| Because of the complex service environment,the erosion of concrete structures in the actual was not caused by a single erosion factors,the mechanism of mutual influence between the various erosion factors are also unclear.In this thesis,the durability of concrete under acid rain and freeze-thaw,acid rain and carbonization was studied,the effects of freezing-thawing and carbonization on the acidity of concrete were discussed thought designing the coupling erosion experiment.The influence of material composition on the durability of concrete under acid rain and freeze thaw and its related mechanism were studied.The life prediction model of concrete under acid rain-freezing thawing interaction was established by gray system theory.The main contents of this paper are as follows:(1)Effect of erosion system on the deterioration of durability of concrete.The performance degradation of concrete specimens under the five erosion systems of 4S,3S-T,T-3S,3S-D and D-3S were studied.Take the change of mass,compressive strength,dynamic modulus,neutral depth,water absorption as the main performance degradation indicators.The results show that the compressive strength and mass of the 3S-T and T-3S specimens are slower than those of the 4S group,but the depth of the neutralization is similar to that of the 4S group.3S-D and D-3S were not significantly different from those in the 4S group,but in the latter several cycles,the rate of deterioration of the strength loss,mass loss and dynamic modulus loss was much higher than that of the 4S group.The service life of concrete under the acid rain corrosion was improved about 25.4% to 26.7%,the effect of freezing-thaw on the erosion of concrete by acid rain is about 1.5;(2)Effect of mineral admixture on performance degradation of concrete under acid rain and freeze-thaw coupling.The effects of mineral admixture on durability of concrete specimen under acid rain-freeze thaw(3S-D)were studied.The results showed that: Compared with the pure cement group,when the content of fly ash is less than 20%,the performance rate of concrete specimen under the 3S-D erosion system is slower,and when the fly ash content is 30%,there is no concrete The anti-erosion ability of the specimen is higher,and the corrosion resistance of the K20 group is the highest when the slag content is 20%;The concrete specimen with gas content of 4.5% has better performance under 3S-D erosion environment.The content of CaO in the corroded area is greatly reduced,the amount of active components such as Al2O3 are also reduced;(CaO,Fe2O3,Al2O3)in the F20 and K20 group were higher than those in the pure cement group,indicating that the erosion rate of the K20 and F20 specimens was lower;The anti-acid corrosion ability of concrete was improved after adding fly ash and slag powder;(3)Using the GM(1,1)model,the acidification depth was used as the object of study to establish the time-dependent equation under the interaction of acid rain and freeze-thaw.The residual compressive strength coefficient when the thickness of the protective layer is 25 mm is calculated by GM(1,1)model,the residual compressive strength under different fly ash content The coefficient is between 47% and 52%,the compressive strength of concrete reaches the end of service life... |
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