Application Of Geopolymer Research Articles

Inhibition of Efflorescence in Na-Based Geopolymer Inorganic Coating.

Coating is one of the most important high-value-added application cases in geopolymer materials. However, efflorescence can easily cause discoloration and reduce the esthetic impression of the coating surface, thus limiting its application; hence, inhibition of efflorescence is one of the most important techniques in the application of geopolymer coatings. Efflorescence is a spontaneous behavior in a Na-based geopolymer, involving the migration of soluble alkalis. Alkalis are dissolved by water and diffuse to the material surface through nocuous pores, and then react with CO2 to produce white carbonate products. To inhibit efflorescence in geopolymer coating, this article reports a structure modification method using polydimethy siloxane (PS) and mica. To explore the inhibition mechanism, the effects of PS and mica on the pore structure, water absorption, alkali leaching, and efflorescence product were investigated. The experimental results showed that a harmful pore structure and instinctive water absorption of the geopolymer strongly contributed to efflorescence. PS and mica could reduce the pore size distribution and porosity and are helpful to establish a waterproof structure, leading to water absorption and the alkali leaching rate being significantly suppressed. Both high water glass and water content play a critical role in the increase of efflorescence, but even under a high content of water glass and water used in geopolymer coating, this method shows an 80–90% efflorescence reduction, which is much higher than that of other studies. In practical engineering, when the geopolymer coating is applied after modification, even if it is exposed to the field environment for a long time, there is no efflorescence deposit on the coating surface. It is feasible to limit water ingression in a geopolymer, which effectively blocks the efflorescence reaction process. This method is simple and practical and can be applied in practical engineering applications of geopolymer coatings conveniently.

Effect of sodium sulfate on strength and microstructure of alkali-activated fly ash based geopolymer

The main objective of this paper focuses on the changes that occur in the strength and microstructural properties of sodium silicate activated fly ash based geopolymer due to varying the sulfate salt and water content. A series of tests including X-ray diffraction, Fourier transform infrared spectroscopy, scanning electron microscopy, physical adsorption and unconfined compressive strength were used to investigate this effect. The results indicate that the higher water content has an adverse effect on the alkali activation and microstructural properties of geopolymer, so the optimum mass ratio of sodium sulfate in alkali-activated geopolymer under different water-to-binder ratios shows a “peak shifting” phenomenon, i.e., the higher the water-to-binder ratio, the higher the optimum mass ratio. Lower presence of sodium sulfate has no significant effect on the alkali-activated geopolymer systems; higher addition of sodium sulfate, however, could cause the symmetrical stretching vibration of Si-O and the symmetrical stretching vibration of Si-O-Si and Al-O-Si, and promote the formation of N-A-S-H gels. Furthermore, the cement effect of the gel and sodium sulfate aggregate could improve the integrity of pore structure obviously. The maximum strength of geopolymer curing at ambient temperature was 52 MPa. This study obtains the rule that the strength properties of alkali-activated geopolymers vary with the water-to-binder ratio and sodium sulfate content. The feasibility of geopolymer co-activated by sodium sulfate and sodium silicate was investigated, and reference for engineering application of alkali-activated geopolymer in salt-bearing areas was provided.

Effects of wetting and drying on alkalinity and strength of fly ash/slag-activated materials

The alkalinity of alkali-activated materials, so-called geopolymer (GP), is attributed to the alkali activator remained in the pores. For the application of GP in reinforced concrete as binder, it is necessary to investigate the alkalinity change of GP concrete in various environments. In this study, after GP concrete (GPC) and GP mortar (GPM) specimens, which used active fillers of fly ash (FA) and ground granulated blast furnace slag (GGBS), were stored in water, wet-dry repeating, accelerated carbonation (AC), and AC-dry repeating environments for a certain period, we observed the coloring reaction to the spraying phenophthalein indicator, measured pH values in different depths and the compressive strengths, and did micro-structure analysis by SEM. A comparison was also performed between GPM and Portland cement (PC) mortar specimens. It was found that, the alkalinity of GP mortar is much easier to decrease no matter in any of above environments, compared to PC mortar. Heat-cured GP has a higher alkali leaching resistance in the wet-dry repeating environment than ambient air-cured GP. Carbonation only decreases the alkalinity in the outer zone, but drying and wetting redistributes the alkalis and promotes the movement of internal alkalis to the outer zone even to the surface of GP, resulting in an alkalinity drop in both the outer zone and the inner zone. The AC-dry repeating causes a greater alkalinity drop than the wet-dry repeating. The AC results in a faster and greater alkalinity drop in the outer zone, compared to the water immersion. Carbonation and water immersion can raise GP’s strength, but intense drying causes cracks to harm the strength of GP.

