The application of Sound wave CT nondestructive technique in the quality inspection of concrete

1. Fundamental principle of sound wave CT nondestructive test 

According to kinematics and dynamic characteristics of elastic wave ,elastic wave imaging method can be divided into two categories one is based on motion feature ray imaging ;second is based on dynamic characteristics wave equation imaging。

As ray tomography inversion of sound waves penetrate, its basic thought is according to sound wave ray geometry kinematics principle ,express traveling time that sound wave from launch point to receive point as detection area medium speed parameter line integral,then by line integral path do back projection to rebuild distribution image of medium speed parameter 。

Concrete sound wave CT nondestructive detection,is according to sound wave ray geometry kinematics principle,utilize  advanced sound wave launch、receive system, launch at the detected block,in another port to receive,use sound wave o scanning detected object,then make use of computer inversing imaging technique,present concrete sound wave speed of tiny unit range in detected object，and then make quality assessment to detect object。

2 witnessed inspection technique

Used for scene observing system is acoustic system,namely at one side to launch,the other side as sector array receive,then gradually synchronization along with section line to move to scan and observe。

Working layout should follow below rules ,launch or receive must respectively in same height,so as to form scanning profile,each launching point and receiving point must accurately measure coordinates;launching point and receiving point are below 0.4m,the distance between launch point and receive point should more than 8m so as to improve ray  density。 

According above rules ,we set ultrasonic launching array at X=20105m,altitudeis78m,75m,72mhorizontal,whenX=20095m,20092m,20092m horizontal straight line respectively set sound wave receiving array,forming three sound wave scanning profile,all sound wave CT information witnessed computer record and save。

Witnessed scene sound wave CT detecting device adopts advanced super magnetic material power sound wave emission source and DB4 sound wave collecting system.the system launch power can up to 1000W,launch system basic frequency is 8K,receiving system frequency is 1K,10k,sampling frequency is 8sets 20MHz ,Sampling interval is 10μs,measured time error lower than 1sampling interval n*10-4μs,repeatability is good。

Witnessed inspections strictly according to 《water conservancy and hydropower exploration procedures》DL-5010-92 standard to operate。

Due to bottom hook face and X=20105m  vertical plane present irregular corresponding form,generating sound wave launch has big difference with receiving angle,make receiving direction in converter diverge main energy area that ultrasonic launches,generating sound wave receiving energy is weak,so change direction of receiving converter to make receiving converter corresponding to acoustic main energy area launched by  launching converter 。

3  information dealing methods

3.1  information preprocessing 

Utilize DB4 sound wave collecting system at random configuration software,make wild collected sound wave full wave form signal redisplay on the computer screen，when it is made by human ,to make sure CT imaging quality,only these fluctuation is strong and clear ,head wave clear to read can be used。

In view of launching ,receiving distance of sound wave penetration is 0.4m,for making sure certain resolution ratio,can adopt 0.5m*0.5m network。

3.2 information dealing method  

tomographic algorithm:adopting ART  SIRT straight line algorithm to deal with information ,suppress negative factors that affect CT imaging ,for getting better image as ultimate goal。

3.3  the generation of graph

Utilize Auto CAD,MAPCAD and other software,producing CT  imaging

Sound wave dealing flow:pick up original longitudinal wave,edit CT imaging database,CT deal with VP database,AUTO CAD ,MAP CAD deal with、edit 、joint , images ,colored laser printer 。

4  application example

Nondestructive detecting result,they are 20-1/20-2/20-3profile CT imaging result,three profiles are concrete construction with different heights。

From 20-1profile can seen,whole wave speed value is high,bigger than 4300m/s occupies 90.75%,lower than 4000m/s just occupies 0.29%,wave speed distribution:left bottom and top right corner  is relevant low speed area,VP is around 4300m/s ,present banding distribution,other parts VP are bigger than 4500m/s。

Wave speed and its distribution feature is almost the same as 20-1 profile，the difference is,relevant low speed part is relative little,its distribution has no continuity。20-3 profile 。

The overall low speed abnormal area form is similar to 20-1.20-2 profile ,but relevant low speed area is less,and present distributed sporadically 。

From overall condition to see:above 3 profiles are similar,sound wave  compares to low speed area distribution position,corresponding is good,reflect this area concrete features:the profile sound wave of top level compare to low speed area is bigger and more,sound wave speed is low:middle layer profile sound wave low speed area is smaller and less,sound wave speed is relevant high;the lowest layer profile sound wave is smaller and less,sound wave speed is higher than up profile ,it states:construction bottom layer concrete condition is better,middle layer is second, upper layer is bad.

According to three gorges project decades concretes testing information ,complete concrete sound wave speed VP more than 4300m/s ,normally is 4500m/s,but concretes with regional slight flaw ,its sound wave speed VP value is 4000-4300m/s (relevant low)  if exists bigger flaw ,then VP value is lower.

Therefore ,we can directly clearly see from graph :1. Detected profile exists concrete compactibility size and its position,2. Profile concrete compactibility ,so as to assess on detected object.