Search

Lead (II) oxide (PbO) has shown high prospect in modifying mechanical, physical, neutron and charge particle interaction properties of geopolymer due to high bonding matrix. In this study, the impact of PbO doping on the microstructure, mechanical strength, neutron and charge particles interaction properties of geopolymer composites was examined. The undoped and doped geopolymer powders were produced and sintered above 1100 °C for 1 h to obtain denser materials. The X-ray diffraction (XRD) analysis showed that the material is rich in cristobalite (C), mullite (M), and lead silicate (P) phases. The EDS analysis of geopolymer gave Si, O, Na and Al with 40.87, 35.37, 6.06 and 17.68% wt respectively as major elements. The Vickers hardness (HV) values for GEO, GEO-10Pb and GEO-20Pb samples were obtained as 595, 647 and 682 HV respectively under 0.5 kg load. The showed that the introduction of 10% and 20% PbO significantly improved the charge particle attenuation, density and Vickers Hardness of the geopolymer while the total fast neutron removal cross-section decreases with increasing lead content. [ABSTRACT FROM AUTHOR]

Non-firing functional oxide materials are attracting significant interest due to their suitability for a wide range of applications, particularly in thermal, electrical, and architectural fields. These materials, which range from natural to synthetic forms, offer a diverse range of properties. While oxides are generally known for their high mechanical strength, temperature resistance, and cost-effectiveness, traditional oxide processing often requires energy-intensive and environmentally unfriendly high-temperature sintering. Therefore, the investigation of energy-efficient non-firing mechanisms for oxides is not only beneficial but crucial. This paper reviews the advancements in non-firing mechanisms, with a focus on material selection, synthesis processes, and potential applications. Special attention is given to non-firing forms such as silica-based and geopolymer materials, which are prepared using low-energy acid-base reactions with either natural or synthetic silica-alumina sources. The review also encapsulates the challenges and solutions associated with these sustainable, non-firing oxide materials. [ABSTRACT FROM AUTHOR]

In order to study the solidification / stabilization effect of environmental protection material geopolymer on lead contaminated soil, based on the research background of heavy metal lead pollution and solid waste resource utilization in arid and semi-arid areas, a new solidified material geopolymer was prepared by using blast furnace slag and cement, and the macroscopic mechanical performance and microscopic mechanism of solidified heavy metal lead were discussed. Based on the cement-based solidification of heavy metal lead-contaminated soil, the strength performance and toxicity leaching performance of geopolymer-cement under different proportions were explored, and the microscopic test characterization of the outstanding performance group was carried out. The test results show that compared with cement-based and other groups, 80% slag geopolymer combined with cement has better performance of solidification / stabilization of heavy metal lead, and the compressive strength and toxicity leaching results under pollution degree ③ are significantly better than other groups. phase analysis of X-ray diffraction (XRD), scanning electron microscope (SEM), nuclear magnetic resonance (NMR) and other tests show that the internal structure of 80% slag geopolymer is complete and dense, the internal changes of cement solidified body are severe, the hydration reaction is inhibited by heavy metals, the overall structure is loose, and the density is low and discontinuous. [ABSTRACT FROM AUTHOR]

It was shown in Part II of this series of articles that geopolymers synthesized with organic bases could be used as precursors to mullite and mullite + glass composites. A natural next step is to determine whether it is possible to synthesize materials outside the Al2O3·SiO2 and alkali oxide·Al2O3·SiO2 phase systems. Hence, the focus of this study was the use of geopolymer‐like processing to make preceramic bodies with magnesium, yttrium, and zinc aluminosilicate and silicate compositions. These preceramics were successfully fired into monolithic bodies of cordierite, mixed yttrium and aluminum silicates, yttrium disilicate, and willemite. The synthesis of these preceramics employed a guanidine silicate solution, a synthetic oxide powder, and in some cases metakaolin to reach the oxide composition of the ceramic. All solidified within 3 days at 20°C or 50°C, depending on the composition. For the first time, this study showed that Y2O3 and ZnO can react with silicate solutions to give some Y‐O‐Si and Zn‐O‐Si bonding analogous to Al‐O‐Si bonding in geopolymers. These results suggest that other silicate compositions may be possible, such as with the rare earth oxides, which might be valuable to process like a geopolymer rather than by traditional ceramic processing. However, the ceramics made here were generally porous due to the expansion of gases within the sample that were trapped by a viscous liquid phase during firing. [ABSTRACT FROM AUTHOR]

The effect of the emulsification process of the organic n‐eicosane as a phase change material (PCM) in an aqueous solution of sodium dodecyl sulfate (SDBS) as a surfactant has been studied regarding the properties of the CaCO3 microcapsules. Such microcapsules aim to limit interactions between the PCM and the matrix (i.e., leakage and unwanted reactions). Optical and scanning electron microscopy (SEM) shows that the mean size of the n‐eicosane capsule is of the order of 5 μm. However, large non‐spherical objects which could be clusters of flocculated capsules or the results of encapsulation of coalescing n‐eicosane droplets, are observed, particularly when mechanical stirring (MS) is used rather than when an ultra‐turrax (UT) or sonotrode (S) is used in the initial emulsification step. These large, partially encapsulated objects could be the cause of the poor results in leakage tests. It is possible to encapsulate n‐eicosane inside a calcium carbonate shell, with a greater than 50% encapsulation ratio. The yield of encapsulated n‐eicosane measured by differential scanning calorimetry (DSC) and thermogravimetric analysis (TGA) is similar and shows that 55% n‐eicosane core in CaCO3 shell can be produced. Up to 33 wt.% CaCO3 microcapsules (with 55% n‐eicosane content) have been successfully incorporated into fresh geopolymer paste. This incorporation of 18% (55% × 33%) of PCM does not modify the hardening conditions of the geopolymer since demolding was possible after 2 days at room temperature. DSC curves confirm that the melting reaction with n‐eicosane is conserved inside the hardened geopolymer. [ABSTRACT FROM AUTHOR]

