Silica Reaction Research Articles

Production and Characterization of Silica from Rice Husk: An Updated Review

Rice is regarded as one of the most valuable sources which is consumed by almost fifty percent of the world’s population. Rice husk ash is a by-product substance obtained from the rice husk by thermal and chemical treatment. The non-crystalline nature of silica content in rice husk, which is converted to crystalline silica such as quartz, tridymite, and cristobalite on thermal treatment. It has been an important material which impacts not only enhances the betterment of industrialization but also protects the environment from pollution. The produced silica was characterized by various analyses such as Fourier transform infrared spectroscopy (FTIR), X-ray diffraction analysis (XRD), Scanning electron microscope (SEM), Transmission electron microscope (TEM), and Thermal analysis. This review is given attention to integrating and investigating processing, properties, characterization, reactivity, and application of rice husk (RH) and rice husk silica (RHS).

Mitigation mechanisms of alkali silica reaction through the incorporation of colloidal nanoSiO2 in accelerated mortar bar testing

Alkali Silica Reactivity (ASR) is a prominent issue concerning the durability of concrete structures. To mitigate this deleterious reaction, a widely accepted practice involves replacing significant cement portions with supplementary cementitious materials (SCMs). Given the scarcity of high-quality SCMs, nanoSiO2 exhibits considerable promise, given its minimal dosage requirement for ASR mitigation, whether applied independently or in conjunction with other SCMs. This research investigates the efficacy and underlying mechanisms of colloidal nanoSiO2 (CNS) in accelerated mortar bar tests according to the ASTM C1260 method. The experimental methodology incorporated two distinct forms of CNSes, CNS1 and CNS2, with average particle sizes of 14 and 67 nanometers, respectively. The outcomes are subsequently compared to the ASR performance of a sample containing silica fume (SF). The results demonstrate that the CNS size is pivotal in governing the pozzolanic reaction rate. The CNS2 and SF exhibited analogous pozzolanic reactions, displaying superior effectiveness in promoting pozzolanic activity compared to the CNS1. At a 4.75% cement replacement level, the CNS2 achieved a 78% reduction in mortar expansion over the control sample. The CNS1, when utilized at 4.75% and 7% cement replacement levels, yielded expansion reductions of 38% and 43%, respectively. It was found that the inclusion of the CNS can increase the porosity of mortar and contribute to silica dissolution from the reactive aggregates. Meanwhile, the addition of CNS improved the bulk resistivity of mortar by 200%-600% and flexural strength by 25%-62% based on the replacement levels and the CNS types. Moreover, improvements in calcium hydroxide consumption and alkali binding in the ASR gel were observed during the test, indicating the underlying mechanisms for expansion mitigation. These research outcomes can accelerate the CNS utilization to mitigate the ASR in practical field applications.

Investigation Of Usability of Sepiolite as a Pozzolan in Production of High Performance Cementitious Composites

The continuous growth of population and urbanization in the world significantly increases the demand for cement. In terms of sustainability, the cement industry needs to develop new and effective pozzolans with the appropriate recycling of alternative raw materials. It is also important to evaluate sepiolite, which has very limited resources in the world compared to other industrial minerals and whose economic deposits are limited to Spain and Türkiye. In this study, the usability of sepiolite as a pozzolan in cement and its effects on physical, mechanical and durability properties were investigated. First of all, the chemical and physical properties of sepiolite in Eskisehir region were investigated. Crude and ground sepiolite calcined at 500 ºC, 700 ºC and 900ºC were substituted for CEM I 42.5 R class standard Portland cement at 5-10-15% and 20% ratios. The pozzolanic activities of produced sepiolite substituted cement were determined according to ASTM C-311. As a result, crude sepiolite retains more water than calcined sepiolite, thus negatively affecting the strength properties of the concrete. Additionally, sepiolite is considered suspicious (harmful-harmless) in terms of alkali silica reactivity except 10%-15%-20% crude sepiolite substitutions. Overall, It has been observed that sepiolite does not have sufficient pozzolanic properties in cementitious composites.

