An Evaluation of the Behavior of Metakaolin-Based Geopolymer Concrete Exposed to Magnesium Sulfate Attack Based on Non-destructive Testing Methods

Abstract

The production of conventional Portland cement (OPC) entails significant consumption of primary raw materials and results in a substantial release of CO2, contributing to greenhouse gas emissions and global warming. To address these environmental challenges, geopolymer concrete has emerged as an alternative that eliminates the need for cement. However, geopolymer concrete may be subjected to potential degradation when exposed to aggressive environments such as seawater, industrial waste, and areas with magnesium sulfate presence, which can affect its mechanical and durability properties. This study focused on evaluating the performance of metakaolin-based geopolymer concrete (MKGPC) exposed to magnesium sulfate attack based on non-destructive testing methods. The MKGPC was prepared using a binder ratio of 1:1.6:3.7 and a sodium hydroxide (NaOH) concentration of 16 molar, mixed with sodium silicate (NaSiO2) at a ratio of 1:2.5. Concrete cubes of 100x100x100 mm were cast, allowed to set and harden for 24 hours, and then subjected to a temperature of 60°C for 24 hours before immersion in a 2.5% magnesium sulfate solution. Tests for compressive strength, ultrasonic pulse velocity, and rebound hammer were carried out at 7, 14, 28, and 56 days. Additionally, a water absorption test was conducted at 28 and 56 days. The experimental results revealed a slight increase in compressive strength of MKGPC samples exposed to magnesium sulfate attack at 7, 14, and 28 days, followed by a decrease of 13.09% at 56 days. Similarly, ultrasonic pulse velocity and rebound number exhibited initial increases at early ages but decreased at 56 days. The study established that prolonged exposure to 2.5% magnesium sulfate solution has a slight negative impact on the mechanical properties of MKGPC. Therefore, it should not be used for infrastructure in environments where the magnesium sulfate concentration is up to 2.5%.