Preparation Of High Active Rice Husk Silica And It's Application To The Super High Performance Concrete

In this paper ,study is carried out on possibility of reducing the sensitivity of rice husk ash SiO₂ crystallization, increasing SiO₂ volcanic activity, and the preparation pre-processing furnace burned rice husk ash(RHA) and gasification power generation RHA(GRHA) high-strength, high-performance concrete. It's found that 2.5h water boil is an obviously convenient and safe, economic and green approach in terms of improving rice husk ash pozzolanic activity, reducing carbon content and rice husk ash SiO₂ crystallization temperature sensitivity, while RHA and reburned GRHA are suitable for preparation of high-strength high-performance concrete.Atomic absorption spectrophotometer shows that 1N hydrochloric acid, sulfuric acid or nitric acid 1h boil pretreatment can be very effective in the removal of metal impurities, particularly alkali metals in rice husk, and 2.5h water boil can remove metal impurities to certain extent.Through the LOI, XRD, conductivity test and mortar test analysis, it's found that alkali metals particularly K are responsible for carbon wrapped in rice husk ash resulting in the fixed carbon black particles unable to be oxidized and the substantial decline in SiO₂ crystallization temperature, but the water boiled and acid boiled rice husks don't exist black particles. Acid pretreatment can make the rice husk SiO₂ crystallization points up to 1200℃retaining 2.5h, and water boil pretreatment up to 900℃retaining 7 h, but unpretreated rice husk SiO₂ crystallized at 600℃retaining 4 h. Water boil pretreatment rice husk at 1000℃retaining 0.5h has a strong crystallization peak similar to the one at 900℃retaining 32h, and SiO₂ crystallization basically completes when the temperature from 1100℃to 1200℃retaining 2.5h, it can be concluded that the temperature is control factor of cristobalite perfect crystallization and extend of retaining time is helpful to growth of nuclei. With the increase in temperature, LOI and pozzolanic activity of rice husk ash decline, and the higher the temperature raises the more pozzolanic activity drops.N₂ adsorption analysis demonstrates that Acid pretreatment can make meso-pores in rice husk ash increase, pore size decrease, pore volume enlarge and specific surface area dramatically grow, water boil has a worse effect than acid boil but both pretreatment means are obviously better than unpretreated one with the same pyrolysis conditions. Temperature rise makes rice husk ash aperture opens, pore volume diminishes and specific surface area declines.SEM and FESEM analysis show that the rice husk ash cross-section is composed of many porous films in connective forms packed tightly by countless SiO₂ particles, pore size is in nano-scale, the result is in fine accordance with that of N₂ adsorption test. The nano-scale SiO₂ particles and nano-scale pores packed by SiO₂ are the fundamental causes for the high pozzolanic activity and high specific surface area of RHA SiO₂.Different water-cement ratios mortar and concrete strength tests show that amorphous rice husk ash can be used in the preparation of all levels of concretes including high-strength concrete, and when water-cement ratio was 0.22 water boiled and furnace burned rice husk ash concrete 28d compressive strength reaches 108.1MPa more than silica fume's; activity of reburned gasifying rice husk ash is higher than that of gasifying rice husk ash, and qualified for the preparation of all types of concretes. When water-cement ratio is 0.19, 28d compressive strength of reburned gasifying rice husk ash increases up to 104.4Mpa. Smaller the water-cement ratio more obvious the enhancement, when water-cement ratio is 0.3, 28d compressive strength of reburned gasifying rice husk ash increases 28MPa compared to the strength of blank concrete. The fluidity of RHA concretes are similar to that of condensation silica fume.The addition of rice husk ash makes concrete chloride ion permeability fall, furnace burned rice husk ash is equivalent to silica fume and better than metakaolin, and the gasifying rice husk ash is a little inferior to them, the greater water-cement ratio the more obvious effect. NEL test and charges passed test results in concrete chloride infiltration grade of the same mix proportion high-strength and high-performance, low water-cement ratio concrete have preferably coherence, but when water-cement ratio was 0.3 these two tests aren't in consistency, charges passed test has an obvious small result leading to at least less than a grade. Used samples shouldn't be reused for the next age NEL and charges passed test of chloride ion permeability, otherwise the results significantly smaller.Marsh and the slump cone method measuring saturation point, these two methods don't synchronize for naphthalene superplasticizer, saturation point from slump cone is higher than that of Marsh; while for polycarboxylate superplasticizer them synchronized. Saturation points from both slump cone and marsh method for polycarboxylate superplasticizer are lower than naphthalene's, which indicate polycarboxylate superplasticizer has a better water reducing effect.Easy to grind, 45 min-1h is enough for rice husk ash to grind to the fineness of about 5μ. Instead, overground would result in agglomeration, therefore reduce the strength of concrete prepared thereby.