Characterization of Modified Crumb Rubber Concrete Adeyemi Oluwaseun Adeboje 1* , Williams Kehinde Kupolati 1 , Emmanuel Rotimi Sadiku 2 , Julius Musyoka Ndambuki 1 1 Department of Civil Engineering, Tshwane University of Technology, Pretoria 0001, South Africa 2 Department of Chemical, Metallurgical & Materials Engineering, Tshwane University of Technology, Pretoria 0001, South Africa Corresponding Author Email: AdebojeAO@tut.ac.za https://doi.org/10.18280/ijsdp.150315 ABSTRACT Received: 9 December 2018 Accepted: 14 December 2019 Concrete is a very important construction material used worldwide for the construction of bridges, buildings, dams, kerbs, patios, pools, roads, walkways and other civil engineering structures. The constituents of concrete are cement, coarse aggregate, fine aggregate and water. Efforts were made in this work to evaluate the suitability of crumb rubber as a partial substitute of sand in concrete mixes. This research evaluated the effects of partial substitution of sand with crumb rubber on the mechanical properties and microstructural formation of modified crumb rubber concrete. The control concrete sample and concrete samples with 1, 2, 3 and 4% sand content in the concrete substituted with crumb rubber were cured for 3, 7, 28, 90 and 120 days, respectively, and then tested. The laboratory experiments conducted on the concrete samples were workability, bulk density, compressive strength, tensile splitting strength, scanning electron microscopy (SEM) and energy dispersive spectroscopy (EDS). Improvement in the strength and densification of the microstructure of the concrete samples occurred as the curing age increased from 3 to 7, 28, 90 and 120 days, respectively. This research further showed that marginal improvement in both the strength properties and microstructural formation of the modified crumb rubber concrete can be achieved by substituting 1% sand with crumb rubber. Keywords: concrete, crumb rubber, mechanical properties, microstructure, walkways 1. INTRODUCTION Waste materials, such as crumb rubber, are yet to be fully utilized for concrete works, other construction purposes or industrial applications, especially in many African countries [1]. Adequate evaluation of the crumb rubber (granulated form of waste rubber tyres) is required before it (crumb rubber) can be recommended as a material to partially replace sand in concrete [2-4]. Owing to its wide usage across the world, about 12 billion tonnes of concrete is consumed globally, on an annual basis. The rise in temperature of the earth is called global warming. Carbon dioxide (CO2) is one of the greenhouse gases and its huge quantities is emitted in the production of cement and concrete. This leads to degradation of the ozone layer of the earth and causes global warming. It thus calls for concern to arrest the situation [2, 3]. Energy used up in the construction industry is about 30% of the total energy consumed from all human activities. Hence, it looks promising to utilize other less thermal conductive materials for construction to achieve efficient operational energy in the production of concrete [3]. The mechanical properties and microstructural formation of fine and coarse aggregates are extremely important features to achieve thermal insulation of concrete; hence, utilization of air entrainments and thermal non-conductive aggregates can enhance concrete’s thermal resistance [3]. Human activities have been on the increase because the global population is constantly increasing [5] and this has resulted in astronomical increment in the volume of waste generated from activities of man. As a result, the total number of vehicles has also increased globally [6, 7]. The astronomic increase in the number of vehicles used worldwide gave rise to an increase in the quantities of waste rubber tyres used and dumped in the environment [8, 9]. It is important to ensure that the waste tyres are efficiently disposed at incinerators, landfills and other means of disposing the waste tyres have proved inefficient, owing to the non- degradable nature of the waste tyre rubber [10, 11]. Disposal of waste tyres on landfills has also led to provision of houses for pests, reptiles and rodents. These insects and reptiles are venomous, they attack human beings and domestic pets, destroy the environment and are deadly to human and destroy ecological balance in the environment [12, 13]. Crumb rubber is produced from waste tyre rubbers. The metal strings in the waste rubbers are removed and the waste rubbers are torn and ground into desired grain sizes [14-17]. Recent advances have ventured on the evaluation of crumb rubber to determine its suitability as a replacement for fine and coarse aggregates for concrete production. Literature has also shown that replacement of sand with crumb rubber reduces the strength properties of concrete [18-21]. This research was an experimental study conducted the applicability of waste crumb rubber as a partial replacement for sand in concrete. This work investigated the effects and suitability of partially substituting sand with crumb on the mechanical properties and microstructural formation of modified crumb rubber concrete. International Journal of Sustainable Development and Planning Vol. 15, No. 3, May, 2020, pp. 377-383 Journal homepage: http://iieta.org/journals/ijsdp 377