The addition of alumina and wollastonite in geopolymer resin is expected to increase the thermal behavior of the geopolymer matrix composite. In this work, fine granules of solid alumina and acicular wollastonite used as filler were mixed with a fly ash-based geopolymer resin paste to form a composite matrix. The filler additions were 2.5% to 10.0% of the total weight with sodium silicates and sodium hydroxide used as activators. The results showed that the addition of alumina and wollastonite as filler did not have much effect on the flexural and compressive strength of the geopolymer matrix composite at room temperature. Wollastonite fiber, which was added in the form of a short-sized fiber, only produced a very small bridging effect. Nevertheless, alumina filler composite showed a good result after being exposed to a temperature at 200°C, although the strength was reduced as the temperature increased. Moreover, wollastonite fibers only managed to maintain 50% of their flexural strength after 2 hours exposure at a temperature of 200°C due to the damage of the wollastonite fiber.

The effect of steel slag substitution as coarse aggregate on compressive strength in fly ash based-geopolymer concrete was studied. The compressive strength was evaluated by measuring the maximum acceptable load using compression testing equipment. Compressive strength depends on several factors, such as time and temperature of curing and the mixing proportion. The compressive strength of geopolymer concrete with steel slag substitution was higher compared to geopolymer concrete with gravel aggregate. The optimum compressive strength was found on the third day of curing at a temperature of 60 o C for both the geopolymer concrete with steel slag substitution and normal geopolymer concrete. Reinforcement corrosion was evaluated by measuring the corrosion current density using a linear polarization potentiostatic scan. The corrosion rate of reinforcing steel in geopolymer concrete with steel slag substitution was found to be higher compared to normal geopolymer concrete without steel slag in seawater medium, whereas in an acid rain environment, steel slag substitution increased corrosion resistance. The corrosion rate of geopolymer concrete with steel slag substitution was found to be lower compared to normal geopolymer concrete. The corrosion rate was found to be very high at an early stage and decreased with time.

Geopolymer concrete with designed strength of 40 Mpa has been mixed from coarse aggregates, sands and geopolymer pastes. Two kinds of pastes are synthesized from different precursors, i.e. fly ash and dehydroxylated kaolin, using sodium silicate solution as the activator. Compression test pieces of 15x15x15 cm3 of both geopolymer and ordinary Portland cement (OPC) concretes (ASTM C39) have been cast and cured. Curing was done at room temperature for 1 day while Portland cement concretes were immersed in water for 28 days to provide complete hydration. After curing, the samples were immersed in ASTM seawater (ASTM D1141-90) for 7, 28, 56 and 90 days. It is found that geopolymer concretes were in general more durable upon seawater immersion than OPC concrete, This is indicated by the compressive strength retained after immersion. Dehydroxylated kaolin geopolymers show the best performance whose strength did not decrease with time of immersion. The strength of fly ash geopolymers decreased by about 20% during 56-day immersion but did not decrease further. Calcium content is suspected to cause the decrease in strength upon immersion. Kaolin geopolymers containing no calcium showed the best performance, while OPC which consist mostly of calcium silicate hydrates as the strength contributor, showed consistent decrease in strength. It is also found from the experiment that room temperature curing of fly ash geopolymer was slow but continued to progress until 28 days both under dry condition (not immersed) and immersed in water.

Various aluminosilicate material have been used as precursor for geopolymer. Geopolymer gets its strength from the polycondensation of silicate and alumina. Metakaolin, calcinated kaolin, is pozzolan with the highest alumina and silicate purity. Indonesia, especially Bangka Island, has a large amount of kaolin deposit that being sold at low price. This price could be increased ten times when being sold as metakaolin. This study aimed to compare mechanical and metallurgical properties of commercial metakaolin and Bangka kaolin which calcinated at 700°C. Both metakaolins reacted with NaOH and waterglass as the activator followed by curing at room temperature for 7, 14 and 28 days and elevated temperature of 60°C for 4, 12 and 24 hours. Mechanical properties will be examined by compressive strength and flexural strength test, while the metallurgical properties will be evaluated with SEM, and TAM. The results of the mechanical test will be used to determine which geopolymer will perform well with the microstructure and thermal activity to support the finding. These attempts will be done in order to improve the properties of Bangka metakaolin geopolymer superior to commercial metakaolin.

Various This paper presents the results of the investigation on the use of Metakaolin (Al2Si2O2) as a supplementary cementing materials to improve the strength of cement. The most effective way to increase the strength of cement is the substitution of a proportion of cement with supplementary cementing materials. One of them was Metakaolin. Metakaolin was produced by thermal treatment calcination from Kaolin at 600-800 Celcius and has highest alumina and silicate purity. By added Metakaolin to Portland Cement type I (OPC), the amount of Calcium Silicate Hydrate (CSH) will increase through binding with Calcium Hydroxide (CaOH). There were two kinds of Metakaolin used in this investigation, commercial metakaolin named Metakaolin Metastar compared with Metakaolin Bangka which derived from Indonesia local resources, Bangka Island. Four Metakaolin replacement levels were employed in this investigation: 5%, 0%, 15%, and 20% with water per cement ratio 0.35, 0.40, and 0.50 both of Metakaolin Metastar and Metakaolin Bangka. The cement pastes cured at room temperature for 7, 14, and 28 days. The mechanical strength examined by compressive strength test, the microstructure were examined by SEM-EDS. The results of the study revealed both Metakaolin Metastar and Metakaolin Bangka enhanced the compressive strength of OPC. The most appropriate strength was obtained for a substitution of 20% metakaolin metastar which had 46,15% higher than OPC and 5% metakaolin Bangka which had 39,06% higher than OPC. The hydration rate was examined by Thermal Analysis Monitor. The results indicated that metakaolin metastar released higher heat than metakaolin Bangka. It can be concluded that Metakaolin metastar was more effective than metakaolin Bangka as additive in OPC.