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Environmental, Physical and Structural Characterisation of Geopolymer Matrixes Synthesised from Coal (Co-)Combustion Fly Ashes
Abstract
The synthesis of geopolymer matrixes from coal (co-)combustion fly ashes as the sole source of silica and alumina has been studied in order to assess both their capacity to immobilise the potentially toxic elements contained in these coal (co-)combustion by-products and their suitability to be used as cement replacements. The geopolymerisation process has been performed using (5, 8 and 12 M) NaOH solutions as activation media and different curing time (6-48 h) and temperature (40-80 degrees C) conditions. Synthesised geopolymers have been characterised with regard to their leaching behaviour, following the DIN 38414-S4 [DIN 38414-S4, Determination of leachability by water (S4), group S: sludge and sediments. German standard methods for the examination of water, waste water and sludge. Institut für Normung, Berlin, 1984] and NEN 7375 [NEN 7375, Leaching characteristics of moulded or monolithic building and waste materials. Determination of leaching of inorganic components with the diffusion test. Netherlands Normalisation Institute, Delft, 2004] procedures, and to their structural stability by means of compressive strength measurements. In addition, geopolymer mineralogy, morphology and structure have been studied by X-ray diffraction (XRD), scanning electron microscopy (SEM) and Fourier transform infrared spectroscopy (FTIR), respectively. It was found that synthesised geopolymer matrixes were only effective in the chemical immobilisation of a number of elements of environmental concern contained in fly ashes, reducing (especially for Ba), or maintaining their leachable contents after the geopolymerisation process, but not for those elements present as oxyanions. Physical entrapment does not seem either to contribute in an important way, in general, to the immobilisation of oxyanions. The structural stability of synthesised geopolymers was mainly dependent on the glass content of fly ashes, attaining at the optimal activation conditions (12 M NaOH, 48 h, 80 degrees C) compressive strength values about 60 MPa when the fly ash glass content was higher than 90%.
... XRD analysis of fly ash as a raw material presents crystalline phases such as mullite, quartz, and hematite. The glassy phase is also evident in fly ash [97][98][99]. After fly ash activation, the same crystalline phases before activation were detected (mullite, quartz, and hematite), as well as a new zeolitic crystalline phase known as chabazite. ...
... On the other hand, the degree of geopolymerization in the activated fly ash is directly related to the intensity of the amorphous silica peak around 30 • [98,99]. Table 5 shows the hydration gels found in the present study. ...
Concrete is the most used construction material, needing large quantities of Portland cement. Unfortunately, Ordinary Portland Cement production is one of the main generators of CO2, which pollutes the atmosphere. Today, geopolymers are an emerging building material generated by the chemical activity of inorganic molecules without the Portland Cement addition. The most common alternative cementitious agents used in the cement industry are blast-furnace slag and fly ash. In the present work, the effect of 5 wt.% µ-limestone in mixtures of granulated blast-furnace slag and fly ash activated with sodium hydroxide (NaOH) at different concentrations was studied to evaluate the physical properties in the fresh and hardened states. The effect of µ-limestone was explored through XRD, SEM-EDS, atomic absorption, etc. The addition of µ-limestone increased the compressive strength reported values from 20 to 45 MPa at 28 days. It was found by atomic absorption that the CaCO3 of the μ-limestone dissolved in NaOH, precipitating Ca(OH)2 as the reaction product. SEM-EDS analysis showed a chemical interaction between C-A-S-H- and N-A-S-H-type gels with Ca(OH)2, forming (N, C)A-S-H- and C-(N)-A-S-H-type gels, improving mechanical performance and microstructural properties. The addition of μ-limestone appeared like a promising and cheap alternative for enhancing the properties of low-molarity alkaline cement since it helped exceed the 20 MPa strength recommended by current regulations for conventional cement.
... As a result, the chemical environment of the Si-O bonds changes [15,2]. If the shift is bigger, it can be assumed that more AlO 4 tetrahedra are embedded in the SiO 4 basic structure than observed in similar analyses of zeolites [16][17][18][19]. This behaviour is explained based on the force constant, which is higher in Si-O than in Al-O bonds. ...
... Untersuchungen von Zeolithen beobachtet wurde [16][17][18][19]. Dieses Verhalten wird über die Kraftkonstante erklärt, die in Si-O-Bindungen höher als in Al-O-Bindungen ist. ...
In the presented work, the influence of increasing brick flour and concrete rubble additions on the setting behaviour and material properties of fly ash-based geopolymers is investigated. The ge-opolymers produced are tested for their compressive strengths, bulk densities and thermal conductivities, among other things. In order to be able to put the material-technical parameters in a meaningful relation to the setting behaviour and the structures that form, both the starting materials and the resulting binders are examined by means of infrared spectroscopy, X-ray diffrac-tion analysis and scanning electron microscopy. The investiga-tions showed that both broken bricks and concrete rubble are well suited as matrix-forming raw materials for geopolymer pro-duction. At the same time, different material properties could be determined and attributed to different setting and strength-forming mechanisms. (The influence of brick flour or concrete rubble on the mechanical properties of fly ash geopolymers was analysed in a first article in ZI 01/2023.)
... The results are presented in Figure 7. Raw and heated travertine is characterized by the presence of mainly stretching bonds, C=O, with wave numbers of 2981.34 cm −1 , 2874.16 cm −1 , and 1798.09 cm −1 , describing calcium carbonates, as well as calcite-wave numbers of 1426.80 cm −1 and 712.70 cm −1 [64][65][66][67][68]. This is confirmed by studies carried out so far on travertine, where it was found that the FT-IR spectrum on this material is a combination of absorption bands occurring for calcite and aragonite [69]. ...
... FT-IR spectrum before and after the sorption process of (a) raw travertine, (b) travertine heated at 700 °C, (c) raw marl, (d) marl heated at 1000 °C, and (e) Polonite ® .Raw marl (RM), heated marl (HM), and Polonite ® (P), in addition to the 1424.74 cm −1 (RM), 1420.10 cm −1 (HM), and 712.780 cm −1 (P) bands corresponding to the tensile bonds characteristic of calcite and carbonates[64][65][66][67][68], also have 875.23 cm −1 (RM), 474.85 cm −1 (HM), and 474.82 cm −1 (P) bands, describing the bonds of Si-O and O-Si-O ...
The paper presents new reactive materials, namely marl and travertine, and their thermal modifications and the Polonite® material, analyzing their phosphorus removal from water and wastewater by sorption. Based on the experimental data, an analysis of the factors influencing the sorption capacity of the materials, such as the material dose, pH of the initial solution, process temperature, surface structure, and morphology, was performed. Adsorption isotherms and maximum sorption capacities were determined with the use of the Langmuir, Freundlich, Langmuir–Freundlich, Tóth, Radke–Praunitz, and Marczewski–Jaroniec models. The kinetics of the phosphorus sorption process of the tested materials were described using reversible and irreversible pseudo-first order, pseudo-second order, and mixed models. The natural materials were the most sensitive to changes in the process conditions, such as temperature and pH. The thermal treatment process stabilizes the marl and travertine towards materials with a more homogeneous surface in terms of energy and structure. The fitted models of the adsorption isotherms and kinetic models allowed for an indication of a possible phosphorus-binding mechanism, as well as the maximum amount of this element that can be retained on the materials’ surface under given conditions—raw marl (43.89 mg P/g), raw travertine (140.48 mg P/g), heated marl (80.44 mg P/g), heated travertine (282.34 mg P/g), and Polonite® (54.33 mg P/g).
... İnşaat sektörü düşünüldüğünde, harç, beton ve çimento üretimi sırasında önemli oranda sera gazı ortaya çıkmaktadır. Çevresel zararları göz önüne alındığında, yan ürünlerin kullanımı ve toksik atıkların yapıya hapsedilmesiyle birlikte ısıya ve aşındırıcı çevre koşullarına dayanıklı malzemeler üreten geopolimerler, bu tür sorunlara alternatif çözümler sunabilir [7]. Geleneksel çimentoya göre geopolimer bağlayıcıların en önemli avantajlarından biri, daha az CO2 salınımının olmasıdır. ...
Türkiye'de seramik sektörü, ekonomik anlamda önemli bir paya sahip olup, ülkemiz seramik kaplama malzemeleri ve vitrifiye üretiminde lider konumdadır. Çanak-çömlek ürünleri seramik üretiminin bir başka kolunu oluşturmaktadır. Ancak, ilgili sektörde ıskartaya ayrılan hatalı ürünlerden kaynaklanan atıkların oluşması çevre kirliliği, depolama, tozlaşma sorunlarını beraberinde getirmekte ve atık üretim miktarı dikkate alındığında sektör atıklarının farklı alanlarda değerlendirilmesini zorunlu kılmaktadır. Bu çalışmada, seramik-karo fabrikası filtre-pres kek, vitrifiye ve çömlek atıklarının, farklı aktivatörlerle uçucu kül ile ve kül olmadan üretilen geopolimer harçların mekanik özellikleri incelenmiştir. Sıvı/bağlayıcı oranı 0.40 olan, NaOH ve Na2SiO3 içeren harç karışımları 24 saat boyunca 90ºC sıcaklıkta ısıl küre tabi tutulmuştur. Numunelere 7, 28 günlük eğilme ve basınç dayanımı deneyleri uygulanmıştır. Na2SiO3 ile üretilen harçların eğilme dayanımlarının NaOH ile üretilenlere göre daha yüksek olduğu, basınç dayanımlarında ise seramik atıklarının ikili ve uçucu küllü üçlü karışımlarının 30 MPa’dan yüksek değerlere ulaştığı belirlenmiştir. Çalışma seramik sektörü atıklarının geopolimer üretiminde başarıyla değerlendirilebileceğini ortaya koymaktadır.
... Furthermore, the asymmetric stretching band at approximately 1420 cm −1 was due to carbonates, which resulted from the reaction of alkali metal hydroxide with atmospheric CO 2 . 36,38,39 While the asymmetric stretching band of carbonates in the wavenumber range from 1400 to 1500 cm −1 disappeared in T900-1 and T1200-3, which could be caused by the thermal decomposition of carbonates. The reaction equations related to carbonates can be seen in eqn (4)- (6). ...
