Use of soda lime glass waste as silica supplier in fly ash based geopolymers

Geopolymers have been primarily proposed for the construction industry as a substitute for Portland cement considering the lower CO2 emissions associated with their production. The relatively high compressive strength and chemical inertness of geopolymers, in addition to the possibility to incorporate in the network hazardous waste materials, increase the current interest in this technology. Geopolymers are usually composed of an aluminosilicate source activated with a solution of sodium silicate and sodium hydroxide. The present study evaluates the feasibility of using waste glass as silica source instead of water glass in geopolymer production, using sodium hydroxide as the only non-waste material.The samples were developed changing the SiO2/Al2O3 molar ratio and the molarity of the sodium hydroxide solution. Fig. 1 shows that the compressive strength tends to rise as the molarity of the solution as well as the SiO2/Al2O3 molar ratio increase. The compressive strength values, around 45 MPa, are comparable to those of traditional Portland cement and they are remarkable considering the high amount of waste glass (70% wt.) incorporated in the matrix . SEM pictures demonstrated the formation of a compact matrix indicating the high reaction degree of the raw materials. Please click Additional Files below to see the full abstract

Glass-Ceramic Foams from 'Weak Alkali Activation' and Gel-Casting ofWaste Glass/Fly Ash Mixtures

A 'weak alkali activation' was applied to aqueous suspensions based on soda lime glass and coal fly ash. Unlike in actual geopolymers, an extensive formation of zeolite-like gels was not expected, due to the low molarity of the alkali activator (NaOH) used. In any case, the suspension underwent gelation and presented a marked pseudoplastic behavior. A significant foaming could be achieved by air incorporation, in turn resulting from intensive mechanical stirring (with the help of a surfactant), before complete hardening. Dried foams were later subjected to heat treatment at 700-900 °C. The interactions between glass and fly ash, upon firing, determined the formation of new crystal phases, particularly nepheline (sodium alumino-silicate), with remarkable crushing strength (~6 MPa, with a porosity of about 70%). The fired materials, finally, demonstrated a successful stabilization of pollutants from fly ash and a low thermal conductivity that could be exploited for building applications

Glass-ceramic foams from 'weak alkali activation' and gel-casting of waste glass/fly ash mixtures

A 'weak alkali activation' was applied to aqueous suspensions based on soda lime glass and coal fly ash. Unlike in actual geopolymers, an extensive formation of zeolite-like gels was not expected, due to the low molarity of the alkali activator (NaOH) used. In any case, the suspension underwent gelation and presented a marked pseudoplastic behavior. A significant foaming could be achieved by air incorporation, in turn resulting from intensive mechanical stirring (with the help of a surfactant), before complete hardening. Dried foams were later subjected to heat treatment at 700-900 \ub0C. The interactions between glass and fly ash, upon firing, determined the formation of new crystal phases, particularly nepheline (sodium alumino-silicate), with remarkable crushing strength (~6 MPa, with a porosity of about 70%). The fired materials, finally, demonstrated a successful stabilization of pollutants from fly ash and a low thermal conductivity that could be exploited for building applications

Extensive reuse of soda-lime waste glass in fly ash-based geopolymers

The possibility of extensive incorporation of soda-lime waste glass in the synthesis of fly ash-based geopolymers was investigated. Using waste glass as silica supplier avoids the use of water glass solution as chemical activator. The influence of the addition of waste glass on the microstructure and strength of fly ash-based geopolymers was studied through microstructural and mechanical characterization. Leaching analyses were also carried out. The samples were developed changing the SiO2/Al2O3 molar ratio and the molarity of the sodium hydroxide solution used as alkaline activator. The results suggest that increasing the amount of waste glass as well as increasing the molarity of the solution lead to the formation of zeolite crystalline phases and an improvement of the mechanical strength. Leaching results confirmed that the new geopolymers have the capability to immobilize heavy metal ions

Modifiche strutturali basate su nanomateriali per condotte in PVC destinate al trasporto di fluidi in pressione

Miglioramento delle proprietà termiche, meccaniche e reologiche del PVC mediante additivazione con nanocarich

