The effects of different production parameters (NaOH concentration, curing regime and replacement ratio of recycled aggregate) on fresh, hardened and elevated temperature performance of geopolymer mortar samples

Abstract

This paper presents the findings of objective to examine the effects of construction and demolition wastes (CDW) as fine aggregate on the performance of geopolymer mortar (GPM) specimens. In order to examine the effect of NaOH concentration on the performance of GPM samples, NaOH solutions with 3 different concentrations (8, 10 and 12 M) were prepared. GPM samples, in which the fine aggregate part was formed by replace of natural aggregate (NA) and CDW at three different ratios (0%, 50% and 100%), were cured in water and ambient conditions for 7 and 28 days. The alkali liquid/binder ratio was not determined as a variable and was kept constant at 0.6 for all GPM samples. Subsequently, compressive strength, workability, water absorption, unit weight and high temperature performance on GPM specimens were investigated in detail. All of these experimental parameters were also supported by microstructural analysis (scanning electron microscopy (SEM), X-ray diffraction (XRD), and Fourier Transform Infrared Spectroscopy (FTIR)). The results showed that the compressive strength values of granulated blast furnace slag (GBFS) based GPM samples can be increased up to 105% in case of choosing of water curing instead of curing in ambient conditions. It was determined that the increase in NaOH concentration decreased the compressive strength values of GPM samples. Furthermore, experimental findings revealed that although CDW had a negative impact on the performance of GPM samples, it could still find potential usage area in the geopolymer production. On the other hand, the increases in NaOH concentration and CDW usage ratio led to decreased workability of GPM samples. Finally, it was underlined that the mechanical and physical characteristics of GPM samples decreased sharply with the increasing elevated temperature values (especially at 750 °C).