Restrained Shrinkage Properties Of Reinforced Concrete At Early Age

Cracking of concrete caused by early age volume changes such as shrinkage and thermal deformation is always a problem for cast-in-place concrete structures. A lot of research has been done focused on free deformation of plain concrete. However, in practice engineering concrete structures are always reinforced. Internal reinforcement, adjacent members, formwork, and basement often restrain free deformation and cause tensile stresses in concrete when the strength of material is relative low. The induced stresses may cause immediate cracking or linger as residual stresses that affect integrity of the structures. The magnitudes of stresses depend on the properties of concrete material, the structural restraint, and the environment conditions.On the basis of experimental research on early age compressive strength, tensile strength, and elastic modulus of different types of concrete, a special rigid restraint frame device for uniaxial-restrained drying shrinkage test is devised. A multi-signals data collecting system is deigned for measuring load, deformation, strain, temperature and humidity during the experiment. Under certain temperature and humidity condition, the uniaxial-restrained shrinkage test of reinforced concrete specimens are performed using the passive rigid frame, and the restrained load, the steel strains, the concrete stresses, and the crack parameters are measured from the beginning of removal of formwork 1 day after pouring concrete. In parallel, two dummy specimens of free shrinkage of plain specimen and RC specimen without end restraint are also tested as comparison.The influence of three main factors: structures, materials, and environment conditions, are considered in experiment programming. On structural level, end restraint and steel bar continuous edge restraint are considered, and three different reinforcement ratios are tested; on material level, normal concrete C30, high strength concrete C60, and self compacting concrete C30 are considered; in some experiment, the shrinkage behaviors under different environmental conditions are compared.In theoretical analysis, the concept of "the degree of restraint" is introduced and...