The Effect of Sodium Silicate to NaOH Ratio on Strength Development of Fly Ash Geopolymer Mortar in Marine Environment

Civil Engineering Department, Faculty of Engineering, Universitas Negeri Surabaya, Surabaya, Indonesia

^* Corresponding author: ariewardhono@unesa.ac.id

Abstract

This paper presents the effect of sodium silicate to NaOH ratio on the strength performance of fly ash geopolymer mortar subjected to continuous immersion in a simulated marine environment during 1-year observation. The geopolymer mortar specimens were prepared using class C fly ash activated with sodium silicate and NaOH 15 Molar combination. The sodium silicate to NaOH ratio varied from 1.4 to 2.7 to keep the water-to-solid ratio and Na2O content at 0.37 and 10, respectively. The strength properties were measured based on compressive strength test, weight, and porosity changes. The compressive strength was investigated at 90, 180, and 360 days after immersion. The results showed that the sodium silicate to NaOH ratio significantly affected the long-term performance of geopolymers in simulated marine environments. A ratio between 1.6 to 2.3 provides better durability by reducing the deterioration rate, i.e., strength, weight, and porosity, of geopolymer specimens in simulated marine environments. However, increasing the ratio by more than 2.30 tends to decrease the performance of the geopolymer. It can be concluded that geopolymer can be used as an alternative construction material in marine environments in a specific sodium silicate to NaOH ratio.