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The effect of loss of ignition, specific gravity, fineness, specific surface area and soluble fly ash to compressive strength of geopolymer paste were studied. Six fly ashes from two different sources and different time of collection were evaluated. Sodium hydroxide and sodium silicate were used as alkali activator. Concentration of sodium hydroxide and mass ratio of sodium hydroxide to sodium silicate were fixed 14M and one respectively. The result indicated that the improvement in compressive strength of geopolymer paste was more influenced by fineness, specific surface area and soluble content of fly ash. Soluble content of fly ash greatly affected the compressive strength of geopolymer paste compare to the compressive strength of cement paste with 20% fly ash replacement.

Concrete has high compression strength but low tensile strength. Therefore fibers are added to enhance the tensile strength. South Kalimantan is one of Indonesia’s largest wetlands, and the banana tree is common in this area. After harvesting, they are accumulated or be burned, causing pollution. Utilizing banana tree waste as fiber in the concrete minimizes it. This paper investigated the effect of banana fiber length and percentage of fiber by volume fraction on the compressive of mortar, tensile, and compressive concrete strength. The correlation between the compressive and tensile strength was further established. The percentage of fiber used in this research was 0.1%, 0.2%, and 0.3%, and the length of the fiber was 7cm and 15cm. The results showed that the addition of banana fiber significantly improved the mechanical properties of mortar and concrete. The compressive strength of mortar with a fiber length of 7cm was higher than 15cm. The higher percentage of fiber causes the lower compressive strength of mortar. The compressive strength of fiber-reinforced concrete was 27.9 MPa, and the ordinary concrete was only 17.91 MPa. The tensile strength of fiber-reinforced concrete was 6.96 MPa, while the ordinary concrete was just 1.93 MPa.

Self-compacting concrete is an innovative concrete technology with higher flowability properties by adding the mineral admixtures such as superplasticizers and not necessary to vibrate concrete. The banana fibers were used in this investigation because banana fiber is an environmentally friendly material with good properties compared to synthetic fiber. The experimental test consisted of two phases of research, i.e., preliminary research, which had the aim to investigate the appropriate percentage of superplasticizer in the mixed composition of self-compacting concrete. The percentages of superplasticizers were 0.7%, 1%, and 1.4%. The second phase of research on the effect of additional banana fiber on self-compacting concrete was carried out, examining workability, compressive strength, and the splitting tensile strength of concrete. In this research, the percentages of fiber were 0.12%, 0.3%, and 0.5% of the cement weight, and evaluated the effect of fiber treatment. The treated fibers mean that the fiber is immersed in NaOH solution or named as a delignification process. The hardened concrete specimen was used for determining the mechanical strengths, such as the compressive strength and split tensile strength tests. The test results found that the optimum value for superplasticizer dosage was 0.7% of cement weight, which can fulfill the whole criteria of fresh concrete and hardened SCC concrete. Furthermore, the specimen with the adding banana fiber of 0.12% by cement weight and treated fiber indicated a decrease in workability. Compared to the control concrete, it inversely increased compressive strength up to 44.36% and tensile strength up to 17.78%.

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