Optimal parameters for producing ferrosilicon from a mixture of diatomite and opoka

In view of the limited reactivity of crystalline silica used in the production of ferrosilicon, it is necessary to search for silica-containing raw materials that have this property to a higher degree. The article presents the results of studies on the production of ferrosilicon from a mixture of amorphous silica-containing rocks – opoka and diatomite in a 1:1 ratio in the presence of coke and steel shavings. The studies have included the electric smelting of the charge in a single-electrode arc furnace and using the second-order rotatable designs of experiments (Box-Hunter plans) followed by graphical optimization. The research has established that FeSi25 (24.5-30% of Si), FeSi45 (41-47% of Si), and FeSi50 (47-51% of Si) grades of ferrosilicon can be smelted from a mixture of diatomite and opoka, depending on the amount of coke and steel shavings. The optimal parameters for producing FeSi25 ferrosilicon (with the extraction of 80-82.4% of silicon into the alloy) were 35.0-37.2% of coke and 33.75-35.0% of steel shavings. FeSi45 ferrosilicon (with extraction of 80-84.6% of silicon) was formed with 38.0-45.0% of coke and 29.2-33.2% of steel shavings. At 40.4-45.0% of coke and 29.2-31.1% of steel shavings, FeSi50 ferrosilicon was formed; the extraction of silicon into the resulting alloy was more than 80-81.5%. At the balance electric smelting of the diatomite and opoka mixture in the presence of 45% of coke and 30% of steel shavings, ferrosilicon of FeSi50 grade (51.8-52.6% of Si) was produced with the 82% silicon extraction degree.

Effect of reactive coarse recycled aggregate with different expansion history on alkali silica reactivity and mechanical properties of new concrete

AbstractRecycled concrete aggregates (RCA) provide an environmentally friendly solution by reducing the depletion of natural resources. This study investigates the impact of the expansion history of RCA on its reactivity with alkalis in newly produced concrete. Parent concrete samples were collected from the RILEM AAR‐4 curing cabinet (60°C and >90% RH) to produce coarse RCA with four different expansion levels (0.00%, 0.05%, 0.12%, and 0.20%). The results show that the expansion levels of the new concrete mixtures decreased as the ASR expansion history of parent concrete increased. The 20‐week compressive strength and elastic modulus of the reactive aggregate concrete containing no mineral admixture and exposed to AAR‐4 test conditions were lower than those of their water‐cured counterparts. However, no decrease was observed in the elastic modulus of concrete mixtures that showed an expansion level lower than 0.03% (the maximum expansion for nonreactive aggregate as recommended by the RILEM AAR‐4 standard).

Mechanical and durability performance of ternary blended calcined clay and pulverized granite mortar composites

ABSTRACT Partially replacing cement with pozzolans, apart from the enormous technical benefits, has been reported as an effective approach to reducing greenhouse gases emanating from cement production. Calcined clay and pulverised granite, in recent years, have been experimented individually for their use as filler or pozzolan in concrete to improve workability and compressive strength. This research includes study of the synergistic characteristics of these two mineral admixtures and their influence on the mechanical and durability properties of mortar. Cement was partially substituted with 5–20% by weight of the composite material to form a ternary blended cement composite. The compressive strengths of the ternary blended cements were evaluated at 3, 7, 28 and 90 days. Durability properties such as alkali silica reactivity (ASR), rapid chloride permeability test (RCPT) and performance of the blended cements in aggressive media have been discussed. Test results indicated that, blended cements containing 5% and 10% of the pozzolan recorded similar compressive strengths at 28 days and outperformed it by 2.4% and 0.6% respectively at 90 days. Beyond 10% replacement, compressive strengths declined. The ternary blended cements were found to be highly reactive, potentially causing ASR in concrete than the reference cement.

Impact of Aggregate Grain Size on ASR-Induced Expansion.

