A life cycle inventory (LCI) is a compilation of the energy and material inputs and the emissions to air, land and water associated with the manufacture of a product, operation of a process, or provision of a service. An LCI is the second step—after goal and scope definition—of a life cycle assessment (LCA). During the assessment phase, the social, economic and environmental aspects are evaluated. The results can be used to choose among competing alternatives the one that has the most favorable attributes. For example, LCA has been used to show that insulating concrete form (ICF) homes have fewer negative impacts than identically sized wood-framed homes.
CTLGroup and Portland Cement Association (PCA) produced a report in 2000, updated in 2002, 2006 and 2007, that presents the results of the LCI of three concrete products: ready mixed concrete, concrete masonry and precast concrete. The newer data reflects improvements in energy efficiency and better environmental controls.
The CTLGroup research team produced results using an average of inputs and emissions associated with one unit volume of concrete produced in the U.S. and, in the case of concrete masonry, 100 CMUs. The system boundary, which defines the scope of the LCI, includes cement and slag cement manufacture; aggregate production; transportation of fuel, cement, supplementary cementitious materials and aggregates to the concrete plant; and concrete plant operations (including truck mixer wash-out in the case of ready mixed concrete).
The team discovered that, due to increases in energy efficiency, newer plants replacing older ones and more accurate data (particularly for concrete plants and aggregate production), the latest LCI results are lower for most of the flows reported in previous editions of the report. For example, for a typical 20-MPa (3,000-psi) concrete mix, embodied energy is 30% lower and CO2 emissions are about 7% lower. For concrete masonry, embodied energy is about 20% lower and CO2 emissions are about the same. For 50-MPa (7,500-psi) precast concrete, embodied energy and CO2 are unchanged because the LCI now includes energy and emissions at the precast concrete plant.
The team gathered data on inputs and emissions from concrete production from industry surveys, emission factors and information provided by relevant industry associations. The data referring to aggregate production and the operations of concrete plants come from published reports and other sources provided by concrete industry associations. The LCI data and results were peer reviewed by the PCA membership and its relevant allied groups.