Chromite ore processing residue (COPR) is a hazardous waste because of leachable chromium, especially Cr(vi). Therefore, ascorbic acid (AA) and blast furnace slag (BFS) have been used to detoxify and solidify COPR. On this basis, environmental stability experiments with high temperature and freeze–thaw cycles were carried out to explore the stability performance of a solidified body with 40% COPR. The environmental stability performance was analyzed through changes in edge length, mass loss, compressive strength development, and leaching concentration of Cr(vi). The result indicated that the high-temperature environment had much more effect on the solidified body than the freeze–thaw cycle environment in these four aspects: after being maintained at 900 °C for 2 h, the compressive strength of the solidified bodies reached its minimum value (35.76 MPa). However, in the freeze–thaw cycle experiments, the compressive strength of the solidified bodies consistently remained above 80 MPa, and the leaching of hexavalent chromium was below the limit (5 mg L⁻¹). In addition, X-ray diffraction (XRD) and Fourier transform infrared spectrometry (FTIR) analysis verified that COPR was effectively solidified through physical and chemical means. Moreover, high temperature changes the molecular structure of the solidified body, thus reducing the compressive strength and curing ability of the solidified body, while the freeze–thaw cycle experiment has little effect on it.
... 58,65 If the shift is more pronounced, it can be assumed that more AlO 4 tetrahedra are incorporated into the SiO 4 backbone, as has been observed analogously in studies of zeolites. [66][67][68][69] This behavior can be explained by the force constant, which is higher for Si-O bonds than for Al-O bonds. Accordingly, a lower force constant leads to lower wavenumbers. ...
Sustainability is becoming an increasingly important factor in the development of new building materials. In terms of the sustainability of concrete components, the biggest challenge is the high energy consumption and associated greenhouse gas emissions in the production of Portland cement. A common strategy used by the construction industry to improve sustainability is to use residuals to develop lower-emission geopolymer concretes that eliminate high-emission cement-based concretes. Because construction and demolition waste, at 3 trillion tons per year worldwide, also represents an environmental risk, this work will investigate the suitability of geopolymers based on real construction waste. In the course of the investigations, the manufactured geopolymer samples are examined for the material parameters relevant to building materials, namely compressive strength, flexural strength, raw density, total porosity, and thermal conductivity. The setting behavior and the forming structures are investigated by infrared spectroscopy, X-ray diffraction analysis and scanning electron microscopy. The present study is intended to contribute to the development of a suitable recycling strategy for the material recycling of construction waste in novel geopolymer material.
... Alkalinity increased with an increase in the concentration of the activator, which enhanced the alkaline activation reaction. As a result of the high concentration of OHin the solution, Si 4+ and Al 3+ dissolve faster, while Na + acts as a charge-balancing cation in the structure [88][89][90][91][92][93]. On the other hand, the decrease in flexural and compressive strength with the increase in NaOH concentration beyond the optimal amount was because the dissolution of silica and alumina from solid precursors usually reaches a steady state under high concentrations of NaOH. ...
This study examined the fresh and hardened characteristics of alkali-activated binders (AABs) based on ternary mixtures of red mud (RM), class F fly ash (FA), and ground granulated blast-furnace slag (GGBFS). The binders were prepared by dry mixing of 50% RM, 25–50% FA, and 0–25% GGBFS. The alkali activators were prepared from sodium hydroxide solution with different concentrations (6–14 mol) and sodium silicate solution. Curing at room temperature was adopted for the preparation of all samples. The flowability, setting time, and compressive and flexural strength tests were used to examine the properties of the resulting binders. To study the microstructural characterization, the scanning electron microscope, X-ray diffraction, and Fourier transformation infrared techniques were used. The results show that the flowability of the AAB decreases with higher GGBFS content, the addition of GGBFS reduces the setting time, and the incorporation of GGBFS increases the flexural and compressive strengths of the AAB. Microstructural and chemical analysis results indicate that in addition to geopolymer gel, calcium silicate hydrate (C–S–H) is formed upon adding GGBFS, producing a denser microstructure.
... Hierdurch ändert sich die chemische Umgebung der Si-O-Bindungen [20,21]. Wenn die Verschiebung stärker ausfällt, ist davon auszugehen, dass mehr AlO 4 -Tetraeder in das SiO 4 -Grundgerüst eingelagert werden, wie es analog in Untersuchungen von Zeolithen beobachtet wurde [22][23][24][25] ...
Die vorliegende Arbeit beschäftigt sich mit der Herstellung von Geopolymeren aus Ziegelmehl und Mischbauschutt mithilfe einer alkalischen Aktivator-Lösung. Die Studie hat zum Ziel, zu untersuchen, ob sich diese Geopolymere mehrfach reaktivieren lassen, ohne neues Ausgangsmaterial hinzufügen zu müssen, und wie sich die Anzahl der Reaktivierungen auf die Struktur und die werkstofftechnischen Eigenschaften auswirkt. Die Ergebnisse zeigen, dass Geopolymere aus einer Mischung aus Ziegelmehl und Mischbauschutt hergestellt werden können und sich bis zu drei Mal aufmahlen und reaktivieren lassen.
The present work deals with the production of geopolymers from brick flour and mixed rubble using an alkaline activator solution. The study aims to investigate whether these geopolymers can be reactivated several times without having to add new starting material, and how the number of reactivations affects the structure and material properties. The results show that geopolymers can be made from a mixture of brick flour and mixed rubble and can be ground up and reactivated up to three times.
... There are many companies in the region where these stones are produced. In these companies, a high amount of cutting waste is generated when forming stones into products [35,36] In this study, the use of volcanic tuff stone cutting wastes released after stone-cutting (SW) in Nevsehir province in geopolymers produced with fly ash and its effect on the mechanical and microstructural properties of geopolymers were investigated. Cutting wastes (red and yellow stone) obtained from the stone enterprise where a high amount of cutting waste is generated were used in geopolymer mortars. ...
In this study, the physical and mechanical properties of the geopolymers formed by substituting red (RSW) and
yellow (YSW) stone-cutting wastes into geopolymer mortars based on class F fly ash at 10–40 wt% rates were
investigated. Sodium hydroxide (NaOH) solution was used as an activator in the production of the mortars.
Produced samples were thermally cured at 90 ◦C for 24 h. Workability, unit weight, flexural strength,
compressive strength, water absorption, porosity, and elevated temperature resistance tests (400, 600, and
800 ◦C) were applied to the produced geopolymer mortars. In addition, the chemical analysis (XRF), crystal
phase analysis (XRD) of wastes/selected mortars, and microstructural analysis (SEM) of before and after elevated
temparature resistance tests were carried out to investigate the effect of stone-cutting wastes on geopolymer
mortars. SW up to 40% enhances mechanical strength up to 26–30.7 MPa from 16.4 MPa due to its high Si/Al
ratios and Ca content and needle-like crystals formed by stone-cutting waste. The crystalline phases are determined to be mullite, quartz, anorthite, and zeolite derived from stone-cutting waste in the selected mortars. As a
result, it was seen that the use of stone-cutting wastes up to 40% improved the physical, mechanical, and
microstructural properties of fly ash-based geopolymer mortars.
... It is created through the chemical reaction of source materials with a high concentration of aluminosilicates within a highly alkaline environment [11]. During this chemical process, the unbound silica (SiO 2 ) and tetrahedral alumina units (AlO 4 ) undergo dissolution and are subsequently released within the mixture [12,13]. Manufacturing of GPC requires approximately 60% energy compared to OPC-based concrete, with the advantage of 80% to 90% lower carbon emission [14]. ...
The experimental work is intended to identify the mix proportion of M100 grade of High-Strength Geopolymer Concrete (HSGPC) by a targeted strength-based method. Concrete ingredients are Ground Granulated Blast Furnace Slag (GGBS), Microfine (MF), Fly Ash (FA), Silica Fume (SF) as a binder, 10 mm natural coarse aggregate, and river sand. Eight different mix proportions of M100-grade concrete were calculated and tested by considering the different fractions of binders. Fresh concrete workability was assessed by a slump test. The compressive, indirect tensile, flexural, and shear strength were evaluated at the age of 7 and 28 days to find the optimum mix proportion of M100 concrete. Technique for Order Preference by Similarity to Ideal Solution analysis was incorporated to find the optimum proportion of M100 concrete with due weightage of sufficient slump value and high mechanical properties. The experimental analysis includes the microstructural behavior of the HSGPC. The results represented that incorporating the SF and MF reduces the workability by approximately 28% but increases the mechanical properties by up to 22%. The promising compressive strength for M100 grade was observed at 28 days with a binders fraction of 55% GGBS, 25% FA, 10% SF, and 10% MF concrete sample as 104 MPa, the highest compressive strength compared to other mixes. Microstructural analysis of HSGPC revealed that mechanical properties were enhanced due to a dense microstructure of different gel formations like C–S–H, Ca–S–H, and Na–S–H gel.
... The highest value of compressive strength was obtained when the ratio was equal to 1.0 and increasing the Na 2 SiO 3 /NaOH ratio caused a decrease in compressive strength. Álvarez-Ayuso et al. (2008) [187] showed that when the NaOH concentration is higher, geopolymerization can be achieved even without soluble sodium silicate. ...
Starting from the context of the principles of Sustainable Development and Circular Economy concepts, the paper presents a synthesis of research in the field of the development of materials of interest, such as cementitious composites or alkali-activated geopolymers. Based on the reviewed literature, the influence of compositional or technological factors on the physical-mechanical performance, self-healing capacity and biocidal capacity obtained was analyzed. The inclusion of TiO2 nanoparticles in the matrix increase the performances of cementitious composites, producing a self-cleaning capacity and an anti-microbial biocidal mechanism. As an alternative, the self-cleaning capacity can be achieved through geopolymerization, which provides a similar biocidal mechanism. The results of the research carried out indicate the real and growing interest for the development of these materials but also the existence of some elements still controversial or insufficiently analyzed, therefore concluding the need for further research in these areas. The scientific contribution of this study consists of bringing together two apparently distinct research directions in order to identify convergent points, to create a favorable framework for the development of an area of research little addressed so far, namely, the development of innovative building materials by combining improved performance with the possibility of reducing environmental impact, awareness and implementation of the concept of a Circular Economy.
... The construction sector produces vast quantities of greenhouse gas emissions during cement manufacturing. Considering the damage caused by such gas emissions on the environment, the usage of wastes in the manufacturing processes of geopolymer materials that are used in the production of materials resistant to heat and corrosive environmental conditions may contribute to the elimination of such problems (Alvarez-Ayuso et al. 2008;Atabey 2017;Maraş 2021). In terms of the environmental impact, and similar/higher mechanical-durability properties the most significant advantage of geopolymers in comparison with cement-based mortar is that geopolymer production releases much less CO 2 . ...