Alkali-silica reaction (ASR) is a sequence of complex chemical processes, resulting in the formation of alkali silica gels with high swelling ability. ASR leads to the expansion of concrete and the degradation of its microstructure. The susceptibility of aggregates to alkali reaction depends, among other factors, on the type and origin of the aggregate, the presence of reactive forms of silica, the mineral composition, and the geometric properties of the aggregate, such as shape and grain size. This study aimed to investigate the impact of the grain size of polymineral post-glacial gravel aggregate, originating from the northern regions of Poland, on its susceptibility to ASR. The expansion of mortars made from polymineral aggregate and the cracking of grains and cement matrix due to the occurring reactions were analyzed. Based on the conducted research, it was observed that the expansion of mortars depends on the grain size of the aggregate. It was demonstrated that the fraction of reactive aggregate generating the most significant elongation of mortars is in the range of 1.0-2.0 mm. The reaction of silica with alkalis continued until the depletion of reactive components in the aggregate. The relationship between the progress of corrosive processes and the grain size of the aggregate was evident in the form of different linear elongation increments of mortars over time. The expansion of mortars was caused by the swelling ASR gel, inducing stress in the grain and the surrounding cementitious paste.

Improvement in Long Term Bonding and Mechanical Performance by Using Glass Concrete in Combination with Xanthan Gum Exposed to Harsh Environment

Abstract Concrete is the mostly used construction material composed of a mixture of cement, water, aggregates (such as sand, gravel, or crushed stone), and often additional additives or admixtures. It is widely used in the construction industry for various applications due to its strength, durability, and versatility. Key characteristics of concrete include strength, durability, versatility, fire resistant, cost effective, weather resistant, insulation and decorative options. Concrete plays a vital role in the construction industry, providing the foundation for most buildings, infrastructure, and many other structures worldwide. Its composition and properties can be tailored to meet specific project requirements, making it an indispensable material in modern construction. Various fibers can be used to enhance the mechanical and bonding properties of concrete. Also waste fibers after recycling can be reduced the environmental burden. Keeping in this view, glass powder sodium silicate glass (SSG) is used as replacement of cement with different percentages 0%,4%,8%, and 12% in combination of xanthan gum 0.2% for all mixes. An experimental study is conducted to investigate the mechanical and durability properties of concrete by performing compression test, flexural test, alkali silica reactivity test, sulfate resistivity test and drying shrinkage test. For this, forty-eight concrete cylinders are prepared for compression test, forty-eight concrete prisms for flexural test and thirty-six mortar bars of four mixes are prepared for durability testing. Workability is checked of fresh concrete during the pouring of concrete cylinders. Poured cylinders’ samples are left for 7, 14, 21 and 28 days of curing. Different tests are performed on hardened concrete and mortar samples to evaluate the mechanical and durability properties. Results concluded that workability of four mixes lies between 60-80mm and compressive strength of concrete has been improved using glass powder (SSG). Optimum results have been achieved at 12% as compared to other mixes 4% and 8% of concrete samples. Fibrous material is used as a binding agent and fibrous concrete is suitable for humid environment where high strength and voids less concrete are required. Quantity of cement can be reduced by using different fibers as a replacement of cement. Research recommended that recycled glass powder can be used in concrete as construction material and 12% replacement is suitable for optimum results.

Role of Surface Defects on Photoinduced Reactivity in SiO2 Nanoparticles

Silica nanostructured materials find application in different fields, since they are cheap, versatile, and easy to functionalize as materials. However, silica reactivity has not been deeply investigated yet, mainly due to a poor understanding of how it is affected by superficial defects. In the present study, the electronic and optical properties of nanoparticles have been investigated using bare silica nanoparticles (SNP) and amino- or phosphonate-functionalized silica nanoparticles (SNP–APTES and SNP-phosphonate), prepared by a sol-gel procedure, and their morphology has been investigated using transmission electron microscopy (TEM) analysis. The prepared silica nanomaterials were characterized by means of reflectance and emission spectroscopies to determine the types of defects that can be found on silica nanoparticles’ surface. In order to understand the effect of surface defects on the reactivity of silica, the nanoparticles were employed for the photocatalytic degradation of Rhodamine 6G (R6G), upon selective irradiation at 320 nm, where only silica colloids absorb. The photoreaction was carried out in ethanol and in water and was monitored following the fluorescence signal of the dye. The evaluation of the fluorescent intensities allowed for the determination of the degradation efficiencies.

