Abstract
Rapid road infrastructure development due to an increasing demand of car users resulted in an increase in paved areas including road sites and suppression of green spaces. An integrated solution that can support a country’s economic development without compromising water pollution is becoming inevitable. Recycling tyres in the form of crumb rubber tyres and mixing it into bituminous paving mixture can increase the recycling rate and minimize cost of incineration process. In dry mixing process, five (5) different variations of Open Graded Wearing (OGW) course road samples were made to make up 1.15 kg in each sample. Each OGW mix contained 4% - 6% bitumen Pen 60/ 70 and fixed 1% of crumb rubber tyres, making the percentage of crumb rubber tyres 14% - 20% of bituminous samples. Bitumen Pen 60/70 mixed with 20% crumb rubber tyres content met the PG 76 bitumen properties. Physical properties of OGW made from crumb rubber modified bitumen (CRMB) were better than standard bitumen only. In a separate water leachate test using ICP-OES equipment, heavy metal leachate of Cu(II), Pb(II), Zn(II) and Cd(II) were present in all OGW CRMB samples at increasing surrounding water temperature from 25℃ to 60℃. However all the heavy metal concentration was very low below the allowable limit of trade effluent standards into water course.
Highlights
Bitumen Pen 60/70 mixed with 20% crumb rubber tyres content met the PG 76 bitumen properties
Physical properties of Open Graded Wearing (OGW) made from crumb rubber modified bitumen (CRMB) were better than standard bitumen only
Bitumen Pen 60/70 mixed with 20% crumb rubber tyres content met the PG 76 bitumen properties i.e. the closest in terms of its penetration and softening point and met the performance and workability requirement
Summary
Economic cost of infrastructure development, including land transport industry, in Singapore has been escalating in recent years. The common idea for the asphalt paving mixes design is to create good quality roads by determining an economical blend, gradation as well as the asphalt binder (bitumen). It will provide a mix with good bonding properties. Some bitumen binders may include styrene butadiene styrene (SBS), styrene-butadiene rubber (SBR), ethylene vinyl acetate (EVA), and crumb rubber modifier (CRM). Using commercial polymers such as SBS, SBR and EVA as bitumen binders will increase the construction cost of road pavements as they are relatively very costly modifiers
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