Climate Change Challenge

Addressing the causes and implications of climate change is a challenge that every industry is having to address. John Barritt, technical advisor to the Aggregates Programme at WRAP (the Waste & Resources Action Programme), looks at how a new tool will help the aggregates and construction industries identify strategies to further reduce their CO₂ emissions

The scientific consensus on climate change is that most of the warming observed over the last 50 years is attributable to human activity, through the emission of greenhouse gases. It is clear that we need to make a profound change in our use of energy and other activities that release these gases.

Minimizing the output of CO₂ during construction activities is therefore highly desirable. Furthermore, CO₂ emissions are being used by both the Government and industry as a key performance indicator to encourage a reduction in global warming. Therefore, by proposing construction schemes that offer reduced CO₂ emissions, contractors and developers can enhance their chances of winning work.

WRAP has been working since 2001 to support the creation of sustainable markets for recycled resources and improve waste minimization and recycling rates. The organization’s focus has now evolved to embrace wider materials resource efficiency, thereby helping reduce greenhouse gas emissions and tackle climate change.

In the aggregates sector, WRAP has been working on a range of initiatives to further stimulate the market for recycled and secondary aggregates. In line with the organization’s wider focus, WRAP commissioned research to identify a modelling tool that could be used to identify the CO₂ emissions generated by typical road construction scenarios. The tool covers four specific applications — unbound, hydraulically bound mixtures, concrete and bituminous bound. The aim was to illustrate how reductions in CO₂ emissions can be achieved through greater use of recycled and secondary aggregates.

The research, carried out by a partnership made up of representatives from the Centre for Sustainability (C4S) at TRL Ltd, Taylor Woodrow Technology (TWT) and Costain, started by trying to identify existing environmental sustainability tools that could effectively measure the CO₂ emitted by construction projects.

Development of the tool

Initially, 26 existing sustainability and environmental assessment tools and approaches were identified. Following initial assessments, the majority of these tools were discounted, as, for a variety of reasons, they were unable to estimate CO₂ emissions for different aggregates sources and construction applications. The following four tools were found to be potentially suitable:

• ESRSA Tool – WRAP (developed by Viridis (now C4S))
• Environmental Wizard tool for cold recycling bitumen-bound material – Roadstone Recycling Ltd
• Life Cycle Inventory Model for Asphalt Pavements – European Asphalt Pavement Association (EAPA)/EuroBitume
• Corporate Stepwise –­ Best Foot Forward.

These were further trialled using a typical road-building scenario to identify the strengths and weaknesses, usability and applicability of each of the models in terms of their ability to provide a measure of CO₂ emissions.

Results varied considerably due to differences in the underlying assumptions made by each of the models and the lack of reliable data on recycled and secondary aggregates. Due to the very specific requirements of this project, none of the tools were able to deliver the data required. WRAP therefore decided to develop its own bespoke tool design specifically to help users decide on construction techniques and aggregate supply alternatives on the basis of the associated CO₂ emissions.

At the outset the project team agreed that the tool should have the following characteristics:

• be easy to use for anyone in the supply chain
• be independent, so not a marketing tool for specific materials
• include the assumption that processing (crushing and screening) of recycled aggregate is the same as for primary crushed rock
• account for impacts from recycled aggregates in a consistent manner
• allow the user to input distances from point of delivery to point of use
• cover the following applications: unbound, hydraulically bound, concrete, bituminous bound, hot and cold processes
• be job specific by calculating the total amount of CO₂ generated by using the materials in a range of applications on the project
• allow for different aggregate options and/or process techniques to be compared in a single run
• calculate estimates of CO₂ generated by adopting each option and calculating savings.

Testing and independent verification

The tool was developed as a Microsoft Excel spreadsheet and tested by the project partners using existing case-study information to ensure accuracy and user-friendliness.

Once this internal development and evaluation phase was complete, the tool was further tested by the Quarry Products Association (QPA) to obtain an independent, external opinion on its accuracy and user-friendliness. The QPA made a number of suggestions to clarify assumptions and data sets used in the tool but, overall, found that the figures obtained were in line with some of their own data and calculations on the subject.

Finally, data from three different examples of typical construction projects were used to test the tool’s sensitivity. This determined which applications are most energy intensive and therefore produce the highest levels of CO₂. The results of this testing showed that the production of binder material has a significant impact on CO₂ emissions due mainly to the relatively high embodied energy of these products.

The user guide

A vital component in ensuring the user-friendliness of the tool was the commitment to develop a comprehensive user guide. This provides step-by-step instructions to lead the user through the inputs required to complete a CO₂ estimation, helpful tips and warnings on using the tool, details of the assumptions and approximations used, and case studies demonstrating CO₂ emissions savings in actual project scenarios.

The instructions provide specific guidance to help with the completion of the input sheets for each of the four applications covered by the tool — unbound applications, hydraulically bound mixtures, concrete and bituminous bound. The guide clearly sets out all the information that needs to be entered into the tool to allow CO₂ calculations to be made.

In addition, the guide provides details of how experienced users can customize both the formulae and data used by the tool to make calculations and to make the tool’s calculations more specific to their own activities. For example, in the input sheets default mixes are provided that can be altered to match specific quantities of material components and techniques. Details are also provided of the assumptions used by the tool to make calculations.

Finally, six case studies are provided within the user guide showing the CO₂ emissions tonnages calculated by the tool for various road-construction options. These clearly identify the CO₂ emissions savings that can be made via the specification and use of recycled and secondary aggregates.

Conclusions

The development and testing of the tool has clearly demonstrated to the project team that using less energy-intensive techniques, selecting sources of aggregates closer to the site and opting for ‘greener’ transport methods are effective ways of reducing energy use and associated CO₂ emissions.

The tool also confirmed that the use of recycled and secondary aggregates also often leads to reductions in CO₂ emissions compared to primary aggregates. When considered in conjunction with the other benefits of recycled and secondary aggregates use, such as reduction in energy costs, conservation of natural resources and minimization of waste, the case for a more sustainable approach becomes compelling.

Availability

The CO₂ emissions calculator tool and associated guidance notes are now available for download free of charge from WRAP’s AggRegain website at: www.aggregain.org.uk/sustainability/try_a_sustainability_tool/co2_emissions.html