High Amorphous Silica Research Articles

Binary and Ternary Blended Portland Cements Containing Different Types of Rice Husk Ash.

Rice husk ash (RHA) is agricultural waste with high silica content that has exhibited proven technical feasibility as a pozzolanic material since the 1970s. Notwithstanding, its use in mortars and concrete is limited by the standards currently utilized in some countries where RHA production is high and the aforementioned pozzolanic material is not standardized. This is the case in Spain, one of the main rice producers in Europe. Nowadays, the high pressure placed on the Portland cement production sector to reduce its energy use and CO2 emissions has given rise to a keen interest in mineral admixtures for cement manufacturing. In this research, we intended to establish the contributions of different RHA types to the final blended Portland cement properties ("H" is used to identify RHA in standardized cements). The experimental results demonstrated that RHA with good pozzolanic properties (large specific surface and high amorphous silica content) had to be limited to 10% cement replacement because of the severe reduction in workability at higher replacement percentages. RHA with lower reactivity, such as crystalline RHA, or fly ash (FA) can be used to prepare binary and ternary blended cements with reactive RHA. It is possible to design the following cements: CEM II/A-H and CEM II/A-(H-V). It would also be possible to design cement (CEM II/B-(H-V) with replacement values of up to 30% and the same 28-day mechanical performance as observed for the Portland cement without mineral addition.

Preparation of Silicon Carbide Powder from Amorphous Silica and Investigation of Synthesis Mechanism

An innovative process for preparing silicon carbide (SiC) from acid leaching residue of ferronickel slag through a carbon–thermal reduction process was proposed in this study. The results indicate that the acid leaching residue is an ideal silicon source for SiC preparation according to its high amorphous silica content of 84.20% and fine particle size of d50 = 29.16 μm. Compared with carbon black, activated carbon, and graphite, coke is the more appropriate carbon source for SiC preparation. A micron-size SiC powder with grade of 88.90% and an average particle size (d50) of 44.68 μm can be obtained under the following conditions: the mass ratio of coke to leaching residue as 1.2:1, in an air atmosphere, reducing at 1600 °C for 3 h, following by decarbonizing at 700 °C for 4 h. The XRD, SEM and FTIR analyses show that the prepared powder is 3C-SiC and belongs to the β-SiC crystal type. Based on thermodynamic analysis and micromorphology observation, it can be concluded that with amorphous silica as the silicon source, the carbon–thermal synthesis of SiC powder follows both the solid–solid reaction mechanism and the gas–solid mechanism. The SiC created through solid–solid reaction is primarily nucleated in situ on amorphous SiO2, with a size close to that of the original acid-leaching slag, while the SiC generated according to the gas–solid mechanism mainly nucleates heterogeneously on the surface of carbon particles, resulting in a smaller particle size and mostly adhering to the surface of solid–solid nucleated SiC particles. This study provides a feasible method for the effective utilization of amorphous silica, which is also significant for the efficient consumption of the vast acid leaching residue.

Effect of Use Sugarcane Bagasse Ash and Rubber Tyre as A Partial Replacement of Cement and Coarse Aggregate in Concrete

Abstract: Recycling and usage of waste products can be a viable option in the waste management of many materials. The present study focuses on the utilization of Sugarcane Bagasse Ash(SCBA) as replacement material for cement and rubber tyre as replacement material for coarse aggregate in concrete production. Noting the increasing volumes and difficulty in the disposal of wastes from rubber tyres and SCBA, this paper discusses test results of use of SCBA and recycled tyres in concrete for possible application in the construction industry. Sugarcane Bagasse ash contains high amorphous silica content and aluminium ion. For experimental investigations, Sugarcane bagasse ash and its chemical properties are obtained from Sakthi sugars private ltd, Aapakoodal, Tamilnadu. Ordinary Portland cement was partly replaced by sugarcane bagasse ash in the ratio of 0%, 10%, 20% and 30% by weight. The results indicate that inclusion of Sugarcane Bagasse Ash in concrete up to 20% level significantly enhanced the strength of concrete. In 2008, around one billion end-of-life tyres (ELTs) were being produced globally each year. As a possible means of disposing the tyres, it is proposed to use rubber tyres as coarse aggregate in concrete. Tyres cut into pieces with maximum size of 20 mm to use as coarse aggregate.It were used in the replacement of 15% of the normal gravel. Grade of concrete used in this paper is M30.Compressive strength, splitting tensile, and flexural strength tests were conducted according to the various BS codes. This paper also demonstrated the variation in the compressive strength of the non-conventional concrete when the BS and ACI methods are used in the design of the mix.

