Geopolymer concrete as green building materials: Recent applications, sustainable development and circular economy potentials

Applications of engineered biochar in remediation of heavy metal(loid)s pollution from wastewater: Current perspectives toward sustainable development goals

Environmental pollution of heavy metal(loid)s (HMs) caused adverse impacts, has become one of the emerging concerns and challenges worldwide. Metal(loid)s can pose significant threats to living organisms even when present in trace levels within environmental matrices. Extended exposure to these substances can lead to adverse health consequences in humans. Removing HM-contaminated water and moving toward sustainable development goals (SDGs) is critical. In this mission, biochar has recently gained attention in the environmental sector as a green and alternative material for wastewater removal. This work provides a comprehensive analysis of the remediation of typical HMs by biochars, associated with an understanding of remediation mechanisms, and gives practical solutions for ecologically sustainable. Applying engineered biochar in various fields, especially with nanoscale biochar-aided wastewater treatment approaches, can eliminate hazardous metal(loid) contaminants, highlighting an environmentally friendly and low-cost method. Surface modification of engineered biochar with nanomaterials is a potential strategy that positively influences its sorption capacity to remove contaminants. The research findings highlighted the biochars' ability to adsorb HM ions based on increased specific surface area (SSA), heightened porosity, and forming inner-sphere complexes with oxygen-rich groups. Utilizing biochar modification emerged as a viable approach for addressing lead (Pb), cadmium (Cd), arsenic (As), mercury (Hg), and chromium (Cr) pollution in aqueous environments. Most biochars investigated demonstrated a removal efficiency >90 % (Cd, As, Hg) and can reach an impressive 99 % (Pb and Cr). Furthermore, biochar and advanced engineered applications are also considered alternative solutions based on the circular economy.

Preparation of Geopolymeric Materials from Industrial Kaolins, with Variable Kaolinite Content and Alkali Silicates Precursors

In the present work, the development of geopolymeric materials with Na or K based on industrial kaolin samples, with variable kaolinite content and alkaline silicates, is studied. XRF, XRD, FTIR and SEM-EDS have been used as characterization techniques. Three ceramic kaolin samples, two from Algeria and one from Charente (France), have been considered. In particular, chemical and mineralogical characterization revealed elements distinct of Si and Al, and the content of pure kaolinite and secondary minerals. Metakaolinite was obtained by grinding and sieving raw kaolin at 80 μm and then by thermal activation at 750 °C for 1 h. This metakaolinite has been used as a base raw material to obtain geopolymers, using for this purpose different formulations of alkaline silicates with NaOH or KOH and variable Si/K molar ratios. The formation of geopolymeric materials by hydroxylation and polycondensation characterized with different Si/Al molar ratios, depending on the original metakaolinite content, has been demonstrated. Sodium carbonates have been detected by XRD and FTIR, and confirmed by SEM-EDS, in two of these geopolymer materials being products of NaOH carbonation.

Properties of Geopolymer Mixtures Incorporating Recycled Ceramic Fines

This research aimed to optimize the production conditions for geopolymer matrices by investigating the combination of heat curing conditions and the incorporation of recycled ceramic fines (CFs) as a partial replacement material for fly ash (FA). The obtained physical and mechanical properties of the composites confirmed the positive impact resulting from increasing the curing temperature from 65 °C to 85 °C and using CFs in the amount of 37.5% as a replacement for FA. The results were from laboratory tests performed to evaluate compressive strength, bending strength, bulk density, and water absorption of the geopolymer mixes. In addition, microscopic observations and porosity assessment were also performed, which confirmed that a further increase in the replacement of FA by CFs causes an increase in the porosity of the mixes and, thus, a decrease in all the assessed properties that are relevant to their practical use.

