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2 2024

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Effect of NaOH Solution on Mechanical Properties and Morphology of Fly Ash Based Cold-Pressed Geopolymer

Shee-Ween Ong, Cheng-Yong Heah, Abdullah Mohd Mustafa Al Bakri, Wan-En Ooi, Yong-Jie Hang, Hoe-Woon Tee, Jia-Ni Lim

Archives of Metallurgy and Materials

2024

Vol. 69, iss. 4

1353--1357

Cold-pressing method is beneficial in reducing the porosity of geopolymer matrix, but the low liquid volume will result in unreacted aluminosilicate materials. This problem can be resolved by increasing sodium hydroxide (NaOH) concentration. This paper thus investigates the effect of NaOH concentration on the properties of cold-pressed geopolymer. The fly ash was activated by sodium silicate (Na2SiO3) and 10, 12, 14 and 16 M of NaOH solution. The dry mix was compacted with a uniaxial hydraulic press and cured for 7 and 28 days. The specimens were measured by porosity and compressive strength measurements. Scanning electron microscopy (SEM) analysis was performed to determine the microstructure of specimens. The geopolymer was optimized at 14 M NaOH with the highest 28-day compressive strength (109.6 MPa) and lowest porosity (8.1%). The SEM micrographs proved that the geopolymer have a dense and compact microstructure.

A Prefatory Sustainability Assessment of One-Part Geopolymers

Wan-En Ooi, Yun-Ming Liew, Abdullah Mohd Mustafa Al Bakri, Shee-Ween Ong, Yong-Jie Hang, Hoe-Woon Tee, Jia Ni Lim

Archives of Metallurgy and Materials

2024

Vol. 69, iss. 3

833--837

This study investigated the sustainability aspect of the fly ash (FA)-based one-part geopolymers (OPGs) with various combinations and amount of alkali activators (AA). The three groups of OPG were: the M-OPG activated with solely sodium metasilicate-anhydrous (Na2SiO3), the MH-OPG with Na2SiO3 and sodium hydroxide (NaOH), and the MC-OPG with Na2SiO3 and sodium carbonate (Na2CO3). The compressive strength, embodied carbon, embodied carbon index, embodied energy and embodied energy index were identified. Test result shows that the M-OPG and MC-OPG with the AA/FA ratio of 0.20 attained 83 MPa and 75 MPa of compressive strengths, respectively. The MH-OPG with AA/FA ratio of 0.15 attained 72 MPa of compressive strength. The embodied carbon and embodied energy of the OPGs were mainly contributed by the Na2SiO3-anhydrous. The values were lowered when the Na2SiO3-anhydrous were partially substituted with NaOH or Na2CO3. Increasing the AA content increased the embodied carbon and energy. The embodied carbon index (3.80 kg CO2/m3/MPa) and embodied energy index (14.72 MJ/m3/MPa) of the MC-OPG with AA/FA ratio of 0.20 were the lowest. The outcome of this study supports the utilisation of Na2CO3 to partially substitute Na2SiO3 for the development of OPGs.