Study on the Compressive Strength of Alkali Activated Fly Ash and Slag under the Different Silicate Structure

Due to its high activation efficiency, waterglass has been widely used for alkali activations in geopolymer. In this study, the n(SiO₂)/n(Na₂O) (Ms) of waterglass was selected as the variable to investigate the role of the silicate structure on the mechanical properties of harden pastes. Ms was changed by the addition of NaOH to obtain the different silicate group, structure and experiments were performed by employing the liquid-sate ²⁹Si nuclear magnetic resonance (NMR), Fourier transform infrared spectroscopy (FTIR), dynamic light scattering (DLS) and gel permeation chromatography (GPC) techniques. Furthermore, selected dissolution, scanning electron microscope (SEM-EDX), X-ray photoelectron spectroscopy (XPS) and FTIR experiments were used to measure the development of the amorphous gel and other materials with different curing condition. Results show that silicate structure of the waterglass was changed via the Si-ONa⁺ formation and the electric charge effect of Na⁺. Under the lower Ms waterglass, the Q⁰, Q¹ and Q_C² structure reverted to the main structure of the silicate group, which was kind of lower seize, molecule weight, linear or circular chain lower geopolymerization degree silicon structure. It would accelerate the geopolymerization speed of prepolymer formation. In addition, higher activity degree of Q⁰ and Q¹ were useful to increase the formation amount of the gel structure with a low Si/Al ratio and size. Thus, silicate structure of waterglass controls the amorphous gel properties to adjust the compressive strength of alkali-activated materials.     

Effect of Solids-To-Liquids,Na2SiO3-To-NaOH and Curing Temperature on the Palm Oil Boiler Ash (Si + Ca) Geopolymerisation System

This paper investigates the effect of the solids-to-liquids (S/L) and Na₂SiO₃/NaOH ratios on the production of palm oil boiler ash (POBA) based geopolymer. Sodium silicate and sodium hydroxide (NaOH) solution were used as alkaline activator with a NaOH concentration of 14 M. The geopolymer samples were prepared with different S/L ratios (0.5, 1.0, 1.25, 1.5, and 1.75) and Na₂SiO₃/NaOH ratios (0.5, 1.0, 1.5, 2.0, 2.5, and 3.0). The main evaluation techniques in this study were compressive strength, X-Ray Diffraction (XRD), Fourier Transform Infrared Spectroscopy (FTIR), and Scanning Electron Microscope (SEM). The results showed that the maximum compressive strength (11.9 MPa) was obtained at a S/L ratio and Na₂SiO₃/NaOH ratio of 1.5 and 2.5 at seven days of testing.     

Resistance to Sulfuric Acid Corrosion of Geopolymer Concrete Based on Different Binding Materials and Alkali Concentrations

Geopolymer binder is expected to be an optimum alternative to Portland cement due to its excellent engineering properties of high strength, acid corrosion resistance, low permeability, good chemical resistance, and excellent fire resistance. To study the sulfuric acid corrosion resistance of geopolymer concrete (GPC) with different binding materials and concentrations of sodium hydroxide solution (NaOH), metakaolin, high-calcium fly ash, and low-calcium fly ash were chosen as binding materials of GPC for the geopolymerization process. A mixture of sodium silicate solution (Na₂SiO₃) and NaOH solution with different concentrations (8 M and 12 M) was selected as the alkaline activator with a ratio (Na₂SiO₃/NaOH) of 1.5. GPC specimens were immersed in the sulfuric acid solution with the pH value of 1 for 6 days and then naturally dried for 1 day until 98 days. The macroscopic properties of GPC were characterized by visual appearance, compressive strength, mass loss, and neutralization depth. The materials were characterized by SEM, XRD, and FTIR. The results indicated that at the immersion time of 28 d, the compressive strength of two types of fly ash-based GPC increased to some extent due to the presence of gypsum, but this phenomenon was not observed in metakaolin-based GPC. After 98 d of immersion, the residual strength of fly ash based GPC was still higher, which reached more than 25 MPa, while the metakaolin-based GPC failed. Furthermore, due to the rigid 3D networks of aluminosilicate in fly ash-based GPC, the mass of all GPC decreased slightly during the immersion period, and then tended to be stable in the later period. On the contrary, in metakaolin-based GPC, the incomplete geopolymerization led to the compressive strength being too low to meet the application of practical engineering. In addition, the compressive strength of GPC activated by 12 M NaOH was higher than the GPC activated by 8 M NaOH, which is owing to the formation of gel depended on the concentration of alkali OH ion, low NaOH concentration weakened chemical reaction, and reduced compressive strength. Additionally, according to the testing results of neutralization depth, the neutralization depth of high-calcium fly ash-based GPC activated by 12 M NaOH suffered acid attack for 98 d was only 6.9 mm, which is the minimum value. Therefore, the best performance was observed in GPC prepared with high-calcium fly ash and 12 M NaOH solution, which is attributed to gypsum crystals that block the pores of the specimen and improve the microstructure of GPC, inhibiting further corrosion of sulfuric acid.     

