Assessment of the effect of varying concrete strength classes on the total carbon dioxide emissions from concrete structures.
Ssemakula, Martin Kirinnya
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Concrete holds a prominent position as a primary construction material and ranks second only to water in terms of consumption. Consequently, reducing the amount of concrete implemented in construction projects can directly contribute to the reduction of carbon dioxide emissions associated with building construction. As building construction is responsible for approximately 40% of annual carbon dioxide emissions, various efforts have been proposed to diminish these emissions. The adoption of a performance strategy, which emphasizes the use of materials like concrete that minimize emissions compared to alternative options, is one such method. This study aimed to evaluate the influence of concrete strength class on carbon dioxide emissions through structural analysis and design of a 40-storey building. Structural design software was employed to determine material sections and total concrete quantities. The life cycle assessment methodology was utilized, incorporating emission factors outlined in the IPCC guidelines and methodologies established by reputable authors in the field. The study specifically focused on the construction stage of the building's life cycle, with concrete strength classes designed according to standards provided by the ACI Committee 211. The findings of this study indicate that employing high-strength concrete resulted in reduced section sizes of structural elements, leading to lower carbon dioxide emissions. Switching from 20MPA concrete to 80MPA concrete resulted in a substantial reduction of 44.6% in total carbon dioxide emissions while transitioning from 20MPA to 40MPA concrete led to a reduction of 31.9%. Additionally, increasing the strength of the concrete from 20MPA to 80MPA significantly decreased the required amount of longitudinal reinforcement by approximately 67%. This reduction can be primarily attributed to the smaller section sizes necessitated by high-strength concrete. To facilitate the quantification of the carbon footprint of structures, a web-based system, accessible via https://tofaliafrica.com/carbon-footprint-calculator, was developed. The system incorporates location-specific variables to calculate total emissions provided material quantities. This is to improve and promote the sustainability of construction projects by providing a system that could influence the preliminary decision-making of stakeholders during the selection of materials.