How can engineers assess the environmental impact of construction materials? Some materials may enjoy a green reputation, but true sustainability requires  a more considered analysis.

Timber, quite literally, grows on trees. It is abundant, captures carbon from the atmosphere, and at the end of its life can decompose naturally, leaving no harmful waste

But some of the highest value timber comes from ancient forests. Demand for this timber can lead to the destruction of forests that will take generations to regrow. Planting forests to cost-effectively grow construction grade timber may devastate biodiversity

Plastic has an increasingly malign reputation, and is almost always made from fossil hydrocarbons. There is increasing concern about the spread of microplastics through our environment, and into our bodies

But how would we have delivered billions of doses of COVID vaccines around the world, and clean syringes to administer them, without plastic? How many millions of people would have lost their lives, or suffered life limiting illness, without it?

How much extra land would need to be dedicated to industrial agriculture, if foodstuffs could not be transported in shelf life-extending plastic packs?

Green and pleasant quarry

Panshanger Park is a large open space in Hertfordshire, just a few miles outside London, and walkably close to the city’s regional rail links. It is the sort of idyllic, rolling, landscape that typifies the English countryside, with dense woodland that offers space for rich biodiversity. Gentle hills offer views of lakes and reedbeds, and space for locals and visitors from the city to exercise and explore

But it did not always look like this. Since the 1980s, parts of it have been used as a quarry, and the whole site is managed by Tarmac. 

“We’re a quarrying business, and in very simple terms, we’re extracting minerals and products out of the ground, to be used in construction materials,” explains Alex Wright, national commercial director at Tarmac.

“That is a primary resource that once it’s gone, it’s gone. But a crucial part of what we do, is [manage] the whole lifecycle of a quarrying process, in terms of our permits and our obligations, and what we do to restore that asset after it’s been extracted.

“At the end of the life of [an] operation, we’ll be restoring something back to the community that will be like a park for the community to use, for education centres and for wildlife reserves.”

As well as helping steer Tarmac’s commercial strategy, Wright also has responsibilities relating to sustainability performance. Achieving improvement in sustainability requires a careful analysis of every impact, throughout a material’s life cycle. Starting with extraction at sites like Panshanger, this must consider how a material is processed, how it is delivered to site, its use during construction, and its performance throughout the life of a building or other structure. 

We can think of our use of materials as a carbon investment. To understand the return made on that investment, it is necessary to think about how long it will be used for, and what will happen to it at the end of its planned use. For how long will it be useful? At the end of its original use, can the structure be reused? Can materials be recovered and recycled? If not, how will they be disposed of?

“We really evaluate our full supply chain when it comes to sustainability, making it front and centre of what we do,” says Wright. “In terms of the extraction, that could be using a large blast less frequently, making it the most efficient it can be. It can mean using less materials, ensuring that the crushing operation is efficient, and using renewable energy on site.”

Counting carbon

Assessing each of those impacts is not a simple process. A naive, intuitive, view can overlook important impacts, both negative and positive.

Emma Hines is a senior construction manager at Tarmac and part of the company’s sustainability team. “My role really is to support our stakeholders, both internally and externally, to ensure that they can consider the right solutions to create a sustainable built environment,” she says. 

“That could be assisting a client or customer such as Balfour Beatty, with modelling a project’s carbon baseline and providing low carbon solutions. Or it could be representing Tarmac in the National Highway sector improvement programme and assisting in their creation of product roadmaps.”

Bates uses a number of tools to assess a project or material’s overall sustainability, and has helped develop some of these.

“The construction and wider design industry have been focusing on carbon and on the impact on the environment for a very long time. The RIBA Plan of Work embeds sustainability, and material and resource efficiency, into the plan that an architect will put together,” she says.

The Plan of Work organises the process of briefing, designing, constructing and operating building projects into eight stages and explains the stage outcomes, core tasks and information exchanges required at each stage. As part of this, architects and design engineers can use RIBA’s Sustainable Outcomes Guide. This aims to provide design principles to achieve a series of measurable sustainable outcomes, and describes approaches that can be used to verify performance.

“Lifecycle analysis can be done using tools that are available already in the marketplace and many organisations use those tools,” says Bates. “Standards such as PAS 2080 can be used to measure carbon use in infrastructure. I’m involved in the rewrite of that right now, to include buildings as well. 

“You’ve got [means of] measurements such as BREEAM standards, and other material lifecycle measurements, such as environmental product declarations. These enable everyone to look at each part of this lifecycle and develop a holistic approach to the construction of whatever project they’re looking at.”