A Clay-Based Geopolymer in Loess Soil Stabilization

Soil erosion has environmental and socioeconomic significances. Loess soils cover about 10% of the global land area. Most of these soils are subjected to increased land uses such as unpaved roads, which increase soil destruction and dust emission to the atmosphere. There is a significant interest in applications for dust control and soil stabilization. Application of geopolymers may significantly reduce environmental impacts. This study examines the use of a metakaolin-based geopolymer for dust control and soil stabilization in a semi-arid loess soil. The application of the geopolymer for dust control in comparison with common products (brine, bitumen, polyvinyl acetate-PVA) resulted in no dust emission. As a soil stabilizer, the geopolymer tested in this study provides remarkably good results in the tensile test. The most successful composition of the geopolymer, which is activation solution of sodium silicate and sodium hydroxide (NaOH) together with an addition of 30% metakaolin, obtained soil strength of 23,900 N after 28 days. The attempt to replace NaOH with lime (CaO) in the activation solution was far inferior to the original composition. There is a strong potential to develop natural soil stabilizers from a mineral base that even surpass their capabilities over existing synthetic stabilizers.

Influence of curing age on high-temperature properties of additive manufactured geopolymer mortar

Some researches have been conducted on the application of geopolymer in 3D printing. However, there is no publication about the high-temperature properties of 3D printed geopolymer made from fly ash, slag, and metakaolin. This paper presents the experimental research on the mechanical properties of 3D printed geopolymer after being exposed to elevated empratures. The effects of curing age on high-temperature properties are analyzed. The heating temperasures were 300 °C, 600 °C, and 900 °C, and the holding time was one hour. After exposure to temperatures, the flexural strength of 3D printed geopolymer exhibited different change trends with increasing curing age for different exposure temperatures. Before and after exposure to elevated temperature, the 3D printed geopolymer experienced significant anisotropic compressive strengths. The change trends of compressive strength at different exposure temperatures wit hincreasing curing ages were different from each other on different loading directions.

Feasibility Study on Fabrication of Geopolymer Bricks by Wasted Grinding Wheel at Room Temperature

In this study, the feasibility of producing eco-friendly bricks by using geopolymer technology and a waste grinding wheel (WGW) from the grinding wheel industries was investigated. Nowadays, in order to meet industrial needs, for instance, in Taiwan, approximately 500,000 grinding wheels are used annually. That is, a large number of “waste” grinding wheels are produced. Furthermore, few studies have been conducted on the use of WGWs as raw materials in geopolymer applications. The use of geopolymer technology to form bricks can avoid the utilization of clay and cement and even prevent the use of a high-temperature process in kilns. Moreover, it can decrease CO2 emission and energy consumption and thus, protect the environment. In this study, the following three major factors were considered: press-forming pressure (70 and 100 kgf/cm2 ), NaOH molar concentration (2 and 4M), and the ratio of binder fineaggregate (1:3, 1:4, and 1:5). Under these conditions, the specimens were tested using the compressive strength test, water absorption test, microstructure analysis, a freezing–thawing test and toxicity characteristic leaching procedure test. The optimal formulation was composed of 1:4 binder fine-aggregate ratio, 4M NaOH concentration, and 100-kgf/cm2 pressure. Furthermore, we used a WGW and achieved a compressive strength of 50.6 MPa after 28 days, which was greater than 32 MPa and conformed to the Grade A brick standard of National Standards of the Republic of China (13295). In conclusion, this brick fabrication method based on geopolymer technology was not only beneficial to the environment but also improved the efficiency of reutilizing WGW.

