Highway PC Bridge Inspection by 3.95 MeV X-Ray/Neutron Source

*Mitsuru Uesaka, Katsuhiro Dobashi, Yuki Mitsuya, Jian Yang and Joichi Kusano*

#### **Abstract**

We have developed portable 950 keV/3.95 MeV X-ray/neutron sources and applied them to inspection of PC concrete thicker than 200 mm within reasonable measuring time of seconds - minutes. T-girder-, Box- and slab- bridges are considered. Now we are to start X-ray transmission inspection for highway PC bridge (box) by using 3.95 MeV X-ray sources in Japan in 2020. By obtaining X-ray transmission images of no-grout-filling in PC sheath and thinning of PC wires, we plan to carry out numerical structural analysis to evaluate the degradation of strength. Finally, we are going to propose a technical guideline of nondestructive evaluation (NDE) of PC bridges by taking account of both X-ray inspection and structural analysis. Further, we are trying to detect rainwater detection in PC sheath, and asphalt and floor slab by the 3.95 MeV neutron source. This is expected to be an early degradation inspection. We have done preliminary experiments on X-ray transmission imaging of PC wires and on-grout-filling in the same height PCs in 450–750 mm thick concretes. Moreover, neutron back scattering detection of water in PC sheath is also explained.

**Keywords:** on-site bridge inspection, highway PC bridge, 950 keV/3.95 MeV X-ray sources, 3.95 MeV neutron source, non-grout-filling, PC wires thinning, rain-water-detection, structural analysis, guideline of nondestructive evaluation

#### **1. Introduction**

Since PC (Pre-stressed) bridges were first constructed, about 40 years has passed. Then, the degradation and problems such as no-grout-filling, rail-waterinvasion, corruption, thinning and disconnection of PC bridges has revealed and been detected. In these tens years, several nondestructive and destructive evaluations have been performed. Depending on the seriousness of degradation, a few PC bridges are under reconstruction and its planning. So far, they have mainly used inspection by eyes and hammering. However, it is very hard to evaluate the problems and degradation of PC by the above methods. There are non-destructive methods to check PC such as ultrasonography, radar, X-ray transmission by X-ray tubes (200– 400 kV), magnetic field detection, etc. But, practically it is difficult to evaluate PC in thicker concrete than 200 mm. We have developed portable 950 keV/3.95 MeV electron linac (linear accelerator)-based X-ray / neutron sources and applied them to inspection of PC concrete thicker than 200 mm within reasonable measuring time of seconds – minutes more than 10 times so far [1–4]. Major poor-construction and degradation of PC bridges to be detected by X-rays and neutrons are unfilled grout,

rainwater intrusion, corrosion and thinning and disconnection of PC wires. Unfilled grout and thinning and disconnection of PC wires can be measured by difference of X-ray attenuation coefficient by X-rays. The three types of the PC bridges and locations of X-ray/neutron source and detector are depicted in **Figure 1**. As for highway bridges, concrete vertical WEB wall is thick as 450–1,000 mm.

There are of course many nondestructive evaluation (NDE) methods to try to detect poor construction such unfilled grout in PC sheath and degradation such as thinning and disconnection of PC wires. RADAR, ultrasonic testing, magnetic testing, 200–400 kV X-ray tube, etc. are candidates as shown in **Figure 2**. However, they are available for thinner concrete than 200 mm. On the other hand, 950 keV / 3.95 MeV X-ray sources can be used for transmission testing for thick concrete of 200–400 mm and 200–1,000 mm based on the calculation and our experience so far [1–4]. We think that only the 950 keV/3.95 MeV X-ray sources can enable transmission imaging of PC structures in 200–1,000 mm thick concrete within minutes.

