Phase and dimensional stability of volcanic ash-based phosphate inorganic polymers at elevated temperatures

Effect of Water-Soluble Polymers on the Rheology and Microstructure of Polymer-Modified Geopolymer Glass-Ceramics

This work explores the effects of rigid (0.1, 0.25, and 0.5 wt. %) and semi-flexible (0.5, 1.0, and 2.5 wt. %) all-aromatic polyelectrolyte reinforcements as rheological and morphological modifiers for preparing phosphate geopolymer glass-ceramic composites. Polymer-modified aluminosilicate-phosphate geopolymer resins were prepared by high-shear mixing of a metakaolin powder with 9M phosphoric acid and two all-aromatic, sulfonated polyamides. Polymer loadings between 0.5-2.5 wt. % exhibited gel-like behavior and an increase in the modulus of the geopolymer resin as a function of polymer concentration. The incorporation of a 0.5 wt. % rigid polymer resulted in a three-fold increase in viscosity relative to the control phosphate geopolymer resin. Hardening, dehydration, and crystallization of the geopolymer resins to glass-ceramics was achieved through mold casting, curing at 80 °C for 24 h, and a final heat treatment up to 260 °C. Scanning electron microscopy revealed a decrease in microstructure porosity in the range of 0.78 μm to 0.31 μm for geopolymer plaques containing loadings of 0.5 wt. % rigid polymer. Nano-porosity values of the composites were measured between 10-40 nm using nitrogen adsorption (Brunauer-Emmett-Teller method) and transmission electron microscopy. Nanoindentation studies revealed geopolymer composites with Young's modulus values of 15-24 GPa and hardness values of 1-2 GPa, suggesting an increase in modulus and hardness with polymer incorporation. Additional structural and chemical analyses were performed via thermal gravimetric analysis, Fourier transform infrared radiation, X-ray diffraction, and energy dispersive spectroscopy. This work provides a fundamental understanding of the processing, microstructure, and mechanical behavior of water-soluble, high-performance polyelectrolyte-reinforced geopolymer composites.

The role of curing temperature and reactive aluminum species on characteristics of phosphate geopolymer

The reaction of an acid phosphate with ferro/aluminosilicate materials is a slow-setting process at room temperature that requires several days to harden. Thus, various setting accelerators are generally used to achieve quick setting and demolding in a short period. This work aims to evaluate the benefits of phosphoric acid-containing soluble aluminum and heat curing on accelerating the reaction kinetic and strength development of phosphate geopolymers. The diluted phosphoric acid (PA, 50 wt%) and acid aluminum phosphate (PA, 50 wt%, Al/P = 1/3) solutions were prepared to activate volcanic ash, and the samples were cured at 20, 40, and 60 °C to produce the phosphate geopolymer binder. The phosphate geopolymer's reaction kinetics, mechanical properties, mineralogy, and microstructure were evaluated. The results revealed that when volcanic ash was activated with diluted phosphoric acid, the reaction mechanism that prevailed was the dissolution-enhancement-precipitation-condensation, and was also fostered when the heat curing was applied. While for the acid aluminum phosphate-activated volcanic ash, the mechanism is dissolution-inhibition-precipitation-condensation. That difference in reaction mechanism led to a higher compressive strength improvement at an early age (1 d, 3 d) for room temperature cured acid aluminum phosphate activated volcanic ash. In contrast, phosphoric acid-activated volcanic ash phosphate geopolymer developed a higher compressive strength at a late age (28 d). Moreover, heat curing is the most crucial parameter having a beneficial effect on compressive strength development as compared to acid aluminum phosphate activating solution.

Feasibilty of valorizing quarry wastes in the synthesis of geopolymer binders: engineering performances and microstructure

The exploitation of volcanic rock quarries generates enormous waste, which causes the problem of disposal, leading to rising dust levels in quarries and depositions on nearby farms by runoffs. To address this issue, the development of sustainable solution for their valorization in construction industries is required. The present investigation aims to valorize granite (GW) and basalt (BW) quarry waste powders as partial replacement (up to 20 wt.%) of iron-rich aluminosilicates in the synthesis of geopolymer binders. Both synthesized series of samples were sealed and cured at 7, 14, and 28 days at room temperature before subjecting to various analytical techniques, including the mechanical properties, XRD, FT-IR, TG/DTG, and SEM-EDS. The results showed that both GW and BW powders are efficient to produce sufficient amounts of geopolymer binder, with ensure good cohesion and connectivity between different components within the final matrices. The values of compressive strength were 7.5-35.9 MPa and 6.2-39.7 MPa for laterite/granite and laterite/basalt geopolymer composites, denoted LGA and LBA, respectively. Moreover, the coexistence of the amorphous Na-aluminosilicate, Ca-aluminosilicate, and Na-polyferrosialate species is responsible for the mechanical properties development of the end-products. Based on the findings, the selected quarry wastes appeared to be sustainable and cost-effective materials for the synthesis of low-energy consumption binder, suitable for the production of construction materials.

Preparation of acid aluminum phosphate solutions for metakaolin phosphate geopolymer binder

This work assessed the potential of synthetic acid aluminum phosphate solutions for the enhancement of the characteristics of metakaolin phosphate geopolymer binders obtained at room temperature. The main parameters dealt with are the concentration of the initial phosphoric acid solution (40 wt%, 50 wt%, and 60 wt%) and the molar ratio Al/P (1/3 and 1.4/3) of the synthesized acid aluminum phosphate solutions. The prepared solutions have different contents and types of mono aluminum phosphate compounds (MAP) and their reactivity is pH-dependent. This is because of the continuous neutralization of the protons due to the dissolution of aluminum hydroxide, which raises the pH and decreases the conductivity. Thus the acid aluminum phosphate solutions with molar ratio Al/P of 1/3 are the most reactive. They have significantly enhanced the compressive strength of the resulting phosphate geopolymer binders. But, when compared to phosphate geopolymer obtained with pure phosphoric acid of the same concentration, the highest rate of compressive strength improvement is recorded for acid aluminum phosphate solutions having an initial concentration of phosphoric acid of 40 wt%. Thus, the modification of the composition of the phosphoric acid with the addition of the appropriate amount of aluminum is beneficial for enhancing the characteristics of phosphate geopolymer binder at any age.