Neuartige Geopolymere aus silikatischen Industrieabfällen

Increasing global warming has raised concerns on the extensive use of Portland cement due to the high amount of carbon dioxide gas associated with its production. For this reason the construction industry is increasingly turning to the use of environmentally friendly materials in order to meet the sustainability targets required for modern infrastructures. Geopolymers are a new class of construction materials developed primarily as an ecofriendly and sustainable alternative to conventional cement-based construction materials. Although research into geopolymers is significantly increasing, most studies have used raw virgin materials or chemical reagents such as metakaolin or sodium silicate, which then raises issues of sustainability and environmental responsibility. To compete with the inexpensive nature of cement and to ameliorate the buildup of waste materials, thus decreasing the strain on landfill space, this study has investigated the use of industrial by-products such as fly ash, waste glass and red mud, in place of virgin raw materials for production of a new family of geopolymers. Initially, fly ash-based geopolymers were developed and the incorporation of red mud or waste glass in the matrix was investigated. The results show that the mechanical properties decrease as the amount of waste glass in the geopolymer increases; on the other hand, the addition of red mud seems to improve the mechanical behavior. Leaching tests were carried out to confirm the capacity of the geopolymer materials to incorporate and stabilize pollutants inside the network. In order to improve the economic and environmental value of geopolymers, the possibility of partially replacing traditional alkaline activators such as sodium silicate, also called waterglass, with urban waste glass was extensively evaluated. Fly ash-based geopolymers and red-mud based geopolymers were developed using waste glass as the silica supplier and sodium hydroxide as the alkaline solution, avoiding altogether the use of waterglass. The incorporation of soda lime glass waste instead of waterglass represents an innovation in geopolymer research. The influence of the addition of waste glass as well as the molarity of the sodium hydroxide solution was investigated for both the microstructure and mechanical strength of the geopolymers. The results suggested that it is possible to incorporate up to a 60 wt.% of waste glass while still achieving comparable strength to Portland cement. This strength is also attained within a relatively short setting time of circa 7 days. The formation of a geopolymer gel was confirmed by XRD and MAS-NMR analyses. In addition, the XRD technique confirmed the formation of crystalline zeolite phases. Red mud-based geopolymers achieved relatively high compressive strength, 45 MPa, which is extremely interesting given the significant amount of red mud incorporated (60wt.%). Moreover, these geopolymers were developed through an economic process that does not require high temperatures or foaming agents. The light-weight geopolymers, synthesized with the same formulation of the dense materials, have high porosity and acceptable mechanical properties (1 MPa), though, the chemical stability should be improved through future research. In order to expand the range of possible applications, wear resistance and a thermal shock test were carried out obtaining satisfactory results for applications where material degradation in wear and under a sudden temperature change is required. 3D printing and mechanical machining of the developed samples were additionally carried out. The geopolymers were successfully extruded with a 3D printing machine and drilled and worked on the lathe achieving complex shapes and components with accurate surface finish, interesting for expanding the applications of the geopolymers in other industrial sectors beyond constructions. Overall, the outcomes of this study highlight geopolymers as a promising candidate not only for building and construction applications but also for other engineering applications. In particular in areas where specific and accurate shapes are required. The present research has contributed new insights and generated knowledge in the geopolymers field. Geopolymer materials represent an innovative solution for the reuse of waste materials while achieving sound mechanical properties and high chemical stability and due to their processing opportunities geopolymers also promise a wide range of applications.In Anbetracht der globalen Klimaerwärmung gibt es bei der Verwendung von Portlandzementen zunehmend Bedenken, da bei deren Herstellung hohe Mengen an Kohlendioxid freigesetzt werden. Daher setzt die Bauindustrie verstärkt auf umweltverträgliche, nachhaltige Werkstoffe. Geopolymere sind eine neue Baustoffklasse, die als umweltfreundliche und nachhaltige