Go Green with Colas!

In February of last year, Gearoid Lohan, CEO of Colas Ireland, launched a “Go Green with Colas” initiative to encourage all Colas subsidiaries to play a more pro-active role in meeting their environmental responsibilities. An additional aspect of this initiative is to raise awareness with our many customers and stakeholders of how Colas can help them meet their carbon reducing targets. 

In March last year, Ireland’s carbon reduction targets were enshrined into law by the Government when it passed legislation committing the country to an overall aim of reducing our carbon emissions by 51 % by 2030 and to reach “net zero” by 2050. These are ambitious targets and will require action and contribution by every sector of industry and community.

Since its establishment over 70 years ago, the Colas Group has led the way in the development of environmentally friendly pavement materials. In fact, the name Colas comes from the words COLd ASphalt. Cold-mix asphalt, as it is called, is similar to the more commonly used “hot-mix” asphalt but is produced by using a bitumen emulsion instead of the conventional hot bitumen. As bitumen emulsions can be used with aggregates at ambient temperatures, as opposed to the high temperatures required to manufacture hot-mix asphalt, there are considerable energy and, hence, carbon savings to be achieved by their use.

Figure 1: Cold-mix asphalt trial in Colas yard in Mallow, 1984

Colas first introduced the cold-mix asphalt technology into Ireland in the 1980’s. In 1990, a cold-mix asphalt called “Grave-émulsion” was used in the base course of a 40 km section of the N8 from Dublin to Cork. At that time, the N8 was the highest trafficked road in the country. But the grave-émulsion cold-mix material well and truly survived the test of time. In fact, when it had reached the end of its design life in 2006, there were no signs of distress or failure, with no cracking, an average rut depth of only 3 mm (versus the failure criteria of > 10 mm) and an IRI smoothness indicator of 1.7, which is well below the smoothness criteria for a new road! Since then, Colas Ireland has led the development and promotion of other emulsion-based materials and techniques such as surface dressing, cold-asphalt micro-surfacing and in situ pavement recycling.

Figure 2: Surface dressing with bitumen emulsion technology is the most environmentally friendly road re-surfacing technique – in addition to being the most cost effective

In addition to being a cold-mix technique, in situ cold recycling is one of the most environmentally sustainable and low carbon maintenance techniques that is available to the Local Authority Engineer. In addition to being a cold technique, use is also made of the aggregate material already in the pavement. Consequently, there is less use of this valuable resource and there is less or no transporting of aggregates from a quarry or asphalt plant to the jobsite. In addition, the bituminous binder already present in the pavement can also be recycled.

Figure 3: Emulsion bound cold in situ recycling

Much of these developments have been made possible thanks to Colas Ireland owning and operating its own speciality chemicals company in Oranmore, Co. Galway. Chemoran’s range of emulsifiers and bitumen additives enables Colas subsidiaries worldwide to design their emulsions and asphalt mixtures to best meet their customers’ needs. Chemoran’s bitumen additive called CWM™ has been used for the production of over 7 million tonnes of warm-mix asphalt worldwide and its adhesion agents extend the service-life of hot-mix asphalt by improving the bond between the binder and the aggregate and, hence, its durability.

In terms of making a change to reduce the industry’s carbon footprint, switching to warm-mix asphalt, instead of hot-mix asphalt, is probably the easiest transition. By simply adding an additive, such as CWM™ into the bitumen, mixing temperatures at the hot-mix plant can be reduced by at least 30 C. Temperature reductions of up to 40 C have been achieved, even with the very dense EME mixtures used in France. 

Needless to say, the further the reduction in mixing temperatures, the greater the savings in energy use at the asphalt mixing plant and, as a consequence, the greater the reduction in greenhouse gas emissions. It has been widely reported in the literature that energy savings of the order 15 to 20 % can be achieved when the mixing temperatures are reduced by 30 to 40 °C. In Ireland’s case, this would equate to a reduction in carbon emissions of the order 15,000 tonnes of CO2 eq. per annum.

In terms of performance, during the past ten years, it has been well established that warm-mix asphalts behave in the same way as conventional hot-mix asphalts. Since 2008, over 7 million tonnes of warm-mix asphalt have been made using the CWM additive alone. Many more millions of tonnes have been produced using other additives. Warm-mix asphalt has been used in every bituminous layer of the pavement from base to surface course, including mixes that contain high percentages of RAP, and under all traffic levels.

Perhaps as importantly, another significant benefit to reduced mixing temperatures is a reduction in VOCs emitted at the laying site, i.e. less smoke and fumes. It has been established that, as a general rule, for every 12 °C degree drop in mixing temperatures, VOC emissions are reduced by half at the job site. At a trial site in Dublin in 2012, the reduction in VOCs was measured and found to be 80 % lower than that of the conventional hot-mix, when the mixing temperatures were reduced by 35 °C.

Figure 4: Laying CWM-modified warm-mix in France (at 40 C lower) – no smoke behind the screed!

Another benefit of reduced mixing and laying temperatures is that the pavement will cool to ambient temperatures more quickly and, therefore, can be reopened to traffic sooner. Consequently, there is a less of an inconvenience on the road user.

In terms of the costs to implement such a change, the cost of the warm-mix additive will be offset by the savings in fuel use. In addition, if the cost of carbon credits is increased to the € 80 per tonne mark (as is now promised by this government), the net increased cost to the asphalt producer and, consequently to the client, i.e. the Irish taxpayer, will be zero!

The road construction/maintenance industry and the asphalt industry, in particular, has within its grasp the ability to play a significant role in achieving Ireland’s carbon reduction targets by promoting and/or even insisting on the use of both warm-mix and cold-mix asphalt. The benefits are obvious and can be implemented immediately. 

For further information on how the Colas Ireland group of companies can help you to reduce your carbon footprint, please contact us at www.gogreenwithcolas.ie .

By Alan Kavanagh, CEng, Technical Director of Colas Ireland Group