Influence of Sustained Load on Durability and Service Life of Reinforced Concrete Structures

摘要

The influence of an applied high compressive load on strength of concrete has been studied both theoretically and experimentally in great detail in the past. It was observed that load bearing capacity of concrete decreases under the influence of sustained compressive stress. In this contribution the influence of high sustained compressive stress on capillary absorption and on chloride penetration will be described. It was found that under the influence of moderate sustained compressive load the amount of capillary absorbed water decreases. If the sustained compressive load overcomes 50 % of the material's strength, the rate of capillary absorption increases. This fact can be explained by reduction of the pore space under moderate compressive stress and formation and time-dependent growth of micro-cracks in the composite structure of concrete. Dissolved chloride is filtered out of the aqueous salt solution and remains accumulated in a surface near layer. In this way a high concentration difference of chloride is built up in a short time. This gradient leads to long lasting diffusion of chloride deeper into the pore space. As the diffusion coefficient of dissolved ions in the pore liquid increases with increasing applied compressive load, service life of structural elements under high compressive load will be reduced significantly when exposed to aggressive environment. This fact has to be taken into consideration if service life of reinforced concrete structures is to be predicted in a realistic way.