Civil Engineering Reference
In-Depth Information
a level that does not significantly affect the basic properties of cement and,
consequently, the concrete.
LCa of cement with supplementary cementitious materials that are by-
products or waste from another industrial process (such as BFS or Fa) is
always connected to allocation procedures. To be used as a substitution for
cement clinker, these by-products must be additionally processed (so-called
secondary process) and this has an impact on the environment, too. The
following question is then raised: should the environmental impacts of the
primary production process (production of the main product) be associated
with the production of the by-product, and how? if BFS and Fa are considered
as waste, no environmental impacts from the primary production process are
allocated to the secondary process. if they are considered as by-products,
then part of the environmental impacts from primary production process are
allocated to the secondary process and it can be done using two different
allocation procedures. according to the mass allocation procedure, the part
of the primary production impacts allocated to by-product production is
determined from the ratio of the mass of the by-product and the total mass
of the main and by-product.
according to the economic allocation procedure, the part of the primary
production impacts allocated to by-product production is determined from
the ratio of the price of the by-product and the sum of the prices of the
main product and by-product. The choice of the allocation procedure is very
important because it significantly affects the environmental impacts of the
by-product. Chen et al. (2010) have shown that a mass allocation procedure
imposes large environmental impacts on BFS and Fa that can jeopardize the
decision to apply these by-products as substitutes for cement clinker. However,
the economic allocation procedure, which imposes smaller environmental
impacts on BFS and Fa, has the disadvantage of being unstable because of
the potential price fluctuations on the market. They have concluded that no
allocation procedure appears to be unquestionable.
3.5 Life cycle assessment (LCA) of concrete: life
cycle impact assessment (LCIA)
3.5.1 Methodology
Choice of impact category and category indicator
Generally, there are two different types of impact assessment methods. The
first one is called the damage-oriented approach (also the top-down approach
or 'endpoints') and the second one is called the problem-oriented approach
(also the bottom-up approach or 'midpoints').
When defining the impact category, the category indicator must be chosen
somewhere in the environmental mechanism. The task of LCia is to establish
