It is 14 years since the opening of Chapman’s Peak Drive as a toll road after the 2000 fires and devastating rockfalls forced the closure of the pass.
The pavement structure and surfacing fared reasonably well over the 14 years, but had reached a stage where a planned intervention was necessary, so as to extend the life of the pavement for another 6 to 10 years.
This was becoming apparent in the increased porosity of the surfacing, allowing water to penetrate into the underlying pavement support layers. Longitudinal and transverse cracking of the surfacing had manifest in certain areas, as well as incidents of “crocodile cracking” of the road surface, indicating that water ingress into the substrate layers was increasing.
In terms of the Entilini’s bid and financial model, a reseal to the road way was provided for and planned at around the half-life of the 30 year concession period. As mentioned above, the purpose of the re-seal is to protect (“waterproof”) the pavement so as to extend its life for a further 6-10 years, before a major rehabilitation/intervention in the latter part of the concession period is undertaken.
This planned intervention was always intended to be a re-seal.
A couple of re-seal treatments were considered for this mid-life re-surfacing of Chapman’s Peak Drive, with the current option being chosen for numerous reasons.
- The binder is bitumen rubber, containing up to 25% of recovered crumb rubber from discarded vehicle tyres. It has the best elastic properties of all binder categories available, and due to its visco-elastic properties, can be sprayed at a higher application rate per square meter than any other conventional or modified binder. This has obvious benefits, in that a 50% thicker layer of bitumen rubber binder as compared with other conventional/modified binders can be sprayed on the road surface to optimise the waterproofing properties of the re-seal.
- The visco-elastic properties of the bitumen rubber binder yield superior performance in bridging micro cracking and lateral deformations of the road surface, and in so doing minimising the ingress of water into the substrate and structural component of the pavement.
- The bitumen rubber binder, (through the incorporation of crumbed rubber), is not as susceptible to attack and degradation from the ultra violet rays of the sun, and hence has an extended life compared to other binders.
- The industry standard road stone (wearing surface) to be applied to bitumen binder is a 14mm aggregate with an 8.2mm Average Least Dimension (ALD). This is the aggregate being applied at Chapmans Peak.
- The bitumen rubber single seal was also preferred to the other surfacing options, as disruption to traffic on Chapman’s Peak would be kept to a minimum, as the road can be re-opened to traffic within a few hours of application, whereas other seals may have necessitated overnight and continuous road closures, and extended disruption to the travelling public.
- Although still within specification, the skid resistance of the 14 year old surface was of concern from a safety perspective, particularly in wet weather. The texture of the reseal will ensure that the skid resistance of the roadway exceeds the required minimum specifications.
