Search Results (95)

Corrosion-induced cracking poses a significant threat to the longevity of reinforced concrete (RC) structures, yet precisely forecasting its advancement continues to be a considerable scientific obstacle. The principal shortcoming of current numerical models is their excessive simplification, frequently presuming totally saturated conditions and disregarding the dynamic interplay between environmental (hygro-thermal) variations and developing mesoscale damage. This study presents a thorough hygro-thermo-electro-chemo-mechanical (HTECM) phase-field model to fill this research need. The model uniquely combines dynamic unsaturated hygro-thermal transport with multi-ion reactive electrochemistry and meso-scale fracture mechanics. A rigorous comparison with published experimental data validates the model’s exceptional accuracy. The anticipated progression of fracture width exhibited remarkable concordance with experimental data, indicating a substantial enhancement in precision compared to uncoupled, saturated-state models. A key finding is the quantification of the damage-induced “transport-corrosion” positive feedback loop: initial corrosion-induced microcracks significantly expedite the transport of local moisture and corrosive agents, leading to nonlinear structural degradation. This work presents a high-fidelity numerical platform that enhances the understanding of linked deterioration in materials science and improves the durability design of reinforced concrete structures. Full article

This study investigates the corrosion performance of reinforced steel in concrete subjected to carbonation and chloride ingress. Four systems were examined: normal concrete (NC15), chloride-exposed (ClC15), carbonated (COC15), and chloride-exposed carbonated concrete (COClC15). A comprehensive assessment was carried out using electrochemical testing, gravimetric weight loss, chloride profiling, Temkin adsorption isotherm modeling, and SEM analysis. Electrochemical results showed a marked increase in corrosion activity under combined chloride–carbonation exposure. The highest corrosion current density (i_corr) was obtained in COClC15 (0.4779 µA/cm²), compared with only 0.0106 µA/cm² for NC15. Gravimetric analysis confirmed these findings, with COClC15 exhibiting a corrosion rate nearly 1.5 times greater than ClC15 and 52 times higher than NC15 after 120 days. Chloride profiling revealed reduced binding efficiency in carbonated concrete; at 5 mm depth, COClC15 bound only 0.06% chloride, while ClC15 retained 0.43%. The Temkin adsorption isotherm further quantified the weakened binding capacity. The binding coefficient (β) of COClC15 was considerably lower than ClC15 and NC15, reflecting the impact of C–S–H decalcification and aluminate phase transformation into carboaluminates, which restrict Friedel’s salt formation. SEM micrographs corroborated these observations, showing extensive microstructural degradation in COClC15. This study revealed that the synergy of carbonation and chloride ingress reduces chloride-binding capacity, accelerates depassivation, and severely compromises the durability of reinforced concrete in aggressive environments. Full article

The construction of large-scale infrastructure, such as power facilities, requires extensive use of reinforced concrete. The durability degradation of reinforced concrete structures in chloride environments involves multi-physics coupling effects, chloride ion diffusion, rebar corrosion, and concrete damage. Existing models neglect the coupling mechanisms among these processes and the influence of mesoscale structural characteristics. Therefore, this study proposes a diffusive–mechanical coupled phase field by integrating the phase field, chloride ion diffusion, and mechanical equivalence for rebar corrosion, establishing a multi-physics coupling analysis framework at the mesoscale. The model incorporates heterogeneous meso-structure of concrete and constructs a dynamic coupling function between the phase field damage variable and chloride diffusion coefficient, enabling full-process simulation of corrosion-induced cracking under chloride erosion. Numerical results demonstrate that mesoscale heterogeneity significantly affects crack propagation paths, with increased aggregate content delaying the initiation of rebar corrosion. Moreover, the case with corner-positioned rebar exhibits earlier cracking compared to the case with centrally located rebar. Furthermore, larger clear spacing delays delamination failure. Comparisons with the damage mechanics model and experimental data confirm that the proposed model more accurately captures tortuous crack propagation behavior, especially suitable for evaluating the durability of reinforced concrete components in facilities such as transmission tower foundations, substation structures, and marine power facilities. This research provides a highly accurate numerical tool for predicting the service life of reinforced concrete power infrastructure in chloride environments. Full article

