Reactive Si Research Articles

Study on the influence of nano-silica substitution of reactive Si on the properties and hydration process of alkali-activated cementitious materials paste

Nano-silica (NS) is one of the most commonly used nanomaterials in alkali-activated materials (AAMs). Differing from other inactive nanoparticles, as an active Si source, the pozzolanic activity of NS has a significant effect on the hydration reaction and properties of alkali-activated materials. In this study, activated Si in the activator was replaced by NS to prepare alkali-activated slag/fly ash cementitious materials. The effects of different dispersion methods (dry-mix (MD), water dispersion (WD), and activator dispersion (AD)) of NS on the fluidity, rheological properties, and setting time of fresh pastes were investigated. Effects of NS and reactive Si in the activator on the hydration process of alkali-activated slag/fly ash paste were investigated using isothermal calorimetry and the Krstulović-Dabić hydration model. ICP-OES was utilized to study the changing behavior of the composition of the fresh paste pore solution during the hydration reaction. The results show that ions in the pore solution change continuously with the hydration time and eventually stabilize. The stabilized pore solution is mainly composed of OH- and Na+. Different NS dispersion methods have significant effects on paste workability, rheology, and setting time. Activator dispersion can elevate the content of active Si in the activator, causing changes in the hydration process of the paste, especially for the initial hydration period. NS has the most significant effect on the hydration process due to its pozzolanic activity compared to nucleation and filling effects. The Krstulovic-Dabic model can roughly simulate the hydration kinetics possessed of alkali-activated NS/slag/fly ash after entering the accelerated period.

Synthesis methodology of pure N–A–S–H gels with wide range of Si/Al ratios at ambient temperature

AbstractThis study presents the development of a synthesis route for sodium aluminosilicate hydrate (N–A–S–H) gels with various Si/Al ratios carried out at ambient temperature. The synthesis is based on a simple “sol–gel” method, where commercial reactants are used to provide highly reactive Si and Al sources. Comprehensive characterization, including scanning electron microscope‐energy‐dispersive spectroscopy (SEM‐EDS), gas pycnometry, inductively coupled plasma (ICP), X‐ray photoelectron spectroscopy (XPS), thermogravimetric analysis (TGA), X‐ray diffraction (XRD), and magic angle spinning (MAS) nuclear magnetic resonance (NMR) (27Al, 23Na, 29Si, and 1H), is employed to verify the morphology, density, chemical composition, long‐range order, and local structure of the gels. Our results show that the synthesized gels are pure, amorphous, and homogeneous with Si/Al final ratio ranging from 1.22 to 2.23. Structural analysis of the gels indicates the synthesis of compounds with high degree of geopolymerization, which are representative of N–A–S–H gel formed in sodium‐based geopolymers.

Chemoselective Adsorption of Allyl Ethers on Si(001): How the Interaction between Two Functional Groups Controls the Reactivity and Final Products of a Surface Reaction.

Selective adsorption of multifunctional molecules is rarely observed when the different functional groups react via nonactivated reaction channels. Although the latter is also the case for ether cleavage and the adsorption of C=C double bonds on the highly reactive Si(001) surface, we find that allyl ethers, which combine both functional groups, react on Si(001) selectively via the cleavage of the molecules' ether group. In addition, our XPS measurements at 90, 150, and 300 K indicate an increased reactivity of the ether group when compared to monofunctional ethers. STM investigations furthermore reveal different final adsorption configurations after ether cleavage of allyl methyl ether when compared to diethyl ether as the monofunctional reference molecule. The interaction of the two functional groups in one molecule thus leads to new reaction channels with higher reactivity for ether cleavage on Si(001). As a further consequence, the reactivity of the C=C double bond is suppressed up to room temperature, leading to the observed selective adsorption.

