Hot-mix asphalts are so-called because the aggregates and binders used to produce them are heated to temperatures of the order 170 to 190°C. Conversely, cold-mix asphalts are so-called because the aggregates used are not heated. This is made possible by the use of a specialist binder called a bitumen emulsion.
This technology was developed by COLAS in the early part of the 20th century and is the origin of our name, i.e. Cold Asphalt.
Because of the different technology that is used to manufacture them, cold-mix asphalts have been found to be more resistant to fatigue cracking, compared to the conventional hot-mix asphalts. As there is no oxidative age hardening of the bitumen during the mixing process (thanks to the lower mixing temperatures), the asphalt remains flexible and retains its cohesion over a longer period of time.
Reduced Carbon emissions
With the growing awareness of global warming and the Irish Government's declaration of a Climate Emergency in May 2019, there is now a trend towards the use of asphalts with lower carbon emissions.
Cold-mix asphalts have the advantage over hot-mix asphalts of lower fuel use (i.e. lower energy) and, as a direct result, reduced carbon emissions at the mixing plant. Consequently, these mixtures are termed "Low-Energy Bound Mixtures" in Clause 8 of the TII's Specification for Roadworks Series 900.
Cold-mix asphalt can be used as the base course for the construction of new roads or as an overlay for the strengthening of regional and local roads. It can be expected to provide a design life up to 20 msa. The material is laid using a conventional paver, steel drum roller and pneumatic tyred roller. The latter is required to knead out as much water from the material as possible before it is sealed - thus achieving its maximum compacted density. After compaction, the material is normally sealed using a fog spray of emulsion and 6 mm chips or grit. This allows for the fresh material to be trafficked immediately. The cold-mix asphalt is then surface dressed or overlaid with a hot-mix asphalt surface course.
Cold-mix asphalt is most suitable for use as an overlay to reshape and strengthen regional and local roads. A document published by the Department of Transport, Tourism and Sport (DTTAS) in 2014 entitled "Guidelines on the Depth of Overlay to be used on Rural Regional and Local Roads", gives advice for the use of cold-mix asphalts such as SWM and Grave-Emulsion.
Both Grave-Emulsion and SWM also satisfy the requirements of Clause 8 of the TII's Specification for Roadworks Series 900.
- Resistant to fatigue cracking.
- A low-energy option for the rehabilitation and maintenance of rural roads in Ireland.
- Satisfies the requirements of Clause 8 of the TII's Specification for Roadworks Series 900.