Material Flow Analysis: A tool for sustainable aggregate sourcing
In a previous article, ‘Sustainable aggregates’ KLH Sustainability highlighted the need for a broader assessment for aggregate selection beyond “recycled/secondary equals good and primary equals bad.”
It was suggested that an assessment methodology could be based around three criteria:
- Local availability of aggregates – defined by regional abiotic depletion potential.
- Social impact of transportation – adapted from the Department for Transport’s freight modal shift methodology.
- Carbon footprint.
 What is abiotic depletion potential?
Environmental product declarations, as defined by BS EN 15804, measure abiotic depletion potential (ADP). ADP is a function of the natural reserves of a resource combined with their rates of extraction. ADP generally includes both the direct resource depletion and the resource depletion associated with the fossil fuel consumption in extraction, processing and transportation of the resource.
BS EN 15804 defines abiotic depletion potential of non-fossil resources as:
[extraction rate of resource (kg/year) / (ultimate reserve (kg))^2] / [extraction rate of antimony resource (kg/year) / (ultimate antimony reserve (kg))^2]
However the standard also recognises that “the depletion of abiotic resources is subject to further scientific development. The use of this indicator is intended to be reviewed during the revision of this standard”.
When applied to aggregates there are two fundamental issues with this definition of non-fossil ADP.
The definition of ADP utilises antimony, of which China is the largest producer, as a reference resource and therefore measures the availability of a given resource on a global scale. Using this definition of ADP, sand, gravel and rock may be considered infinite, and indeed the global ultimate reserve of aggregates is more or less infinite. However, given the relatively low value and high bulk of aggregates, geographic proximity is paramount to economic utilisation. As sands and gravels are not transported over a long distance, it seems more important to have a territory-based approach to evaluate the availability of aggregate resources.
The estimate of the reserve of aggregate resources is also problematic. The ultimate reserve has historically been defined as the quantity of resource that is ultimately available. It is estimated by multiplying the average natural concentration of the resource in the primary extraction media (e.g. the earth’s crust) by the mass or volume of these media (e.g. the mass of the crust assuming a certain depth of for example 10 km). There are, of course, a range of complex economic, social and environmental factors that dictate whether a given reserve is exploited or not.
 What is the alternative?
KLH Sustainability have been exploring the concept of material flow analysis (MFA). MFA is an analytical method of quantifying flows and stocks of material or substances in a well-defined system. It is an important tool in assessing the physical consequences of human activities and needs, and aids the sustainable management of material flows.
The methodology used provides an estimate of the time to exhaustion and the reserve in a given region by analysing the historic social metabolism of the area (the manner in which human societies organise their growing exchanges of energy and materials with the environment). Using this reserve estimate and the trend in domestic mineral consumption, along with an understanding of the available capacity of the local recycled and secondary markets, we are able to calculate a figure for the regional ADP.
It is then possible to provide an estimate of the regional reserves and time to exhaustion of quarried stone, land based sand and gravels and marine minerals.
The 2013 Aggregates Mineral Surveys data will provide a further data point for analysis which will allow trends to be observed from 16 years of historic data.
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