Physicochemical and structural properties of silica films prepared from perhydropolysilazane using vacuum ultraviolet irradiation

Developing techniques to form functional films at low temperatures is crucial for enabling their application on materials with limited heat resistance. In this study, silica films were prepared by irradiating a perhydropolysilazane (PHPS) precursor, which contains reactive Si–H and N–H groups and is free from organics, with vacuum ultraviolet (VUV) light under a controlled atmosphere. To investigate the quality of the resulting films and mechanisms behind photochemical conversion, infrared and electron spectroscopic measurements were performed. The results revealed that VUV irradiation converted the top surface of the film into silica, irrespective of the atmospheric conditions. However, differences in the oxygen concentration affected both the VUV light intensity penetrating the film and the oxygen diffusion into it, leading to the formation of silica or silicon oxynitride within the film. Under irradiation, PHPS was converted to silica not only from the surface but also from the interface with the substrate. In addition, silica was formed even at long irradiation distances, in which case VUV light barely reached the PHPS surface owing to absorption by atmospheric oxygen. These findings demonstrate that the silica-film formation involved two processes: breaking of chemical bonds induced by VUV photons and oxidation due to oxygen diffusion from the surface. The spectroscopic measurements and X-ray reflectivity results indicated that the composition, chemical state, Auger parameter, and density of the prepared silica film were comparable to those of a silica film prepared through heat treatment at 500°C. Further, the prepared silica film using VUV irradiation had a smoother surface than that of the heat-treated film. The thickness of the prepared film remained unchanged before and after VUV irradiation, indicating that the formation process using VUV irradiation suppressed the shrinkage of the film during the conversion of PHPS to silica.

Utilization of carbonated alkaline solid wastes in ordinary Portland cement-metakaolin-limestone ternary mixture: Underlying the role of low grade-sustainable calcium carbonate sources

Alkaline solid wastes are widely generated as by-products annually from construction demolition, steel making, and metal refining industries. Consequently, there is high pressure on their disposal and environmental protection. Carbonation treatment of alkaline solid wastes provides a potential way to valorize CO2 and produce low-grade artificial limestone particles. This study investigates the utilization of carbonated alkaline wastes, including recycled cement fines, steel slag, iron recycled steel slag, and magnesium slag in green ternary cement (limestone-metakaolin-cement system) production. The detailed characterization of carbonated alkaline solid wastes and the performance of metakaolin-cement based ternary systems were evaluated. The reaction mechanism of carbonated alkaline wastes in metakaokin-cement based binder is proposed. The results indicated carbonated alkaline solid waste powder containing relatively low calcite (14.4%–50.38%) and negative surface charges. In addition, the amount of reactive Si at Q3 and Q4 were observed. The precipitated calcite on the surface of particles resulted in the deterioration of the workability of ternary mixtures compared to natural limestone. However, the equivalent amount of CO3-AFm phases produced by precipitated calcium carbonate and additional hydrates from the reaction of amorphous silica in carbonated alkaline solid wastes contributed to a comparable mechanical performance (49.5 MPa–50.82 MPa) and compact microstructure of ternary binders. Carbonated alkaline solid wastes can be a sustainable component to replace natural limestone in green ternary cement production.

Microalgal biochar assisted simultaneous removal of particulate matter, formaldehyde, and total volatile organic compounds (TVOC's) from indoor air

Biochar-based materials for air treatment have gained significant attention for removing health-detrimental volatile organic compounds (VOCs) and particulate matter (PM) in indoor air settings. However, high turnaround time, multiple pretreatment processes involved, and high pore size and low surface area (>10 μm, <100 m2 g−1) of lignocellulosic feedstocks demand alternative biochar feedstock material. Considering this, we designed a simple first-of-its-kind indoor air scrubbing material using diatoms-enriched microalgae biochar. In the present study, the microalgae were cultivated on waste anaerobic digestate (biogas slurry) and were pyrolyzed at three different temperatures: 300 °C (BC300), 500 °C (BC500), and 700 °C (BC700). The BC500 and BC700 showed the highest removal efficiencies (99 %) for total volatile organic carbons (TVOCs) and formaldehyde (HCHO) at concentrations of 1.22 mg m−3 HCHO and 8.57 mg m−3 TVOC compared to 50% efficiency obtained with commercially available surgical, cloth, and N95 masks. The biochar obtained showed a high Brunauer–Emmett–Teller (BET) surface area of 238 m2 g−1 (BC500) and 480 m2 g−1 (BC700) and an average pore size of 9–11 nm due to the mesoporous characteristic of diatom frustules. The comparatively poor performance of BC300 was due to lower surface area (150 m2 g−1) arising from incomplete organic removal, as evidenced by FESEM-EDX and FTIR. The high removal efficiencies in BC500 and BC700 were also attributed to the presence of reactive functional groups such as –OH and R–NH2. Concurrently, the average particulate matter (PM10, PM2.5, and PM1) removal efficiency for BC500 and BC 700 ranged between 66 and 82.69 %. The PM removal performance of BC500 and BC700 was lower (15–20%) than commercially available masks. Overall, the present study highlights the importance of diatoms (reactive Si) present inside the pores of microalgal biochar for enhanced removal of PM, TVOCs, and HCHO at temperatures above 500 °C. This complete approach signifies a step towards establishing a self-sustainable and circular process characterized by minimal waste generation for indoor air treatment.

