| Based on Rayleigh wave technique,the wave field response characteristics of cracked concrete are studied in this paper.Firstly,various types of real concrete cracks are prepared by fine crack making technology and grouting technology at the upper part of cracks,and they are repaired by epoxy resin grouting.After each repair,the wave field data are obtained by ultrasonic testing system,including surface wave velocity,amplitude in time domain,amplitude in frequency domain,main frequency change and energy change in low frequency and high frequency.Secondly,the feasibility of using different materials as simulated cracks in concrete is discussed,and the wave field response of cement mortar upper repair is studied by using quantitative simulated cracks made of copper and PTFE.Finally,the location of invisible cracks on the surface is simulated.The results show that the amplitude of Rayleigh wave increases at different speeds in all kinds of cracks,but with the increase of repair times,the amplitude energy of all kinds of cracks is restored to more than 80% of the level of intact samples after repair.It is found that the measured wave field scattering can also be used to evaluate the repair effect of real cracks,and the repair effect is determined by CT system,which forms a good correspondence with the wave field response characteristics.For repairing the simulated cracks on the upper part of mortar,five kinds of repairing conditions,namely 0%,25%,50%,75% and100%,were studied in detail.The transmission coefficient recovered to 0.72 when repairing25%,and completely recovered when repairing 100%,which formed a good correspondence between the repairing conditions and Rayleigh wave field response.In addition,the direction and scale of invisible cracks on the surface are determined by the change of transmission coefficient.In previous experiments,simulated cracks are often used to study the repair effect.This experiment proves that the simulated cracks with shallow depth and large opening are not sensitive to the wave field response of repair.At the same time,various concrete cracks are made by using the concrete real crack making technology,and some repair conditions of real cracks are studied for the first time,including vertical single cracks,vertical double cracks,inclined cracks,dip cracks and upper repair cracks.Their repair conditions have obvious effects on Rayleigh wave propagation,and the wave field response increases with the repair times.In addition,a simulation experiment is carried out for another typical repair method in practical engineering,namely mortar repair.The repair situation corresponds well with Rayleigh wave,and the evaluation of engineering crack repair is studied in many aspects.In practical engineering,the repair of internal cracks can be quickly understood by comparing the wave field response difference between the crack repair survey line and the intact survey line after the crack position is determined.This study provides some theoretical guidance for the evaluation of repairing effect of concrete cracks. |
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