**4. Rainwater detection in PC sheath by 3.95 MeV neutron source**

Now we are going to explain detection of rainwater intrusion by neutrons. Images of rainwater intrusion in PC bridge and slab type bridge are depicted in **Figure 14**. Rainwater intrusion at unfilled grout in PC sheath causes corrosion of wires to thinning and disconnection, and finally degradation of strength of bridge. We try to detect them by the 3.95 MeV neutron source and 3 He gas detector via neutron backscattering. It is expected to be monitoring of early degradation of bridge strength before corrosion of PC wires.

Here we have just started basic experiment on water detection by neutron backscattering considering the situations depicted in **Figure 14**. **Figure 15** shows the experimental configuration. We just put a 50 mm thick bottle of water on a T girder concrete sample cut from a real old bridge. Neutrons from the 3.95 MeV source are scattered in water in the bottle. Backscattered neutrons are detected by the 3 He detector, and the TOF method is applied to measure the time of flight from the scattering point to the detector. Flight distance divided by the measured time

becomes the velocity of neutron, v and its kinetic energy is obtained as, <sup>1</sup> <sup>2</sup> , <sup>2</sup> *mv* for nonrelativistic case.

Measured results of neutron counts as a function of TOF and converted energy are given in **Figures 16(i)** and **(ii)**, respectively. Neutron counts as a function of measurement time and converted neutron energy in cases of unfilled and filled water are plotted in (i) and (ii), respectively. Since the neutron source with about 107 n/s is not necessarily intense, the difference with/without water is not remarkable. But we can clearly observe component of neutron backscattering below 1 eV as predicted in **Figure 8**. It can be understood that Proof-of-Principle has been verified.

**49**

**Figure 16.**

**Figure 15.**

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

*Experimental configuration modeling rainwater detection by neutron scattering.*

*Comparison of measured backscattered neutron count as a function of TOF with and without water.* 

*(i) Neutron counts as a function of TOF. (ii) neutron energy spectra.*

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

**Figure 14.**

*Images of rainwater intrusion in PC bridge and slab type bridge.*

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

*Computational Optimization Techniques and Applications*

thinning and disconnection can be analyzed.

evaluate the far side PC sheath.

• In any cases, PC iron wires can be easily found due to their rather black images. Then, the existence and location of PC sheath is detected. Furthermore,

• In case of several same vertical level PC sheaths and horizontal X-ray ejection, only nearest PC sheath is clearly seen and others are hidden behind it.

• In case of several same vertical level PC sheaths and upward shifted and declining X-ray ejection, they form separate images. Thus, we can detect and

• Unfilled grout can be evaluated by gray value with respect to rather black image of PC wires in positive image processing. We may be able to form a correlation between measured relative gray value and stage of unfilled grout.

Now we are going to explain detection of rainwater intrusion by neutrons. Images of rainwater intrusion in PC bridge and slab type bridge are depicted in **Figure 14**. Rainwater intrusion at unfilled grout in PC sheath causes corrosion of wires to thinning and disconnection, and finally degradation of strength of bridge.

neutron backscattering. It is expected to be monitoring of early degradation of

Here we have just started basic experiment on water detection by neutron backscattering considering the situations depicted in **Figure 14**. **Figure 15** shows the experimental configuration. We just put a 50 mm thick bottle of water on a T girder concrete sample cut from a real old bridge. Neutrons from the 3.95 MeV source are scattered in water in the bottle. Backscattered neutrons are detected by

He detector, and the TOF method is applied to measure the time of flight from the scattering point to the detector. Flight distance divided by the measured time becomes the velocity of neutron, v and its kinetic energy is obtained as, <sup>1</sup> <sup>2</sup>

Measured results of neutron counts as a function of TOF and converted energy are given in **Figures 16(i)** and **(ii)**, respectively. Neutron counts as a function of measurement time and converted neutron energy in cases of unfilled and filled water are plotted in (i) and (ii), respectively. Since the neutron source with about

 n/s is not necessarily intense, the difference with/without water is not remarkable. But we can clearly observe component of neutron backscattering below 1 eV as predicted in **Figure 8**. It can be understood that Proof-of-Principle has been verified.

He gas detector via

, <sup>2</sup> *mv* for

**4. Rainwater detection in PC sheath by 3.95 MeV neutron source**

We try to detect them by the 3.95 MeV neutron source and 3

bridge strength before corrosion of PC wires.

*Images of rainwater intrusion in PC bridge and slab type bridge.*

**48**

**Figure 14.**

the 3

107

nonrelativistic case.

