Hydrated Silica Research Articles

Orbital identification of widespread hydrated silica deposits in Gale crater

The Mars Science Laboratory has been investigating the central mound of Gale crater since 2012 and revealed evidence of silica enrichment in several locations, suggesting that the geologic processes related to the formation of hydrated silica could be widespread. A reanalysis of orbital data over Aeolis Mons indicates the existence of an extensive unit rich in hydrated silica. These silica-enriched deposits, found at the base of Aeolis Mons, span elevations from -4513 m to -3351 m. The mapped hydrated silica deposits are spatially adjacent to an erosion-resistant capping unit, previously mapped as the mound skirting unit, which lies beneath the terminal deposits from local canyons and valleys. We hypothesize that the hydrated silica-bearing unit precipitated from groundwater which migrated upwards or deposited as a volcaniclastic silica-rich layer which was rehydrated during the late-stage canyon and valley forming events. The silica-bearing unit beneath the capping unit is protected against erosion by younger fan-shaped deposits and became exposed only recently. The mineralogy and stratigraphic relations with Mount Sharp units imply that the aqueous activities leading to silica diagenesis were likely a basin-wide process that occurred long after the formation of lakes in Gale crater's geological history and experienced limited water-rock interaction since then.

Influence of slag on water resistance of magnesium silicon potassium phosphate cement

The poor water resistance of traditional magnesium phosphate cement (MPC) limits its wider application in engineering fields. So far, research on enhancing the water resistance of MPC has been relatively limited. Therefore, this paper optimizes the slag content based on magnesium silicon potassium phosphate cement to prepare slag-magnesium silicon potassium phosphate cement (S-MSPPC). The research results indicate that slag contains various active components, and its appropriate addition can refine the pore structure of the paste. With the increase in slag replacement rate, the paste setting time increases, and the fluidity decreases slightly. The hydration of silica fume to produce SiO(OH)3‐ and SiO2(OH)22‐ ions significantly enhances the alkalinity of the paste and provides conditions for activating the activity of the slag. The S-MSPPC hardened paste can maintain alkalinity for the long term. Moreover, the water resistance of the S-MSPPC paste was significantly improved while ensuring mechanical properties. The water resistance coefficients of S-20 with 20 % slag increased by 49.23 % and 40.64 % at 28 days and 56 days compared to the reference group S-0. This improvement was due to the participation of silica fume and slag in the hydration reaction to form M-S-H and C-(A)-S-H gels in the paste. These gel products fill the pores and microcracks in the paste, optimize the pore size distribution, reduce porosity, and enhance density. In addition, the alkaline environment within the paste effectively slows the dissolution rate of K-struvite in water, further enhancing the water resistance of S-MSPPC.

Effect of inorganic salt impurities on seeded precipitation of silica hydrate from sodium silicate solution

To clarify the precipitation of silica hydrate from the real desilication solutions of aluminosilicate solid wastes by adding seeds and improve integrated waste utilization, the seeded precipitation was studied using synthesized sodium silicate solution containing different inorganic salt impurities. The results show that sodium chloride, sodium sulfate, sodium carbonate, or calcium chloride can change the siloxy group structure. The number of high-polymeric siloxy groups decreases with increasing sodium chloride or sodium sulfate concentration, which is detrimental to seeded precipitation. Calcium chloride favors the polymerization of silicate ions, and even the chain groups precipitate with the precipitation of high-polymeric sheet and cage-like siloxy groups. The introduced sodium cations in sodium carbonate render a more open network structure of high-polymeric siloxy groups, although the carbonate ions favor the polymerization of siloxy groups. No matter how the four impurities affect the siloxy group structure, the precipitates are always amorphous opal-A silica hydrate.

Recycle of steel slag as cementitious material and fine aggregate in concrete: mechanical, durability property and environmental impact.