Multiphoton process investigation in silica by UV femtosecond laser

We investigated the interaction processes between high intensity femtosecond ultraviolet laser pulses and amorphous silica, leading to permanent refractive-index changes that are at the basis of advanced manufacturing for photonics devices. The experiment, carried out as a function of the laser power, improves our understanding on the strong-field ionization process by the monitoring of the 1.9 eV and 2.65 eV emissions, related to nonbridging oxygen hole centers and self-trapped exciton, respectively, induced in the exposed glass region. Our results clearly proved that the UV laser light band-to-band absorption is allowed in the multiphoton ionization limit, whose consecutive relaxation leads to the generation of these photoluminescence (PL) signatures. Furthermore, we coupled the online PL investigation with post mortem analysis of the irradiated volume through phase contrast microscopy, Raman and steady state PL, providing a complete view of the silica-femtosecond laser interaction.

Evaluation of corn straw ash as supplementary cementitious material: Effect of acid leaching on its pozzolanic activity

The use of biomass ash is an environmentally friendly practice in the search for sustainable construction materials. This study aimed to produce pozzolanic ash from corn straw with a high amorphous silica content, low carbon content, and high specific surface area via controlled acid leaching, two-step burning, and grinding. The effect of pretreating corn straw on the properties of the material was assessed by comparative analysis with corn straw and rice husk ashes produced without acid pretreatment. To this end, characterization data, hydration heat, chemically bound water, and portlandite consumption in pastes, and mortar compressive strength were used to evaluate the pozzolanicity of the ashes. The results indicated that all the ashes exhibited pozzolanic behavior and that the leaching process significantly improved the physical and chemical properties of corn straw ash, with reduction in portlandite content. The calorimetric results showed a change in hydration kinetics with an increase in ash in the cement mixes. Moreover, the compressive strength of leached corn straw ash-based mortars was greater than that of the other mortars, primarily for high levels of cement replacement (20 and 30% by mass).

Infrared transparent mullite ceramics fabricated by solid-state reactive sintering

Infrared transparent mullite ceramics were fabricated by solid-state reactive sintering under vacuum without pressure. High purity α-alumina and amorphous silica (molar ratio, 63: 37) powders were used as raw materials. The densification process and mullitization process of the mixed powders were investigated and compared with the sintering of mullite powder. As the sintering temperature increased to 1400 °C, mullite formed and silica transformed into cristobalite. Cristobalite disappeared at 1600 °C and α-alumina did at 1650 °C. However, α-alumina precipitated when the temperature increased to 1750 °C. For the sintering of mullite powder, shrinkage happened at 1400 °C. While, shrinkage almost finished for the reactive sintering of alumina and silica. When reactive sintered at 1780 °C, the transmittance of the mullite ceramics was the highest, which was 65% at 4.1 μm. The method used in this work is promising for the preparation of large and complex shaped transparent mullite ceramics.

Development of zero cement composite for the protection of concrete sewage pipes from corrosion and fatbergs