Strength, porosity and life cycle analysis of geopolymer and hybrid cement mortars for sustainable construction

Owing to the application of industrial wastes, geopolymers are generally regarded as a sustainable alternative to traditional construction materials. However, their lack of adoption on the industrial scale demands detailed investigations. This study conducts a comparative analysis of the compressive strength of different geopolymer and hybrid cement mortars with varying proportions of sodium hydroxide (from 5 to 25 wt%) and ordinary Portland cement (OPC) (from 15 to 35 wt%), respectively. The porosity of all designed mixtures was also analyzed using X-ray computed tomography (XCT) and water absorption tests. ReCiPe 2016 Midpoint (H) method was used for the Life cycle analysis of the geopolymer and hybrid cement mortars. Multi-criteria decision making (MCDM) approach was used to assess the sustainability potential of the designed mixtures based on compressive strength, porosity and overall environmental impact. Experimental results revealed that the increase in sodium hydroxide in geopolymer mortars up to 15 wt% offered its maximum compressive strength. Superior compressive strength was obtained at 35 wt% of OPC in hybrid cement mortars due to the formation of more C-S-H, C-A-S-H and N-A-S-H gels which fill up the voids and pores. Analysis of the macro and micro-porosity revealed that hybrid cement mortars yield denser structure than geopolymer mortars. Life cycle analysis based on 8 distinct impact categories showed that hybrid cement mortars outperform the geopolymers in all impact categories except 'mineral resource scarcity'. However, the overall environmental impact assessment using the 'coefficient of performance' depicts that hybrid cement mortars offer a significantly lower environmental burden than geopolymers. MCDM analysis shows that hybrid cement mortar with 5 wt% of sodium hydroxide and 35 wt% of OPC is the best choice for construction applications. This idea of sustainable hybrid cement mortar will be helpful for the construction industry to limit the environmental impact without compromising their structural performance.

Study on the relation between macro-mechanical properties and micro-structure of geopolymers with different activator modulus

The fly ash-based geopolymer (FABG) containing slag has distinct advantages in field applications. In this work, given that the activator modulus is a significant parameter affecting the properties of FABG, the influence mechanism of activator modulus (SiO2/Na2O from 1.1 to 1.5) on the macro-mechanical properties and micro-structure composition of FABG containing slag is explored. According to the experimental results, the early product of FABG containing slag is mainly C-A-S-H gel, and N-(C)-A-S-H gel with high cross-linking degree is formed at a later stage. Both C-A-S-H and N-A-S-H gels are distinguished in reaction products by using 29Si NMR. The Si/Al ratio of N-A-S-H gel and C-A-S-H gel decreases with the increase of modulus, resulting in an increase of MCL in C-A-S-H. Appropriate activator modulus can effectively activate slag and fly ash to yield more gels and form a more uniform and dense micro-structure, resulting in a lower threshold pore size and macroporosity, and an associated increase of the material strength. Meanwhile, the gel amount has a positive effect on the strength development in the FABG.

Circular economy and its implementation in cement industry: A case point in Pakistan

The cement industry contributes substantially to world emissions. Sustainable and circular practices are adopted globally to mitigate such emissions. Developing countries like Pakistan lack adaptation to circular and sustainable practices. The study proposes an alternative mix of coal and crop residues that can be used for cement production. The study aims to find the best mixtures of coal with crop residue for combustion purposes in cement industries. The Life Cycle Assessment (LCA) and Life Cycle Cost Analysis (LCCA) are implemented for the environmental and economic viability of the proposed material mixtures. Moreover, the study seeks to explore risks associated with the implementation of circular practices in the cement industry of a developing country. The study adopts Modified Safety Improvement Risk Assessment (SIRA) for assessing the risks. The results suggest that the partial replacement of coal with bagasse is the most viable mixture with lower environmental emissions and is economically feasible among other alternate mixtures. In terms of risk assessment, there is a lack of governmental support for adopting circular economy (CE) practices and profit uncertainties of these CE practices.

An economic and sustainable approach to transform aluminosilicate-rich solid waste to functionally graded composite foam for high-temperature applications

The present study proposes an economical and effective approach for recycling coal overburden and similar solid wastes to fabricate lightweight and high-strength composite foam with industrial applications. Reaction-generated thermo-foaming technique has been used to develop functionally graded mullite-embedded silicate composite foam in a single step. The developed foams with gradient pores exhibit superior thermo-mechanical properties. In situ-growth of mullite phase within the silicate phase results in better mechanical strength of the foam. They possess bulk density, compressive strength and thermal conductivity in the range of 0.31-1.34 g/cm3, 2.97-15.06 MPa and 0.0843-0.2871 W/(m∙K), respectively. Thermal treatment irreversibly transforms the heavy metals present in the solid waste into stable mineral phases, further inhibiting the leaching of heavy metals from the developed foam. The developed foam with tuneable and gradient microstructure is seen as a potential material for thermal insulation and other applications such as refractories, molten metal and hot flue gas filters.

