Silico-Aluminophosphate and Alkali-Aluminosilicate Geopolymers: A Comparative Review

Abstract

Chemically activated materials (often termed as geopolymer) have received attracting attentions in civil, material and environmental research fields as a toolkit alternative to traditional Portland cement in specific applications. This paper presents a comparative review on silico-aluminophosphate (SAP) geopolymers in terms of definition, chemistries involved during geopolymerization, mechanical performance, durability, environmental impacts, and their potentials in applications relative to conventional alkali-aluminosilicate (AAS) geopolymers. Recommendations for future applications are also highlighted. It is found that S-A-P gels with six-coordinated aluminum environment dominate in SAP geopolymers, while the aluminum in N-A-S-H gels formed in the AAS geopolymers is characterized by four-coordinated features. Besides, the slow performance development of SAP geopolymer matrix under ambient temperature curing can be compensated through incorporating additional countermeasures (e.g., metal sources) which allow the tailored design of such geopolymers for certain in-situ applications. Generally, the calcium-bearing C-(A)-S-H gels co-existing with N-A-S-H gels are dominant in AAS geopolymers, while the S-A-P gels enhanced by phosphate-containing crystalline/amorphous phases are the main products in SAP geopolymers. The SAP geopolymers show their environmental friendliness relative to the AAS geopolymers due to the utilization of phosphate activators that require lower production energy relative to silicate-containing activators. However, the higher cost of phosphate activators may confine the applications of SAP geopolymers in some exquisite or special fields.

Effects of activator properties and GGBFS/FA ratio on the structural build-up and rheology of AAC

“…The peaks, observed during the rapid increasing structural build-up stage, might also be related to the condensation stage. Because, in the condensation stage, a large amount of water is released by the condensation of Si(OH) 4 species [65,66]. Therefore, this extra water probably increased the loss factor and also revealed more liquid-like behavior of the pastes in this stage.…”

The impact of the curing process on the efflorescence and mechanical properties of basalt fibre reinforced fly ash-based geopolymer composites

“…Another possibility for avoiding efflorescence is surface modification [22,23]. If the surface of the geopolymer becomes hydrophobic, the leaching of water-soluble alkali ions is significantly reduced.…”

Protective Geopolymer Coatings Containing Multi-Componential Precursors: Preparation and Basic Properties Characterization

“…Mechanical strength of geopolymer presented in the literature varied widely because of the specific attributes of constitute materials, methods of preparation and exposed conditions [ 51 ]. However, there is very limited research that has been performed on comprehensive evaluation of the influencing parameters.…”

“…The strength reduction of the seawater-immersed specimens could be attributed to dilution of excessive water rather than the corrosion of seawater. Water reservoir also inhibited the polycondensation to some extent [ 36 , 51 ]. Due to excellent impermeability of the GPC, the dilution effect was limited to the surface layer.…”