Re ECF Project: 2012-08

Project Title: The use of rubberized asphalt mixture incorporated with warm asphalt additives on urban road pavements in Hong Kong

Applicant: Dr. Yuhong Wang, Department of Civil and Environmental Engineering, The Hong Kong Polytechnic University

Total Approved Grant: $323,500 (ECF & WWGF: 50/50)

Duration: 1/8/2014 to 31/7/2017

Project Status/Remarks: Project completion to be reviewed by the ECF Research Projects Vetting Subcommittee

This project aims to design rubberized asphalt mix incorporated with warm asphalt additives and to promote its use in Hong Kong. Particular interest will be placed on its engineering performance in Hong Kong’s climate and traffic conditions, potential benefits under reducing emissions, odour, energy consumption and traffic noise, and the strategy to facilitate its use in Hong Kong.

Summary of the Findings/Outcomes:
Different technologies can be used to incorporate crumb rubber particles from waste tyres into bituminous pavements. This project adopted a relatively new technology, terminal-blend (TB) rubberized asphalt. Warm mix additive is added to TB rubberized asphalt to further reduce mixing temperature and improve its workability. A unique feature of TB rubberized asphalt is that rubber particles almost dissolve in bitumen; hence, it can be stored at normal temperature without the need for continuous heating and agitation. In addition, additives such as warm-mix additives and polymers can be easily blended in the bitumen to generate desired engineering properties.
In this study, the TB rubberized asphalt was formulated, produced, and finally used in full-scale test sections in Hong Kong. The overall process involves 3 major stages: (1) production of TB rubberized asphalt in bitumen production plant; (2) production of bituminous mixtures using the special bitumen; and (3) construction of full-size pavement sections. All the stages were carried out as if this was implemented in a real road construction project. Sample cores were taken from the full-scale pavement sections and tested for various engineering properties.
The engineering, economic, and environmental performance of the rubberized asphalt materials was analyzed, and found that stone-mastic asphalt (SMA) mixtures using TB binder have better rutting resistance as compared with SMA using PG 76 bitumen and regular Pen 60/70 bitumen. The fatigue resistance of SMA mixture using TB binder is between the fatigue resistance of SMA mixture using PG 76 binder and the fatigue resistance of SMA mixture using Pen 60/70 binder. The cost of TB binder is comparable with PG 76 binder, if warm-mix additives and SBS polymer are added. If no such additives are used, the cost of TB binder is even lower than the regular Pen 60/70 binder. The use of TB binder can help reduce inert solid waste generated from scrapped rubber tyres, and the addition of warm-mix additives can cut down energy use, greenhouse gas emissions, and odour. It was found that asphalt fumes generated from SMA mixtures using TB binder with warm-mix additives are at a low level, likely attributed to the reduced temperature. The detected chemicals in the vapour phase are different for the 3 types of bitumen used in this study. The smell from the mixture using TB bitumen is noticeable, but it is not obnoxiously strong because of the low temperature of the mixture. In conclusion, TB bitumen is a feasible technology to effectively use recycled crumb rubber in Hong Kong.