0.243 0.134 0.108 0.078 0.119 0.243 0.123 0.169 0.209 30mm 0.222 0.125 0.102 0.077 0.120 0.241 0.122 0.170 0.285 0% 14D 10mm 0.250 0.201 0.180 0.133 0.124 0.134 0.127 0.113 0.213 20mm 0.282 0.212 0.174 0.134 0.138 0.131 0.120 0.106 0.365 30mm 0.298 0.219 0.166 0.133 0.147 0.117 0.110 0.102 0.283 5% 7D 10mm 0.270 0.253 0.150 0.114 0.143 0.306 0.182 0.247 0.763 20mm 0.360 0.200 0.133 0.105 0.146 0.297 0.180 0.249 0.700 30mm 0.354 0.184 0.128 0.103 0.148 0.294 0.179 0.254 0.789 5% 14D 10mm 0.128 0.105 0.081 0.069 0.074 0.134 0.126 0.122 0.471 20mm 0.126 0.103 0.079 0.068 0.075 0.134 0.127 0.122 0.466 30mm 0.126 0.104 0.077 0.067 0.076 0.132 0.124 0.123 0.470 10% 7D 10mm 0.166 0.122 0.090 0.075 0.087 0.136 0.134 0.144 0.831 20mm 0.166 0.116 0.089 0.073 0.093 0.137 0.137 0.147 0.818 30mm 0.158 0.111 0.084 0.068 0.093 0.133 0.134 0.145 0.797 10% 14D 10mm 0.221 0.172 0.136 0.109 0.123 0.148 0.135 0.162 0.559 20mm 0.212 0.157 0.123 0.099 0.127 0.147 0.136 0.161 0.560 30mm 0.202 0.145 0.113 0.093 0.127 0.145 0.134 0.161 0.540 15% 7D 10mm 0.198 0.161 0.130 0.101 0.143 0.209 0.163 0.180 0.891 20mm 0.191 0.150 0.122 0.098 0.145 0.208 0.162 0.181 0.870 30mm 0.194 0.147 0.119 0.097 0.146 0.207 0.161 0.184 0.815 15% 14D 10mm 0.440 0.280 0.199 0.151 0.091 0.130 0.145 0.121 0.315 20mm 0.439 0.279 0.198 0.151 0.092 0.129 0.140 0.121 0.318 30mm 0.433 0.271 0.200 0.152 0.093 0.129 0.137 0.122 0.311 5. Conclusion In this study, flexural, compressive, and split tensile strength, properties generally increase with curing but decrease with the addition of rubber due to changes in the concrete's structural integrity. Adding rubber particles will reduce the flexural strength, compressive strength, and split tensile strength of concrete. Rubber particles can act as voids or weaken the bonding between concrete and aggregates, leading to lower strength compared to standard concrete. Based on the results, it demonstrates a consistent trend across compressive, tensile, and flexural strengths: the addition of the waste tyres negatively impacts the strength of the concrete. For compressive strength, the concrete with 0% wt exhibits the highest compressive strength, while the 15% wt mixture has the lowest. The 0% wt mixture reaches its peak strength 55.36 N/mm2 at 28 days, while the 15% wt mixture peaks at 14 days. Next, the tensile Strength, which similar to compressive strength, the concrete with 0% wt shows the highest tensile strength, with the 15% wt mixture exhibiting the lowest. The 0% wt mixture reaches its peak strength 3.50 N/mm2 at 28 days, while the 15% wt mixture peaks at 14 days. The trend continues with flexural strength, where the 0% wt mixture displays the highest strength, and the 15% wt mixture has the lowest. While the 0% wt mixture reaches its peak strength 5.01 N/mm2 at 28 days, the 15% wt mixture peaks earlier at 14 days. Interestingly, the 15% wt mixture shows a higher flexural strength at 14 days compared to the 0%wt mixture, suggesting a potential positive effect on early strength development. The sound absorption coefficient improves with the addition of rubber and can vary with curing. Initially, SAC increases due to increased porosity, but it stabilizes or decreases slightly once the concrete is fully cured. Adding rubber enhances the SAC of concrete, particularly at mid to high frequencies. Rubber increases the material's porosity and elasticity, improving sound absorption. The findings indicate that while the optimal strength is achieved with 0% rubber content, the addition of rubber, especially at lower percentages, can significantly improve sound absorption without drastically compromising structural integrity. However, the 15% rubber mixture demonstrates a unique early strength development, suggesting that rubber may facilitate initial curing benefits. Overall, this research highlights the dual benefits and trade-offs of using crumb rubber in concrete, paving the way for its application in sound-sensitive environments while necessitating careful consideration of strength requirements in structural applications. References [1] Aliabdo, A. A., Abd Elmoaty, A. E. M., & Abdelbaset, M. M. (2015). Utilization of waste rubber in non-structural 35 applications. 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