Comparison of Currently Used Prediction Models for Creep and Shrinkage of Concrete

Abstract

Time-dependent deformation of concrete may be dependent or independent of stress. Stress-dependent strain is called creep. These strains are defined as the difference between the increases in strain at the time of a specimen exposed to constant stress and strain sustained independent of load measured on the unloaded specimen. The creep depends on the material properties of the concrete components and the properties of the surrounding environment. It may be considered proportional to the volumetric share of the cement paste. Increases with increasing capillary porosity, with an increasing water ratio. Decreases with increasing age of the concrete at the time of introduction of load. Thin concrete elements takes shape more quickly because they are subject to rapid loss of moisture. [1] The same physical processes influence associated phenomenon called stress relaxation. Relaxation stress is the stress drop with time at constant deformation. Deformation not depending on stress is called the shrinkage (or swelling that occurs at a relative humidity greater than 95%). Shrinkage can be divided into two components, on autogenous and shrinkage of drying out. Autogenous shrinkage is related to chemical changes in hardening concrete. It arises due to the volume reduction during the hydration of cement, i.e. volume of the hardened cement paste is less than the volume of cement and water prior to the start of a chemical reaction. Shrinkage of drying is affected by loss of water in the concrete. The primary cause of the changes in capillary tension of pore system of hydrated cement paste and the change in surface energy due to the hydration products of changes in moisture content. Shrinkage is defined as the time-dependent change in volume of the concrete members, not subject to any external stress at constant temperature. Factors affecting shrinkage are concrete composition, density (strength) of concrete, ambient humidity, dimensions and cross-sectional shape and period of concrete curing of concrete [1]. Deformation of concrete can be divided according to several aspects listed in the table: