The CSIR and the Southern African Bitumen Association (Sabita) have developed and conducted research on HiMA mixes suitable for heavily-trafficked roads in South Africa. CSIR infrastructure engineering researchers used local materials and performance-related testing to develop a product with significantly-improved properties compared to conventional asphalt mixes. HiMA mixes have been developed to be suited to South African circumstances for use on roads that carry high volumes of traffic.
“HiMA is a composite material consisting of graded mineral aggregate blended with a hard bituminous binder. It has a greatly-improved resistance against permanent deformation and, due to its high stiffness, provides better protection of underlying road layers. It also has good durability due to its high binder content,” explains Denneman, the project leader.
“It is important for road materials to be able to cope with the significant increases in traffic volumes and loads. Such materials should also offer road owners long-term, virtually maintenance-free solutions in light of curbing congestion and minimising road user costs,” comments Saied Solomons, CEO of Sabita. The specific HiMA mix used at the Durban harbour entrance was produced by a company called National Asphalt.
eThekwini Municipality was the first road authority to implement the use of HiMA technology. “We believe that HiMA offers a better solution, taking into account the challenges posed by the weather and high volumes of heavy, slow-moving traffic around the Durban harbour. Any interruption of traffic in that area affects the national economy,” says Krishna Naidoo, senior manager of the municipality’s road rehabilitation branch.
“One of the HiMA mix designs used at the Durban harbour contains 20% reclaimed asphalt and can carry significantly higher traffic loads than traditional mixes. With less frequent rehabilitation, we can thus reduce the pollution generated by traffic jams when roads are being repaired and also ensure the reduced use of virgin materials, all of which will assist in meeting our objectives of implementing more environmentally-friendly road-building solutions,” Naidoo notes. eThekwini is looking at implementing HiMA technology more widely within its municipal region.
HiMA can be used on main routes, high-volume urban roads and at airports. “The technology is in the process of being transferred to the South African industry for routine road design and construction,” says Solomons.
“The CSIR is involved with the planned implementation of HiMA technology on projects elsewhere in the country, in collaboration with various asphalt producers,” Denneman comments.
Design guidelines for HiMA mixes
Extensive laboratory research on HiMA mixes by the CSIR and Sabita resulted in the development of preliminary guidelines for the design of South African HiMA mixes and roads containing HiMA layers. The guidelines will feed into the updated, comprehensive South African Road Design Method undertaken by the CSIR and others for the South African National Roads Agency Ltd (SANRAL).