Jobran Hammoud of Cyril Sweett examines the opportunities for, and costs associated with, increasing the use of recycled materials in construction
When people think about sustainable buildings, their first thought is often about energy efficiency and carbon emissions. However, making more efficient use of materials in construction is increasingly important for policy makers, clients, developers and contractors - for both economic and environmental reasons.
Site waste minimisation, recycling and the use of higher recycled content are practical and often cost saving or at least cost-neutral. In addition, they reduce demand for finite natural resources and the amount going to landfill.
Construction clients and developers are increasingly looking to set requirements for re-used and recycled content. They see it as a relatively simple, practical and cost-neutral way of making a difference. Demonstrating measurable improvements on a project can assist:
- Developers who are using sustainability as a differentiator when attracting corporate clients
- Contractors needing an edge when tendering
- Developers aiming to satisfy planning authorities' environmental demands
- Blue-chip companies wanting to demonstrate commitment to corporate responsibility
- Local authorities and schools keen to "walk the talk" of recycling.
This datafile considers the issue of the recycled content in construction projects, how it is measured and how it can be increased - with minimum effort, and without increasing risk or cost of materials. A case study project - the York Building, a British Land development currently under construction - analysed by Cyril Sweett provides a practical example of the application of these principles.
What is recycled content and how does it aid carbon efficiency?
Construction is one of the biggest users of materials in the economy, consuming about 420 million tonnes of materials each year. It also generates more than one-third of total UK waste materials. Yet only half of construction and demolition waste is currently recycled or reclaimed for use in the sector.
Case studies show that the overall recycled content in a project can be increased significantly with no increase in the cost of materials. This is achieved by simple substitution with alternative products where the manufacturer has used a higher fraction of recycled materials as inputs - for example, pulverised fuel ash and waste glass. Such products are readily available and satisfy the technical standards. These "quick wins" can be found in common product types such as bricks, blocks, boards, concrete products and flooring - using mainstream brands - as well as through the more traditional reprocessing of demolition waste.
Cost-neutral good practice has been estimated to deliver a tenfold increase in the tonnage of recovered materials potentially diverted from landfill on a housing or schools project. In the longer term, this "demand-pull" will make recycling of site waste more economic.
The government's Sustainable Buildings Task Group and the Scottish Executive have both proposed a benchmark requirement for resource efficiency in public procurement of major construction projects - at least 10% of the overall value of materials should derive from re-used and recycled content. A number of local authorities have already set this requirement in design briefs and tender specifications.
To enable the benchmark to be used with minimum effort, WRAP (Waste and Resources Action Programme - a government-funded organisation) has developed a range of tools and resources.
Assessing the recycled content of a complex building would be a time-consuming task if the quantity surveyor had to identify the recycled content for each of the specification items in the building and manually combine this with the existing cost and quantity data. However, WRAP has recently launched an online tool (available free of charge at www.wrap.org.uk/construction/rctoolkit) that enables rapid assessment. The tool allows the user to:
- Estimate the baseline and good practice levels of recycled content in their project
- Identify the top 10 quick-win opportunities to improve environmental performance by substituting cost-competitive products with a higher than standard recycled content
- Refine the analysis to reflect actual product choices and design details
- Quantify the projected recycled content and report how it will be achieved.
Construction clients, planners, policymakers and landowners are taking the lead in setting requirements for recycled content, although at least one leading contractor has proactively responded by committing to a higher performance standard as a way of differentiating itself. Typically, a clear statement is included in the tender invitation or the project or design brief, setting a minimum percentage figure for the whole building. Ideally this would included a further requirement on the designer or contractor to demonstrate the adoption of some elements of "good practice", such as the top 10 quick-win opportunities. WRAP provides guidance to assist the procurement process.
How recycled content is measured
Recycled content by value is a function of the material value of a component, the quantity used and the percentage of the component by mass that is derived from recycled content. Thus, if brickwork costs £20/m2 (excluding labour cost) and has 20% recycled content by mass, the recycled content by value of 100 m2 would be:
£20/m2 × 100 m2 × 20% = £400
By summing the recycled content by value of all the components in a building and dividing this by the total material value of all the components in the building, it is possible to estimate the total percentage of recycled content by value of the building.
What is recycled content?
Recycled content is the proportion by mass of recycled material in a product. Materials include post-consumer wastes such as recovered glass, secondary materials such as china clay and slate waste, and manufacturing waste such as plastic offcuts. This excludes rework and scrap re-used within the same manufacturing process that generated it. A formal definition is given in ISO 14021.
Levels of recycled content
- Standard practice is defined as what is most commonly available, such as the most likely material to be used if no request is made for recycled content.
- Good practice is defined as a level of recycled content which is better than standard and readily available with little or no additional effort at competitive cost.
- Best available is defined as the highest recycled content currently available on the UK market.
