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This article investigated compressive strength and microstructure of lateritic soil-used coffee grounds stabilized fly ash geopolymer. Fly ash (FA) was obtained from the Mae Moh power plant, Lampang Province. Used coffee grounds (CG) was collected from the coffee shop in Nakhon Ratchasima area. Liquid alkaline activator was mixed of sodium silicate (Na2SiO3) and sodium hydroxide (NaOH). The Na2SiO3:NaOH ratio was 50:50. The concentration of NaOH was 5 molar. The compressive strength of samples at curing time of 7 days was examined. Test results show that the unit weight of lateritic soil-CG FA geopolymer decreases with increasing the CG. The maximum unit weight of sample is 20.12, 19.75, 18.96 and 18.05 kN/m3 for CG content of 0, 10, 20 and 30% by weight, respectively. The decrease in unit weight causes high porosity in particles of CG. The lateritic soil-CG FA geopolymer at curing time of 7 days and optimal water content gives the maximum compressive strength which is 2.57, 1.82, 1.40 and 0.88 MPa for GC content of 0, 10, 20 and 30%, respectively.
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