To develop a sustainable geopolymer concrete (GC), the efficacy of using fine recycled concrete powder (FRCP) and recycled aggregates (RA) as partial replacements for fly ash (FA) and natural aggregates (NA), respectively, was investigated. The compressive strengths of different GCs were measured. The durability performance was assessed by means of capillary suction tests, initial surface absorption tests and acid attack performed at ambient curing. The compressive strength of the GC made with 50% RA (both coarse and fine) and FRCP was found to be comparable to that of GC made with NA. Similarly, the inclusion of FRCP in the GC mixes resulted in a pore-blocking effect, restricting water ingress to the GC through capillary suction and surface absorption, even with the use of 50% coarse RA and 25% fine RA. The results demonstrated that sustainable GC can be developed using appropriate doses of FRCP and RA. [ABSTRACT FROM AUTHOR]

It was previously demonstrated that geopolymers can be synthesized using organic bases rather than alkali hydroxides, thereby removing the alkali cations from the composition and allowing other ceramics to be made. This work compared the microstructures of Al2O3·2SiO2 and Al2O3·4SiO2 bodies made using guanidine and tetramethylammonium hydroxide (TMAOH) with equivalent sodium geopolymers. The guanidine and sodium samples were similar, whereas TMAOH caused a clear difference in structure. Sodium and guanidine geopolymers with overall compositions of 3Al2O3·2SiO2 were also synthesized with the aim of developing a castable route to bulk mullite. The development of crystalline phases was followed by powder x‐ray diffractometry for all of these compositions after thermal treatment at temperatures up to 1600°C. The microstructures after firing at 1600°C were examined by scanning electron microscopy. When heated, the Al2O3·2SiO2 and Al2O3·4SiO2 compositions transformed from amorphous phases into a mixture of fine, needle‐shaped, mullite crystals and amorphous silica, while 3Al2O3·2SiO2 compositions became entirely mullite, with the shape of the mullite crystals being dependent on the type of precursors used. All samples exhibited substantial amounts of porosity, which could be reduced with improved processing techniques. This work demonstrated that alumina‐rich guanidine geopolymers are a potential route to casting bulk mullite bodies. [ABSTRACT FROM AUTHOR]

Multifunctional building materials with self-sensing capability have great potential for civil engineering applications. The self-sensing capability of typically calcium aluminosilicate matrices of cementitious or geopolymer materials is adopted by admixing electrically conductive admixtures in an amount that ensures optimal electrical properties and their proportionality to mechanical loading. The paper aims to evaluate the self-sensing capability of 4 metashale geopolymer mortars with graphite powder (GP) and carbon fibers (CF) in different ratios, including MGF 5/0, MGF 4.5/0.5, MGF 4/1, and MGF 3/0. The 4-probe measurements at 21 V DC input voltage on (100 × 100 × 100) mm3 samples with embedded copper-grid electrodes evaluate the gauge factor, which corresponds to the monitored changes in electrical resistivity. Despite the limitations of DC measurements, the self-sensing capability is observed for all the mixtures. The most promising response to dynamic loading with an FCR of 0.018%, is observed for the MGF 4.5/0.5 sample. [ABSTRACT FROM AUTHOR]

Geopolymers assume an irreplaceable position in the engineering field on account of their numerous merits, such as durability and high temperature resistance. Nevertheless, geopolymers also demonstrate brittleness. In this study, geotextiles with different layers were added to geopolymer to study its compressive strength and stability. Laboratory materials such as alkali activators, geotextiles and granite residual soil (GRS) were utilized. The samples were characterized via XRD, TG-DTG, SEM-EDS and FT-IR. The results indicate that the toughness of geopolymer is significantly enhanced by adding geotextiles, and the strength increase is most obvious when adding one layer of geotextile: the strength increased from 2.57 Mpa to 3.26 Mpa on the 14th day, an increase of 27%. Additionally, the D-W cycle has a great influence on geotextile polymers. On the 14th day, the average strength of the D-W cyclic sample (1.935 Mpa) was 1.305 Mpa smaller than that of the naturally cured sample (3.24 Mpa), and the strength decreased by 40%. These discoveries offer a novel approach for further promoting the application of geopolymers, especially in the field of foundation reinforcement. [ABSTRACT FROM AUTHOR]

The safe and secure encapsulation or immobilization of nuclear waste, particularly low to intermediate‐level waste (accounting for ∼97% of the total volume of nuclear waste), has been a significant concern. Consequently, numerous studies have been conducted on various materials such as ordinary Portland cement‐based, bitumen, and ceramics for the purpose of waste encapsulation/immobilization. However, these studies generally offer a broad overview of materials performance without focusing on specific radioisotopes of concern. Cesium (Cs) and strontium (Sr) are important radioactive nuclides to consider for encapsulation, but the existing studies on immobilizing these elements are fragmented and lack a comprehensive understanding. This critical review article offers a thorough qualitative and quantitative analysis to uncover the primary trends/knowledge gaps within the field. It comprehensively delves into waste classifications/management and leaching assessments, followed by an exploration of the immobilization performance and durability issues of various traditional and advanced cementitious materials including low‐temperature chemically bonded ceramics such as alkali‐activated matrices and Mg‒K phosphates for the immobilization of Cs and Sr. Furthermore, the review article provides fresh insights and perspectives, including recommendations for improvements, novel technologies, and future trends in this domain. [ABSTRACT FROM AUTHOR]

