This paper presents an optimization of fly ash geopolymer mixtures by Taguchi method, and a study on the mechanical properties and durability of concrete produced from the optimal mixes. A total of nine mixtures were evaluated by considering the effects of aggregate content, alkaline solution to fly ash ratio, sodium silicate to sodium hydroxide ratio, and curing method. Ordinary Portland Cement (OPC) concrete of 55 MPa strength was used as a control mix. Three optimal mixtures (T4, T7 and T10) were identified. Results show that the geopolymer concrete can be produced with of 55 MPa at 28 days. They had higher tensile and flexural strength, produced less expansion and drying shrinkage, and showed moduli of elasticity that were 14.9-28.8% lower than those of the OPC control mix. The compressive strength of all geopolymer mixtures changed significantly at each wetting-drying cycle, but the weight losses were higher than that of the OPC concrete. Half-cell potential measurement showed that the geopolymer mixes were generally more prone to corrosion, although showed low-level corrosion activity and exhibited times to failure that were 3.86-5.70 times longer than those of the OPC concrete. The test results confirmed that the mechanical properties of the geopolymer mixtures tested are competitive with those of OPC concrete and provide a more durable alternative to the OPC concrete in a seawater environment.

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Kulit kerang merupakan bahan yang dapat digunakan sebagai bahan pengganti agregat kasar, pengganti pasir, filler, dan sebagai bahan pengganti semen. Kandungan CaO dari kulit kerang berpotensi untuk meningkatkan kekuatan beton dan memperbaiki sifat-sifat beton. Pada penelitian ini abu dari kulit kerang lokan digunakan sebagai bahan tambah atau filler pada mortar dalam rendaman NaCl. Kulit kerang lokan dibakar, dihaluskan dan disaring menggunakan saringan no.200 untuk mendapatkan ukuran partikel yang halus sehingga dapat memberikan reaksi pozzolanik yang lebih baik dan lebih mudah untuk mengisi pori pada pasta semen. Variasi penggunaan abu kulit kerang lokan sebagai bahan tambah atau filler adalah 0%, 5%, dan 10%. Proses perawatan benda uji adalah 28 hari perendaman air biasa dan dilanjutkan dengan perendaman dalam larutan NaCl. Tahap pengujian yaitu pengujian kuat tekan, pengujian porositas, dan perubahan berat. Hasil pengujian menunjukkan bahwa penambahan abu kulit kerang lokan dapat meningkatkan kekuatan beton dan kinerja beton. Mortar dengan penambahan abu kulit kerang lokan sebanyak 5% dan 10% memiliki kekuatan tekan yang  tinggi, porositas rendah dan perubahan berat kecil dibandingkan mortar 0%. Diperoleh nilai optimum dari mortar dengan penambahan abu kulit kerang lokan sebanyak 5% dalam rendaman NaCl.

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This paper presents performance of blended geopolymer mortars prepared from fly ash (FA) and palm oil fuel ash (POFA). Both materials are used their Si and Al elements were activated by alkaline solution. The alkaline solution was prepared by mixing sodium silicate and sodium hydroxide. The optimum mix proportion of geopolymer mortar with FA:POFA mass ratio was 90:10. The ratio of sodium silicate solution to sodium hydroxide solution by mass was 2.5:1. The mass ratio of sand to blended ashes was 2.75:1. The mortar specimens were prepared using 5×5×5 cm cube and cured at room temperature (28oC) for 3 days before subsequently heat-cured at 110oC for 24 hours. The specimens were immersed in distilled water and peat water with pH 4-5 for 120 days. The compressive strength change, porosity, and sorptivity tests were taken. In general, the results shows there was a decrease in strength, an increase in porosity and sorptivity of the blended geopolymer mortars. Fourier Transform Infra Red (FTIR) test revealed that interaction of geopolymers mortar with the acidic peat water can also cause replacement of the exchangeable cations (Na, K) in polymers by hidrogen or hydronium ions. Formation of some new zeolitic phases in blended FA-POFA geopolymer mortar exposed to acidic peat water were observed.

Chloride is not the only main cause of corrosion of reinforced concrete structures in seawater environment. Microorganisms, such as bacteria and microalgae, in the seawater can induce microbiologically influenced corrosion (MIC) that leads to degradation of the concrete structures by formation of biofilm on the metallic surface. In this preliminary study, the impact of microalgae on the corrosion of steel reinforced bars in fly ash geopolymer concrete was studied. Corrosion potential, algae cells number, and pH measurement were carried out for fly ash geopolymer concrete and a control mix (Ordinary Portland Cement) samples. The results indicate that the corrosion potential of fly ash geopolymer concrete was influenced by the cathodic reaction during photosynthesis activities. The geopolymer concrete in algae-inoculated medium was found to be more tolerant to algal growth than the control mix (OPC concrete). There was a positive correlation between algae cell densities and the potential reading of the geopolymer.