| Concrete located in the coastal and offshore engineering structures are usually subjected to the coupling effects of various loads and harsh environmental conditions.In addition,within a short time,the loads may sometimes reach up to 60 percent of the ultimate load,or even higher.The transport of water and aggressive ions(e.g.chlorine salt,sulfate,etc.)in concrete is always important to investigate the durability of concrete.In general,the damage of concrete caused by the coupled action of environment and load is an important factor to affect the durability and mechanical properties of reinforced concrete structures.In this process,the ingress of water plays an important role in the performance deterioration of concrete structures.This is because water is regarded as the main transport carrier for chlorine ion,sulfate ion and other aggressive media into the concrete interior to cause the corrosion of steel bar and deterioration of concrete.Although the time of some loads,such as the extreme wind,wave,ocean current and overload vehicles is short,it may cause the severe damage of structures.On one hand,it is able to affect the safety of structures;on the other hand,the cracks within concrete due to the overload action will form a large number of migration channel,accelerating the transport speed of water and chloride ions and reducing the durability of concrete.For the marine concrete structures in service,it has the important theoretical value and engineering guiding significance to investigate mass transport mechanism of concrete subjected to the short-term overload action for accurately understanding the durability of concrete,reasonably predicting the service life of concrete structure,and ensuring the safety of structures.It has important.Based on this,the experimental research and mesoscale numerical simulation of mass transport properties of concrete under short-term sustained high compressive stress were conducted in this study.The influence of compressive stress level and sustained loading time on the behavior of water penetration into concrete was further analyzed.The mesoscopic lattice model of mass transport in damaged concrete after short-term high compressive stress was established.This model was used to simulate the process of water transport in concrete and its profiles of penetration depth.The distribution of water content and chloride concentration in damaged concrete after loading was predicted by means of theoretical analysis.The main research contents and conclusions are as follows:(1)The test setup of capillary water absorption by concrete was designed based on the principle of the connecting device,which was used to conduct the experiment of capillary water absorption of hollow cylinder high-strength concrete specimens subjected to short-term compressive load(60%,70% and 80% of the ultimate strength of concrete,respectively).The axial and circumferential strains of concrete during the process of loading were measured in real time.The damage variable within concrete was defined by the change of volumetric strain to develop the relationship between the performance of capillary water absorption and compressive stress levels,aiming to obtain the influence of compressive stress level and loading time(0.5h and 1h)on the behavior of capillary water absorption.The experimental results indicate that the curves of the amount of capillary water absorption and absorption time for concrete specimens in the studied range of compressive stress levels show the trend of bilinearity variation.When the value of stress level is in the range of 60%-80%,the performance of capillary water absorption by concrete gradually increases with the increase of the compressive stress level and with an increase of loading time.When the stress level is greater than 70%,the effect of loading time on water absorption is more obvious than that of stress level.(2)The theory of capillary water absorption was adopted to develop a theoretical model,which is used to describe the water transport in damaged concrete after loading.At the mesoscopic level,it is that the damaged concrete is assumed to be a kinds of four-phase composites,which is composed of mortar,aggregate,interfacial transition zone(ITZ)and microcracks.The technology of the Voronoi division was used to establish a two-dimensional lattice network model of damaged concrete for simulating the process of water penetratin into concrete.The comparison between numerical simulation and experimental results shows that the mesoscale simulation of water transport in concrete under the short-term high compressive stress was reasonably verified.The distribution cloud chart of water content within concrete could be obtained,and indicated that when the compressive stress level is more than 60%,not only the sorportivity of concrete and penetration depth gradually increase with the increase of stress level.(3)Based on the unsaturated fluid theory,the hydraulic diffusion coefficients of concrete described in the form of exponential and power function were respectively used to predict the the distribution of water content and penetration depth in concrete subjected to the short-term high compressive stress.The prediction results of water content distribution were further adopted to predict the chloride profiles in concrete damaged by short-term high compressive loading.The comparison between them validated the accuracy of model.The results show that there is little difference between the predicted water distribution and the measured waterdistribution.The experimental results of chloride concentration distribution were higher than the predicted results at the surface depth and lower than the predicted results at the deeper depth. |