**Figure 15.** *Experimental configuration modeling rainwater detection by neutron scattering.*

**Figure 16.**

*Comparison of measured backscattered neutron count as a function of TOF with and without water. (i) Neutron counts as a function of TOF. (ii) neutron energy spectra.*

As a next step, we are to perform numerical analysis using Monte Carlo code considering the case to detect rainwater in the configuration for slab bridge type. Multilayer sample with asphalt (~75 mm thick), water (more than few mm thick) and concrete (very thick) is first adopted.

#### **5. 3D structural analysis using finite element method**

In order to accurately reflect the influence of more detailed degradation conditions obtained by X-ray imaging on structural performance, three-dimensional finite element analysis is required. This chapter aims to evaluate structural strength degradation more precisely by performing structural calculation using finite element analysis software, Du COM-COM3 [7], that can simulate the nonlinear behavior peculiar to concrete with high accuracy. Effect of degradation is evaluated through stress distribution in the cross section of the bridge obtained by the analysis.

The software used for the analysis is DuCOM-COM3 which continues to be developed by the Concrete Laboratory, Department of Civil Engineering, Faculty of Engineering, University of Tokyo [7]. DuCOM-COM3 is used to calculate the mechanical behavior of structures with multi-spans from dynamic characteristics such as earthquake motion and wind vibration to long-term deformation behavior over several decades. DuCOM, which is responsible for the calculation of movement and material deterioration, is coupled to construct structures at various scales from the molecular-scale microscale to the structure-level macroscale.

We introduce an example to use DuCOM-COM3 for evaluation of strength degradation due to measured PC flaws. **Figure 17** shows X-ray transmission images of thinning and disconnection of PC wires of a box type bridge and evaluation of cross section reduction. Degradation of this bridge due to salty water used in winter is rather serious. At the most serious cross section, several PC sheaths are broken and PC wires are heavily thinned and disconnected. We try to evaluate reduction of PC wire cross section as shown in the table of the figure. Then, we input the data to DuCOM-COM3 analysis. **Figure 17** shows one example of box type bridge.

#### **Figure 17.**

*X-ray transmission images of thinning and disconnection of PC wires of a box type bridge and evaluation of cross section reduction.*

**51**

**Figure 19.**

*degraded part.*

**Figure 18.**

*the bridge.*

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

of bending moment, stress, strain and displacement.

We consider a partial block of one span of a four-span PC bridge (see **Figure 17**). We measured most degraded floor cross section by using our X-ray source. Several X-ray transmission images were obtained as shown in the figure. Due to long term corrosion due to salty water, several PC sheaths are broken and some PC wires are thinned and disconnected. Reduction of PC wires cross section is approximately evaluated as shown in the figure. Those data are used for the structural analysis. 3D mesh model is depicted in **Figure 18**. The whole mesh structure corresponds

to a part of one span of a four span box type PC bridge. We adopt specialized boundary condition and standard vertical load. Then, we calculate 3D distribution

*3D mesh model for the box type bridge with cross section reduction of PC wires at a certain cross section of* 

*Comparison of 3D stress distribution of initial (healthy) and degraded states. Circle indicates the* 

*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*

We consider a partial block of one span of a four-span PC bridge (see **Figure 17**). We measured most degraded floor cross section by using our X-ray source. Several X-ray transmission images were obtained as shown in the figure. Due to long term corrosion due to salty water, several PC sheaths are broken and some PC wires are thinned and disconnected. Reduction of PC wires cross section is approximately evaluated as shown in the figure. Those data are used for the structural analysis.

3D mesh model is depicted in **Figure 18**. The whole mesh structure corresponds to a part of one span of a four span box type PC bridge. We adopt specialized boundary condition and standard vertical load. Then, we calculate 3D distribution of bending moment, stress, strain and displacement.

#### **Figure 18.**

*Computational Optimization Techniques and Applications*

**5. 3D structural analysis using finite element method**

the molecular-scale microscale to the structure-level macroscale.

We introduce an example to use DuCOM-COM3 for evaluation of strength degradation due to measured PC flaws. **Figure 17** shows X-ray transmission images of thinning and disconnection of PC wires of a box type bridge and evaluation of cross section reduction. Degradation of this bridge due to salty water used in winter is rather serious. At the most serious cross section, several PC sheaths are broken and PC wires are heavily thinned and disconnected. We try to evaluate reduction of PC wire cross section as shown in the table of the figure. Then, we input the data to DuCOM-COM3 analysis. **Figure 17** shows one example of box type bridge.

*X-ray transmission images of thinning and disconnection of PC wires of a box type bridge and evaluation of* 

and concrete (very thick) is first adopted.