End-Of-Use Fly Ash as an Effective Reinforcing Filler in Green Polymer Composites

The aim of this study is to use fly ash powder in an environmentally friendly matrix, in a novel way, addressing environmental and disposal problems. Fly ash/epoxy composites were prepared and studied varying the filler content. An investigation of structural and morphological characteristics was conducted using of X-ray diffraction patterns and scanning electron microscopy images, which revealed the successful fabrication of composites. Thermomechanical properties were studied via dynamic mechanical analysis and static mechanical tests. The composites exhibited an improved mechanical response. Broadband dielectric spectroscopy was used to investigate the dielectric response of the composite systems over the frequency range from 10-1 to 107 Hz and the temperature range from 30 to 160 °C. The analysis revealed the presence of three relaxation processes in the spectra of the tested systems. Interfacial polarization, the glass-to-rubber transition of the polymer matrix, and the rearrangement of polar side groups along the polymer chain are the processes that occur under a descending relaxation time. It was found that dielectric permittivity increases with filler content. Finally, the influence of filler content and the applied voltage under dc conditions was analyzed to determine the ability of the composites to store and retrieve electric energy. Fly ash improved the efficiency of the storing/retrieving energy of the composites.

Review of Geopolymer Nanocomposites: Novel Materials for Sustainable Development

The demand for geopolymer materials is constantly growing. This, in turn, translates into an increasing number of studies aimed at developing new approaches to the methodology of geopolymer synthesis. The range of potential applications of geopolymers can be increased by improving the properties of the components. Future directions of studies on geopolymer materials aim at developing geopolymers showing excellent mechanical properties but also demonstrating significant improvement in thermal, magnetic, or sorption characteristics. Additionally, the current efforts focus not only on the materials' properties but also on obtaining them as a result of environment-friendly approaches performed in line with circular economy assumptions. Scientists look for smart and economical solutions such that a small amount of the modifier will translate into a significant improvement in functional properties. Thus, special attention is paid to the application of nanomaterials. This article presents selected nanoparticles incorporated into geopolymer matrices, including carbon nanotubes, graphene, nanosilica, and titanium dioxide. The review was prepared employing scientific databases, with particular attention given to studies on geopolymer nanocomposites. The purpose of this review article is to discuss geopolymer nanocomposites in the context of a sustainable development approach. Importantly, the main focus is on the influence of these nanomaterials on the physicochemical properties of geopolymer nanocomposites. Such a combination of geopolymer technology and nanotechnology seems to be promising in terms of preparation of nanocomposites with a variety of potential uses.

Performance Optimization of FA-GGBS Geopolymer Based on Response Surface Methodology

Many scholars have focused on the workability and mechanical properties of fly ash (FA)- ground granulated blast furnace slag (GGBS) geopolymer. To enhance the compressive strength of geopolymer, zeolite powder was added in the present study. A series of experiments were carried out to investigate the effect of using zeolite powder as an external admixture on the per-formance of FA-GGBS geopolymer, 17 sets of experiments were designed and tested to deter-mine the unconfined compressive strength based on the response surface methodology, and then, the optimal parameters were obtained via modeling of 3 factors (zeolite powder dosage, alkali exciter dosage, and alkali exciter modulus) and 2 levels of compressive strength (3 d and 28 d). The experimental results showed that the strength of the geopolymer was the highest when the three factors were 13.3%, 40.3%, and 1.2. Finally, a combination of scanning electron microscopy (SEM), X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FTIR), and ²⁹Si nuclear magnetic resonance (NMR) analysis was used to conduct micromechanical analysis and explain the reaction mechanism from a microscopic perspective. The SEM and XRD analysis revealed that the microstructure of the geopolymer was the densest when the zeolite powder was doped at 13.3%, and the strength increased accordingly. The NMR and Fourier transform infrared spectroscopy analyses revealed that the absorption peak wave number band shifted toward the lower wave number band under the optimal ratio, and the silica-oxygen bond was replaced by an aluminum-oxygen bond, which generated more aluminosilicate structures.

