Study On Concrete With High Strength And High Properties Using Of Large Dosage Fly Ash

1 ton CO₂ gas will be let off when 1 ton cement clinker is manufactured in the technology of cement and concrete. Coming to light, CO₂ will results in greenhouse effect seriously. With the developing of society, the demanding to cement will increases with time in our country. The industry of cement and concrete need to research approaches developing harmoniously with environment urgently. A large of industrial waste residue bring heavily burden on environment resulting from the developing of the world industry. A lot of researchers in the working of cement and concrete have been making a large of investigation and using on industrial waste residue. The fly ash has been utilized for more than half of a century among these waste residues. It was used in the large mass concrete work to decrease the effect of the rising of temperature resulting of hydration of cement initially. Later with the emerging of the problems in the durability of cement and concrete continuously, fly ash was recognized that it can be used to improve many properties of cement and concrete. Either the fluidity of the fresh mix or the durability of concrete used, it can contribute a good effect. Resulting from the increasing of the numbers of papers about fly ash in many international meetings, it can be noted that the utilization of waste residue have become a hot topic. The developing level of the investigation to fly ash in our country drops behind other countries.Fly ash can be classed to two kinds: high-calcium fly ash and low-calcium fly ash. Most of fly ash is low-calcium fly ash in our country. The characteristic of low-calcium fly ash is that the content of CO₂ is less than 10% and the pozzolanic activity is low. When the content of fly ash instead of cement is less than 20%, there is little effect on the strength of concrete, especially on the initial strength, but the fluidity of the fresh mix and the durability of hardened concrete will be increased obviously. If fly ash is instead of large of cement, the initial strength of concrete would decrease seriously and the carbonate resistance would be weak.Aiming at above-mentioned problem, this paper investigates the transnaturing treatment effectively to low-calcium fly ash and manufacturing fly ash concrete with high strength and high properties using of large dosage fly ash. Main outcomes investigated follow:(1) Improve the initial(3day) pozzolanic activity of fly ash effectively using thetreating method grinding the activator and fly ash together. Concrete which the content of fly ash occupies 50-70 percentage of binding materials can be made of through adopting technology measures decreasing water to binding materials ratio and improving total dosage of binding materials in concrete. Strength of this concrete in 3day and 28day been higher than 42.5MPa and 85MPa especially, is more than 100MPa 1year later. With high strength and high properties, this fly ash concrete using of large dosage fly ash has a good fluidity in plastic state.(2) Analyzing the pozzolanic activity of transnarured fly ash in fly ash concrete using of large dosage of fly ash based on the method pozzolanic activity to strength supported by professor Xingcheng Pu, when activity factor A=l, the strength of concrete using of fly ash is equal to the basic strength of concrete. When the dosage of transnarured fly ash is between 50-70%, the activity factor arrives at 0.572, 0.678, 0.683 especially. It arrives at 1.050, 0.972, 0.956 especially in 28day.(3) The carbonizing-resisting of fly ash concrete using large dosage of fly ash has been improved in a certain extent. Curing for 56day and carbonizing accelerated for 28day, the depth of carbonizing of concrete is 6.5mm, 8.7mm, 9.0mm. Guessing according to that carbonizing accelerated for28day is equal to natural carbonization for 50year, the depth of natural carbonization for 100year will arrive at 13mm, 17.4mm, 18mm. Normal protecting depth in structure of reinforcement concrete is 25mm, so the natural carbonization will not arrive at the surface of steel in 100year. Concrete using large dosage of fly ash has a good volume stability. The value of dry shrinkagefor 180day is 560×16^-6.(4) lyear later the value of pH of the concrete using of large dosage of fly ash is 12.19, 12.01, 12.00 especially by measuring the value of pH and the content of Ca(OH)₂ in the mortar using of large dosage of fly ash. The content of Ca(OH)₂ is more than 15.2mg/g.(5) The pozzolanic react start to act from the surface of the particles of fly ash in the SEM photos at 3day, by observing the hydration products and their appearance of the mortar of cement using of large dosage of fly ash adopting with X-ray and SEM. The pozzolanic react decreases the content of Ca(OH)₂ .(6) Analyzing the pore structure of mortar using of large dosage of fly ash, it note that large dosage of fly ash do not decrease the porosity of mortar and the internal structure, but decrease the number of baneful big pore, at the same time increase the number of hurtles small pore with 最可几孔.Fly ash can be instead of cement in concrete largely to manufacture concrete with high strength and high properties. It is a effective approach to realize developing continuously in the industry on cement and concrete with environment, so it can be defined as green concrete with high properties.