**Figure 3** summarizes major poor construction of unfilled grout, early degradation such as rainwater intrusion and finally serious degradation of thinning and disconnection, and suitable NDE methods and successive structural analysis. If there is unfilled grout in PC sheath, rainwater may intrude from the edges and is stored there. Then, the rainwater makes PC wires and sheath wall be corroded. Volume expansion of PC sheath due to corrosion and oxidation induces cracks in near concrete. The cracks gradually become larger and reach the concrete surface, When the sheath wall is broken, the rainwater exude out and intrude into concrete and surface. As the corrosion is enhanced, superficial oxidized iron leaves and thinning of PC wires occurs. Even, the disconnection may happen since the wires are tensile. Among the above temporal change of state, the structural changes such as unfilled grout and thinning/disconnection of wires can been detected by X-ray transmission imaging. On the other hand, material property change such as rainwater intrusion can be detected by neutron scattering in water. Since concrete vertical WEB wall is thicker than ~450 mm, 3.95 MeV X-ray source is appropriate with respect to transmission ability. Iron components of PC such as wires can be clearly seen with good contrast to concrete. Their thinning and disconnection are observed with the spatial resolution of 1 mm. Since tension is added to PC wires at its construction, they tend to be attached to the upper wall of PC sheath. Therefore, unfilled grout should be recognized under PC wires with certain change of contrast. Measured flaws such as unfilled grout and thinning/disconnection are inputted to structural analysis described in Chapter 5. Thus, initial poor construction of unfilled grout and serious thinning and disconnection of PC wires are diagnosed and then their affect to

**41**

**Figure 3.**

**Figure 2.**

*Highway PC Bridge Inspection by 3.95 MeV X-Ray/Neutron Source*

lack and degradation of strength is quantitatively evaluated by structural analysis. Finally, maintenance, repairing and reconstruction are planned. Moreover, there is a possibility to detect rainwater intrusion inside PC sheath by portable 3.95 MeV

*Poor construction and degradation of PC bridges, suitable NDE methods and structural analysis.*

*Advantage of 950 keV/3.95 MeV X-ray sources over other NDE methods for thicker concrete than 200 mm.*

We use X-band (9.3 GHz) linac based 3.95 MeV X-ray sources for the inspection of the actual bridge [1–3]. The systems are shown in **Figure 4**. The electrons are accelerated up to 3.95 MeV by radio frequency (RF) fields. We also adopted the side-coupled standing wave type accelerating structure. Electrons are injected into

neutron source [5], which is discussed in Section 3.2.

**2. 3.95 MeV electron X-ray/neutron sources**

*DOI: http://dx.doi.org/10.5772/intechopen.96959*

**Figure 1.**

*On-site X-ray/neutron inspection by 3.95 MeV system for three types of highway PC bridge.*

*Highway PC Bridge Inspection by 3.95 MeV X-Ray/Neutron Source DOI: http://dx.doi.org/10.5772/intechopen.96959*

#### **Figure 2.**

*Computational Optimization Techniques and Applications*

bridges, concrete vertical WEB wall is thick as 450–1,000 mm.

*On-site X-ray/neutron inspection by 3.95 MeV system for three types of highway PC bridge.*

rainwater intrusion, corrosion and thinning and disconnection of PC wires. Unfilled grout and thinning and disconnection of PC wires can be measured by difference of X-ray attenuation coefficient by X-rays. The three types of the PC bridges and locations of X-ray/neutron source and detector are depicted in **Figure 1**. As for highway

There are of course many nondestructive evaluation (NDE) methods to try to detect poor construction such unfilled grout in PC sheath and degradation such as thinning and disconnection of PC wires. RADAR, ultrasonic testing, magnetic testing, 200–400 kV X-ray tube, etc. are candidates as shown in **Figure 2**. However, they are available for thinner concrete than 200 mm. On the other hand, 950 keV / 3.95 MeV X-ray sources can be used for transmission testing for thick concrete of 200–400 mm and 200–1,000 mm based on the calculation and our experience so far [1–4]. We think that only the 950 keV/3.95 MeV X-ray sources can enable transmission imaging of PC structures in 200–1,000 mm thick concrete within minutes. **Figure 3** summarizes major poor construction of unfilled grout, early degradation such as rainwater intrusion and finally serious degradation of thinning and disconnection, and suitable NDE methods and successive structural analysis. If there is unfilled grout in PC sheath, rainwater may intrude from the edges and is stored there. Then, the rainwater makes PC wires and sheath wall be corroded. Volume expansion of PC sheath due to corrosion and oxidation induces cracks in near concrete. The cracks gradually become larger and reach the concrete surface, When the sheath wall is broken, the rainwater exude out and intrude into concrete and surface. As the corrosion is enhanced, superficial oxidized iron leaves and thinning of PC wires occurs. Even, the disconnection may happen since the wires are tensile. Among the above temporal change of state, the structural changes such as unfilled grout and thinning/disconnection of wires can been detected by X-ray transmission imaging. On the other hand, material property change such as rainwater intrusion can be detected by neutron scattering in water. Since concrete vertical WEB wall is thicker than ~450 mm, 3.95 MeV X-ray source is appropriate with respect to transmission ability. Iron components of PC such as wires can be clearly seen with good contrast to concrete. Their thinning and disconnection are observed with the spatial resolution of 1 mm. Since tension is added to PC wires at its construction, they tend to be attached to the upper wall of PC sheath. Therefore, unfilled grout should be recognized under PC wires with certain change of contrast. Measured flaws such as unfilled grout and thinning/disconnection are inputted to structural analysis described in Chapter 5. Thus, initial poor construction of unfilled grout and serious thinning and disconnection of PC wires are diagnosed and then their affect to

