The geopolymerization reaction is a chemical process involving the dissolution of amorphous, semi-crystalline and crystalline phases following alkaline or acid attack at ambient or at low temperature ...(T˂100 °C). Together with precondensed entities of the used activator solution the dissolved parts form a geopolymer network which glues together all remaining unreacted parts as ingredients of the artificial stone. The fate of the mineralogical phases present in the precursors used in the synthesis of alkaline and acid geopolymers is reviewed in this article. The different starting materials used in the synthesis of geopolymers and the different techniques used to modify the reactivity of these materials are reported. The mineralogical evolution of the amorphous, semi-crystalline and crystalline phases after activation at ambient and at low temperatures (T < 100 °C) is also reported. This study shows that for the mineralogical investigation of raw material, precursors and geopolymers, XRD is the most widely used analytical method. The most commonly used method to confirm the participation of crystalline phases in geopolymerization is the comparison of the diffractograms of the raw material to those of the products. It also indicates that, in addition to the amorphous aluminosilicate phases, certain semi-crystalline, and crystalline phases participate in this geopolymerization dynamic either by undergoing total or partial dissolution to form an inorganic macromolecule with an amorphous structure of the zeolitic type and other new minerals. The composition of the phases formed depends on the base material. Increasing the synthesis temperature promotes the dissolution of phases, the formation of geopolymer networks, and in some cases, the formation of new phases such as sodalities, zeolite A and zeolite P. Little work has been done to quantify the mineralogical phases before and after precursor activation, making it impossible to assess dissolution, the degree of geopolymerization, and mineral formation. The exact structure of the phases formed is often questionable, as most of the papers do not mention their reference structure number. There is also a lack of quantification of the amorphous phase resulting from the hardening of the activating solution and the evaluation of the fraction of the amorphous phase contained in the precursor remains unreacted. The mineralogical investigation must also extend to the quantification of phases using Rietveld refinement with internal standards to correlate these with the physical and mechanical properties of geopolymer products. Additional mineralogical study techniques, such as thin sections, should be used in future work for in-depth mineralogical investigation of geopolymers.
Natural stones have been utilized to meet various needs of human civilization since ancient times. The exploitation of any resource is associated with the production of redundant materials called ...wastes. Sandstone waste (SW) is one such waste obtained during the industrial processing of sandstones. Due to its siliceous composition, extensive yield, and disorganized dumping, noxious conditions related to land and human health are promoted. However, the lack of comprehensive engineering studies, mineralogical analysis, and design methodologies associated with the utilization of sandstone processing wastes restricted their applicability only to fillers or partial substitutes with pozzolans and traditional cement in meager volumes. In the past, limited efforts have been made to utilize SW as a construction entity, particularly for binding purposes. Thus, to enhance the scope of its utilization, a comprehensive investigation has been performed in this research to transform sandstone waste into a novel construction material by geopolymerization. Mix design tailoring and laboratory tests were implemented to understand the effects of sodium hydroxide concentration and sodium silicate to sodium hydroxide ratio on the dissolution and physio-mechanical characteristics of SW-based geopolymers. The activator-to-binder ratio was restricted to 0.4 to obtain pastes with sufficient workability without hindering the properties of the matrix. Besides, a high temperature-curing regime was selected based on SW's crystallographic and reactivity analysis. Subsequently, a total of 48 samples were prepared and tested at the curing age of 28 days. Detailed characterization of SW and SW-based geopolymer samples was performed using optical, X-ray, and infrared spectroscopies aided by electron imaging and thermogravimetric techniques. SW-based geopolymer samples showed compressive strengths in the range of 6-12 MPa, ~2 to 3 times higher than those obtained in previous experimentations. Phase analysis and microstructural examinations confirmed SW's participation in geopolymerization. Overall, it could be advocated that geopolymerization is an innovative approach for solving issues related to the disposal and re-utilization of SW, extending its possible application to the fields of cement mixes, wall tiles, mortars, and masonry as per the commendations of ASTM and ACI committee.
