Hardened properties of self-consolidating high performance concrete including rice husk ash

This paper mainly presents the key hardened properties of self-consolidating high performance concrete (SCHPC). Various SCHPCs were produced with different water/binder (W/B) ratios, rice husk ash (RHA) contents, and air contents. The required filling ability and air content were achieved in all freshly mixed SCHPCs. The hardened SCHPCs were tested for compressive strength, ultrasonic pulse velocity, water absorption, total porosity, and true electrical resistivity. The effects of W/B ratio, RHA content, and air content on these hardened properties were observed. Test results revealed that the compressive strength, ultrasonic pulse velocity, and electrical resistivity increased whereas the water absorption and total porosity decreased with lower W/B ratio and higher RHA content. In addition, the air content decreased the compressive strength, ultrasonic pulse velocity, water absorption, and total porosity but increased the electrical resistivity. Based on the overall effects of rice husk ash, the optimum RHA content for SCHPC has been defined.     

Use of ultrafine rice husk ash with high-carbon content as pozzolan in high performance concrete

Rice husk ash (RHA) has been generated in large quantities in rice producing countries. This by-product can contain non-crystalline silica and thus has a high potential to be used as cement replacement in mortar and concrete. However, as the RHA produced by uncontrolled burning conditions usually contains high-carbon content in its composition, the pozzolanic activity of the ash and the rheology of mortar or concrete can be adversely affected. In this paper the influence of different grinding times in a vibratory mill, operating in dry open-circuit, on the particle size distribution, BET specific surface area and pozzolanic activity of the RHA is studied, in order to improve RHA’s performance. In addition, four high-performance concretes were produced with 0%, 10%, 15%, and 20% of the cement (by mass) replaced by ultrafine RHA. For these mixtures, rheological, mechanical and durability tests were performed. For all levels of cement replacement, especially for the 20%, the ultra-fine RHA concretes achieved superior performance in the mechanical and durability tests compared with the reference mixture. The workability of the concrete, however, was reduced with the increase of cement replacement by RHA.     

Short-period synthesis of high specific surface area silica from rice husk char

Porous silica with high specific surface areas is prepared from rice husk char within a short period by avoiding the commonly used hydrothermal treatment step and using polyethylene glycol (PEG, molecular weight = 20,000) as a template. The preparation process mainly involves sodium silicate production, precipitation with ortho-phosphoric acid, and calcination. The amount of used PEG significantly affects the silica textural properties like the specific surface area, total pore volume and mesopore volume. The reason should be attributed to the amount of PEG removed from the PEG-silica composites by calcination. By varying the PEG dosage from 100 to 176 mg, porous silica with specific surface areas ranging from 709 to 936 m²/g could be successfully prepared within 10 h.     

Coral-like hydroxy sodalite particles from rice husk ash as silica source

Coral-like hydroxy sodalite (HS) particles were prepared from rice husk ash as silica source in the presence of other aqueous-based precursor materials following a simple process under hydrothermal condition at 90 °C for 15 h. The particles obtained at 90 °C for different times (6, 10 and 15 h) were characterized by X-ray diffraction (XRD), Fourier transform infrared (FTIR) spectroscopy and field emission scanning electron microscopy (FESEM). The HS crystals along with a small amount of zeolite A particles were observed at 90 °C/6 h while phase pure HS particles were obtained at 90 °C for 10 and 15 h. The characteristic vibration bands of the HS particles were confirmed by FTIR spectroscopy. FESEM images showed that the HS particles obtained at 90 °C/15 h were coral-like morphology which were formed through the self-assembly of the smaller particles generated at the initial stage of reaction (6 and 10 h) under the same experimental conditions. A proposed mechanism for the formation of coral-like HS particles was also illustrated.     