This study aims to evaluate the pottery waste obtained from a pottery company in Cappadocia (Turkey) in the production of geopolymer mortars (GMs), which is becoming increasingly interesting in construction technology. For this purpose, mortars were prepared by replacing the fly ash with pottery wastes at proportions of 0%, 10%, 20%, 30%, and 40% by weight. Flow table, water absorption, apparent porosity, flexural strength, compressive strength, and high-temperature resistance tests were applied to GMs. Diopside, calcium silicate hydrate, and wollastonite crystals were observed in phase analyses performed by XRD for mortar containing 40% pottery waste. The observed microstructure analysis of before and after high-temperature tests was performed to investigate the effect of pottery waste on GMs. Consequently, better results were obtained at high-temperature strength up to 800 °C compared to the reference (0% pottery waste) by replacing up to 40% of fly ash with pottery waste to improve the physical and mechanical properties. Pottery waste replacement enhanced the flexural strength and compressive strength at 28 days by up to 26% and 64%, respectively, compared to reference mortar at ambient conditions. Furthermore, considering the overall mechanical and microstructural analysis, GMs with pottery waste promise sustainable mortar production and waste elimination. The pottery waste is a potential alternative material to be successfully recycled in the eco-friendly geopolymer mortars as a replacement of fly ash up to 40% level.
... Furthermore, as shown in Fig. 4, teff straw ash was more highly amorphous than fly ash. During alkali activation, amorphous phases in the source materials dissolve faster than crystalline phases, resulting in a more stable and strong geopolymer binder [72,73]. Moreover, the addition of TSA favours the formation of other mineralogical phases, which helps in improving the compressive strengths of geopolymer mortar, as discussed further in Section 4.5.1. ...
Although geopolymer cement (GPC) is a substitute for Portland cement, its application is restricted due to the need for high-temperature curing (40–90 °C), which makes it challenging to utilise for onsite applications. To address this issue, the current study examined the potential of substituting fly ash (FA) with teff straw ash (TSA) in geopolymer mortars cured at ambient temperature. The findings revealed that substituting FA with TSA can eliminate the need for high-temperature curing, and the compressive strengths of FA-TSA-based geopolymer mortar mixtures cured for 28 days ranged from 45 to 53 MPa. Further, increasing the TSA content enhanced the mortar's flexural and direct tensile strengths. A teff straw ash level of 10% increased compressive, flexural, and direct tensile strengths by 40%, 59%, and 30% at 28 days, respectively. Furthermore, the mineralogical phases of the mortar after 28 days confirmed the presence of gismondine coexisting with other phases, and microstructural analysis indicates that the inclusion of TSA resulted in a denser structure. These findings suggest that TSA could be a potential substitute for FA in GPC applications to lower energy usage and environmental impact.
... It is well accepted that the chemical reaction process of AAFA involves two main stages, namely, dissolution and polymerisation [5,6]. In the dissolution stage, the reactive components of SiO 2 and AI 2 O 3 in fly ash are dissolved under a strong alkaline condition [7], whilst in the polymerisation stage, the dissolved reactive Si(OH) 4 and Al(OH) 4 − polymerise to produce the main reaction product, sodium aluminosilicate hydrate (N-A-S-H gel), and a small number of zeolites [2], leading to the formation of a well-compacted cementitious matrix. ...
The reaction products and microstructure of an 8 M NaOH-activated fly ash (AAFA) cured with microwave and thermal oven curing were comparatively investigated. The results show that the formation of an Al-rich N-A-S-H gel with a flaky morphology and crystalline chabazite-Na between fly ash particles were favoured under the microwave curing, whilst a Si-rich N-A-S-H gel with a fibrilllar morphology and crystalline hydroxysodalite on the surface of fly ash particles were dominant under the thermal oven curing. The formation of these unique reaction products and microstructure under the microwave curing is attributed not only to the thermal effect of microwaves which can increase the temperature of AAFA volumetrically, but also to the non-thermal effects of microwaves which can promote the dissolution and diffusion of silica and alumina during the AAFA reaction process. This explains why AAFA can achieve a high early strength within a short period of microwave curing.
... These processes utilize the chemical properties of cement materials, both basic (e.g., Portland cement) and synthetic binders, such as zeolites and geopolymers. These binders are most often obtained from fly ash, clay, metakaolin, and blast furnace slag (Álvarez-Ayuso et al., 2008;Hefni et al., 2018). The advantage of using the presented methods of stabilizing and neutralizing waste from electroplating plants is a reduction of carbon dioxide emissions to the atmosphere, an easier preparation process, and lower costs of raw materials for production, energy savings, synthetic binders' higher resistance to chemical corrosion compared to traditionally obtained cements, and their physicochemical properties (Mehta & Siddique, 2017;Xu et al., 2017). ...
The article presents the results of research on the leachability of selected heavy metals (cadmium, nickel, chromium, cobalt, lead, and copper) from solid waste obtained in laboratory processes involved in the industrial treatment of wastewater generated in metal surface treatment plants. The test sludges were precipitated using sodium hydroxide solution, calcium hydroxide suspension, 45% solution sodium trithiocarbonate (Na2CS3), 15% solution trimercapto-s-triazine, sodium salt (TMT), and 40% solution sodium dimethyldithiocarbamate (DMDTC). The precipitates were treated with artificial acid rain and artificial salt water. After 1, 7, 14, and 21 days of leaching, the concentration of Cd, Co, Cr, Cu, Pb, and Ni in the leachate was determined. Artificial acid rain leached Ni and Cd to a maximum concentration of 724 mg/L and 1821 mg/L, respectively, from the sludge obtained after the application of Na2CS3, while artificial salt water leached Ni in the maximum amount of 466 mg/L and Cd—max. 1320 mg/L. When Ca(OH)2/NaOH was used, the leaching of Cr reached a similar level for both leaching agents, i.e., the maximum for artificial acid rain was 72.2 mg/L and the maximum for artificial salt water 71.8 mg/L. The use of Na2CS3 or Ca(OH)2/NaOH poses a risk of some heavy metals entering the environment, which may have a negative impact on living organisms, whereas the sludges obtained with the use of DMDTC and TMT as precipitants were the most stable under the experimental conditions and did not pose a potential environmental hazard.
... Subsequently, the polymerization of active surface groups and soluble species occurs to form a gel, which then generates a hardened geopolymer structure. In most cases, only a small amount of the silica and alumina present in particles needs to dissolve and take part in the reaction for the entire mixture to solidify [19]. ...
resumo: Portland cement remains the main material of choice in construction due to its thermal, mechanical and durability properties. However, there is growing concern about the large amount of energy consumed and the environmental pollution generated during its production. The objective of this study, therefore, was to evaluate the potential of the fine residual material produced by crushing basalt rocks to form a supplementary cementitious matrix through alkaline activation. Basalt powder with a particle size of less than 53µm was prepared and activated with a sodium hydroxide solution, with a sodium silicate solution as an adjuvant. The curing process of the material was also carried out at 5 temperature levels, 75, 85, 100, 115, 125°C, according to the experimental design. The paste was dry curing at a standard digital laboratory oven for 24 hours. After curing, the compressive strength of the material was evaluated, reaching a mean value of 10.21 MPa for the H5S15T125 mixture at 28 days. The microstructure analysis was performed by X-ray microtomography, presenting the reconstruction of the internal pores and cracks, leading to the conclusion that higher curing temperatures formed more porous matrices, although with more strength. Based on the collected data, the statistical analysis of the design was performed showing that sodium hydroxide and temperature have a statistically significant effect on the response variable compressive strength. As such, the alkali-activation of basalt powder can potentially produce a cementitious material of moderate strength, giving purpose to the residue and reducing the emission of harmful particles into the atmosphere.
... AAMs are waste materials in general mixed with alkaliactivating agents. Alkali activator can be either a calciumrich or aluminum-abundant precursor [55]. AAMs require less energy and emit less CO 2 [56]. ...
Due to urban sprawl, the demand for land has increased for the purpose of construction. It is unlikely that soil available at different construction sites will be suitable for designed structures. For improving the load-bearing capacity of the soil, different soil binders are used, which are present in distinct states. In this review, the authors have collected details about various binders, which are generally used in the soil stabilization, and their effect as a binding agent on the soil. In this article, the authors tried to review different traditional binders. After studying various research articles, the authors found that lime, ground-granulated blast slag (GGBS) polypropylene, polyurethane grouting, and asphalt mix are frequently used binders. However, the authors also gathered information about the negative environmental impact of these traditional soil binders, which led to the need for alternatives to these commonly used soil binders. To diminish this issue, different alternate hydraulic and non-hydraulic binders are discussed. The authors found alternatives to cement and lime with the alkali-activated material consisting of Na2O and silica modulus and belite-calcium sulfoaluminate ferrite, which is also known as “Aether™.” According to the research, both alternatives emit 20–30% less CO2 into the environment and also improve the compressive strength of the soil. The various studies promotes bitumen modification. Incorporating 20-mesh crumb rubber and bio-oil into the bitumen reduces its viscosity and improves its fatigue value. When waste oil is mixed with asphalt, it revitalizes the bitumen, improves fatigue resistance, and increases compressive strength. The soil particles treated by Eko soil are held together by enzymes, which give them the same strength as cement. Apart from that, low-carbon binders such as basic oxygen furnace slag, bamboo fiber, enzyme-based soil treatment, zebu manure for stabilization, and lignin-contained biofuels and coproducts are discussed. Replacing these traditional binders helps with energy savings. All waste products are recycled, and energy is saved by not manufacturing traditional binders. Additionally, energy is saved, which is required to avoid the detrimental effects of these conventional binders, making them energy-efficient alternate binders. The authors also summarize the methods used, impacts, and changes that occur in soil properties after using substitutes in place of traditional binders. From the review, the authors determined that different binders have various properties in terms of chemical and physical compositions, and they show different variations in terms of strength when added to soil with low bearing capacity or poor stability.