Thermal Properties of Geopolymers with Silica Fume

Fly ash-based geopolymer is a renewable technology to minimize the use of cement in the construction field. The development was not only the use of fly ash but also the addition of other materials such as silica fume to geopolymer paste. Insulating materials is one of the examples of fly ash-based geopolymer applications. This paper examines the influence of varied activating solution of fly ash ratio and silica fume on the behavior of thermal properties of the geopolymer paste. The activating solution of fly ash ratio (A/F) was 40%, 45%, and 50%. Silica fume acts as a substitution of fly ash varied from 1%, 2%, and 4%. The activating solution was mixed with NaOH 10 M and Na2SiO3 with Na2SiO3/NaOH ratio constant at 2. Geopolymer paste was subjected to different tests such as thermal conductivity, bulk density, and compressive strength. The results showed that the geopolymer paste with substitution of silica fume had thermal conductivity, bulk density and compressive strength in the range of 0.051 to 0.932 W/m.C, 1752.457 to 1870.309 kg/m3 and 25.41 to 38.48 MPa respectively. The thermal conductivity values for all variations are below 1 W/m.C. Results from this work shows that the mixture suitable as a thermal insulation material.

Evaluating Fly Ash‐Based Geopolymers as a Modifier for Asphalt Binders

Severe Canadian winter conditions and growing traffic volumes are vital factors resulting in a reduction of the service life of flexible pavements. Researchers and engineers strived to develop several additives to develop balanced asphalt mixers capable of resisting distresses that caused deterioration of flexible pavements in Canada. In this study, a critical literature review regarding the use of geopolymers and their application in construction materials is provided. Moreover, an experimental matrix of laboratory testing was conducted to study the rheological and microstructural properties of the PG 58‐28 asphalt binder, with different percentages (0%, 3%, 6%, and 9%) of geopolymer. The effect of geopolymer‐curing time on rheological properties was investigated. Rotational viscometer, dynamic shear rheometer (DSR), and environmental scanning electron microscopy (ESEM) imaging devices were used to compare the performance of control binder with a binder with different percentages of geopolymers. Results indicated that the increase in the geopolymer content and the curing time affect the rheological behavior of the asphalt binder by increasing its viscosity, complex shear modulus, and failure temperature. Samples with higher geopolymer percentage exhibited better performance in terms of rutting resistance. Moreover, an increase in the failure temperature of modified asphalt binder with 9% geopolymer is recorded as 8.58%, 14.2%, and 15.2% for curing times of 2, 7, and 14 days, respectively, compared with virgin asphalt. Furthermore, the nanoparticles appear to be well dispersed in the binder, and increasing the percentage of the geopolymer does not seem to affect the microstructure of the binder. Overall research conclusion is that geopolymer application resulted in a potential enhancement of some of the properties of the asphalt binder.

Immobilization mechanism of Se oxyanions in geopolymer: Effects of alkaline activators and calcined hydrotalcite additive

Geopolymers have been widely adopted to stabilize the cationic pollutants. However, few studies have focused on the immobilization of anionic species. In this study, the immobilization of SeO32– and SeO42– was explored for the first time using geopolymer activated by different alkaline solutions (NaOH and Na2SiO3) with and without calcined hydrotalcite (CHT), characterized by TCLP, XRD, FTIR, TG, NMR, XAFS, and N2 adsorption-desorption isotherm. Na2SiO3-activated geopolymers without CHT additive showed lower leaching percentages of SeO32– and SeO42– (approximately 10 % and 18 %) than NaOH-activated geopolymers (approximately 58 % and 74 %). It has been proven that electrostatic interaction is the main association mode of SeO32– and SeO42– in both NaOH- and Na2SiO3-activated geopolymers. Hence, compactness plays a vital role in the Se leaching from geopolymer. The addition of CHT reduced the compactnesses of both NaOH- and Na2SiO3-geopolymers. Due to the formation of hydrotalcite, the CHT additive contributed to immobilize SeO32– and SeO42– in NaOH-activated geopolymers. However, this phenomenon was not observed in Na2SiO3-activated geopolymers. Thus, the leaching amount of Se greatly increased from Na2SiO3-activated geopolymers with CHT additive. This study provides new insights on the application of geopolymer to immobilize anionic pollutants.