Crater-free monolayer graphene above the 2D Si film on SiC(0001) formed via SiSn cointercalation and Sn deintercalation

When Si atoms are intercalated under the graphene-like zero layer (ZL) generated on the SiC(0001) substrate, the resulting quasi-free-standing monolayer graphene (QFMLG) has lots of crater-like defects due to a strong Si-C reaction. Here, a method for creating crater-free QFMLG above a two-dimensional Si film is investigated using scanning tunneling microscopy and photoemission spectroscopy. The method involves forming a SiSn interfacial film as a precursor via cointercalation performed by sequential Sn and Si deposition on the ZL at room temperature and annealing at 650–700 °C. The Sn atoms prevent reactive Si atoms from directly contacting the ZL, which would otherwise cause SiC defects. The sample is then annealed at 750 °C to selectively remove the Sn atoms from the SiSn interfacial film, leaving a well-ordered Si film. The SiSn film composed of a bottom Si layer and top Sn atoms has a short-range-ordered “2 × 2” or a long-range-ordered 2×7 superstructure depending on the annealing temperature and the Sn coverage. Both the superstructures are semiconducting and induce less n-doped QFMLG than the pure Si film.

Energetic characteristics of highly reactive Si nanoparticles prepared by magnesiothermic reduction of mesoporous SiO2

In this study, highly reactive silicon nanoparticles (h-Si) were successfully prepared by an improved magnesiothermic reduction process with ∼ 100 nm mesoporous silica nanoparticles as templates. The prepared h-Si have an average particle size of 18 nm, an active content of 85 %, and a specific surface area of 69.2 m2/g. Meanwhile, the preparation process is simple, green (avoiding the use of HF), and shows a great improvement in the inhibition of side reactions. The energetic characteristics of h-Si were compared with those of commercially available silicon nanoparticles (c-Si) by using ultrasonically mixed KClO4 as the oxidizer. Thermal analysis indicates that h-Si/KClO4 has an advanced reaction onset temperature, increased heat release, and lower reaction activation energy. In constant-volume combustion tests, h-Si/KClO4 shows excellent ignition and combustion characteristics in the fuel-rich state. In addition, electrostatic discharge sensitivity tests indicate that the minimum ignition energy of stoichiometric h-Si/KClO4 exceeds 100 mJ, which is much more insensitive than that of n-Al/KClO4 (∼2 mJ). Overall, h-Si show enhanced reactivity and have attractive advantages in applications where suitable combustion properties and low electrostatic sensitivity are required.

Effect of enhanced pozzolanic activity in nickel slag modified with Al2O3 on mechanical properties of cemented fine tailings backfill

