Detecting Technique Research On Cement Concrete Slabs With Ultrasonic Method

At present,detection of the index of the strength and thickness of cement concrete slabs during construction and transportantion is accomplished through coring. However, this method has some shortcomings, including being destructive to some degree,slow, having poor performance, and so on. Furthermore, the position of coring must be restored in time, thus bringing about some potential quality problems.So it is in urgent need to deveop a fast and accruate method to evaluate the index of the strength and thickness of cement concrete slabs without causing any damage to them at the same time.Ultrasound is a popular and widely used method of measurement. It becomes the first choice of structure detection because it has advatanges such as having strong penetrating power,being convenient and fast. Penetrating method of ultrasonic directive wave is studied much in detection of structures or components having two or more planes. The research of it is comparatively mature because it can accurately identify the position of the takeoff point of directive longitudinal wave. However, there exist several problems including of minor precision, minor SNR and being different to identify takeoff of reflection wave,when index of thickness and strength of cement concrete construction with single detection surface are evaluated, so the paper carried out the relevant research.Firstly, because when ultrasonic flatting method is used to evaluate strength index of cement concrete, the precision of strength regression model of single parameter evaluation is rather low. In order to improve the precision of evaluation of cement concrete slabs with ultrasound, this paper carried out apply research on multi-parameter strength estimation model of cement concrete slabs with the strength level of C20, C25,C35 and C40. Other parameter also changes because physical property of medium changes in the course of sound propagation besides velocity, and this change should be considered in mathematical model. So the multi-parametric mathematical models were founded through theoretical analysis including velocity of sound, damping coefficiency I and compressive strength, velocity of sound, damping coefficiency II and compressive strenth, velocity of sound, damping coefficiency I, damping coefficency II and compressive strenth . By Comparing the relative index of single-parameter model with the statistics got by practical test of the preserved test modules, the accuracy of the estimation of the strength of the multi-parameter is relatively high. Research of the application of the strength model of multi-parameter in estimation of compresive strength of cement slabs is preliminarily carried out by making minor test slabs in full size with the stength levels of C20, C30, C35and C40 in the laboratary.Secondly, because there exist several kinds of noise when detecting cement concrete slabs with method of ultrasound which will result in lower signal noise ratio of ultrasonic signal if the method of filtering wave is not proper. Takeoff point of reflection wave was difficult to identify when thickness index of cement concrete slabs was detected with ultrasonic flatting method. So the paper carried out the research of the technique on signal filtering of multi-wavelet lifting scheme of cement concrete slabs with ultrasonic method. Basis wavelet of lifting scheme of multi-wavelet is made of conventional wavelet. Different single wavelet may be chosen according to the requirement of practical application. In the model, choosing several wavelets to lift, and incorporating syntheses method of threshold filtering, the research identified optimum basis wavelet on the basis of signal noise ratio and root mean square error. So application of signal denoising technique can be realized for cement concrete slabs of ultrasonic detection through lifting scheme of multi-wavelet.Finally, the takeoff point is hard to identify when the thickness of cement concrete is being evaluated with the method of ultrasound reflection. So this paper carried out the research of method of identifying the takeoff point of reflection wave. The paper adopted a two-phase method to identify takeoff point position of the first wave of reflection wave. This method is based on Huygens principle, incorporating the spreading nature of ultrasound, applying mathematical analysis and waveform analysis to verdict takeoff point position of the first wave of reflection wave, so its relevant acoustical parameter can be identified. Minor test cement slabs in full size of different strength levels, different thickness and for different road bases were poured in library to carry out apply research of the technique of identifying the takeoff point of reflection wave and have achieved relatively satisfactory result.Based on the above accomplishments and also with the support of the key project of the nation's science & technology supporting program(serial number: 2006BAJ18B05)of the nation's"the Eleventh 5-Year Plan", researchers carried out practical testing on Guizhou-zunyi expressway, during which thickness index of cement concrete slabs were evaluated. In addition, researchers also carried out contrast test of theoretical thickness and actual measuring thickness of the core. The result showed that evaluation precision was higher for cement concrete slabs with the method.