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Preparation of High Active Rice Husk Silica and It’s Application to the Super High Performance Concrete

Author: CaiRuiHuan
Tutor: OuYangDong
School: Jinan University
Course: Structural Engineering
Keywords: Rice husk pretreatment Rice husk ash Gasification of rice husk ash SiO2 High performance concrete Durability Super volcanic ash
CLC: TU528
Type: Master's thesis
Year: 2008
Downloads: 358
Quote: 3
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Abstract


In this paper, reducing rice husk ash SiO 2 crystal sensitivity, improve SiO 2 pozzolanic activity, and pretreatment electric furnace pyrolysis of rice husk ash and gasification of rice husk ash used in high-strength the possibility of high-performance concrete from rice husk ash pozzolanic activity, effectively removing the carbon content and reduce the rice husk ash SiO 2 crystal temperature sensitivity of view, the atmospheric pressure water boiling 2.5h pretreatment is effective and safe economic green water boiling process pyrolysis of rice husk ash and uncrystallized gasification of rice husk ash can be used for secondary combustion of high strength, high performance concrete. By atomic absorption spectrophotometer, 1N hydrochloric acid, sulfuric acid and nitric 1h boiling treatment can be very effective in removal of the the husk metal impurities, especially alkali metal content, and the water boiling 2.5h may be a certain degree of removal of metal impurities. Analysis showed that the rate of loss on ignition, XRD, conductivity testing and mortar test, alkali metal, especially K rice husk ash carbon is wrapped, resulting in oxidation unable to remove the fixed charcoal black particles and makes SiO 2 particle crystallization temperature dropped significantly important reason; However, due to the boiling water and acid boiling pretreatment, pyrolysis of rice husk ash does not exist the phenomenon of black particles. The acid processing can make the rice husk SiO 2 crystallization point to 1200 ℃ for 2.5h after boiling water treatment up to 900 ° C insulation 7h, without dealing with rice husk SiO 2 crystallization point is 600 ℃ for 4h. Boiling water pretreatment of rice husk insulation 0.5h at 1000 ℃ and 900 ℃ insulation 32h similar crystallization peak temperature between 1100 ℃ and 1200 ℃ insulation 2.5h the SiO 2 The crystallization is substantially complete, and shows the temperature is to control the the cristobalite crystals main factors contribute to the growth of the nuclei, and to extend the holding time. As the temperature rises, the rice husk ash obtained activity rate decline and loss on ignition, and the greater the higher the temperature activity decline. N 2 adsorption analysis that makes rice husk ash hole after acid treatment increased aperture thinning, pore volume, larger than the surface area of ??the sharp rise in the water boiling poor results in the acid treatment, both pre-treatment means are significantly better than the unprocessed same pyrolysis of rice husk ash obtained. Temperature rise so that the rice hull ash aperture open, the pore volume is smaller than the surface area declined. SEM and FESEM analysis shows that the section of the rice husk ash by many through nanometer scale SiO 2 particles are closely piled up porous thin sheet structure cross-linking a porous network structure, the pore size in the nano-level, which a result and N 2 adsorption results coincide. The nanoscale SiO 2 particles and SiO 2 pore of nano-scale particles closely packed together amorphous rice husk ash of SiO 2 has enormous than the root cause of the surface area and the volcanic ash activity. Different water-cement ratio of mortar and concrete strength tests indicated that no crystalline rice husk ash can be used in the preparation of each grade concrete, including the ultra-high-strength concrete, water-cement ratio 0.22 Boiling water treatment electric furnace pyrolysis of rice husk ash concrete 28d compressive strength reached 108.1MPa, better than the condensed silica fume. Compared to the secondary combustion and gasification of rice husk rice husk ash activity, completely can be used for the preparation of various types of concrete, water-cement ratio 0.19 28d compressive strength of 104.4 MPa and metakaolin close; and water-cement ratio the greater the enhanced effect is more obvious, the water-cement ratio of 0.3, 28d enhanced strength than the blank concrete 28MPa. Rice husk ash addition of chloride ion permeability of concrete fell more obvious, the greater the effect of water-cement ratio. EAF pyrolysis of rice husk ash effect metakaolin and the fairly condensed silica fume, and gasification of rice husk ash effect is somewhat less than they. The NEL law and electric flux method testing of high strength, low water-cement ratio of concrete on chloride ion penetration level assessment is consistent with, and in the water-cement ratio of 0.3 Concrete chloride ion permeability for grading inconsistencies the measured value of the electric flux method is the small difference of one level makes the assessment results. Test specimen can not be repeated for the the next instar NEL law and power law chloride ion penetration test, otherwise results significantly smaller. Naphthalene based superplasticizer there is not synchronous the Marsh Act and the slump cone Determination superplasticizer saturation point found, slump cone method proceeds saturation point above the Marsh Act; polycarboxylate super The plasticizing agent is synchronized. The the Marsh Act and the slump cone Determination, the polycarboxylate superplasticizer saturation point be lower than the naphthalene-based superplasticizer acid superplasticizer water reducing effect. Husk ash is very easy grinding, polishing time of 45min-1h about 5μm can be achieved, but too long a polishing but will make the rice husk ash agglomeration, and affect the strength of the preparation of concrete.

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