This paper presents a study of the flexural strength of geopolymer concrete beam using high calcium content fly ash (FA) in marine environment, without high heat curing. Two series of beam specimens were loaded to failure to study the effect of chloride environment on the flexural strength of geopolymer concrete beams. Series I specimens were subjected to sea environment, whereas series II were kept at room temperature. Tests performed on concrete cylinders show that the sea water has no effect on compressive and splitting tensile stress of high calcium content FA based geopolymer concrete. However, the ratio of splitting and compressive strength for both series was approximately 44%, almost double than that of normal concrete. In addition, the flexural test of concrete beams shows that the average cracking load for series I specimens was 275% higher than that of series II. However, the ultimate load, crack pattern and deflection characteristic for both series were very similar.

This study is conducted to determine the effect of four variables on compressive strength of geopolymer concretes. These four variables are binder/aggregate, Alkalinene/fly ash, effect of superplasticizer (SP) addition and curing system. The compressive strength is important mechanical properties for construction material. Taguchi experimental design method is used to compile the concrete composition of geopolymer to achieve the maximum compressive strength. Specimens concrete used is a cylinder with 100 mm diameter and 200 mm height. Compressive strength test is performed at 28 day using SNI 03-6825-2002, Indonesian National Standard. This study concludes that the chloride environment has a beneficial effect on the compressive strength of the concrete. In addition, the Alkalinene/fly ash ratio and binder/aggregate give a significant effect on the compressive strength of geopolymer concretes.

Geopolymer concrete is an example of innovative concrete that does not use cement as a binder and generally fly ash used in recent research. However, fly ash is categorized as a hazardous and toxic waste [8]. This research studied about another binder, besides fly ash, in this case is rice husk ash made as a geopolymer paste alkali activated by a chemical mixture of sodium silicate (Na2SiO3) and sodium hydroxide (NaOH) confronted to a fly ash mixture paste as comparative material. The compositions made were, 100% rice husk ash, a mixture of 50% rice husk ash and 50% fly ash, and 100% fly ash as control mixture. After making the mixture, the composition will be tested to setting time-test in the form of paste. The size of specimen was cylindrical 2,5 cm in diameter 5 cm in height and cube size 15 cm x 15 cm x 5 cm. Each type of specimen was projected to porosity test, compressive strength test, UPV (Ultrasonic Pulse Velocity) and permeability test on 3 days, 28 days and 56 days of sample’s age. From the result of setting time, it was found that the composition of 100% rice husk ash had the longest on binding, which were 129 minutes for early binding and 170 minutes for late binding. The lowest result of porosity test was 100% of fly ash at 56 days of sample’s age testing with a porosity of 20%. The lowest result of compressive strength was 100% of rice husk ash tested in 3 days of sample’s age showed a compressive strength at 0.65 MPa. Based on the test results of UPV (Ultrasonic Pulse Velocity), the lowest value of wave velocity was 531.667 m/s, belong to 100% rice husk ash mixture at 3 days of sample’s age testing, with very poor binder quality qualification. The test result of highest permeability kT value with very poor-quality index binder was 100% rice husk ash with period of testing time in 3 days 0,047.10-16 m2.

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This study is conducted to determine the effect of five variables on mechanical properties of geopolymer binders. These five variables are chloride environment, NaOH molarity, Na2SiO3/NaOH ratio, fly ash/alkaline activator (FA/AA) ratio and superplasticizer (SP) addition. The mechanical properties considered are compressive strength, porosity and density. Taguchi experimental design method is used to compile the binder composition of geopolymer to achieve the maximum compressive strength. Specimens binder used is a cylinder with 25 mm diameter and 50 mm height. Compressive strength test is performed at 28 days using SNI 03-6825-2002 (Indonesian National Standard) and porosity of the binder is determined using vacuum saturation apparatus similar to that developed by RILEM. The density of the binder is measured using Ultrasonic Pulse Velocity (UPV). This study concludes that the chloride environment has a beneficial effect on the compressive strength of the binder. In addition, the FA/AA ratio and NaOH molarity give a significant effect on the compressive strength of geopolymer binders.