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The current work aimed to explore the effect of Na/Al ratios of 0.43, 0.53, 0.63, 0.73, 0.83, and 0.93, using NaOH to alter the molar ratio, on the mechanical properties of a geopolymer material, with fixing of the Si/Al molar ratio. While fixing the Na/Al molar ratio, alteration of the Si/Al ratios to 1.7, 1.75, 1.8, 1.85, 1.9, 1.95 was used, with silica fume and sodium silicate as a silica corrector. The influence on the micromorphology and macro-strength of samples was characterized through SEM, EDS, and compressive strength characterization methods. The results show that Si/Al and Na/Al molar ratios play a significant role in the microstructure and mechanical behavior of MK-based geopolymers, and revealed that the optimal molar Si/Al and Na/Al ratios for attaining maximum mechanical strength in geopolymers are 1.9 and 0.73, respectively. Under various Si/Al ratios, the macro-strength of the geopolymer mainly relies on the formation of NASH gel, rather than zeolites or silicate derivatives. The appropriate Na/Al molar ratio can contribute to the geopolymerization, but a ultra-high Na/Al molar ratio caused a high alkali state that destroyed the microstructure of the geopolymers. Regardless of the amount of water contained in the initial geopolymer raw material, the water content of Si/Al = 1.65 and Si/Al = 1.75 after curing for 10 days was almost the same, and the bound water content of the final geopolymer was maintained at about 15%. Structural water exists in geological polymer gels in the form of a chemical structure. It has effects on the structural performance strength, while free water affects the volume stability of the geological polymer. Overall, the current work provides a perspective on the elemental composition analysis, combined with the molecular structure and micromorphology, to explore the mechanical performance of geopolymers.

Concrete is the basic building material in the world, and cement is the main material used in the production of concrete. However, there is an urgent need to reduce the consumption of cement, where cement production leads to 5–8% of global emissions of carbon dioxide. Geopolymer concrete is an innovative building material produced by alkaline activation of pozzolanic materials such as fly ash, granulated blast furnace slag, and kaolin clay. Geopolymers are widely used in the production of geopolymer concrete due to their ability to reduce carbon dioxide emissions and reduce high energy consumption. During the present study, the environmental impact of two strength grades (30 MPa and 40 MPa) of metakaolin geopolymer concrete (GPC) was evaluated to study its applicability in the construction sector. The kaolin clay extracted from the Aswan quarries was activated by a mixture of sodium hydroxide and sodium silicate solution. To introduce geopolymer concrete in the Egyptian industry sector, its environmental performance, together with its technical performance, should be competitive to the cement concrete used mainly for the time being. The cost of this new concrete system should also be evaluated. The environmental impact of GPC was evaluated and compared with cement concrete using life cycle assessment analysis and IMPACT 2002+ methodology. The cost of production was calculated for 1 m3 of geopolymer concrete and conventional cement concrete. Metakaolin geopolymer concrete achieved a high compressive strength of ~ 56 MPa, splitting tensile strength of 24 MPa, and modulus of elasticity of 8.5 MPa. The corrosion inhibition of metakaolin geopolymer concrete was ~ 80% better than that of conventional cement concrete. Geopolymer concrete achieved a reduction in global warming potential by 61% and improved the human health category by 9.4%. However, due to the heavy burdens of sodium silicate, the geopolymer concrete negatively affected the quality of the ecosystem by 68% and showed a slightly higher impact than cement concrete on the resource damage category for low strength grade of 30 MPa. The high cost of the basic ingredients of the geopolymer resulted in a high production cost of geopolymer concrete (~ 92 US $) that was three times that of cement concrete (~ 31 US$ ). Based on the environmental results, geopolymer concrete based on locally available metakaolin clay can be applied in the construction sector as a green alternative material for cement concrete.Graphic abstract

This study was related to produce colored geopolymer concrete using metakaolin and adding two types of red (iron oxide) and green (chromium oxide) pigments with three additional ratios for each of the listed colors (0, 2, 4, 6 )% wt of metakaolin, and study some mechanical properties of colored geopolymer concrete. The experimental investigation has dealt with the fresh properties(slump) of the colored geopolymer concrete mixes as well as some of the mechanical properties of the hardened concrete by testing specimens in compressive strength, modulus of rupture, Rebound number (RN), and ultrasonic pulse velocity (UPV). Show us that (2% wt) pigment percentage gives the best results.

Metakaolin-based geopolymers possess excellent corrosion and high-temperature resistance, which are advantageous compared to ordinary Portland cement. The addition of slag in metakaolin-based geopolymers is a promising approach to improve their mechanical properties. Thus, this study investigated the effect of slag content on the strength and shrinkage properties of metakaolin-based geopolymers. Increasing the slag content and Na2O content was beneficial to the reaction of alkali-activated metakaolin-based geopolymers, thereby improving their compressive strength and density. After 56 days of aging, a maximum compressive strength of 86.1 MPa was achieved for a metakaolin-based geopolymer with a slag content of 50 mass%. When the Na2O content was 12%, the compressive strength of the metakaolin geopolymers with a slag content of 30% was 42.36% higher than those with a Na2O content of 8%. However, as the slag and alkali contents increased, the reaction rate of the metakaolin-based geopolymers increased, which significantly decreased the porosity, increased the shrinkage, and decreased the volumetric stability of the system. In this paper, in-depth study of the volume stability of alkali-activated metakaolin-based geopolymers plays an important role in further understanding, controlling, and utilizing the deformation behavior of geopolymers.

