Research On The Technology Of Quick Identification And Repair Of Cracks In Semi-rigid Base

The material of Semi-rigid base has been widely used as expressway pavement base in china,because of its perfect field performance.However,reflection crack frequently appeared in semi-rigid base poses a major threat to pavement quality and life.Traditional detection methods like sand replacement method and core-drilling method with their inefficiency and bad randomness,can damage the road.Therefore,new detection method has become the focus of researchers all over the world.Besides,the application of high-performance crack mending materials is of crucial importance to quick repairing of cracks in semi-rigid base in economic and social dimensions.This research aims at applying GPR and PFWD method simultaneously to identify cracks in semi-rigid base quickly,and determine whether the cracks need to be repaired.Meanwhile grouting material is researched and developed to repair the cracks in time.In the aspect of detection method of cracks depth in semi-rigid base,the cracks depth was evaluated by using GPR and PFWD.The results show that:(1)The depth of cracks in semi-rigid base cannot be evaluated by GPR for reasons of complex road structure,small width and large depth cracks,low frequency of GPR antenna.(2)In combination with the range of action of the PFWD and the deflection value difference between the center of the crack and the maximum deflection,the depth of the crack can be evaluated effectively.In the aspect of crack repair material,the polymer modified sulphoaluminate cement with fly ash and admixture was used to repair the cracks,which was designed according to rheology principle.The main conclusions are as follows:(1)The stress control mode can accurately measure the static yield stress of the slurry,and the smaller the container,the rheological behavior of the slurry will be more accurate;(2)By studying the influence of the static yield stress of crack repair material of the water cement ratio,dosage of fly ash and polymer,the water cement ratio,fly ash content and polymer content range of polymer modified high performance cracks repair system are determined,which are 0.57-0.63,10%-20%,4%-8%,respectively;(3)Because the compatibility of sulphoaluminate cement and superplasticizers is different,combined with the slurry natural sedimentation model,the yield stress ratio of the slurry under different height(yield stress coefficient)was used to evaluated the compatibility of sulphoaluminate cement and superplasticizers.By comparing the yield stress coefficient of 2651,1641,FK,s-400 and p-295,the superplasticizer of FK has the best compatibility with sulphoaluminate cement.(4)The influence factors of polymer modified high-performance crack repair materials on workability,mechanical properties and the influence of long-term performance were researched through orthogonal test,and the best ratio of polymer modified rapid hardening cement grouting material was determined for 0.57 of water cement ratio,10% dosage of fly ash,6% of polymer,0.03% of superplasticizer;(5)The verification results show that this optimum formula had better performance,initial fluidity 11 s,setting time 1.5h,bond strength of 3d 2.3MPa,contact angle42°,respectively.