Nano filter from sintered rice husk silica membrane

A nano filter showing the Knudsen flow was demonstrated by a modification of a membrane constructed from rice husk silica. The membrane was prepared by pressing and sintering micron sized rice husk silica with 4 nm pores. The membrane showed a permeability of 5.2 x 10(-8) mol m(-1) sec(-1) Pa(-1) for H2 and ratios of gas permeability 2.1 and 3.2 for k(H2)/k(CH4) and k(H2)/k(CO2), respectively. When the membrane was treated by filtration of approximately 100 nm sized rice husk silica particles, the permeability decreased to 4.9 x 10(-8) mol m(-1) sec(-1) Pa(-1) and the ratios increased to 2.2 and 3.4. In the case of the membrane after treatments with the dispersion and chemical deposition of tetraethylorthosilicate (TEOS), the corresponding permeability and ratios of the membrane were 1.8 x 10(-8) mol m(-1) sec(-1) Pa(-1), and 2.9 and 4.5, respectively. From the change of the ratio of gas permeability for the membrane with modifications, it is suggested that approximately 100 nm sized rice husk silica particles pack the large pores among the micron sized rice husk silica particles while the chemical deposition of tetraethylorthosilicate (TEOS) reveals the gas flow through 4 nm pores in the rice husk silica by blocking large pores.     

稻壳基白炭黑的制备研究

以炭化稻壳为原料,Na2CO3为活化剂,采用沉淀法对稻壳基白炭黑的制备工艺进行了研究.结果表明沉淀法制备白炭黑的最佳工艺条件为:反应温度100℃,Na2CO3溶液浓度为13％(w/w),稻壳灰与Na2CO3溶液质量配比为1:40,反应时间4h,提取率可以达到93％以上.整个工艺流程中,Na2CO3溶液循环回用,有利于工业化放大,产品的相关质量检测均符合国家标准.     

Corrosion performance of medium-strength and silica fume high-strength reinforced concrete in a chloride solution

High-strength reinforced silica fume–cement concrete slabs with a compressive strength of 70 MPa were tested for chloride diffusion and corrosion activity after partial immersion in a 2% chloride solution. Similar slabs with 32 MPa conventional concrete were tested in the same environment. Chloride diffusion in high-strength concrete was extremely low. In contrast, a high level of chloride concentration well beyond the depth of steel was noted in 32 MPa concrete. The corrosion potentials in 32 MPa concrete continued to gain larger negative values, far more than the threshold value of −350 mV (CSE). The potential values in high-strength concrete remained fairly stable and were in the vicinity of −200 mV (CSE). Corrosion current density in 32 MPa concrete acquired active values in relatively short time. In high-strength concrete, corrosion current density did not approach the threshold activation value. There is evidence that improvement in corrosion resisting property in high-strength concrete continues after the first 28 days of curing while such improvement does not occur in conventional concrete of 32 MPa. It is concluded that high-strength concrete containing 10% silica fume possesses exceedingly high corrosion resistance.     

High-purity nano silica powder from rice husk using a simple chemical method

A highly pure, small particle-sized and high surface area nano silica powder was prepared from rice husk using alkali extraction, followed by an acid precipitation method. The composition, phase, morphology, size and surface area of the as-synthesised nano silica powder was investigated by energy-dispersive spectroscopy, Fourier transform infrared spectroscopy, X-ray diffraction, transmission electron microscopy, particle size analyser and BET surface area analyser. High-purity nano silica powder was obtained by sodium hydroxide (NaOH) purification treatment (0.5, 1, 1.5, 2 and 2.5?N). The high purity of silica (～99.9%) was obtained at 2.5?N NaOH treatment. The pure nano silica powder that is obtained shows an average particle size of ～25?nm with a high-specific surface area (SSA) of 274?m²?g^?1, with an average pore diameter of 1.46?nm.     

Synthesis and characterization of high-purity silica nanosphere from rice husk

The work reports the synthesis, characterization, and the properties of high-purity silica nanospheres from low-cost rice husk. Primarily, the rice husk was washed with distilled water (DW) and subjected to acid leaching to remove the impurities. The treated rice husk was annealed at different temperatures (620 and 900 degrees C) for varied time periods to achive the desirable silica nanospheres. The annealing temperature and time considerably affected the properties of the synthesized silica nanospheres. The morphology studies confirmed that the size of nanospheres were of approximately 50-60 nm. The photoluminesence studies revealed that the synthesized silica nanospheres showed less structural defects and good optical properties. On the basis of the formation and the characterization of silica nanospheres a possible mechanism was suggested. Inductively coupled plasma mass spectrometry (ICP-MS) analysis confirmed that the synthesized silica nanospheres contained approximately 99.93% purity.     

