Civil Engineering Reference
In-Depth Information
Figure 11.2
The mass balance model
The mass balance for the whole economy is represented by the flows:
A = B + C
Inputs
Use
Outputs
Raw materials
Products
Economic
System
Fossil fuels
Wastes
A
B
C
In the model, the environment is portrayed as having a similar relationship to
the economy as a mother to an unborn child in so far as it provides sustenance and
carries away wastes. An alternative perspective is to view the environment as a large
protective shell surrounding the economic system. Unfortunately, this shell is often
treated as a 'free' good and was for many years ignored by traditional economics.
The relevance of the mass balance model is referred to in the
Strategy for
Sustainable Construction
(HM Government 2008). This report noted that the
industry absorbs nearly a quarter of all raw materials used in the economy (an
estimated 420 megatonnes annually from a total of 1508 megatonnes). This makes
the construction industry the biggest user of materials in the UK, and its resource
efficiency is therefore central to the sustainability agenda.
Data derived from the first trials to audit resource flows in the construction
industry should clarify the significance of the mass balance theory. As stated, the
industry uses about 420 megatonnes of material each year, of which the additions to
stock (buildings, roads and other infrastructure) account for about 270 megatonnes.
This leaves a balance of 150 megatonnes of waste (nearly 3 tonnes of construction
waste per capita in the UK). It was estimated that approximately 46 megatonnes
of materials were recycled and, although this is clearly not an adequate amount, it
should be acknowledged that it is not possible to quantify resources that are reused
on site without processing, such as excavated soils or hardcore that may be 'reused'
as part of 'cut and fill' works on the same site (Smith et al. 2003; Forum for the
Future 2006).
Although the precision of the data is questionable, the magnitude of the figures
highlights the important role that the construction industry plays within the
economy and its potential environmental impact. Governments across Europe are
now beginning to account for resource flows; regular updates on material flows
through the economy can now be found in the UK environmental accounts, which
are updated annually. This data monitoring is part of a government drive to improve
resource productivity and it is clearly related to achieving sustainable development.
The data and concepts arising from the mass balance reports should encourage
businesses to think beyond traditional resource intensive methods of production.
Resource inefficiency reduces competitiveness, eats up primary resources, and