This paper studies the alkali activation of iron-rich aluminosilicates (laterites). Three activating alkaline solutions were prepared from sodium hydroxide solution (8, 10 and 12 M) with sodium ...silicate (Na2SiO3) in order to obtain the sodium silicate solutions with moduli of SiO2/Na2O equal to 0.75, 0.92 and 1.04; H2O/Na2O = 9.78, 10.45 and 12.04. The effects of above-defined solutions on the setting time, physical and microstructural properties of geopolymer binders from calcined laterite (600 °C), containing metakaolinite, as the sole binder at room temperature are reported and discussed. A laterite from Eloumden and one from Odza were used. The synthesized products were labelled GPEL(i=1.04, 0.92 and 0.75) and GPOD(i=1.04, 0.92 and 0.75) series. The dry compressive strength measured after 7 and 28 days were 4–10 and 10–18 MPa, respectively. It was typically found that the geopolymer paste from sodium hydroxide with molar concentration 12 M and the molar ratio SiO2/Na2O of the silicate solution equal to 0.75 produced the highest compressive strength (~ 18 MPa). These samples also have a denser matrix. The dry bulk densities of both series increased with the decrease of silica moduli and were in the range 2.31–2.43 and 2.32–2.52 g/cm3 and the water absorptions were in the range of 8.21–11.40% and 7.23–13.03% for geopolymers GPEL and GPOD series, respectively. The setting time decreased with increasing molarity of NaOH solutions. The physicochemical properties and the mineralogy of both iron-rich aluminosilicates were influenced by the silicate modulus of activating solutions and the best compositions were achieved with characteristic SiO2/Na2O = 0.75 and H2O/Na2O = 9.78.
The manufacturing of cement demand burning of huge quantities of fuel as well as significant emissions of CO2 resulting from the decomposition of limestone that consequently resulted in severe ...environmental impact that is estimated by one ton of CO2 per ton of cement. Geopolymerization technology is an effective method for converting wastes (containing alumina and silica) into useful products. It can reduce CO2 emissions significantly from the cement industry. The geopolymerization process usually starts with source materials based on alumina/silicate in addition to alkaline liquids. The compressive strength, setting time, and workability of the final product depends mainly on the type and proportions of the precursors, the type and strength of the activator, the mixing and curing conditions. The structural performance of a geopolymer is similar to that of ordinary Portland cement (OPC). Therefore, geopolymer can replace OPC, and thus decreasing the energy consumption, reducing the cost of the building materials, and minimizing the environmental impacts of the cement industry. This review summaries the mechanism of geopolymerization, including the controlling parameters and different raw materials (fly ash, kaolinite and metakaolin, slag, red mud, silica waste, heavy metals waste, and others) with particular focus on recent studies and challenges in this area.
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•Geopolymer can replace OPC, and thus decreasing energy consumption.•Mechanism of geopolymerization, including the controlling parameters summarized.•Different geopolymer raw materials are thoroughly discussed.•Geopolymer reduces the environmental impact of the cement industry.
The growing demand for non-ferrous metals (Aluminium, Copper, Nickle, Lead and Zinc) has grown the non-ferrous metallurgical industry, which generate huge amount of solid waste. Most common method ...for the disposal of these solid wastes is dumping at sites, which pollutes the soil and water and covers the useful land. Geopolymerization technique can be very helpful for the safe disposal of these solid wastes, which converts the solid wastes into valuable construction materials such as binders, mortar, bricks, paving blocks and concrete etc. However, to commercialize the use of these construction products, some key aspects require detailed examination. Alternative techniques and materials will have to be identified to increase their reactivity in geopolymerization and in-depth knowledge of reaction mechanism, mix design, strength and durability characteristics of resulting geopolymer will have to be studied. The present paper reviews the important studies on geopolymerization of different solid wastes produced from non-ferrous industry. The optimum synthesis parameters such as alkali activators, curing temperature, curing time and molar ratio etc. for the geopolymerization of these solid wastes are reported and exiting gaps and future trends are also discussed.
•Different solid wastes produced from non-ferrous industry have been reviewed.•Optimum synthesis parameters for geopolymerization of solid wastes are reported.•Valued construction materials can be obtained by geopolymerization of solid wastes.•Key barriers in geopolymerization are processing methods & activators availability.•Future research required on properties of resultant geopolymer from solid wastes.
Acid mine/rock drainage (AMD/ARD), effluents with low pH and high concentrations of hazardous and toxic elements generated when sulfide-rich wastes are exposed to the environment, is considered as a ...serious environmental problem encountered by the mining and mineral processing industries around the world. Remediation options like neutralization, adsorption, ion exchange, membrane technology, biological mediation, and electrochemical approach have been developed to reduce the negative environmental impacts of AMD on ecological systems and human health. However, these techniques require the continuous supply of chemicals and energy, expensive maintenance and labor cost, and long-term monitoring of affected ecosystems until AMD generation stops. Unfortunately, the formation of AMD could persist for hundreds or even thousands of years, so these approaches are both costly and unsustainable. Recently, two alternative strategies for the management of AMD and mine tailings are gaining much attention: (1) prevention techniques, and (2) mine waste recycling. In this review, recent advances in AMD prevention techniques like oxygen barriers, utilization of bactericides, co-disposal and blending, and passivation of sulfide minerals are discussed. In addition, recycling of mine tailings as construction and geopolymer materials to reduce the amounts of wastes for disposal are introduced.
