Corrosion products on the rebar in concrete structures induce the tensile stress in cement-paste sticking the rebar. The elastic-dynamical formulation was applied to estimate the critical thickness of corrosion product around the rebar. The corrosion morphologies developing on the rebar are general corrosion due to carbonation of cement-paste and pitting corrosion by chloride ions. The induction duration for cracking initiation in cement-paste mainly depends on organizing the condition with starting corrosion.
Concrete structures has been coated from the point of environmental harmonization by coloring. But concrete degradations has been found in many cases due to some reasons. Coating technology has achieved controlling bar-corrosion or some other concrete degradations. Concrete Organic coatings for concrete is reviewed.
Hydrogen entry behavior into steel in alkaline environment was investigated using hydrogen permeation method and thermal desorption analysis method from the viewpoint of hydrogen concentration in steel and hydrogen over-potential. Hydrogen permeation current density was proportional to the square root of applied current density. Hydrogen concentration in steel in Ca(OH)2 solution was higher than that in NaOH solution from hydrogen permeation method and thermal desorption analysis. This result was the same as the result reported by Lillard and Scully. The critical hydrogen over-potential that hydrogen can enter into steel in alkaline environment was 0.05 V. Here, hydrogen was not able to enter into steel in this immersion test from the viewpoint of hydrogen over-potential because the corrosion potential in alkaline environment was −0.6 V (SCE). Finally, logarithm of hydrogen permeability was proportional to hydrogen over-potential in alkaline environment as well as in acid and neutral environments.
Dry and wet corrosion tests were performed to clarify the corrosion propagation behavior (corrosion area, corrosion loss, and localized corrosion depth) of stainless steel reinforcing bars (SUS304-SD, SUS410-SD) in chloride attack concrete and chloride attack & carbonation concrete. As a result, even if the chloride ion concentration of the concrete was high, the corrosion loss of SUS304-SD and SUS410-SD were significantly small compared with that of carbon steel bars and it was estimated that the influence of the rust content was small on the crack of concrete.
In cathodic protection (CP) by impressed current method, polarization decay, a shift in potential following the switch-off of CP current, is used as parameter of adequate operation especially in the media of high resistivity, where iR-drop compensation is indispensable. Instant-off potential, sampled immediately after switch-off of CP current, is an essential parameter that represents effective ON-potential (with iR-drop compensation) and a baseline for the polarization decay. A detailed analysis of potential transient demonstrated that a transition from iR-drop to electrochemical relaxation starts within a millisecond in concrete. A novel portable instant-off potentiometer that allows direct reading of the instant-off potential was developed. The potentiometer consists of (a) generation of timing pulses for driving MOS switches and triggering an AD converter, (b) switching of CP current with variable ON/OFF interval and duty ratio, and (c) fast AD conversion triggered synchronously with ON/OFF timing followed by storing and computing the average. Noise level was minimized by properly selecting the sampling interval and by synchronizing the logging timing with the power-line wave but dispersing phase shifts of sampling points. A typical example of data logging interval and timing, duty cycle, and sampling number for averaging is shown for minimizing noise level of power-line origin. The potentiometer allowed direct display of the instant-off potential with the interval of 1.6 s. The measurements by model concrete block and concrete bridge on-site have proven the effectiveness and validity of the potentiometer.
In Japan, chloride- corrosion damaged concrete bridges have emerged from almost 30 years ago. The measures including technical guidelines are almost seems as if it were established, several essential issues have been left in practical field as protection design and construction. For selecting suitable measures, some decision have to be made through considering including not only technical standards but comprehensive backgrounds including history. such as the origin of chloride corrosion damaged problem, how was started to develop such measures and what are evaluated today. This paper would help to select the appropriate design and measure to protect corrosion damages of concrete bridge.