... He also used sodium silicate (Na2SiO3) to chemically activate fly ash to achieve a 2-day compressive strength of 2N/mm 2 and a 28-day compressive strength of 45N/mm 2 . In a like manner, Morenoa et al (2008) also activated class F fly ash with NaOH from different sources and achieved a 28-day compressive strength of between 29 and 66N/mm 2 . Another study by Sofia et al (2007) used class F fly ash with one or more of the following component; Sodium Carbonate (Na2CO3), Sodium Silicate (Na2SiO3) and Sodium Hydroxide (NaOH), to achieve 7-day compressive strengths in the range of 35 to 44 N/mm 2 and a 28-day compressive strength in the range of 47 to 57N/mm 2 . ...
Alkaline activation of industrial wastes as alternative to ordinary Portland cement is attracting more attention especially in developed nations. But there is paucity of information on the use of bio-wastes. In this paper, the potential of alkaline activation of coconut shell ash (CSA) as binder in mortar was investigated. Coconut shells were collected and calcined at 800 o C for 1 hour to produce CSA. Chemical composition of the ash was then determined using XRF technique. Sodium hydroxide (NaOH) of different concentrations (10, 12, 14 and 16M) was used as alkaline activator, while mortar of mix ratio 1:3 was produced with alkaline-CSA ratio of 0.5. Mortar prisms of size 40 mm 40 mm 160 mm were cast and cured in oven at a temperature of 80 o C for 7, 28, 56, 90 and 120 days. Thereafter, flexural and compressive strengths were determined at the end of each curing ages, following standard procedure. The results showed that CSA contained high silica content, which when combined with its alumina and ferrous oxide was above 70% accepted as minimum for pozzolanic materials. Both the compressive and the flexural strengths were found to be increasing with increase in activator concentration up to 14M. At 120 days, the compressive strength was 13.9 N/mm 2 while the flexural strength was 6.88 N/mm 2. These values were higher than the strengths recommended by Nigerian Industrial Standard (NIS) for load bearing blocks. It was concluded that activation of CSA with NaOH could be used as binder for non-structural use. However, further optimization could achieve higher strength for structural use.
... The Author also used sodium silicate (Na 2 SiO 3 ) to chemically activate fly ash to achieve a 2-day compressive strength of 2 N/mm 2 and a 28-day compressive strength of 45 N/mm 2 . Similarly, Morenoa et al. (2008) also activated class F fly ash with NaOH from different sources and achieved a 28-day compressive strength of between 29 and 66 N/mm 2 . Another study by Sofia et al. (2007) used class F fly ash with one or more of the following component; Sodium Carbonate (Na 2 CO 3 ), Sodium Silicate (Na 2 SiO 3 ) and Sodium Hydroxide (NaOH), to achieve 7-day compressive strengths in the range of 35 to 44 N/mm 2 and a 28-day compressive strength in the range of 47 to 57 N/mm 2 . ...
In this paper, potential of alkaline activation of coconut shell ash (CSA) as binder in mortar was investigated. Coconut shells were collected and calcined at temperature ranges between 500 and 900°C at interval of 100 for 30, 60 and 90 minutes to determine optimum burning condition that produces ash of higher silica content. Chemical composition of the ashes was then determined using X-ray Florescence (XRF) technique. Sodium hydroxide (NaOH) of different concentrations of 10, 12, 14 and 16 Molar (M) was used as alkaline activator, while mortar of mix ratio 1:3 was produced, while ratio of the alkali to CSA was of 0.5. Mortar prisms of size 40 mm × 40 mm × 160 mm were cast and cured in an oven at a temperature of 80 ℃ for 7, 28, 56, 90 and 120 days. Thereafter, flexural and compressive strengths were determined at the end of each curing ages, following standard procedures. Scanning Electron micrographs of the hydrated mortar at 120 days were obtained using scanning electron microscopy (SEM) The results showed the oxide composition did not follow any pattern with increase in temperature but CSA produced at 800 ℃ for 1h gave the highest combined silica, alumina and ferric oxides above 70%, which is accepted as minimum value for pozzolanic materials. Both compressive and flexural strengths of the activated mortar samples were found to increase with increase in activator concentration up to 14M and decline thereafter. At 120 days, the compressive strength was 13.9 N/mm 2 while the flexural strength was 6.88 N/mm 2. These values were higher than the strengths recommended by Nigerian Industrial Standard (NIS) for load bearing blocks. It was concluded that activation of CSA with NaOH could be used as binder for non-structural use. The SEM results indicated that mortar made from 14 M had structure that was densely packed compared to other mortar samples produced from other concentrations
... The larger the number of gels, the higher the strength of cement-based materials and the better the impermeability [46]. Studies have confirmed that the gel in the geopolymer paste is composed of gel particles with a diameter of 5~10 nm, and pores with a diameter of 2~50 nm are formed between the particles [47]. It can be seen that the gel formed is closely combined with the unreacted mineral raw material particles, and the pore structure is mainly gel pores. ...
In this study, geopolymer pastes with 60% metakaolin (MK) and 40% ground granulated blast-furnace slag (GGBFS) were synthesized. To determine the influence of the alkaline activator concentration, modulus, and the liquid/solid (L/S) ratio on setting time and compressive strength, the geopolymerization process and microstructures of MK/GGBFS-blended geopolymer pastes were analyzed using isothermal calorimetry, X-ray diffraction, mercury intrusion porosimetry, and scanning electron microscopy. Acid dissolution was employed to measure reaction extent. The results showed that the initial setting time of the geopolymer pastes was between 68 and 226 min, and the initial setting and final setting time was apart about by 10 min. For the same variable, the total heat released was positively correlated to the reaction extent. Available silicate content increased the reaction rate and intensity at the initial stage, whereas the OH− concentration controlled the reaction extent in the long term. A limited reaction extent existed in the geopolymeric reaction even if the system contained sufficient alkali content and medium. An increase in the L/S ratio increased the reaction extent. The highest reaction extent of 86.3% was found in the study. Additionally, increasing the L/S ratio reduced the compressive strength by increasing the porosity.
... As for the effect of the residues on the compressive strength, on one hand, Nasvi et al. [4] reported that the fly ash-based geopolymer did not acquire a considerable increase in strength above 60 • C, and on the other hand, some researchers found that the optimal curing temperature for higher strength was 75-85 • C [98,102]. These conflicting results could be attributed to the type of activators and the level of alkalinity of the activators [4,103]. ...
The reuse of industrial wastes to produce concrete and mortar is an environmental solution for their disposal as well as for the development of ecological and sustainable concrete. A large number of previous studies summarized in this review paper focused on adding different types of waste in the concrete and mortar mix in the form of fine aggregates, coarse aggregates or cement additives, and investigated the physical and mechanical properties of the enhanced material. Reusing waste in concrete and mortar mix design significantly affects the material’s fresh and hardened properties. This literature review offers a general insight to the civil and industrial engineering community on ecological waste-based concrete and mortar that can serve as a basis for construction and future work in this field.
... The peaks at 1456, 887, and 748 cm −1 correspond to magnesite. Other peaks in the 800-600 cm −1 region are associated with the presence of quartz and mullite in the FA [42][43][44][45]. The broad band at 3432 cm −1 (stretching O-H vibrations) in the spectra of the blends is due to adsorption of H2O from air by the (FA + magnesite) blend during MA. ...
Ca/Mg carbonate minerals, such as calcite and dolomite, play an increasingly important role in the development of alkali-activated binders or geopolymers, which are regarded as promising sustainable cement materials. In contrast to studies on calcite and dolomite, the effect on geopolymer properties of the addition of natural magnesite (magnesium carbonate) to aluminosilicate raw materials has not been investigated. The aim of this study is to investigate the influence of mechanical activation (MA) and natural magnesite addition to fly ash (FA) on the compressive strength of geopolymers based on the natural magnesite-FA blend. Magnesite substitutes FA in amounts of up to 20 wt.%. Geopolymers were prepared using NaOH solution as an alkaline agent. XRD, FT-IR spectroscopy, thermogravimetry, SEM, and a dissolution test are used to investigate the geopolymerization process. The major reaction product was sodium-containing aluminosilicate hydrogel. Magnesite is found to transform, to a minor degree, to hydrotalcite. MA of the blend significantly improves geopolymer strength. For geopolymers based on (FA + magnesite) blends mechanically activated for 180 s, the strength is on average 8.0 ± 1.5, 3.0 ± 0.9, 1.5 ± 0.2, and 1.7 ± 0.5 times higher than that for the geopolymers based on the blends mechanically activated for 30 s at the age of 7, 28, 180, and 360 d, respectively. Although blending FA with magnesite does not increase geopolymer strength, for the mixtures containing 1%-10% magnesite, in general, the strength is either not reduced or it is reduced to a small degree compared to the geopolymers based on 100% FA. Using previously obtained data, for the first time, the effect of the addition of three Ca/Mg carbonate minerals to FA and MA on geopolymer performance is compared. Under similar conditions, geopolymer strength decreases in the order calcite > dolomite > magnesite. The main factors affecting the strength of geopolymers based on the mechanically activated blends of FA with magnesite including filler, dilution, and chemical effects are discussed.
... Thus, based on the results reported for the incinerated state, incorrect information on the chemical composition of the sample in the state as provided for testing may be obtained. The general principle is that if the sample submitted for testing is not a sample obtained in a high-temperature industrial process (e.g., binder, cement, refractory material, slag, coal/biomass/alternative fuel fly ash) and there is a risk that it may contain organic matter before preparing the borate bead, it needs to be incinerated with a simultaneous determination of the loss on ignition [19][20][21][22]. Another inconvenience arising from the analysis of fused samples is that, due to the high dilution with flux, many heavy metals occurring in the tested sample at trace levels (from a few to several ppm) cannot be determined or are determined with low accuracy due to the low intensities of the analytical lines, which may be considered as a serious drawback in environmental protection applications. ...
Determination of the content of chemical elements occurring in waste in large, small and trace amounts was performed using two instrumental analysis techniques: ICP-OES-Inductively Coupled Plasma Optical Emission Spectrometry and WDXRF-Wavelength Dispersive X-Ray Flu-orescence Spectrometry. Since such analyses are expensive and time-consuming, the objective of the work presented in this paper was the development of a quick and inexpensive method for preliminary , scanning-based identification of the chemical composition of tested samples (solid, bulk or powder) using standardless, semi-quantitative analysis. An optimized method of preparing samples for X-ray measurements by pressing into a durable tablet, universal for all materials tested, was developed. Moreover, limits of quantification were determined, and the uncertainty of the results obtained was estimated by comparing them with the results acquired with the use of the accredited calibration method, employing standards and certified reference materials.