Mechanical Properties and Microstructural Characterization of Metakaolin Geopolymers Based on Orthogonal Tests

Metakaolin was used as a raw material for the preparation of geopolymers, where two types of alkali activators (Na₂SiO₃ + NaOH and Na₂SiO₃ + NaOH) were used to prepare metakaolin geopolymers at room temperature. The mechanical properties and microstructures of the metakaolin geopolymers were analyzed. A three-factor, four-level orthogonal test was designed to investigate the mechanical properties of the metakaolin geopolymer with different ratios. The compressive and flexural strength of different specimens were tested for 7 and 28 days. Both the Na-based and K-based geopolymers exhibited excellent mechanical properties, but the K-based geopolymer had better mechanical properties. The optimal compressive strength and flexural strength of the K-based geopolymer were 73.93 MPa and 9.37 MPa, respectively. The 28-day optimal compressive strength of the Na-based polymer was 65.79 MPa, and the flexural strength was 8.71 MPa. SEM, XRD, and FTIR analyses showed that the mechanical properties of the geopolymers could be greatly improved by using a higher alkaline solution concentration, proper Na₂SiO₃/MOH mass ratio, and proper mass ratio of alkali exciter to metakaolin. Amorphous silicoaluminate was more favorable for the dissolution of silicon–alumina raw materials, promoted the formation of an amorphous silicoaluminate gel, and caused the internal structure of the geopolymer to be more compact.     

Evaluation on the Mechanical Properties of Ground Granulated Blast Slag (GGBS) and Fly Ash Stabilized Soil via Geopolymer Process

This study intended to address the problem of damaged (collapsed, cracked and decreased soil strength) road pavement structure built on clay soil due to clay soil properties such as low shear strength, high soil compressibility, low soil permeability, low soil strength, and high soil plasticity. Previous research reported that ground granulated blast slag (GGBS) and fly ash can be used for clay soil stabilizations, but the results of past research indicate that the road pavement construction standards remained unfulfilled, especially in terms of clay’s subgrade soil. Due to this reason, this study is carried out to further investigate soil stabilization using GGBS and fly ash-based geopolymer processes. This study investigates the effects of GGBS and ratios of fly ash (solid) to alkaline activator (liquid) of 1:1, 1.5:1, 2:1, 2.5:1, and 3:1, cured for 1 and 7 days. The molarity of sodium hydroxide (NaOH) and the ratio of sodium silicate (Na₂SiO₃) to sodium hydroxide (NaOH) was fixed at 10 molar and 2.0 weight ratio. The mechanical properties of the soil stabilization based geopolymer process were tested using an unconfined compression test, while the characterization of soil stabilization was investigated using the plastic limit test, liquid limit test, scanning electron microscopy (SEM), X-ray diffraction (XRD), and Fourier transform infrared spectroscopy (FTIR). The results showed that the highest strength obtained was 3.15 MPA with a GGBS to alkaline activator ratio of 1.5 and Na₂SiO₃ to NaOH ratio of 2.0 at 7 days curing time. These findings are useful in enhancing knowledge in the field of soil stabilization-based geopolymer, especially for applications in pavement construction. In addition, it can be used as a reference for academicians, civil engineers, and geotechnical engineers.     

