This study explores the innovative use of rubber sludge (RS) from glove manufacturing as a partial replacement for fly ash (FA) in geopolymer production. The research investigates the physical properties, functional group analysis, microstructural analysis, phase analysis and compressive strength. The partial replacement of different types of RS, such as activated sludge (AS), pre-leaching sludge (PLS) and coagulant sludge (CS), will affect differently on the geopolymer integrity and performance. CS enriched with high calcium content, facilitated the formation of a denser geopolymer matrix with C(N)-A-S-H gel in conjunction with C-S-H, C-A-S-H and N-A-S-H gels, enhancing the compressive strength of FA/CS geopolymers up to 70.4 MPa, surpassing FA/AS and FA/PLS geopolymers. The fly ash/rubber sludge geopolymers exhibited compressive strengths ranging from 20.5 to 70.4 MPa, not only meeting ASTM standards for construction but also effectively immobilizing hazardous metals, particularly Zn (>98.4 %), the Zn leaching in geopolymers was reduced by more than 87.4 % compared to the rubber sludge itself, thereby mitigating environmental toxicity. This utilization addresses significant industrial waste management issues, providing a cost-effective and environmentally friendly alternative for construction. The findings contribute to advancing sustainable building materials and advocate for equitable utilization of industrial waste resources.

This paper investigates the physico-mechanical and acoustic properties of fly ash geopolymers via casting and pressing methods. The existing research lacks comprehensive insight into the relationship between variations in geopolymer density and their impacts on both physico-mechanical properties and sound insulation and absorption capabilities. Geopolymers, as sustainable construction materials, are pivotal in mitigating noise and providing structural strength. To surpass these limitations and achieve either higher or lower densities in geopolymers, alternative approaches are necessary. Casting (non-foamed and foamed with 1.0, 2.0 and 3.0 foam-to-geopolymer paste ratio) and pressing methods were employed to produce a range of geopolymer densities between 1400 kg/m3 – 2200 kg/m3. The pressing method produced a highly dense geopolymer with an excellent compressive strength of 116 MPa. While the lightest geopolymer produced by adding a foaming agent had a compressive strength of 13 MPa. Good sound transmission loss (66.1 dB) was achieved by highly dense pressed geopolymers. Highly porous geopolymers achieved an excellent sound absorption coefficient of 0.79. The density variation and preparation methods greatly affected the pore size and distribution which subsequently affected the acoustical properties of the geopolymers. Manipulating the density and porosity of the geopolymers is essential for creating spaces with optimal acoustics to meet building codes and noise control regulations.

The commitment to promoting circular economy and durable construction materials has led to the advocacy for one-part geopolymer (OPG), as an eco-friendly substitute for traditional ordinary Portland cement (OPC). Solid alkali activator is the fundamental component of OPG and significantly influences the sulphate resistance. To identify the types of solid alkali activators best suited for the development of sulphate-resistant OPGs, OPGs activated with Na2SiO3 2 SiO 3 (M-OPG), Na2SiO3+Na2CO3 2 SiO 3 +Na 2 CO 3 (MC-OPG), Na2SiO3+NaOH 2 SiO 3 +NaOH (MH-OPG) and Na2SiO3+NaAlO2 2 SiO 3 +NaAlO 2 (MA-OPG) were exposed to 5 % and 10 % of MgSO4 4 solutions for 28 days. The fine pore structures of MH-OPG and MC-OPG mitigated deterioration from the more concentrated MgSO4 4 solution, resulting in higher residual compressive strengths after exposure to the 10 % MgSO4 4 compared to the 5 %. Exposure to the 5 % MgSO4 4 solution resulted in strength deterioration for M-OPG, MH-OPG and MC-OPG due to the discontinuity of the aluminosilicate structure, as evidenced by the diminished Q4(3Al) 4 (3Al) sites. Conversely, the MA-OPG exhibited a 24.1 % increase in compressive strength, accompanied by the emergence of sodium magnesium aluminium silicate hydrate ((N,M)-A-S-H) gel. Hence, Na2SiO3+NaAlO2 2 SiO 3 +NaAlO 2 should be acknowledged as the primary candidate for solid alkali activators in the development of sulphate-resistant OPGs.