The pursuit of environmental friendly alternatives for ordinary Portland cement (OPC) finds increased attention when the latter poses serious durability issues in major infrastructure applications, such as sewage drainage pipes. The presence of large quantities of free lime in OPC concrete used in the manufacturing of sewage pipes, exposes them to (i) concrete corrosion in acidic sewage environment, and (ii) clogging of sewage network due to the formation of calcified fatbergs. There appears to be very limited or no research on the development of an eco-friendly zero cement composite that can protect the concrete sewage pipes from corrosion and can eliminate the free lime that contributes towards the formation of fatbergs. Therefore, to address this research gap, an experimental investigation was undertaken on quaternary blended cement composites containing nano-silica, fly-ash, slag, and hydrated lime. These cement composites were tested for compressive strength to identify their mechanical properties, and an acid attack durability test exposed to 3.5% sulfuric acid solution to identify their corrosion performance in an aggressive acid environment. X-ray diffraction, thermogravimetric and scanning electron microscopic analysis were carried out to ascertain the physicochemical properties of the cement composites. The results show that an eco-friendly zero cement concrete developed with a quaternary blended mix of nano-silica, fly-ash, slag and hydrated lime successfully addresses the mechanical and durability requirements of the concrete sewage pipes. It surpasses ASTM's minimum strength requirement for the sewage pipes, and brings about a significant improvement in withstanding an aggressive acidic environment as evident from the 96% reduction in its mass loss due to concrete corrosion, compared to that of the OPC concrete. Moreover, the high amorphous silica content present in nano silica, slag and fly-ash assists in totally consuming the free lime that interacts with fat, oil and grease to produce fatbergs.

Effect of Acid Leaching on Different State of Rice Husk

Rice husks (RH) are agricultural wastes available abundantly in rice producing country. A by-product obtained from combustion of rice husk is rice husk ash (RHA) which is rich in silica (SiO2) contents. This paper focused on the effect of acid leaching treatment on rice husk to produce high-purity silica. There are 4 different states of conditions involved; raw rice husk (RRH), treated rice husk (TRH), rice husk ash (RHA), and treated rice husk ash (TRHA). Citric acid; C6H8O7 was used as a leaching agent. TRH and TRHA was leached to see whether treated rice husk before combustion (TRH) or treated rice husk after combustion (TRHA) will produce more high-purity silica. Chemical composition analysis shows high amorphous silica content which is 98.47% with low metallic impurities at 1.0M C6H8O7, 70 oC for treated rice husk (TRH). X-ray diffraction (XRD) pattern shows the presence of amorphous silica in treated rice husk (TRH) and crystalline silica in treated rice husk ash (TRHA). Fragmentation of TRH into small pieces after acid leaching is seen where there is significant increase in the exposed surface areas. High-purity amorphous silica with more than 98% was prepared via citric acid leaching treatment and combustion process.

Extraction of high purity amorphous silica from rice husk by chemical process

High purity amorphous silica (SiO2) is extracted from agriculture waste (rice husk) that supplied from Al-Najaf province, Iraq. Silica is the major inorganic constituent of the rice husk. It is prepared with using acid pretreatment of (3N HCl), then burned it at (700°C) for 4 hrs, and followed with leaching process by 1.5, 2, 2.5, and 3N NaOH. The extracted results are high-surface area of amorphous silica particles. Extracted results are silica particles were high surface area of amorphous silica particles. These particles were characterized by X-Ray diffraction (XRD), and X-Ray Fluorescence (XRF) and Atomic force microscopy (AFM) techniques. High pure amorphous silica observed from rice husk ash was confirmed by XRD diffraction. The silica purity results measured by X-Ray fluorescence was 99.714% for leaching at 3N NaOH. Results from (AFM) of silica with nanoscale sizes and microparticles with diameters ranging from (87-114) nm.

Effect of silica and lignocellulosic additives on the formation and the distribution of meso and macropores in foam metakaolin-based geopolymer filters for dyes and wastewater filtration

This work investigates how silica and lignocellulose additives affect the production of metakaolin based-geopolymer foam filters. Lignocellulosic material from wood powder sawdust (S), silica from rice husk ash (RHA), calcined (Sa) and uncalcined (Sab) sand were separately used together with high amorphous silica fume (foaming agent) and integrated into the matrix (metakaolin and solution). The different geopolymer pastes were cured at 70 °C to enhance the pore formation. Results presented the geopolymer foams filter as sponge-like composites having 58–68% of porosity with 1–4 MPa of compressive strength. RHA and Sa lead to materials with more meso and macropores. Sawdust based-geopolymer (the hardest foam) containing channel pores predominated by coarse pores exhibited a flow rate of 4 mL min−1. The absence of the bands of MB from FT-IR spectra and UV spectra (663 nm) of MB filtrate (totally blue discoloured) indicated that, geopolymers foams filters designed are suitable for dyes and wastewater filtration.

