Civil Engineering Reference
In-Depth Information
material, the functional unit can include the quantity (m
3
), the mechanical
properties (in appropriate units) and durability related properties (in years).
For a building, the functional unit can include the size (m
2
), the lifetime
(years), the need for maintenance or the materials used. The results of the
study will directly relate to the chosen functional unit. For example, if the
functional unit is one cubic meter of concrete of certain quality, the result
will be the amount of resources, waste and emitted pollutants per each cubic
meter of such a concrete.
The system boundaries determine what part of the life cycle will be
considered. The complete life cycle of the concrete structure is shown in Fig.
3.3. it includes the production of raw materials, the production of concrete,
construction and service phase, demolition or dismantling, and disposal or
recycling of waste materials.
Generally, there are two possible different situations when assessing the
environmental burdens of the concrete. The first is the assessment of the
environmental impact of the concrete as a building material or a specific
structural element (for example, a precast bridge girder), i.e. the assessment
of the production phase only. This is a cradle-to-gate type of analysis (Fig.
3.3) and the result of the study is called environmental product declaration
(EPD). The second is the assessment of the environmental impact of the
concrete structure or structural element as a part of a building, bridge, road
or some other kind of the construction work. This is a cradle-to-grave type of
analysis (Fig. 3.3). The type of assessment and system boundaries are chosen
depending on the goal of an LCa study: whether the goal of the study is
to evaluate the environmental impact of the concrete as a building material
(cradle-to-gate) or the goal of the study is to evaluate the environmental
impact of the building, bridge, road, etc., as a whole (cradle-to-grave).
among various environmental impacts, for a specific product or process,
some impacts are more and some impacts are less important. at this point,
the relevant impact for concrete should be determined, which is discussed in
detail in Section 3.5. Then, the necessary data for calculation of the chosen
environmental impacts must be collected. This is done within the next step
of LCa - life cycle inventory phase.
3.4 Life cycle assessment (LCA) of concrete - life
cycle inventory (LCI)
Based on the decisions made in the goal and scope phase, the process tree is
drawn, as shown in Fig. 3.3. Each of the different phases in the life cycle of
concrete is made up from different unit processes. For example, the cement
production within the raw or constituent material production phase consists
of many unit processes (Fig. 3.4).
To calculate the environmental impacts, energy and materials flows as
