Research On Control Of Cracks During Concrete Construction Of Maanshan Yangtze River Highway Bridge

In modern society, with universal application of concrete technology, concrete structure cracks have been gotten more and more attention in engineering, which has become an important research direction in concrete structure. This paper is based on the western subject "The research of early cracks in the concrete shrinkage on Maanshan Yangtze River Highway Bridge". For the development of mechanisms of early cracks in concrete structures, the paper demonstrates that the early cracks in the concrete at present is mainly caused by concrete earlier shrinkage and temperature through theoretical analysis, experimental research and numerical simulation. Main contents in this paper are experiments on early shrinkage of concrete, experiments on hydrate heat of cement and simulation on hydrate heat of tower. It Sums up the laws of influence of the concrete shrinkage and hydration heat on the early cracks and suggests some improvements or suppression measures to control early cracks. The main work and research results are as follows:1) It explains that the early Concrete cracks in constructions mainly caused by early shrinkage and temperature through theoretical analysis. Then it introduces influences of early shrinkage and temperature on the Concrete cracks in construction respectively. Also it collects six shrinkage prediction models, and some early concrete thermodynamics formulas.2) Early self-made concrete shrinkage test apparatus for early shrinkage performance four concrete shrinkage test blocks were tested. Shrinkage strain of the test pieces is measured from the form removal to the age of 30 days. For concrete shrink the size of fly ash on shrinkage of concrete and reinforced concrete shrinkage suppression, pilot studies and theoretical analysis and experimental and theoretical values are compared to understand of early shrinkage of concrete deeply.3) To study the influence of hydration heat on early concrete shrinkage, the paper conducts a more systematic research. For this reason test hydration heat of cement and cement added fly ash, and draw the heat of hydration heat contrast ratio curves of cement sample, and based on the measured heat of hydration curve fitted to reflect hydration heat rate rise and fall lognormal law formula, fitting a lognormal distribution formula than the current number of existing empirical formula to better reflect the real exothermic heat of hydration.4) Bridge towers construction process ars simulated by ANSYS finite element software to identify the most unfavorable position of the structure. The pylon is divided into 41 segments of concrete, using ANSYS to simulate the bridge column construction process, observing the temperature and stress distribution segments each of the first three days, and to find the location most likely to occur cracks during construction segment.5) This paper collects construction method of the Tower of Maanshan Yangtze River Road Bridge. Studies are focused on temperature and humidity, reinforced protective layer thickness, template, removal time and conservation methods. According to the content of the discussion, It summarized some of the reasons leading to the cracks of construction,and proposes some control measures and recommendations.