Cemented tailings backfill has gained widespread acceptance in mining industries due to its stable performance and environmental advantages. However, Ordinary Portland cement (OPC), based on engineering experience, falls short in meeting the requirements of cost-effectiveness and environmental protection criteria for cemented fine tailings (median size d50 <20 µm) backfill. Nickel slag (NS), an industrial solid waste with potential reactivity derived from nickel manufacturing processes, is currently employed as a concrete additive at a low rate. In this work, a modification was conducted by melting-quenching the NS-Al2O3 mixtures, followed by a physicochemical analysis of the resulting granulated samples (GAN) using BET and X-ray fluorescence. The mineralogy and structural properties were examined for the GAN samples using X-ray diffraction and Fourier transform infrared spectroscopy. Each of the T-CGAN pastes was formulated by replacing 40 wt% of OPC with the GAN, and then blended with fine tailings at 1:4. The flowability and compressive strength were measured for the T-CGAN pastes, while the hydration products and microstructures of the paste samples were analyzed by derivative thermogravimetry and scanning electron microscope, respectively. The results indicate that the addition of Al2O3 not only provides abundant network formers to GAN glass, but also facilitates the conversion of [SiO4] tetrahedrons from Q4 with strong bond energy to Q3 and Q2 with lower ones, thereby significantly enhancing the pozzolanic activity of the original NS. The T-CGAN slurries exhibit slight decreases in slump values from 228.8 to 224.9 mm compared to T-OPC slurry (236.5 mm), attributed mainly to the strong water absorption of GAN. T-CGAN pastes with higher Al2O3 addition acquired greater compressive strengths during the whole curing ages. After 90 days of curing, T-CGAN20 paste achieves the maximum compressive strength (5.14 MPa), higher than that of the T-OPC by 1.03 MPa. The T-CGAN pastes richer in Al2O3 release more reactive Si and Al to participate in the pozzolanic reaction with calcium hydroxide, contributing to additional formations of C-S-H gel and C-A-H, with SEM micrographs showing a compact microstructure with elevated ratios of Ca/Si, Al/Si, and Fe/Si. This study suggests an effective and environmental way to enhance the pozzolanic activity of the original NS by incorporating Al2O3. The modified NS can then be utilized as a high-performance cement substitute for cemented fine tailings backfill, which also significantly enhances the sustainability for both mining and building industries.

An investigation into the characteristics of reactive silicon pools of coastal marine sediments

Many studies use traditional alkaline leach digestions to quantify biogenic silica (bSiO2) in sediments. Studies from river-plume systems demonstrate this methodology precludes information on other operational Si reactive pools, missing potentially valuable information on early diagenetic products. We build on previous studies by broadly examining the reactive Si pools in Mississippi River plume-influenced coastal sediments. The magnitude of Si released among operational pools across the region revealed large spatial variations in the conservation of detrital materials. Contrary to other analyses using different approaches, we suggest the availability of detrital sourced components (i.e. Al, Fe and Mn) may be a factor limiting authigenesis and resulting Si storage capacity in coastal sediments by this chemical mechanism. Overall, these data suggest authigenic precipitates may be forming as a function of bSiO2 accumulation, thereby implying that bSiO2 acts as the primary substrate for formation of authigenic products. The amount of authigenic Si products, relative to bSiO2, appears to be larger in this region than other systems studied to date, and this may be due to regional eutrophication which has led to an increase in sediment bSiO2 compounding the substrate available for authigenic precipitates. Thus, regions which have all experienced increased sediment bSiO2 accumulation coincident with eutrophication, may be primed for substantial authigenic product formation and increased Si sequestration.

Behavior of magnesium phosphate cement with addition of sulphoaluminate cement at elevated temperatures

Magnesium phosphate cement (MPC) as repair materials of the structures or package materials for wastes may be exposed to elevated temperatures during fire attack. When MPC paste was exposed to about 1300 °C, a sharp increase in compressive strength was observed due to sintering. However, MPC exposed to elevated temperature, especially below 1000 °C showed a sharp decrease in compressive strength. Ye'elimite mineral in sulphoaluminate cement (CSA) has been proven to take part in the hydration of MPC and form some amorphous phases. The introduction of CSA in MPC could provide reactive Al and Si, which may be beneficial to improving the high temperature resistance of MPC. The present study aims to introduce CSA into MPC to improve its thermal properties at elevated temperatures. MPC pastes with pure dead burned MgO and various contents of CSA were prepared and exposed at elevated temperatures from 200 to 1100 °C. The compressive strengths, strength retention, dimensional changes, weight loss, phase changes, microstructures and open porosities of MPC pastes with CSA at elevated temperatures were studied. The proper addition of CSA in MPC pastes could form some new amorphous phases, reduce the open porosities, promote the sintering progress and enhance the strengths at elevated temperatures. To promote the properties of the MPC pastes at elevated temperatures, 10% and 30% CSA were recommended to replace dead burned MgO in MPC pastes at exposure temperatures above 1000 °C and below 400 °C, respectively.