Membrane-based water and wastewater treatment technologies: Issues, current trends, challenges, and role in achieving sustainable development goals, and circular economy

Membrane-based technologies are recently being considered as effective methods for conventional water and wastewater remediation processes to achieve the increasing demands for clean water and minimize the negative environmental effects. Although there are numerous merits of such technologies, some major challenges like high capital and operating costs . This study first focuses on reporting the current membrane-based technologies, i.e., nanofiltration, ultrafiltration, microfiltration, and forward- and reverse-osmosis membranes. The second part of this study deeply discusses the contributions of membrane-based technologies in achieving the sustainable development goals (SDGs) stated by the United Nations (UNs) in 2015 followed by their role in the circular economy. In brief, the membrane based processes directly impact 15 out of 17 SDGs which are SDG1, 2, 3, 5, 6, 7, 8, 9, 11, 12, 13, 14, 15, 16 and 17. However, the merits, challenges, efficiencies, operating conditions, and applications are considered as the basis for evaluating such technologies in sustainable development, circular economy, and future development.

A comparative cradle-to-gate life cycle assessment of geopolymer concrete produced from industrial side streams in comparison with traditional concrete

Traditional concrete production is a major contributor to global warming. Industrially produced geopolymer concrete is a viable substitute to limit the negative impacts of concrete production. Thus, this study developed novel geopolymer concrete mix designs using industrial side streams, such as bark boiler ash, construction and demolition waste (CDW), fibre waste, and mine tailings. A cradle-to-gate life cycle assessment (LCA) methodology was conducted to evaluate the potential impacts of these different geopolymer concrete (GPC) mix designs in comparison with traditional concrete. The results showed that industrial-based geopolymer concrete with lower amounts of sodium silicate and metakaolin exhibited better environmental performance. Specifically, a 10 % reduction in metakaolin content reduces the global warming impact by 16 % compared with traditional concrete. The processing and curing of industrial waste for concrete formulations has an environmental impact of less than 1 %. From a sustainability perspective, the environmental performance of geopolymer concrete produced from industrial side streams can be further improved by increasing the concentration of recycled waste in the concrete mixes. In addition, the effective use of industrial side streams can improve the waste management, sustainability, and strength of concrete.

Microscopic Mechanism of Tunable Thermal Conductivity in Carbon Nanotube-Geopolymer Nanocomposites

Geopolymer has been considered as a green and low-carbon material with great potential application due to its simple synthesis process, environmental protection, excellent mechanical properties, good chemical resistance, and durability. In this work, the molecular dynamics simulation is employed to investigate the effect of the size, content, and distribution of carbon nanotubes on the thermal conductivity of geopolymer nanocomposites, and the microscopic mechanism is analyzed by the phonon density of states, phonon participation ratio, spectral thermal conductivity, etc. The results show that there is a significant size effect in the geopolymer nanocomposites system due to the carbon nanotubes. In addition, when the content of carbon nanotubes is 16.5%, the thermal conductivity in carbon nanotubes vertical axial direction (4.85 W/(m k)) increases by 125.6% compared with the system without carbon nanotubes (2.15 W/(m k)). However, the thermal conductivity in carbon nanotubes vertical axial direction (1.25 W/(m k)) decreases by 41.9%, which is mainly due to the interfacial thermal resistance and phonon scattering at the interfaces. The above results provide theoretical guidance for the tunable thermal conductivity in carbon nanotube-geopolymer nanocomposites.

