Research On Ultrasonic Testing Of The Quality Of Early-age Concrete

The setting time of concrete has a great effect on work performance, control of construction process and durability of concrete. It is an important matter to quality concrol of early-age concrete.Therefore, it is of great significance in project application to exactly test the setting time of concrete.Ultrasonic testing of the quality of early-age concrete is mostly investigated in this dissertation. The hardening and structure forming process of concrete is discussed. Based on various nondestructive testing techniques presently applied to quality control of early-age concrete at home and abroad, monitoring of the setting and hardening of early-age concrete by ultrasonic method has been proposed. Wavelet analysis is used to eliminate the noise of the ultrasonic signals.With dynamic monitoring of the setting and hardening of early-age concrete by ultrasound, four samples of common concrete with different additives and a sample of RCC are tested and the graph describing the change of acoustic parameters with age is made, in which corresponding relationship between the feature point of acoustic parameters and state transform point of material is set up which can hardly be realized by traditional penetrometer test. By analyzing the graph, 'three folding line' is brought forward to describe the rule of change and to get the setting time of concrete. The setting time decided by ultrasound is more accurate than that decided by traditional penetrometer test. The successful application of the ultrasonic testing has provided a new research method that will promote the study on the performance of early-age concrete.A more suitable elimination noise method is put forward by comparing to three different methods. After eliminating noise, Signal-to-Noise has been greatly improved. Both the first signal of ultrasound which is obviously becoming clear and the graph of signal which is becoming smooth are useful to distill correlation acoustic parameters of the ultrasonic signal. So the wavelet analysis has good prospect in the ultrasonic testing of early-age concrete.At the end of the dissertation, the characteristic and existing problems of the application of ultrasonic method and wavelet analysis to the early-age concrete nondestructive detecting are analyzed. Further problems which needed to be studied are listed.