This paper presents an experimental study of fly ash-based geopolymerconcrete with various alkaline activator solution dosages. The alkalineactivator solution consisted of sodium silicate solution and sodiumhydroxide solution with a concentration of 12M. The specimens wereprepared with various alkaline activator solution / fly ash (AAS / FA) ratiosof 0.3, 0.4, and 0.5. The sodium silicate solution to sodium hydroxidesolution ratio was preselected at 2.5 by weight. The specimens were cured at65°C in a dry oven for 24 hours and then continued curing at roomtemperature for 7, 14, and 28 days. Test results indicated that compressiveand flexural strengths significantly increased with an AAS / FA ratio in arange of 0.3–0.5. At 28 days, the compressive and flexural strengths gained33.30–41.1 MPa, and 3.41–5.61 MPa, respectively. Moreover, the strengthsignificantly developed being cured in temperature conditions at early agesand then slowly increased at long-term ages. Then, based on the obtaineddata, this study used the ACI code to determine the compressive strength att-day based on 28 days. Finally, correlations between flexural strength–compressive strength, compressive strength–ultrasonic pulse velocity,flexural strength–ultrasonic pulse velocity, and elastic modulus–ultrasonicpulse velocity were also obtained.