Application of Geopolymers Modified with Chitosan as Novel Composites for Efficient Removal of Hg(II), Cd(II), and Pb(II) Ions from Aqueous Media

In the present paper, two amorphous aluminum silicates (i.e. geopolymers) were synthesized via the interaction of 23.57 mmol of sodium metasilicate pentahydrate with 5.18 or 10.35 mmol of aluminum chloride hexahydrate. The synthesized geopolymers using 5.18 and 10.35 mmol of aluminum chloride hexahydrate were abbreviated as G1.25 and G2.50, respectively. Also, the synthesized geopolymers were modified with chitosan as novel composites. The synthesized composites using G1.25 and G2.50 were abbreviated as G1.25/Ch and G2.50/Ch, respectively. Besides, the synthesized geopolymers and their chitosan composites were characterized using different tools such as XRD, FT-IR, SEM, and EDX. Moreover, the synthesized geopolymers and their chitosan composites were utilized as efficient adsorbents for the removal of Hg(II), Cd(II), and Pb(II) ions from aqueous media. The Langmuir isotherm and pseudo-first-order kinetic model were more consistent with the removal of metal ions from aqueous media. Furthermore, the adsorption processes were spontaneous, exothermic, and chemisorption. In the case of Hg(II), the maximum adsorption capacity of G1.25, G2.50, G1.25/Ch, and G2.50/Ch were 131.93, 140.85, 166.67, and 173.91 mg/g, respectively. In the case of Cd(II), the maximum adsorption capacity of G1.25, G2.50, G1.25/Ch, and G2.50/Ch were 118.34, 134.95, 159.49, and 166.11 mg/g, respectively. In the case of Pb(II), the maximum adsorption capacity of G1.25, G2.50, G1.25/Ch, and G2.50/Ch were 102.15, 118.91, 128.21, and 156.01 mg/g, respectively.

Synthesis and characterization of fly ash and slag based geopolymer concrete

This paper presents the formulation and characterization of composite fly ash and slag based geopolymer concrete. Potassium hydroxide (KOH) and potassium silicate (K2SiO3) liquid alkaline activators were used in the preparation of the geopolymer concrete. The mechanical response of the best recipe was investigated through compressive, tensile and flexural strength tests after 3, 7 and 28 days of curing. One batch was tested for compressive strength after 16 and 32 weeks of curing. The microstructure of the concretes was characterized using scanning electron microscopy (SEM). The testing results are compared with a reference ordinary portland cement-based concrete. After 28 days of curing, test results showed that the geopolymer concretes can approach the compressive strength of the reference ordinary concrete. Moreover, the tensile strength and flexural strength attained reached up to 68% and 80% of the reference cement, respectively. The results indicated the potential application of geopolymer that can satisfy the standard strength requirement. After longer time of curing, 32 weeks, some of the geopolymer preparations exhibited 111% compressive strength, compared to the ordinary cement reference.

Effects of Si/Al ratio on the efflorescence and properties of fly ash based geopolymer

Abstract Efflorescence seriously affects the practical application of geopolymer. In this study, fly ash based geopolymer was prepared by raw materials containing different Si/Al ratios. A test method of the efflorescence degree of geopolymer was proposed and applied. The effects of the Si/Al ratio on products, microstructure, pore structures, compressive strength, water loss rate and efflorescence of geopolymer were systematically investigated. The reaction products and structures of geopolymer were tested by XRD, FTIR, TG-DTA, SEM-EDS and BET. The results showed that the efflorescence degree of different samples can be compared by the test method simply, effectively and quantitatively. The products of geopolymer were mainly amorphous gels N(C)-A-S-H containing large amounts of Si and Al components. The structures, properties and efflorescence degree of the geopolymer were different due to the different Si/Al ratio. When the Si/Al ratio of geopolymer was 1.5, the content of [AlO4]- structures was highest, while the volume and size of pore were relatively small. The dense matrix and [AlO4]- structures of geopolymer can reduce the efflorescence degree significantly. This study can provide a reference for future investigation about efflorescence inhibition and efflorescence test methods of geopolymer.