In-flight vitrification of granitic aggregate: Characterization and performance of a scalable supplementary cementitious material

Using supplementary cementitious material (SCM) to replace clinker is the cheapest and most effective way to lower CO2 impact of concrete, but supply of conventional SCMs is not currently sufficient. Manufactured SCMs must scale to help meet demand. Traditional calcination approaches up to 1000 °C are only able to activate mineral groups like hydrous clays and zeolites that are not available in all markets. To manufacture SCM from even more abundant and widespread lithologies, a new in-flight vitrification technique was developed. Microspherical glassy SCM was made from archetypal granitic rock sourced from low-value construction aggregate. Vitrified granitic SCM has excellent pozzolanic reactivity compared to a well-known commercial Class F fly ash, as measured by strength activity index of mortar, R3 calorimetry, rapid alkali silica reactivity testing, and realistic concrete mix designs. Aggregate mines with silicate mineralogy are an overlooked feedstock resource for vitrified SCM manufacture with this new technique.

Improving Concrete Infrastructure Project Conditions by Mitigating Alkali–Silica Reactivity of Fine Aggregates

Alkali–silica reactivity (ASR) is one of multiple reactions responsible for premature loss in concrete infrastructure service life. ASR results in the formation of expansive, white-colored gel-like material which results in internal stresses within hardened concrete. ASR-induced stresses result in concrete cracking, spalling, and increased reinforcement steel corrosion rates. The main objective of this research is to improve the conditions of concrete infrastructure projects by mitigating ASR’s damaging effect. The expansion of accelerated mortar bars poured using fine aggregates collected from different sources is measured versus time to evaluate the aggregates’ reactivity. Different percentages of supplementary cementitious materials (SCMs), including class C fly ash and microsilica, were used in remixing mortar bars to evaluate the efficiency of different types of SCMs in mitigating mortar bar expansion. The research findings showed that SCMs can mitigate ASR, thus decreasing mortar bar expansion. The efficiency of SCMs in ASR mitigation is highly dependent on the incorporated SCM percentage and particle fineness. Silica fume, having the smallest particle size, displayed higher rates of ASR mitigation, followed by fly ash. The outcomes of this research will assist design engineers in avoiding future losses due to ASR cracking in concrete infrastructure projects, and reduce the excessive need for maintenance, repair, and replacement activities.

Evaluation of metakaolin pozzolan for cement in South Africa

This paper presents findings of an experimental study conducted to evaluate the performance of metakaolin (MK) for potential use as a supplementary cementitious material or cement extender in South Africa. In this study, various proportions consisting of 0%, 5%, 10%, 15% MK were incorporated into ordinary Portland cement CEM I 52.5 N, then used to prepare mortar mixtures. Various mechanical and durability properties were measured comprising flowability, compressive strength, pozzolanic activity with lime, drying shrinkage, alkali - silica reaction (ASR) and sulphate resistance. Analytical studies were done using X - ray diffraction and scanning electron microscopy. It was found that incorporation of 10%–15% MK into Portland cement led to improved flowability, compressive strength increase and lower drying shrinkage, while ASR and sulphate attack processes were effectively mitigated. Results showed that the MK extender satisfied ASTM C618 specified criteria for ‘Class N’ pozzolan. Incorporation of 15% MK into Portland cement also met the requirements categorising the blend as CEM II/A–P 42.5 N cement type of SANS EN 50197–1.

Alkali–Silica Reactivity Potential of Reactive and Non-Reactive Aggregates under Various Exposure Conditions for Sustainable Construction

