Investigation of geopolymer efflorescence durability problems: Causes and possible solutions

Experimental investigations were conducted to assess the impact of factors such as relative humidity (RH%) and the H₂O molarity of waterglass on the efflorescence behavior of geopolymer composites. Samples with sodium (Na) and potassium (K) bases were prepared, having varying waterglass molarities (M) (at 11 and 13 moles of water). These samples were categorized into three groups exposed to different average RH ranges: (i) 0%–70% RH, (ii) 70%–90% RH, and (iii) 90%–100% RH. This study analyzed the occurrence of efflorescence and its stability, employing analytical techniques such as x-ray diffraction, scanning electron microscopy, and energy-dispersive spectroscopy to examine the formation and characteristics of efflorescent deposits. Additionally, mechanical testing was conducted to evaluate the compressive and flexural strengths of the geopolymer samples, considering the impact of efflorescence on their durability. For instance, in the composite geopolymer specimen containing 11 M water, at a RH of 80%, the compressive strength is decreased by approximately 25% from 56.4 to 42.3 MPa. The findings revealed that when the RH falls within the 70%–90% range, a decrease in water molar content from 13 M to 11 M leads to a more pronounced occurrence of efflorescence when compared to other conditions. Efflorescence may also occur in different RH ranges and water molarities, but its occurrence is significantly lower compared to the 70%–90% RH and 11 M water.