... The third band (3) corresponds to wavenumber 1420 cm − 1 and indicates the stretching of C -O -C vibrations; additionally, it indicates the presence of carbonyl groups (CO 3 2-) [59,61,62]. This band is associated with the formation of sodium carbonate in the geopolymer matrix through the reaction of unreacted and leached sodium with CO 2 from the atmosphere [63]. ...
Geopolymeric binders are materials with properties equivalent to Portland cement, which may present lower CO2
emissions associated with the production cycle. To produce sustainable geopolymeric binders, it is necessary to
use raw materials with a low carbon footprint and energy consumption, characteristics found in biomass ash. In
this sense, this work proposes the evaluation of oat husk ash (OHA) as a partial replacement material for metakaolin
in the production of geopolymer paste. OHA has replaced metakaolin at levels up to 20%. In addition to
routine microstructural (XRD and FTIR) and mechanical analyses, i) the pore size distribution by nitrogen
adsorption in cubic samples, and ii) an extensive rheological investigation in which it was determined the model
that best fits the analyzed matrix. Furthermore, the determination of CO2-e emission embodied energy and the
cost of the pastes was carried out. The results showed that the insertion of 20 wt% of OHA i) increased the
dynamic yield stress (40.2%) and the equivalent viscosity (13.7%) compared to plain paste, ii) reduced the
cumulative heat after 168 h by 29.7%, which is related with the lower reactivity of OHA compared to MK.
Nevertheless, iii) did not cause significant chemical and mineralogical changes, (iv) maintained compressive
strength statistically equal to the control mixture, and v) reduced up to 34% and 23%, respectively, the embodied
energy and the cost of producing the matrices. Thus, the investigation made possible the valorization of OHA for
the production of technically and economically viable and environmentally friendly geopolymer matrices
... BAx2-VPC35, instead, shows the additional presence of amorphous glass together with geopolymers, as indicated by second broad band shifted to lowest angles (Fig. 4). These two bands attributable to amorphous materials with different initial crystalline order [51][52][53] are also detectable on BAx3-VPC35 profile (Fig. 4). The presence of non-reactive amorphous material (amorphous glass) limits the formation of zeolite, thus explaining the absence of this newly formed mineral in both BAx2VPC35 and BAx3VPC35C (Fig. 3). ...
In this work, three samples of bauxite were used as inexpensive sources for the zeolite formation by a green process based on vapor-phase crystallization (VPC) method. The synthesis was carried out using a water bath with deionized water heated at 35, 45, 60 or 90 °C. During the process, NaOH pre-fused bauxites were contacted only with vapor from the liquid. The results indicate that sodalite formed in all the samples after VPC at higher temperatures (60 °C and 90 °C). Large amount of zeolite A was instead synthesized in the sample characterized by SiO 2 /Al 2 O 3 ratio next to 1 and after vapor treatment at 35 °C and 45 °C. These data highlight the determining role of both raw material chemical composition and amount of water molecules in type of zeolite formed by vapor crystallization method. Moreover, the results indicate that VPC process made it possible to synthesize zeolite generating no water waste.
... The peaks around 1000 cm −1 wavenumber are attributed to the vibrational stretching mode of Si-O-Si of SiO 4 tetrahedral structure (Rubio et al., 1997). In addition, the flattening of the peak around 1060 cm −1 for 10G1.5 within the range indicates the formation of a new product (Álvarez-Ayuso et al., 2008;Criado et al., 2005). Wavenumbers less than 1000 cm −1 correspond to the formation of Si-O vibrational bonds before and after geopolymerization of the precursors. ...
This article reports a comparative analysis between glass waste and fly ash (which is the most studied waste for the alkali-activated products) to measure their effectiveness as a sole precursor to produce geopolymers. Globally, around 11.4 million tonnes of glass waste is generated per annum, and this needs to be managed properly. To address this issue, in this study, glass waste which was mostly manufactured bottles and containers was used in pulverized form. The molarity of the sodium hydroxide (NaOH) solution was kept as 6 M, 8 M, and 10 M. The sodium silicate-to-sodium hydroxide (Na2SiO3/NaOH) solution mix ratio was varied between 1.5 and 3.5. Mechanical (compressive and flexural strength) and durability (resistance to different levels of sulfuric acid) aspects were studied along with micro-analysis (structural, elemental, and thermal). Controlled ambient temperature curing was followed for all the samples. Our findings showed that mechanical properties were dependent on the molarity, silicate modulus, and alkaline mixture (AM) ratio. The glass waste showed substantial amount of long-term strength development over fly ash with a maximum compressive strength gain at 28 d and 90 d curing age of 90% and 194% for 8M1.5AM and 6M1.5AM mixture, respectively. For flexural strength, it was 49% and 62% gain at 28-d and 90-d curing, respectively, for 10M1.5AM mixture. The glass waste also offered relatively higher resistance to acid attack with a maximum compressive strength loss of 61% and 55.7%, whereas fly ash-based mixtures recorded 75% and 71.73% reduction for 5% and 3% H2SO4 attack for 28 d, respectively. Field emission scanning electron microscopy (FE-SEM) revealed that the glass waste specimens were more compact than fly ash-based specimens. Thermogravimetric analysis (TGA) results indicate that glass waste-based geopolymers are more thermally resistant than fly ash-based geopolymers when exposed to a systematic increment in temperature. Ultimately, promising results in terms of mechanical and durability aspects propose the use of glass waste as a binder in geopolymeric masonry mortar applications. Glass waste has a full potential to be a sole precursor to produce geopolymer under ambient temperature curing conditions. This will contribute towards sustainable environment by paving path for an effective utilization of the glass waste.
The bioaccumulation of lead in soil poses a significant human health risk. The solidification/stabilization (S/S) technique, employing binders like Portland cement or lime, is a common method for remediating lead-contaminated soil. However, cement production has adverse environmental impacts, prompting the exploration of eco-friendly alternatives like alkali-activated materials (AAMs). This study assesses AAM efficacy in the S/S of lead-contaminated soil. The effects of several factors, including varying amounts of volcanic ash (VA), lead concentration, curing temperatures, and curing times are investigated. Unconfined compressive strength (UCS), toxicity characteristic leaching procedure test (TCLP), X-ray diffraction (XRD), Fourier-transform infrared spectroscopy (FTIR), and field emission scanning electron microscope-energy-dispersive spectroscopy-mapping analyses (FESEM/EDS/mapping) analyses are used to study the specimens. The findings indicated a substantial increase in the UCS of lead-contaminated soil treated with 15% VA (under oven curing (OC) conditions), and 10% VA (under ambient curing (AC) conditions) exhibited remarkable increases of up to 600% and 458%, respectively. Moreover, the leaching of Pb²⁺ ions from samples contaminated with 10,000 mg/kg (under OC conditions) and 2500 mg/kg (under AC conditions) experienced significant reductions of 87% (from 135.14 to 13.36 ppm) and 91% (from 26.32 to 2.21 ppm), respectively. The S/S process in these samples operated through three primary mechanisms of chemical bonding, physical encapsulation, and the formation of insoluble silicate. The formation of N-A-S–H and hydroxy sodalite structures played a vital role in facilitating these mechanisms. Therefore, alkali-activated VA demonstrated excellent performance in the remediation of lead-contaminated soil.
Graphical Abstract
Portland cement is one of the principal sources of anthropomorphic CO2 emissions. It is estimated that cement production contributes up to 10% of greenhouse gas emissions and annual cement production over 4 billion tons. This has led to the development of a range of alkali activated materials (AAM), the most common precursor materials being class F fly ash and blast furnace slag. At present Class C Fly Ash is not widely utilized as an AAM due to the chemical composition and activation requirements. However, initial research on high Calcium German Class C Fly Ash suggests that the material may have potential for application as an AAM. This paper reports the development of ambient cured alkali activated mortar optimised by varying the alkali modulus and w/b ratio. The evolution of the mechanical and microstructural properties is reported over the initial 28 day period. Compressive strength in excess of 10 MPa at 7 days and 15 MPa at 28 days was achieved at ambient temperature. Similar strengths were observed for both 10% and 15% dosage but as dosage increases the optimal Alkali Modulus reduces.
In light of the urgent need to develop environmentally friendly materials that, at some point, will allow the reduction of concrete and, consequently, cement consumption—while at the same time allowing the reuse of waste and industrial by-products—alkali-activated fly ash (AAFA) geopolymer composite emerges as a material of great interest. The aim of this study was to investigate the physico-mechanical performance of composites based on AAFA binders and the effect of different types of aggregates on these properties. The experimental results indicate variations in flexural and compressive strength, which are influenced both by the nature and particle size distribution of aggregates and the binder-to-aggregate ratio. The analysis of the samples highlighted changes in porosity, both in distribution and pore size, depending on the nature of the aggregates. This supports the evolution of physico-mechanical performance indicators.
One-part alkali-activated materials (AAMs) can preserve natural resources and lower embodied carbon of the built environment by accommodating various wastes, industrial by-products, and end-of-life materials in their composition. This study investigates the feasibility of using end-of-life bricks in two physical states, powder and aggregate, to partially replace fly ash precursor and natural aggregate in AAMs, respectively. The mechanical characteristics, microstructure, water absorption, freeze-thaw and fire resistance of the modified AAMs were evaluated. The effect of adding different ratios of nano graphite platelets was also investigated. Results showed that brick-based one-part AAMs can achieve mechanical properties, pore structure, water absorption and freeze-thaw resistance comparable to fly ash-based AAM while having 65% better fire resistivity. Incorporating bricks as aggregate resulted in a maximum improvement of 17% and 27% in the AAMs' compressive and flexural strength levels, respectively, and a general enhancement in the freeze-thaw resistance with showing no reduction in compressive strength after exposure to elevated temperature. Incorporating 0.1 wt% nano-graphite further enhanced flexural strength by 30%, decreased water absorption by 18% and improved freeze-thaw resistance compared to the mix without nano-graphite. Moreover, adding up to 0.5% nano-graphite enhanced the fire resistivity of the composite, allowing it to exhibit 19% better strength performance than before exposure.