Geopolymers are inorganic polymers whose formation is based on the reaction between precursors and reagents, which may be alkaline or acidic. The geopolymerisation process involves the reaction between alumina and silicate materials, known as precursors and reagents, which produces a three-dimensional polymeric network. This review provides a detailed classification of precursors used globally for geopolymer concrete (GPC) production, along with their various oxide contents. As the precursors used in the process of geopolymerisation involve a wide range of variations in their physio-chemical features, it is difficult to control the properties of GPC without going into a micro-level understanding of the precursor characteristics that affect the geopolymerisation mechanism. A comprehensive study was conducted on the influence of these physio-chemical precursor characteristics on the geopolymerisation process and the development of GPC properties. Finally, critical observations are drawn for the design of suitable precursors, along with possible methods to achieve the desired GPC property development. [ABSTRACT FROM AUTHOR]

Compared with traditional cement pastes, geopolymer pastes can effectively alleviate environmental and economic problems caused by the construction industry as they are characterised as low carbon dioxide materials, with energy reduced energy consumption and emissions. However, the mechanical properties of geopolymer pastes are greatly affected by the composition of the alkaline activators used in their preparation, and existing research results on this influence is not consistent. In this study, the effects of alkaline activators composed of varying concentrations of sodium hydroxide (NaOH) solution under standard curing conditions on the mechanical properties and material characteristics of geopolymer pastes made with fly ash and slag were investigated. Under standard curing conditions, the mechanical properties of the geopolymer pastes increased with an increase of sodium hydroxide solution (SHS) concentration in the alkaline activator. The use of alkaline activator with 16 M SHS led to the greatest flexural and compressive strengths of the geopolymer pastes at 28 days, reaching values of 5.43 MPa and 39.13 MPa, respectively. Increasing the SHS concentration in the alkaline activator promoted the production of gel products such as N-A-S-H, which formed a dense microstructure and led to higher mechanical properties. [ABSTRACT FROM AUTHOR]

The durability properties of geopolymer mortars prepared using different contents of slag and glass powder (GP) were examined and compared with the properties of Portland cement mortar (PCM). The slag–GP mixes were activated with a 6 M sodium hydroxide solution at a liquid-to-solid ratio of 0.35. The performance of 28-day cured specimens after high-temperature exposure, wetting–drying and freezing–thawing cycles, water slaking, surface abrasion and alkali–silica reaction (ASR) were examined. Scanning electron microscopy was carried out to identify the microstructural changes in the materials. The results showed that an appropriate GP content (10%) enhanced the performance of the slag–GP binary geopolymer and improved its durability. However, ASR expansion was found to increase marginally. The geopolymer specimens achieved higher strength and durability than PCM due to their dense and compact microstructure with significant gel formation. [ABSTRACT FROM AUTHOR]

The high shrinkage of metakaolin-based geopolymers (MKGs) dramatically limits their application as high-performance green cementitious materials. In this study, microscopic tests and microstructure analysis of the polymerization reaction products are employed to examine the drying shrinkage properties of MKG under different alkali equivalents. The results indicate an enhancement in the strength of MKG mortar with increasing alkali equivalent; however, it undergoes shrinkage in the later stages. Notably, the drying shrinkage increases with the alkali equivalent, mainly attributed to the fact that the increase in alkali equivalent does not change the types of hydration products in MKG. Instead, it promotes the dissolution of active silicon oxide and alumina in metakaolin (MK) particles, accelerating the hydration reaction process and, resulting in a higher amount of sodium aluminosilicate hydrated gel (N─ A─ S─ H) gel. Furthermore, the alkali equivalents modify the pore size distribution, leading to an increase in the 10–50-nm pore volume and capillary negative pressure, ultimately causing an increase in drying shrinkage. [ABSTRACT FROM AUTHOR]

Geopolymers are inorganic polymers projected as feasible alternatives to Portland cement due to their lower CO2 emissions and high mechanical properties. In recent times, however, their impact on other environmental indices such as abiotic depletion, freshwater toxicity, marine ecotoxicity, terrestrial ecotoxicity, acidification, and human toxicity has become questionable, thus the need to investigate alternative eco-friendly precursors and activators. This work aims to manufacture an eco-efficient geopolymer by utilising biomass ash leachate as an alternative to the conventional alkali silicate solution. The leachate was obtained by soaking the rice husk ash (RHA) in a 10 M concentration of NaOH solution and filtering to obtain a clear solution. The effects of the calcination temperature of the kaolin and the RHA content in the alkaline solution were investigated, and a factorial design of experiments was developed considering three levels of calcination temperature (700°C, 800°C, and 900°C) and five levels of RHA content (0 g, 5 g, 10 g, 15 g, and 20 g). Physical and mechanical tests were performed on the synthesised geopolymer pastes, and chemical analysis was performed using X-ray diffraction and X-ray spectroscopy. The impacts of replacing the synthetic alkali silicates with rice husk ash-based activators were compared. The results showed that the calcination temperature of the kaolin and the content of the RHA both contributed significantly to the flexural and compressive strength at the 0.01 level of significance. A compressive strength of 10.4 MPa was obtained for the MK915 binders, which showed a 100% increase from samples without RHA content. This research proves that utilising RHA-based activators in metakaolin-based geopolymers can be feasible for less critical applications where a very high compressive strength will not be required.