Alternative zu konventionellen zementartigen Baustoffen entwickelt wurden. Obwohl verstärkt an Geopolymeren geforscht wird, werden in den meisten Studien Metakaolin oder Natriumsilikat als Rohstoffe bzw. Ausgangschemikalien verwendet, was dann wiederum Fragen der Nachhaltigkeit und der Umweltverantwortung aufwirft. In dieser Arbeit werden als Ausgangsstoffe zur Herstllung einer neuen Familie von Geopolymeren industrielle Nebenprodukte wie Flugasche, Altglas und Rotschlamm verwendet und dargestellt, wie diese Materialien in die Zementmatrix eingebaut werden. Damit wird gleichzeitig ein kostengünstiger Herstellungsweg für Zemente und eine Verwendungsmöglichkeit für industrielle Abfallstoffe aufgezeigt. Im ersten Schritte wurden in dieser Arbeit Geopolymere auf der Basis von Flugasche und Geopolymere unter Verwendung von Altglas oder Rotschlamm hergestellt. Es stellte sich heraus, dass die mechanischen Kennwerte der Geopolymere mit zunehmender Menge an Glasabfall im Geopolymer abnehmen, jedoch scheint der Zusatz von Rotschlamm das mechanische Verhalten andererseits zu verbessern. Schadstoffe können in das Netzwerk eingebaut und stabilisiert werden, was durch einen Auslaugungstest bestätigt wurde. Die Möglichkeit wurde umfassend untersucht, traditionelle alkalische Aktivatoren wie Natriumsilikat (Wasserglas) mit Kalk-Natron-Altglas zu ersetzen. Dies stellt eine Innovation in der Geopolymerforschung dar, was den wirtschaftlichen und ökologischen Wert von Geopolymeren enorm verbessert. Auf Flugasche und auf Rotschlamm basierende Geopolymere wurden unter Verwendung von Glasabfall als Kieselsäurelieferant und Natriumhydroxid als alkalische Lösung entwickelt, wobei die Verwendung von Wasserglas insgesamt vermieden wurde. Der Einfluss der Zugabe von Altglas sowie die Molarität der Natronlauge auf die Mikrostruktur als auch auf die Festigkeit der Geopolymere wurde untersucht. Dabei stellte sich heraus, dass es möglich ist, nach einer relativ kurzen Abbindezeit von ca. 7 Tagen bis zu 60 Gew .-% Altglas einzuarbeiten und eine mit Portlandzement vergleichbaren Festigkeit zu erreichen. Die Bildung eines Geopolymergels wurde durch XRD- und MAS-NMR-Analyse bestätigt. Die Bildung von kristallinen Zeolithphasen wurde mit XRD nachgewiesen. Rotschlamm-basierte Geopolymere erreichten eine relativ hohe Druckfestigkeit von 45 MPa, welche angesichts der signifikanten Menge an eingebautem Rotschlamm (60 Gew .-%) äußerst interessant ist. Darüber hinaus wurden diese Geopolymere durch einen wirtschaftlichen Prozess entwickelt, der keine hohen Temperaturen oder Schaummittel erfordert. Leichte Geopolymere, die vergleichbar mit dichten Materialien synthetisiert wurden, haben eine hohe Porosität und gute mechanische Eigenschaften, obwohl die chemische Stabilität noch durch zukünftige Forschungen verbessert werden sollte. Um den Anwendungsbereich zu erweitern wurden Verschleißfestigkeit- und Thermoschocktests durchgeführt, wodurch zufriedenstellende Ergebnisse für Anwendungen, bei denen ein Materialabbau durch Abrieb und plötzliche Temperaturänderungen erforderlich ist, erreicht werden konnten. Die hergestellten Geopolymere wurden außerdem erfolgreich mit einer 3D-Druckmaschine extrudiert und auf einer Drehmaschine bearbeitet, wodurch komplexe Formen und Komponenten mit einer präzisen Oberflächengüte erreicht wurden, welche für die Erweiterung der Anwendungen der Geopolymeren in anderen industriellen Bereichen außerhalb von Konstruktionen von Interesse sein können Insgesamt weisen die Ergebnisse dieser Studie darauf hin, dass Geopolymere vielversprechende Kandidaten nicht nur für Anwendungen im Bauwesen sind, sondern auch für andere technische Bereichen, insbesondere in Bereichen, in denen spezifische und präzise Formen erforderlich sind. Die vorliegende Forschung konnte daher neue Einsichten und Wissen auf dem Gebiet der Geopolymere generieren. Geopolymere stellen eine innovative Lösung für die Wiederverwendung von Abfallstoffen dar, weisen gute mechanische Eigenschaften und eine sichere chemische Stabilität auf und bieten aufgrund ihrer vielfältigen Verarbeitungsmöglichkeiten eine breite Palette von möglichen Anwendungen

Fly ash-based geopolymers containing added silicate waste. A review

This review summarizes different types of industrial wastes such as biomass ash, red mud, recycled glass and heavy metals waste, in their application for geopolymer production. These wastes, which are currently abundant and urgent to dispose of, cannot be used alone in the geopolymer process because they do not provide a suitable SiO2/Al2O3 molar ratio for this technology. For this reason, these by-products are commonly used in addition to other aluminosilicate sources such as fly ash or metakaolin. Important parameters which affect the properties and performance of fly ash based geopolymers with addition of a variety of wastes are discussed based on a comprehensive literature review