The alkali–silica reaction (ASR) is a primary cause for premature concrete degradation. An accelerated mortar bar test is often used to access the detrimental phenomena in concrete caused by the ASR of aggregates. However, this test requires a certain environmental conditioning as per ASTM C1260. The objective of this study is to explore the effects of the cement alkali content, exposure solution concentration, temperature, and test duration on mortar bar expansion. Factorial experimental design and analysis was conducted to delineate the effects of the individual factors as well as their interaction. Five different aggregates with various mineralogical properties were used, representing reactive and non-reactive aggregates. Various dosages of cement alkalis (0.40, 0.80, and 1.20 Na2Oe), sodium hydroxide (NaOH) solution concentrations (0.5, 1.0, and 1.5 N), and temperature (40 °C, 80 °C, and 100 °C) were the studied variables. Mortar bar expansion was measured at 3, 7, 14, 21, 28, 56, and 90 days. Mortar bars incorporating Jhelum aggregates incurred expansion of 0.32% at 28 days, proving to be reactive aggregates as per ASTM C1260. Similarly, specimens incorporating Taxila aggregates showed expansion of 0.10% at 28 days, indicating non-reactive nature. It was observed that specimens with Sargodha aggregates showed expansion of 0.27% at 28 days for 0.50 N NaOH solution concentration compared to 0.31% expansion for identical specimens exposed to 1.5 N solution. Moreover, expansion increased with exposure duration for all the tested specimens. Experimental results showed that the cement alkali contents had relatively lesser effect on expansion for 1.0 N NaOH; while, in the case of 0.5 N and 1.5 N NaOH, the cement alkali had a significant effect. It was noted that expansion increased with an increase in the temperature. Jhelum aggregates showed 28-day expansion of 0.290% when exposed to 40 °C, but at a temperature of 100 °C, expansion increased to 0.339%. Factorial analysis revealed that the exposure solution had a major contribution towards the expansion of mortar bar specimens. This study highlights the contribution of various exposure conditions on the ASR expansion, which leads to a decisive role in selecting the aggregate sources for various applications and exposure conditions leading to sustainable construction.

Scalable cooling cementitious Composites: Synergy between Reflective, Radiative, and Evaporative cooling

Promoting the sustainability of the building industry is one of the major approaches to addressing energy depletion and climate change. Here, we developed scalable cementitious cooling composites (CCCs) with superior energy-free cooling performance and environmental applicability. Optical properties, phase composition, microstructure, and silica reactivity of composites are characterized and analyzed. Onsite measurements are conducted to evaluate the surface/internal cooling capacities and validate the cooling principles and such composites’ climatic applicability. Results show that calcite, CSH phases (especially tobermorite), and a higher water-to-powder ratio can increase the solar reflectivity (Rsun). Meanwhile, CSH and calcite can also increase the spectral emissivity in the atmospheric window (εaw). Optimal sizes of 0.5 μm (particles) and 1.0 μm (pore size) for Mie scattering are determined by Finite-Difference Time-Domain simulations. The Rsun of 0.90 and εaw of 0.88 are simultaneously achieved, which are comparable to exquisitely designed polymer-based coatings, metamaterials, and multi-layer composites. The surface cooling of 17.3 ℃, internal cooling of 9.2 ℃ by solar reflection, internal cooling of 4.8 ℃ by evaporative cooling, and internal cooling above 2.8 ℃ by mid-infrared (MIR) emission are observed. CCCs are proven to provide efficient cooling in different conditions, with low investment, facile production, and high environmental resistance.

Ultrasonic assisted reactive synthesis and characterization of Al–MgAl2O4 in-situ composite

The current study investigates the impact of Ultrasonic Treatment (UT) upon the microstructure and mechanical characteristics of Al–MgAl2O4 in-situ composite prepared using SiO2 oxide source and Al-2wt.% Mg alloy. According to the findings, because of UT in composite melt SiO2 reaction has been enhanced (86%) resulting MgAl2O4 particles of size ranging from 0.2 to 5 μm. The released Si after the silica reaction with Al–Mg has made in-situ alloying with matrix resulting Mg2Si phase formation along with α-Al. In UT composite 67% decrease in overall grain size was observed in the matrix material in comparison with Al–MgAl2O4 non-UT composite. The reinforcement of MgAl2O4 particles, combined with grain size refinement, has substantially enhanced the mechanical properties of the UT composite specifically hardness and tensile yield strength by 40 and 47%, respectively.

A LITERATURE REVIEW ON ALKALI SILICA REACTIVITY OF CONCRETE IN PAKISTAN

Pakistan has variety of topographic features including planes, sub-mountainous andmountainous ranges. These mountainous and sub-mountainous ranges possess a vast potential forconcrete aggregates. However, alkali silica reactivity has largely been observed in the past, due toreactive nature of these aggregates. This study was planned to explore the possible causes of alkalisilica reaction (ASR) and their consequences in the environment of Pakistan. Several materials can beused economically to mitigate alkali silica expansion. Among all possible remedies, use of granulatedblast furnace slag is the most effective and economical option to control ASR. Use of other materialssuch as calcined or bentonite clay, rice husk ash, bagasse ash and silica fume may be effective againstASR.

