Morne LABUSCHAGNE – Much Asphalt –
Latest Developments in emulsions in South Africa
The Double Spray bar system comprises of a binder distributor equipped with a primary- as well as a secondary spray bar. The primary spray bar applies the bitumen emulsion onto the substrate, as would be the case during traditional tack coat applications. A catalyst (breaking agent) is then introduced into the tack coat by means of the secondary spray bar. The catalyst chemically destabilises the tack coat which ultimately results in accelerated curing of the bitumen emulsion. This system can be utilised for the application of both tack coats during chip seal construction as well as bond coats in conjunction with HMA applications Trackless bond coats are becoming increasingly popular in SA. Improved bond strengths, improved adhesion (especially on concrete substrates), quicker construction traffic accommodation as well as improved compaction of the asphalt layer are some of the advantages that can be expected when comparing trackless bond coats to their conventional alternatives.
SBS modified bitumen emulsions are rapid setting cationic emulsions primarily intended for use as tack coats during chip seal construction. These emulsions are alternatives to traditional SBR modified bitumen emulsions. In the case of SBS modified bitumen emulsions, the emulsion’s exit temperature after the mill during production, is above the boiling point of water and therefore heat exchangers are required in order to create a back pressure in the system and increase the boiling point. Many advantages can be expected from SBS modified bitumen emulsions, compared to traditional SBR modified bitumen emulsions.
Rheologically modified bitumen emulsions are generally Cationic rapid setting bitumen emulsions with binder contents varying between 60 – 70%, used as tack coats during chip seal applications. These emulsions are thixotropic which allows them to be easily applied due to the shear thinning effect when pumped and/or sprayed with increased resistance to flow, once applied. Some of these tack coats can be applied without the risk of run-off at very steep gradients.
Bitumen emulsion primes and pre-coating fluids have become increasingly popular in South Africa and the use of cutback based products have declined in South and Southern Africa over the past number of years. Bitumen emulsion suppliers have been striving towards further reducing the solvent content of the bitumen emulsion based primes and pre-coating fluids to the lowest possible levels. The ultimate achievement would be to produce these emulsions which are completely free of solvent.
Bitumen emulsion suppliers are at varying levels of equipment- and product development in terms of the above mentioned technologies. Some suppliers introduced certain technology more than 5 years ago while others are currently un able to offer the South African Industry the same or similar. Certain developments, although believed to have a lot of potential are not very popular.
More aggressive marketing may therefore be required which may result in a bigger buy in from Industry. Although proprietary specifications are available from manufacturers, no national guideline or specification exists for some of the technology and developments.