Preparation of high silica microporous zeolite SSZ-13 using solid waste silica fume as silica source

Silica fume (SF) is a kind of solid waste that produced in the process of industrial silicon smelting. The disposal of SF for environmental problem is of great urgency. Here, a facile and novel one-step approach of high silica microporous materials SSZ-13 (SF-SSZ-13) were hydrothermally synthesized using silica fume (SF) as silica source. This method requires significantly shorter reaction times (48?h) compared to conventional SSZ-13. The as-synthesized SF-SSZ-13 exhibited high purity structure, popcorn-like morphology, and a large BET surface area of 545.74?m²?g^?1. Additionally, on the basis of controlled growth under different hydrothermal times, the formation mechanism of the SF-SSZ-13 outlined for further extension to other materials. The results on time- and energy-efficient of SF-based preparation of SSZ-13 pave the way for the reducing the cost of production of raw materials and decreasing environment load of solid waste, and also extend the application of silica fume.     

The influence of silica fume on the corrosion resistance of steel in high performance concrete exposed to simulated sea water

This investigation examined the influence of silica fume on the corrosion behaviour of steel in high performance concrete (HPC) by comparing the behaviour of HPC concretes with and without a 10% by mass of cement addition of silica fume. Reinforced concrete prisms (500 × 100 × 100 mm) with embedded corrosion probes were loaded in three-point bending to achieve a 0.3 mm crack and exposed to simulated sea water for up to four years. Corresponding prisms without induced cracks were also studied as controls. For the HPC with silica fume, pore size distribution measurements showed that after exposure to the simulated sea water, the hydration and pozzolanic reactions near the induced crack blocked almost all continuous pores in the 0.01 to 10 m range. This affected the type and distribution of corrosion products that formed by restricting the access of chlorides and oxygen to the surface of the steel. Thus, only magnetite (Fe₃O₄) formed and was confined the space provided by the induced crack, effectively plugging the crack. In HPC without silica fume, oxygenated corrosion products such as goethite (-FeOOH) and akaganeite (-FeOOH) formed in the induced crack region. The implications of these observations on the service life of high performance concrete structures are discussed.     

Composition and structure of amorphous silica produced from rice husk and straw

We have studied amorphous silica samples prepared by a thermal method and precipitation from rice processing waste: straw and grain shells (husk and peelings). We have determined their true and bulk densities, silica content, and sorbed water vapor content. The porosity of the samples has been evaluated by different techniques: nitrogen desorption (Barrett-Joyner-Halenda method) and adsorption (BET analysis), water vapor adsorption, sorption of organic dyes (methylene blue and brilliant green), and positron annihilation spectroscopy. The effect of the nature of raw materials and processing procedure on the physicochemical properties of amorphous silica is examined.     

Preparation of an efficient humidity indicating silica gel from rice husk ash

An efficient humidity indicating silica gel was prepared using rice husk ash as a raw material via sodium silicate extraction and acid neutralization method. Cobalt chloride was impregnated into the silica gel as a colour indicating material. A low concentration of cobalt chloride solution (0·0005 mol dm^?3) was used for the impregnation. The effect of pH of the impregnating solution on the colour development behaviour of the gel was investigated. The specific surface area of the gel was determined by Brunauer-Emmett-Teller method. The gel has been characterized using X-ray diffraction, scanning electron microscopy and visible spectroscopy. The moisture adsorption and desorption kinetics of the desiccant were evaluated using simultaneous thermogravimetry and differential scanning calorimetry.     

Rheological behaviour of ultra-high performance cementitious composites containing high amounts of silica fume

This study investigates the rheological behaviour of ultra-high performance cementitious composite mortars containing 15–25 % of silica fume. The utilization of two Portland cements with different mineralogical compositions and their influence on yield stress of mortar was monitored. The coaxial rheometer was used for determination of flow curves of tested samples. It was found that besides the relation between flow and water-to-binder ratio, there is also a substantial relationship with the mortar composition, in particular with the content of silica fume. The yield stress can be described by an exponential function of volume content of solids in the mortar. Such a function can describe not only the influence of granulometry but also the impact of structure formation on early age Portland cement hydration. It was found that the estimation of yield stress can be done even by a simple modular in-field technique such as a spread flow test.     

