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This paper elucidates the influence of borax decahydrate addition on the flexural and thermal properties of 10 mm thin fly ash/ladle furnace slag (FAS) geopolymers. The borax decahydrate (2, 4, 6, and 8 wt.%) was incorporated to produce FAB geopolymers. Heat treatment was applied with temperature ranges of 300 °C, 600 °C, 900 °C, 1000 °C and 1100 °C. Unexposed FAB geopolymers experienced a drop in strength due to a looser matrix with higher porosity. However, borax decahydrate inclusion significantly enhanced the flexural performance of thin geopolymers after heating. FAB2 and FAB8 geopolymers reported higher flexural strength of 26.5 MPa and 47.8 MPa, respectively, at 1000 °C as compared to FAS geopolymers (24.1 MPa at 1100 °C). The molten B2O3 provided an adhesive medium to assemble the aluminosilicates, improving the interparticle connectivity which led to a drastic strength increment. Moreover, the borax addition reduced the glass transition temperature, forming more refractory crystalline phases at lower temperatures. This induced a significant strength increment in FAB geopolymers with a factor of 3.6 for FAB8 at 900 °C, and 4.0 factor for FAB2 at 1000 °C, respectively. Comparatively, FAS geopolymers only achieved 3.1 factor in strength increment at 1100 °C. This proved that borax decahydrate could be utilized in the high strength development of thin geopolymers. [ABSTRACT FROM AUTHOR]

The flexural properties and thermal performance of 10 mm-thin geopolymers made from fly ash and ladle furnace slag were evaluated before and after exposure to elevated temperatures (300 °C, 600 °C, 900 °C, 1100 °C and 1150 °C). Class F fly ash was mixed with liquid sodium silicate (Na 2 SiO 3) and 12 M sodium hydroxide (NaOH) solution using aluminosilicate/activator ratio of 1:2.5 and Na 2 SiO 3 /NaOH ratio of 1:4 to synthesise thin fly ash (FA) geopolymers. 40 wt% of ladle furnace slag was partially replacing fly ash to produce fly ash/slag-based (FAS) geopolymers. Thermal treatment enhanced the flexural strength of thin geopolymers. In comparison to the unexposed specimen, the flexural strength of FA geopolymers at 1150 °C and FAS geopolymers 1100 °C was increased by 161.3% to 16.2 MPa and 208.9% to 24.1 MPa, respectively. A more uniform heating was achieved in thin geopolymers which favoured the phase transformation at high temperatures and contributed to the substantial increase in flexural strength. The joint effect of elevated temperature exposure and the incorporation of ladle furnace slag further improved the flexural strength of thin geopolymers. The calcium-rich slag refined the pore structure and increased the crystallinity of thin geopolymers which aided in high strength development. [Display omitted] • Thermal treatment enhanced the flexural strength of 10-mm thin geopolymers. • FA geopolymers increased flexural strength by 161.3% to 16.2 MPa at 1150 °C. • FAS geopolymers increased flexural strength by 208.9% to 24.1 MPa at 1100 °C. • Uniform heating was achieved in thin geopolymers, aided the phase transformation. • Ca-rich LFS refined the pore structure and increased geopolymers' crystallinity. [ABSTRACT FROM AUTHOR]

This paper presents an innovative application of a one-part geopolymer for microwave absorption. The influences of frequency, ageing time and mixing formulations on the mechanical, dielectric, and microwave-absorbing performance of the one-part binary geopolymer using fly ash and ladle furnace slag were investigated. The mixing formulations included alkali activators-to-aluminosilicate sources, sodium metasilicate-to-sodium hydroxide, and water-to-binder ratios. The results demonstrated that the dielectric constant decreased while the dielectric loss and loss tangent increased and remained constant with increasing frequency. The geopolymers have the highest dielectric values at an early age and diminish with ageing time. These resulted in the geopolymers having excellent microwave absorption (50 – 80%) at high-frequency levels and later ages. A higher water content resulted in higher porosity, reducing mechanical strength but enhancing microwave absorption. An optimal water content must be attained to achieve dual mechanical strength and microwave absorption performance. • One-part binary geopolymer based on FA and LFS was synthesized. • Geopolymers show excellent microwave absorbing performance at higher frequency. • Microwave absorption of the geopolymers improved at later age. • Porosity creates path to attenuate the microwave energy. [ABSTRACT FROM AUTHOR]