•Acid mine drainage (AMD) causes serious environmental problems around the world.•AMD generation can continue for decades until sulfide minerals are exhausted.•Remediation options are effective but unsustainable.•Prevention techniques are of importance to overcome AMD problems sustainably.•Recycling of mine tailings can help reduce the amounts of tailings for disposal.
Geopolymer is a new environment-friendly cementitious material, and the development of geopolymer can reduce the carbon dioxide emission caused by the development of cement industry. Geopolymer ...materials not only have excellent mechanical properties, but also have a series of excellent properties such as fire resistance and corrosion resistance. Most industrial solid waste and waste incineration bottom ash are piled up at will, which not only occupies land resources, but also has a bad impact on the environment. Recycling them can be used as raw materials for preparing geopolymers. Geopolymer materials can effectively adsorb heavy metals, dyes, and other radioactive pollution, which is very beneficial to society's future development. However, due to the excellent properties of geopolymer materials, its application goes beyond that. Some useful information about geopolymer materials was introduced in this paper. The paper included the geopolymerization, the source of raw materials, the types of activators, the preparation methods, and the different application fields of geopolymer materials. The factors affecting the fresh properties and mechanical properties of geopolymer materials were discussed. In this paper, the shortcomings and application limitations of geopolymer materials were summarized, and their progress was summarized to lay a theoretical foundation for the long-term development of geopolymer materials.
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•Geopolymerization, the material source, and activators were summarised.•The preparation and properties of geopolymer materials were analysed in detail.•The application of geopolymer materials was reviewed.•Existing restrictions on the development of the geopolymer materials were summarised.•Several methods of developing geopolymers were proposed.
•The raw materials and reaction kinetics of GP synthesis are reviewed.•The various application potential of GP products are reviewed extensively.•Challenges and future research recommendations are ...provided.
Geopolymers, combining some characteristics of organic polymers, cements and ceramics for its special poly-condensed network structure, have received extensive attention of the researchers as a green cementitious material because of favorable and unique characteristics. This study mainly presents an overview on the progress of geopolymers research and development in recent decades. The works on raw materials, geopolymerization kinetics, the applications development and challenges of geopolymers are reviewed. This paper focuses on the applications progress of geopolymer as green civil engineering materials, rapidly-repair and dealing with poisonous and radioactive waste materials, coatings, novel ceramic materials, functional composite, three-dimensional printing materials and biological materials, etc. The main contribution of this review is to systematically summarize the complex and diverse of published results on geopolymers application in reality and present future challenges, which is beneficial to the further research activities of civil engineers, environmental scientists, chemists and materials scientists. The current investigation indicates that the geopolymers not only exhibit widespread application prospect to be used as sustainable construction materials, but also have great potential in the fields of three-dimensional printing materials, biological materials and other emerging geopolymer functional materials.
Chemically activated materials (often termed as geopolymer) have received attracting attentions in civil, material and environmental research fields as a toolkit alternative to traditional Portland ...cement in specific applications. This paper presents a comparative review on silico-aluminophosphate (SAP) geopolymers in terms of definition, chemistries involved during geopolymerization, mechanical performance, durability, environmental impacts, and their potentials in applications relative to conventional alkali-aluminosilicate (AAS) geopolymers. Recommendations for future applications are also highlighted. It is found that S-A-P gels with six-coordinated aluminum environment dominate in SAP geopolymers, while the aluminum in N-A-S-H gels formed in the AAS geopolymers is characterized by four-coordinated features. Besides, the slow performance development of SAP geopolymer matrix under ambient temperature curing can be compensated through incorporating additional countermeasures (e.g., metal sources) which allow the tailored design of such geopolymers for certain in-situ applications. Generally, the calcium-bearing C-(A)-S-H gels co-existing with N-A-S-H gels are dominant in AAS geopolymers, while the S-A-P gels enhanced by phosphate-containing crystalline/amorphous phases are the main products in SAP geopolymers. The SAP geopolymers show their environmental friendliness relative to the AAS geopolymers due to the utilization of phosphate activators that require lower production energy relative to silicate-containing activators. However, the higher cost of phosphate activators may confine the applications of SAP geopolymers in some exquisite or special fields.
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