Courtesy : designingbuildings.co.uk

Sustainable materials for construction

Introduction

Constructing with sustainable materials is not only good for the planet and common sense, it can save the client money, help preserve our heritage, respond to planning policies and help get credits in BREEAM, GGBC and other environmental assessment tools.

A sustainable material is one that:

• Does not deplete non-renewable (natural) resources.
• Has no adverse impact on the environment when used.

In practice, both these objectives are impossible to achieve, but they do show us the direction we should aim.

We can preserve natural resources in many ways:

• Avoiding using scarce (non-renewable) materials, such as peat and weathered limestone.
• Creating less waste.
• Using less; by not over-specifying performance requirements, by designing minimum weight structures and by matching demand to supply (such as supply balancing cut & fill).
• Using reclaimed, rather than new materials.
• Using renewable materials (crops).

We can reduce the impact on the environmental of using construction materials by:

• Using materials with low(er) embodied energy.
• Reducing transport of materials and associated fuel, emissions and road congestion.
• Preventing waste going to landfill.
• Designing and constructing for ease of reuse and recycling at end-of-life (design for deconstruction).

Tools and techniques

There are now many tools and techniques for selecting construction materials that are less damaging to the environment. Detailed analysis of the impacts of materials using these techniques can then be reduced to relatively straightforward guidance for the designer or specifier, for example:

• ‘Environmental preference’ methods that use star-ratings to substitute ‘normal’ materials and components with more ‘environmental‘ alternatives.
• Methods that calculate a single numerical score, such as an EcoPoint, for the impact of each material (per kilogram) and aggregates these according to the quantities in different types of construction for a given building. This approach underpins the Green Guide to Specification developed by the UK Building Research Establishment.
• Methods that use embodied energy or carbon dioxide emissions as the single measure of impact, which are then processed using ‘carbon accounting‘.

Another approach is to tackle the use of materials by adopting a strategic and hierarchical approach to decisions – beginning with the ‘best’ from an environmental point of view, then the next best, and so on.

For example:

1. Choose materials and construction techniques that progress from:

• A linear approach to using materials: extract, process, manufacture, use, demolish, throw away.

towards

• ‘Closed-loop’ thinking or a ‘zero-waste‘ society: extract, process, manufacture, use, reuse (as many times as possible), dismantle or disassemble, recycle (as many times as possible), then finally, only when no further use remains, throw away.

2. Re-use materials or components in situ:

• Reuse a whole building, upgrading it as necessary.
• Reuse part of a building such the structural frame, masonry façade or foundations.
• Build upon the existing ground floor slab of a previous building.
• Reuse an existing retaining wall or embankment.

3 Use reclaimed materials or components with little processing:

• Steel beams and columns from a dismantled building.
• Demolition arisings (such as crushed aggregate) can be used for landscaping or backfilling excavations.
• Crushed glass can be used as a bedding material for paved or block surfaces.
• Reclaimed paving stones or slabs.
• Railway sleepers or telegraph poles.
• Steel tube from the oil industry can be used as piles.
• Recycled black-top.

4. Use manufactured materials or components with significant and known recycled content:

• The Recycled Content (RC) of entire construction works can easily be more than 20% (this was achieved at the London Olympics site) and this can gain GGBC or BREEAM credits.
• Concrete made with Recycled Crushed Aggregate (RCA – typically up to 40%, depending on the source). For example using demolition arisings or ‘waste‘ from quarries.
• Concrete using cement replacement materials such as Pulverised Fuel Ash (PFA) or Ground Granulated Blast-furnace Slag (GGBS – 5-15% RC).
• ‘Recycled Roads‘.
• Precast concrete blocks, paviours, kerbs, etc, made using RCA (more than 60% RC).
• Concrete pipes, drains, etc. made using RCA (more than 60% RC).
• Plastic street furniture (bollards, barriers etc.) made from 100% RC plastic.
• Decking, furniture etc made from 100% RC ‘plastic lumber’ that looks like timber.
• Plastic drain or soil pipes made using recycled plastic (50-100% RC).
• Cast iron drain pipes made using recycled cast iron (up to 96% RC).
• Tarmac with crushed glass fill, up to 30% RC.
• Geo-textiles made from 100% RC plastic.
• Any ‘forest product‘ using ‘waste‘ timber, such as chipboard, blockboard and some glulams.

5. Use natural materials that have low embodied energy and / or environmental impact:

• Timber (in preference to steel).
• Concrete reinforced with timber, bamboo or natural fibres.
• Geo-textiles and other products made from crops.
• Straw bales.
• Materials that are accredited as being responsibly sourced (such as FSC timber).

Project management issues

As often with sustainable construction, there are few technical barriers to these many alternatives, but there are other challenges, for example:

• Persuading the client.
• Guaranteeing material quality and performance.
• Ensuring the supply of goods and materials.
• Educating the project team.
• Identifying economic paybacks.
• Measuring benefits and success.