As compared to alkali-activated geopolymers with phosphoric acid which may be used in high concentrations resulting in disposal concerns, acid-based geopolymers may have superior properties. A novel green method of converting waste ash to a geopolymer for use in adsorption applications such as water treatment is presented here. We use methanesulfonic acid, a green chemical with high acid strength and biodegradability to form geopolymers from coal and wood fly ashes. The geopolymer is characterized for its physico-chemical properties and tested for heavy metal adsorption. The material specifically adsorbs iron and lead. The geopolymer is coupled to activated carbon forming a composite, which adsorbs silver (precious metal) and manganese (hazardous metal) significantly. The adsorption pattern complies with pseudo-second order kinetics and Langmuir isotherm. Toxicity studies show while activated carbon is highly toxic, the geopolymer and the carbon-geopolymer composite have relatively less toxicity concerns.
The aim of this work was to investigate the effect of Phase Change Materials on the insulation properties - thermal conductivity coefficient [λ], of fabricated foamed geopolymer panels. Phase Change Materials have been widely reported in the public literature, making them increasingly popular in recent times. PCMs have the ability to accumulate heat, which they can absorb or release due to thermal transformation, which contributes to energy efficiency. This paper presents the results of research on geopolymers based on fly ash with the addition of microencapsulated and macroencapsulated phase change materials (PCMs). Geopolymer composites were prepared by adding 0%, 5%, 10% and 15% PCM and the curing process was carried out at 60°C. Three different phase change materials with melting points of 28°C (MicroCapsPCM28 (Slovenia)) and 25°C and 42°C (PX25 and GR42 (Germany), respectively) were used. All the phase change materials used belong to the paraffin group. The obtained composite sheets were subjected to thermal conductivity tests in 3 temperature ranges (0-20°C; 20-40°C; 30-50°C). The paper also presents the density results of the foamed composites investigated, as well as the visual evaluation and the morphology of the porous structure using scanning electron microscopy. As a result of the study, it was found that foamed geopolymer composites without PCM addition have lambda coefficient values of 0.06 - 0.07 [W/m*K], while with the addition of phase change materials 0.07 - 0.085 [W/m*K]. The obtained test results give the potential to use these materials in construction as insulating materials. The use of these substances in building partitions results in the decrease of daily temperature amplitudes inside the building, as well as in the phase shift of the time of release of stored heat.
In recent years, new climate targets in EU have led to a growing demand for construction materials with a lower carbon footprint. This implies a demand for research on materials with comparable properties and reduced CO2 emission to replace those currently in use. Geopolymers belong to the group of alkali-activated aluminosilicates, whose advantages include high compressive strength and high corrosion resistance. Examples of aluminosilicate materials used to produce geopolymers are fly ash, metakaolin or volcanic tuff. Recently, there have also been papers discussing the use of diatomite as a replacement for metakaolin in geopolymer materials. The purpose of this work is to investigate the use of diatomite as a fly ash replacement in the production of foamed geopolymers. For this purpose, fly ash based geopolymer samples with different amounts of diatomite (5%, 10%, 50%) were foamed using hydrogen peroxide as a foaming agent. Then, to observe the microstructure of the produced samples, they were subjected to scanning microscope observations. Compressive strength tests according to EN 12390-3 standard were carried out to check the strength properties after 30 days of curing. In addition, the thermal conductivity coefficients of the samples were investigated to better determine their potential industrial application. The expected result is a change in strength and thermal properties with increasing diatomite content.
Geopolymer is a new type of green gelling and environmental protection material, but the curing temperature limits the application of geopolymer in the construction industry. In this paper, the effects of NaOH on the pore structure and mechanical properties of ultrafine metakaolin (UMK) geopolymers under room temperature curing conditions were investigated. In this experiment, different concentrations of alkaline activators were prepared by changing the concentration of NaOH in the composite alkaline activator, and geopolymers were prepared with different alkaline activators and UMK. Different UMK geopolymers have been extensively analyzed to characterize their pore distribution, pore structure, and mechanical properties. The relationship between NASH gel and NaOH concentration was quantified by simultaneous thermal analysis (TG-DTG) and X-ray diffraction (XRD). The evolution of pore distribution and pore structure of UMK geopolymers with NaOH concentration was characterized by scanning electron microscopy (SEM) and proton nuclear magnetic resonance spectroscopy (¹H NMR). The results show that UMK only generates the NASH phase in the geopolymerization reaction. With the increase of sodium hydroxide concentration, the formation of NASH gel increases, and the crystallinity of the sample increases. SEM and ¹H NMR results show that the UMK geopolymer prepared with a high concentration of NaOH is fully hydrated and has a dense structure. Through comparative analysis of UMK geopolymer pore distribution and pore structure characteristics, it was found that the porosity of UMK geopolymer decreased with the increase of sodium hydroxide concentration. The proportion of small pores did not change much, while the large pores gradually evolved into mesopores. In addition to this, curing time was found to have no significant effect on geopolymer microstructure and strength development. This research provides a theoretical basis for the practical engineering application of UMK.
The large-scale stacking of alkaline industrial solid wastes such as soda residue (SR) and calcium carbide residue (CCR) has caused serious environmental problems. Therefore, a new type of cementitious material was developed in our previous study by using SR-CCR synergistically activated blast furnace slag (BFS)-fly ash (FA), which abbreviated as SCBF. This paper further studied the effects of various curing methods on the compressive strength and microstructure of SCBF, which was expected to provide guidance for its application in the field of non-reinforced products such as baking-free brick. The results show that the optimal curing scheme was heat curing at 75 °C for 12 h. The optimal scheme significantly promoted an early hydration reaction and provided the 3d/28d strength values of 16.4/24.7 MPa, exceeding those of room-temperature (RT) sealed curing and water curing by 154/24.5 % and 264/31 %, respectively. Besides, the optimal scheme accelerated the formation of CSH gel, Hydrotalcite (6MgO·Al2O3·CO2·12H2O), Hydrocalumite (3CaO·Al2O3·CaCl2·10H2O), and other crystal products, as well as increased the consolidation rate of chlorine ion from 37.9 % (in RT sealed curing) to 64.3 %. These hydration products were evenly distributed, effectively filling the pores and reducing the macroporosity from 9.30 (in RT sealed curing) to 1.54 %, thus improving the early and later-age strength. Too high curing temperature (exceeding 75 ℃) or prolong heat curing period (exceeding 12 h) would cause microstructure deterioration, significantly increase the number of macropores and microcracks in the matrix, ultimately leading to strength retrogression.
Ecotoxicological analysis of construction products is a relatively unexplored area at international level. Aquatic toxicity tests on construction products has been recommended recently for freshwater environment. However, the biological effects of alternative materials on marine ecosystem are still not considered. In this study, the main aim was to assess the environmental impact of alternative mortars proposed as artificial reefs (ARs) materials. The ARs specimens were developed by 3D printing, based on cement and geopolymer mortars using recycled sands of glass and seashells. For this purpose, a leaching test and two different toxicity bioassays, luminosity reduction of marine bacteria Vibrio fischeri (Microtox®) and the success of embryo-larval development of sea-urchin Paracentrotus lividus, were conducted. From the leaching results it should be noted that the mobility of all trace elements considered in both, raw materials and mortars, meet the inert landfill limits, except As, Mo, Se or Sb in the leachates geopolymer mortars. However, the results obtained from the both bioassays show low environmental acceptability for those mortars containing shell sand, probably due to the degradation of the organic matter adhered to the shells. On the other hand, cement mortars obtain better results than geopolymer mortars, regardless of the aggregate used, showing certain consistency with the leaching behaviour, since they present the lowest mobility of trace chemical elements. Therefore, the results supporting the environmental acceptability of its potential use as alternative materials in the production of ARs.
Geopolymer cement, high-alkali (K-Ca)-Poly(sialate-siloxo) cement, results from an inorganic polycondensation reaction, a so-called geopolymerisation yielding three dimensional zeolitic frameworks. High-tech Geopolymer K-Poly(sialate-siloxo) binders, whether used pure, with fillers or reinforced, are already finding applications in all fields of industry. These applications are to be found in the automobile and aeronautic industries, non-ferrous foundries and metallurgy, civil engineering, plastics industries, etc. Geopolymer cement hardens rapidly at room temperature and provides compressive strengths in the range of 20 MPa, after only 4 hours at 20°C, when tested in accordance with the standards applied to hydraulic binder mortars. The final 28-day compres- sion strength is in the range of 70-100 MPa.The behaviour of geopolymeric cements is similar to that of zeolites and feldspathoids; they immobilize hazardous materials within the geopolymeric matrix, and act as a binder to convert semi-solid wastes into adhesive solids. Their unique properties which include high early strength, low shrinkage, freeze-thaw resistance, sulphate resistance and corrosion resistance, make them ideal for long term containment in surface disposal facilities. These high-alkali cements do not generate any Alkali-Aggregate-Reaction. Preliminary study involving 27Al and 29Si MASNMR spectroscopy and the proposed structural model, reveal that geopolymeric cements are the synthetic analogues of natural tecto-alumino-silicates.
Spectacular technological progress has been made in the last few years through the development of new materials such as 'geopolymers', and new techniques, su.ch as 'sol-gel'. New state-of-the-art materials designed with the help of geopolymerisation reactions are opening up new applications and procedures and transjorming ideas that have been taken for granted in inorganic chemistry. High temperature techniques are no longer necessary to obtain materials which are ceramic-like in their structures and properties. These mate rials can polycondense Just like organic polymers, at temperatures Lower than 100 °C. Geopolymerization in volves the chemical reaction of alumina-silicate oxides (Af+ in !V-fold coordination) with a/kali polysilicates yielding polymeric Si-0-Al bonds; the amorphous to semi-crystalline three dimensional silico-aluminate structures are of the Poly(sialate) type (-Si-O-Al-0-), the Poly(sialate-siloxo) type (-Si-O-AlO-Si-0-), the Poly(sialate-disiloxo) type (-Si-O-Al-O-Si-O-Si-0-).
This new generation of materials, whether used pure, withfillers or reinforced, is already .fin.ding applications in ail fields of industry. Some examples:
- pure: for storing taxie chemical or radioactive waste, etc.
- jïlled: for the manufacture of special concretes, molds for molding ther- moplastics, etc.
- reinforced:for the manujàcture of molds, tooling, in aluminum alloy foundries and metallurgy, etc.
These applications are to be found in the automobile and aerospace industries, non-ferrous foundries and metallurgy, civil engineering, plastics industries, etc.
