Formulation of Asphalt Concrete Using Crumb Waste Tyres

Abstract

Third world and developing countries are realizing tremendous growth in their economies. The factors that increase the growth of the economy of a country are transport infrastructural facilities, including roads, airports, railways, and water. Building reliable roads is the solution to developing a sustainable road transport network in a country. This is achieved by investing much in research on improving road construction materials' performance. The ability of roads to transport goods, people, and services within acceptable costs in terms of comfort, time, and safety is governed by road pavement life. Pavement permanent deformation in asphalt concrete mixes is among the most prevalent road pavement distress noticed on many roads in Kenya that affect the pavement life. These permanent deformations occur mainly in the wheel paths because of heavy traffic and high temperatures, resulting in depression on the pavement surface along where the wheels pass causing axial and lateral displacement, making it a risk for the motorist. The materials used in road construction are bitumen, cement, lime, aggregates, bitumen emulsions, and cutbacks. Bitumen is a critical component of road pavement; it’s excellent performance increases pavement life. Other studies have shown that waste-crumbed rubber can be used to modify bitumen binders, enhance their characteristics and improve their performance. This study aimed to characterize the effects of modifying bitumen with waste-crumbed rubber to enhance the pavement life and determine the rubber content for asphalt concrete mix design. The penetration, softening point, viscosity, ductility, and aging characteristics of bitumen that are known to be improved positively by modification with rubber were determined. The samples of waste tyre rubber were obtained from the dump sites in Donholm and bitumen samples for penetration grade 80/100, aggregates of different single sizes ranging from 0/6, 6/10, 10/14, and 14/20 mm were also purchased from Colas East Africa and Aristocrats in Nairobi County. The results obtained in this study showed that penetration of bituminous binders reduced from 88 to 44 tenths of a mm at 20 % rubber content. It shows that the modified binders can withstand the elevated temperatures of asphalt pavement surfaces. Softening point, a candidate also crucial for pavement temperature susceptibility, increased from 48.8oC to 62.3oC at 20 % added rubber content. The flashpoint and specific gravity of the neat and rubber-modified binders did not significantly change. Viscosity at 135oC increased from 304.3cSt to 330.7cSt at a rubber content of 12% and became unworkable when determined using the standard reverse flow viscometers method as more rubber was added. Ductility at 25oC reduced from135.3 cm to 50.9 cm as 3% to 20% rubber was added, implying that the rubber makes bituminous binders stiffer. The determination of the suitable amount of rubber that can be used to modify bitumen a mix design was done as per the procedures given in Road Design Manual Part III of the Ministry of Transport and Infrastructure, Kenya. The Mix design for asphalt concrete was carried out using the Marshall Test procedure, where an asphalt concrete mix of 5.5 % binder content was obtained. This binder content was further refined at the refusal by the vibrating hammer method, where an optimum binder content of 5.1 % was considered optimum for the design used to deduce the suitable amount of bitumen and single-size aggregates in the mix. At the optimum bitumen content of 5.1 % different proportions of rubber content were used to deduce the suitable amount of rubber for the mix. 10.0 % rubber content was considered the optimum for improving the performance of asphalt and asphalt concrete formulations. The study also assessed how the varied intrinsic characteristics of the modified bitumen affected the modified asphalt concrete formulation. Characteristics of flow, stability, tensile strength, density, and resistance to rutting, moisture-induced damage at elevated temperatures of 60 oC for both the neat bitumen formulation and the rubber-modified bitumen formulation were analyzed. The results obtained shows that density, stability, tensile strength and elastic modulus of rubber modified bitumen formulation increased to a maximum of 2.262 g/cc, 15.4 kN, 842 kPa and 5236 MPa respectively as more rubber of 3 % to 20 % was added, and reduced to 2.205g/cc, 10.3 kN, 398 kPa and 2528 MPa respectively, implying that the formulations became stiffer with increased rubber content