Influence of Accelerating Admixtures on the Reactivity of Synthetic Aluminosilicate Glasses

This research aims at gaining a further understanding of the impact of accelerating admixtures on the reactivity of supplementary cementitious materials (SCMs), which are widely used as a clinker replacement in blended cements. This was done on synthetic glasses with controlled composition and structure that mimic two types of real SCMs (slag and calcium-rich fly ash). The effects of DEIPA, TIPA, NaSCN and Na₂S₂O₃ on the glass dissolution, hydration kinetics and reaction products were investigated. The obtained results concluded that the pH of the NaOH solution and the composition of the synthetic glass play a key role on the effect of the admixtures. In 0.1 M NaOH (pH = 13.0), all the studied admixtures inhibited the dissolution of slag-like glasses while they enhanced the dissolution of Ca-rich fly ash-like glasses, being Na₂S₂O₃ the admixture that led to the highest increase of the dissolution rate of the Ca-rich fly ash-type glasses. In 1 M NaOH solutions (pH = 13.8), only the alkali admixtures (NaSCN and Na₂S₂O₃) enhanced the degree of reaction of both glasses. In slag-type glasses pastes mixed with 1 M NaOH, the addition of 2% Na₂S₂O₃ induced the highest increase of their reactivity as inferred by the total heat release and the amount of bound water. This is related to the formation of a high amount of S(II)-AFm, in addition to C-A-S-H, that would increase the aluminium undersaturation of the pore solution and consequently the further dissolution of the glass.     

Use of Gypsum as a Preventive Measure for Strength Deterioration during Curing in Class F Fly Ash Geopolymer System

This study discusses strength deterioration during the curing process of fly ash geopolymer and the use of CaSO₄·2H₂O (gypsum) as a deterioration remedy when the ash was synthesized using a 10M NaOH and Na-silicate solution. The strength decline was mainly due to the widespread formation of nanometer-sized cracks that were related to excessive Na and Si concentrations at an early age. Use of 2 wt% CaSO₄·2H₂O resulted in the best measured strength by temporarily reducing Na and Si concentrations; Na was absorbed by SO₄²⁻, up to 11% in the matrix within one day, and formed Na₂SO₄ (thenardite), which gradually dissolved over time, slowly releasing Na ions. However, more than 4% gypsum suppressed overall strength development because too many Na ions were locked into Na₂SO₄ and could not participate in geopolymerization. The addition of gypsum impeded glass dissolution and even halted the process when more than 4% gypsum was used.     

The Durability of Mortar Containing Alkali Activated Fly Ash-Based Lightweight Aggregate

Beneficiating fly ash as valuable construction material such as artificial lightweight aggregate (LWA) could be an alternative solution to increase the utilization of the industrial by-product. However, generally, LWA is characterized by high porosity and a related high water absorption, which on the one hand allows production of lightweight mortar, but on the other hand can affect its performance. Thus, in this research, the durability performance of mortar composed with alkali-activated fly ash-based LWA, and commercial expanded clay (EC) LWA was investigated. The fly ash LWA was prepared in a pan granulator, with a 6-molar solution of NaOH mixed with Na₂SiO₃ in a Na₂SiO₃/NaOH weight ratio of 1.5 being used as activator (FA 6M LWA). The results revealed that mortar containing FA 6M LWA had equivalent mechanical strength with mortar containing EC LWA. The mortar containing FA 6M LWA had comparable capillary water uptake and chloride migration resistance with the reference and EC LWA mortar. Furthermore, the addition of FA 6M LWA was proven to enhance the carbonation resistance in the resulting mortar, due to the denser interfacial transition zone (ITZ) of mortar with LWA.     