Mitigation of Alkali- Silica reactions in concrete pavements using supplementary cementitious materials

Mitigation of Alkali- Silica reactions in concrete pavements using supplementary cementitious materials

Evaluation of ultralightweight foamed glass aggregates in precast concrete

AbstractThis project investigates the use of foamed glass aggregates in lightweight precast concrete. Precast mixes are evaluated for compression and split‐tension strength, and durability is assessed through rapid chloride permeability, thermal conductivity, alkali silica reactivity, and freeze–thaw performance. Mixes containing a 100% or 50% replacement of gravel with foamed glass aggregates are evaluated. The 100% mixes have a 28‐day compression strength = 23.3–27.89 MPa which is acceptable per structural lightweight concrete standards (ASTM C330), but the split‐tension strength falls short of ASTM C330 requirements. The 50% mixes have acceptable strength but exceed the maximum density allowed for lightweight concrete in ASTM C330. The mixes exhibited low–moderate permeability but poor freeze–thaw resistance. All of the proposed mixes with one exception have acceptable expansion due to alkali silica reactivity. The thermal conductivity of the mixes varies from typical lightweight to normal weight concrete ranges with respect to the aggregate replacement ratio.

Alkali -silica reaction and its dynamic relationship with cement pore solution in highly reactive systems

Despite extensive research, the relationship between the progression of alkali-silica reaction (ASR) and the cement hydration mechanism, particularly the influence of the pore solution composition on the nature of reaction products is not thoroughly understood. A multi-analytical approach was applied to study ASR mechanism under accelerated conditions using a mortar system comprising of fused silica aggregates. For the first time, large field SEM mapping was used to correlate physical expansion with the composition, distribution and amount of ASR reaction products produced over time. A three-stage behavioral model was proposed to explain the dynamic relationship between ASR progression and pore solution composition. The results confirmed the co-existence of two phases within the ASR products: a CSH- type gel and an ASR-type gel. The relative abundance of one gel type over the other was dictated by their accessibility to the pore solution, which in turn influences how ASR propagates through the microstructure.

Adsorption behavior of molecular hydrogen in forsterite

Recent experimental studies have already discussed the existence of molecular hydrogen in mantle minerals. Here, we investigate the adsorption behavior of molecular hydrogen in forsterite with 0–15 Å intercrystalline pore at 0–519 MPa and 300–1800 K by using the Grand Canonical Monte Carlo (GCMC) method. Molecular hydrogen fills the interstitial positions of nonporous forsterite in an adsorbed state, whereas the filling of intercrystalline pore includes the adsorbed and free states. The adsorption of molecular hydrogen on the crystal surface of forsterite intercrystalline pore belongs to physisorption. The interaction between the adsorbate molecular hydrogen and the adsorbent forsterite framework weakens with pressure and strengthens with temperature, which is a crucial factor, and intercrystalline pore size. The adsorption capacity of molecular hydrogen in the intercrystalline pore of forsterite increases with pressure and intercrystalline pore size and decreases with temperature. By contrast, the adsorption capacity of molecular hydrogen in nonporous forsterite is controlled by pressure above 1200 K. Variations in intercrystalline pore size above 5 Å have a negligible effect on the capacity of adsorbed state molecular hydrogen at a given temperature and pressure. The adsorption of molecular hydrogen on different crystal faces of forsterite is anisotropic, with stronger adsorption on (001) and (100) than on (010) crystal faces. The adsorption capacity of molecular hydrogen in the intercrystalline pore decreases with the increase in oxygen fugacity at a given pressure, temperature, or intercrystalline pore sizes. The significant amount of molecular hydrogen stored in forsterite can provide a rich material basis for the short-term seismic precursor anomaly of hydrogen concentration and the formation of water through the reaction of silica with molecular hydrogen in the mantle.