Experimental Study On Dry Shrinkage Of C60 High Strength Concrete

The shrinkage characteristics of C60 high strength concrete used in large span bridges are studied in this paper.The effect of fly ash content?component size and reinforcement ratio on dry shrinkage of C60 high strength concrete under natural environment is studied.The commonly used drying shrinkage prediction models are compared and analyzed,and the accuracy and accuracy of the commonly used prediction models are compared by comparing the experimental values with the calculated values.The following conclusions are drawn.(1)There is obvious difference on concrete shrinkage between condition natural drying and of standard drying.First the shrinkage curve of concrete is uneven along with the fluctuation of age and second with the increase of drying age the shrinkage strain curve of concrete does not show the rapid development of early stage and slow development in later period,with the humidity changes,it is sometimes fast and sometimes slow.Third the shrinkage strain of concrete is not gradually increasing with the age but fluctuates with the age,and the change of environmental temperature has no obvious effect on the shrinkage of concrete.(2)Fly ash can significantly reduce the shrinkage of concrete and with the increase of volume the degree of shrinkage is more obvious.Dry shrinkage of concrete with fly ash content of 10%is 7%lower than that without fly ash and dry shrinkage of concrete with fly ash content of 20%is 15.3%lower than that without fly ash and dry shrinkage of concrete with fly ash content of 30%is 37.8%lower than that without fly ash.Fly ash can obviously inhibit the early strength of concrete(7d/28d)and has little effect on later strength of concrete.(3)At the same age,the smaller the section size of the specimen,the bigger Shrinkage strain is.The size effect disappears When the internal and external humidity of concrete is balanced and the shrinkage values at different ages do not decrease linearly with the increase of the section size of members.(4)The restraining effect of reinforcement to concrete shrinkage is not obvious enough.With the increase of reinforcement ratio the restraining effect of reinforcement to concrete gradually appears.Similar to the size effect,the shrinkage values at different ages do not decrease linearly with the increase of reinforcement ratio.(5)The shrinkage values of low strength C15?C25 concrete is generally overestimated by the prediction values of the JTG-04 model.For high strength C50?C65 and C70 concrete,the prediction value is generally underestimated and the higher the strength grade,the more obvious the undervaluation is.Comparatively speaking,for the C30?C40 strength ordinary concrete,the shrinkage prediction value of the JTG-04 model is in good agreement with the experimental value.(6)For the shrinkage of high strength concrete,the prediction result of GL2000 model is the best,followed by B3 model,and the worst is JTG-04 model and ACI 92 model.