Using steel slag (SS) as cementitious material and fine aggregate in concrete is an effective and environmental method for SS consumption and cost reduction. In this paper, SS was recycled in large volumes in concrete as partial cementitious material and fine aggregate. The compressive strength and reaction mechanism of cementitious material with different SS powder contents including 20%, 25%, 30%, and 35% were presented. The results indicated that 20% of SS powder improved the compressive strength by 34.57% and the hydration products were ettringite (AFt) and calcium silica hydrate(C-(A)-S-H). Furthermore, the mechanical and durability performance of concrete with SS as fine aggregate were investigated. When the SS substitution rate was 75%, the compressive strength was increased by 37.83%. The volume shrinkage rate and 28d-carbonation depth were reduced nearly by 64% for 90days and 2.33mm, respectively. The chloride ion penetration resistance reached the optimal grade Q-V and abrasion resistance was improved by nearly 24%. Along with the reduced CO2 by 210-294kg/m3 and the decreased cost by 12.61 USD/m3, it is regarded as an effective method to consume steel slag. As such, this research provided a scientific and systematic basis for the large-scale disposal and utilization of industrial waste residues as well as recycled materials preparation.

Investigation properties of ultra-high performance concrete incorporating pond ash

Abstract The study aims to substitute river sand used in ultra-high performance concrete (UHPC) with pond ash (PA), a waste by-product from the Sikka thermal power station in Gujarat, India, at replacement levels ranging from 0 to 20%. Also, 20% of the cement was replaced with ground granulated blast-furnace slag, which is a sustainable, eco-friendly material. As a result, this concrete is both environmentally and economically feasible. Experimental analysis evaluated the workability, compressive strength, split tensile strength, flexural strength, and microstructure of the UHPC mixtures. Incorporating 10% PA as a sand replacement enhanced the compressive strength, reaching 117 MPa at 90 days, as well as the flexural strength of 23 MPa and the split tensile strength of 14 MPa. The strength is positively impacted when 10% of the river sand is replaced with PA, while the strength of UHPC appears to be diminished if PA content is increased beyond 10% replacement of sand. Petrographic microscopy and X-ray diffraction were used to study the microstructure of UHPC made with PA. When PA was used instead of sand, the mortar mass solidified and became denser, resulting in an improved microstructure of the UHPC with fewer surface cracks. With the inclusion of PA, the calcium silica hydrate gel content of the concrete increases, and enhanced performance of UHPC up to a certain amount of replacement has been observed.

APTES/Calcium silica hydrate nano-hybrid composites with enhanced mechanical properties

Reducing the cement content in the concrete mix by developing cementitious materials with enhanced properties can contribute considerably to cut the CO2 emissions produced by the cement industry. In this work, we used a bottom-up approach to enhance the mechanical performance of the calcium silicate hydrate (C-S-H), by the covalent bonding of the 3-aminopropyltriethoxysilane (APTES), to create a nano-hybrid C-S-H/APTES. The intercalation of APTES within the C-S-H contributes to increase the bulk modulus by 35 % due to the stiffening along all the lattice directions. The stiffer behavior along a- and b- lattice directions is due to the formation of covalent bonds between the APTES molecules and the non-bonding oxygens of the C-S-H, blocking the silicate chain relaxation and increasing the overall stiffness of the ab-plane. In the c-direction, the stiffening is attributed to the densification of the hydrogen bond network in the interlaminar space caused by the APTES intercalation.

Hyperspectral (VNIR-SWIR) analysis of roll front uranium host rocks and industrial minerals from Karnes and Live Oak Counties, Texas Coastal Plain