Currently, there are materials from industry that, under certain physical conditions, can contribute to the improvement of soils mechanical properties. Materials such as brick dust (BD) and fly ash (FA) have high SiO2 and Al2O3 contents, which denote pozzolanic activity. In addition, it has been shown that these materials can be activated when combined with lime. This generates internal cementation processes when the particle size is 0.075 mm. Rural roads in Colombia have one of the highest percentages of the entire road infrastructure, and only about 7% are in good condition. Difficult access conditions, soil susceptibility, the financial impossibility of intervening in this entire network and the need to implement circular economy processes, make these materials attractive in terms of stabilization to improve traffic conditions. BD and FA were applied in dosages of 0%, 3%, 6%, 9%, 12% and 24% in finogranular soils (silt and clay) and sandy soils, compaction was evaluated, and a factorial experimental design was carried out to evaluate the influence of the material on the variable unconfined compressive strength (UCS), through an ANOVA analysis. To evaluate the performance of BD and FA, a test track was made on a low traffic volume road in northern Colombia, which had a sandy soil. BD and FA were added at 12% and activated with lime, in 30 m long cells. To establish a comparative pattern, other cells were made in the same geometric conditions with materials that are usually used in this type of application, such as cement. These cells were evaluated over a period of 16 months. Characteristics such as resilient modulus, international roughness index (IRI) and slip resistance coefficient were measured during this period. The results indicate that when these materials are added to finogranular soils (silts and clays), the UCS increases by 150% with respect to the unstabilized soil, while for sandy soils the strength increases from 70% to 125%. During the evaluation period, the BD and the FA were able to increases of over 50% in the resilient modulus with respect to the unstabilized soil. However, the FA showed comparable results with respect to the cement-stabilized cell. In addition, although the sections deteriorated over time, they maintained their roughness index within the admissible ranges indicative of a good serviceability index. [ABSTRACT FROM AUTHOR]

Novel ultra-high-performance concretes (UHPCs) made with calcium-oxide-activated materials (CAM), modified synthetic macro (MSM) fibres, glass fibres and steel fibres were developed. The mechanical and durability properties of UHPC-CAM specimens made with the different fibre types were tested and compared. The microstructure of the samples was examined using scanning electron microscopy (SEM). The environmental impacts of the mix designs were assessed using the Impact 2002+ method, a life cycle assessment tool. The results showed that the UHPC-CAM made with glass or MSM fibres had a high compressive strength (>110 MPa) and improved ductility. These specimens also had low water absorption and high electrical resistance, indicating low corrosion risk. SEM analyses showed that the MSM fibres created a denser geopolymer matrix than the glass fibres. The UHPC-CAM was found to have a lower environmental impact than conventional UHPC in terms of human health, ecosystem quality, carbon dioxide footprint and use of resources. MSM fibres were determined to be the most eco-friendly fibres for UHPC-CAM production. [ABSTRACT FROM AUTHOR]

Geopolymers are in many applications a perfect alternative to standard cements, especially regarding the sustainable development of green building materials. This experimental study therefore deals with the investigation of different factors, such as the water content and the binder to aggregate ratio, and their influence on the workability of fresh mortar and its mechanical properties and porosity on different size scales. Although increasing the water content improved the workability and flow behaviour of the fresh mortar, at the same time, a reduction in compressive strength in particular and a lesser reduction in flexural strength could be demonstrated. This finding can be attributed to an increase in capillary porosity, as demonstrated by capillary water uptake and mercury intrusion porosimetry measurements. At the same time, the increasing water content led to an improved deaeration effect (low air void content) and to initial segregation (see the µXCT measurements). An alternative approach to enhance the compressive and flexural strengths of the mortar specimens is optimization of the binder to aggregate ratio from 1 to 0.25. This study paves the way for a comprehensive understanding of the underlying chemistry of the geopolymerization reaction and is crucial for the development of sustainable alternatives to cementitious systems. [ABSTRACT FROM AUTHOR]

This study explores the potential of biosilica including diatom and diatomaceous earth as alternative silica sources for metakaolin-based geopolymers. Diatomaceous earth, composed of fossilised diatom frustules rich in amorphous silica, and diatoms, a sustainable source of renewable biosilica, are investigated for their effectiveness in enhancing geopolymer properties. Through detailed analyses including FTIR, XRD, and SEM, the study evaluates the impact of these biosilica sources on geopolymer compressive strength and microstructure, comparing them with conventional sodium silicate. Results show that diatoms exhibit significant promise, achieving 28-day strength up to 17.9 MPa at a 30% mass fraction, while diatomaceous earth reaches 26.2 MPa at a 50% addition rate, demonstrating their potential as active silica sources. Furthermore, the study elucidates the role of organic matter in biosilica on geopolymerisation, highlighting its influence on active silica release and the strength performance of products. This study proposes a novel pathway to enhance the sustainability of geopolymers through the utilisation of biosilica from diatoms, contributing to advancements in eco-efficient construction materials. [ABSTRACT FROM AUTHOR]

Diatomite, a natural adsorbent rich in active silica, serves as a valuable precursor for geopolymer synthesis. The safe disposal of diatomite as a failed lead (Pb(II)) adsorbent is critical to prevent secondary contamination. This study investigated the immobilisation efficiency of geopolymerisation for Pb(II)-rich diatomite sludge. Low-grade diatomite with high ignition loss was utilised in the synthesis of alkali-activated geopolymers. It was demonstrated that the geopolymers achieved a compressive strength of 28.3 MPa with a 50% replacement rate of metakaolin by diatomite sludge, which was not a compromise in strength compared to that of the geopolymer with no Pb(II) (26.2 MPa). The leaching behaviour of Pb(II) was evaluated using water and acetic acid, yielding concentrations below 3 mg/L and immobilisation efficiencies of 95% in both scenarios. Analytical techniques including Fourier transform infrared spectroscopy (FTIR), X-ray diffraction (XRD), and scanning electron microscopy (SEM) elucidated the mineral composition and chemical environment of the geopolymers. These analyses revealed that Pb(II) migrated from diatomite pores, potentially forming soluble hydroxides under sufficient hydroxide, which then participated in condensation with silicon and aluminium monomers, effectively immobilising Pb(II) within amorphous aluminosilicate gels. Furthermore, the formation of the amorphous gels within diatomite pores hindered Pb(II) leaching, encapsulating Pb(II) effectively. This study presents a novel approach to immobilising heavy metals within building materials, enhancing mineral resource utilisation efficiency while addressing environmental contamination concerns. [ABSTRACT FROM AUTHOR]

