The environmental impact of reinforced concrete structures occurs during all phases of the building's life cycle, with emphasis on the stages of extraction and transport of raw materials and concrete production. An effective way to reduce the impact of these structures is to reduce the consumption of materials with the use of optimization techniques. The present study evaluates carbon dioxide emissions of concrete with two different compressive strengths for the region of Chapecó, SC. With these data, the optimization of structural elements was performed aiming to minimize their environmental impact. The carbonation of optimized elements was also evaluated. Among the results, it was observed that concretes with lower strength have better CO2 absorption rates (for the elements analyzed 20MPa concrete absorbed about 90% and 112% more CO2 than 35MPa concrete to columns and beams, respectively). In addition, it was observed that local factors can strongly influence the impacts, with the transport of materials reaching up to 6.4% of total emissions.

The building industry is one of the greatest environmental impact causers in the planet. Cement is the second most used material in the world and the consumption of concrete ranges between 20 to 30 Gt yearly. This demand for the materials ten ds to increase for the next 100 years. The increase of concrete strength to reduce the material consumption is one of the options proposed in literature to reduce the environmental impacts in building industry. However, few studies have been carried about the actual advantages of this strategy in building production. In this paper, a 15-storey reinforced concrete building was designed with three different concrete grades for its columns: 30 MPa, 40 MPa and 50 MPa. The results for the volume of concrete and the amount of reinforcing steel to produce the columns were used to perform a cradle-to-gate life cycle assessment (LCA) to determine the alternative with less environmental impacts in the production stage. Results indicate an advantage to adopt higher strength concretes in columns to reduce environmental impacts and the consumption of materials. Direct effects of higher strength in concretes made possible to reduce the consumption of concrete by 15%. There was also a significant reduction caused by indirect effects of higher strengths in concrete, with the reducing of steel consumption up to 22%. With the combination of the direct and indirect effects of higher compressive strengths, it was possible to reduce the environmental impacts of reinforced concrete in all categories studied in the LCA.