VNIR-SWIR (400–2500 nm) reflectance measurements were made on the surfaces of various cores, cuttings and sample splits of sedimentary rocks from the Tertiary Jackson Group, and Catahoula, Oakville and Goliad Formations. These rocks vary in composition and texture from mudstone and claystone to sandstone and are known host rocks for roll front uranium occurrences in Karnes and Live Oak Counties, Texas. Spectral reflectance profiles, 569 in total, were reduced to 125 representative spectral signatures, which were analyzed using the U.S. Geological Survey's (USGS) Material Identification and Characterization Algorithm (MICA). MICA uses an automated continuum-removal procedure together with a least-squares linear regression to determine the fit of observed sample spectral absorption features to those of reference mineral standards in a spectral library. The reference minerals include various clay, mica, carbonate, ferric and ferrous iron minerals and their mixtures. In addition, absorption feature band-depth analysis was done to identify rock surfaces exhibiting absorption features related to uranium and zeolite minerals, which were not included in the command files used to execute MICA.Rocks from each of the four geologic units produced broadly similar spectral signatures as a result of comparable mineral compositions, but there were some notable differences. For example, Ca- and Na-montmorillonite was matched most frequently to the spectral absorption features in 2-μm (∼2000–2500 nm) wavelengths, while goethite occurred often at 1-μm (∼400–1000 nm) wavelengths. The latter is related to limonitic iron-staining in and around oxidized zones of the uranium roll front as described in previous papers. Rocks of the Jackson Group differed from those of the Catahoula, Oakville and Goliad units in that the former exhibited spectral features we interpret as being due to the presence of lignite-bearing mudstone layers. Goliad rocks exhibit spectral features related to dolomite, gypsum, anhydrite, and an unidentified green clay mineral that is possibly glauconite. Jackson Group rocks also exhibit weak but well-resolved absorption features at 964 and 1157 nm related to either or both zeolite minerals clinoptilolite and heulandite. These zeolite minerals and a few spectra exhibiting hydrous silica absorption features are indicative of alteration of volcanic glass in tuffaceous mudstone and claystone layers. A few sample spectra exhibited strong absorption features at around 1135 nm related to the uranium mineral coffinite. Both the 1135 nm coffinite and 1157 nm zeolite absorption features overlap somewhat, potentially making them difficult to distinguish without additional hyperspectral field, laboratory or remote sensing data.The results of this study were compared to mixtures of minerals described for ore, gangue and alteration minerals in deposit models for sandstone-hosted uranium, sedimentary bentonite and sedimentary zeolite. Use of these spectra can help facilitate mapping of both waste materials from the legacy mining of the above commodities, as well as future exploration and resource assessment activities.

Investigation on the impact of elevated temperature on sustainable geopolymer composite

Geopolymer concrete (GPC) is an eco-friendly, sustainable, cementless and green concrete. It could be an alternative to the conventional concrete. In alkaline circumstances, the alumina and silica concentration in geopolymer concrete creates the geopolymer bond, while regular concrete creates C-S-H (calcium silicate hydrate bond). The final result of the geopolymer bond does not include any water. At elevated temperatures, geopolymer concrete would thus be more stable. Due to its greater strength and durability quality, geopolymer concrete may be the ideal replacement for ordinary portland cement (OPC) concrete. This research intends to examine how specimens of geopolymer concrete and regular concrete respond to exposure to increased temperatures between 100°C and 800°C. Mass loss, ultrasonic pulse velocity, compressive strength, X-ray diffraction, thermogravimetric analysis and derivative thermogravimetric analysis were all examined throughout the experimental examination. Both concrete specimens lose mass or weight as the exposure temperature rises; OPC concrete samples spalls at 600°C, while GPC sample fail at 800°C. GPC specimens lose around 12% of their original mass after being exposed to temperatures of 800°C, while OPC specimens lose about 7%. The GPC specimens maintained 60% of their initial compressive strength after being exposed to a temperature of 700°C, but the OPC concrete specimens only kept 52%. With each increase in exposure to extreme temperatures, the peaks of quartz and cristobalite are lowered. Only the form or structure of the mineral oxide would change; the chemical linkages would remain. The GPC samples subjected to temperatures of 100°C exhibit effective thermal stability than all other specimens exposed to extreme temperatures. As the exposure temperature rises, the GPC specimens become more thermally stable. According to the experimental findings, the GPC specimens’ bonding structure makes them more resistant to high temperatures than regular concrete specimens. Micropores are present in the voids of the geopolymer matrix, while mesopores and micropores are present in the voids of the OPC matrix. While OPC bonding is C-S-H formed by the hydration of lime and silica contained in the cement, the geopolymer bonding did not include the water content in the final or end result of geopolymerisation for strengthening.