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.

The flexibility of conductive polymer composites (CPCs) has become an area of interest, especially to the electronic industry for the application of interconnects. The incorporation of maleic anhydride-grafted polypropylene (MAPP) within polypropylene (PP)/ carbon black (CB) conductive polymer composites as a compatibiliser was essential in order to improve the interaction between conductive filler and polymer matrix. The PP/CB and PP/CB/MAPP (5 wt% MAPP) CPCs at various loading of CB were prepared using an internal mixer. The prepared composites were then hot pressed to form suitable size samples for characterisation and testing. It was found that the electrical conductivity of the composites was increased with increasing CB loadings due to formation of network path. Moreover, the electrical conductivity for CPCs with the additions of MAPP was further increased compared to without MAPP. The electrical conductivity of PP/CB/MAPP with 5 wt% of CB loading achieved 78.5 μS/cm by an increment of 6.4 % compared to PP/CB with 5 wt% of CB loading. However, increasing CB loading led to a decrease in tensile strength and elongation at break of PP/CB and PP/CB/MAPP composites. Nevertheless, additions of MAPP had improved the CPCs tensile strength. The addition of MAPP in 5 wt% of CB loading in CPC recorded a tensile strength of 25.93 MPa, an increased by 4.17 % compared to PP/CB composite. The optimum tensile and electrical properties obtained were at 5 wt% of CB loading in PP/CB/MAPP composite as it has higher tensile strength and achieved the percolation threshold. Furthermore, the thermal analysis carried out using differential scanning calorimetry (DSC) found that the crystallinity of PP was affected and the scanning electron microscopy (SEM) showed the distribution of CB particles within PP matrix that led to the changes observed in the mechanical properties and electrical conductivity of CPCs.

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.

Geopolymers are semi-crystalline inorganic materials with ceramic-like properties which possess good thermal properties. The analysis of the thermal properties of geopolymers through thermoanalysis and dilatometry shows several regions with a high thermal load. They are mainly divided into dehydration of free water, interstitial water, structural water, dehydroxylation, densification, and crystallization. The presence of different forms of water in the geopolymer sample governs the internal and external damage induced during the thermal exposure. The addition of additives such as silica fume and rice husk ash has a positive effect on the thermal stability of geopolymers. The use of different precursors in geopolymer formation affects the main backbone of the geopolymer materials and thus their thermal resistance. In most cases, geopolymer paste experiences thermal shrinkage, while geopolymer mortar and concrete expanse when heated. The incorporation of filler or aggregates with a low coefficient of thermal expansion reduces the thermal mismatch between the paste and aggregate. Thermal conductivity measurement provides information on the suitability of geopolymer as a thermal insulation material. Overall, geopolymer has high potential as a thermally insulated building material, considering its lower thermal conductivity value compared to ordinary construction materials. The composition of the geopolymers, moisture content, and pore distribution are the key factors affecting the thermal conductivity value. Foamed geopolymers, or the inclusion of porous fillers in geopolymers, help to further reduce the thermal conductivity of geopolymers. Thus, it is of great importance to properly tailor the mixing parameters and composition of geopolymers in order to achieve good thermal stability and thermal insulating properties.

Durability and sustainability is essential serviceability concern for alkali-activated composites used in construction. The incorporation of natural fibers in alkali-activated materials is beneficial considering its availability, low density, and acceptable mechanical performances. There are two types of natural fibers which are plant and animal fibers. The plant fiber composes of cellulose, hemicellulose, lignin, pectin, and waxy substances. The durability of natural fiber-reinforced alkali-activated composites influences by several factors including type and content of fiber, dispersion and size of fiber, fiber modification, fiber moisture content, fiber alkaline degradation, and fiber mineralization. Besides, this chapter indicates the durability of natural fiber-reinforced alkali-activated composites in terms of crack resistance and toughness, high-temperature resistance, wet/dry cycles, freeze-thaw cycles, chemical resistance, and carbonation resistance.