•The effect of cracks on chloride diffusion coefficient under two experimental mechanisms is discussed separately.•The influence of crack width on corrosion behavior (current density and velocity) is ...discussed in this paper.•Corrosion rate and chloride ion diffusion coefficient under two mechanisms are quantitatively compared.•The different composition and distribution of corrosion products between techniques are demonstrated.
The aim of this paper is to investigate the corrosion relationship between reinforced concrete exposed to natural marine environment and applied current acceleration. Chloride ions migration and reinforcement corrosion behaviour in different cracked concrete are studied by two testing methods: 700-day exposure in a marine tidal zone and applied current accelerated corrosion. The mechanism comparison of chloride ion diffusion between two techniques is discussed. The results show that cracks have more influence on reinforced concrete under electrochemical corrosion than that under natural exposure. The corrosion rates of natural and accelerated corrosion were quantitatively compared: the latter is two orders of magnitude faster than the former when the crack width is over 0.20 mm. The different composition and distribution of corrosion products between techniques are demonstrated.
Chloride penetration, facilitated by drying-wetting cycles, poses significant threats to reinforced marine concrete structures. In this study, the corrosion inhibition effects of triethanolamine ...dodecylbenzene sulfonate (TEA·C18H30O3S, TDS) and triethanolamine phosphate (TEA·H3PO4, TP) were investigated using mortar specimens. Electrochemical tests including electrochemical impedance spectroscopy and potentiodynamic polarization test were performed. The morphology and Vickers hardness of the steel/mortar interface were analyzed. Molecular dynamics and quantum mechanical simulations were conducted to explore the interactions between the inhibitors and the iron surface. The results demonstrated that the inhibition efficiency of TP was high, while TDS only presented some effect within limited drying-wetting cycles. After 24 wetting-drying cycles, the inhibition efficiency of TP reached 59.29 %, TDS exerted a detrimental effect on reinforcement corrosion, and the inhibition efficiency was −410.96 %. At the mortar/steel interface, the irregular defects were curtailed and the Vickers hardness was improved by TP. Meanwhile, TDS entrained large hydration pores. The adsorption of the inhibitors on the iron surface is primarily through the benzene ring, PO and NC bonds, where the TEA-Fe adsorption is the most stable among the studied chemical components.
•Two types of TEA-containing inhibitors were systematically investigated.•Defects at the SMI were reduced due to the incorporation of TP.•Vickers hardness value in blank specimens increases with distance from SMI.•Benzene ring, PO bonds, and NC bonds contribute to inhibition mechanism.•TEA owns the largest energy gap, suggesting the most stable adsorption.
The critical chloride content (Ccrit) of reinforcement corrosion in concrete is of great importance for the condition assessment of existing structures and for the service life design of new ...structures in chloride exposure environments. Here, we review the extensive body of literature on Ccrit published in Chinese since the 1960s. In agreement with earlier reviews considering European and North American literature, we find that Ccrit scatters widely and cannot be predicted on the basis of parameters such as w/b ratio, binder type, steel surface condition, etc. It appears that the stress state of the reinforcing steel may play a more important role than generally assumed. On the basis of this review, complementing earlier reviews, we conclude that the state-of-the-art on Ccrit has advanced negligibly over the last decades. The time is now to change the way corrosion initiation in concrete is scientifically addressed. Recommendations for further work are made.
•Five-year corrosion lab study of steel in carbonating concrete.•The presence of reinforcement influences the carbonation depth.•Highest corrosion rates were measured in fly ash concrete.•The general ...applicability of guidelines for corrosion assessment is questioned.•Similar ranking of carbonation resistance was found in lab and field exposure.
Carbonation development and reinforcement corrosion were investigated on concretes exposed for a five-year period at 90% RH, 20 ℃, and 5% CO2, and for a six-year period at natural carbonation. Portland cement-based binders with 0%, 18%, and 30% fly ash were investigated. The fly ash blends showed lower carbonation resistance compared to PC both at laboratory and field exposure, a large difference in carbonation performance was observed between the laboratory exposed specimens. The carbonation rate was fastest on the laboratory specimens and showed square-root time dependency the first 2.5 years, but reduced rate at later age. Deeper carbonation depths were in general observed in the vicinity of the reinforcement compared to the unreinforced laboratory exposed specimens. Not all specimens were fully carbonated at the steel-concrete interface. The correlation between degree of carbonation of the steel-mortar interface, the open circuit potential, and the observed corrosion of the steel bars varied between binders and bar position (top or bottom). The measured corrosion rate in the laboratory exposed (90% RH, 20 ℃, and 5% CO2) carbonated concrete was on average 0.2 μA/cm2, with an upper value of 0.6 μA/cm2. The highest corrosion rate was measured in the fly ash concrete. No corrosion rate data are yet available for the field exposed concretes.
•Seismic behavior of seismic-damaged corroded RC joints rehabilitated with BFRP was investigated.•Detailed rehabilitating scheme for damaged RC joints was proposed.•The ductility and energy ...dissipation of rehabilitated joints were improved.•The equations for evaluating the shear strength of the joint were proposed.
