The effect of alkali activation solutions with different water glass/NaOH solution ratios on geopolymer composite materials

Abstract

In this study, geopolymer materials were produced from fly ash (FA) supplied from Isken Sugözü Thermal Power Plant located in Adana, Turkey. FA and Rilem Cembureau Standard Sand were used together with the ratio of 0.50. At first, two different alkaline solution/material ratio (FA+standard sand) (L/M) were selected as 0.20 and 0.40 for the design parameters. In the production of geopolymer composite material, sodium silicate (Na2SiO3) and sodium hydroxide (12 M NaOH) were used together within the ratio of 1, 1.5, 2, 2.5 and 3 by weight, respectively. A totally of 20 mixes were cured at 70 and 100 oC for 24 hrs, respectively and thereafter kept in room temperature until testing age. Physical characteristics of hardened mortar were determined via the bulk density, water absorption and porosity values at 28 days while the strength of geopolymers was obtained on the results of compressive strength and flexural strength tests conducted at 7, 28 and 90 days. Considering the testing parameters, geopolymer material with the highest compressive strength was found as 76.0 MPa (28-days) on the mixture produced with L/M ratio of 20% by weight; the alkaline solution consisted of a mixture of Na2SiO3 and 12 M NaOH in weight ratio of 2 by curing at 70 oC for 24 hrs. However, test results showed that there was an optimum limit for the alkaline solution ratio, such that exceeding this limit gave the reverse effect for the strength characteristics of the geopolymer material.