The increasing global demand for cement significantly impacts greenhouse gas emissions and resource consumption, necessitating sustainable alternatives. This study investigates fresh geopolymer (GP) pastes incorporating 20 wt.% of five industrial wastes—suction dust, red mud from alumina production, electro-filter dust, and extraction sludges from food supplement production and from partially stabilized industrial waste—as potential replacements for traditional cement. Consistent synthesis methods are used to prepare the geopolymers, which are characterized for their physicochemical, mechanical, and biological properties. Ionic conductivity and pH measurements together with integrity tests, thermogravimetry analysis (TGA), and leaching analysis are used to confirm the stability of the synthesized geopolymers. Fourier-transform Infrared (FT-IR) spectroscopy is used to follow geopolymerization occurrences. Results for ionic conductivity, pH, and integrity revealed that the synthesized GPs were macroscopically stable. TGA revealed that the main mass losses were ascribable to water dehydration and to water entrapped in the geopolymer networks. Only the GP filled with the powder of the red mud coming from alumina production experienced a mass loss of 23% due to a partial waste degradation. FT-IR showed a red shift in the main Si-O-(Si or Al) absorption band, indicating successful geopolymer network formations. Additionally, most of the GPs filled with the wastes exhibited higher compressive strength (37.8–58.5 MPa) compared to the control (22 MPa). Only the GP filled with the partially stabilized industrial waste had a lower mechanical strength as its structure was highly porous because of gas formation during geopolymerization reactions. Despite the high compressive strength (58.5 MPa) of the GP filled with suction dust waste, the concentration of Sb leached was 25 ppm, which limits its use. Eventually, all samples also demonstrated effective antimicrobial activity against Escherichia coli and Staphylococcus aureus due to the alkaline environment and the presence of metal cations able to react with the bacterial membranes. The findings revealed the possibility of recycling these wastes within several application fields. [ABSTRACT FROM AUTHOR]

In this paper, based on the advantages of fly ash geopolymer-stabilized soil, two kinds of low-calcium fly ash was used as the raw material, sodium hydroxide and water glass as the exciter to study the factors affecting the unconfined compressive strength of the geopolymer stabilized silty soil through three kinds of sample preparation method. The results show that among the three influencing factors, sample preparation method has the greatest influence on the unconfined compressive strength, followed by the type of activator and the fineness of fly ash. At 7 days of curing, the unconfined compressive strength of fly ash-based geopolymer stabilized soil activated by NaOH demonstrated a greater increase compared to that activated by Na2SiO3. However, at the 28-day curing mark, the activation effect of Na2SiO3 on the soil's strength surpassed that of NaOH. Directly mixed components exhibit unconfined compressive strengths that are 30% to 50% higher than those of sequentially mixed components that have undergone soil confinement. Through SEM observation and pore analysis of the specimens under different factors, it was found that the gap in the material was mainly filled by the generated geopolymer gel material, to reduce the porosity and improve the compressive strength of the stabilized soil. [ABSTRACT FROM AUTHOR]

The application of geopolymers has recently been given significant attention to address climate change and the growing scarcity of construction materials in the 21st century. Researchers have utilized industrial waste or supplementary cementitious materials containing high levels of silica and alumina as precursors along with different alkaline activators. Furthermore, the technical challenges associated with waste brick management or recycling include both land use changes and financial implications. The existence of amorphous aluminosilicates in waste clay bricks, which can be used as geopolymer binders, has drawn attention recently. This paper reviews the recent advancements of the integration of clay brick wastes in geopolymer applications, individually as well as its use with other alternative materials. Prior studies suggest that waste clay bricks can effectively serve as the primary source material in geopolymer applications. This review covers various aspects, including the assessment of fresh, mechanical, microstructure, and durability-related properties. It specifically focused on enhancing these properties of waste clay bricks through mechanical and thermal treatments, through varying curing conditions, utilizing different types of alkaline activators, and considering their properties and corresponding ratios in the development of geopolymer products using waste brick powder. Furthermore, this paper portrays a critical review of the sustainability implications of the utilization of clay brick waste in geopolymer applications. Conclusively, this review provided the lessons learnt, research gaps, and the future direction for investigation into the feasibility of geopolymers derived from waste clay brick powder. [ABSTRACT FROM AUTHOR]

Waste incineration ash is the product of domestic waste after high temperature calcination. The resource utilization of ash has become one of the hot topics today. The effects of alkali equivalent, silicon-sodium molar ratio and ash content on the compressive strength of waste incineration ash-tuff base geopolymer were studied by response surface method. The preparation parameters of waste incineration ash-tuff base geopolymer were optimized, and the response surface model of geopolymer compressive strength was established. The results show that the significant degree of each factor affecting the compressive strength of ash-tuff base geopolymer from large to small is: alkali equivalent > ash content > silicon-sodium molar ratio. The optimal preparation parameters of ash-tuff based geopolymer are alkali equivalent of 9. 49%, silicon-sodium molar ratio of 1. 71, and ash content of 17. 85% . Under the optimal preparation parameters, the predicted value of 28 d compressive strength is 24. 18 MPa, and the experimental value is 24. 77 MPa. The experimental value is basically consistent with the predicted value. The research results not only provide theoretical reference for the preparation parameters and practical application of ash-tuff base geopolymer, but also provide an effective and feasible way for the resource utilization of waste incineration ash. [ABSTRACT FROM AUTHOR]

