Research On Mechanical Properties And Non-destructive Testing Of Early-age High Performance Concrete Used For Bridges

High performance concrete is widely used in high-rise buildings, large-spanbridges and other projects due to its high workability, high durability, highdimensional stability and other characteristics. In modern construction project ofbridge especially its upper structure, concrete may be at earlier age usually whenthe prestressing steel tension because of project task is heavy and tight schedule.Concrete creeps will lead to increases when the prestressed tension elasticmodulus of concrete in a lower state, especially in the larger box girder spancontinuous rigid frame bridge and several years after the completion of the(operating time is much less than the design base period) produces scratch andcrack down beyond regulatory requirements, which will affect the safe operationand durability of the bridge. Currently, concrete strength and elastic modulusdual control is it required in the construction of the highway bridge upperprestressed concrete structures, in order to ensure the strength of the bridgestructure, job stability and durability. Therefore, there is great significance tostudy of evolution of concrete elastic modulus and compressive strength under different curing conditions and different ages.Under the auspices of the National Natural Science Foundation of China(51278325) and Shanxi Communications Department science and technologyprojects (2013-1-40), combined entity engineeringh used C55, C50high-performance concrete; the relevant studies are as follows:1. Through the the test to compressive strength and elastic modulus of highperformance concrete under standard curing conditions and curing conditionswith the conditions of early age (3d,5d,7d) and late age (28d,56d). Study itsvariation with age, the results showed that the concrete compressive strength,elastic modulus change with age with a certain regularity, and to establish thecorresponding regression model; there is large influence to the curing conditionson the mechanical properties of concrete development, the test results ofspecimens in Ca(OH)2saturated solution are larger than the specimen on shelfat standard conservation standard, and the specimen on standard curing largerthan the same curing condition, the specimen in summer and autumn samecuring condition larger than specimens in winter and spring.2. Through measure the value of concrete rebound and sonographic featuresat early age, then research on the relationship between the ultrasonic,reboundand concrete compressive strength and elastic modulus of concrete at differentages and different curing conditions, and established the correspondingestimation model, Analysis showed that the use of appropriate estimation modelunder certain conditions with high accuracy, and multi-parameter estimation model accuracy than single-parameter model.3. Application of X-ray CT scanning technology and mercury test on highperformance concrete at early age microstructure was analyzed to reveal itsinternal microstructure evolution with age, the results showed that the age ofgrowth, internal porosity of concrete, with the number of holes decreases, thesmaller the pore aperture gradually infill, concrete micro-structure tends tocompact.