Process Development of Fly Ash-Based Geopolymer Mortars in View of the Mechanical Characteristics

This study aimed to determine the effects of design parameters, including the liquid/solid ratio (L/S), Na₂SiO₃/NaOH weight ratio, and curing temperature, on class F fly ash-based geopolymer composites. For this purpose, two disparate sources of fly ash were supplied from Çatalağzı (FA) and İsken Sugözü (FB) Thermal Power Plants in Turkey. Two different L/S ratios of 0.2 and 0.4 were used. The Na₂SiO₃/NaOH ratios in the alkaline solutions were 1, 1.5, 2, 2.5, and 3 by weight for each type of geopolymer mixture. Then, 40 different mixes were cured at two specific temperatures (70 °C and 100 °C) for 24 h and then preserved at room temperature until testing. Thereafter, the physical water absorption properties, apparent porosity, and bulk density were examined at 28 days on the hardened mortars. Additionally, compressive and flexural tests were applied to the geopolymers at 7, 28, and 90 days. It was found that the highest compressive strength was 60.1 MPa for the geopolymer manufactured with an L/S of 0.2 and Na₂SiO₃/NaOH ratio of 2. Moreover, the best thermal curing temperature for obtaining optimal strength characteristics was 100 °C for the FB.     

Hybrid Lime–Pozzolan Geopolymer Systems: Microstructural,Mechanical and Durability Studies

This work studies the possibility of using geopolymer materials to enhance the mechanical and durability properties of hydrated lime–pozzolan mixtures, which gave rise to the so-called “hybrid systems”. Two different waste types were used as pozzolan in the lime–pozzolan system: rice husk ash (RHA) and spent fluid catalytic cracking (FCC). The geopolymer fabricated with FCC was activated with commercial reagents (NaOH and Na₂SiO₃), and also with alternative sources of silica to obtain a lower carbon footprint in these mixtures. The alternative silica sources were RHA and residual diatomaceous earth (RDE) from the beer industry. The geopolymer mixture substituted the lime–pozzolan mixture for 30% replacement in weight. The hybrid systems showed better mechanical strengths for the short and medium curing ages in relation to the lime–pozzolan mixtures. Thermogravimetric analyses were performed to characterise the types of products formed in these mixtures. In the durability studies, hybrid systems better performed in freeze–thaw cycles and obtained lower capillarity water absorption values.     

Influence of Silica Modulus and Curing Temperature on the Strength of Alkali-Activated Volcanic Ash and Limestone Powder Mortar

This present study evaluates the effect of silica modulus (M_s) and curing temperature on strengths and the microstructures of binary blended alkali-activated volcanic ash and limestone powder mortar. Mortar samples were prepared using mass ratio of combined Na₂SiO_3(aq)/10 M NaOH_(aq) of 0.5 to 1.5 at an interval of 0.25, corresponding to M_s of 0.52, 0.72, 0.89, 1.05 and 1.18, respectively, and sole 10 M NaOH_(aq). Samples were then subjected to ambient room temperature, and the oven-cured temperature was maintained from 45 to 90 °C at an interval of 15 °C for 24 h. The maximum achievable 28-day strength was 27 MPa at M_s value of 0.89 cured at 75 °C. Samples synthesised with the sole 10 M NaOH_(aq) activator resulted in a binder with a low 28-day compressive strength (15 MPa) compared to combined usage of Na₂SiO_3(aq)/10 M NaOH_(aq) activators. Results further revealed that curing at low temperatures (25 °C to 45 °C) does not favour strength development, whereas higher curing temperature positively enhanced strength development. More than 70% of the 28-day compressive strength could be achieved within 12 h of curing with the usage of combined Na₂SiO_3(aq)/10 M NaOH_(aq). XRD, FTIR and SEM + EDX characterisations revealed that activation with combined Na₂SiO_3(aq)/10 M NaOH_(aq) leads to the formation of anorthite (CaAl₂Si₂O₈), gehlenite (CaO.Al₂O₃.SiO₂) and albite (NaAlSi₃O₈) that improve the amorphosity, homogeneity and microstructural density of the binder compared to that of samples synthesised with sole 10 M NaOH_(aq).     