Thousands of coastal reinforced concrete structures using HRB400 bars have served for over three decades in China. Their reinforcement simultaneously endures chloride corrosion and seismic action, yet studies on performance degradation remain limited. This paper investigates the low-cycle fatigue (LCF) behavior of HRB400 bars under various strain amplitudes, systematically analyzing corrosion morphology, cyclic stress–strain response, fatigue life, and underlying mechanisms. Corrosion is induced by an adjusted accelerated method that replicates field conditions. Observations reveal that corrosion pits act as primary crack initiation sites. Crack paths and fracture surfaces progressively follow the local pit geometry as strain and corrosion grow. The detrimental effect of corrosion on LCF life is more pronounced for smaller bars. At a γ of around 8%, 20 mm bars lose 60.7% of the half cycles to failure at ε = ±1.5%, but only 37.5% at ε = ±5.0%. Predictive corrosion-inclusive strain amplitude (ε_a)–fatigue life models are proposed, yielding R² = 0.952 (16 mm) and 0.928 (20 mm). A unified LCF predictive model, calibrated on a database of 310 corroded/uncorroded bar tests, is established. The final model comprehensively considers the characteristics of rebars, seismic action, and corrosion damage, improving the conventional relationship between LCF life and seismic loading. This work contributes to the understanding of the fatigue behavior of HRB400 bars and provides support for time-dependent seismic reliability analysis of aging reinforced concrete structures in corrosive environments. Full article

The proliferation of electrified rail systems has intensified stray current effects on chloride-induced corrosion in underground reinforced concrete (RC) structures, yet coupled mechanisms of stray current and chloride ingress—particularly in cracked concrete—remain insufficiently researched. This study establishes numerical models integrating chloride diffusion and electromigration to investigate stray current impacts on chloride transport in intact and cracked RC structures. Results reveal that stray current accelerates chloride ingress, with non-uniform electric fields causing 20–50% faster depassivation time of rebar than uniform fields at equivalent intensities. Cracked concrete exhibits 2–5 times shorter depassivation times of rebar compared to intact concrete, where crack depth–concrete cover thickness ratios exceeding 0.6 reduce service life by 40–60%. A novel deterioration coefficient β is formulated, demonstrating quadratic dependence on stray current voltage and linear correlation with cover thickness. These findings provide a predictive framework for durability assessment and corrosion mitigation in underground infrastructure exposed to synergistic chloride-stray current aggression. Full article

The application of sub-terahertz waves is being considered as a method to view the corrosion status of internal steel bars. In this study, reflectance intensities were measured for six specimens with different moisture contents using electromagnetic waves from 7.5 to 17.5 GHz. The results showed that the differential reflectance intensity decreased with increasing water content. An equation for estimating the water content at a cover thickness of 10 mm was also calculated. Regarding chloride ion content, no common trend was observed, and it was confirmed that there was a trend in the amount of chloride ions at each cover thickness. Full article

Chloride-induced reinforcement corrosion primarily contributes to the deterioration of concrete structures. Cracks provide natural pathways for chloride ions, which accelerate the corrosion process and shorten the service life of structures. In this study, the morphologies of flexural cracks in the pure bending section are extracted through destructive testing, and a crack database containing 51 samples is established. These samples are defined as four crack morphologies as follows: equal-width, wedge-shaped, two-step, and three-step cracks. Subsequently, cracked concrete models were constructed, followed by a full factorial design containing 144 operating conditions to investigate the effects of crack morphology, width, depth, and their interactions on chloride diffusion. The results show that crack morphology significantly affects chloride diffusion behavior. The equal-width crack model exhibits the highest chloride diffusion rate, whereas the wedge-shaped crack model exhibits the lowest. At a crack width of 0.15 mm and a depth of 35 mm, the maximum relative error in chloride concentration between the two models is 94.5%. As the crack depth increases, the effect of crack morphology on chloride diffusion becomes increasingly significant, whereas increasing crack width tends to diminish this effect. Additionally, a rebar corrosion initiation assessment method based on the guarantee rate is proposed, and the effect of crack morphology on the corrosion initiation time is analyzed via a case study. Full article

