The Theory And Control Technology Of Shrinkage Cracking At Early Age Of Concrete And Application In Bridge Engineering

The shrinkage and cracking problem of concrete bridge decks and beams at early age were given widespread concern in bridge engineering.Cracks in concrete bridge structures reduce overall durability by allowing the penetration of water and aggressive agents, thereby accelerating the deterioration of the reinforcing steel.So it is very important to prevent or delay the shrinkage and cracking of concrete bridge decks and beams at early age.In concrete bridge engineering, the cracking mechanism at early age is very complex and synthetical.Many factor such as structural design, construction methods, environmental condtions, raw material selection, mix design, additive and admixtures all impact the the generation and development of early age cracks from different angles and in varying degree.In this paper, author study deeply the theory of concrete shrinkage and put forward that the main influencing factors of early age crack are material stiffness,shrinkage value,shrinkage rate and creep relaxation.In theory,when concrete is prevented from shrinking freele,tensile stresses develop exceeding the material resistance result in cracking.The material resistance and tensile stresses at early age is constantly changing over time,and the variation is closely related to the degree of hydration of concrete.In this paper, the large-scale experimental on various strength grade have been done and a new prediction model of early-age strength and elastic modulus were proposed. Models are universal applicability and provide good prediction of the development of mechanical properties of concrete structures in aging; Author studied the dynamical theory of hydration of concrete and proposed the prediction model of degree of hydration; The mechanism of autogenous shrinkage was been studied and proposed the new prediction model of autogenous shrinkage model of concrete, and experimental results showed that the calculated values and experimental test results had good consistency;Afracture mechanics modeling approach was developed to predict the behavior of restrained concrete specimens.A favorable correlation was observed between the prediction of the fracture-based model and experimentally results observed by amended restrained shrinkage ring test.This modeling approach developed a new way to theoretically explain the relations between cracking propagation and aggregates embedded, size effects and geometric shape.Three-dimensional nonlinear finite element simulation was been done to study the developing law of thermal and shrinking stresses of bridge massive concrete in construction,it provides the reference for control the crack of bridge massive concrete in construction.Early drying shrinkage cracks of concrete were tested by slab drying experiment. This paper studied the influence of shrinkage reducing agent, expansive agent, polypropylene fiber and steel bars on early drying shrinkage cracks of concrete, and probed the method of prevention of the early cracking of concrete bridges.