Reuse of Red Mud and Bauxite Tailings Mud as Subgrade Materials from the Perspective of Mechanical Properties

In order to reuse red mud and bauxite tailings mud (two typical aluminum industrial wastes) to reduce the occupation of land resources and environmental damage, these two wastes were combined to develop subgrade materials for the first time. With different combinations, the effects of the amounts of red mud, tailings mud, and cementitious materials on the strength of tested subgrade materials were investigated. The mechanism of strength growth was analyzed by a micro-test. The test results showed that the material strength of three combinations met the requirements when the unconfined compression strength (UCS) of all combinations increased with age. The UCS of the A₁BC₂ combination (the mass ratio of red mud and tailings mud was 2:1, the mass ratio of cement and quicklime was 1:1, and the mass ratio of waste and cementitious materials was 1:0.2) was the best, with the UCS being 3.03 MPa in 7 days. Microscopic imaging showed that specimens with high red mud contents had compact structures without cracks. The strength of these materials is mainly due to hydration reactions and pozzolanic reactions; the cementitious products generated by the reactions solidify Na⁺ and inhibit the release of OH⁻, while the addition of tailings mud can reduce the content of Na₂O in the material, which makes the environmental compatibility of the A₃BC₂ combination the best (the mass ratio of red mud and tailings mud was 1:2, the mass ratio of cement and quicklime was 1:1, and the mass ratio of waste and cementitious materials was 1:0.2). Its pH value was 8.75. This experiment verifies the feasibility of the combined application of red mud and tailings mud in subgrade materials. To this end, a feasible scheme for the simultaneous consumption of these two kinds of aluminum industrial wastes has been proposed.     

Application of Gene Expression Programming (GEP) for the Prediction of Compressive Strength of Geopolymer Concrete

For the production of geopolymer concrete (GPC), fly-ash (FA) like waste material has been effectively utilized by various researchers. In this paper, the soft computing techniques known as gene expression programming (GEP) are executed to deliver an empirical equation to estimate the compressive strength fc′ of GPC made by employing FA. To build a model, a consistent, extensive and reliable data base is compiled through a detailed review of the published research. The compiled data set is comprised of 298 fc′ experimental results. The utmost dominant parameters are counted as explanatory variables, in other words, the extra water added as percent FA (%EW), the percentage of plasticizer (%P), the initial curing temperature (T), the age of the specimen (A), the curing duration (t), the fine aggregate to total aggregate ratio (F/AG), the percentage of total aggregate by volume (%AG), the percent SiO₂ solids to water ratio (% S/W) in sodium silicate (Na₂SiO₃) solution, the NaOH solution molarity (M), the activator or alkali to FA ratio (AL/FA), the sodium oxide (Na₂O) to water ratio (N/W) for preparing Na₂SiO₃ solution, and the Na₂SiO₃ to NaOH ratio (Ns/No). A GEP empirical equation is proposed to estimate the fc′ of GPC made with FA. The accuracy, generalization, and prediction capability of the proposed model was evaluated by performing parametric analysis, applying statistical checks, and then compared with non-linear and linear regression equations.     

Preparation of Mineral Admixture from Iron Tailings with Steel Slag-Desulfurization Ash and Its Application to Concrete

