Life Cycle Assessment (LCA) is a fundamental tool for evaluating the environmental sustainability of products, processes and systems.
Through this methodology, it is possible to assess environmental impact throughout the entire life cycle of a product – from the production phase to final disposal.
The importance of LCA is recognized at the international level, with specific standards governing its application in order to ensure methodological rigor, transparency and comparability of results.
LCA thus constitutes a systematic and quantitative approach that is essential for supporting informed decision-making in resource management and in the development of strategies with low environmental impact.
LCA in relation to the recent Minimum Environmental Criteria
In road infrastructure, environmental impacts are often assessed through LCA studies. This focus aligns with recent Minimum Environmental Criteria (MEC) for roads. MEC encourages using recycled materials, cutting emissions during asphalt and concrete production and placement, and adopting a circular approach to road design, construction, and maintenance.
Clearly, LCA and MEC are aligned. Therefore, integrating LCA into road design and management is a strategic tool for delivering and retaining sustainable and resilient infrastructures – in line with current environmental policies and the objectives of ecological transition.
To produce eco-sustainable bituminous concrete, what characteristics should a plant have?
The plant must:
- Be capable of processing high percentages of recovered materials;
- Release low atmospheric emissions;
- Produce asphalt concrete with lower energy consumption and low CO2 emissions.
Let us therefore consider MEC for roads, namely the LCA analysis. If we refer to the entire life cycle of the pavement, Figure 2 summarizes and describes the most significant phases. It allows us to numerically express the overall impact for each ton of produced bituminous concrete (in terms of kilograms of CO2 equivalent).
The LCA calculation is carried out with the aid of software that draws on a data base (energy consumption, emissions, etc.). The database is shared and updated.
The process begins with the extraction of the stone material (generally from a quarry) and its processing and transport up to the plant (phases A1 and A2). It then proceeds to phase A3, which we will focus on in particular, namely the production at the plant (phase A3). This is followed by material transport, placement and rolling (phases A4 and A5 respectively).
The subsequent steps of greatest interest are: demolition for partial rebuilding or maintenance or for end-of-life (phase C1); the transport of the millings (phase C2); their partial disposal and transformation into asphalt conglomerate granulate (phase C3); or their disposal as waste or for other use (phase C4).
The values reported are the result of calculations carried out by the technical staff of Ammann. The values are fully consistent and corroborated both with the findings from participation in international research projects and with what is confirmed by the literature on the subject. (See, for example, the study conducted by the European Asphalt Pavement Association, EAPA https://eapa.org/).
In the gray columns, you will find the CO2 equivalent value produced across the entire life cycle A1-C4. In the red columns, only phase C3 is reported, i.e., the CO2 eq emissions per ton of conglomerate released only by the production plant.
The columns on the left, labelled, “Traditional asphalt plant,” describe a process that does not follow MEC guidelines or adopt recent technologies aimed at improving efficiency and sustainability.
Use of recycled material
The 12.4% reduction obviously applies to the entire life cycle of the pavement due to the lower demand for virgin aggregates and new bituminous binder. If we focus only on phase A3, however, the use of aggregate from a technical-mathematical energy balance perspective does not result in any appreciable percentage reduction in CO2eq.
Here it is worth highlighting the RAH100 technology, i.e., the heating system for asphalt aggregate granules using hot air. Of these applications, there are more than 80 in Europe, consisting of the installation of two distinct drying drums placed at different elevations:
- The ground dryer is dedicated to virgin aggregates and corresponds to a drum of very high efficiency in counterflow;
- The elevated dryer, dedicated to asphalt granulate and located vertically atop the mixer, is a counterflow dryer. It is specially designed to heat up to 100% of the aggregate without direct contact with the heat source, using only the hot air generated by the burner. The flow of hot air transferred to the granulate is at controlled temperature and flow rate. It therefore prevents the aging of the bitumen (a phenomenon aggravated by exposure or contact of the binder in the granulate with aggregates or flames at high temperatures). Slow and gradual heating – even “gentle,” in a sense – through the hot air allows the binder’s rheological properties to be preserved, reactivated and brought to a temperature up to 160 °C for proper final mixing. This yields a final mixture of exceptionally high quality and prevents overheating of the virgin aggregates (with further enormous benefits in terms of both energy and finished product quality).
