A Review of Crumb Rubber Modification in Dry Mixed Rubberised Asphalt Mixtures

Abstract

This paper provides an overview of crumb rubber modified asphalt mixtures with particular reference to the dry process. The dry process involves the blending of crumb rubber with hot aggregates prior to mixing with bitumen. In comparison to the wet process (process of incorporating crumb rubber into bitumen prior to mixing with aggregates), this mixture type has a number technical issues. The lack of standards and inconsistent performance have resulted in scepticism among practitioners and researchers in accepting the dry process for rubber modification even though it has the potential to recycle more crumb rubber compared to the wet process. This has resulted in the overwhelming majority of asphalt paving projects involving crumb rubber using the wet process. Therefore, to better understand the mixture, details pertaining to dry mixed rubberised asphalt are discussed in this paper with sufficient information from previous research. The discussions highlight several critical issues regarding its modification concept (the function and behaviour of rubber particles within the mixture), mixture design criteria and mechanical performance of this mixture type. This is necessary in order to identify the factors that play a significant role in improving the mixtures properties for future studies. Additionally, the review will be a positive step in the direction of achieving an appropriate design standard for dry mixed rubberized asphalt mixtures.

Functionalization of Crumb Rubber Surface for the Incorporation into Asphalt Layers of Reduced Stiffness: An Overview of Existing Treatment Approaches

“…In terms of recycling, many industries in the field of construction materials and other engineering fields use CR from ELTs in various forms for applications such as rubberized asphalt concretes [3][4][5], non-structural materials, especially for thermal and acoustical insulation [6,7], as well as playgrounds and artificial turf surfaces [8,9]. Indeed, the ELTs rubber benefits are well-known in civil engineering, particularly in the road pavement sector, since the first rubberized asphalt was produced in the last century.…”

“…The elasticity of rubber has been proven to positively influence the mechanical performance, i.e., the pavement layers' durability, while its low stiffness can contribute to abate the noise generation [2]. As a matter of fact, in the latest years, the CR obtained from ELTs following different possible processes has been proven to be an efficient solution to reduce the accumulation of waste tires while contributing to the sustainability and carbon footprint reduction of road transport [3,10,11].…”

“…Depending on the time and temperature of the mentioned interaction, the rubber particles are known to swell in asphalt by adsorbing the bitumen's lightweight components [12]. The small molecular size of maltenes diffuse inside the rubber particles, and rubber volume expands [3]. The described phenomenon is not happening just because of each component's chemical properties; the size distribution of rubber and, mostly, the time and temperatures of interaction have a considerable effect on rubber swelling within the asphalt binder.…”

Recyclability of Asphalt Mixtures with Crumb Rubber Incorporated by Dry Process: A Laboratory Investigation

“…In the last few decades, the methodology that guarantees a better performance of CR modified mixtures has been developed [17]. Along with it, different treatments have been studied to chemically activate the rubber particles with the aim to enhance their interaction within the asphalt matrix [15,[17][18][19][20][21][22][23][24]. The current rubber solutions can now offer a double function in the behavior of the asphalt mixture.…”

“…These two functions have been found to improve the resistance to cracking at low temperature, permanent deformation, and fatigue cracking [18][19][20][21][22][23]. Furthermore, the influence on mixture performance of different variables, such as size and quantity of the CR, mixing time, binder content, volumetric properties, or the digestion (conditioning) time, has been broadly evaluated [8,17].…”