Alkali Binder Based on Waste Glass and Limestone

Abstract

Investigation was carried out about to characterize the reaction products and strength of pastes of alkaline binders based on urban waste glass and limestone activated at 20, 40 and 60 ℃ with 6, 9 and 12% Na₂O using NaOH, Na₂CO₃ and a mixture of these. The waste glass and limestone were ground to pass through the #50 (150µm) and #325 (45µm) sieves. The investigation was developed in two stages. First, the Taguchi Method, which is a fractional experimental design, was used to determine the conditions that promote the greatest compression strength. Second, pastes were prepared using a factorial experimental design to be able to evaluate and compare the effect of activators on compressive strength and microstructure. The results showed that the use of Na₂CO₃ promotes the highest compressive strength (71 MPa), but the structural stability decreases after 14 days of curing at temperatures greater than 40 ℃. The use of the Na₂CO₃/NaOH mixture was considered optimal, according to Taguchi statistical method, the compressive strength at 28 days of curing was of 64.8 MPa ± 15 MPa, maintaining structural stability in late curing ages. The pastes prepared with NaOH developed the least strength at early ages, but in later stages it can promote compressive strength similar or greater than those developed by the pastes prepared with the other activators used (59 MPa, 28 days). The characterization carried out by XRD, SEM and TGA-DSC indicates that the reaction products formed were pirssonite, gaylussite, recrystallized calcium carbonate and C-S-H intimately intermingle with silica gel.