Abstract
The early age volume deformation is the main course for the cracking of high-performance concrete (HPC). Hence, the shrinkage behavior and the restrained stress development of HPC under different restraints and curing conditions were experimentally studied in this paper. The method to separate the stress components in the total restraint stress was proposed. The total restrained stress was separated into autogenous shrinkage stress, drying shrinkage stress and thermal stress. The results showed that the developments of the free shrinkage (autogenous shrinkage and drying shrinkage) and the restrained stress were accelerated when the drying began; but the age when the drying began did not significantly influence the long-term shrinkage and restrained stress of HPC; the autogenous shrinkage stress continuously contributed to the development of the total restrained stress in HPC; the drying shrinkage stress developed very rapidly soon after the drying began; and the thermal stress was generated when the temperature dropped. The thermal stress was predominant at the early age, but the contributions of the three stresses to the total restrained stress were almost the same at the age of 56 d in this study.
Highlights
Concrete is prone to cracking due to the early age volume deformation under restrained conditions.Early-age cracking is the result of a complex interaction between various phenomena or properties of concrete [1], mainly including the autogenous shrinkage, drying shrinkage, thermal deformation, creep, elastic modulus, tensile strength, etc
Where, σc means the restrained stress in concrete (MPa); Es is the elastic modulus of the rebar, which was 2.10 × 105 MPa; εs is the strain of the rebar, which was recorded by the strain gauges; As is the section area of the rebar; and Ac is the section area of the concrete specimen
The results of the restrained stress tests in this study showed that the autogenous shrinkage resulted in 10–30% of the total restrained stress under different conditions at early ages
Summary
Concrete is prone to cracking due to the early age volume deformation under restrained conditions. Early-age cracking is the result of a complex interaction between various phenomena or properties of concrete [1], mainly including the autogenous shrinkage, drying shrinkage, thermal deformation, creep, elastic modulus, tensile strength, etc. The early age cracking of cement-based materials in the ring tests mainly resulted from the stress caused by the (autogenous and drying) shrinkage. Invented a variable restraint frame device to investigate the viscoelastic behavior of concrete under restraints to the drying shrinkage deformation With this test method, the elastic strain, tensile creep and tensile stress induced by restrained shrinkage and elastic modulus of the early age concrete could be assessed simultaneously [4]. The results of this study could reveal the main cause of the early age cracking of HPC structures and could provide guidance for the proportion design of HPC from the point of view of cracking potential.
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