Effect Of Curing Temperature On Creep Character Of Fly Ash Concerte

Fly ash can improve the workability of concrete, to improve concrete resistance to sulfate attack, chloride ion penetration resistance and resistance to alkali aggregate reaction performance, reduce the hydration heat of concrete, reduce the risk of cracking due to temperature difference, has remarkable technical and economic effect, and does not need to grinding, preparation concrete FA has become a indispensable key components. As a long-term deformation of concrete performance, creep can make the loss of prestress and the increase of deformation of the prestressed reinforced concrete structures. At the same time, the creep is a focal point that whether fly ash can be used widely in the prestressed reinforced concrete structures such as large bridges, etc. The study of fly ash concrete creep performance has become the key work of hundreds of researchers.The atmospheric steam curing can accelerate the strength development of concrete products and save curing time. Fly ash is active under high temperature. Fly ash can react with Ca(OH) 2 easily under high temperature, and this reaction is sensitive to the temperature. The result of the reaction would influence the quantity and microstructure of hydration products, and then influence the creep of fly ash concrete. In order to avoid the influence of other factor on the creep of fly ash concrete, the fly ash concretes are loaded with equivalent strength. To investigate the effect of curing temperature on creep behavior of fly ash concrete, the specific creep of concretes, with the water-binder ratio of 0.33 and different fly ash replacements of 20% and 40%, cured under temperatures of 20 ℃, 50 ℃ and 90 ℃ was examined. All concrete specimens were loaded at 33% of their compressive strength to measure the creep, when they had an equivalent cubic strength of(48.0±2.0) MPa. Based on the amount of non-evaporable water, the porosity and pore size distribution of hardened cement pastes, the scanning electron microscope(SEM) morphology of hydration products and X-ray diffraction(XRD) analysis, the influence of curing temperature on creep of fly ash concrete was analyzed.The results show that when concretes were loaded with the same stress level, the main factor influencing creep of fly ash concrete was the quantity and microstructure of C-S-H gel. Compared with the concrete with 20 % fly ash dosage under the curing temperature of 20 ℃, the concrete cured under the temperature of 50 ℃ produced more hydration products, with a slight decrease of Ca(OH)2, and the specific creep of which is close to the reference concrete. At the curing temperature of 90 ℃, concrete also produced more C-S-H gel, with a great decrease of Ca(OH)2, and the total specific creep after 360 days is 87.1% of the reference concrete. The hydration products had a trend of crystallizing under temperature of 90 ℃ and fly ash concrete might produce a few hydration products of Tobermorite which could reduce the creep evidently. The concrete with 40 % fly ash dosage under the cuing temperature of 50 ℃ also produced more hydration products, but the specific creep of which increases significantly and is 119.5% of the reference concrete.