As a next step, we are to perform numerical analysis using Monte Carlo code considering the case to detect rainwater in the configuration for slab bridge type. Multilayer sample with asphalt (~75 mm thick), water (more than few mm thick)

In order to accurately reflect the influence of more detailed degradation conditions obtained by X-ray imaging on structural performance, three-dimensional finite element analysis is required. This chapter aims to evaluate structural strength degradation more precisely by performing structural calculation using finite element analysis software, Du COM-COM3 [7], that can simulate the nonlinear behavior peculiar to concrete with high accuracy. Effect of degradation is evaluated through stress distribution in the cross section of the bridge obtained by the analysis. The software used for the analysis is DuCOM-COM3 which continues to be developed by the Concrete Laboratory, Department of Civil Engineering, Faculty of Engineering, University of Tokyo [7]. DuCOM-COM3 is used to calculate the mechanical behavior of structures with multi-spans from dynamic characteristics such as earthquake motion and wind vibration to long-term deformation behavior over several decades. DuCOM, which is responsible for the calculation of movement and material deterioration, is coupled to construct structures at various scales from

**50**

**Figure 17.**

*cross section reduction.*

*3D mesh model for the box type bridge with cross section reduction of PC wires at a certain cross section of the bridge.*

#### **Figure 19.**

*Comparison of 3D stress distribution of initial (healthy) and degraded states. Circle indicates the degraded part.*

#### *Computational Optimization Techniques and Applications*

3D stress distribution of initial (healthy) and degraded states are given in the upper and lower images of **Figure 19**, respectively We can observe discontinuous distribution around the degraded part indicated by the circle. **Figure 20** also shows the fracture points confirmed by the overall 3D model in this model and analysis.

**Figures 21** and **22** show the moment-stress distribution and moment-strain distribution at the lower edge of the bridge section for the initial and degraded states. In both cases, the horizontal axis is the moment, and the vertical axis is the stress and strain. If we can eliminate the moment, we can get standard stress – strain relation. Anyway, we can clearly observe yield phenomenon and yield stress. The upper and lower curves represent the results for the initial and degraded states. Reduction of yield stress is clearly seen due to the degradation. The reduction is 5% in this case. This reduction would be rather serious for the maintenance of the bridge. Actually, it has been decided that this bridge should be reconstructed.

**Figure 20.** *Confirmation of fracture site in the 3D model.*

**53**

**Figure 23.**

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

**6. Guidelines for special inspections using 950 keV/3.95 MeV** 

The Public Works Research Institute and the University of Tokyo are developing new technical guidelines for special inspections of bridges using 950 keV/3.95 MeV X-ray sources. An overview is provided in **Figure 23** [4]. First, visual and hammer sound inspection screening should be performed based on regular inspection guidelines. Advanced hardware and software techniques such as drawn and acoustic analysis are adopted in this step. If degraded parts are found, the special X-ray transmission inspection is performed using the 950 keV or 3.95 MeV X-ray sources, depending on the thickness of the concrete containing the degraded parts (see **Figure 2**). Here, the states of PC wires such as unfilled grout and thinning/disconnection are quantitatively evaluated with spatial resolution of 1 mm. Especially, the state of unfilled grout can be evaluated quantitatively by measuring

*Guidelines for special X-ray transmission inspection using 950 keV/3.95 MeV X-ray sources accompanied with* 

*visual and hammering-sound inspections, structural analysis, final repair, and/or reinforcement.*

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

*Moment-strain graph at bottom edge of bridge section.*

**X-ray sources**

**Figure 22.**

**Figure 21.**

*Moment-stress graph at bottom edge of bridge section.*

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

*Computational Optimization Techniques and Applications*

analysis.

reconstructed.

**Figure 20.**

*Confirmation of fracture site in the 3D model.*

*Moment-stress graph at bottom edge of bridge section.*

3D stress distribution of initial (healthy) and degraded states are given in the upper and lower images of **Figure 19**, respectively We can observe discontinuous distribution around the degraded part indicated by the circle. **Figure 20** also shows the fracture points confirmed by the overall 3D model in this model and

**Figures 21** and **22** show the moment-stress distribution and moment-strain distribution at the lower edge of the bridge section for the initial and degraded states. In both cases, the horizontal axis is the moment, and the vertical axis is the stress and strain. If we can eliminate the moment, we can get standard stress – strain relation. Anyway, we can clearly observe yield phenomenon and yield stress. The upper and lower curves represent the results for the initial and degraded states. Reduction of yield stress is clearly seen due to the degradation. The reduction is 5% in this case. This reduction would be rather serious for the maintenance of the bridge. Actually, it has been decided that this bridge should be

**52**

**Figure 21.**

**Figure 22.** *Moment-strain graph at bottom edge of bridge section.*