**40**

**Figure 1.**

*Advantage of 950 keV/3.95 MeV X-ray sources over other NDE methods for thicker concrete than 200 mm.*

#### **Figure 3.**

*Poor construction and degradation of PC bridges, suitable NDE methods and structural analysis.*

lack and degradation of strength is quantitatively evaluated by structural analysis. Finally, maintenance, repairing and reconstruction are planned. Moreover, there is a possibility to detect rainwater intrusion inside PC sheath by portable 3.95 MeV neutron source [5], which is discussed in Section 3.2.

#### **2. 3.95 MeV electron X-ray/neutron sources**

We use X-band (9.3 GHz) linac based 3.95 MeV X-ray sources for the inspection of the actual bridge [1–3]. The systems are shown in **Figure 4**. The electrons are accelerated up to 3.95 MeV by radio frequency (RF) fields. We also adopted the side-coupled standing wave type accelerating structure. Electrons are injected into


#### **Figure 4.**

*3 95 MeV portable X-band linac based X-ray source and its major parameters. The system consists of four units: X-ray head, magnetron, power, and chiller units.*

a Tungsten target that generates bremsstrahlung X-rays. The generated X-rays are collimated by a Tungsten collimator into the shape of a cone which has an opening angle of 17 degrees. Most important is the X-ray intensity, which is 2 Gy/min at 1 m for a full magnetron RF power of 1.8 MW. The system consists of a 200 kg (including local Pb radiation shielding) X-ray head, 100 kg magnetron box, and stationary electric power source and water chiller unit. The X-ray head and magnetron box are portable, and because they are connected to each other by a flexible waveguide, only the position and angle of the X-ray head are finely tuned. We have optimized the design with respect to X-ray intensity, compactness, and weight. The parameters of the 3.95 MeV X-ray source are summarized in the table in the figure.

We place an X-ray detector on the opposite site of the X-ray source between the object and source to detect the transmitted X-rays through the object. We use a flat panel detector (FPD) by Varian Co. for the detector. The detect and its specification are given in **Figure 5.**

In order to be able to perform neutron TOF measurement, a pulsed neutron source is needed. Usually this kind of neutron source were produced by large-sized, high-energy particle linear accelerator, but by using X-Band type electron linac which compensate its small size with high frequency, the size of the neutron source can be reduced greatly and even possible for mobility.


**43**

**Figure 7.**

*neutrons scattered by water.*

**Figure 6.**

*Highway PC Bridge Inspection by 3.95 MeV X-Ray/Neutron Source*

When we put a Beryllium target in from of the 3.95 MeV X-ray source, it

Be(γ, n)8

*Neutron source by neutron target in front of 3.95 MeV X-ray source. (i) Photograph (ii) inner structure.*

*Produced neutron energy distribution measured by 3He gas detector and TOF method and energy range of* 

photo-neutron target (50 mm × 50 mm × 50 mm) has been combined with a lead beam collimator, a boric acid resin layer for neutron shielding, and a lead layer for X-ray shielding. Since mainly fast neutrons are used in the neutron source, a beam line using a high Z material that does not moderate the neutrons is used. Optimization of the beryllium target size and neutron/X -ray shielding simulation is performed using the Monte-Carlo code. The target weight is about 100 kg.