High purity and amorphous silica (SiO2) prepared from oil palm frond (OPF) through sol–gel method

Malaysia is known as the second largest oil palm producer in the world which subsequently also producing abundant of oil palm biomass either from milling site or plantation site. Oil palm frond (OPF) is one such oil palm biomass that usually produced abundantly in oil palm plantation site and thus it has potential for research of its application and used. This study aims to establish the utilization of OPF in silica synthesis through sol–gel method and its possibility in producing high purity and amorphous silica. To achieve this, OPF processed via several stages of combustion, acid leaching treatment with citric acid and finally silica synthesis via modified sol–gel method. The results obtained shown that from per kg of OPF, ∼3.5% or about 34.7 g of ash was produced that later subjected to acid leaching treatment and managed to recover approximately 18.7 g of acid leached oil palm frond ash (OPFA) or ∼53.9%. From this amount, 68.4% of silica or about 12.8 g of silica successfully produced from the acid leached OPFA. The synthesized silica then characterized using FTIR and presented almost identical spectra with commercial silica specifically at peak at peak 3350–3390 cm−1, 1600–1640 cm−1 and 1040–1100 cm−1 which represent Si-OH bond and Si-O-Si asymmetric bond respectively. The lack of peak at 622 cm−1 indicate that the silica is amorphous in nature and with the acid leaching treatment performed prior sol–gel, possible high purity silica was successfully produced.

The Study of Thermal Decomposition of Rice Husk in Silica Production: The Effect of Hydrochloric Acid Leaching

The effect of hydrochloric acid leaching on thermal decomposition process and morphology of the rice husk in silica production have been investigated. Amorphous silica can be obtained by thermal decomposition of rice husk in acid solution. The aim of this study is to investigate the stages of thermal decomposition of rice husk and its morphology. In this work, thermal decomposition of rice husk has been investigated in neutral and acid solution (hydrocloric acid 1%v/v, 3%v/v). The thermal decomposition study was performed at 225°c, 450°c, 700°c. The thermal behavior were investigated using DSC while the microstructure and properties of rice husk were characterized by SEM, FTIR, XRD. The results showed that the pre-treatment of the rice husk with acid leaching accelerated thermal decomposition of organic components at slight lower temperature as showed by differential scanning calorimetry (DSC) and scanning electron microscope (SEM) analysis. This knowledge may provide better insight in order to obtain high grade amorphous silica.

Use of residual diatomaceous earth as a silica source in geopolymer production

The use of binders as an alternative to Portland cement has gained importance in recent years. Among them, geopolymeric binders, developed by the reaction between an aluminosilicate precursor and a high alkalinity solution, have become one of the most promising alternatives. The activating solution generally comprises waterglass and sodium hydroxide. Since waterglass is the most expensive material and has a high environmental impact, using alternative silica sources will lead to more sustainable binders. Previous studies have successfully used rice husk ash (RHA) as a silica source. This research aims to assess the possibility of using diatomaceous earth (or diatomite) as an alternative silica source, like the previous studies with RHA. Diatomite is a sedimentary rock with a high amorphous silica content formed by fossilized diatom remains. In this work, the geopolymer was obtained using a fluid cracking catalyst residue as the precursor and six different activating solution types prepared with commercial products, residual diatomite (from beer and wine industries) and RHA. The results open a new possible route for the reuse and recovery of diatomaceous earth residue, although the compressive strength results of the mortars were slightly lower than those for mortars prepared with RHA or commercial reagents.