Proteomic and functional analysis of HDL subclasses in humans and rats: a proof-of-concept study

BackgroundThe previous study investigated whether the functions of small, medium, and large high density lipoprotein (S/M/L-HDL) are correlated with protein changes in mice. Herein, the proteomic and functional analyses of high density lipoprotein (HDL) subclasses were performed in humans and rats.MethodsAfter purifying S/M/L-HDL subclasses from healthy humans (n = 6) and rats (n = 3) using fast protein liquid chromatography (FPLC) with calcium silica hydrate (CSH) resin, the proteomic analysis by mass spectrometry was conducted, as well as the capacities of cholesterol efflux and antioxidation was measured.ResultsOf the 120 and 106 HDL proteins identified, 85 and 68 proteins were significantly changed in concentration among the S/M/L-HDL subclasses in humans and rats, respectively. Interestingly, it was found that the relatively abundant proteins in the small HDL (S-HDL) and large HDL (L-HDL) subclasses did not overlap, both in humans and in rats. Next, by searching for the biological functions of the relatively abundant proteins in the HDL subclasses via Gene Ontology, it was displayed that the relatively abundant proteins involved in lipid metabolism and antioxidation were enriched more in the medium HDL (M-HDL) subclass than in the S/L-HDL subclasses in humans, whereas in rats, the relatively abundant proteins associated with lipid metabolism and anti-oxidation were enriched in M/L-HDL and S/M-HDL, respectively. Finally, it was confirmed that M-HDL and L-HDL had the highest cholesterol efflux capacity among the three HDL subclasses in humans and rats, respectively; moreover, M-HDL exhibited higher antioxidative capacity than S-HDL in both humans and rats.ConclusionsThe S-HDL and L-HDL subclasses are likely to have different proteomic components during HDL maturation, and results from the proteomics-based comparison of the HDL subclasses may explain the associated differences in function.

Electrocoagulation with Fe-Al hybrid electrodes for the removal of arsenic, fluoride, and silica from natural groundwater

This communication is about the removal of arsenic (As), fluoride (F−) and hydrated silica (HS) from real underground water (initial concentration: 28 µg L−1 arsenic, 1.55 mg L−1F−, 155 mg L−1 HS, 35 mg L−1 sulfate, pH 7.4, and 470 µS cm−1 conductivity) by electrocoagulation (EC). The novel EC reactor consists of eight horizontally stacked cells using Fe and Al plates as sacrificial anodes with an upward flow. The abatement of As and the elimination at the same time of F− and HS was performed by analyzing the influence of the mean linear flow velocity (1.2 < u < 4.8 cm s−1) at different current densities (3 < j < 7 mA cm−2) imposed on the EC system. The best condition was carried out at j = 7 mA cm−2 and u = 1.2 cm s−1, achieving complete arsenic elimination, and a remaining F− concentration of 0.45 mg L−1, fulfilling the World Health Organization (WHO) guideline for arsenic (< 10 μg L−1) and fluoride (< 1.5 mg L−1). The remaining HS reached a value of 10 mg L−1. Spectroscopic techniques applied to the Fe-Al flocs evidenced the generation of iron oxides and hydroxides, as well as the formation of aluminosilicates.

Effect of incorporating fibers in reactive powder concrete – A review

Modified form of High-Performance Concrete is a Reactive- Powder Concrete(RPC) which was first found by PierreRichard and Marcel Cheyrezy, they successfully built France laboratory using RPC. High compressive strength of over 200 MPa has been achieved, with flexural strength up to 40 MPa, and in certain cases crushing strengthup to 800 MPa with the introduction of hybrid fibre reinforcement. Cement OPC grade, silica fume, quartz sand, crushed quartz flour, water, a superplasticizer, and fibre reinforcement all contribute to making RPC.These materials have high durability characteristics as a result of their extremely low porosity, low permeability, limited shrinkage, and higher corrosion resistance. To increase package density, the powder combination of RPC should have a variety of granular particle classes. By dense packaging theory and grading optimization technique, the absence of coarse aggregate increased compactness. Because of its compactness, it reaches high strength. The rapid hydration of cement and silica fume at a high curing temperature of 100 °C as compete to 27 °C is something that causes the higher early strength. This paper discusses about the hybrid fibers incorporation in RPC under various curing conditions and its enhancement in strength than single fibers. Using micro and macro fibers dramatically improves the properties of RPC and thermal properties with various types of fiber. The mechanical characteristics of the RPC beam without the hybrid fiber, on the other end, are the lowest of all the mixtures. Apart from these characteristics, RPC can be utilized for industrial and nuclear waste storage facilities due to its ultra-dense microstructure, which provides ultra-high strength even at elevated temperature and water resistance. This paper infers that the addition of hybrid fiber in RPC considerably reduces the spalling of concrete at elevated temperatures and it exhibits superior strength and durability.