Digital light processing fabrication of porous cordierite ceramics from polysilxoane-based slurries

Herein, a pohotosentive polysiloxane (PSO)/talc/Al2O3 slurry was prepared for the digital light processing printing. Liquid photosensitive PSO was exploited as a triple-functioned material, acting both as the resin matrix, a high reactive Si source and a pore generator. Through adjusting the raw material components, polysiloxane can be sintered with talc and Al2O3 fillers after being pyrolyzed to 1200 oC while pores with variable diameters can be generated. Ternary component slurry prepared based on the above strategy possesses the characteristics of low viscosity, high reaction activity and good homogeneity. Sintering schedule of the printed thin-walled precursor was investigated to guarantee the morphology of cordierite product was consistent with the printed model. This work aims to provide a new strategy for DLP printing of MgO-Al2O3-SiO2 ternary and other polymer derived ceramics.

Correlation between dissolubilities of Si, Al, and Fe from aluminosilicate precursor and strength of fly ash-based geopolymer

Fly ash (FA) is the most used aluminosilicate precursor to synthesize geopolymer. However, as a coal-combustion by-product, the inherent characteristics of FA can be significantly altered by multiple factors such as coal sources, combustion temperatures, particle size, and impurity level. Thus, unstable performances of FA-based geopolymer due to extremely varied reactivity of FA have been widely reported in the literature and are limiting the further valorization of FA. To offset the inconsistent characteristics of FA, this study provides a universal index to quantify and evaluate its reactivity to be used as aluminosilicate precursor feedstock. Alkali leaching tests were conducted on seven types of FA sourced from six different coal power plants in the Southeast Queensland region to determine the dissolubilities and dissolution efficiencies of reactive Si and Al within 2 h. The dissolubility and dissolution efficiency demonstrated decent correlations with the mechanical properties of the resultant FA-based geopolymer, especially 7-day strength. Moreover, bulk and reactive Si/Al molar ratios were derived to distinguish each type of FA further and verified by scanning electron microscopy / energy-dispersive X-ray spectroscopy. Lastly, a reactivity index considering the dissolution efficiency of Si, Al, and Fe and reactive Si/Al molar ratios was developed and correlated to the mechanical properties of FA-based geopolymer. Dissolubility at a leaching time of 30 min best reflected the reactivity of FA, having the highest correlation coefficient of 0.82.

Green synthesis, formation mechanism and oxidation of Ti3SiC2 powder from bamboo charcoal, Ti and Si

Using low-cost and highly reactive bamboo charcoal, Ti and Si elemental powders as starting materials, Ti3SiC2 powder was synthesized via a simple and cost-efficient pressureless sintering technique in argon atmosphere. The influences of synthesis temperature, holding time and Si content on the Ti3SiC2 content of the synthesized products were investigated, and the analysis indicated that the relative content of Ti3SiC2 reached 98.9 wt% with a molar ratio of 3Ti/1.2Si/2.2C at 1400 °C for 1.5 h. The Ti3SiC2 with good crystallinity and homogeneous nanolayered structure was synthesized at lower temperatures due to the high reactivity and high specific surface area of bamboo charcoal. The non-isothermal oxidation behavior showed that Ti3SiC2 powder was stable in air below 540 °C. With the temperature increasing up to 1300 °C, continuous and dense TiO2 and SiO2 oxidation layers were formed on the surface of Ti3SiC2 particles, which conferred good oxidation resistance to Ti3SiC2 powder.

Strengthening mechanism of granulated blast-furnace slag on the uniaxial compressive strength of modified magnesium slag-based cemented backfilling material

