Environmentally Friendly Manufacturing of Fly Ash Geopolymer Mortar
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Abstract
This research presents the environmentally friendly manufacturing (green manufacturing) of geopolymer mortar, focusing on the unit weight and compressive strength of geopolymer made from Mae Moh fly ash from Lampang Province. Graded sand in a dry condition was used in this investigation. The fly ash/sand ratio was set at 1:2.75. Sodium hydroxide (NaOH) and potassium hydroxide (KOH) solutions were used at concentrations of 2.5, 5, and 7.5 molars (M), respectively. The ratios of Na2SiO3/NaOH and Na2SiO3/KOH were controlled at 0.5:1, 1:1, and 2:1, respectively. The solution/fly ash ratio was set at 0.6. The temperatures for curing the geopolymer mortar were controlled at 30°C and 60°C, respectively. The compressive strength test of geopolymer mortar was conducted at the ages of 7, 28, and 56 days, respectively. Tap water was used to mix the geopolymer mortar, similar to that used in cement mortar for strength comparison.
The results indicated that the concentration of the alkaline solution can affect the rate of polymerization. Higher concentrations can lead to faster polymerization such as at a NaOH concentration of 7.5 M and a Na2SiO3/NaOH ratio of 1:1, a maximum compressive strength of 210 ksc was obtained at 56 days of testing (after 1 day of curing at 60°C). Similarly, at a KOH concentration of 7.5 M and a Na2SiO3/KOH ratio of 1:1, a maximum compressive strength of 240 ksc was obtained at 56 days of testing (after 1 day of curing at 60°C). Comparatively, the compressive strength of samples mixed with KOH solution was a bit higher than those mixed with NaOH solution. Furthermore, elevated curing temperatures can accelerate the geopolymerization process, enhancing strength in a shorter time frame. As it was clearly found that heat curing at 60°C provided higher compressive strength than curing at room temperature (30°C). Nevertheless, due to the aspect of environmentally friendly manufacturing of geopolymer mortar, a curing temperature close to room temperature (approximately 30°C) can yield a reasonable compressive strength within the range of 160-220 ksc, when stored in air for duration of 56 days, therefore, lengthening the curing time results in higher strength, as it allows more complete polymerization which contributes to the density and interconnectivity of geopolymer structure.
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