The Path to Climate-Neutral Road Construction

Machine manufacturers and construction companies around the globe are currently searching for ways to achieve the ultimate goal of climate-neutral construction. The challenge here is to successively reduce CO₂ emissions as well as other harmful gases (expressed as a CO₂ equivalent: CO₂e) to zero globally over the coming decades. In the road construction sector, this transformation is inextricably linked to the improvement and further development of production and working processes. In the future, machines and construction materials will also be assessed on the basis of the climate-harmful emissions arising from their production and use. The focus is, however, not on individual machines, but on the entire process leading up to the finished product – a road. Ultimately, the deciding factor is the emissions generated per mile of newly built or rehabilitated road – CO₂e per unit of work done.

Sustainability Targets in the Road Construction Sector

The construction industry already faces specific on-site requirements with respect to the use of non-fossil fuels or the deployment of machines with local zero emissions – in the Nordic nations, for instance. In light of this and their obligations to future generations, many leading players in the construction sector and numerous small and mid-size companies are currently setting their own goals to mitigate climate change.

The Greenhouse Gas Protocol

The Greenhouse Gas (GHG) Protocol has established itself globally as a holistic accounting method for CO₂e emissions. In a similar way to business accounting, it enables companies and institutions to systematically determine their levels of harmful emissions and identify their sources.

As a manufacturer of road construction machines, the Wirtgen Group has also set itself concrete goals, broken down into specific steps. For example, Wirtgen, Vögele, Hamm, and Kleemann will further increase the availability of machines powered by hybrid or fully electric drive systems by 2026. In addition, all Wirtgen Group product brands, including Benninghoven, will offer machines and plants that can be operated with non-fossil or climate-neutral fuels. Last but not least, the digitalization of machines will make a significant contribution to process optimization and, in turn, lead to further reductions in harmful emissions.

The Goal: Sustainable Reduction of Emissions

The ultimate goal of all these measures is a considerable reduction in the carbon footprint of Wirtgen Group machines, plants, and systems by 2030. In concrete terms, we are aiming to reduce scope 1 and scope 2 emissions by over 50%. For scope 3, we plan to reduce upstream and downstream emissions by at least 30%. These primarily include emissions made by machines throughout their service life, but also things like the emissions produced along the supply chain. To this end, John Deere, the parent company of the Wirtgen Group, has joined the Science Based Targets initiative (SBTi) and has had its own goals assessed and validated.

In order to achieve the greatest possible reduction in overall emissions, it is essential that we focus the efforts of all actors across the road construction industry. The key question we must ask ourselves is: How can we construct or rehabilitate roads with minimal or zero harmful emissions?

The CECE 4-Pillars Approach

CECE is a pan-European organization representing construction machine manufacturers and related industries They have identified four areas in which CO₂e emissions can be reduced: (Source: CECE)

A holistic approach that takes all aspects of road construction into consideration is essential in order to achieve maximum reduction of CO₂e emissions. As the pan-European organization representing construction machine manufacturers and related industries, the CECE has already proposed a number of courses of action. Considerable savings potential can be leveraged by further improvement of machine efficiency, improved construction processes and procedures, and more-efficient operating concepts. At the same time, alternative, non-fossil fuels and electric drive systems can play an important role on the road to climate neutrality.

Smart Assistance Systems and Alternative Energy Sources

The Wirtgen Group has already developed numerous solutions over the years to significantly reduce fuel consumption. These include intelligently-designed drive systems and efficiency-optimized controls. One example of this is Wirtgen’s ”Mill Assist”: an assistance system for cold milling machines that automatically adjusts to meet the performance and quality requirements entered by the machine operator and consistently guarantees the most favorable balance between milling performance and operating costs. This simultaneously reduces diesel fuel consumption and minimizes pick wear. Another example is the Dash 5 generation of road pavers from Vögele, which feature environmentally-friendly machine technologies that also ensure lower fuel consumption.

Machines from Wirtgen, Vögele, Hamm, and Kleemann whose engines fulfil the requirements of the US EPA Tier 4f exhaust emission standard or EU Stage V can already be powered by alternative fuels. They are approved for use with alternative paraffinic fuels like HVO (Hydrotreated Vegetable Oils: fuels made of vegetable oils or animal fats) or XtL fuels (X-to-Liquid: synthetic fuels made of solid, liquid, or gaseous energy resources). There are already corresponding solutions for asphalt mixing plants from Benninghoven. These can be fueled with wood dust or BtL (Biomass-to-Liquid).

CO₂e Reduction Potential Through Material Recycling

To holistically assess a jobsite and the methods used in construction, you need to consider not only the emissions from individual machines and/or plants, but also all the emissions that arose or will arise in the production of the construction materials and mixes and in their transportation to and from the construction site.

To illustrate CO₂e reduction potential through the use of recycling technologies, the graph below shows the emissions from a variety of construction methods used for the rehabilitation of the surface layer and binder course of a single-lane roadway. In all of these cases, we have assumed that the construction machines and transport vehicles use B7 diesel fuel and that the asphalt mixing plant is fueled by lignite dust. The transport distances reflect typical distances between mixing plants and jobsites.

The left column depicts emissions from conventional methods: Existing material is milled off and removed from the site before a new surface is paved with an asphalt mix produced entirely from fresh material. Emission calculations show that the majority of emissions come from the production of the asphalt mix and the materials this process requires.

In the center column, you can see the new proportions once 80% of the asphalt mix is made of recycled material, that is, re-used milled material. Modern asphalt mixing plants are already capable of producing such material, and Retrofit solutions are available for existing plants as well. This by itself reduces CO₂e emissions by an impressive 27%.

An even greater reduction is possible if the construction materials are not heated before processing. As the column on the left shows, this is where a large proportion of CO₂e emissions arises. Tried-and-tested alternatives are already in use around the globe. The most important of these are low-temperature asphalt production and cold recycling. Cold in-situ recycling in particular consumes up to 90% fewer resources requires up to 90% less transport movement. In the example scenario, this reduces CO₂e emissions by 43% (see right column) when building a surface layer of new material over the cold recycled layer. When completely rehabilitating the entire roadway, this method can actually reduce CO₂e emissions by up to 60% with no reduction in quality. Additional practical benefits of this method include faster project completion and longer-lasting road surfaces.

Exploiting the Opportunities of Digitalization

Regardless of the measures employed, a transparent and verifiable system for determining and assessing emissions is essential. This is where the tremendous opportunities offered by digitalization can play a decisive role. These days, for example, telematics systems are already able to register the fuel consumption of machines. For Wirtgen Group product brands alone, the number of machines outfitted with such systems is projected to rise to 42,000 by 2030,

meaning these values can be documented under real conditions to provide much more accurate data than predetermined testing cycles. With the aid of digital solutions like these, it is possible to document consumption figures “per work done” – i.e., on a jobsite or project basis.