Corrosion of steel bar is one of key factors undermining reinforced concrete (RC) structures in a harsh environment. This paper attempts to review the non-destructive procedures from the aspect of the corrosion measurement techniques, especially their advantages and limitations. Systematical classification of diagnostic methods is carried out to determine any probable corrosion issues before the structures become severe, and helps choose the suitable method according to different construction features. Furthermore, the three electrochemical factors method is introduced to inspire researchers to combine various techniques to improve corrosion evaluation accuracy. The recommendations for future work are summarized, in conclusion.

Fiber-optical corrosion sensor (FOCS) is the research hotspot of corrosion monitoring sensor in recent years. It has the advantages of lightness, simplicity, anti-electromagnetic interference and distributed measurement, so it has an attractive application prospect. In this paper, the mechanism of metal corrosion is introduced. Several common methods for detecting optical fiber corrosion sensors are presented, and the latest progress of optical fiber corrosion sensors in recent years is described. We need to design a set of sensor devices that can directly monitor the corrosion of reinforcing steel bars directly, and propose a method of time dependent reliability assessment based on monitoring data, so as to form a complete research path.

The reinforcement corrosion detection has received considerable attention in the field of structural health monitoring (SHM) due to the rising awareness about the safety and longevity of reinforced building structures particularly the steel bars. In this study, we propose a corrosion-monitoring device based on a tapered polymer optical fiber sensor (TPFS) for steel bars. The sensing principle of the proposed sensor was based on the corrosion expansion law and the attenuation loss equation to the transmitted light. In the test, TPFS with three different taper diameters were characterized in the separate accelerated corrosion test with a steel bar immersed in the 3.5 wt% NaCl solution. Experimental results show that each TPFS had a unique characteristic response corresponding to the increasing corrosion products that build up around the steel bar. In addition, the sensitivities of three types of TPFS were compared in terms of the two stages, and results indicated that the sensor with 0.6 mm tapered size would be an ideal alternative for corrosion monitoring of steel bars.

We present a transient, one-dimensional dispersion-concentric (D-C) model to numerically study the charging and discharging behaviors of the molten-salt thermal energy storage system filled by PCM capsules with cascaded phase change temperatures (PCTs). Three different storage systems including the non-cascaded system, the cascaded system with 3 PCTs and the cascaded system with 5 PCTs are investigated. Detailed characteristics of heat transfer between molten salt and the packed PCM capsules are revealed, and various numerical results are examined, including the temperature distributions of molten salt and PCM capsules, the variations in the molten-salt outlet temperature, the accumulated charging and discharging ratios, etc. The results show that for cascaded systems, some stored latent heat in PCM capsules with relatively lower PCTs may not be effectively used. On the other hand, the non-cascaded system could suffer from low accumulated charging ratio and much longer charging time due to the constrains of PCT. The cascaded systems especially with 5 cascaded PCTs are found to have both a fast discharging rate and a fast charging rate, and thus cascaded systems are very promising to be used as the compact high-temperature TES system using liquid as the heat transfer fluid.