[Display omitted] • The acid resistance of one-part geopolymers (OPGs) was studied. • Formation of hydrate gels during acid exposure led to a slight strength recovery. • High sorptivity made Na 2 SiO 3 and NaOH-based OPG more susceptible to acid attack. • The incorporation of NaAlO 2 and Na 2 CO 3 enhanced OPG's acid resistance. In this study, the durability of one-part geopolymers (OPGs) made from high calcium fly ash is assessed by investigating their resistance to acid attacks. The predominant use of less environmentally sustainable sodium metasilicate (Na 2 SiO 3) and sodium hydroxide (NaOH) in OPG, along with the limited understanding about the influence of solid alkali activators on OPG's acid resistance propelled the investigation and comparison of acid resistance of OPGs activated using both conventional activators and potential alternatives like sodium aluminate (NaAlO 2) and sodium carbonate (Na 2 CO 3). The OPGs developed were exposed to sulphuric acid (H 2 SO 4) solution for 28 days. The MH sample (activated with Na 2 SiO 3 and NaOH) was vulnerable to acid attack, with a 66% compressive strength drop after 5% H 2 SO 4 solution exposure, due to high sorptivity. In contrast, the MA sample (activated with Na 2 SiO 3 and NaAlO 2) demonstrated excellent acid resistance, with only a 32% strength reduction, attributed to its Al-rich hydrated gel. The MC sample (activated with Na 2 SiO 3 and Na 2 CO 3) exhibited a 41% strength reduction, where the formation of calcite reduced extensive ion exchange, gradually mitigated deterioration. The residual compressive strength of MA and MC samples increased by 7% and 9% from 7 to 28 days of immersion in 5% H 2 SO 4 solution, respectively. The NaAlO 2 and Na 2 CO 3 are potential activators for OPG, serving as alternative construction materials to OPC and traditional geopolymers in acidic environments. [ABSTRACT FROM AUTHOR]

[Display omitted] • A study of fly ash based pressed and cast geopolymer was proposed. • Compressive strength of pressed geopolymer nearly twice that of cast geopolymer. • Flexural strength of pressed geopolymer was 5 times higher than cast geopolymer. • The highly compacted pressed geopolymer reduced the tendency of efflorescence. • The low alkali activator of pressing method lowered EE, ECO 2 and ECI of geopolymer. The high liquid content of cast geopolymer not only limits its strength development and durability but also leads to high energy consumption and carbon dioxide (CO 2) emissions. Thus, a study of the cast and pressed geopolymer was performed. The geopolymers were cured for 1, 7 and 28 d before testing and characterizations. With the incorporation of pressure compaction, higher bulk density (2158–2227 kg/m3) was recorded for pressed geopolymer in comparison to cast geopolymer (1842–1854 kg/m3). The dense matrix in pressed geopolymer improved the inter-particle contact, increasing the 28 d degree of reaction to 39.7%, higher than that of cast geopolymer (33.0%). This feature was proved by SEM micrographs wherein the pressed geopolymer was well-compacted and denser in microstructure, with less unreacted/partially reacted fly ash and pores. The compressive and flexural strengths of pressed geopolymer reached 114.2 and 29.9 MPa after 28 d, higher than that of cast geopolymer (60.0 and 6.2 MPa, respectively). The strength reduction of pressed geopolymer (31.7%) after the accelerated efflorescence test was lower than that of cast geopolymer (60.2%). The ecological analysis inferred that pressed geopolymer was ecologically superior to the casting method in terms of embodied energy (EE) and embodied carbon dioxide emission (ECO 2), in which 50% and 59% of reductions are acquired. Besides, the embodied carbon index (ECI) of pressed geopolymer was about 21% of cast geopolymer. [ABSTRACT FROM AUTHOR]

This paper compared the thermal stability between fly ash (FA) and fly ash-ladle furnace slag (FA-LS) geopolymers. FA-LS geopolymer was prepared by mixing FA and LS (FA:LS weight ratio of 80:20) with an alkali activator. Geopolymers were aged at room temperature for 28 days before being exposed to high temperatures (200 °C – 1000 °C). Unexposed FA and FA-LS geopolymers had a compressive strength of 38.9 MPa and 40.5 MPa, respectively. The FA and FA-LS geopolymers retained 61.6% and 91.3% compressive strength, respectively, when exposed to temperatures up to 1000 °C. FA-LS geopolymers experienced smaller variation in the density (2.6 – 5.5%) and pores (17.4 – 23.0%) compared to FA geopolymers (density and porosity of 2.9 – 25.2% and 19.0 – 30.0%, respectively). The formation of crystalline peaks, densification of matrix, pores and their connectivity, cracks and dimensional changes influenced the compressive strength of exposed geopolymers. FA-LS geopolymers could be potentially applied as heat-resistance material. [ABSTRACT FROM AUTHOR]