**7. Conclusion**

*Computational Optimization Techniques and Applications*

the gray value, namely the X-ray attenuation coefficient, under the criterion from 0 (white: vacant) through 1 (black as PC wire) (see **Figure 24**). NDE of unfilled grout by γ-emitter radioisotope using such a phase control and decision to proceed to destructive evaluation to obtain more precise information are under way by IFSTTAR (French Institute of Science and Technology for Transport Development and Networks) in France [8]. Then, we plan to perform 3D structural analysis to evaluate the degradation of the structural strength quantitatively as shown in **Figure 25**. We have introduced one example of the structural analysis and evaluation of reduction of yield stress due to thinning and disconnection of PC wires by using DuCOM-COM3 in Chapter 5. We propose regular X-ray transmission inspection and structural analysis every five years and record the change of yield stress. In order to confirm validity of numerical results, we plan to use not only DuCOM-COM3 code but also ATENA code [9]. The results by the two codes are compared and checked. If we observe remarkable change in both results, we may proceed to more careful consideration. Based on this evaluation, repair, reinforcement, or other decisions should be taken into account. We are going to start practical

*Phases of unfilled grout and relation with gray value of X-ray attenuation coefficient.*

*Proposal of quantitative criterion for regular X-ray inspection and structural analysis with respective to* 

**54**

**Figure 25.**

*measured property of mechanical strength.*

**Figure 24.**

We are going to apply our 3.95 MeV X-ray source to highway PC bridge inspection in Japan in 2020. Among T-girder-, box- and slab-type bridges, we first inspect box type bridge with 550–750 mm thick WEB wall. We use 950 keV/3.95 MeV x-ray sources for thinner than 300 mm and 300–1,000 mm WEB walls, respectively. Main purpose is to visualize and evaluate unfilled grout in PC sheath. We performed preliminary experiments considering real situations to obtain X-ray transmission images of wires and unfilled grout of several PC sheaths. We successfully obtain one X-ray transmission image within 10 s. We also adopt boundary enhancement image processing to check the state of PC sheath, wires and grout. We also succeeded in obtain separate images of same vertical level PC sheaths by changing vertical location and angle of the X-ray source. In all cases, PC wires can been easily seen by black images and then we can recognize the location of PC sheath. Next, we check unfilled grout beneath the wires. We propose to use the gray value, namely relative X-ray attenuation coefficient, to evaluate of the state of unfilled grout.

Moreover, we try to apply 3.95 MeV neutron source in order to detect rainwater between surface asphalt and concrete. We successfully detected the existence of water via neutron back scattering in water. As a next step, we try to verify the rainwater detection in slab type bridge.

We also performed 3D structural analysis for box type bridge by using DuCOM-COM3 code. 5% reduction of yield stress due to thinning and disconnection PC wires via rainwater corrosion was evaluated. From now on, we are going to analyze mechanical strength reduction due to unfilled grout.

Finally, we propose a guideline for regular maintenance control by making use of 950 keV/3.95 MeV X-ray sources and structural analysis codes of DuCOM-COM3 and ATENA. After we verify the inspection of box type bridge in 2020, we plan to inspect other box- and T-girder-bridged in 2021.