Reinforced concrete structures in harsh environments are highly vulnerable to structural damage caused by rebar corrosion. However, there remains a critical shortage of high-performance, environmentally friendly repair materials that integrate both structural restoration and long-term corrosion protection functionalities to address this issue. To meet this demand, this study innovatively developed an eco-friendly, high-performance repair material using lotus leaf extract (LLE)-modified mortar and systematically evaluated its corrosion protection performance and mechanisms under chloride attack conditions. The primary chemical constituents of LLE include alkaloids and flavonoids, rich in polar functional groups such as O–H, N–H, and C–O. The LLE modifier increased the fluidity of fresh cement paste, thereby improving its construction workability. A low dosage of LLE modifier promoted cement hydration. When the LLE dosage was 0.2 wt%, the 7-day and 28-day flexural strengths of the LLE-modified mortar increased by 16.8% and 7.48%, respectively, compared to those of unmodified mortar, while the compressive strengths increased by 30.6% and 14.5%, respectively. The LLE-modified mortar demonstrated significant protection against chloride corrosion, effectively inhibiting rebar corrosion. Electrochemical corrosion results indicated that compared to unmodified mortar, the modified mortar containing 0.5 wt% LLE exhibited an 80% improvement in protection efficiency against chloride corrosion. These results demonstrate that an appropriate dosage of LLE modifier can simultaneously optimize the fundamental properties of mortar and provide excellent chloride corrosion protection. Therefore, LLE-modified mortar shows promising application potential in integrated repair and corrosion protection engineering for reinforced concrete structures. Full article

The aim of this paper is to present the results of an experimental and numerical investigation into the degradation of reinforced concrete (RC) specimens subjected to an accelerated corrosion process using impressed current in the presence of chloride ions. The corrosion of the rebars was carried out using three current densities (50, 100, and 200 µA/cm²) and various exposure times. The experimental results characterised the internal degradation of the RC specimens through measurement of the corrosion product thicknesses at the steel–concrete interface; the widths, lengths and orientations of internal concrete cracks; and the external concrete crack widths. In addition, numerical modelling of the corroded RC specimens was conducted to describe the crack patterns. The comparison between the experimental and numerical results demonstrated a high degree of correlation, providing insights into the degradation process of RC specimens due to corrosion. Full article

This article presents a probabilistic methodology for assessing corrosion initiation in reinforced concrete structures exposed to chloride ingress. The approach addresses key limitations of conventional analytical models by accounting for non-diffusive barriers and incorporating a rigorous statistical treatment of censored data to mitigate biases introduced by limited simulation durations. A combination of analytical solutions for diffusion from opposite sides with time-dependent boundary conditions is also proposed and validated. The probabilistic study includes the depassivation assessment of a hollow pier section. The blocking effect caused by rebars is statistically characterised through correction factors derived from finite element simulations. These factors are used to adjust analytical solutions, which are computationally inexpensive. Results show that neglecting the rebar blocking effect can overestimate the mean corrosion initiation time by up to 42%, while the use of censored data reduces bias in lifetime estimates. The observed frequency of censored events reached up to 20% when simulations were truncated at 100 years. The corrected analytical models closely match the finite element results, statistically validating their application. The case study indicates premature corrosion initiation (less than 10 years to achieve target reliability), underscoring the need to better reconcile the desired levels of reliability with realistic input parameters for depassivation. Full article

Electrochemical treatment by means of direct current (DC) is usually used as a measure for steel rebar corrosion protection, e.g., cathodic protection (CP), electrochemical chloride extraction (ECE), and re-alkalization (RA). However, the passage of an electrical charge through the pore system of concrete or mortar, coupled with the migration of ions, concentration changes, and resulting phase changes, may alter its chloride penetration resistance and, subsequently, the time until rebar corrosion activation. Porosity changes in hardened Portland cement mortar were studied by means of mercury intrusion porosimetry (MIP) and electrochemical impedance spectroscopy (EIS), and alterations in the mortar surface phase composition were observed by means of X-ray diffraction (XRD). In order to innovatively investigate the impact of DC treatment on the properties of the mortar–electrolyte interface, the cathode-facing mortar surface and the anode-facing mortar surface were analyzed separately. The corrosion of steel coupons embedded in DC-treated hardened mortar was monitored by means of the free corrosion potential (E_oc) and polarization resistance (R_p). The results showed that the DC treatment affected the surface porosity of the hardened Portland cement mortar at the nanoscale. Up to two-thirds of the small pores (0.001–0.01 µm) were replaced by medium-sized pores (0.01–0.06 µm), which may be significant for chloride ingress. Although the porosity and phase composition alterations were confirmed using other techniques (EIS and XRD), corrosion tests revealed that they did not significantly affect the time until the corrosion activation of the steel coupons in the mortar. Full article