These tools and standards help materials suppliers, and their customers, assess the impact of projects as they are built. But structures continue to have environmental impacts long after their construction. In the UK, there has been much discussion recently of what to do with buildings that no longer fit their original purpose. If these are demolished and new structures built in their place, then their environmental impact over the long term is increased.

“I think that’s a conversation that has to be had with the client,” says Hines, “It’s important to understand that they’re investing a huge amount of money to build a structure that they may only be using for 20, 30 years, maybe even less than that. The question should be, how do we make sure that when we’re investing carbon into these constructions of these buildings, how do we make sure that they can be reused? 

“That already happens with a lot of concrete structures. There’s a beautiful post office building in Sheffield, that was adapted into apartments and because it was built with a long life concrete structure, it enabled the internal workings of that building to be adapted and changed. 

“If we’re going to invest carbon into steel, concrete, asphalt, or whatever materials we’re using, they all have a carbon impact. If we’re going to invest in that, let’s think about making sure we can advance and extend that life for as long as possible.”

Green lanes

While Tarmac’s parent company supplies a vast array of building materials, the division’s core focus is on road building. Just as with buildings and other structures, precise records of how a road has been constructed allow for more efficient use of carbon investments.

It also takes the development of new material components, and techniques. These includes Rap, or recycled asphalt planings; Sami, or stress absorbing membrane interfaces; and GGBS, or ground granulated blast furnace slag.

All of these are used by Tarmac to reduce the carbon costs of paving roads. They can improve roads’ long term performance, which reduces the need to spend carbon on travel to site and remedial works. And they can help make better use of materials recovered from roads at the end of their life.

Roads are built to tight standards, and any organisation that wants to depart from these standards will need to demonstrate to regulators that this will bring benefits, without negatively impacting the road’s performance.

Phil Greenin is Tarmac’s framework delivery manager for the south of England. He works alongside National Highways, and other suppliers, to support the delivery and maintenance of the road network, including the M25 London orbital motorway.

“Clients are now looking for whole life costs in relation to carbon,” he says. “[They want to know], how long the product is going to last, and how to reduce the number of interventions needed over the pavement’s design life,

“They’re also looking for product longevity. Does it work? Does it last longer? Does it heal itself? Can we use recycled aggregates? Can we use new sustainable products as opposed to traditional quarried minerals?”

To answer these questions, Tarmac has developed a Carbon Footprint Calculator that allows them to capture date on the impact of a vast range of different design changes and construction techniques 

“We’re able to automate that capture,” says Greenin. “In the initial stages in the development of the carbon calculator, we have been able to capture the carbon footprint of the material from its source in the quarry, via its journey by train to the asphalt plant, and then its onward journey, invariably in a lorry to site. We can capture our own carbon footprint, including the machinery and plant we use.

“[That allows us to work with clients] to analyse a design in the early stages. With early contractor involvement, we can adjust the design, to reduce the depth or volume of material, or the number of layers of material that are used. And then we can look back and understand how we have reduced the carbon footprint from the original design concept stage.”

This detailed capture of data allows Tarmac to not just demonstrate the benefits of small tweaks to an original design, but to make the case for much more substantial departures from standard.

“Highways England are much more willing to undertake trials of new and innovative practices, products and procedures,” says Greenin. The latest version of Highways England’s Design Manual for Roads and Bridges, or DMRB, has been developed to reduce the need for approval of departures from standard, cutting costs for the agency while giving roadbuilders space to innovate.

One innovation Tarmac helped pioneer was the use of warm mix asphalt. This allows for reduced energy consumption, compared to previous hot mix approaches. “It is now the rule, not the exception,” says Greenin, “And that has been possible because Tarmac has been able to document its benefits, and to demonstrate that these do not introduce new risks. [Agencies like Highways England] are looking for quality of data. They’re looking for regularity. They’re looking for us to demonstrate confidence in the data, for a chain-of-custody, and a responsible sourcing and development process. 

“The quality of the data is key.  We’re now able to feed data automatically into a cloud-based system, so that the management requirements of the asset we’re working on are there in a digital format for the years to come.”

Tarmac now routinely captures this data when a road is laid, and stores this in the cloud. Road scanning equipment can return later, and capture more detail on how the road has performed over time. “With the data that we’re collecting, we’re building a huge data bank, all around the asset. It will inform our lifecycle analysis and our budgets. It will inform our projected forecast of workflows, not over a 12 month period, or a two year period, but seven, twelve, twenty years into the future, because we know how the asset is performing.”