Valorification of Egyptian volcanic tuff as eco-sustainable blended cementitious materials

Rhyolite rocks extend from southern Egypt to northern Egypt in the Eastern Desert, and no effective economic exploitation of them has been discovered so far. The pozzolanic activities of different volcanic tuffs (VT) supplied from the Eastern Desert located in Egypt have been investigated as natural volcanic pozzolan materials to develop new green cementitious materials for achieving sustainability goals in the construction field. Experimentally in this paper, the pozzolanic activities of seven diverse specimens of Egyptian tuffs taken with standardized proportions of 75:25% (Cement: volcanic tuffs) were investigated. Pozzolanic features of such tuffs are examined comparatively via strength activity index (SAI), TGA, DTA, and the Frattini's test. Chemical composition, petrographic, and XRD analysis were also performed for tuffs samples. The pozzolanic reaction degrees were determined according to the compressive strengths at 7, 28, 60 and 90 days with different replacement ratios (20, 25, 30 and 40%) of tuffs samples. Additionally, the micro-filler effects in mortar and concrete were determined by measuring the heat of hydration in mortar samples and the compressive strength of concrete with different additive ratios for tuffs samples besides, the concrete slump test. The results show that TF6 gives a lower cement heat of hydration value which is less than 270 J/g at 7 days. Also, its performance in concrete is better than silica fume at late strength (28 days) since the concrete index value is 106.2% by compared to the concrete index of silica fume 103.9 and therefore it can be used as an alternative to high price and quality variable silica fume (SF) for producing high-performance green concrete. Due to the good pozzolanic behavior proved by nearly most volcanic tuffs, along with their low cost, this study will be profitable for very auspicious the use of Egyptian volcanic tuffs for developing sustainable and eco‑friendly blended cement.

Mechanical performance and thermal stability of hardened Portland cement-recycled sludge pastes containing MnFe2O4 nanoparticles

This study focused on investigating the possibility of using different ratios (5, 10, 15 mass%) of recycled alum sludge (RAS) as partial replacement of ordinary Portland cement (OPC), to contribute to solving the problems encountered by cement production as well as stockpiling of large quantities of water-treated sludge waste. MnFe₂O₄ spinel nanoparticles (NMFs) were used to elaborate the mechanical characteristics and durability of different OPC-RAS blends. The outcomes of compressive strength, bulk density, water absorption, and stability against firing tests fastened the suitability of utilization of RAS waste for replacing OPC (maximum limit 10%). The inclusion of different doses of NMFs nanoparticles (0.5, 1 and 2 mass %) within OPC-RAS pastes, motivates the configuration of hardened nanocomposites with improved physico-mechanical characteristics and stability against firing. Composite made from 90% OPC-10% RAS-0.5% NMFs presented the best characteristics and consider the optimal choice for general construction applications. Thermogravimetric analysis (TGA/DTG), X-ray diffraction analysis (XRD), and scanning electron microscope (SEM) techniques. affirmed the positive impact of NMFs particles, as they demonstrated the formation of enormous phases as ilvaite (CFSH), calcium silicate hydrates (CSHs), MnCSH, Nchwaningite [Mn₂ SiO₃(OH)₂ H₂O], [(Mn, Ca) Mn₄O₉⋅3H₂O], calcium aluminosilicate hydrates (CASH), Glaucochroite [(Ca, Mn)₂SiO₄, and calcium ferrite hydrate (CFH). These hydrates boosted the robustness and degradation resistance of the hardened nanocomposites upon firing.

Elaboration of geopolymer package derived from uncalcined phosphate sludge and its solidification performance on nuclear grade resins loaded with 134Cs

Nuclear-grade Spent Organic Resin (SOR) contains high concentrations of radioactive nuclides and metal contaminants, while phosphate sludge contains high amount of fine clayey particles and CO₃^2-, both posing a major threat to the biosphere. In this study, a novel geopolymer package (GP) was proposed to directly solidify SOR loaded with ¹³⁴Cs by incorporating uncalcined phosphate sludge (UPS) as feedstocks, activated by NaOH/KOH. The results showed that alkali-mixed reagents-activated GP is more advantageous in terms of chemical stability and mechanical properties than NaOH-activated GP, recording compressive strength values greater than the waste acceptance criteria and OPC. The 28-day compressive strength of solidified packages can exceed 31 MPa at the highest amount of 42 wt% UPS. The addition of NaF powder into the solidified packages generates more hybrid type gels, which are more conducive to partial dissolution and bonding UPS particles, thereby producing stable and stronger GP. Leaching results of solidified GP in presence of up to 13 wt% SORs showed that only 0.15 % of total ¹³⁴Cs was leached, even under aggressive solutions. Solidification mechanism revealed that activation of UPS-MK blend forms N,K-A-S-H, (N,K,C)-A-S-H/C-S-H gels coexisting with unreacted particles, thereby solidify/stabilize metal contaminants and Cs⁺ by a synergetic immobilization action of hydration products via substitution and encapsulation. This study provides a promising paradigm for effective solidification of nuclear-grade resins and synergetic harmless treatment of industrial/phosphate mine solid wastes.

