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Present concerns about global warming due to the greenhouse emissions in the atmosphere have pushed the cement industry to research alternatives to ordinary Portland cement (OPC). Geopolymer binder may constitute a possible breakthrough in the development of sustainable materials: understanding the effectiveness and the influences of superplasticizers on geopolymer systems is one of the essential requirements for its large-scale implementation. This study aims to investigate the possibility of using commercially available chemical admixtures designed for OPC concrete, to improve fresh properties of fly ash-based geopolymers and mortars. A special emphasis is laid upon evaluating their influence on mechanical and microstructural characteristics of the hardened material realized under room-temperature curing conditions. Results indicate that the addition of a polycarboxylic ether-based superplasticizer, in the amount of 1.0 wt. % by mass of fly ash, promotes an improvement in workability without compromising the final strength of the hardened material. Moreover, the addition of the polycarboxylic ether- and acrylic-based superplasticizers induces a refinement in the pore structure of hardened mortar leading to a longer water saturation time. [ABSTRACT FROM AUTHOR]

Alkali activation of fly ash can be considered as one of the more promising alternative systems to traditional hydraulic binders, particularly if the process can be carried out at room temperature. With the aim of finding the best solution chemistry for room temperature activation, two types of fly ash have been activated using Na 2 O/SiO 2 molar ratio ranging from 0.12 to 0.20. It was found that the behaviour of the resultant geopolymer and mortars in the fresh and hardened state is more influenced by the type of fly ash, in particular by their fineness and mineralogical composition, than by the increasing proportion of sodium silicate solution in the mix. [ABSTRACT FROM AUTHOR]

This study investigated the potential application of geopolymeric material for the separation of oil-in-water emulsions in wastewater treatment. For the first time, an asymmetric membrane made of geopolymers was developed for this specific separation process. The performances of the geopolymeric membrane in oil separation were compared with those obtained by a commercial ceramic membrane. The study also aimed at exploring the effects of emulsion formulation and emulsion properties (surfactant type and concentration, pH, and zeta potential) and membrane parameters (surface charge and material) on permeate volumetric flux and chemical oxygen demand (COD) rejection. Emulsions were prepared using 3% (w/v) dodecane oil in distilled water, with surfactant concentrations of 1x and 10x critical micelle concentration (CMC) and three surfactants of different nature (Oleth-10, Brij 76, and CTAB) at pH values of 2, 5, and 8. Results showed that for the best operating conditions of the geopolymeric membrane, initial and final permeate flux values of 42 and 26 L h−1 m−2, respectively, were achieved. COD rejection values ranged from 95.0 to 99.4% using the geopolymeric membrane thus indicating a very similar behavior between geopolymeric and ceramic membranes. These findings suggest that geopolymers are promising to produce membranes for oil-in-water emulsion microfiltration, promoting an interesting alternative for the treatment of industrial wastewater more sustainable in terms of environmental effects and costs compared to ceramic membranes. • Novel geopolymeric asymmetric membrane was synthetized. • Geopolymer selective layer was successfully deposited on pressed geopolymer support. • The geopolymeric membrane showed excellent fluxes and removal efficiencies. • Flux and rejection properties vary with surfactant concentration and emulsion pH. • Geopolymer membrane performs similarly to a commercial microfiltration ceramic one. [ABSTRACT FROM AUTHOR]

This study reports on the possibility of applying one-part pressed geopolymers as a support for microfiltration membranes. The mineralogical, physical, mechanical, microstructural and hydraulic properties of the investigated materials are presented. Metakaolin-based geopolymeric membrane flat supports were synthesized by uniaxial pressing a dry-mixed powder (Si/Al = 1.45, Na/Al = 0.9, Na/Si = 0.62, H 2 O = 12%), with pressure between 2 and 20 MPa and a curing temperature of 70 °C. Mixing and pressing optimization resulted in samples with a total open porosity up to 39%, a modal pore diameter up to 23.5 μm and a flexural strength up to 20.4 MPa. Permeation measurement with demineralized water and ethanol-water solutions were carried out using a dead-end geometry membrane apparatus. A hydraulic permeability up to 31.3 · 103 L h−1 m−2 bar−1 has been obtained. Furthermore, permeation tests using water-ethanol solutions have demonstrated that the material is hydrophilic. These results highlighted the potential of geopolymers as microfiltration support. • Pressed one-part geopolymers are suitable to be used as membrane supports. • Geopolymer membrane supports possess a peculiar threshold pressure. • Geopolymer supports have similar characteristics to ceramic membrane supports. [ABSTRACT FROM AUTHOR]

Graphical abstract Highlights • Fly ash was successfully alkali activated at room temperature. • The use of expanded perlite and H 2 O 2 allowed obtaining lightweight mortars. • Numerical simulations predicted a satisfactory fire behaviour. • Alkali activated lightweight mortars were able to outperform cement-based ones. Abstract Alkali activated lightweight mortars, obtained by room temperature activation of coal fly ash, were studied as passive fire protection systems for steel elements. Physical, mechanical and thermal properties were investigated as a function of the compositional Si/Al molar ratio and of the amount of lightweight aggregate and foaming agent. Experimental findings were used as input data to assess their fire resistance by finite volume simulations. Results pointed out that the optimized alkali activated lightweight mortars are able to outperform alternative commercial cement-based mortars, thus representing a promising technology. [ABSTRACT FROM AUTHOR]

Steel fiber reinforced geopolymer matrix (S-FRGM) composites are explored as a new tool in strengthening applications of reinforced concrete (RC) structures. The suitability of fly ash geopolymers as the matrix employed in S-FRGMs is investigated in this paper. Geopolymer matrix is used to embed galvanized steel fibers and bond the composite to a concrete substrate. By varying the molar concentration of the NaOH activating solution, three different geopolymer matrices are obtained and the influence of the alkaline environment on the bond behavior between fibers and matrix is examined. Physical, mechanical, and microstructural properties of the three matrices are measured and related to the interfacial bond behavior of S-FRGM-concrete joints. Results show that the decrease of the molar concentration of the NaOH activating solution leads to an increase of the interfacial bond behavior between matrix and fibers, which in turn improves the effectiveness of the composite action of the strengthening system. [ABSTRACT FROM AUTHOR]