116 Section 2 Construction Materials
Round edge to
prevent splinters
1 × 2 or 2 × 2,
Length at least
equal to depth
of form
Figure 6-13. A puddling stick is made from lumber. Figure 6-14. This hand tamping device is called a
jitterbug. (Marshalltown Company)
Life-Cycle Assessment
A life-cycle assessment is a tool used to determine the environmental impact associated
with each stage in the life cycle of a process or product. The life cycle includes all stages, from
raw materials to disposal or recycling. The results of the assessment are interpreted and used
by designers, contractors, and consumers to choose products that have minimal impact on the
environment.
To get a better idea of what is involved in life-cycle assessment, consider what stages
would need to be evaluated to assess the impact of producing just one ingredient of concrete,
Portland cement. Limestone and other forms of rock or shale are major raw materials from
which Portland cement is produced. Large earthmoving machines, explosives, and trucks are
required to extract these raw materials from the earth and move them to the cement plant. The
rock is crushed before being mixed with other raw materials and fed into a huge rotating kiln.
Inside the kiln, the raw materials are heated to burn off unwanted ingredients and form a new
material called clinker. Once cooled, the clinker is ground into Portland cement.
A complete life-cycle assessment would consider everything involved in each step of the
process to produce Portland cement. For example, what impact does making, operating, and
recycling each of the machines used to quarry limestone have on the environment? Are the
gases given off by the kiln damaging the environment? What other questions do you think
should be included in a life-cycle assessment for Portland cement?
Other limited forms of life-cycle assessment also being used include the following:
•
Cradle-to-cradle assessments are done for products that are recycled into the original form.
•
Well-to-wheel assessments are done for fuel for vehicles.
•
Life-cycle energy analysis considers all the energy inputs required to produce, use, and
dispose of or recycle a product. The by-products that result from making and using the
energy are also included.
Green Construction