Research Of Technology Of Reparation And Cause Of Concreted Freeze-thaw Damage About Port Structures

The number of China's port infrastructure now ranks first in the world,most of which facilities are the concrete structures.In frozen area,freezing and thawing action is the one of the main reason of concrete destruction.At present,in order to improve the construction efficiency and carrying capacity,new materials and structures are used in the engineering construction.Among them,the PHC pile has been applied for its rapid and standardized production procedure and high strength.However,for the studies of the frost resistance of PHC pile,it is concluded that the results are different,limiting the application of PHC pile.In addition,the existing concrete structures appear to more freeze-thaw damage.There is little research on the repair methods about concrete's freeze-thaw damage,especially on the durability of concrete after reparation.Therefore,it is of great practical significance to study the reparation and reinforcement of the freeze-thaw concrete and the frost resistance of PHC pile,which solves the freeze-thaw damage of concrete in the frozen area and guides the maintenance of wharf facilities.The main contents are summarized as follows:1.The freezing and thawing condition of the concrete structure in Tianjin Port is investigated,and the method of qualitative judgment and quantitative detection of concrete's freeze-thaw damage is established.It is found that the material,stress state and environment of concrete are the three main factors affecting the frost resistance of concrete.2.Considering the temperature,stress and seepage field,the freeze-thaw cycle is simulated by Comsol Multiphysics software.During the freeze-thaw cycle,The first and third principal stresses of the concrete have high peak values,which causes damage to the concrete.3.Ultra high toughness cementitious material(UHTTC)or penetrating crystalline material(CCCW)were used as repairing and reinforcing technology in the freeze-thaw damage of concrete with CCCW as the interface agent.Comparing the specimens which was repaired and reinforced by UHTTC and CCCW after rapid freeze-thaw experiment,we tested the splitting tensile strength,mass loss rate and relative dynamic elastic modulus of the specimens.The test result showed that after 125 freeze-thaw cycles,the mass loss of repaired specimens with UHTTC and CCCW were both less,the loss rates of the splitting tensile strength were both less than 30%,and the repairing effects were both good.4.Under the consideration of the components,molding and curing process of concrete,the frost resistance of PHC piles is investigated based on strength index.Besides,the simulation on the cooling of PHC piles is also performed with Abaqus.It is indicated that the centrifugal process,steaming curing with adding silica fume and autoclave curing will significantly contribute to the strength and frost resistance of concrete.Moreover,the simulation indicates that the frost resistance of PHC piles is poor even with double autoclave curing when the tensile stress of concrete is more than 7MPa during the unreasonable cooling process.