The role of demolition waste reduction and recycling to reduce energy demand, greenhouse gas emissions and resource consumption: a Case study from Vienna

Abstract

Modern urban societies consume large amount of raw materials. This consumption leads to negative impacts on the environment. In order to reduce these impacts, cities have defined sustainable development strategies. One example is the city of Vienna. In its Smart City Wien Framework Strategy, Vienna aims to reduces not only its greenhouse gas emissions, but also its energy demand in housing and the consumption-based material footprint, which is the equivalent of the total material requirement, by -30% until the year 2030 and by -50% until the year 2050. The most important sector responsible for energy and material consumption in urban areas is the building sectors. For this reason, implementation of material reduction strategies must target this sector first. The study at hand aims to provides both, presenting an ex-post as well as a scenario-based analysis of the energy demand, the greenhouse gas emissions, and the consumption-based material footprint of the urban building sector, considering different degrees of waste reduction by avoiding the demolition of buildings, and maximum recycling of mineral demolition waste and the mineral fraction of municipal solid waste incineration bottom ash, to be used as construction materials and using the case study of Vienna. To do so, a bottom-up material flow and stock analysis was carried out to calculate the consumption-based material footprint for the building construction sector in Vienna, considering the most important construction materials (asphalt, brickwork, concrete, glass, gravel & sand, selected plastics). In the first step, the material stocks and flows (inputs of raw materials and outputs of demolition wastes) were calculated for the building construction sector for the years 1991-2015. In the second step, extreme urban development scenarios were designed for both sectors, i.e. deep renovation vs. demolition & new construction in the building sector. Both were compared to a business as usual scenario. For these as well, material stocks and flows were determined. By also calculating net- and gross floor areas for different age and use periods of buildings, considering also deep renovation by thermal insulation, the heating energy demand and associated greenhouse gas emissions were calculated. By using a life-cylce approach, greenhouse gas emissions on a life-cycle basis as well as the total material requirement, were calculated for the urban development scenarios. Since construction minerals are the most important materials in buildings, finally, the results of the total material requirement of the urban development scenarios were combined with a maximum recycling scenario of mineral demolition waste and a maximum recycling scenario of the mineral fraction from treated municipal solid waste bottom ash. The analysis of past developments of the consumption-based material footprint (total material requirement) in Vienna shows an increase in the building construction sector in the past. However, the business as usual scenario show a decrease for the future. This also counts for the heating energy demand and the greenhouse gas emissions. For all indicators, the renovation scenario performs best, while the demolition scenario performs worst. Nevertheless, the reduction targets for greenhouse gas emissions, energy demand, and consumption-based material footprint cannot be meet. The renovation scenario, however, comes closest to meet the targets. When combining these urban development strategies by an enhanced recycling scenario of mineral wastes, for the consumption-based material footprint, the business as usual and the renovation scenario can reach the target, while even the demolition scenario comes close to this bench mark. This means that sustainable development as targeted my many cities, including Vienna, requires both, sound urban development strategies that reduce the number of buildings demolished and thus wastes generated, but also enhanced recycling of mineral wastes, particularly waste incineration bottom ash and demolition waste.