Be, having the lowest threshold

Be to generate neutrons. A beryllium

*DOI: http://dx.doi.org/10.5772/intechopen.96959*

energy for photo-nuclear reaction <sup>9</sup>

becomes a neutron source, too (see **Figure 6**). 9

**Figure 5.** *X-ray flat panel detector (FPD) and its specification.*

#### *Highway PC Bridge Inspection by 3.95 MeV X-Ray/Neutron Source DOI: http://dx.doi.org/10.5772/intechopen.96959*

When we put a Beryllium target in from of the 3.95 MeV X-ray source, it becomes a neutron source, too (see **Figure 6**). 9 Be, having the lowest threshold energy for photo-nuclear reaction <sup>9</sup> Be(γ, n)8 Be to generate neutrons. A beryllium photo-neutron target (50 mm × 50 mm × 50 mm) has been combined with a lead beam collimator, a boric acid resin layer for neutron shielding, and a lead layer for X-ray shielding. Since mainly fast neutrons are used in the neutron source, a beam line using a high Z material that does not moderate the neutrons is used. Optimization of the beryllium target size and neutron/X -ray shielding simulation is performed using the Monte-Carlo code. The target weight is about 100 kg.

**Figure 6.**

*Computational Optimization Techniques and Applications*

a Tungsten target that generates bremsstrahlung X-rays. The generated X-rays are collimated by a Tungsten collimator into the shape of a cone which has an opening angle of 17 degrees. Most important is the X-ray intensity, which is 2 Gy/min at 1 m for a full magnetron RF power of 1.8 MW. The system consists of a 200 kg (including local Pb radiation shielding) X-ray head, 100 kg magnetron box, and stationary electric power source and water chiller unit. The X-ray head and magnetron box are portable, and because they are connected to each other by a flexible waveguide, only the position and angle of the X-ray head are finely tuned. We have optimized the design with respect to X-ray intensity, compactness, and weight. The parameters of the 3.95 MeV X-ray source are summarized in the table in the figure.

*3 95 MeV portable X-band linac based X-ray source and its major parameters. The system consists of four units:* 

We place an X-ray detector on the opposite site of the X-ray source between the object and source to detect the transmitted X-rays through the object. We use a flat panel detector (FPD) by Varian Co. for the detector. The detect and its specification

In order to be able to perform neutron TOF measurement, a pulsed neutron source is needed. Usually this kind of neutron source were produced by large-sized, high-energy particle linear accelerator, but by using X-Band type electron linac which compensate its small size with high frequency, the size of the neutron source

can be reduced greatly and even possible for mobility.

*X-ray flat panel detector (FPD) and its specification.*

**42**

**Figure 5.**

are given in **Figure 5.**

**Figure 4.**

*X-ray head, magnetron, power, and chiller units.*

*Neutron source by neutron target in front of 3.95 MeV X-ray source. (i) Photograph (ii) inner structure.*

#### **Figure 7.**

*Produced neutron energy distribution measured by 3He gas detector and TOF method and energy range of neutrons scattered by water.*

**Figure 8.**

*Neutron energy profiles of 3 He gas (n,p) cross section, incident neutrons and backscattered neutrons from concrete with and without water cell. (i) Neutrons scattered by water in concrete. (ii) energies of incident and scattered neutrons in water and 3 He gas detector efficiency.*

The calculated neutron yield in the neutron source is approximately ~107 n/s (neutrons/second), which is more intense than ~106 n/s of 252Cf (1 μg) moister detector used for NDE in chemical plants. The distribution of neutron energy produced is measured by 3 He gas detector and TOF (Time of Flight) method, as shown in **Figure 7**.

Rainwater detection using the 3.95 MeV neutron source is performed by irradiating concrete with fast neutrons and detecting backscattered moderated neutrons due to multiple elastic scattering with light elements especially hydrogen nuclei (see **Figure 8(i)**). Neutron detection using the 3 He gas is attributed to high reaction cross section with neutrons in the thermal region. Therefore, the count of detectors increases with the existence of water as shown in the figure.

