Study On Volume Deformation Of Steel Tube Confined Concrete Based On The Adjustment Of Internal Relative Humidity

Steel TubeConfined Concrete(STCC) is a combination structure by stuffed steel tube with concrete. The main reason for its excellent advantages is the cooperating function between the steel tube and the core concrete. In order to achieve this aim, both of them must be combined closely. Due to some causes such as the contraction of the core concrete, the mixed expansive agent are insufficient to expand from lack of water, the core concrete and the wall of steel tube are inclined to separation and form a cavum, which will decline the load strength and may bring the hidden trouble.This paper argued that water-entrained material which could adjust the internal relative humidity is introduced to the concrete. The water-entrained material could reserve some water in advance and release them when internal relative humidity of the inner concrete decrease rapidly, which could decrease the self-contraction of the concrete at one hand, resolve the difficulty of expanding of the expansive agent from lack of the water. Plenty of work has been done to study the releasing water performance of the water-entrained material and the relationship between water-entrained material and internal relative humidity, resistance rate, expansion and shrinkage rate. The main results are written below:The relativity of the absorbing and releasing water performance of the water-entrained material and some factors such as its type, apparent density, grading, environmental humidity were studied. Results showed that type of water-entrained material was crucial, and the absorbing and releasing water performance which made by clay exceeded that which made by shale. The methord and expression to calculate the volume and the quality of cementing materials which could be covered by internal curing of the water-entrained material and the practical W/C were argued. The results showed that the water-entrained material can work out most cementing materials, so as to resolve the problem of lacking of water during the later expanding of the hydratation of the steel tube-confined concrete.The influnce and the change rule of the factor such as W/C, expanding agent, type of water-entrained material, density rank and fly ash upon the internal relative humidity, expansion and shrinkage rate, resistance rate were studied systematically. The analyse on the data showed that where was a linearity relationship between internal relative humidity and expansion-shrinkage rate, a index relationship between internal relative humidity and resistance rate, a logarithm relationship between expansion-shrinkage rate and resistance rate.XRD, SEM and DTA/TG were used to study the influence of internal curing of water-entrained material on the hydration and the microstructure of cement. Results showed that internal curing could ameliorate conditions when finding expanding agent unable to expand from lack of water under the low W/C, increase the resultant of ettringite, which finally make a more dense structure.