Sustainability evaluation of concretes with mixed recycled aggregate based on holistic approach: Technical, economic and environmental analysis.

This research combines technical, economic and environmental analysis of the use of recycled aggregates from construction and demolition wastes in concrete production. Firstly, an experimental campaign to evaluate the effect of recycled aggregate on mechanical properties was developed. The mixture designs studied were: a reference concrete (without recycled aggregate), two concretes with 20% and 100% replacement of coarse natural aggregate by recycled concrete aggregate; and three concretes with 20, 50 and 100% replacement of coarse natural aggregate by mixed recycled aggregate. To analyze their technical feasibility, these concretes were made in the laboratory and in a concrete plant. The economic viability was also studied indicating the additional costs incurred due to the utilization of recycled aggregate in different economic scenarios. Finally, the differences in environmental impacts were analyzed for each concrete. For this purpose, energy consumption, global warming, eutrophication, acidification, photochemical ozone creation, waste generation, and abiotic depletion were accounted. 20% replacement of recycled concrete aggregates does not cause practically variations in the cost or the environmental loads, only a reduction of waste generation and abiotic depletion of 8% and 10.6% respectively. In contrast, the use of 100% replacement by mixed aggregates may increase the global warming indicator an 11% when double transport distance is assumed. But in exchange, the waste generation decreases 35% and the abiotic depletion 50%. Aggregate transport distance is a key factor that will determine the cost, energy consumption, and global warming of the mixed recycled aggregate.

Concretes and mortars with waste paper industry: Biomass ash and dregs.

This article describes a study on the viability of using waste from the paper industry: biomass boiler ash and green liquor dregs to fabricate mortars and concretes. Both types of ash were characterized by obtaining their chemical and mineralogical composition, their organic matter content, granulometry, adsorption and other common tests for construction materials. Seven different mortars were fabricated, one for reference made up of cement, sand, and water, three in which 10, 20, or 30% of the cement was replaced by biomass ash, and three others in which 10, 20, or 30% of the cement was replaced with dregs. Test specimens were fabricated with these mortars to conduct flexural and compression tests. Flexural strength is reduced for all the mortars studied. Compressive strength increases for the mortars fabricated with biomass ash and decreases for the mortar with dregs. Finally, 5 concretes were made, one of them as a reference (neither biomass ash nor dregs added), two of them with replacements of 10 and 20% of biomass ash instead of cement and another two with replacements of 10 and 20% of dregs instead of cement. The compressive and tensile splitting strength increase when a 10% of ash is replaced and decrease in all the other cases. The modulus of elasticity always decreases.