Iron tailing solid waste not only has a high annual output but also has a low comprehensive utilization rate. Low utilization rate of iron tailings seriously restricts the development of comprehensive utilization of solid waste. In order to prepare an iron tailings-based ternary solid waste admixture and to verify its application to concrete, first, the effect of solid waste synergy on the strength of an iron tailings-steel slag-desulfurization ash admixture (ISD) system was investigated. Second, the effect of chemical activator dosing on the strength of an ISD system was studied and the mechanism of chemical activator action on the ISD system was investigated by thermogravimetric analysis (TG-DTA) Then, the effect of this admixture on the strength of concrete was studied. Finally, the mechanism of the effect of this admixture on the strength of concrete was clarified by mercury intrusion porosimetry (MIP) and backscattering electron tests (BSE). The results showed that the 7 d and 28 d compressive strengths of the ISD admixture were significantly higher than those of iron tailings single admixture. The 7 d and 28 d compressive strengths of the ISD system reached 24.9 MPa and 36.1 Mpa, respectively, when the ratio of iron tailings:steel slag:desulfurization ash = 1:1:1. Na₂SiO₃ is suitable for the early strength agent of the ISD admixture, but the amount of admixture should not exceed 0.6% of the admixture. TG-DTA shows that Na₂SiO₃ is enhancing the early strength of the ISD system by promoting the consumption of Ca(OH)₂ in the ISD system to produce C-S-H. However, in the late reaction of the ISD system, Na₂SiO₃ inhibits the late strength development of the ISD system by suppressing Ca(OH)₂ production. Concrete with ISD dosing of 30% or less meets the C40 requirement. MIP and BSE show that ISD provides a filling effect to concrete, but also causes a reduction in the active reactants of concrete and the combined effect of microfilling and active effects affects the strength development of ISD concrete. This study provides a theoretical and scientific basis for the preparation of iron tailings-based ternary solid waste dopants, and, in addition, the study promotes the consumption of iron tailings solid waste and the development of multiple solid waste dopants.     

Fabrication of Low-Temperature Sintering Building Bricks Using Drilling Cutting and Geopolymeric Technology

This study explores the practicability of using drill cutting (DC) as raw material to fabricate building bricks through the high-temperature sintering method and low-temperature geopolymeric setting (LTGS) process. Drilling mud can be recycled and reutilized after certain treatment procedures and is considered as a non-hazardous waste. However, the treatment process is time-consuming and not cost-effective. For the sintering method, low porosity and high mechanical strength bricks can be sintered at temperatures above 800 °C and meet CNS standards. For the low-temperature geopolymeric setting process, sodium silicate was selected as an activating agent for geopolymerization of drill cutting. Several process parameters, such as Si₂O/Na₂O modulus of alkali solution and low-temperature geopolymeric setting temperature, were investigated. The physical and mechanical properties of the fabricated brick were evaluated. According to the test results, 72.4 MPa compressive strength building bricks with low porosity (13.9%) and water absorption (6.0%) can be fabricated with 2.0 Si₂O/Na₂O alkali solution at 500 °C. The drill cutting brick fabricated not only meets the CNS 382.R2002 common brick standard, but also solve its disposal problem.     

Regulating Effect of Cement Accelerator on High Content Solid-Wastes Autoclaved Aerated Concrete (HCS-AAC) Slurry Performance and Subsequent Influence

Adverse side-effects occurred in slurry foaming and thickening process when carbide slag was substituted for quicklime in HCS-AAC. Cement accelerators were introduced to modify the slurry foaming and coagulating process during pre-curing. Meanwhile, the affiliated effects on the physical-mechanical properties and hydration products were discussed to evaluate the applicability and influence of the cement accelerator. The hydration products were characterized by mineralogical (XRD) and thermal analysis (DSC-TG). The results indicated that substituting carbide slag for quicklime retarded slurry foaming and curing progress; meanwhile, the induced mechanical property declination had a negative effect on the generation of C–S–H (I) and tobermorite. Na₂SO₄ and Na₂O·2.0SiO₂ can effectively accelerate the slurry foaming rate, but the promoting effect on slurry thickening was inconspicuous. The compressive strength of HCS-AAC obviously declined with increasing cement coagulant content, which was mainly ascribed to the decrease in bulk density caused by the accelerating effect on the slurry foaming process. Dosing Na₂SO₄ under 0.4% has little effect on the generation of strength contributing to hydration products while the addition of Na₂O·2.0SiO₂ can accelerate the generation and crystallization of C–S–H, which contributed to the high activity gelatinous SiO₂ generated from the reaction between Na₂O·2.0SiO₂ and Ca(OH)₂.     