Reinforcement corrosion and seismic damage considerably affect the seismic performance of reinforced concrete (RC) members. In present research, five RC beam-column joints were designed and tested under cyclic loadings. These joints included one reference specimen, one uncorroded specimen rehabilitated with basalt fiber-reinforced polymer (BFRP) sheets, as well as three seismic-damaged corroded specimens with corrosion rates of 0, 3%, and 9% rehabilitated with BFRP sheets. The seismic behavior of tested specimens, involving the hysteretic responses, ductility, and energy dissipation was discussed. Test results demonstrated that the seismic behaviors of seismic-damaged corroded specimens were effectually upgraded after being rehabilitated with BFRP sheets. The spalling and crushing of concrete, as well as the buckling of stirrups were postponed by the utilization of BFRP sheets, while ductile behaviors of rehabilitated specimens could be observed in the test. Besides, the ultimate displacements, final stiffness, and total cumulative energy dissipation of the rehabilitated specimens were considerably improved with the maximum increase of 14.9%, 16.7%, and 23.3%, respectively. Equations considering the influences of reinforcement corrosion, seismic damage, and FRP rehabilitation on the shear strength of the core area of RC joints rehabilitated with FRP sheets were proposed, and good agreements could be found between the theoretical and experimental results.
•Cross-sectional area distribution of non-uniform corroded steel bars varies with increasing corrosion rate.•Relative yield strength decreases linearly and relative ultimate elongation decreases ...exponentially.•Little effect of corrosion on the yield strength and ultimate strength of the steel bars.•Non-uniform corroded steel bars have shorter necking length and tend to brittle failure.
In this work, to investigate the characteristics of non-uniform corrosion of steel bars more accurately, a new experimental method was proposed, which can rapidly generate non-uniformly distributed rust around steel bars in concrete. The precise average and critical cross-sectional area along the longitudinal direction of corroded steel bars were then obtained using the three-dimensional (3D) laser scanning. Based on critical section loss rate, the effects of non-uniform corrosion on the degradation of mechanical properties of steel bars were studied. The corrosion morphology, mechanical properties, and tensile failure patterns of uniformly and non-uniformly corroded steel bars were compared and elaborated.
•Eight 20-years-old corroding reinforced concrete cores are studied through X-ray CT.•OPC-specimens had lower corrosion resistance than blended-cement specimens.•The deepest pits are found at the ...outer side of the steel and close to interfacial voids.•Interfacial voids should be considered the locations where pits propagate the most.
Although reinforcement corrosion is a well-known issue, which are the locations of the steel/concrete interface most sensitive to pitting corrosion is still an unclear issue. In this study, X-ray computed tomography is used to characterize eight 20-years-old reinforced concrete cores naturally deteriorated due to chloride-induced corrosion. The deepest and most frequent corrosion pits were observed at the portion of the reinforcement oriented to the outdoor environment and in proximity to interfacial air voids. Therefore, the presence of interfacial air voids should be considered as a relevant factor when assessing the risk of corrosion of reinforced concrete structures.
•A review about corrosion mechanism of rebars and relevant morning or detection devices.•A revised theoretical model was proposed.•A novel monitoring system was introduced.
It is widely acknowledged ...that corrosion of reinforced bars is a tremendous challenge against durability performance of reinforced concrete (RC) structures, especially under aggressive environment. Correspondingly, corrosion mechanism has been in-depth investigated all over the world, moreover, amounts of monitoring or detection apparatus have been developed in order to obtain or visualize the damage degree of corroded reinforcements inside concrete, which cannot be recognized by naked eyes. This paper aims to make a short review about corrosion mechanism as well as relevant morning or detection devices based on various physical backgrounds, which include optics, electromagnetism, acoustic, X-ray CT, radarand others. The result shows that much more studies are focusing on the development or upgrading of novel monitoring equipment against reinforcement corrosion, and a revised theoretical model is also putted forward based on non-uniform corrosion type for judging the corrosion-triggered cracks more accurately. Moreover, a suggestive idea has been raised about establishing an intelligent monitoring system which includes novel sensors, data collection and transmission device, and also evaluation procedure as well.
•Full scale experimental tests on RC columns with corroded and uncorroded rebars have been performed under cyclic loads.•Preliminary tests for the calibration of the corrosion process have been ...carried out both on bare and embedded bars.•The influence of the corrosion effects on the cyclic response of the elements is shown and discussed.
Corrosion of reinforcement is one of the leading causes of the deterioration in reinforced concrete structures. RC structures damaged by reinforcement corrosion can exhibit not only reduction of the bearing capacity but also an alteration of the collapse mechanism with a reduction of the structural ductility. In order to study the problem, full scale experimental tests on column specimens have been performed under cyclic loads. Preliminary tests for the calibration of the corrosion process have been carried out both on bare and embedded bars. The results of the cyclic experimental tests show how the reinforcement corrosion can lead to a reduction of the structural ductility, such that it could become a critical aspect particularly for buildings in seismic regions.
Limestone Calcined Clay Cement (LC3) has good chloride (Cl−) binding capacity and is reported as a qualified binder for concrete manufacture with desalinated sea sand. In this study, corrosion ...mechanism of reinforcement in LC3 under coupled Cl− and carbonation attack was studied. Electrochemical measurement, optical microscopy and X-ray photoelectron spectroscopy were applied to assess safety of embedded reinforcement; OH− and Cl− profiles in LC3 paste were monitored to evaluate progress of carbonation degree. Results showed that LC3 pastes were carbonated with a pronounced speed, which was due to the decrease in calcium hydroxide content during its hydration stage. Due to decomposition of Friedel's salt and release of Cl−, obvious increase and redistribution of free Cl− were detected and progressed with carbonation duration. Depassivation of mild steel were observed at early stage of carbonation when CO2 had not reached its location, thus it was resulted from carbonation-induced Cl− increase rather than alkalinity decrease under the applied exposure. In summary, LC3 performed a good protection on embedded reinforcement under impact of the premixed Cl−, but this protection diminished quickly at a carbonation scenario.
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