Effect of Curing Conditions on the Mechanical Properties of Fly Ash-Based Geopolymer without Sodium Silicate Solution

Abstract

Geopolymer is associated with the alkali activation of materials rich in Si and Al, and alkali activator such as sodium hydroxide is used for the dissolution of raw material with the addition of sodium silicate solution to increase the dissolution process. However, the trend of strength development of geopolymer using sodium hydroxide alone is not well established. This paper presents an evaluation on compressive strength of fly ash–based geopolymer by varying curing time with respect to different curing temperature using sodium hydroxide as the only activator. The samples were cured at room temperature and at an elevated temperature (60°C). Further analysis on the microstructure of geopolymer products cured at 60°C was carried out using Field Emission Scanning Microscopy (FESEM). It can be observed that the compressive strength increased as the curing time increased when cured at room temperature; whereas at elevated temperature, the strength increased up to a maximum 65.28 MPa at 14 days but gradually decreased at longer curing time. Better compressive strength can be obtained when the geopolymer was cured at an elevated temperature compared to curing at room temperature.

Effect of Solid to Liquid Ratio on the Mechanical and Physical Properties of Fly Ash Geopolymer without Sodium Silicate

“…Based on Figure 2, the compressive strength increased up to 14 days but started to decrease later for all solid/liquid ratios. The similar trend was reported in previous study [9]. It has been reported that prolong curing time at elevated temperature can damage the structure of geopolymer and lead to the decrease of compressive strength [10].…”

“…Based on Figure 1, the increase of solid/liquid ratio used results in reduction of setting time. This can be associated to the less of water available as the solid/liquid ratio increased and result in faster hardening of gel phase and more rapidly bonding of the geopolymeric framework [9].…”

“…The success of geopolymer is evaluated based on the compressive strength obtained [6], [9]. High compressive strength obtains shows that geopolymer can be used as partial replacement for OPC and as coating material.…”

Comparison of Using NaOH and KOH Activated Fly Ash-Based Geopolymer on the Mechanical Properties

“…The supply of heat seems to accelerate geopolymerisation process until it reaches optimum strength at 14 days. However, prolong curing time after 14 days in elevated temperature result in destruction of geopolymer bonding and produced lower compressive strength [10].…”