Structural characterizations of fly ash-based geopolymer after adsorption of various metal ions

ABSTRACT Geopolymer, an amorphous substance, has been viewed as good adsorbent or catalyst and attracted much attentions from all over the world. In order to achieve the better applications of geopolymer in these fields, a deep understanding of the microstructure of geopolymer would be strongly required. In the present study, geopolymer was synthesized from coal fly ash, and the structural analysis of geopolymer after adsorption of various metal ions (Li+, Cs+, Sr2+ and Co2+) was studied using XRD, SEM-EDX, FTIR, UV-VIS DRS, TG-DTA as well as surface area and pore distribution analysis. Pair distribution function preferably illustrated that geopolymer was successfully prepared from calcined fly ash. Geopolymer possesses different affinities towards various metal ions. After exchanging with other metal ions, the main structure of geopolymer was maintained. Metal ions with a large radius would have greater effect on the existing state and amount of water molecules in geopolymer. Moreover, the specific surface area of geopolymer after exchanging with metal ions decreased as a function of the radius of them. The spectra corresponding to d-d transitions indicated that the Co2+ could be incorporated into the deformed six-member rings or eight-membered rings. It could be deduced that the sites for ion exchange could be different rings or even cavities distributed on the surface layer of geopolymer. Furthermore, the rings distributed in the geopolymer structure were predominant in the 6-, 8-, 10- or even 12-member rings to maintain the structure stability and charge balance with the cations.

A novel composite of layered double hydroxide/geopolymer for co-immobilization of Cs+ and SeO42− from aqueous solution

Geopolymers are always considered as promising materials for the treatment of radioactive wastes. In order to extend the application of geopolymer to the immobilization of anionic species, a novel composite of layered double hydroxide/geopolymer (LDH/GEO) was synthesized and applied for cosorption of Cs+ and SeO42−. The ability of LDH/GEO to sorb Cs+ was maintained as that of pure GEO, even though the surface of geopolymer was homogeneously covered by the LDH platelets. The sorption of Cs+ onto LDH/GEO composite occurred via ion exchange, which was controlled by particle diffusion. It is different with Cs+ sorption onto pure GEO governed by film diffusion. Therefore, “Pocket diffusion” was proposed for the particle diffusion as the case of LDH/GEO because this kind of diffusion would be restricted in a certain distance around the ring entrance gate due to the amorphous essence of GEO. For SeO42− sorption by LDH/GEO, ion-exchange with the interlayer NO3− and surface sorption could be the main mechanisms. Importantly, the sorption speed of SeO42− achieved by LDH/GEO composite was much faster than that by pure LDH. In the binary system (Cs++ SeO42−), the sorption of Cs+ was slightly suppressed compared to the single system, which might be due to the formation of ion-pair complex of [CsSeO4]−. However, it did not have negative effect on the SeO42− sorption. In the presence of other cations or anions, the cosorption performances of Cs+ and SeO42− were satisfactorily obtained. Furthermore, the Cs+ and SeO42- sorption densities were superior to the previously reported values. The combined MgAl-LDH/geopolymer composite could be a promising material for the immobilization of Cs+ and SeO42−, and this work would provide guidance for the development of geopolymer-based materials for environmental applications.

