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

Abstract

Geopolymer synthesis has two main requirements to fulfil which are the source material that is rich in Silicon (Si) and Aluminum (Al) and alkali activator such as sodium/potassium hydroxide. Sodium hydroxide (NaOH) is widely used for the synthesis of geopolymer compared to potassium hydroxide (KOH) with addition of silicate solution for the purpose of increasing dissolution process. However, the comparison of using different activator in the absence of silicate solution for geopolymer synthesis is not well established. This paper presents an evaluation on compressive strength of fly ash–based geopolymer by using different activator (KOH and NaOH) with respect to different curing conditions (time and temperature) in the absence of sodium silicate. The samples were mixed using mortar mixer and prepared in 50mm x 50mm x 50mm mould for determination of compressive strength. It can be observed that the highest compressive strength up 65.28 MPa was obtained using NaOH. Meanwhile, synthesis using KOH only recorded 28.73 MPa. The compressive strength was better when cured at elevated temperature (60°C) than room temperature (25°C). Further analysis on the microstructure of the highest compressive strength geopolymer samples for both activators was carried out using Field Emission Scanning Microscopy (FESEM) and Raman spectroscopy.

Synthesis and characterization of coal fly ash and palm oil fuel ash modified artisanal and small-scale gold mine (ASGM) tailings based geopolymer using sugar mill lime sludge as Ca-based activator

“…In this process, aluminosilicates are dissolved in highly-concentrated alkali hydroxide or silicate solution to form a structurally stable material composed of amorphous, interconnected Si–O–Al polymeric matrices via a combination of diffusion, coagulation and polycondensation ( Abdel-Gawwad and Abo-El-Enein, 2016 ; Rajamane et al., 2009 ). Geopolymers have excellent mechanical properties that are sometimes comparable to concrete or fired bricks when prepared under optimum conditions ( Abdul Rahim et al., 2015 ; Caballero et al., 2014 ).…”

A Critical Appraisal of Soil Stabilization Using Geopolymers: The Past, Present and Future

“…For example, geopolymer treatment of a Pb-contaminated soil recorded a maximum UCS value of 4.35 MPa as compared to a UCS value of 1.2 MPa after treatment of silty clay [43,56]. On the other hand, a trend of high UCS values (65.28 MPa, 35.12 MPa, 48.55 MPa) was noted for geopolymer pastes when tested [31,60,63]. This shows that the geopolymer paste (alkali + pozzolan) on its own has the tendency to resist a lot more compressive load.…”

“…Conversely, Abdul Rahim et al [31] compared the use of KOH and NaOH (8 M each) activated fly ash on the mechanical properties of geopolymer paste. It was observed that the highest compressive strength up 65.28 MPa was obtained using NaOH.…”

“…Past research efforts towards improving the sustainability index of concrete have yielded promising results with the use of geopolymers, resulting in early compressive strength, low permeability, excellent chemical, and fire resistance [86,[115][116][117][118][119]. More importantly, within the context of geopolymer-stabilized soils, sustainability is estimated in terms of a parameter called Sustainability Index (I Sus ), which is based on a weighted multi-criteria framework recently introduced at University of Texas at Arlington [13,31]. The I Sus of a material was proposed to be a function of its resource consumption, environmental impact, and socio-economic impact, as shown in Eq.…”

Binders alternative to Portland cement and waste management for sustainable construction—part 1

“…122 Geopolymers derived from a K-based activator dissolve or degrade more readily compared with Na-based geopolymers whether foamed or not. 123,124–126…”