Ternary blending of cement with fly ash microsphere and condensed silica fume to improve the performance of mortar

The addition of condensed silica fume (CSF) to fill into the voids between cement grains would release the water entrapped there to form water films for lubrication. However, the large surface area of CSF would thin down the water film thickness (WFT). By adding also a cementitious material that is finer than cement but not as fine as CSF, such as fly ash microsphere (FAM), the water entrapped in the voids could be released without excessively increasing the surface area. This may produce a larger WFT and better flowability than adding CSF alone. In this research, ternary blending of cement with FAM and CSF was studied by testing mortar mixes with different amounts of FAM and CSF added. It was found that the WFT is the key factor governing the properties of mortar and that ternary blending of cement with both FAM and CSF does offer some advantages.     

A study of the combined influence of condensed silica fume and a water reducing admixture on water demand and strength of concrete

In recent years condensed silica fume has been acknowledged as one of the most effective pozzolans ever added to concrete. Properly used in adequate amounts and combined with a water reducing admixture, many important qualities of concrete are achieved or secured. The principle of dosage of water reducing admixture adopted in this combination has been to dose a quantity proportional to the amount of silicate fume. The positive effect on concrete strength from this combination of admixtures has been described as an “efficiency factor” for 1 kg silica fume between two to five when the efficiency of 1 kg cement is the unit. This study shows first that the dosing principle used until now is contradicted by experimental evidence and secondly that the water reducing admixture (lignosulfonate) used in the experimental series studied is responsible for 60% or more of the strength gain at 28 days, whereas the silica fume has to be credited for less than 40%. A more correct “efficiency factor” can then be calculated.     

A sustainable route for the preparation of activated carbon and silica from rice husk ash

An environmentally friendly and economically effective process to produce silica and activated carbon form rice husk ask simultaneously has been developed in this study. An extraction yield of silica of 72-98% was obtained and the particle size was 40-50 nm. The microstructures of the as-obtained silica powders were characterized by X-ray diffraction (XRD) and infrared spectra (IR). The surface area, iodine number and capacitance value of activated carbon could achieve 570 m(2)/g, 1708 mg/g, 180 F/g, respectively. In the whole synthetic procedure, the wastewater and the carbon dioxide were collected and reutilized. The recovery rate of sodium carbonate was achieved 92.25%. The process is inexpensive, sustainable, environmentally friendly and suitable for large-scale production.     

Properties of autoclaved aerated concrete incorporating rice husk ash as partial replacement for fine aggregate

This study examines the effects of rice husk ash (RHA) on the physical, mechanical and microstructural properties of autoclaved aerated concrete (AAC) produced at a temperature of 180 °C for 8 h and 18 h. The RHA was used as an aggregate at various replacement ratios. The results demonstrated that RHA substitution for sand reduces compressive strength and unit weight. In terms of the microstructure, the highly reactive silica in RHA strongly affected the tobermorite transformation. At 8 h of autoclaving time, the lath-like and plate-like tobermorite formed in mixtures containing up to 50% RHA was replaced by a glass-like, silica-rich CSH structure at increased replacement ratios. However, extended processing had no significant effect on these properties, which indicates that the substitution of RHA for sand has a tendency to reduce the autoclaving time or autoclaving temperature required.     

Using fume silica as heavy metals' stabilizer for high alkali and porous MSWI baghouse ash

In this study, we have proved that heavy metals in high porous and alkali baghouse ash could be fixed effectively by fume silica powder alone, or with the incorporation of colloidal aluminum oxide (CAO). The optimum amount is about 100g of fume silica per kilogram of baghouse ash. Results have indicated that fume silica has a better fixation efficiency of lead in high porous baghouse ash. In addition, the reaction mechanism of fume silica is also discussed.