A two-step approach for calculating chloride diffusion coefficient in concrete with both natural and recycled concrete aggregates

This paper presents an analytical approach to calculate the effective diffusion coefficient of chlorides in concrete with both natural and recycled concrete aggregates. In the approach the concrete is treated as a composite consisting of three phases, namely mortar, natural aggregate plus interfacial transition zone, and recycled concrete aggregate plus interfacial transition zone. The effective diffusion coefficient of chlorides in the composite is calculated through two steps. The first step is to calculate the effective diffusion coefficients of chlorides in the natural aggregate plus interfacial transition zone and in the recycled concrete aggregate plus interfacial transition zone by using multilayer spherical approximation, the results of which provide the information about the quality of recycled concrete aggregate in terms of chloride penetration resistance. The second step is to calculate the effective diffusion coefficient of chlorides in the three-phase concrete composite by using effective medium approximation, the results of which provide the information about the influence of recycled concrete aggregate on the diffusivity of recycled aggregate concrete. The analytical expression of the effective diffusion coefficient is derived and carefully compared with the results obtained from both the experiments and numerical simulations, which demonstrates that the present analytical model is rational and reliable. The analytical expression presented can be used to predict the service life of recycled aggregate concrete exposed to chloride environment.

Role of microalgae in achieving sustainable development goals and circular economy

In 2015, the United Nations General Assembly (UNGA) set out 17 Sustainable Development Goals (SDGs) to be achieved by 2030. These goals highlight key objectives that must be addressed. Each target focuses on a unique perspective crucial to meeting these goals. Social, political, and economic issues are addressed to comprehensively review the main issues combating climate change and creating sustainable and environmentally friendly industries, jobs, and communities. Several mechanisms that involve judicious use of biological entities are among instruments that are being explored to achieve the targets of SDGs. Microalgae have an increasing interest in various sectors, including; renewable energy, food, environmental management, water purification, and the production of chemicals such as biofertilizers, cosmetics, and healthcare products. The significance of microalgae also arises from their tendency to consume CO2, which is the main greenhouse gas and the major contributor to the climate change. This work discusses the roles of microalgae in achieving the various SDGs. Moreover, this work elaborates on the contribution of microalgae to the circular economy. It was found that the microalgae contribute to all the 17th SDGs, where they directly contribute to 9th of the SDGs and indirectly contribute to the rest. The major contribution of the Microalgae is clear in SDG-6 "Clean water and sanitation", SDG-7 "Affordable and clean energy", and SDG-13 "Climate action". Furthermore, it was found that Microalgae have a significant contribution to the circular economy.

Fuzzy Logic Tools Application to the Characterization of Stress-Strain Processes in Waste Construction Dam Geopolymers: A New Circular Mining

The ceramics industry dedicated to the manufacture of building materials is a very significant cause of environmental pollution, and various research projects are being carried out to reduce the associated environmental impact. One of the most important research lines is the generation and development of new materials, from waste, through more sustainable production processes. All of this is framed in circular mining. In this research study, geopolymers were developed with biomass bottom ashes and brick dust in order to replace the traditional ceramics used to construct bricks. For this, different families of test tubes were formed with different percentages of both residues, and their physical and mechanical properties were studied. In this way, the properties of geopolymers could be compared with traditional ceramics. In addition, in order to determine the cause-effect relationships between physical properties and compressive strength, data were processed using fuzzy logic and data mining techniques. The results showed the feasibility of geopolymers generation with biomass bottom ashes and brick dust with acceptable properties to replace conventional ceramics. In addition, the fuzzy logic analysis allowed for establishing clear and objective relationships between the physical properties and the compressive strength of the geopolymers, with the aim of developing the highest quality geopolymer.