The geopolymers potassium polysialate (K-PS) and potassium sialate disiloxo (K-PSDS) have been found to possess extremely good thermal stability. K-PS shows little sign of melting up to 1400 jC, its amorphous structure being replaced by the crystalline feldspars leucite and kalsilite at 1000 jC. 27 Al and 29 Si MAS NMR confirm the ease of this thermal reaction which involves only slight changes to the tetrahedral Al environment. Silica-rich K-PSDS becomes friable and porous at >1200 jC, with less complete crystallisation of K-feldspar, the formation of some cristobalite and the retention of a degree of amorphous geopolymer. 39 K NMR suggests that the charge-balancing alkali ions in the K-PS and K-PSDS geopolymer networks behave similarly to those of Na geopolymers, dehydrating on heating and moving into the feldspar lattice >1000 jC. D 2002 Elsevier Science B.V. All rights reserved.
This paper describes research into the use of granulated blast furnace slag as an active filler in the making of geopolymers. During this work it was found that geopolymer setting time correlates well with temperature, potassium hydroxide concentration, metakaolinite and sodium silicate addition. The physical and mechanical properties of the geopolymer also correlated well with the concentration of alkaline solution and the amount of metakaolinite that is added. The highest compressive strength achieved was 79 MPa. For fire resistance tests, a 10 mm thick geopolymer panel was exposed to a 1100 °C flame, with the measured reverse-side temperatures reaching less than 350 °C after 35 min. The products can be fabricated for construction purposes and have great potential for engineering applications.
A representative group of Spanish fly ashes has been characterised in order to determine its capacity for being alkali activated and give place to a material with cementitious properties. The characterisation studies have been carried out through chemical analysis, laser granulometry, Blaine, BET, particle size distribution, XRD and 29Si MAS NMR. Compressive mechanical strength test was used to determine the reactivity of the fly ashes as alkaline binders. The results obtained have demonstrated that all investigated fly ashes are suitable to be alkali activated. Additionally it has also been demonstrated that the key factors of their potential reactivity are: the reactive silica content, the vitreous phase content and the particle size distribution.
The alkali activation of waste materials (especially those coming from industrial and mining activities) has become an important area of research in many laboratories because it is possible to use these materials to synthesize inexpensive and ecologically sound cementlike construction materials. In the present paper, the mechanism of activation of a fly ash (no other solid material was used) with highly alkaline solutions is described. These solutions, made with NaOH, KOH, water glass, etc., have the common characteristic of having a very high OH− concentration. The product of the reaction is an amorphous aluminosilicate gel having a structure similar to that of zeolitic precursors. Temperature and time of curing of specimens together with the solution/fly ash ratio are some of the variables that were studied. These variables have been shown to notably influence the development of the mechanical strength of the final product. Mechanical strengths with values in the 60 MPa range were obtained after curing the fly ash at 85°C for only 5 h.
The alkali activation of metakaolin is a way of producing high strength cementitious materials. The processing of these materials has been the subject of numerous investigations. The present paper describes the results of a research project initiated to study the stability of these materials when exposed to aggressive solutions. Prisms of mortar made of sand and alkali-activated metakaolin were immersed in deionized water, ASTM sea water, sodium sulfate solution (4.4% wt), and sulfuric acid solution (0.001 M). The prisms were removed from the solutions at 7, 28, 56, 90, 180, and 270 days. Their microstructure was characterized and their physical, mechanical, and microstructural properties were measured. It was observed that the nature of the aggressive solution had little negative effect on the evolution of microstructure and the strength of these materials. It was also found that the 90-day and older samples experienced a slight increase in their flexural strengths with time. This tendency was most pronounced in those samples cured in sodium sulfate solutions. This behavior may be related to the change in microstructure of the cementitious matrix of the mortars cured longer than 90 days. Some of the amorphous material present had crystallized to a zeolite-like material belonging to the faujasite family of zeolites.
The alkaline activation of metakaolin leads to high mechanical performance inorganic polymers.
A JAF conduction calorimeter was used to follow the reaction of metakaolin with NaOH solutions. The alkaline activation of
metakaolin to yield a cementitious material is an exothermic process involving three steps: an initial and very fast process
of dissolution, which is strongly exothermic, followed by an induction period in which the heat exchange rate decreases, and
finally an exothermic step of reaction reactivation in which cementitious materials precipitate and after which the heat exchange
rate decreases.
The calorimetric curves lead to the following findings:
- The induction period is lengthened as the NaOH solution concentration and the liquid percentage increase.
- The induction period is shortened as the temperature increases.
- The total heat increases as the liquid percentage and the NaOH concentration increase.
Geopolymerisation can transfer large scale alumino-silicate wastes into value-added geopolymeric products with sound mechanical strength and high acid, fire and bacterial resistance. However, due to the complexity of source materials as well as the interaction between source materials during the geopolymerisation, previous studies have mostly dealt with single or bi-component systems, which could potentially narrow the application of this technology. The present work selects three industrial materials, i.e. fly ash, kaolinite and albite to investigate various combinations. The results show that when appropriate reaction parameters are used, the three component system gives geopolymers possessing the highest compressive strength and the lowest probability of cracking. It is believed that the higher reactivity of the fly ash and albite, the interaction between the source materials and the gel phase, and the reinforcing effect caused by the large unreacted albite particles are responsible for this satisfactory mechanical behaviour.
This paper reports the results of the study of the influence of elevated temperature curing on phase composition, microstructure and strength development in geopolymer materials prepared using Class F fly ash and sodium silicate and sodium hydroxide solutions. In particular, the effect of storage at room temperature before the application of heat on strength development and phase composition was studied. X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FTIR) and SEM were utilised in this study.Long precuring at room temperature before application of heat was beneficial for strength development in all studied materials, as strength comparable to 1 month of curing at elevated temperature can develop in this case only after 24 h of heat curing. The main product of reaction in the geopolymeric materials was amorphous alkali aluminosilicate gel. However, in the case of sodium hydroxide activator in addition to it, traces of chabazite, Linde Type A, Na-P1 (gismondine) zeolites and hydroxysodalite were also present. The type of zeolite present and composition of aluminosilicate gel were dependent on the curing history.
A matrix-flushing method for quantitative multicomponent analysis by X-ray diffraction is reported. It is simpler and faster than, yet as reliable as, the conventional internal-standard method. In this new method, the calibration-curve procedure is shunted; a more fundamental `matrix-flushing' concept is introduced. The matrix-flushing theory gives an exact relationship between intensity and concentration free from matrix effect. Contrary to most theoretical methods the working equation is very simple, no complicated calculations are involved. The matrix-flushing theory and the analytical procedure are presented. Eight illustrative examples are drawn to demonstrate how this theory is applied to multicomponent analysis and amorphous-content determination. A novel `auto-flushing' phenomenon of binary systems was observed which appears to make the analysis of any binary system a simple matter.
A set of reference intensities, ki, are required for the quantitative interpretation of X-ray diffraction patterns of mixtures. Each ki was heretofore determined individually from binary mixtures of a one-to-one weight ratio. A procedure for the determination of all ki's of interest simultaneously is presented. The X-ray diffraction patterns of multicomponent mixtures usually contain overlapping peaks. This overlapping problem can be avoided by choosing an arbitrary reference material already present in the mixture and/or using the strongest resolved reflections directly. These concepts are substantiated by ten examples. The maximum standard deviation of the matrix-flushing method has been estimated to be 8% relative.
Fundamental research into the geopolymerisation process is increasing rapidly because of the potential commercial application of this technology. Despite this, however, very little work has been undertaken to determine the relationship between composition and temperature on the final chemical and physical properties of geopolymeric products derived from waste materials. The present study shows that the differences in reactivity of source materials, used during the synthesis of waste-based geopolymers, significantly affect the final properties of the geopolymeric material. It is proposed that these observed changes in material properties are due to the incomplete dissolution of the waste material. The water content, the fly ash/kaolinite ratio, as well as the type of metal silicate used have a substantial effect on the final properties of the geopolymer. In particular, the current work shows that the thermal history of the source materials, such as kaolinite, as well as the curing regime for the geopolymer are important factors that must be taken into consideration when designing a geopolymer product for a specific application.
The alkali activation of waste materials (especially those coming from industrial and mining activities) has become an important area of research in many laboratories because it is possible to use these materials to synthesize inexpensive and ecologically sound cementlike construction materials. In the present paper, the mechanism of activation of a fly ash (no other solid material was used) with highly alkaline solutions is described. These solutions, made with NaOH, KOH, water glass, etc., have the common characteristic of having a very high OH− concentration. The product of the reaction is an amorphous aluminosilicate gel having a structure similar to that of zeolitic precursors. Temperature and time of curing of specimens together with the solution/fly ash ratio are some of the variables that were studied. These variables have been shown to notably influence the development of the mechanical strength of the final product. Mechanical strengths with values in the 60 MPa range were obtained after curing the fly ash at 85°C for only 5 h.
The burning of brown coal for electricity generation produces thousands of tonnes of fly ash each year. Treatment of the fly ash can reduce leach rates of metals and allow it to be disposed in less prescribed landfill. A geopolymer matrix was investigated as a potential stabilisation method for fly ash obtained from electrostatic precipitators and ash disposal ponds. The ratio of fly ash and geopolymer was varied to determine the effects of different compositions on leaching rates. The major element leachate concentrations obtained from pond ash were lower than that of precipitator fly ash. Conversely, precipitator ash-geopolymers were better for trace heavy metal stabilisation. Effective reduction of elemental concentrations in the leachate has been achieved, particularly for calcium, arsenic, selenium, strontium and barium. Scanning electron microscopy revealed the distribution of metals originated from fly ash and from added geopolymer material. It also showed that some elements are leached from ash particles to the geopolymer phase and others remained as undissolved particles. Qualitative analysis showed that fly ash particles interacted with the geopolymers phase through surface reactions.
