Durability and environmental impact of concrete combining various waste and recycled materials

Utilization of waste and recycled materials in concrete is necessary to rcducc environmental impact but may have an adverse affect on mechanical properties. This paper investigated the effect of various combinations of fly ash, blast furnace slag, and low-grade recycled aggregates in concrete at three different water-binder ratios on mechanical and environmental performance. The balance between durability and environmental impact for a given strength level similar to normal-use concrete was also examined using analytic hierarchy process. Results showed that increasing the water-binder ratio and volume of recycled aggregate reduced compressive strength and increased air permeability and drying shrinkage. However, compared to normal-use concrete similar or better performance could be achieved, which was attributed to improvement of low-grade recycled aggregate performance when combined with fly ash. Similarly, CO₂ emissions and volume of raw materials were lower than the normal-use concrete for all mixes. Concrete mixes with low air permeability and low CO₂ footprint had the best balance of durability and environmental impact, as decreasing raw material volume tended to more greatly reduce durability.