Sustainable aggregates

[edit] Introduction

UK quarries and marine dredging sites produce approximately £3billion worth of products per annum and employ around 40,000 people. Quarried products represent the cornerstone of our economy. With each person using approximately 4 tonnes of aggregate per annum, that’s around 200 million tonnes. These products are used to create vital infrastructure, homes and services, yet aggregates have a relatively low value. Their low value combined with their high bulk means that, unlike other valuable minerals, they are not traded globally.

This interesting juxtaposition of high worth but low intrinsic value, combined with the ever-increasing pressures on land use, raises issues around what a sustainable aggregate industry looks like for the UK. It’s a bit surprising to note that more than 40% of our permitted land-won aggregate reserves are in areas with an environmental designation, whether National Park, Site of Special Scientific Interest or Green Belt.

Research by --KLH Sustainability has uncovered a number of interesting facts.

[edit] The recycled and secondary aggregate market

BREEAM is still the assessment methodology of choice for clients who wish to demonstrate their sustainability credentials. However, BREEAM currently only awards credits for secondary and recycled aggregate use.

Over 80% of recycled and secondary aggregates, approximately 42 million tonnes, is produced from recycling construction and demolition waste (C&D waste). Although data on recycled aggregates is considered variable and inconsistent, national surveys state that most of the evidence indicates that C&D waste is actually being recycled into aggregate rather than landfilled as waste.

But what about secondary aggregates? The annual production of secondary aggregates in England is approximately 13 million tonnes. The China Clay industry in Cornwall represents 8.3 million tonnes of this production, of which 1.2 million tonnes is currently used, mainly in the construction industry. The next most significant sources of secondary material for use as aggregates are colliery spoil and pulverised fuel ash (PFA) in the Humber area at 1.97 million tonnes and 1.07 million tonnes respectively, of which a total of 1.31 million tonnes is used in the construction and other industries. The remaining 2 million tonnes of secondary aggregate produced annually in England is widely distributed and of a marginal scale.

These numbers are relatively small compared to demand. The economic viability of the aggregates industry, and indeed the environmental sustainability of the industry is a function of the distance to market. Recycled aggregates have an advantage over secondary aggregates as they are often produced in locations with a future requirement for extensive aggregate use such as redevelopment and regeneration areas. The distance to market from the secondary aggregate reserves in Cornwall is likely to be a limiting factor to the sustainable use of these materials in the industry.

[edit] Pushing recycled and secondary materials up the value chain

It seems there is little opportunity for BREEAM to drive increased diversion of C&D waste from landfill as the market already operates at near capacity. But perhaps there is a sustainable benefit in pushing recycled materials up the value chain as BREEAM aims to?

Analysis of the Collation of Results of the Aggregate Minerals Survey for England and Wales and the Mineral Extraction in Great Britain demonstrates that significant quantities of primary materials continue to be used as construction fill and other graded construction uses.

These types of uses generally have fewer technical constraints and are a prime market for recycled aggregates. These lower value end uses also provide a valuable demand for ‘waste’ by-products generated at crushed rock sites whose production profile is driven by demand for concreting and asphalt products. In 2005, the UK quarrying industry produced more than 55 million tonnes of quarry ‘fines’ and 24 million tonnes of ‘quarry waste’ in addition to 216 million tonnes of saleable aggregate, however these quarried by-products still attract the Aggregates Levy and are therefore not defined as a waste product under legislation or within BREEAM.

In theory, both waste products from crushed rock quarries or recycled products could be further processed to drive them up the value chain.

Either option has the potential to reduce unused stockpiles of overburden, scalpings and crushed rock waste and put them to good use:

• If recycled aggregates undergo additional processing to move them up the value chain the quarried by-products will likely replace them in the lower value chain uses such as sub-base and engineered fills.
• Additional processing of these quarried by-products could push them further up the value chain.

As BREEAM does not quantify these quarried waste products as secondary material, the criteria for BREEAM is biased towards recycling industry investment in additional processing to push recycled materials up the value chain, ignoring the opportunity to process quarried by-products for low value fill. Favouring additional processing for recycled aggregates without considering other options is likely to require significant quantities of water and energy. There is no clear evidence base as to why recycled materials specifically should be pushed up the value chain when a demand is then created for low value materials; one that is too often met by primary aggregates, rather than quarried by-products.

[edit] An alternative approach

KLH Sustainability are developing an alternative approach to the assessment of sustainable sourcing and use of aggregates that responds to the limitations identified within existing methodologies (having looked extensively at the ability of Environmental Product Declarations to help differentiate between sources of aggregates, too).

The assessment methodology is based on key impact factors that have been identified through analysis of existing data and research and include:

• Local availability of aggregates defined by regional Abiotic Depletion Potential.
• Social impact of transportation defined by the Department for Transport freight modal shift methodology.
• Carbon footprint. The focus here is not in establishing an absolute carbon footprint for aggregate sources and respective end uses but to understand the key differentials that should influence decision making.

Economics are not directly included in the analysis as market complexities prevent a robust analysis of the economic viability of using specific aggregates in given products and regions. This is not considered to be a significant limitation of the proposed methodology as the sustainability assessment criteria selected indirectly considers cost in the form of carbon, transportation and abiotic depletion potential.

KLH Sustainability provide more detail in the definition and calculation of regional Abiotic Depletion Potential in Material Flow Analysis: A tool for sustainable aggregate sourcing.

See aggregate for more information.

[edit] Related articles on Designing Buildings Wiki

• Aggregate.
• Alluvium.
• Ballast.
• Building on fill.
• Chert.
• Coal ash.
• Construction materials.
• Cut and fill.
• Gravel v hardcore v aggregates.
• Gravel.
• Hardcore.
• Measuring stockpiles using image-based 3D reconstruction.
• Sand.
• Trench fill foundations.
• Types of soil.