Studies on Prediction of Drying Shrinkage Cracking of High strength and fluidity Concrete

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1.Mechnical properties of high strength and fluidity concreteFirst, the mix proportion designs for high strength and fluidity concrete were studied. Next, the compressive strength, Young's modulus and drying shrinkage of these concrete were measurd. In order to discuss these experimental results based on "composite theory" , the compressive strength Young's modulus and drying shrinkage of cement paste of low water-cement ratio were mesured.An mathematical expression for estimating Young's modulus of concrete was proposed in this study.Experimental results showed drying shrinkage of high strength and fluidity concrete was not only influenced by unit water content but by water-cemnt ratio.Creep of cement paste was also measured.2.Changes in the strength of high strength concrete specimens which were laid in a drying atmosphere at the various starting ages of dryingChanges of the compressive, tensile, flexural and splitting strength of high strength concrete specimens exposd to drying at the age of 3,7,28,112 were tested. The results showed that the tendancy of the change of the strength was larger in high strength concrete than in normal strength one.The stress analysis was also done for drying concrete specimens from a point of view that these changes in the strength were caused by the drying shrinkage stress generated in concrete specimens during dryness.3.Cracking tests due to drying shrinkage of concrete and analysis of drying shrinkage stresses in concreteCracking tests due to dring shrinkage of concrete were carried out according to JIS draft. The tensile forces generated in confined concrete specimens were known by mesuering the strain of the restraint steel frame. Next, the prediction of cracking due to drying shrinkage was discussed based on comparing these forces with the tensile strength of concrete.