CLIMATE-SMART CONCRETE APPLIED ON A SLAB FRAME BRIDGE

Sammanfattning: This study examines alternative actions that are applied to an existing structure in Stockholm in order to reduce the global warming effect, in the form of carbon dioxide emissions. The structure consists of a slab frame bridge with belonging piles in the foundation, of which the building material is reinforced concrete with two different concrete types, namely concrete type C35/45 and concrete type C50/60. This work considers four different cases, of which the first case, Case I, shows the amount of carbon dioxide emissions for the existing structure. The next three cases and their results are hence compared with the first case, where the last case, Case IV, is a combination of the actions applied in Case II and Case III. Case II examines the exchange from standard concrete to climate-smart concrete by replacing CEM I with CEM II, which contains fly ash, but also by adding the supplementary material GGBS. Case III, on the other hand, deals with the increase of the water-cement ratio in those parts of the structure where it is possible, i.e. minimising the amount of cement in the concrete. Further, an investigation for the steel reinforcement is also carried out, where a comparison between newly produced, non-recycled steel and recycled steel is done, where an assumption that the former occurs in the existing structure is made.   The method used in this work is based on carbon dioxide emission values ​​for certain products determined by RISE. In order to be able to calculate the CO2 emissions for the various cases, limitations and assumptions had to be made, such as considering only carbon dioxide emissions from the cement and the supplementary materials. The recipes for the two concrete types in Cases II-IV are based on the recipes from the first case, which in turn have been obtained from the concrete supplier Swerock, and have thus been adjusted to adapt them in accordance with the desired w/c.   The result indicates that Case II gives a better outcome than Case III in terms of carbon dioxide emissions. This means that increasing the water-cement ratios in standard concrete is a less effective action than replacing standard concrete with climate-smart concrete, which is more optimal and sustainable. On the other hand, carbon dioxide emissions are further minimised by a combination of these two cases, i.e. Case IV, which results in a 40% reduction of the carbon dioxide emissions compared to the emissions from Case I. More ultimate results are achieved through a further action for Case IV, which involves usage of recycled steel instead of non-recycled steel. Compared with the carbon dioxide emissions from the current structure, this results in a total reduction of 52%.