The extraction of phosphorite ore in Tunisia has resulted in the discharge of substantial amounts of phosphatic sludge into the region's water system. To mitigate this environmental issue and prevent heavy metal leaching, a geopolymerization process was employed using two types of Tunisian calcined phosphate sludges (Cal-PS1 and Cal-PS2) as substitutes for alkali-activated metakaolin. This study aimed to investigate and compare the physical and mechanical properties of the resulting geopolymers. The optimal substitution ratio of metakaolin with calcined phosphate sludge was determined to be 1.5, equivalent to 20 wt.% of calcined phosphate sludge. Compressive strength tests conducted after 28 days of curing revealed values of 37 MPa for Cal-PS1 specimens and 28 MPa for Cal-PS2 geopolymers while compressive strength of geopolymers soaked in water for 28 days showed a decrease with the addition of phosphate sludges. The specific surface areas of Cal-PS1 geopolymers ranged from 16.3 to 16.9 m2/g and from 17.62 to 18.73 m2/g for Cal-PS2 specimens exhibiting a mesoporous structure. The elasticity modulus of the geopolymers was found to increase with the increase of the apparent density of geopolymers and with the sludges content but it tended to be lower than the Portland cement elasticity modulus. Leaching test was conducted to evaluate the potential environmental applications of the geopolymers. This test demonstrated effective containment of heavy metals within the geopolymers' network, except for low levels of arsenic. [ABSTRACT FROM AUTHOR]

As the world becomes increasingly aware of the devastating effects of climate change, the need for sustainable building materials that are both durable and environmentally friendly increases. Geopolymer and alkali-activated materials formed by a chemical reaction between an alkaline activator solution and an aluminosilicate source have gained popularity in recent years. The alkaline activator solution dissolves the aluminosilicate source, which then undergoes a polycondensation reaction to form a three-dimensional geopolymeric gel network. The development of this network ensures the strength and durability of the material. Today, this phenomenon of durability has been studied in detail to enable the development of superior construction materials, taking into account degradation mechanisms such as carbonation, leaching, shrinkage, fire, freezing and thawing, and exposure to aggressive environments (chlorides, acids, and sulphates). Although there are many unsolved problems in their engineering applications, slag-based alkali-activated materials appear to be more advantageous and are promising as alternative materials to ordinary Portland cement. First of all, it should not be ignored that the cure sensitivity is high in these systems due to compressive strength losses of up to 69%. Loss of strength of alkali-activated materials is considered an important indicator of degradation. In binary precursors, the presence of fly ash in slag can result in an improvement of over 10% in compressive strength of the binary-based alkali-activated materials after undergoing carbonation. The binary systems can provide superior resistance to many degradation mechanisms, especially exposure to high-temperature. The partial presence of class F fly ash in the slag-based precursor can overcome the poor ability of alkali-activated materials to withstand high temperatures. Due to the desired pore structure, alkali-activated materials may not be damaged even after 300 freeze–thaw cycles. Their superior permeability compared to cementitious counterparts can extend service life against chloride corrosion by more than 20 times. While traditional (ordinary Portland cement-based) concrete remains the most widely used material in construction, geopolymer concrete's superior performance makes it an increasingly emerging option for sustainable and long-lasting infrastructure. [ABSTRACT FROM AUTHOR]

In this study, the aim is to investigate and predict the compressive strength of geopolymer concrete (GPC). The effects of curing method, curing time and concrete age on the compressive strength of GPC were evaluated experimentally. Four curing methods, namely room temperature (25°C), mobile dryer (50°C), heating cabinet type 1 (80°C) and heating cabinet type 2 (100°C) were adopted. Additionally, three curing times, of 8 h, 16 h and 24 h, as well as three concrete ages, of 7 days, 14 days and 28 days, were considered. To predict the compressive strength of GPC, 679 test results were collected to develop various machine learning models. The test results indicated that increasing the curing temperature, curing time and concrete age all led to improvements in the compressive strength of GPC. The mobile dryer showed promise as a curing method for cast-in-place GPC. The proposed machine learning models demonstrated good predictive capacity for the compressive strength of GPC with relatively high accuracy. Through sensitivity analysis, concrete age was identified as the most influential variable affecting the final compressive strength of GPC. [ABSTRACT FROM AUTHOR]

Geopolymers can act as a facile forming route to aluminosilicate ceramic composites due to being processed as fluids rather than as powders. However, the compositions available via typical alkali geopolymers are limited by the presence of alkali cations, introduced by the alkali silicate solution precursors. In order to expand the ceramic compositions that are accessible by geopolymer processing, this study explored the use of three strong organic bases (guanidine, tetramethylguanidine [TMG], and tetramethylammonium hydroxide [TMAOH]) as alternatives to inorganic alkali hydroxides in geopolymer synthesis. Silicate solutions were able to be produced with all three bases and favorable silica speciation was identified in the guanidine and TMG silicate solutions. Monolithic bodies were produced using guanidine and TMAOH, while no TMG samples hardened. By 27Al and 29Si nuclear magnetic resonance spectroscopy and powder X‐ray diffraction, the guanidine samples were determined to be structurally similar to those made using sodium hydroxide and hence can be called geopolymers, while the solids made with TMAOH were not structurally similar to sodium geopolymers and contained one or more unknown phases. This study has demonstrated that geopolymers can be made using organic bases rather than alkali hydroxides and that the speciation of dissolved silica alone does not indicate that an organic base silicate solution will be reactive. [ABSTRACT FROM AUTHOR]