This research examines the effect of sodium hydroxide (NaOH) concentration on the synthesis, the physical and mechanical characteristics of metakaolin-based geopolymer mortars. Geopolymers were cured at 65?C with different NaOH molarities (6-16 M), and their bulk density, total porosity, compressive strength, and flexural strength were meticulously analyzed. The inquiry used sophisticated microstructural analysis by X-ray diffraction (XRD) to elucidate significant phase shifts and structural alterations. The findings indicate that the geopolymers produced with both lower and higher NaOH concentrations had enhanced physical and mechanical capabilities. XRD examination verified the existence of predominant crystalline phases of metakaolin and the development of a novel amorphous geopolymeric phase. This thorough methodology elucidates the ideal circumstances for improving geopolymer efficacy, offering significant insights for advanced material innovation.

The fresh, mechanical, and durability characteristics of geopolymer concrete produced using ground granulated blast furnace slag, metakaolin, and nano silica as source materials are examined in this paper. 9 concrete mixes were created, comprising 8 geopolymer concrete variations based on various binary and ternary binder combinations and control mixture. Because of the finer particle sizes and high reactivity of metakaolin and nano silica, the slump test revealed that geopolymer concrete mixes showed a slight decrease in workability when compared to the control mixture however, superplasticizers helped achieve good workability. The results of the strength tests also confirmed that, in comparison to conventional concrete, all geopolymer concrete formulations had greater compressive, split tensile, and flexural strengths. In that respect, GC7, which contained 2% nano silica, turned out to yield the best performance, resulting from improved gel formation and internal matrix densification. Durability tests also indicated lower saturated water absorption and improved resistance to sulfuric acid attack in all geopolymer concrete mixtures, with an absorption continually decreasing with age. These findings confirm that GGBS–MK–NS-based geopolymer concrete has better strength and durability characteristics, which further reinforces its potential as an eco-friendly and high-performance alternative to traditional OPC concrete.

In the last three decades, the gigantic demand for sustainable and environmentally friendly concrete with reduced environmental footprints has resulted in the development of low carbon concretes such as geopolymer concrete. Metakaolin which is commonly used as an admixture or partial replacement of cement owing to its most effective pozzolanic properties, which improve the microstructure and strengthen the mechanical and durability properties of cement concrete, has been investigated as a precursor in geopolymer concrete. Several studies have been conducted to comprehend the effect of metakaolin as an additive in geopolymer mortar and concrete prepared with various aluminosilicate sources as precursors such as fly ash and rice husk ash to enhance geopolymerization, densify microstructure, and elevate durability. The present paper recapitulates these investigations primarily concentrating on the various properties of metakaolin-based concrete. The effect of various factors such as alkali content, solids/liquids ratio, alkali reactant ratio, molar ratio, water content, and curing regime has been compiled. Most of them revealed that metakaolin is used as a precursor and yields better geopolymer products. XRD studies reported the peaks demonstrating the development of enhancement in hydration products in comparison to other precursors. Examination of SEM graphs reveals that the addition of a smaller quantity of silica-rich materials densifies the microstructure of geopolymers and produces higher mechanical strength. Durability studies reveal that metakaolin geopolymers possess better water resistance, thermal resistance, and anti-corrosion properties. The possible applications of metakaolin-based geopolymeric materials are also pointed out. The comprehensive knowledge presented here is expected to support the prospective researchers to decide their future course of the research area. Graphical abstract

This research aims to determine the effectiveness of a novel geopolymer as an adsorbent material for the removal of heavy metals, specifically nickel (Ni), cadmium (Cd), and chromium (Cr). Various design procedures were employed to create a series of geopolymers at room temperature, which were tested for their adsorption abilities under isothermal conditions. Clay (kaolin) and metakaolin were combined with additives of sodium silicate and sodium hydroxide to produce the geopolymers. The synthesized geopolymer samples were systematically characterized through XRF, XRD, and SEM. The adsorption properties of these materials were evaluated by varying the Si/Al ratio in their composition. An optimal ratio of 1:2 was identified for effectively removing nickel, chromium, and cadmium from contaminated water. The GP4 geopolymer design had the maximum removal efficiency for all tested heavy metals. The adsorption process included both the outer surface area and the entrance pores of the geopolymers. This work provides new ideas for the fabrication of low-priced, efficient, and easy-to-synthesize adsorbent materials for water treatment and other environmental remediation applications.

Despite the extensive use of mortars materials in constructions over the last decades, there is not yet a reliable and robust method, available in the literature, which can estimate its strength based on its mix parameters. This limitation is due to the highly nonlinear relation between the mortar’s compressive strength and the mixed components. In this paper, the application of artificial intelligence techniques toward the prediction of the compressive strength of cement-based mortar materials with or without metakaolin has been investigated. Specifically, surrogate models (such as artificial neural network, ANN and adaptive neuro-fuzzy inference system, ANFIS models) have been developed to the prediction of the compressive strength of mortars trained using experimental data available in the literature. The comparison of the derived results with the experimental findings demonstrates the ability of both ANN and ANFIS models to approximate the compressive strength of mortars in a reliable and robust manner. Although ANFIS was able to obtain higher performance prediction to estimate the compressive strength of mortars compared to ANN model, it was found through the verification process of some other additional data, the ANFIS model has overfitted the data. Therefore, the developed ANN model has been introduced as the best predictive technique for solving problem of the compressive strength of mortars. Furthermore, using the optimum developed model an ambitious attempt to reveal the nature of mortar materials has been made.