Microstructure and microhardness property of the interface between a metakaolin/GGBFS-based geopolymer paste and granite aggregate

The application of geopolymers as an alternative to Portland cement has received significant attention in concrete development due to the promotion of sustainability. Interfacial transition zone (ITZ) has been characterized as the weakest link in ordinary Portland cement concrete and usually deteriorates the mechanical properties and durability of concrete. To further understand the performance of geopolymeric concrete, the microstructure and properties of the interface zone in geopolymeric concrete are investigated in this study. Metakaolin and ground granulated blast-furnace slag (GGBFS) were used as the raw materials for geopolymer synthesis. Cubic splitting tests were conducted to investigate the interfacial bond strength between the geopolymer and the granite aggregate for different activator moduli and liquid/solid ratios. The morphology and mechanical properties of the ITZ between the geopolymer and granite aggregate were studied with the aids of scanning electron microscopy, energy-dispersive X-ray spectroscopy, and microhardness testing. The results indicate that the bond strength between the geopolymer and aggregate is higher than that between the cement paste and granite aggregate, and it decreases with the increase of the activator modulus and liquid/solid ratio. An ITZ was observed between the geopolymer paste and granite aggregate, and its microstructure and chemical components were different from those of the geopolymer. Obvious inhomogeneity can be observed for the ITZ along the aggregate body. The microhardness of the ITZ is lower than that of the geopolymer binder, and an increase in the activator modulus and liquid/solid ratio leads to an increase in the width of the crack in the ITZ and a decrease in the microhardness.

Preparation, Characterization, and Application of Metakaolin-Based Geopolymer for Removal of Methylene Blue from Aqueous Solution

Metakaolin-based geopolymers are aluminosilicate materials that can be used as cationic dye adsorbents in aqueous system treatment. Our aim in this paper is to study the ability of geopolymer powder produced from metakaolin and alkaline activators to act as an adsorbent to remove methylene blue (MB). The solid materials were systematically analyzed by X-ray fluorescence (XRF), X-ray diffraction (XRD), Fourier-transform infrared spectrometery (FTIR), scanning electron microscopy (SEM), energy dispersive X-ray analysis (EDX), and the point of zero charge. XRF, FTIR, XRD, SEM, and EDX analyses confirmed the formation of a geopolymer composite by geopolymerization reaction. The influence of various experimental factors such as geopolymer dosage, pH, initial dye concentration, contact time, and temperature was assessed. Adsorption isotherms were evaluated by Langmuir, Freundlich, Temkin, and Dubinin–Radushkevich isotherms. Kinetics data were studied using pseudo-first-order, pseudo-second-order, and intraparticle diffusion models. The thermodynamic parameters, namely, Gibbs free energy (ΔG°), enthalpy (ΔH°), and entropy (ΔS°), were determined. The results indicated that the maximum decolorization was found in high pH values. The collected isotherm data were best fitted by the Langmuir isotherm, and the maximum adsorption capacity of dye onto the geopolymer was 43.48 mg/g. The experiment kinetics followed the pseudo-second-order kinetic models. The thermodynamic results demonstrated that the adsorption of the obtained material occurs spontaneously as an endothermic process. The results confirmed that the prepared adsorbent can be used for remediation of water contaminated by MB dye.

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

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 state-of-the-art review on silico-aluminophosphate (SAP) geopolymers in terms of definition, chemistries involved during geopolymerization, mechanical and durability performance, environmental impacts, and their potentials in applications as compared 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, i.e., calcium-bearing C-(A)-S-H gels co-existed with N-A-S-H gels are dominant in AAS geopolymers, while S-A-P gels enhanced by phosphate-containing crystalline/amorphous phases are the main products in SAP geopolymers. Another advantage of SAP geopolymers is 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.

Lightweight Geopolymer Concrete Containing Recycled Plastic Beads

Utilizing recycled plastic beads (RPB) as lightweight waste aggregates in the concrete and geopolymer application is quite attractive. This study presented the mechanical behavior, density, porosity, water absorption, abrasion resistance, thermal conductivity, and ultrasonic pulse velocity (UPV) of geopolymer lightweight concrete containing RPB. River sand in each mixture was replaced by various proportions of RPB ranging between 0-100% by weight. Sodium hydroxide concentration of 15 M, activator solution to fly ash ratio (L/A) of 0.40, sodium silicate and sodium hydroxide ratio of 1.0, and aggregate to fly ash ratio of 1.0 were used throughout the experiment. The results indicated that the replacement of sand by 25% and 50% of RPB had a positive impact on the weight, density, water absorption, and thermal insulating property. The strength and density of the concretes met the minimum requirements of structural lightweight concrete according to ASTM C330.