Recycling plastics waste into concrete represents one of the possible approaches for its valorization, offering both economic and environmental benefits. Although numerous studies have explored the mechanical properties of concrete with plastics waste, its durability performance remains largely unexplored. In this context, this study aims to assess the electrochemical behavior of rebars embedded in reinforced concrete modified by partially replacing natural aggregates with recycled plastics, comparing their behavior to that of conventional concrete. The corrosion of reinforcing steel bars was evaluated by wet and dry cycles (w/d) in calcium chloride solutions, monitoring corrosion potential and potentiostatic polarization resistance, and recording electrochemical impedance spectroscopy (EIS) and polarization curves. In addition, the chloride diffusion tendency and the mechanical performances were assessed in unreinforced samples. The findings indicate that in environments with lower chloride concentrations, concrete with plastic granules provides good protection against rebar corrosion. Although the mechanical results of the studied mixes confirmed that incorporating plastic granules as aggregates in the concrete matrix causes a reduction in compressive strength, as known in the literature, the modified concrete also exhibits improved post-cracking behavior, resulting in enhanced ductility and fracture toughness. Full article

Chloride-induced corrosion is a major contributor in the degradation of standardised steel-based products (e.g., rebars and fibres) commonly used for reinforcing concrete structures. Since cracked reinforced concrete elements are determined to be more susceptible to corrosion on the one hand, and fibres are effective in arresting crack growth and improving the post-cracking mechanical behaviour on the other hand, the use of fibres emerges as a promising strategy to enhance durability. This review is focused on the degradation of the load-bearing capacity, caused by chloride corrosion, in concrete elements reinforced with fibres and conventional rebar. Based on the recorded values of ultimate loads and the corresponding deflections in the reviewed studies, a lower decrease in the load-bearing capacity and less severe degradation of ductility were observed in elements where fibres (either steel or macro-synthetic) were used in combination with rebar compared with elements where only rebar was used. Furthermore, the recorded values of corrosion potential (E_corr), corrosion current density (i_corr) and gravimetric measurements indicated lower corrosion damage, delayed corrosion initiation and a prolonged propagation phase of corrosion. However, due to many differences in the methodology among the reviewed studies, the optimal fibre type or quantity cannot be identified unless more studies are performed. Full article

Interest in incorporating natural fibers as reinforcements in concrete has grown in parallel with the increasing need to reduce the environmental impact of construction. These fibers, known for their renewability, low cost, and life-cycle superiority, exhibit technical advantages such as light weight and high tensile strength. This study experimentally evaluated the influence of abaca fibers (AF) previously subjected to alkaline treatment and incorporated in reinforced concrete on workability, mechanical behavior, and durability, with a particular focus on the mechanisms affecting steel rebar corrosion. The characterization techniques included compressive and flexural testing; porosity, capillary water absorption, ion chloride penetration, and carbonation depth measurements; and corrosion rate monitoring via electrochemical methods. The results indicated that the addition of AF did not compromise the fresh-state properties or compressive strength but improved the flexural strength by 7.3%. Regarding durability, the porosity and water absorption increased by 4.1% and 8.2%, respectively, whereas the chloride penetration and carbonation depth remained within the requirements. Notable effects were observed regarding steel corrosion performance, where the incorporation of AF led to higher variability and an increasing trend in the corrosion rate compared with that of the reference concrete. Nevertheless, estimations suggest that abaca-fiber-reinforced concrete can meet the 100-year service life. These findings support the potential of AF as a viable reinforcement material for mechanical improvement; however, their influence on long-term durability, particularly corrosion, requires further investigation to deepen their feasible application for sustainable construction. Full article

This study investigates the long-term corrosion behavior of reinforced concrete (RC) under accelerated chloride exposure for about 1600 days, using electrochemical methods like galvanostatic pulse (GP) testing. Two concrete mixes (T1 and T2), incorporating distinct supplementary cementitious materials (SCMs), were evaluated to determine their performance in aggressive environments. Specimens with varying reservoir lengths were exposed to a 10% NaCl solution (by weight), with electromigration applied to accelerate chloride transport. Electrochemical assessments, including measurements of rebar potential, concrete solution resistance, concrete polarization resistance, corrosion current, and mass loss, were conducted to monitor the degradation of embedded steel. The findings revealed that smaller reservoirs (2.5 cm) significantly restricted chloride and moisture penetration, reducing corrosion, while larger reservoirs (10 cm) resulted in greater exposure and higher corrosion activity. Additionally, T1 mixes (partial cement replacement with 20% fly ash and 50% slag) showed higher corrosion currents and mass loss, whereas T2 mixes (partial cement replacement with 20% fly ash and 8% silica fume) demonstrated enhanced matrix densification, reduced permeability, and superior durability. These results underscore the importance of mix design and exposure conditions in mitigating corrosion, providing critical insights for improving the longevity of RC structures in aggressive environments. Full article