A Bibliometric Analysis of Research Trends in Geopolymer

Geopolymer is an inorganic material formed through the chemical reaction of an aluminosilicate precursor and an alkaline or acidic activating solution. It is seen as a green new alternative binder to ordinary Portland cement (OPC) for sustainable infrastructure development. The strength of the unary or blended geopolymer product is dependent on the composition and properties of the polymeric gel influenced by the ratios of Al₂O₃/SiO₂, CaO/SiO₂, CaO/(SiO₂ + Al₂O₃), Na₂SiO₃/NaOH, SiO₂/Na₂O, and liquid/binder (L/B). Essential scientific inquiry has been progressively addressed by utilizing expert assessment and research metrics. The network visualization of bibliometric co-occurrence and co-citations is of particular significance. The present study aims to highlight the trends and progress of the most influential publication sources, keywords, authors, articles, and countries in geopolymer research in the last 10 years. Bibliometric data were retrieved through Scopus and visualized in VOSviewer to create bibliometric networks. The yearly distribution and growth trends (April 2011-2022) of geopolymer, geopolymer mortar, and geopolymer concrete before (after) applying inclusion criteria were from 754 to 9887 (5186), 47 to 1374 (866), and 145 to 3721 (2253), respectively, attributed to the discoveries in more precursor materials such as laterite and the growing interest in fire and heat-resistant structures, water and wastewater treatment, cement and concrete, and brick manufacturing. The top three journals in terms of prestige for geopolymer publications were the Journal of Hazardous Materials with an impact factor equal to 14.224 and h-index equal to 307, Cement and Concrete Research with an impact factor equal to 11.958 and h-index equal to 239, and the Journal of Cleaner Production with an impact factor equal to 11.072 and h-index equal to 232. The top three journals in terms of average citation per document were Cement and Concrete Research (135.75), Materials and Design (75), and Cement and Concrete Composites (68.35). Keywords such as "geopolymers", "inorganic polymer", "geopolymer", "compressive strength", "fly ash", and "geopolymer concrete" had the highest occurrences in publications. John Provis-University of Sheffield, Prinya Chindaprasirt-Khon Kaen University, and Jay Sanjayan-Swinburne University of Technology had the highest total citations of 6377, 5626, and 4311, respectively. The highest number of publications were from China, India, Australia, the United States of America, and Malaysia. The bibliometric findings from this study can act as a tool for academicians and policymakers to exchange research expertise, collaborate on novel geopolymer research, and create innovative joint ventures.

Enhanced Congo Red Adsorption and Photo-Fenton Oxidation over an Iron-Impeded Geopolymer from Ferruginous Kaolinite: Steric, Energetic, Oxidation, and Synergetic Studies

An iron-impeded geopolymer (Fe/GP) was synthesized from natural ferruginous kaolinite and optical waste for enhanced decontamination of Congo red (CR) dye. The adsorption properties of Fe/GP were assessed using an advanced monolayer equilibrium model of one energy (R ² > 0.99). Fe/GP possessed an active site density of 391.3 mg/g, which induced an adsorption capacity of 634 mg/g at the saturation state. The number of adsorbed CR molecules per site (n = 1.56-1.62) reflected the possible uptake of two molecules per site via a multimolecular mechanism. The adsorption energy (5.12-5.7 kJ/mol) reflected the physical adsorption of the CR molecules via hydrogen bonding and/or van der Waals forces. As a catalyst, notable activity toward photo-Fenton oxidation was achieved even at high CR concentrations. Complete oxidation was observed after 30 (CR concentration: 10 mg/L), 50 (20 mg/L), 80 (30 mg/L), 120 (40 mg/L), and 140 min (50 mg/L). High oxidation efficiency was achieved using 0.1 g/L Fe/GP, 0.1 mL of hydrogen peroxide (H₂O₂), and a visible light source. Increasing the Fe/GP dosage to 0.3 g/L resulted in complete oxidation of CR (100 mg/L) after 220 min. Therefore, synthetic Fe/GP can be used as a low-cost and superior catalyst and adsorbent for the removal of CR-based contaminants via adsorption or advanced oxidation processes.