EFFECTS OF DIATOMITE AS FILLER ON THE POROUS ASPHALT MIXTURES PROPERTIES

Diatomite is a kind of mineral containing high amorphous silica content which is a very durable substance. Due to its useful characteristics such as lightweight, high porosity, high surface area, low density and high absorptive capacity, diatomite is identified with potential to be used as a filler to improve the performance of asphalt mixture. Porous asphalt is known to have poor strength and durability due to its open structure and high air void contents which exposed the structure to air and water. These factors may influence the adhesive strength of binder-aggregate and lead to cohesive failure within the binder film, which contribute to stripping and moisture damage. The addition of fillers has been identified to improve the adhesion and cohesion properties by stiffening the asphalt binder and enhance the bonding strength between aggregate and binder. Therefore, this study was undertaken to evaluate the potential of diatomite as filler in porous asphalt mixtures and compared with ordinary Portland cement. Field Emission Scanning Electron Microscopy (FESEM) was conducted to investigate the microstructure of the fillers. The compacted samples of porous asphalt mixture with Malaysian aggregate gradation were prepared using Superpave gyratory compactor at the target air voids content of 21%. Each sample was incorporated with 2% of filler and polymer modified binderof PG76 as a binder. The sampleswere then tested for abrasion loss, resilient modulus and indirect tensile strength. The test results show that the samples prepared with diatomite havelower abrasion loss compared to those with cement. Besides, the samples incorporating diatomite show enhanced resilient modulus and indirect tensile strength. Thus, these indicate that the diatomite filler has good potential to improve resistance to stripping and moisture damage compared to cement.

Reactivity of Glass Powder in Aqueous Medium

Recycled glass powder (GP) has recently been widely used as a complementary cementitious material to replace a part of the Portland cement in concrete. However, unlike the chemistry of the Portland cement hydration, more studied and mastered, the mechanism of GP reaction that occurs in-situ during the mixture hydration, is less studied. To overcome this, a first study was focused on the reactivity of the anhydrous glass powder surface over time and its effect on physico-chemical and mechanical properties of concrete. The results showed a very good stability of GP surface. Actually, Portland cement mortars incorporating 20% GP at different ages exhibited the same required properties. The second step, which is the subject of this paper, consists of studying the behavior of GP alone in water and identifying species likely to involve in the hydration reaction in presence of the cement. pH of suspensions and chemical composition of leachates were monitored respectively by pH-meter and inductively coupled plasma mass spectrometry (ICP-MS) as a function of contact time, water-to-solid mass ratio (W/S) and GP particle size. Results reveal an instantaneous increase of pH after mixing GP with water resulting in the passage of surface alkali ions in the solution. Moreover, an enhancement of silicon content in solution is observed suggesting a partial dissolution of the glass network. The dissolution rate increases with increasing W/S ratio and decreasing particle size. Thus, dissolved silica species would react with portlandite from cement hydration explaining good mechanical properties generally observed in concrete containing GP at long term. Accordingly, due to its high amorphous silica content, GP could be an excellent alternative for conventional supplementary cementitious materials such as fly ashes which are not locally available.

EFFECT OF SUGARCANE BAGASSE ASH ON STRENGTH PROPERTIES OF CONCRETE

The present study focuses on the utilization of Sugarcane Bagasse Ash as replacement material for cement in concrete production. Sugarcane Bagasse ash contains high amorphous silica content and aluminium ion. For experimental investigations, Sugarcane bagasse ash and its chemical properties are obtained from KCP sugar factory, Andhra Pradesh. Ordinary Portland cement was partly replaced by sugarcane bagasse ash in the ratio of 0%, 5%, 10%, 15%, 20% and 25% by weight and the influence of Sugarcane bagasse ash as a partial replacement material has been examined on fresh concrete tests by Compaction factor test and Slump cone test as well as on hardened concrete with tests for Compressive strength, Split tensile strength, Flexural strength and Modulus of Elasticity. The results indicate that inclusion of Sugarcane Bagasse Ash in concrete up to 20% level significantly enhanced the strength of concrete. The highest strength was obtained at 10% Sugarcane bagasse ash replacement level.

