Thermomechanical properties of environmentally friendly slag-based geopolymer foam composites in different curing conditions

Abstract

This study investigates the effect of curing temperature and foam/slag ratio on Na2SiO3- and NaOH-activated slag-based geopolymer foam composites (GFC) having thermal insulation properties. In this regard, samples used in the study were produced by adding foam at three different ratios (12.5, 15, and 17.5% by weight of slag) to the slag-based GFC having solutions with two different activator concentrations (7M NaOH and 3M Na2SiO3). Then, these samples were exposed to three different curing temperatures (40, 60, and 22°C). The compressive strength, dry density, unit weight, water absorption, capillarity, apparent porosity, ultrasonic pulse velocity, and thermal conductivity tests were performed on the GFC samples for 1, 3, 7, and 28days. Scanning electron microscopy (SEM) analyses were also conducted to characterize the pore structure and crack development of the GFCs. In addition, XRD analyses were performed on selected series to determine the formed reaction products of GFCs. As a result, it was observed that high curing temperature both improved mechanical strength and physical properties in GFC samples. The highest mechanical strength was obtained in the GFC with a 12.5% foam ratio and curing at 60°C, while the lowest thermal conductivity coefficient was achieved in GFC with a 17.5% foam ratio and cured at 60°C. In general, with the increase of foam ratio in slag-based GFC samples, unit weight, compressive strength, and ultrasonic pulse velocity results decreased, while capillarity, water absorption, and apparent porosity results increased. According to the results, it was seen that slag-based GFCs could be used in the construction of load-bearing and non-load-bearing walls.