| There is a large amount of unhydrated cementitious material in concrete with low water-to-binder ratio.These unhydrated cementitious materials can continue to hydrate after being exposed to water.During the service of a concrete structure,the hydration reaction between the internal unhydrated cementitious material and external water is called the rehydration reaction.Rehydration has a significant effect on the long-term mechanical properties and durability of concrete structures and needs to be paid more attention.In order to study the effect of rehydration on the performance of damaged concrete,the uniaxial compression test was carried out to get the concrete damaged,and then the rehydration test of damaged specimens were carried out considering the factors such as loading degree,rehydration environment,fly ash and steel fibers.The effect of rehydration on the mechanical properties,water absorption characteristics,and hydration degree of the damaged concrete was analyzed.The main work and conclusions of the paper were as follows:(1)The influence of compression loading degree on the performance of C60 high performance concrete(C60),reactive powder concrete without steel fiber(RPC-0),and reactive powder concrete with 2%volume fraction of steel fibers(RPC-2)was investigated.The results showed that different concretes had different sensitivity to the load history,and the compressive strengths of C60,RPC-0 and RPC-2 began to deteriorate when their loading degree reached 30%,90%and 100%respectively.Preloading had different damage degree to different concretes.When the loading degree was 70%,the damage degrees of splitting tensile strength of C60,RPC-0 and RPC-2 were 28.47%,12.92%and 6.22%respectively.The tensile property was more sensitive to the load history than the compressive property.The damage degree of splitting tensile strength was 6.5 times of the compressive strength for C60 with 50%loading degree.(2)The simulated rehydration test using 30℃ water was carried out on the damaged concrete.The results showed that for concrete with little initial damage,rehydration damaged it first and then repaired it;for concrete with serious initial damage,rehydration repaired it first and then injured it;but for concrete with more serious initial damage,rehydration repaired it continuously.After 90 days of rehydration,the compressive strength of RPC-2 specimens with 100%and 2×100%loading degree increased by 20.02%and 33.95%respectively,and the compressive strength recovered to the state of non-destructive specimens.(3)The effect of rehydration on the water absorption characteristics and bound water content of the damaged concrete was studied.The results showed that the total capillary water absorption and capillary water absorption coefficient of C60 first decreased and then increased with the increase of rehydration time,but the total capillary water absorption and capillary water absorption coefficient of RPC showed a downward trend.The bound water content of damaged concrete increased with the increase of the rehydration time,and the higher the loading degree was,the greater the bound water content was.The bound water content of RPC-0 with 0%、50%、70%and 90%loading degree after 90 days rehydration increased by 9.09%,11.15%,13.08%,and 16.94%,respectively,compared with the value that before rehydration.(4)The effects of rehydration environment,fly ash and steel fibers on rehydration were studied.The results showed that the rehydration effect in the 30℃ water environment was most significant among the five rehydration environments(sealed,50%humidity,70%humidity,30℃ water and wet/dry cycle).Fly ash helped improve repairing effect of rehydration,and the long term strength of concrete with fly ash was higher.Steel fibers inhibited the destructive effect of rehydration on concrete. |
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