Research On Mechanism And Control Measures Of Early-Age Shrinkage Cracking For Long-span Prestress Concrete Box Girder Bridge

In this paper, the distribution and main causes of early cracks in long span PC box girder bridge is summarized,with regards to early age shrinkage cracking of Yu Zha Jin sha jiang River Main Bridge. The early shrinkage cracks are likely to appear in bridge construction, especially in the start segment and closure segment. Early shrinkage of High-strength and High-performance Concrete, the differences of age between segments and the concrete hydration heat effect are three important cause of box girder early shrinkage cracking. The Start Element diaphragm plate of box girder is the most prone to early shrinkage cracks. Cracks are usually characterized by vertical cracks.Due to the age of the concrete between different segments and the factors of temperature gradient, the web plate, roof and floor of closure segment, the possibility of the early shrinkage cracks are likely to appear in closure segment.Also in this paper, early shrinkage performance tests of high-strength concrete under dry and hot weather conditions in valley region. The results showed that, dry and hot weather conditions have great impact on early shrinkage performance of high-strength concrete, but this impact can be reduced by using conservation measures. Reasonable conservation measures can inhibit early shrinkage of concrete by delaying the drying shrinkage of concrete. In dry-hot valley weather conditions, drying shrinkage rate of high-strength concrete is very large in early age, and most of them can complete within60d.Early shrinkage cracks of long span PC box girder bridge can be controlled by reducing early shrinkage of concrete and improving the crack resistance of concrete.Preferably raw materials, optimize the mixing ratio, well-designed, reasonable construction, concrete early shrinkage cracking is reduced to a minimum.