Designing low-carbon cement-free binders for stabilization/solidification of MSWI fly ash

Low-carbon and high-efficiency binder is desirable for sustainable treatment of municipal solid waste incineration fly ash (MSWI FA). In this study, CaO or MgO was used to activate ground granulated blast furnace slag (GGBS) to form calcium silicate hydrate and magnesium silica hydrate gel for stabilization/solidification of hazardous MSWI FA. Experimental results showed that potential toxic elements (PTEs), such as Pb and Zn, significantly inhibited the formation of reaction products in CaO-GGBS system due to the complexation between Ca(OH)2 and PTEs, whereas PTEs only had insignificant inhibition on transformation from MgO to Mg(OH)2 in MgO-GGBS system, resulting in lower leachabilities of PTEs and higher mechanical strengths. Stabilization/solidification experiments demonstrated that MSWI FA (70 wt%) could be recycled by MgO-GGBS binder (30 wt%) into blocks with desirable 28-day compressive strengths (3.9 MPa) and PTEs immobilization efficiencies (99.8% for Zn and 99.7% for Pb). This work provides mechanistic insights on the immobilization mechanisms of PTEs in CaO/MgO-GGBS systems and suggests a promising MgO-GGBS binder for low-carbon treatment of MSWI FA.

Revealing the static and dynamic nanomechanical properties of diatom frustules—Nature's glass lace

Diatoms are single cell microalgae enclosed in silica exoskeletons (frustules) that provide inspiration for advanced hybrid nanostructure designs mimicking multi-scale porosity to achieve outstanding mechanical and optical properties. Interrogating the structure and properties of diatoms down to nanometer scale leads to breakthrough advances reported here in the nanomechanical characterization of Coscinodiscus oculus-iridis diatom pure silica frustules, as well as of air-dried and wet cells with organic content. Static and dynamic mode Atomic Force Microscopy (AFM) and in-SEM nanoindentation revealed the peculiarities of diatom response with separate contributions from material nanoscale behavior and membrane deformation of the entire valve. Significant differences in the nanomechanical properties of the different frustule layers were observed. Furthermore, the deformation response depends strongly on silica hydration and on the support from the internal organic content. The cyclic loading revealed that the average compliance of the silica frustule is 0.019 m/N and increases with increasing number of cycles. The structure–mechanical properties relationship has a direct impact on the vibrational properties of the frustule as a complex micrometer-sized mechanical system. Lessons from Nature’s nanostructuring of diatoms open up pathways to new generations of nano- and microdevices for electronic, electromechanical, photonic, liquid, energy storage, and other applications.

Zircon processing in sodium carbonate melt

The process of alkaline zircon processing with soda and a mixture of soda with intensifying additives carbon and NaOH was studied. As a result, a complete exclusion of acid-soluble sodium zirconosilicate formation was ensured. The introduction of carbon into soda melt increased the agent’s reactivity due to the formation of highly reactive Na2O. At 1100 °C, the optimal amount of introduced carbon is 4 wt.%, while the duration of the process is reduced to 10 minutes. Zircon processing in two stages – at 1150 °C and 1000 °C with the soda addition from 2.5 to 4.0 wt.% provided the production of metazirconate and sodium silicate, excluding the transition of silicon to the solid phase, providing an opening degree > 99%. The novel bakor-lined electric furnace of high operational reliability has been successfully tested. Carbonization of the sodium silicate solution in the presence of water vapor ensures complete precipitation of hydrated silicon dioxide, with a bulk density of 150 g/L. The optimal concentration of CO2 is ~ 8%, which allows using off-gases from thermal power plants for carbonization. The presence of water vapor in the gaseous phase increases the utilization of CO2 and Na2CO3 regeneration.

