Initial steps of corrosion and oxide characteristics

Abstract

Simulation of cracking of concrete cover due to reinforcement corrosion has attracted numerous investigations in recent years, although has been more scarce its experimental determination. Numerous works are based in accelerating testing because of the duration of natural processes. This acceleration of the corrosion introduce differences with respect to slower corrosion rates, which should be taken into account as well as that the maximum value observed in real conditions is around 100-200 μA/cm 2. On the other hand, the cracks appear due to the expansive character of the oxides formed. In the paper, some features of the accelerated testing of corrosion will be commented and the observations made in the first steps of the oxide formation in solution and in concrete, will be summarized. The oxides are of mixed colors evolving in function of the time to contact open air and they have not mechanical consistency, being apparently hydrophilic by retaining large amounts of water. These oxides evolve or "age" with the drying. It seems then, that a generalization of the oxide characteristics is not feasible. Regarding the crack generation and evolution due to the oxide formation, it is explained how to measure its width through strain-gages and the detected steps in its evolution.

Experimental investigation of corrosion effect on bending deflection of shield tunnel segment containing transverse cracks

“…To simulate the corrosion mechanism of tunnel segments under the action of the stray current and chloride ion simultaneously, the artificial corrosion system 38 is chosen in this study. The rebar corrosion system was mainly composed of the corrosion solution device and electric current device.…”

Effects of cracks on chloride‐induced corrosion initiation and propagation of carbon and stainless steel rebar

“…15 At this regard, more studies considering natural propagation of corrosion in presence of cracks would be useful to deepen the knowledge on the corrosion propagation phase, since many studies involve accelerated corrosion (through the application of an external current), which anyway may be not fully representative of corrosion in real structures. 16 Moreover, most of the studies investigate transversal cracks, while few studies focus on longitudinal cracks, which in real structures may be generated by loading (e.g., in bidimensional elements with reinforcement in two directions), or may be bond cracks and plastic settlement cracks. 17 Cracks longitudinal to reinforcement can be, from the point of view of corrosion development, more dangerous than transverse cracks, since chlorides, moisture and oxygen can easily reach a wider area of steel surface.…”

“…Reduced corrosion initiation times in cracked RC have been reported in several studies, 12–15 associated to an increase in corrosion rate during propagation stage, 12,13 which could anyway be more marked for short exposure times, decreasing with time 10,14 and become negligible in the long‐term 15 . At this regard, more studies considering natural propagation of corrosion in presence of cracks would be useful to deepen the knowledge on the corrosion propagation phase, since many studies involve accelerated corrosion (through the application of an external current), which anyway may be not fully representative of corrosion in real structures 16 …”

Actual achievements and future challenges of HPFRC for structural rehabilitation of bridges

“…The number of bridges showing signs of inadequacy to the new traffic demands is constantly growing. This is mainly due to the deterioration of the infrastructures, primarily related to corrosion [1,2,3] and to the increase of vehicle weight and number.…”