Integrated Life Cycle Environmental Impact Assessment Of Fly Ash Concrete

Concrete is the most widely used construction material around the world. However, in the process of concrete manufacturing, there are serious problems of resource and energy consumption and environment pollution, especially in the process of cement production, a main constituent of concrete. Every ton of cement manufactured for use in concrete emits a ton of the greenhouse gas (GHG) into the atmosphere. Fly ash is the most widely used supplementary cementious material. If part of cement is replaced with fly ash in concrete mix, the cement and clinker content can be reduced resulting in a decreasing environmental impact and a changed mechanical performance and durability of concrete. Most of the existing researches focused on solely investigating the environmental impact of fly ash concrete, or comprehensively considering the relationship between environmental impact and mechanical performance or durability only for one stage. The relevant research on the comprehensively investigation of environmental impact, mechanical performance and durability of fly ash concrete from a perspective of life cycle is deficient. In this paper, from the view of the life cycle of fly ash concrete, i.e. production stage, use stage and final disposal stage, we analyzed energy consumption and GHG emissions quantitatively, by investigating the effects of mechanical performance and durability on the energy consumption and GHG emissions as well. In addition, in consideration of the measuring units of energy consumption and GHG emissions, an indicator named environmental cost was presented to measure the environmental impact by a monetization method, which providing a new way for sustainability assessment of fly ash concrete. The following works are mainly conducted:(1) By considering the influence of fly ash content on the strength and strength development of concrete, two indicators combining environmental impact with compressive strength (energy consumption per strength and carbon emissions per strength) were proposed to assess the integrated performance of fly ash concrete during its production stage. In addition, a monetization method was adopted to measure the environmental impact, and the fitted relation was established among fly ash content, compressive strength and environmental cost of fly ash concrete.(2) Based on the existing indicator of binder intensity, a new indicator named carbon intensity was put forward. By using the method of literature investigation, a large number of experimental data was obtained and the relationship between binder intensity, carbon intensity and compressive strength was analyzed for estimating the carbon emissions of fly ash concrete, respectively. Besides, for the discreteness of compressive strength of fly ash concrete, the strength reliability was used as function unit to analyze the carbon emissions of concrete with different fly ash content.(3) Service life prediction was conducted by using Monte Carlo simulation to analyze the service life of fly ash concrete. According to the life prediction results of fly ash concrete, an integrated indicator combining compressive strength, durability and environmental impact was presented. In addition, a comparative analysis of the assessment results with different indicators was conducted.(4) Two maintenance strategies were presented to consider the influence of maintenance effect and maintenance times on the environmental impact. In addition, a time dependent environmental cost assessment model was provided. The model considered both the time value of money and the characteristic that environmental governance cost would change over time.(5) In the final disposal stage, a comparative research was conduct to analyze the environmental impact of two ways to disposal wasted fly ash concrete, i.e. direct landfill and recycling. The types of environmental impact include energy consumption, carbon emission and land occupation. In addition, the dual attributes of recycled aggregate were taken into consideration, and the environmental impact of recycled aggregate was obtained. At last, the environmental impact of recycled fly ash concrete was analyzed by consider the effect of compressive strength and transport distance of recycled aggregate.