A State-of-the-Art Review on the Incorporation of Recycled Concrete Aggregates in Geopolymer Concrete

Geopolymer concrete (GC) has the potential to incorporate recycled concrete aggregates (RCA) obtained from construction and demolition waste. This research aims to review the current state-of-the-art knowledge of the RCA in GC and identify the existing knowledge gaps for future research direction. This paper highlights the essential factors that impact the GC’s mechanical and durability properties. Moreover, the influence of various percentages of coarse and fine RCA and the pattern of their replacement will be assessed. The effect of aluminosilicate material, alkaline activators, and curing regime also will be evaluated. Besides, the durability-related characteristics of this concrete will be analysed. The impact of exposure to a higher temperature, freeze–thaw cycles, marine environment, and acid and alkali attack will be comprehensively reviewed. A literature review revealed that increasing alumina silicate content, such as slag and metakaolin, and increasing the Na2SiO3/NaOH ratio and alkali-activator-to-binder ratio improve the hardened GC. However, increasing slag and metakaolin content and the Na2SiO3/NaOH ratio has an adverse impact on its workability. Therefore, finding the optimum mix design for using RCA in GC is vital. Moreover, there is a scope for developing a self-compacting GC cured at ambient temperature using RCA.

A Comprehensive Review on Fly Ash-Based Geopolymer

The discovery of an innovative category of inorganic geopolymer composites has generated extensive scientific attention and the kaleidoscopic development of their applications. The escalating concerns over global warming owing to emissions of carbon dioxide (CO2), a primary greenhouse gas, from the ordinary Portland cement industry, may hopefully be mitigated by the development of geopolymer construction composites with a lower carbon footprint. The current manuscript comprehensively reviews the rheological, strength and durability properties of geopolymer composites, along with shedding light on their recent key advancements viz., micro-structures, state-of-the-art applications such as the immobilization of toxic or radioactive wastes, digital geopolymer concrete, 3D-printed fly ash-based geopolymers, hot-pressed and foam geopolymers, etc. They have a crystal-clear role to play in offering a sustainable prospect to the construction industry, as part of the accessible toolkit of building materials—binders, cements, mortars, concretes, etc. Consequently, the present scientometric review manuscript is grist for the mill and aims to contribute as a single key note document assessing exhaustive research findings for establishing the viability of fly ash-based geopolymer composites as the most promising, durable, sustainable, affordable, user and eco-benevolent building materials for the future.

Orthogonal Experimental Study on Concrete Properties of Machine-Made Tuff Sand

Machine-made sand instead of natural sand has become an inevitable choice for the sustainable development of the concrete industry. Orthogonal experiment and grey correlation analysis were used to investigate the performance of machine-made tuff sand concrete. The optimal concrete mix ratio of machine-made sand was obtained by orthogonal test and its working performance was verified. Grey correlation analysis was applied to compare the factors affecting the mechanical properties of the machine-made sand concrete. The test results show that the sand rate has the greatest degree of influence on slump and slump expansion. The mineral admixture has the greatest effect on the 7-day compressive strength of the concrete. Additionally, the water–cement ratio has the greatest influence on the 28-day compressive strength. The mechanical and working properties of the machine-made sand concrete reach the optimum condition when the mineral admixture is 20%, the sand rate is 46%, the stone powder content is 10% and the water–cement ratio is 0.30. Comparing different fine aggregate concretes of similar quality, we conclude that the mechanical and working properties of tuff sand concrete and limestone sand concrete and river sand concrete are similar. The compressive strengths of the mechanism concrete show the greatest correlation with roughness and the least correlation with stone powder content. The stone powder content has almost no effect on the compressive strength of concrete when the stone powder content does not exceed a certain range. The results of the study point out the direction for the quality control of concrete with machine-made sand.