Rapid Synthesis and Formation Mechanism of Core-Shell-Structured La-Doped SrTiO3 with a Nb-Doped Shell

To provide a convenient and practical synthesis process for metal ion doping on the surface of nanoparticles in an assembled nanostructure, core-shell-structured La-doped SrTiO₃ nanocubes with a Nb-doped surface layer were synthesized via a rapid synthesis combining a rapid sol-precipitation and hydrothermal process. The La-doped SrTiO₃ nanocubes were formed at room temperature by a rapid dissolution of NaOH pellets during the rapid sol-precipitation process, and the Nb-doped surface (shell) along with Nb-rich edges formed on the core nanocubes via the hydrothermal process. The formation mechanism of the core-shell-structured nanocubes and their shape evolution as a function of the Nb doping level were investigated. The synthesized core-shell-structured nanocubes could be arranged face-to-face on a SiO₂/Si substrate by a slow evaporation process, and this nanostructured 10 μm thick thin film showed a smooth surface.     

First-Principles Calculation of the Bonding Strength of the Al2O3-Fe Interface Enhanced by Amorphous Na2SiO3

In this paper, the interfacial adhesion work (W_ad), tensile strength, and electronic states of the Fe-amorphous Na₂SiO₃-Al₂O₃ and Fe-Al₂O₃ interfaces are well-investigated, utilizing the first-principles calculations. The results indicate that the Fe-amorphous Na₂SiO₃-Al₂O₃ interface is more stable and wettable than the interface of Fe-Al₂O₃. Specifically, the interfacial adhesion work of the Fe-amorphous Na₂SiO₃ interface is 434.89 J/m², which is about forty times that of the Fe-Al₂O₃ interface, implying that the addition of amorphous Na₂SiO₃ promotes the dispersion of Al₂O₃ particle-reinforced. As anticipated, the tensile stress of the Fe-amorphous Na₂SiO₃-Al₂O₃ interface is about 46.58 GPa over the entire critical strain range, which is significantly greater than the Fe-Al₂O₃ interface control group. It could be inferred that the wear resistance of Al₂O₃ particle-reinforced is improved by adding amorphous Na₂SiO₃. To explain the electronic origin of this excellent performance, the charge density and density of states are investigated and the results indicate that the O atom in amorphous Na₂SiO₃ has a bonding action with Fe and Al; the amorphous Na₂SiO₃ acts as a sustained release. This study provides new ideas for particle-reinforced composites.     

Geopolymer Concrete with Lightweight Artificial Aggregates

This article presents the physical and mechanical properties of geopolymer concrete with lightweight artificial aggregate. A research experiment where the influence of fly ash–slag mix (FA-S), as part of a pozzolanic additive, on the properties of geopolymers was carried out and the most favorable molar concentration of sodium hydroxide solution was determined. The values of three variables of the examined properties of the geopolymer lightweight concrete (GLC) were adopted: X₁—the content of the pozzolanic additives with fly ash + flay ash–slag (FA + FA-S) mix: 200, 400 and 600 kg/m³; X₂—the total amount of FA-S in the pozzolanic additives: 0, 50 and 100%; X₃—the molarity of the activator NaOH: (8, 10 and 12 M). In order to increase the adhesion of the lightweight artificial aggregate to the geopolymer matrix, the impregnation of the NaOH solution was used. Based on the obtained results for the GLC’s compressive strength after 28 days, water absorption, dry and saturated density and thermal conductivity index, it was found that the most favorable parameters were obtained with 400 kg/m³ of pozzolanic additives (with 50% FA-S and 50% FA) and 10 NaOH molarity. Changes in the activator’s concentration from 8 to 10 M improved the compressive strength by 54% (for a pozzolana content of 200 kg/m³) and by 26% (for a pozzolana content of 600 kg/m³). The increase in the content of pozzolanic additives from 200 to 400 kg/m³ resulted in a decrease in water absorption from 23% to 18%. The highest conductivity coefficient, equal to 0.463 W/m·K, was determined, where the largest amount of pozzolanic additives and the least lightweight aggregate were added. The structural tests used scanning electron microscopy analysis, and the beneficial effect of impregnating the artificial aggregate with NaOH solution was proved. It resulted in a compact interfacial transition zone (ITZ) between the lightweight aggregate and the geopolymer matrix because of the chemical composition (e.g., silica amount), the silica content and the alkali presoaking process.