Experimental determination of quartz solubility in H2O-CaCl2 solutions at 600–900 °C and 0.6–1.4 GPa

Abstract Fluid-mediated calcium metasomatism is often associated with strong silica mobility and the presence of chlorides in solution. To help quantify mass transfer at lower crustal and upper mantle conditions, we measured quartz solubility in H2O-CaCl2 solutions at 0.6–1.4 GPa, 600–900 °C, and salt concentrations to 50 mol%. Solubility was determined by weight loss of single-crystals using hydrothermal piston-cylinder methods. All experiments were conducted at salinity lower than salt saturation. Quartz solubility declines exponentially with added CaCl2 at all conditions investigated, with no evidence for complexing between silica and Ca. The decline in solubility is similar to that in H2O-CO2 but substantially greater than that in H2O-NaCl at the same pressure and temperature. At each temperature, quartz solubility at low salinity (XCaCl2 &amp;lt; 0.1) depends strongly on pressure, whereas at higher XCaCl2 it is nearly pressure independent. This behavior is consistent with a transition from an aqueous solvent to a molten salt near XCaCl2 ~0.1. The solubility data were used to develop a thermodynamic model of H2O-CaCl2 fluids. Assuming ideal molten-salt behavior and utilizing previous models for polymerization of hydrous silica, we derived values for the activity of H2O (aH2O), and for the CaCl2 dissociation factor (α), which may vary from 0 (fully associated) to 2 (fully dissociated). The model accurately reproduces our data along with those of previous work and implies that, at conditions of this study, CaCl2 is largely associated (&amp;lt;0.2) at H2O density &amp;lt;0.85 g/cm3. Dissociation rises isothermally with increasing density, reaching ~1.4 at 600 °C, 1.4 GPa. The variation in silica molality with aH2O in H2O-CaCl2 is nearly identical to that in H2O-CO2 solutions at 800 °C and 1.0 GPa, consistent with the absence of Ca-silicate complexing. The results suggest that the ionization state of the salt solution is an important determinant of aH2O, and that H2O-CaCl2 fluids exhibit nearly ideal molecular mixing over a wider range of conditions than implied by previous modeling. The new data help interpret natural examples of large-scale Ca-metasomatism in a wide range of lower crustal and upper mantle settings.

Dissolution of Glass–Ceramic Scaffolds of Bioactive Glasses 45S5 and S53P4

Although the initial in vitro dissolution of bioactive glasses (BAG) is well characterized, the long-term behaviour of crystallized BAG scaffolds in a continuous fluid flow is incompletely understood. A detailed understanding of the long-term dissolution of scaffolds is vital for predicting their behaviour in clinical applications. Here, we explored the dissolution and reaction mechanisms of partly crystalline and glass–ceramic scaffolds based on the bioactive glasses S53P4 and 45S5 using a continuous flow-through method in Tris-buffer (Tris) and simulated body fluid (SBF) for up to 21 days. Granules of the parent glasses were used as references. The main crystalline phase in both scaffolds was sodium-calcium-silicate. The scaffolds’ dissolution suggested that the sodium-calcium-silicate crystals dissolved incongruently to yield hydrous silica. The silica phase then provided abundant nucleation sites for hydroxyapatite precipitation, resulting in fine-grained crystalline structures. When exposed to Tris, the scaffolds almost completely dissolved within the test period, leaving only highly porous remnant phases. For the 45S5 scaffolds, the calcium phosphate reaction layers that formed on their surfaces effectively slowed the dissolution in SBF. In contrast, this effect was less apparent for the S53P4 specimens.

Impact of Properties of Hydrated Silicon Dioxide as Core Material on the Characteristics of Drug-containing Particles Prepared by the 2-step Process Melt Granulation Technology, MALCORE®.

Drug-containing particles (DCPs) are frequently used as cores in the development of solid oral dosage forms. The wet layering technique, which is a typical approach for preparing DCPs, requires the use of solvents and a long manufacturing time. In our previous study, we developed a novel manufacturing technology, MALCORE®, which can solve these problems through melt granulation. However, particle size control methods for DCPs in MALCORE® and the effect of the physical properties of the hydrated silicon dioxide (HSD) used for the core have not been clarified. The aim of this study was to examine the effects of the particle and pore sizes of HSD on the properties of the prepared DCPs. The results showed that the DCPs prepared using MALCORE® could be controlled by the particle size of HSD. The drug-loading efficiency tended to decrease as HSD particle size increased. Additionally, the amount of drug layering in DCPs increased as the pore size of HSD increased, but HSDs with a pore size much larger than the particle size were not able to properly layer the drug. These findings are helpful for applying MALCORE® to a variety of oral drug formulations.

