Study On The Durability Of Cement Concrete Quickly Repaired Pavement

Much attention has been attracted to the research on the quick repairing material of cement concrete pavement.Although there are many repairing materials at present,the durability of materials and the durability of repairing systems are seldom studied,which affects the application and promotion of repairing cement concrete.Therefore,this paper focuses on the durability of fast repairing cement concrete and fatigue bond durability of repairing system.Firstly,according to the characteristics of repairing materials,the raw materials of cement concrete for rapid repairing are determined.The proportion of sulfoaluminate-silicate composite cement system and the types and amount of additives were determined by experiments.By means of orthogonal test method,the mix proportion of fast repairing cement concrete is optimized,and the reference mix proportion is finally determined.Its flexural strength in 4 h is over 4.0 MPa after optimization.Secondly,this paper studies the durability of repairing concrete itself.Through the analysis of the macroscopical indexes,such as dynamic modulus of elasticity,mass loss,and surface loss of salt frost,the influence of different ratio on frost resistance performance was clarified.The results show that the frost resistance of the rapidly repaired concrete can be improved obviously by the addition of air-entraining agent,which can increase by up to 125%.With the same gas content,silica fume content of 2.5%showed the best frost resistance.The microstructure mechanism of freezing-thawing was analyzed by NMR scanning system.It is found that the damage process is actually the process of pore structure change.The T₂spectrum of 150 freeze-thaw cycles was analyzed.After freeze-thaw cycles,the area of T2 spectrum changed by 124%.The effects of silica fume content and air content on chloride ion permeability and shrinkage resistance were analyzed.When the silica fume content is 7.5%,the lowest 6 h electric flux is 732C.When the gas content is 5%,the minimum shrinkage is 140 um/m.The correlation analysis of durability evaluation index was carried out.Based on the entropy weight method,a comprehensive durability index is proposed as a durability evaluation parameter.The durability of the mixtures was evaluated by irrelevant characteristic indexes.It is found that the comprehensive durability index of the typical mix ratio is 0.9402,which is 2.4 times higher than that of the same grade concrete.Then,the bond performance analysis method of the repair system is designed and studied.It is found that the bond strength of new and old concrete is affected by the treatment method of bond interface,repair mode,mix ratio and freeze-thaw cycles.The splitting bond strength can reach 2.4 MPa and the flexural bond strength can reach 4.3 MPa.It is found that the air entraining agent can not only improve the frost resistance of the repaired concrete itself,but also reduce the bond strength loss of the repaired system after freeze-thaw cycles,whose contribution is significant,about 50%.Finally,the life of the repair system under the coupled conditions of freeze-thaw and fatigue load is studied.It is found that the semi-logarithmic S-N curve can well fit the expected life,and its correlation coefficient is above 0.98.Under the same stress level,the curves of materials before and after freezing and thawing are similar.Under the same stress,the fatigue life before freezing and thawing is higher than that after freezing and thawing.The life under each stress level obeys Weibull distribution,and the P-S-N curve with 95%guarantee rate is obtained.