Synthesis of sodium waterglass from white rice husk ash as an activator to produce metakaolin-based geopolymer cements

Rice husk from source in Cameroon was leached in HCl (5M) to remove the most of metallic ingredients and then calcined at 600°C in order to produce white rice husk ash. This white ash were applied for producing sodium waterglass with different molar ratios SiO2/Na2O (0.31; 0.47; 0.62; 0.78; 0.93; 1.09 and 1.25) and then used to synthesize metakaolin-based geopolymer cements. The obtained white rice husk ash shows the loss of crystalline mineral and reveals high amorphous silica with quartz as impurity. Geopolymers GPi (i varying from 1 to 7) were obtained using different synthesis sodium waterglass (NWG) with a mass ratio NWG/MK=0.87. It could be observed that the 28 days compressive strength (4/5/7/9/32/34/36MPa) increase with increasing the molar ratios SiO2/Na2O defined in this work in the course GP1/GP2/GP3/GP4/GP5/GP6/GP7. The micrographs show the formation of more geopolymer gels when the molar ratios SiO2/Na2O in alkaline activators are between 0.93 and 1.25. Sodium waterglass from white rice husk ash proved to be an effective alkaline activator in geopolymers preparation. It can be concluded that it is possible to replace quartz sand and sodium carbonate which is responsible to greenhouse gas emitted during the production of commercial sodium silicate solution by using rice husk as silica sources.

Decoupling the physical and chemical effects of supplementary cementitious materials on strength and permeability: A multi-level approach

Supplementary cementitious materials (SCMs) represent an alternative for the industry to achieve sustainability by reducing cement contents without significant compromises of the mechanical properties and enhancing durability. SCMs play a dual role during hydration: a physical effect promoting nucleation and cement hydration and a chemical effect through pozzolanic activity. Rice husk ash (RHA) and natural pozzolans (NP) were evaluated using compressive strength and durability tests in a multi-level experimental program. RHA increased the strength more than NP, which is well explained by its prominent chemical effect (78%) assessed by isothermal calorimetry and its high amorphous silica content. Both RHA and NP produced significant reductions in the permeability of the concrete, which is mostly explained by the chemical effect. Decoupling the physical and chemical effects of a SCM allows for optimisation of its manufacturing process.

Structure and Properties of Silica Glass Densified in Cold Compression and Hot Compression

Silica glass has been shown in numerous studies to possess significant capacity for permanent densification under pressure at different temperatures to form high density amorphous (HDA) silica. However, it is unknown to what extent the processes leading to irreversible densification of silica glass in cold-compression at room temperature and in hot-compression (e.g., near glass transition temperature) are common in nature. In this work, a hot-compression technique was used to quench silica glass from high temperature (1100 °C) and high pressure (up to 8 GPa) conditions, which leads to density increase of ~25% and Young’s modulus increase of ~71% relative to that of pristine silica glass at ambient conditions. Our experiments and molecular dynamics (MD) simulations provide solid evidences that the intermediate-range order of the hot-compressed HDA silica is distinct from that of the counterpart cold-compressed at room temperature. This explains the much higher thermal and mechanical stability of the former than the latter upon heating and compression as revealed in our in-situ Brillouin light scattering (BLS) experiments. Our studies demonstrate the limitation of the resulting density as a structural indicator of polyamorphism, and point out the importance of temperature during compression in order to fundamentally understand HDA silica.

Laboratory processing of Colombian rice husk for obtaining amorphous silica as concrete supplementary cementing material

Rice husk is an agro-industrial waste with few applications. However, its elevated amorphous silica content has turned it into a promising raw material, especially due to its possibility to be transformed into a cement supplement for concrete mixtures. Investigating plant materials as new sources of high quality amorphous silica has a number of important advantages resulting in a process that may involve fewer steps than usual. Determining the suitability of the specific silica materials obtained from Colombian rice husk ash for them to be used in concrete mixtures involves the assessment of several features such as percentage of amorphous silica, particle size, surface area and specific gravity. The current work focused on the laboratory ash production process, whose appropriate temperature, grinding and burning time conditions were assessed through their effect on the compressive strength of concrete cylinders supplemented with the obtained materials. This, in turn, ensures obtaining an elevated percentage of amorphous silica and provides an adequate conceptual framework for industrial production.