Considering uncertainty in life-cycle carbon dioxide emissions of fly ash concrete

Concrete, the most widely used construction material in the world, consumes a large amount of resources and emits significant greenhouse gases during production. Previous studies have adopted a deterministic method to confirm that substituting fly ash for cement in concrete can reduce carbon dioxide emissions. However, the life-cycle assessment involves a lot of assumptions and associated uncertainties. This paper reports on an investigation to consider those uncertainties. Two types of uncertainty - parameter uncertainty and uncertainty due to the choice of functional units - were investigated using the Monte Carlo simulation method and scenario analysis method, respectively. The results indicated that results varied significantly with the preset functional units. When considering volume and strength, although the addition of fly ash in concrete can reduce emissions, compressive strength is also decreased resulting in a zero net change in emissions performance. When adopting other functional units, the addition of fly ash has emission-reduction potential. By considering parameter uncertainty, although average emissions decrease with addition of fly ash, the standard deviation increases with addition, indicating an increasing discreteness. It is concluded that considering the uncertainty in the life-cycle emission analysis of fly ash concrete leads to more rational decision-making for concrete selection.