The influence of seismic attack and chloride-induced corrosion on a life cycle inventory assessment of different concrete mixtures Public Deposited

http://ir.library.oregonstate.edu/concern/graduate_thesis_or_dissertations/8k71nm63k

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  • The life cycle assessment (LCA) process is a systematic approach to determining the environmental impacts of different products and processes. LCA is a relative approach that requires functional equivalence for the results to be compared. A method is presented that achieves functional equivalence by equating the reliability indexes being compared. An example of the method is completed on a hypothetical bridge located in Astoria, OR. The bridge is modeled for three possible construction materials: concrete with ordinary portland cement, concrete with recycled concrete aggregate and concrete with high volume fly ash. These three materials have different mechanical properties that affect the seismic resilience of the bridge as well as the degradation of the structure over time. The reliability index for a bridge made out of each material is determined by modeling the occurrence of a Cascadia Subduction Zone earthquake, and accounting for the deterioration of the bridge due to chloride ingress. Accurate data on the modeling parameters of recycled concrete aggregate and high volume fly ash are not well documented, so an incremental approach is taken. The recycled concrete aggregate is modeled with increasing coefficients of variation for compressive strength, and the high volume fly ash is modeled with increasing resistance to chloride ingress. Compressive strengths required to achieve the same reliability index as the ordinary portland cement model are calculated using structural reliability methods. Simplified mixture designs are presented for each material and a life cycle inventory assessment is completed. The life cycle inventory assessment data, based on carbon emissions, energy and virgin aggregate usage, are then compared. The objective of this project is to determine the importance of achieving functional equivalence for an LCA, and to present a simplified method for how this can be done. For this reason the life cycle inventory assessment data are compared to a mixture design that does not achieve functional equivalence. The method shows a decrease in the reliability of a recycled concrete aggregate mixture design, which requires an increase in the compressive strength to achieve functional equivalence. An increase in compressive strength produces more carbon emissions, uses more energy and uses less virgin aggregate. The high volume fly ash mixture design requires a decrease in the compressive strength which reduces the amount of carbon emissions and energy use and increases the amount of virgin aggregate required. The fluctuations in the carbon emissions and energy usage show the importance of considering functional equivalence properly in an LCA. Areas in which improvement can be made are identified and discussed.
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