### **3. X-ray transmission detection and evaluation for highway bridge by 3.95 MeV X-ray source**

We plan to do NDE by 3.95 MeV X-ray source for highway PC bridge in 2020. Its goal is to detect and visualize unfilled grout via X-ray transmission imaging. **Figure 9** shows transvers and longitudinal cross sections, possible location of unfilled grout and typical X-ray transmission images by 950 kV source for filled and unfilled grouts. Since tensile PC wires tends to attach the upper inner surface in PC sheath, the grout is filled in the lower space there. Therefore, in general, unfilled grout occurs in the lower space (see (i), (ii)). In construction stage, grout is pushed and filled from one side of sheaths so that unfilled grout tends to occur at an ascending part of the opposite side as shown in (iii). The unfilled grout in PC sheathe in 200–250 mm thick T girder WEB was measured and visualized at the ascending part as show in (iv). The unfilled part looks white comparing gray or black part of filling. Phase of unfilled can be evaluated by quantitative evaluation of gray value, namely X-ray attenuation coefficient. Appearing X-ray transmission imaging of filled and unfilled grout would be a goal of the coming task for highway PC bridges.

Here we consider PC bridges of box type and T girder Typical cross section, location of PC sheath, X-ray head and detector are summarized in **Figure 10**. X-ray head is movable 200 kg weigh component among the four. It can be accessed to the WEB with RF source via flexible waveguide for RF power delivery for electron beam acceleration. For example, the thickness of WEB of Box type and T girder are

**45**

**Figure 11(i)**.

**Figure 9.**

**Figure 10.**

*WEB. (iii) T-girder WEB.*

*filled and unfilled grouts.*

all cases as shown in the figure.

is 750 mm and 10 iron PC wires of 70m*<sup>ϕ</sup>*

*Highway PC Bridge Inspection by 3.95 MeV X-Ray/Neutron Source*

750, 550 and 450 mm, respectively. Closed circles represent typical locations of PC sheaths. Vertical arrays of PC sheaths are arranged in the zigzag way ((i), (ii)) and at the same vertical level ((iii)). When we allocate the X-ray head and eject X-rays horizontally, PC sheaths can form separate images at the detector for two zigzag arrays (see (ii)). However, in the lower case of (i) two images of the PC sheaths at the same vertical level are overlapped at the detector. In order to obtain two transmitted images for the above case, we allocate the X-ray head higher by about 100 mm and decline it by about 10 degrees as shown in the upper case of (i) and (iii). WE have almost finalized the way of access and allocation of the X-ray head to

*Typical WEBs and locations of X-ray source and detector for box-type and T. (i) Box thick WEB. (ii) box thin* 

*Transvers and longitudinal cross sections, possible and typical X-ray transmission images by 950 kV source for* 

We have carried out the simulating experiments for real highway bridges inspection in the configuration of **Figure 10(i)**–**(iii)**. In order to simulate the concrete thickness and number and location of PC sheaths, we use cut samples from real old PC bridges which were deconstructed after finishing their roles as shown in

First, we explain the results of separate X-ray transmission images for two PC sheaths at different vertical level as shown in **Figure 11(ii)**. Total concrete thickness

shot duration is 10 s and it is summed by 100 times. Original image is (ii) and (iii) is the boundary enhanced image by the principle of local contrast enhancement using gray level of the neighborhood pixels [6]. The two PC sheaths and wires are clearly

are inserted to vacant Sheath 1 and 2. X-ray

*DOI: http://dx.doi.org/10.5772/intechopen.96959*

*Highway PC Bridge Inspection by 3.95 MeV X-Ray/Neutron Source DOI: http://dx.doi.org/10.5772/intechopen.96959*

#### **Figure 9.**

*Computational Optimization Techniques and Applications*

trons/second), which is more intense than ~106

(see **Figure 8(i)**). Neutron detection using the 3

**by 3.95 MeV X-ray source**

increases with the existence of water as shown in the figure.

sured by 3

**Figure 8.**

*Neutron energy profiles of 3*

*scattered neutrons in water and 3*

The calculated neutron yield in the neutron source is approximately ~107

*He gas detector efficiency.*

used for NDE in chemical plants. The distribution of neutron energy produced is mea-

*concrete with and without water cell. (i) Neutrons scattered by water in concrete. (ii) energies of incident and* 

cross section with neutrons in the thermal region. Therefore, the count of detectors