New plants
The percentage reduction – both overall and for the A3 phase alone – is significant and results from optimization and improved design of next-generation plants. This is the case even when comparing new plants to those introduced just 8 to 10 years ago. Ongoing company research has led to the development of drying drums with more efficient heat exchange, reducing energy consumption per ton produced. New-generation insulation materials have significantly minimized thermal losses, while updated designs have further cut losses caused by thermal bridges.
Screens with higher frequency and greater sorting capacity have reduced the volume of rejected material that would have otherwise been heated unnecessarily. These are just some of the improvements in new-generation installations such as HRT, Universal and Unibatch plants. While not necessarily the most significant, these changes are among the easiest to understand.
Software efficiency
It’s truly remarkable that software alone can reduce emissions by 5%. It is the result of the ongoing improvement and development of automation software that optimizes and examines each and every step to find efficiencies. Specific opportunities include: rationalizing production by managing recipes by mix type and temperatures; managing recipes; dynamically varying the percentage of granulate from one recipe to another; conserving heated materials; using energy from photovoltaic panels to heat electric tanks; and stabilizing burner power as a function of the temperature of the inerts exiting the dryer drum and the flue gas temperature (ADX).
Other features aimed at improving energy performance include: Peak Load Management (prevents short-term, costly load peaks, indicates trend within a given period and has forecasting and alarm functions as well as automatic shutoff of utilities); Predictive Emission Management (provides the information necessary for the CEMS – Continuous Emissions Monitoring System – based on the current TVOC value, from which a forecast is made for possible exceedance of the semi-hourly average TVOC value); and IMM Integrated Maintenance Management to support staff by planning the necessary maintenance activities (essential to reducing the risk of plant downtime or to avoid working in a non-optimal and energetically disadvantageous manner).
Humidity reduction
It is observed that the reduction, in absolute terms, is quite remarkable – an almost 20% reduction in CO2 emissions. As can be seen from Figure 6, for each percentage point of humidity, there is an increase or decrease of about 8 kWh/t.
Depending on the type of fuel used, we quickly calculated how much CO2 is saved. The simplest solution is equally effective as the more elaborate and complex one: namely covering the piles of inert materials (particularly sands) and of aggregate (which has a high capacity to absorb water).
Warm-mix asphalt
As with the previous point 2.4, the reduction of temperatures (down to 120° C as provided in the road MEC, for example) for the production of warm-mix asphalt mixtures (WMA) lowers as CO2 emissions by as much as 25% per ton produced.
Natural gas and hydrogen
The two elements, respectively, allow a reduction of 25.8% and 89.9% of CO2e per ton of produced conglomerate, compared to using a fuel oil such as BTZ in Italy. There is nothing more to say on this aspect, and the math is straightforward. The burner technology offered today by Ammann is unique worldwide, namely:
- All burners can be fed with a mixture of natural gas and hydrogen with the second component up to 28%;
- It is possible to reach 60% through the combined use of natural gas and hydrogen and an additional liquid or solid fuel;
- By using the 100% H2 burner, the plant can be fed using hydrogen and/or natural gas in a variable ratio depending on fuel availability, from 0 to 100% hydrogen.
Conclusions
An ultra-modern plant equipped with the described drying drum represents a technical proposal capable of meeting the challenges of the coming decades. It combines the best technologies available on the global market with a product platform designed for future technical and technological upgrades that may be necessary.
The advantages are several, indeed numerous:
- Competitive: Owning a productive asset such as HRT+RAH100 enables competing with any rival business in terms of productive capacity, blend quality, low operating and production costs.
- Environmental sustainability: The technology enables packaging blends up to 100% granulate, far beyond the “conservative” parameters used in this report. Moreover, the issue of gaseous emissions in the atmosphere remains addressed both in terms of VOCs (related to the gentle heating of the granulate with the drying drum) and CO2eq (related to the efficient energy process).
- Economic: The benefits of RAP have been repeatedly demonstrated. There is high productivity, and thus shorter production times; lower CO2eq emissions and therefore lower taxes; lower energy consumption and thus lower production costs. The sum of these and other factors leads to the conclusion that not only is the choice right, but the economic differential between this plant and less expensive initial-investment solutions is quickly closed, especially since the HRT plant continually ensures ever-greater margins over time, thereby creating value in every respect.
Content produced in association with Ammann Group.
