This research is firstly presented the thermal resistance of a ceramic backing made from metakaolin-based geopolymer for stainless steel welding. The general problems such as lack of fusion, hydrogen inclusion, porosity and corrosions of stainless steel welded specimens were found because, largely, stainless steel presents an affinity to gases as oxidation. Therefore, during welding, if these gases do not escape from the weld pool before solidification of weld metal, it results in porosities or hydrogen inclusions. In this case, it can be solved by properly using inert gas backing. The welder usually uses the steel backing plate with a gas release hole to support weld root and gas transmission for completed weld penetration and superior weld quality. Since the geopolymer shows a good property of thermal resistance, researchers are interested in using the ceramic backing made from geopolymer instead of the commercial ceramic backing. The ceramic backings from the geopolymer were designed merely in 3 types as follows: Narrow curved groove without gas release hole, narrow curved groove with gas release holes and wide curved groove with gas release holes. Consequently, two pieces of stainless steel were welded by gas tungsten arc welding and then the weld quality such as defects, porosity and root penetration of welded specimens was inspected. Moreover, the surface failure of ceramic backing after the welding process was also considered. The results revealed that ceramic backing from a geopolymer with wide curved groove and gas release holes gave completed penetration at the root when inspecting with non-destructive testing such as visual test, penetration test, and radiography test. It was concluded that the geopolymer could be used as ceramic backing in stainless steel welding by gas tungsten arc welding. Moreover, it could be used as backing for aluminum and steel welding as well.

This study explores the potential of biosilica including diatom and diatomaceous earth as alternative silica sources for metakaolin-based geopolymers. Diatomaceous earth, composed of fossilised diatom frustules rich in amorphous silica, and diatoms, a sustainable source of renewable biosilica, are investigated for their effectiveness in enhancing geopolymer properties. Through detailed analyses including FTIR, XRD, and SEM, the study evaluates the impact of these biosilica sources on geopolymer compressive strength and microstructure, comparing them with conventional sodium silicate. Results show that diatoms exhibit significant promise, achieving 28-day strength up to 17.9 MPa at a 30% mass fraction, while diatomaceous earth reaches 26.2 MPa at a 50% addition rate, demonstrating their potential as active silica sources. Furthermore, the study elucidates the role of organic matter in biosilica on geopolymerisation, highlighting its influence on active silica release and the strength performance of products. This study proposes a novel pathway to enhance the sustainability of geopolymers through the utilisation of biosilica from diatoms, contributing to advancements in eco-efficient construction materials.

Conventional cement production process emits tons of carbon dioxide gas which is one of the greenhouse gases that influence the environment across the world. Discovering the alternative construction material with the eco-friendly process and the performance similar to or greater than ordinary Portland cement has been attractive to find out. This research presented green construction materials or so-called geopolymers from metakaolin substituted by high calcium fly ash by 20, 40, 60, 80 and 100 wt%. Some researches reported that geopolymer produced from metakaolin and fly ash with alkali solution gave a great result, but usually, they used fly ash containing very low calcium component. Compressive strength at 3, 7 and 28 curing days and flowability were conducted. The compressive strength of geopolymers blended with high calcium fly ash was still developed as the curing day increased and revealed the highest at 28 days especially on MK40 (high calcium fly ash 60 wt%). Geopolymer pastes prepared with a higher amount of high calcium fly ash exhibited less viscous. It was proved that the high amount of high calcium fly ash could be applied and gave extraordinary compressive strength. Furthermore, X-ray diffraction and X-ray fluorescence were used to investigate chemical properties as well as microstructure by a scanning electron microscope. For phase analysis, the existence of oxides of calcium and sulfur in high calcium fly ash resulted in the formation of thenardite, calcite, portlandite and C-S-H phase associating with geopolymeric phase. Therefore, this research proposed the opportunity for geopolymer production by using abundant high calcium fly ash to raise the value of the industrial waste products and green alternative construction material compared with OPC.

Diatomite, a natural adsorbent rich in active silica, serves as a valuable precursor for geopolymer synthesis. The safe disposal of diatomite as a failed lead (Pb(II)) adsorbent is critical to prevent secondary contamination. This study investigated the immobilisation efficiency of geopolymerisation for Pb(II)-rich diatomite sludge. Low-grade diatomite with high ignition loss was utilised in the synthesis of alkali-activated geopolymers. It was demonstrated that the geopolymers achieved a compressive strength of 28.3 MPa with a 50% replacement rate of metakaolin by diatomite sludge, which was not a compromise in strength compared to that of the geopolymer with no Pb(II) (26.2 MPa). The leaching behaviour of Pb(II) was evaluated using water and acetic acid, yielding concentrations below 3 mg/L and immobilisation efficiencies of 95% in both scenarios. Analytical techniques including Fourier transform infrared spectroscopy (FTIR), X-ray diffraction (XRD), and scanning electron microscopy (SEM) elucidated the mineral composition and chemical environment of the geopolymers. These analyses revealed that Pb(II) migrated from diatomite pores, potentially forming soluble hydroxides under sufficient hydroxide, which then participated in condensation with silicon and aluminium monomers, effectively immobilising Pb(II) within amorphous aluminosilicate gels. Furthermore, the formation of the amorphous gels within diatomite pores hindered Pb(II) leaching, encapsulating Pb(II) effectively. This study presents a novel approach to immobilising heavy metals within building materials, enhancing mineral resource utilisation efficiency while addressing environmental contamination concerns.