The stability of cementitious materials under the harsh environment they will experience when used for radioactive waste disposal is incredibly important. Therefore, understanding the irradiation resistance of geopolymer cement, a potential alternative binder for the treatment of nuclear waste, is of the utmost importance when trying to develop a safety case for these materials. The study presented here addresses the structural and chemical changes of metakaolin‐based geopolymers, designed with different water contents, and exposed to a total cumulative dose of 1 MGy of gamma radiation. The range of formulations that were tested showed a significant loss of free water related to the irradiation process, which has led to an increase in the porosity. Analysis of the chemical structure has shown minimal changes in the main binding type‐gel phase, demonstrating high microstructural stability. Results showed that in samples cured for longer than 20 h, the bound/gel structure water remained in the sample when the water content was kept low enough. As the porosity and water content increase, more gel water is removed due to radiation exposure. However, the degree to which the water is removed from the gel structure is very small, and minimal changes can be seen across the geopolymers tested. Overall, metakaolin‐based geopolymers appear resistant to irradiation up to 1 MGy, which offers a potentially viable alternative for the immobilization of problematic intermediate‐level waste. [ABSTRACT FROM AUTHOR]

The objective of this study is to perform a comparative analysis of the impact of incorporating alkaline earth metal carbonates (MCO3, where M–Mg, Ca, Sr, Ba) into low-calcium fly ash (FA) on the geopolymerization processes and the resultant properties of composite geopolymers. Mechanical activation was employed to enhance the reactivity of the mixtures. The reactivity of the mechanically activated (FA + alkaline earth carbonate) blends towards NaOH solution was experimentally studied using XRD analysis and FTIR spectroscopy. In agreement with thermodynamic calculations, MgCO3 demonstrated the most active interaction with the alkaline solution, whereas strontium and barium carbonates exhibited little to no chemical interaction, and calcite was situated in the transition region. As the calcite content in the mixture with FA increased, the compressive strength of the geopolymers continuously improved. The addition of Mg, Sr, and Ba carbonates to the FA did not enhance the strength of geopolymers. However, the strength of geopolymers based on these blends was comparable with that of geopolymers based on 100% FA. The strength of geopolymers synthesized from the 100% FA and from the (90% FA + 10% MCO3) blends, mechanically activated for 180 s, at the age of 180 days was 11.0 MPa (0% carbonate), 11.1 MPa (10% MgCO3), 36.5 MPa (10% CaCO3), 13.6 MPa (10% SrCO3), and 12.4 MPa (10% BaCO3) MPa, respectively. The influence of carbonate additives on the properties of the composite geopolymers was examined, highlighting filler, dilution, and chemical effects. The latter determined the unique position of calcite among the carbonates of alkaline earth metals. [ABSTRACT FROM AUTHOR]

Copyright of Economics & Environment / Ekonomia i Środowisko is the property of Fundacja Ekonomistow Srodowiska i Zasobow Naturalnych and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

This study investigates the impact of residue soil (RS) powder on the 3D printability of geopolymer composites based on fly ash and ground granulated blast furnace slag. RS is incorporated into the geopolymer mixture, with its inclusion ranging from 0% to 110% of the combined mass of fly ash and finely ground blast furnace slag. Seven groups of geopolymers were designed and tested for their flowability, setting time, rheology, open time, extrudability, shape retention, buildability, and mechanical properties. The results showed that with the increase in RS content, the fluidity of geopolymer mortar decreases, and the setting time increases first and then decreases. The static yield stress, dynamic yield stress, and apparent viscosity of geopolymer mortar increase with the increase in RS content. For an RS content between 10% and 90%, the corresponding fluidity is above 145 mm, and the yield stress is controlled within the range of 2800 Pa, which meets the requirements of extrusion molding. Except for RS-110, geopolymer mortars with other RS contents showed good extrudability and shape retention. The compressive strength of 3D printing samples of geopolymer mortar containing RS has obvious anisotropy. [ABSTRACT FROM AUTHOR]

A study was undertaken into the preparation and properties of fly-ash-based geopolymers that can be used to make multistage-pore materials able to adsorb gases such as carbon dioxide. The influence of steel slag on the mechanical properties and microstructure of the final precursor products was investigated and characterised by mechanical strength tests, X-ray diffraction, Fourier transform infrared spectroscopy, thermogravimetry–differential thermal analysis, scanning electron microscopy–energy-dispersive X-ray spectroscopy and mercury intrusion porosimetry. The results showed that a low dose of steel slag significantly promoted the early compressive strength of a multistage-pore geopolymer. However, when the slag dose reached 30%, the strength decreased dramatically. The pore classification effect was more obvious when the capillary pores in the geopolymer disappeared and the pores mainly existed in the form of gel pores and voids. [ABSTRACT FROM AUTHOR]

