Aggregate carbon demand : the hunt for low-carbon aggregate

Abstract

Construction projects are increasingly concerned with environmental sustainability. Schemes such as the BREEAM Green Guide include ‘mineral resource extraction’ as part of their environmental impact rating of construction materials, such as aggregate. One means of assessing environmental impact is to determine the 'embodied energy' used (or 'embodied CO2' emitted) to produce aggregate; this is equivalent to the 'carbon footprint' of an operation. This ‘energy audit’ takes into account everything from extraction and processing through to offices and workshops and waste and water management. The Mineral Products Association publishes embodied CO2 (as kilograms per tonne, kg/t) figures for aggregate, crushed rock, sand and gravel, ready mixed concrete, asphalt and cement. The leading aggregate producers report embodied energy (as kilowatt hours per tonne, kWh/t) or embodied CO2, or even both. Research at the British Geological Survey has been carried out to quantify the likely embodied energy of aggregate resources without the use of an energy audit. A modified work index (‘crushability’) test device has been used to determine the embodied energy of aggregate resources. The initial research has focused on Carboniferous limestone as worked in central and northern England. The ultimate aim is to provide baseline information on the likely ‘carbon demand’ of as yet unworked aggregate resources. This could be presented as spatial data complementary to existing, digital, mineral resource maps. These data will assist in future spatial planning for crushed rock resources and bring a fresh perspective to Mineral Policy Statement 1 which requires that the environmental benefits and constraints of working mineral resources are considered