Sustainable Concrete Production Using Fly Ash and Recycled Glass Powder: Environmental and Mechanical Performance Evaluation

Cement manufacturing is a major source of carbon dioxide (CO2) emissions globally. Cement replacement materials are increasingly used to minimize the environmental impact of concrete production. In the present study, the mechanical and environmental performance of concrete mixtures containing fly ash and recycled glass powder as partial cement replacements at levels of 10%, 20%, and 30% were investigated. Workability, unit weight, compressive strength, and water permeability tests were conducted to evaluate the effects of replacements on concrete behavior. Carbon emissions decreased as the substitution ratio increased, with the highest reduction (28.9%) observed in the mixture containing 30% fly ash. Compressive strength values ranged from 21.9 to 27.0 MPa, indicating that all mixtures fell within the intended strength range. Two types of cement replacements—fly ash (FA) and recycled glass powder (GP)—were evaluated separately. Compared to GP mixtures, FA mixtures generally exhibited lower permeability (up to 50%) and better strength retention (up to 9.6 percentage points), though both materials contributed to reducing embodied carbon. The mixture containing 30% fly ash demonstrated the highest environmental efficiency, with a carbon intensity of 10.84 kg CO2/MPa, corresponding to a 19.2% reduction compared with the control. For recycled glass powder, the 20% replacement level offered the most balanced performance, while higher replacement ratios led to more pronounced strength losses. This study provides a direct comparison of FA and GP under identical mixture conditions using performance-normalized environmental indicators. The results indicate that, under the tested conditions, fly ash exhibits a better combination of carbon emission reduction and mechanical strength than recycled glass powder.