Fly ash usually requires high-temperature maintenance owing to its low volcanic ash activity, which greatly limits its application. In this study, fly-ash-based geopolymer grouting materials were prepared by modifying them with suitable alkali activators and metakaolin at room temperature. The results of the orthogonal experiments showed that the content of metakaolin had the most significant effect on the 1-, 7- and 28-day mechanical properties of the material. The optimum mix proportion was determined as metakaolin content (mMK/mP) = 15%, sodium silicate modulus (Ms) = 1.0 and sodium silicate content (mSS/mP) = 50%. The compressive strengths of the materials at 1, 7 and 28 days were 12.6, 24.9 and 36.3 MPa, respectively. The results of X-ray diffraction, Fourier transform infrared spectroscopy, mercury intrusion porosimetry and scanning electron microscopy showed that the reaction mechanism of fly ash was subject to a bidirectional alkaline attack. Meanwhile, the unreacted fly ash particles proved the inertness of fly ash, while metakaolin mostly dissolved and formed hydrated sodium aluminosilicate gel to increase the mechanical strength of the geopolymer. The material developed in this study can meet the specification requirements of inorganic cementitious material for road grouting in terms of compressive strength and fluidity, increasing the usage of fly ash and contributing to environmental protection. [ABSTRACT FROM AUTHOR]

Geopolymers are green and sustainable cementitious materials that are a possible alternative to cement due to lower energy consumption and emissions. Volcanic ash can be used as raw material to prepare geopolymers by alkali activation owing to its high silica and alumina content. However, research on volcanic-ash-based geopolymers is still limited and no consensus on the optimal alkali activator and reaction mechanism has been obtained. This study investigates the effect of alkali activators with different cations on the mechanical properties and microstructure of volcanic-ash-based geopolymers. The flexural and compressive strengths were evaluated. X-ray diffractometry, Fourier transform infrared spectrometry, scanning electron microscopy coupled with energy-dispersive spectroscopy and silicon-29 (29Si) magic-angle spinning nuclear magnetic resonance were used to characterise the microstructural properties. The results showed that the alkali activation effect of sodium hydroxide (NaOH) on volcanic ash was superior to those of lithium hydroxide (LiOH) and potassium hydroxide (KOH), particularly at a concentration of 8 mol/l, with 28-day flexural and compressive strengths of 3.0 and 28.3 MPa, respectively. Microstructural results indicated that the sodium hydroxide-activated geopolymers formed dense, continuous, highly polymerised silica–aluminate gels. This paper provides a proper ratio scheme for activating the volcanic ash from similar deposits and promoting practical applications conducive to sustainable engineering development in the future. [ABSTRACT FROM AUTHOR]

The main goal of this work is to characterize wood ash as a waste product from tree trunks burning and utilize it for geopolymer production. The geopolymerization was achieved by a chemical reaction between calcined kaolin and different ratios of wood ash in an alkali solution of sodium silicate (Na2SiO3) and sodium hydroxide (NaOH). The produced geopolymers' physical, chemical, and microstructural characteristics were investigated. The synthesized geopolymer with 50% wood ash showed lower density, higher water absorbability, and higher porosity than the free wood ash geopolymer. The microstructural analysis indicated the formation of zeolitic and amorphous phases that were causing an increase in micropores and a high specific surface area, as revealed by XRD, SEM, and BET analyses. Therefore, the potential use of the developed geopolymer for Pb+2 removal from an aqueous solution was investigated. It was found that the generated geopolymer has a higher removal efficiency than the raw materials. The studied adsorption isotherms showed that the Langmuir isotherm model explains the experimental results well than the Freundlich model. [ABSTRACT FROM AUTHOR]

Novel ceramic membranes present unquestionable potential in wastewater treatment among the emerging technologies, while a few challenges such as cost, energy consumption, durability, and resistance in harsh mediums still limit their commercialization. Here, we review the capability of available industrial aluminosilicate waste materials in the fabrication of novel ceramic membranes using green and economical alkali‐activation synthesis method. The different sources of alkali‐activated aluminosilicate wastes including ashes, mining wastes, glass and ceramic wastes, slags, construction wastes, industrial byproducts, and agricultural wastes are introduced and the chemistry of geopolymers is reviewed. In this review, the major points are the following. 1) The alkali‐activated structures present reasonable chemical, frost, carbonation, and mechanical resistance as well as the ability to immobilize the toxic materials. 2) The synthesis aspects of porous and nonporous alkali‐activated ceramic membranes are explored by characterization methods. Furthermore, the durability analysis in harsh environments reveals that alkali‐activated ceramic membranes possess high resistance against acidic, alkaline, and other antifouling chemical washing methods. In summary, it is demonstrated that the studied membranes have an undeniable capability in the separation of organic solvents in the pervaporation process as well as toxic material removal from water with high ion‐exchange capacity. [ABSTRACT FROM AUTHOR]

The use of geopolymer in place of ordinary Portland cement for concrete design and constructure is gaining attraction due to environmental and health considerations. Geopolymers must have high gamma radiation shielding competence in order for them to be useful for radiation shielding concrete. In an attempt to improve the gamma absorption capacity of a metakaolin-based geopolymer matrix, 10 % (GEO-10Y), and 20 % (G-20Y) yttria (Y2O3) was mixed with GEO through a solid-state reaction process. In this study, the influence of adding yttria on the physical and gamma shielding parameters of GEO was investigated. The densities of GEO, GEO-10Y and GEO-20Y were obtained as 2.28, 2.52 and 2.37 g/cm3, respectively. Through simulation using FLUKA code, the mass attenuation coefficients (MAC) and other relevant shielding quantities were estimated. The MACs of GEO, GEO-10Y, and GEO-20Y were within the range of 0.0213–6.6429 cm2/g, 0.0282–13.3923 cm2/g, and 0.0291–14.5136 cm2/g, respectively. The addition of yttria improved the gamma photon shielding competence of the metakaolin-based geopolymer by increasing the MAC and reducing photon buildup factors within 15 keV–15 MeV photon energy range. The shielding effectiveness of the yttria-doped GEO compares well with conventional shielding materials. Yttria-doped geopolymer can be used to produce effective and environmentally-friendly gamma shielding concrete.