The hydrating active mineral in the modified magnesium slag-based (MMS-based) backfilling material is mainly β-phase dicalcium silicate characterized with slow speed of hydration and low early strength. This disadvantage restricts the application of modified magnesium slag (MMS) as cementitious material in backfilling mining to some extent. In this work, the strengthening mechanism of granulated blast-furnace slag (GBFS) on the uniaxial compressive strength (UCS) of MMS-based cemented backfilling material has been investigated systematically. The hydration heat tests reveal that the duration of induction and acceleration periods are gradually shortened and the appearance time of the second exothermic peaks are obviously advanced as the proportion of GBFS increases. The total normalized hydration heat releases of MMS-based pastes containing 0, 1%, 2%, 3% and 4% (solid-mass proportion) GBFS at 120 h are 15.76, 16.02, 18.40, 22.31, and 25.54 J/g, respectively. Compared with the blank control group, the hydration heat release of MMS-based paste at 120 h increased by 62% with addition of 4% (solid-mass proportion) GBFS. In addition, the TG-DTG tests shown that the final mass-losses of MMS-based cemented backfilling materials tend to increase with the increase of the amount of GBFS. The 3- and 7-days UCSs of MMS-based backfilling mortars tend to increase dramatically with the increase of proportion of GBFS. A small amount of GBFS (1 wt%) can significantly improve the 28- and 56-days UCSs of the MMS-based mortars. Compared with the blank control group, the UCSs of MMS-based mortars cured 3, 7, 28, and 56 days increased by 74.2%, 94.6%, 38.0%, and 24.1% respectively with addition of 5% (solid-mass proportion) GBFS. The SEM, XRD, FTIR, and TG-DTG tests show that the MMS-based mortars containing GBFS generated more hydration products, yielded more compact microstructures, and consumed CH more quickly compared with that of blank control group. Compared with fly ash (FA), GBFS dissolves faster in alkaline media (leaching reactive Al and Si early), and releases much more hydration heat and Ca2+ ions during the process of pozzolanic reaction. The above three factors strengthen the UCS of MMS-based mortar. The results of this study can provide theoretical guidance for the raw material ratio design and field application of MMS-based cemented backfilling paste.

Calcined Clays from Nigeria-Properties and Performance of Supplementary Cementitious Materials Suitable for Producing Level 1 Concrete.

In this work, four naturally occurring (two kaolinite-rich and two smectite-rich) clay samples were collected from different areas around the Ashaka cement production plant, located in Gombe State, Nigeria and calcined in a laboratory. The mineralogical characterization of the clays was carried out by XRD. The hydration kinetics of the calcined clay-cement systems were monitored by isothermal calorimetry. Workability was determined using the flow table method. The reactivity of the calcined clays was determined from the solubility of Si and Al ions and the strength activity index. All calcined clays studied met the requirements of ASTM C618 for the use of natural pozzolans as a partial replacement for hydraulic cement. The metasmectite clays yielded a higher specific surface area, increased water demand, and less reactive Si and Al ions compared to the metakaolin clays. The two calcined clay groups require the addition of superplasticizer to achieve a workability class similar to the Portland cement mortar system. They can be used to replace Portland cement at replacement levels of up to 45%, in combination with limestone powder to form an LC3 cement, thereby achieving at least a "Level 1" reduction in greenhouse gas emissions.

Role of carbon fiber in the electrothermal behavior and geopolymerization process of carbon fiber-reinforced FA-GBFS geopolymer composite

Carbon fiber-reinforced geopolymer composite (CFGC) can be used as the energy conversion layer of airport pavement, thus converting electromagnetic energy into heat energy via induction heating technology to melt snow and ice on pavement surface. In this study, fly ash (FA), granulated blast furnace slag (GBFS) and carbon fibers were used to prepare carbon fiber-reinforced FA-GBFS geopolymer composite (CFFGC). Then, the modification mechanism of carbon fibers on the electrothermal and mechanical properties of CFFGC was studied, in which important effects arising from the geopolymerization process within CFFGC were focused on. Results show that the gullies on carbon fiber surface can provide nucleation sites for the geopolymerization and calcium silicate hydration reaction in CFFGC, which accelerates the precipitation of reactive Si(OH)4 and [Al(OH)4]- in the raw materials and promotes the generation of geopolymer gels and CSH gels, thus enhancing the mechanical performance of CFFGC. In addition, when the carbon fiber dosage reaches 0.4 wt%, a substantial conductive network is formed inside CFFGC, which shortens the conductive path and greatly improves the charge transfer capability in CFFGC. Once the carbon fiber dosage exceeds 0.4 wt%, the agglomerated carbon fibers within CFFGC can intensify the phonon scattering, thus reducing its thermal conductivity.

