The Research On Control Of Concrete Early Cracks In Cantilever Pouring Segment Of Continuous Rigid Frame Beams

Most of the continuous rigid frame beam adopts cantilever pouring construction method,which is limited by the working face,it is difficult to carry on the curing to the outer webs and bottom surface of the frame beam rationally and effectively,and the early performance is different from ordinary concrete because of the change of the composition of the high performance concrete.A large number of continuous rigid frame concrete beam bridges have appeared in the construction process,especially the outer webs of the box and the bottom of the bottom plate,which has caused great harm to the structural durability.It is very important to find the occurrence and development regularity of early crack in continuous rigid frame beam to prevent the early crack to deal with it effectively after its appearance.This article investigates and analyzes the causes of early cracks in continuous rigid frame beam and their research status.On this basis,Combined the technology research and development project of “Research on Control of Concrete early Cracks in Cantilever Pouring Segment of Continuous Rigid Frame Beams of Wanli Expressway” test data,analyzing the effect of admixture,mold-laying and environment parameters on the early performance of concrete,fitting curves of shrinkage,creep and elastic modulus of concrete with age are fitted with finite element method suitable for temperature field conduction theory.using the finite element software establish a concrete entity model of two adjacent sections of the frame beam of the Longju Bridge,and analyzing the temperature and shrinkage stress under different conditions,proving the rationality of compound curing method.Specifically carried out the following work:(1)Researching on the existing non-structural cracks in continuous rigid frame beam in our country,analyzing the reason from construction,management,and curing,etc.,and summarizing the causes of early cracks in frame beams.(2)Basing on the early performance requirements of concrete,study the impact of concrete of aggregate grading,dosage of cement material and fiber properties,and considering the concrete workability,strength and economy,and combining the design requirements to determine the C55 frame beam Concrete mixture ratio.Through experiments,analyzing the effects of admixtures,mold-laying and environmental parameters on the early performance of concrete;(3)According to different material empirical formulas and measured data,fittng curves of shrinkage,creep and elastic modulus of concrete with age;using the finite element software Midas/Fea to establish a concrete model of two adjacent sections of the frame beam of the Longju Bridge,and analyzing the temperature and shrinkage stress under different conditions,proving the rationality of compound curing method;(4)Combining with the research results of the Ministry of Transport's western traffic construction science and technology project” Influence and Countermeasure of Fineness and Components of Cement on Properties of Concrete in Bridge Engineering”,,raw material selection-mix proportion optimization-composite curing applied in the Longju bridge,and evaluate the effect of its application?...