We plan to do NDE by 3.95 MeV X-ray source for highway PC bridge in 2020. Its goal is to detect and visualize unfilled grout via X-ray transmission imaging. **Figure 9** shows transvers and longitudinal cross sections, possible location of unfilled grout and typical X-ray transmission images by 950 kV source for filled and unfilled grouts. Since tensile PC wires tends to attach the upper inner surface in PC sheath, the grout is filled in the lower space there. Therefore, in general, unfilled grout occurs in the lower space (see (i), (ii)). In construction stage, grout is pushed and filled from one side of sheaths so that unfilled grout tends to occur at an ascending part of the opposite side as shown in (iii). The unfilled grout in PC sheathe in 200–250 mm thick T girder WEB was measured and visualized at the ascending part as show in (iv). The unfilled part looks white comparing gray or black part of filling. Phase of unfilled can be evaluated by quantitative evaluation of gray value, namely X-ray attenuation coefficient. Appearing X-ray transmission imaging of filled and unfilled grout would be a goal of the coming task for highway

Here we consider PC bridges of box type and T girder Typical cross section, location of PC sheath, X-ray head and detector are summarized in **Figure 10**. X-ray head is movable 200 kg weigh component among the four. It can be accessed to the WEB with RF source via flexible waveguide for RF power delivery for electron beam acceleration. For example, the thickness of WEB of Box type and T girder are

**3. X-ray transmission detection and evaluation for highway bridge** 

He gas detector and TOF (Time of Flight) method, as shown in **Figure 7**. Rainwater detection using the 3.95 MeV neutron source is performed by irradiating concrete with fast neutrons and detecting backscattered moderated neutrons due to multiple elastic scattering with light elements especially hydrogen nuclei

*He gas (n,p) cross section, incident neutrons and backscattered neutrons from* 

n/s (neu-

n/s of 252Cf (1 μg) moister detector

He gas is attributed to high reaction

**44**

PC bridges.

*Transvers and longitudinal cross sections, possible and typical X-ray transmission images by 950 kV source for filled and unfilled grouts.*

#### **Figure 10.**

*Typical WEBs and locations of X-ray source and detector for box-type and T. (i) Box thick WEB. (ii) box thin WEB. (iii) T-girder WEB.*

750, 550 and 450 mm, respectively. Closed circles represent typical locations of PC sheaths. Vertical arrays of PC sheaths are arranged in the zigzag way ((i), (ii)) and at the same vertical level ((iii)). When we allocate the X-ray head and eject X-rays horizontally, PC sheaths can form separate images at the detector for two zigzag arrays (see (ii)). However, in the lower case of (i) two images of the PC sheaths at the same vertical level are overlapped at the detector. In order to obtain two transmitted images for the above case, we allocate the X-ray head higher by about 100 mm and decline it by about 10 degrees as shown in the upper case of (i) and (iii). WE have almost finalized the way of access and allocation of the X-ray head to all cases as shown in the figure.

We have carried out the simulating experiments for real highway bridges inspection in the configuration of **Figure 10(i)**–**(iii)**. In order to simulate the concrete thickness and number and location of PC sheaths, we use cut samples from real old PC bridges which were deconstructed after finishing their roles as shown in **Figure 11(i)**.

First, we explain the results of separate X-ray transmission images for two PC sheaths at different vertical level as shown in **Figure 11(ii)**. Total concrete thickness is 750 mm and 10 iron PC wires of 70m*<sup>ϕ</sup>* are inserted to vacant Sheath 1 and 2. X-ray shot duration is 10 s and it is summed by 100 times. Original image is (ii) and (iii) is the boundary enhanced image by the principle of local contrast enhancement using gray level of the neighborhood pixels [6]. The two PC sheaths and wires are clearly

**47**

**Figure 13.**

**Figure 12.**

*Highway PC Bridge Inspection by 3.95 MeV X-Ray/Neutron Source*

Now the findings are summarized in the following.

*and – 10 degree declining ejection of X-ray source.*

*Image of three PC sheath at the same vertical level and X-ray horizontal ejection.*

calculated X-ray attenuation in the upper graph of **Figure 2**.

