Durability Research Of Service Concrete

The issue is from the National Science Foundation project "durability of concrete in service", grant No.:51068023.As known to all, durability of concrete is restricted by three factors:first, quality of materials; second, pore structure; third, corrosion agent. Now the method to test concrete durability was only established on materials. The factors of quality of materials and corrosion agent can be agreed with practice, however, pore structure is not corresponded to actual. In fact, concrete must be accepted load. Pore structure endured load will happen great variety. So concrete durability tested by material maybe cause a great difference with actual concrete.To solve the test problem of durability of concrete accepted load, the first thing to solve is how to simulated concrete on loading at laboratory, which made the pore structure of concrete test specimen corresponded to concrete in actual using, and can be easy to solve durability test problem. Therefore, the subject has provided a detailed study about loading manner and loading system, using loading-unloading cycle for the load method. This program has made detail research on loading manner and loading system on test specimen. The loading system:loading and unloading speed is set at 0.5MPa/s. the constant time is set at 120s, loading-unloading cycles to 3 times. Upon examination, the test specimen after unloading nearly has retained the original pore structure.Besides, the relation of pore structure of service concrete and stress level has been concluded. Concrete pore structure relation characteristic parameter and distribution of pore size has been tested by mercury intrusion method. As stress level increasing, porosity first decreases and then increases. Once stress level attained 40%, harmful pore is increasig. The result shows that relative to the "pure material" concrete, concrete pore structure of the state service has changed.The property of carbonation resistance of service concrete was studied, and it's law has been ascertained. The result indicates that carbonation resistance of service concrete is probably only 80% of the "pure material", and concrete of different strength levels from 40%～60% stress level, the property of carbonation resistance is nearly the same. Beside, author has predicted carbonation model of service concrete, carbonation influence coefficients is as follows:Kσ= 1.0-0.3088σ+0.7384σ(C20), Kσ=1.0+0.5574σ+0.9219σ2 (C40), the carbonation depth prediction model is D=KtKRHKCO2 KσKC(?), the error rate is smaller than 5%.The research result has laid a solid foundation to more accurately design and estimate the life of concrete structure.