Life cycle assessment of a geopolymer mixture for fireproofing applications

Alkali-activated materials, also known as geopolymers, are considered promising assets in the sustainable materials industry. Given the excellent properties in terms of thermal stability and low thermal conductivity, geopolymer-based matrices can effectively substitute cementitious binders in the preparation of passive fire protection (PFP) systems. The present study aims at evaluating the environmental footprint of a newly proposed geopolymer-based fireproofing material. The results are compared to a reference commercial lightweight cement-based coating with equal PFP performance. The boundaries of the system assessed were based on a cradle-to-grave life cycle. A preliminary scale-up of the laboratory protocol allowed the evaluation of the industrial production of the geopolymer-based PFP mix. An ancillary life cycle analysis was performed, comparing the environmental footprint of a geopolymer-based concrete block to the relevant literature studies for the same system in order to validate the approach of the present study. The functional unit of the main study was defined, taking into account the material performance in terms of resistance to heat exposure, allowing a functional comparison with lightweight cement-based PFP. The impact assessment phase used the CML-IA methodology as a characterization method. The ancillary LCA confirmed the alignment of the assumptions of the current study with previous analyses. The analyzed geopolymer-based fireproofing material exhibited a life cycle impact which is 27% lower than the lightweight concrete reference in terms of the global warming indicator, mainly thanks to the avoided CO2 emissions from the clinker process in cement manufacturing. Therefore, the greenhouse gas reduction described in previous studies on geopolymer application as a strong environmental advantage of the geopolymer technologies is also confirmed in this case. However, the other considered impact categories, such as resource depletion, acidification, eutrophication, and human toxicity, resulted in indicator values higher than the reference, as a consequence of the energy-intensive production process for the alkali activators (in particular, sodium silicate). Though the reduction of greenhouse gas emissions is confirmed, the overall sustainability of geopolymers for PFP applications is hindered by the relevant environmental footprint of the sodium silicate production process. However, a substantial reduction of the impacts could be achieved by selecting the production process of sodium silicate which takes advantage of renewable energy supplies (e.g., hydrothermal route) or by reducing the amount of sodium silicate in the geopolymer recipe in favor of waste-based alkali activators.

Method of Optimisation for Ambient Temperature Cured Sustainable Geopolymers for 3D Printing Construction Applications.

Since the initial introduction of geopolymers, these materials have been characterised as environmentally-friendly sustainable substitutes for ordinary Portland cement (OPC). There is a routine increase in the application of geopolymers, especially in advanced technologies. Because of its better rheological characteristics compared to OPC, geopolymers are appropriate materials for extrusion-based 3D printing technologies. This paper focuses on the optimisation of an ambient temperature cured geopolymer for 3D printing construction applications. The effects of mixture parameters, including the type of hydroxide solution (HS), the type of silicate solution (SS) and the mass ratio of SS to HS on the workability, extrudability, shape retention ability and mechanical performance of different geopolymer mixtures were investigated. Accordingly, an optimum mixture was identified for geopolymers cured at ambient temperatures. Mechanical properties of the optimised mixture, including flexural and compressive strengths, were measured in different directions with respect to the printed layers. Further, uniaxial tension tests were also conducted on the optimised mixture to measure its interlayer bond strength. The results showed that among the activators investigated, the sodium-based activator composed of sodium hydroxide and sodium silicate solutions, with a SiO2/Na2O ratio of 3.22, was the most effective activator, providing appropriate workability and extrudability, along with reasonable strength and a high shape retention ability. The acquired mechanical properties exhibited anisotropic behaviour in different testing direction. The strength of the interlayer bond was found to be adequate to avoid interfacial shear failure.