OTHER RECYCLED MATERIALS
CEMENT MANUFACTURE
The major environmental impact caused in the manufacturing of concrete blocks derives from the use of cement. The manufacture of cement is responsible for between 5 – 7% (depending on source) of the world’s carbon dioxide emissions. 40% of the total cement emissions are due to the use of fossil fuels (usually coal) to heat the cement kilns to 1500°C and the remaining 60% is from the transformation of limestone at high temperatures (‘de carbonation’).
RAMMED EARTH
• Rammed earth walls (aka pise) are constructed by the compacting (ramming) of moistened subsoil into place between temporary form work panels. When dried, the result is a dense, hard monolithic wall. • Rammed earth is an ancient form of construction, usually associated with arid areas. There remain plentiful examples of the form around the world – evidence that rammed earth is a successful and durable way of building. A few historical rammed earth buildings are to be found in the UK. • The likely future for the application of rammed earth is as: - Thermal mass. - Internal load-bearing unstabilised walls. - External load-bearing stabilised walls. • Because of rammed earth’s poor thermal performance, extra insulation will be required. • Rammed earth is hygroscopic. Wherever walls are clad externally, cladding systems and finishes must be vapourpermeable to allow evaporation. This is important for unstabilised walls, but less-so for stabilised walls where the stabilising agent will impair breathing. Non-the-less, it might be wise to consider vapour permeable solutions for both instances to reduce the chance of condensation build-up on the inside face of insulation.
CONCRETE Reduction in amount of energy use in manufacture
The UK cement industry has reduced the energy used to make Portland cement by almost 25%. In turn, CO2 emissions have been lowered by over three million tonnes, much of which is due to a significant investment in energy efficient technologies, along with the use of alternative fuels and the incorporation of materials such as slag, ash and limestone.
Reduction In Cement
Cement combinations incorporating limestone, fly ash or ground granulated blast-furnace slag can be specified and, in some exposure conditions, may be more appropriate. Embodied impacts are also reduced, for example, cements incorporating 50% slag will reduce the embodied CO2 of concrete by some 40%.
Recycled Reinforcement
UK reinforcement utilises 100% recycled scrap steel sourced from the UK as feedstock. At the end of its life, all reinforcing steel can be recovered, recycled and used again.
Recycled Aggregate
Aggregates, including sand, gravel and crushed rock account for approximately 80% of a typical concrete mix. Here the concrete industry is actively pursuing a policy of recycling concrete in order to reduce the use of these natural resources. Concrete is 100% recyclable and concrete from a demolished building or infrastructure can be crushed and recycled as aggregate for new construction.
High thermal mass
The excellent thermal capacity or thermal mass of concrete enables it to absorb, store and later radiate heat, stabilising the internal temperature of a building. In all buildings, heat is generated by people, electrical equipment, computers, lighting and solar gain which means that buildings can overheat during the summer. Exposed concrete absorbs much of this heat, and can reduce daytime temperatures by up to 4°C or 5°C.
Inherent sustainable benefits
A further sustainable benefit of concrete is its inherent fire resistance and long-term performance. It requires no additional fire protective coverings, chemical preservatives or paint systems that may release Volatile Organic Compounds (VOCs), effecting internal air quality, and which can require ongoing maintenance.
8