Optimum compressive strength of geopolymer concrete in variations comparison of ingredients and mixing time

Abstract

Concrete has been criticized more recently because of the greenhouse gas (carbon dioxide) emissions it produces in the cement portland production process. With these considerations, a new concrete binder called geopolymer concrete was developed. One of the materials used in the manufacture of geopolymer concrete is fly ash. Using fly ash as a substitute for cement is considered to be able to preserve the environment and reduce development costs. In this study, the specimen used was cylindrical, with a diameter of 15 cm and a height of 30 cm. The concrete compressive strength test was carried out at the age of 28 days. Variations in concrete testing include: Test the strength of the concrete on the variation of the binder ratio: coarse aggregate of 20%:80%, 25%:75%, 30%:70%, 35%:75% 40%:60% and the variation of stirring time 5 minutes, 7.5 minutes, 10 minutes, 15 minutes. From the test results, it can be concluded that the optimum mixing time for the concrete mix is 7.5 minutes. If it is less than 7.5 minutes it will result in less than maximum binder binding power. And if the mixing time is more than 7.5 minutes it will decrease the adhesion of the binder. Regarding the variation of concrete on the amount of use of fly ash, it can be concluded that the higher the fly ash content, there is a tendency for low compressive strength, this is due to the influence of the water content used in the mixture is obtained based on the weight of fly ash in each variation. So if the weight of fly ash is higher, the water demand will also be higher and it will result in too dilute fresh concrete, so that the compressive strength of the concrete decreases.