Evolutionary characteristics of microstructural hydration and chloride diffusion in UHPC

This paper presents the evolutionary characteristics of microstructural hydration and chloride migration in ultra-high performance concrete (UHPC). The physicochemical interactions of constituents are simulated in conjunction with a random walk algorithm. When the hydration of cementitious pastes proceeds, accompanied by the evolution of hardening, the quantity of silicates becomes larger alongside irregularly dispersed byproducts (calcium silica hydrate, C-S-H, and calcium hydroxide, CH). Owing to the formation of pozzolanic C-S-H consuming CH, the silicate reactions of UHPC are less than the reactions of the ordinary concrete. The implications of tricalcium silicate (C3S) are notable for the early-age strength gain of UHPC in comparison with its dicalcium silicate (C2S) counterpart. The matured pozzolanic reactions and invariable packing density of UHPC are responsible for preserving the proportion of silica fume in the mixtures. Relative to UHPC, the ordinary concrete releases more heat caused by exothermic reactions that are a function of saturated pores and silica fume with the contribution of C3S. Regarding corrosion durability, the chloride contents of a bridge deck cast with the ordinary concrete exceed the content of a deck with UHPC. As part of technology transfer, the notion of performance-based design applies and practice guidelines are suggested.

Effect of binary combination of waste gypsum and fly ash to produce building bricks

South Africa's production of wet flue gas desulfurization (WFGD) gypsum and fly ash (FA) has increased significantly owing to the country's dependence on coal power plant for electricity. These wastes are mainly dumped in landfills, which contributes to environmental pollution. Recycling WFGD gypsum to generate value-added products may benefit the country economically and ecologically. Given the chemical compositions of WFGD gypsum and fly ash, it is feasible to mix them to create a binder material. On the time when the study was done, no evidence of study had been conducted on the binary combination of FA and WFGD gypsum produced locally to create building materials. This study proposes a novel approach to lowering environmental pollution by using two South African wastes, FA and WFGD gypsum, to produce sustainable building materials. The mixture of WFGD gypsum and FA is intended to produce binding phases comprising ettringite and calcium silicate hydrate (CSH). Ettringite can be formed by hydration of alumina (Al2O3) in fly ash with calcium sulfate (CaSO4) and calcium oxide (CaO) of WFGD gypsum, while CSH can be generated by hydration of silica (SiO2) in fly ash under the same conditions. FA was employed moderately to substitute WFGD gypsum in the production of FA: WFGD composite blocks. Composite mixes were produced by substituting 0–40 wt% of WFGD gypsum with FA. Composites bricks obtained were characterized using compression test and wet-dry cycles. Toxicity characteristic leaching procedure (TCLP) were done to determine perilous elements existing in the study sample and scanning electron microscopy (SEM) and energy dispersive spectroscopy (EDS) for morphology analysis. X-ray diffraction (XRD) was utilized to establish the crystallinity of the material. The strength results showed that FA used in this study was poorly reactive. As the partial replacement of WFGD gypsum by FA increased from 0 to 40%, the strength of the composite material decreased. The pessimum effect of FA is mainly related to the low pH of the binary mixture and low pozzolanicity of FA used. Incorporation of 20 wt% FA and curing temperature of 40 °C seemed to be suitable for the preparation of WFGD:FA composite bricks. The composite bricks' highest UCS of 2 MPa exceeded the minimum strength for Class III mortar as per SANS 10145. Therefore, WFGD:FA composite bricks may be used as building materials.

Dense hydrous silica carrying water to the deep Earth and promotion of oxygen fugacity heterogeneity

Water has remarkable effects on the properties of mantle rocks, but, owing to the high temperatures in the mantle, uncertainties remain about how and how much water is transported into the deep Earth. Recent studies have shown that stishovite and post-stishovites as high-pressure phases of SiO2 have the potential to carry weight percent levels of water into the Earth’s interior along the geotherm of the subducting oceanic crust. As slabs are subducted to the deepest mantle, dehydration of these dense hydrous silica phases has the potential to change the physicochemical properties of the mantle by reducing melting points, forming new high-pressure phases, and enhancing the oxygen fugacity heterogeneity of the lower mantle.