‘Big Data’ sets like this are now being used to train AI and machine learning systems. These will be able to make long term forecasts of a road’s performance and maintenance needs. By considering factors like the location and availability of materials that are ready for recycling, or of nearby virgin materials, extracted from quarries, road owners and suppliers can develop the most effective asset forward management plan. This has a major impact on clients’ capital and carbon costs

“We can now provide road owners with a 30 year suggested maintenance plan for their assets,” says Greenin, “And with a small tweak to a conventional approach, you can reduce interventions and save them maybe 20% over the lifecycle of the pavement.”

Links along the supply chain

The creation of big data sets like this is often seen as the preserve of big companies. And, as they engage directly with major clients and government authorities, it does often fall to them to compile, analyse, and present it.

But it also requires input from smaller suppliers. As larger companies move towards achieving Net Zero under Scope 3 of the Greenhouse Gas Protocols. This requires them to not just consider their own emissions, covered by Scope 1 of the protocols, or the impacts of generating the energy they use, in Scope 2.

Scope 3 requires companies to consider environmental impacts across their supply chain. At Tarmac, responsibility for assessing and managing these supplier impacts falls to Jonathan Harry, CRH’s procurement director for the UK and Ireland.

“Procurement for a long time was about smashing suppliers over the head to get a cheaper price. But if you keep changing suppliers and acting in a very tactical way, you’re not going to get value from your supply chain.”

Jonathan Harry, procurement director, CRH

“I’m very keen on maximising the value from our supply chain,” says Harry, “That’s not just in delivery, that is in sustainability, that is in making sure we pick the right partners from a health and safety point of view, from a relationship point of view. And from people who share our desire to drive towards Net Zero.”

It’s no longer good enough to just offer the cheapest way to pave a road, using standard procedures. Instead, organisations must show how it is possible to create new approaches whthatich reduce the long term carbon impacts of their products and services. The role of procurement experts like Harry has changed equally radically.

“Procurement for a long time was about smashing suppliers over the head to get a cheaper price,” says Harry. “But if you keep changing suppliers and acting in a very tactical way, you’re not going to get value from your supply chain. You’re going to get your product and you’re going to get your service, but you’re not going to get the value add, you’re not going to get the first mover advantage on new technology.”

Tarmac has worked closely with a range of suppliers to reduce its impacts. These include a new fully electric concrete mixer, supplied by Renault. By using this alongside rail transport, they can, on suitable sites, completely eliminate the need for diesel power. It took three years of close collaboration with the equipment manufacturer to bring this into use. In London, the company is also using the world’s first electric bond coat sprayer.

“These innovations take a lot of time and a lot of effort,” says Harry. :But they’re worth it because they drive change. If you’ve got that first mover advantage, then you can commercialise that advantage.

“The commercial guys talk about being a supplier of choice to our customers, I want us to be a customer choice to our suppliers. We’ve got 3,000 suppliers, and I want to make sure that the cream of those suppliers, we get the best technology and new ideas first.

“The e-mixer came out of our first Innovation Challenge. We set up a Tarmac Innovation Challenge, and went out not just to our suppliers, but to universities and to other companies. We had it open to anybody, and said ‘Who’s got any good ideas for our drive to net zero? The best ideas will go through and be shortlisted and the best ideas will win a prize and get promotion and be rolled out in the business.”

“And the e-mixer didn’t win. But it got shortlisted. And a couple of people were working really hard in the background, for the last two and a half years, to secure the first one in the UK.” 

Thinking big

Large companies can support smaller suppliers by committing to long term contracts. They can foster and promote new ideas with programmes like the Innovation Challenges. But the biggest impacts are often achieved by close collaboration with the biggest suppliers.

“We’ve also created the Tarmac Decarbonisation Club,” says Harry. “It’s a club of around 16 big suppliers, who we have committed to work with on a whole myriad of different ideas, driving towards net zero: the likes of Shell, Total, and Trafigura. We’re looking at ideas like biobitumens, as a way to decarbonize together.”

Projects like this are a vital part of a whole-of-supply-chain approach to sustainability. “We all have a responsibility to to be a good steward over the land that we’re managing, from the start of the quarrying process to how we restore and leave that piece of land at the end of its quarrying life, and what actual benefits we can bring after that as well,” says Hines. “It’s incredibly important to consider impacts like biodiversity net gain.  We need to understand the ecological and environmental systems [we operate in], and ask, ‘How can we operate to have a net gain on that and a positive impact in the future?”