Electrochemical corrosion behaviors of Ti3SiC2/Cu composites in a 3.5% NaCl solution

AbstractThe electrochemical corrosion behaviors of Ti3SiC2/Cu composite and polycrystalline Ti3SiC2 in a 3.5% NaCl medium were investigated by dynamic potential polarization, potentiostat polarization, and electrochemical impedance spectroscopy. The polycrystalline Ti3SiC2 was tested on the identical condition as a control. The characterizations of XRD, X‐ray photoelectron spectroscopy, scanning electron microscope, and energy‐dispersive spectrometer were used to study the relevant passivation behavior and corrosive mechanism. The self‐corrosion current density of Ti3SiC2/Cu (6.46 × 10−6 A/cm2) was slightly higher than that of Ti3SiC2 (1.64 × 10−7 A/cm2). Under open circuit potential, the corrosion resistance of Ti3SiC2/Cu was better than that of Ti3SiC2. Ti3SiC2/Cu exhibited a typical passivation feature with a narrow passivation interval and a breakdown phenomenon. The better corrosion resistance of Ti3SiC2 was due to the more stable Si layer of the former. In comparison, for Ti3SiC2/Cu composites, Cu reacted with the reactive Si layers in Ti3SiC2 to form Cu–Si compounds and TiC, destroying the weak interaction between Si layers and Ti–C layers. In the other hand, the as‐formed Cu–Si compounds and TiC dissolved during the corrosion of Ti3SiC2/Cu in the 3.5% NaCl medium, causing to the destruction of the passivation film on its surface.

Performance enhancement of cementitious soil stabilizers using incorporated nanosilica

This investigation aims to study the performance of different hybrid binders as environmentally-friendly cementitious soil stabilizers as well as Nanosilica as a reactive powder. Mechanical properties and microstructural analysis in addition to the molecular and mineralogical specifications were investigated to evaluate the performance of stabilized soil samples. For this purpose, a series of experimental tests including scanning electron microscopy (SEM), Fourier-transform infrared spectroscopy (FTIR), and X-ray diffraction (XRD) are considered as well as mechanical tests to investigate the various aspects of the material. The results showed that the incorporation of Nanosilica not only improved the unconfined compressive strength (UCS) of the stabilized samples, but also the elastic modulus which is indicative of Nanosilica's tendency to increase the ductility of samples. In Portland cement (PC) and phosphorus slag blended cement (SBC)-based samples, the results confirmed that samples containing Nanosilica possess an intensified C–S–H phase compared to other samples. It appeared that the supplied reactive Nanosilica to the matrix showed better participation reaction of Ca2+ of Portlandite for formation of extra C–S–H phase due to the observed phase change of needle-like crystals of Portlandite in lower amount with smaller particles. Moreover, the microstructure results revealed that the presence of Nanosilica leads to more densified binder matrix with more coverage of soil particles. The incorporation of Nanosilica in SBC exhibited a more densified matrix with higher UCS values compared to PC samples. The presence of 2 wt% of Nanosilica in the alkali-activated phosphorus slag cement (AAC)-based samples resulted in lengthening the aluminosilicate chain with more substituted Al with reactive Si. In AAC-based samples, with incorporated Nanosilica a compact interfacial bond of matrix and soil particles was observed.

Recycling of unseparated construction and demolition waste (UCDW) through geopolymer technology

Geopolymer technology has been recognized as an ideal option for recycling construction and demolition waste (CDW) streams as new value-added products. However, most research efforts have been devoted to the geopolymer derived from the individual fraction separated from CDW. Given the technological complexity presented in separating CDW fractions on a commercial scale, using unseparated CDW (UCDW) in geopolymer application can achieve higher environmental and economic benefits. This paper investigated the feasibility of using UCDW consisting of various constituents, i.e., unbound aggregates (UA), red clay bricks (RCB), waste concrete (WC), waste glass (WG), and waste tiles (WT), in geopolymer production. The effects of these constituents on the reactivity of UCDW and the performance of the resulting geopolymer paste were studied. Results showed that all UCDW constituents can provide reactive phases and highly reactive bonds. RCB, WG, and WT can serve as the aluminosilicate source, while UA and WC mainly offer silica and calcium. The changes in constituents affected the mechanical performance of the UCDW-based geopolymer by conditioning the content of reactive Si, Al, and Ca in the precursor. A Si/Al molar ratio of 5–8 and a Ca/Si of 1.5 were found to achieve the higher compressive strength (up to 29.7 MPa) of geopolymer. In addition, a fitting formula was proposed to predict the compressive strength of UCDW-based geopolymer paste. This work contributes to understanding the alkali-activated performance of UCDW and promotes its utilization as a mineral precursor in geopolymer production.