• Transmission image of 750 mm thick concrete is completely obtained in 10 s by 3.95 MeV X-ray source. We should understand this fact comparing to the

*Configuration and transmission images of three PC sheaths at the same vertical level and 100 mm level up* 

*DOI: http://dx.doi.org/10.5772/intechopen.96959*

#### **Figure 11.**

*Separate X-ray transmission images for two PC sheaths at different vertical level.*

recognized separately in both images. In the boundary enhanced image, the sheath and unfilled grout looks clearer than the original, although its background becomes noisy. Instead, the original image is totally ambiguous, but the sheaths wires can be recognized.

Second, we measured three PC sheaths at the same vertical level and horizontal X-ray ejection as shown in **Figure 12**. From the left X-ray source as (i), (ii), 10 wires are inserted in the lower space of the first PC sheath 1. Grout remains in the half space of the second PC sheath 2. The third PC sheath is vacant. X-ray transmission images were obtained by 10 s duration times 1 and 100 as shown in (iii), (iv), respectively. There is almost no remarkable difference as to the quality of image. Only wires in the lower space and upper vacant space, which corresponds to unfilled grout, in the PC sheath 1 can be seen and the PC sheaths 2, 3 are hidden behind it. Since PC wires are attached to the upper inner surface of sheath in a real case, real image is upside down of these images.

Third, the configuration and transmission images for three same vertical level PC sheaths and 100 mm up −10 degree declining X-ray ejection are given in **Figure 13**. Here we try to get separate images for the three same vertical level PC sheaths at the detector. Images by 10 s duration times 1 and 100 shots are shown in (ii) and (iii), respectively. Again there is no remarkable difference with respective to image quality between them. Here the three PC sheaths are becoming separate, but still partially overlapped. We can surely recognize that PC wires are inserted from the right hand side and stop in front of the left edge in the nearest PC sheath 1 to the X-ray source. Over the PC sheath 1, we can see the PC sheath 2 with partially filled grout. The oblique edge of grout is seen in the left hand side. Finally, vacant PC sheath 3 is observed over the PC sheath 2.

## **Figure 12.**

*Computational Optimization Techniques and Applications*

recognized separately in both images. In the boundary enhanced image, the sheath and unfilled grout looks clearer than the original, although its background becomes noisy. Instead, the original image is totally ambiguous, but the sheaths wires can be

*Separate X-ray transmission images for two PC sheaths at different vertical level.*

Second, we measured three PC sheaths at the same vertical level and horizontal X-ray ejection as shown in **Figure 12**. From the left X-ray source as (i), (ii), 10 wires are inserted in the lower space of the first PC sheath 1. Grout remains in the half space of the second PC sheath 2. The third PC sheath is vacant. X-ray transmission images were obtained by 10 s duration times 1 and 100 as shown in (iii), (iv), respectively. There is almost no remarkable difference as to the quality of image. Only wires in the lower space and upper vacant space, which corresponds to unfilled grout, in the PC sheath 1 can be seen and the PC sheaths 2, 3 are hidden behind it. Since PC wires are attached to the upper inner surface of sheath in a real case, real

Third, the configuration and transmission images for three same vertical level PC sheaths and 100 mm up −10 degree declining X-ray ejection are given in **Figure 13**. Here we try to get separate images for the three same vertical level PC sheaths at the detector. Images by 10 s duration times 1 and 100 shots are shown in (ii) and (iii), respectively. Again there is no remarkable difference with respective to image quality between them. Here the three PC sheaths are becoming separate, but still partially overlapped. We can surely recognize that PC wires are inserted from the right hand side and stop in front of the left edge in the nearest PC sheath 1 to the X-ray source. Over the PC sheath 1, we can see the PC sheath 2 with partially filled grout. The oblique edge of grout is seen in the left hand side. Finally, vacant

**46**

recognized.

**Figure 11.**

image is upside down of these images.

PC sheath 3 is observed over the PC sheath 2.

*Image of three PC sheath at the same vertical level and X-ray horizontal ejection.*

#### **Figure 13.**

*Configuration and transmission images of three PC sheaths at the same vertical level and 100 mm level up and – 10 degree declining ejection of X-ray source.*

Now the findings are summarized in the following.

• Transmission image of 750 mm thick concrete is completely obtained in 10 s by 3.95 MeV X-ray source. We should understand this fact comparing to the calculated X-ray attenuation in the upper graph of **Figure 2**.