The feasibility of using ultrasound to enhance the geopolymerisation of metakaolinite/sand and fly ash/metakaolinite mixtures was investigated. The introduction of ultrasonication into the geopolymerisation systems increased the compressive strength of the formed geopolymers and the strength increased with increased ultrasonication up to a certain time. The dissolution of metakaolinite and fly ash in alkaline solutions was enhanced by ultrasonication, hence releasing more Al and Si into the gel phase for polycondensation. SEM analysis demonstrated that ultrasonication improved the distribution of the gel phase in the geopolymeric matrices and strengthened the binding between the particle surfaces and the gel phases. XRD patterns showed that ultrasonication enhanced the formation of semi-crystalline to crystalline phases in the formed geopolymers. The 27Al MAS-NMR spectra showed 27Al chemical shifts at around 55 ppm for the geopolymers synthesised with and without ultrasonication, indicating that Al was tetrahedrally coordinated in the form of Al(4Si). 29Si MAS-NMR studies showed that ultrasonication largely improved the interlinkage between Si and Al species, increased the concentrations of polysialate species and enhanced the ordering of the Si and Al tetrahedra in the gel phase in geopolymerisation. Both 27Al and 29Si MAS-NMR spectra indicated an increased extent of polymerisation between Al and Si species in the presence of ultrasonication. The thermal analysis indicated that ultrasonication improved the thermal stability of the formed geopolymers. The improved performance of the ultrasonically formed geopolymers in terms of compressive strength and thermal stability could be attributed to the accelerated dissolution of the Al—Si source materials, the strengthened bonds at the solid particle/gel phase interfaces, the enhanced polycondensation process and the increased semi-crystalline and crystalline phases.
Geopolymerization, a fairly new technology based on a very old principle, has emerged during the last few years as a possible
solution to some waste stabilization and solidification problems. Some commercial successes have been achieved, although the
technique remains fairly unknown as well as seemingly unpopular. It has been shown that most waste materials containing sources
of silica and alumina should be capable of taking part in a geopolymerization reaction. In this article, flyash was used as
a reactant in creating a geopolymeric matrix for the immobilization of process water containing 25,000 ppm of Cu or Pb cations.
By means of X-ray diffraction, scanning electron microscopy (SEM), infrared spectroscopy, Brunauer-Emmett-Teller (BET), compressive
strength, as well as kinetic leaching analyses, the main factors influencing matrix stability, immobilization efficiency,
and therefore leaching behavior were investigated and discussed qualitatively. It was found that relatively high strengths
could be obtained using low Ca flyash. The environment and coordination number of source aluminum and silica seemed to play
a major role in the eventual matrix stability. Other factors influencing matrix stability include the alkali metal cation
used as well as the type of metal being immobilized. The kinetics of leaching of immobilized metals from the geopolymerized
flyash were qualitatively found to proceed along a combination of pore diffusion and boundary diffusion control mechanisms.
It is finally concluded that immobilization of metals in geopolymerized flyash proceeds by a combination of physical encapsulation
and chemical bonding, with adsorption also thought to play a role.
In this paper, the basic properties viz., workability and strength of geopolymer mortar made from coarse lignite high calcium fly ash were investigated. The geopolymer was activated with sodium hydroxide (NaOH), sodium silicate and heat. The results revealed that the workable flow of geopolymer mortar was in the range of 110 ± 5%–135 ± 5% and was dependent on the ratio by mass of sodium silicate to NaOH and the concentration of NaOH. The obtained compressive strength was in the range of 10–65 MPa. The optimum sodium silicate to NaOH ratio to produce high strength geopolymer was 0.67–1.0. The concentration variation of NaOH between 10 M and 20 M was found to have a small effect on the strength. The geopolymer samples with high strength were obtained with the following practices: the delay time after moulding and before subjecting the sample to heat was 1 h and the optimum curing temperature in the oven was 75 °C with the curing duration of not less than two days.
The stabilisation and solidification of waste materials by the technology of geopolymerisation is receiving increasing attention from researchers; immobilisation of metal contaminants in these structures seems to be a viable alternative to present stabilisation techniques. This paper presents some experimental evidence concerning the effect of the inclusion of mainly Cu and Pb on the physical and chemical characteristics of geopolymers manufactured from fly ash. A variety of experimental and analytical techniques were used in this investigation, including compressive strength testing, specific surface area analyses, transmission electron microscopy, nuclear magnetic resonance, X-ray diffraction, and infrared spectroscopy. It was found that contaminants are being immobilised through a combination of chemical bonding and physical encapsulation. The nature of the contaminant seems to have a fairly large effect on both the physical and chemical characteristics of the final product, with subsequent long-term implications as far as durability is concerned. It is therefore concluded that a definite interaction exists between matrix-forming components and the immobilisation of the contaminant, where the amount of contaminant is a critical factor in the analysis.
Finding means of utilising waste products is a very important field of research at the moment. In this study, fly ash, a waste product of the electricity and petrochemical industries, was investigated as a basic ingredient of a new geopolymeric material. The similarity of fly ash to natural pozzolans has encouraged the use of this waste product in the synthesis of geopolymers, which, in turn, can best be viewed as consisting of a polymeric Si–O–Al framework. Manufacturing of the geopolymers was conducted by mixing fly ash, kaolinite, sodium silicate solution, NaOH and water. The samples were cured at 40, 50, 60 and 70 °C for different time intervals (6, 24, 48 and 72 h). The optimum condition was found to be at 60 °C for a period of 48 h. Compressive strength measurements show a maximum strength of almost 8 MPa after 28 days. Infrared spectroscopic measurements were obtained of the samples after 7 and 28 days. X-ray diffraction measurements show quartz as the main constituent with the largest part of the geopolymer structure being amorphous and glass-like.
During the last decade geopolymerisation has emerged as a possible technological solution for the effective stabilisation and immobilisation of toxic materials. Despite the fact that this technology is based on a very old principle, surprisingly little is known about the nature of these reactions or their products. It is only in the last fifteen years that it has been rediscovered and attention has been drawn to its useful chemical and physical properties. This paper will therefore attempt to briefly discuss the available literature on geopolymerisation in terms of its history, reaction kinetics and structure as well as investigations into the application of geopolymerisation to various waste forms. It is evident from the literature that factors governing the formation of geopolymers are still poorly understood, although the physical and chemical properties suggest that these matrices are well suited for the immobilisation of toxic materials and specifically toxic metals. It is finally concluded that geopolymers offer attractive options towards simple industrial applications where large volumes of waste materials need to be stabilised. It must also be acknowledged that these advantages can only be applied optimally once all relevant interactions regarding the formation of geopolymers from waste materials have659 been quantified scientifically. Hence, further research is required regarding the formation of geopolymers and their application in industry.
The stabilisation and solidification of waste materials by the technology of geopolymerisation is fairly unknown and has not been studied in any depth. This paper presents some experimental evidence as to the physical and chemical characteristics of geopolymers manufactured from fly ash originating from two different regions. It has become apparent that these materials could be used for a wide variety of environmental and other applications such as the immobilisation of heavy metals and the fabrication of structural products. In this study compressive strength testing, specific surface area determinations, Transmission Electron Microscopy (TEM), Nuclear Magnetic Resonance (NMR) and leaching tests were used in characterising a number of geopolymer matrices. It is also shown how the inclusion of heavy metal ions, alkali metal cations and different processing conditions affect the physical and chemical characteristics of the final product.
When crystalline aluminosilicates partially dissolve in a concentrated alkaline medium, an amorphous geopolymeric gel is formed interspersed with undissolved crystalline particles. Some aluminosilicates dissolve more readily than others to give an equilibrium ratio of aluminium to silicon in the gel. In this case study, kaolinite and stilbite mixtures were used to investigate the relative reactivity of different minerals when present in different ratios. XRD and 29Si and 27Al MAS-NMR were used to determine when a specific mineral was completely transferred into the gel phase. Electron diffraction using transmission electron microscopy (TEM) and high-resolution transmission electron microscopy (HREM) were employed to establish the amorphous nature of the gel phase. Scanning electron microscopy (SEM)/energy dispersive X-ray (EDX) and TEM/EDX were then used to determine the composition of the gel. By using simple mass balance assumptions, the quantity of gel and the extent of partial dissolution of an aluminosilicate could then be calculated. It was found that a geopolymer containing a higher weight percentage of CaO in its gel, a lower ratio of (average surface area)/gel, and where the undissolved crystalline particles have a higher hardness had higher mechanical strength. The method developed in this paper is also applicable to other cementitious materials.
In recent years geopolymers have emerged as novel materials having unique and highly desirable chemical and mechanical properties. The technology of geopolymerisation is gaining commercial interest because it has been demonstrated that, in certain cases, the properties of geopolymeric materials are superior to existing cementitious systems. Source materials used during the synthesis of geopolymers from industrial by-products such as fly ash have an important role in determining the final properties of the geopolymer matrix. It is proposed in the current work that this is caused by the fact that not all of the waste material is dissolved and, therefore, some of the original structures of waste particles remain intact, becoming part of the new geopolymer structure and serving to either weaken or strengthen the newly formed structure. The current work uses XRD and FTIR techniques to characterise fly ash obtained from different sources in order to gain a greater understanding of the effect of phase composition on the dissolution behaviour, reactivity, and final physical and mechanical properties of fly ash-based geopolymeric materials.
Current regulations classify fly ash as a prescribed waste and prohibit its disposal in regular landfill. Treatment of the fly ash can reduce the leach rate of metals, and allow it to be disposed in less prescribed landfill. A geopolymer matrix was investigated as a potential stabilisation method for brown coal fly ash. Precipitator fly ash was obtained from electrostatic precipitators and leached fly ash was collected from ash disposal ponds, and leaching tests were conducted on both types of geopolymer stabilised fly ashes. The ratio of fly ash to geopolymer was varied to determine the effects of different compositions on leaching rates. Fourteen metals and heavy metals were targeted during the leaching tests and the results indicate that a geopolymer is effective at reducing the leach rates of many metals from the fly ash, such as calcium, arsenic, selenium, strontium and barium. The major element leachate concentrations obtained from leached fly ash were in general lower than that of precipitator fly ash. Conversely, heavy metal leachate concentrations were lower in precipitator fly ash than leached pond fly ash. The maximum addition of fly ash to this geopolymer was found to be 60wt% for fly ash obtained from the electrostatic precipitators and 70wt% for fly ash obtained from ash disposal ponds. The formation of geopolymer in the presence of fly ash was studied using 29Si MAS-NMR and showed that a geopolymer matrix was formed. X-ray diffraction (XRD) analysis and scanning electron microscopy (SEM) imaging showed the interaction of the fly ash with the geopolymer, which was related to the leachate data and also the maximum percentage fly ash addition.
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Microstructural characterisation of geopoly-mers synthesised from kaolinite/stilbite mixtures using
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Leaching characteristics of moulded or monolithic building and waste materials. Determination of leaching of inorganic components with the diffusion test
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