Case study: Assessing recycled content at the York Building
Summary of the building
The York Building is a £40m mixed-use scheme in central London. Construction began in summer 2005 and is due for completion by the end of 2006. It comprises six floors of commercial space and seven floors of residential apartments, including a ground floor retail space. In addition, there is a basement floor that houses a casino, and parking space for 30 cars.
Baseline recycled content of the building
An assessment of recycled content in the materials specified for the building gives a baseline recycled content level of 20.84%, the structural elements being the largest contributor to this result.
The figure below shows those elements in the York Building specification that have the highest recycled content by value. Many of these elements have the potential to achieve a higher percentage of recycled content through substitution of products that have above-standard recycled content.
Potential for increasing recycled content
Cyril Sweett estimated the recycled content levels for the building at standard, good and best practice levels. The actual specifications used in the York Building achieved a result that was slightly higher than the outcome if all products had been used solely with standard practice recycled content.
The recycled content in the building could have been increased through various product substitutions, with a further 3.6% recycled content potentially achievable without incurring a cost premium. The figure on the right shows those building components that have the greatest potential to increase the overall recycled content of a building by the use of cost-neutral products meeting a good-practice specification.
Increasing recycled content in various building elements
Recycled content in structural concrete elements can be enhanced through the use of recycled concrete aggregates (RCA) or cement replacement. Many contractors hesitate to use RCA for concrete above C20 or C30 strength because of limited supply and concerns regarding the consistency and reliability of the feedstock. However, cement replacements such as PFA and ground granulated blast furnace slag are commonly used in the UK. It is technically and commercially feasible to use PFA and GGBS up to 40% and 70% respectively, although this may impact the strengthening speed of the concrete. However, high usage of cement replacements is common in substructures because of the significant durability benefits these materials confer.
The York Building already incorporates a certain level of cement replacement which can be increased when pouring and strengthening conditions allow.
The opportunities to increase recycled content in the shell elements of the York Building are more constrained. This is because large parts of the cladding and roofing systems are made from either metal or pre-cast concrete and there is little opportunity to obtain higher levels of recycled content in the current market. The only product substitution that would significantly impact the building's recycled content is the pre-cast concrete paviors on the roof. Paviors can be obtained with 70% recycled content, while standard products for this specification might have no recycled content.
The overall increase that can be achieved in the shell elements contributes an extra 0.65% towards the building total.
Increases in the recycled content in internal finishing elements can be achieved through product substitution and alternative specifications. Different specifications are available for suspended ceilings and raised flooring, while higher recycled content products can be found for floor carpets and plasterboard. While slight changes in performance and cost may be encountered for high recycled content suspended ceilings and raised flooring (due to a change of material), floor carpets and plasterboard with higher recycled content should have the same performance and cost.
Increasing recycled content in various building elements
The recycled content of the whole building can be increased by up to 4.35% using products and specifications with higher recycled content. This can be achieved at a negligible additional cost with the least impact on building performance. An additional 0.45% can be achieved by using a high percentage of cement replacements although this might lead to delays in the concrete strengthening time for the building frame.
Setting a requirement for recycled content
The figure right summarises the key steps involved in setting and delivering a requirement for recycled content, depicting mainly the traditional procurement route. There will be some slight differences in responsibilities and timing when using different procurement routes, but the core steps should be the same for most projects. The process is simple:
1. The client sets a requirement for the overall project outcome (alongside other quantitative indicators such as energy efficiency)
2. Designers and contractors quantify what can be achieved and identify the available good practice options
3. The project team focuses on implementing the top 10 quick wins
4. The client benefits through being able to report the improvement on baseline practice.
With developers such as British Land showing an increasing interest, and cost and policy pressures driving contractors to use materials more efficiently, this is a topic area of growing importance.
WRAP's online tool for assessing recycled content
This tool has been developed by Faithful and Gould, Cyril Sweett and Solstice Associates. It is based on reference values for recycled content and materials costs for around 500 standard specifications and includes data from BRE, AMA Research and Davis Langdon. It is available to use free of charge at www.wrap.org.uk/construction/RCtoolkit and project teams influencing substantial construction budgets may be eligible for free training to enable them to take full advantage of the toolkit's capabilities. Interest in training can be registered by e-mailing firstname.lastname@example.org.
Other WRAP resources include:
- Procurement guidance Practical guidance on the procurement process, including model clauses to incorporate in project briefs, tender documentation and so on.
- Case studies These show what levels of recycled content are readily achievable, at no extra cost across various types of construction including education, housing, offices and refurbishment.
- Product information Information on the recycled content of mainstream products commonly used in construction.
- Good practice guides Advice on site waste management, demolition and recovery of waste materials, and guidance on Quick Wins in using higher recycled content.
All of WRAP's information, guidance, publications and tools are available free of charge via www.wrap.org.uk/construction.
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