Performance Of Reinforced Concrete Structures Research Articles

Thin-layer Ultra-High-Strength Engineered Cementitious Composites (UHS-ECC) reinforced with small-diameter FRP bars for structural strengthening

This study proposed a novel strengthening system for reinforced concrete (RC) structures using a thin layer of Ultra-High-Strength Engineered Cementitious Composites (UHS-ECC) reinforced with small-diameter Fiber-Reinforced Polymer (FRP) bars. Experimental investigation, digital image correlation analysis, and numerical simulation were conducted to evaluate the flexural performance and failure mechanism of RC beams strengthened with 20-mm UHS-ECC layers and 3-mm FRP bars. It was found that the 20-mm UHS-ECC layer alone improved the load capacity of RC beams by 8.3 %, though with reduced deflection, whereas incorporating two 3-mm FRP bars increased load capacity by up to 40.4 %, without sacrificing deflection. Failure in all specimens was caused by concrete crushing; however, FRP-reinforced UHS-ECC layers mitigated early crack localization, significantly enhancing both strength and ductility. This study also revealed that cast-in-place FRP-reinforced UHS-ECC layers exhibited higher load capacity and could avoid ECC/concrete interfacial cracks compared to epoxy-bonded prefabricated layers. A three-dimensional finite element model was proposed for the strengthening system, and the flexural behavior was successfully predicted. It is revealed that the FRP-to-UHS-ECC bond had a marginal influence on performance, while the bond at the UHS-ECC-to-concrete interface significantly impacted flexural behavior. Remarkably, the small-diameter FRP bar achieved 75 % of its tensile strength at the ultimate stage. These findings underscore the potential of FRP-reinforced UHS-ECC layers as an effective solution for enhancing the mechanical and durability performance of RC structures.

Effect of longitudinal reinforcement ratio on residual flexural capacity of high-strength reinforced concrete beams exposed to impact loading

In this study, it was aimed to investigate the dynamic impact and post-impact performances of high-strength reinforced concrete (RC) beams, which have different ductility and load-bearing capacities. The dynamic behavior and impact damages of RC beams were compared after exposure to a constant magnitude of impact energy. The applied impact energy was obtained by dropping a mass of 360 kg from a certain height of 3 m. The cross-section dimensions and length of the specimens were selected to carry out the experiments in full-scale. The tested specimens were designed with five different longitudinal reinforcement ratios for demonstrating distinct structural behavior mechanisms that vary from pure flexure to pure shear, representing different ductilities, load-bearing capacities and potential failure characteristics. The post-impact behavior of the impacted RC beams was also assessed by performing quasi-static bending tests on the impact-damaged specimens and the obtained results were compared with the identical undamaged reference RC beams. The results demonstrated that the longitudinal reinforcement ratio (which was intentionally designed for different specimens to exhibit different structural responses from pure shear to pure flexural and different shear-flexure mechanisms) significantly influences the dynamic response and damage intensity of the beams, which, in turn, affect their post-impact static performance. Key structural characteristics, including residual displacement, ductility, energy dissipation, load-carrying capacity, and stiffness, were analyzed. It was found that the mechanical properties of the beams deteriorated markedly after impact exposure. A crucial finding of this research is the notable shift in failure modes from flexural to shear after impact, depending on the damage severity. In RC beams, shear damage remains insignificant under both impact loading and subsequent static loading when the ratio of shear strength to flexural strength (Vr/Mr) exceeds 1.5. Conversely, when this ratio is less than 1.5, the behavior transitions to being shear-critical or shear-dominant. This study presents, for the first time, comprehensive experimental results on the impact-induced damage progression, failure mechanisms, and residual behavior of high-strength RC beams. These insights are vital for understanding the performance of RC structures under impact loads and contribute significantly to the field of structural engineering, particularly in designing impact-resilient structures.

Life-cycle performance prediction and interpretation for coastal and marine RC structures: An ensemble learning framework

Long-term exposure to coastal and marine environments accelerates the aging of reinforced concrete (RC) structures, impacting their structural safety and society impact. Traditional assessments of long-term performance deterioration in RC structures involve complex, nonlinear, and time-intensive studies of physical mechanisms. While existing machine learning (ML) methods can assess the lifetime of these structures, they often prioritize data regression over mechanistic interpretation. To enhance the efficiency and interpretability of predicting the life-cycle performance of RC structures, this study introduces a generic framework based on interpretable ensemble learning (EL) methods. The framework predicts life-cycle performance efficiently and accurately, with optimal hyperparameters automatically tuned through Bayesian optimization. Interpretability algorithms clarify the influence of environmental, durability, and mechanical parameters on structural durability and mechanical predictions. Validation employs real-world cases of RC hollow beams in the coastal area of the Guangdong-Hong Kong-Macao Greater Bay Area (GBA). The comprehensive model for RC structures integrates actual data on temperature, humidity, and surface chloride content in the GBA, considering diffusion, convection, and binding effects of chloride ions, corrosion non-uniformity, and crack impact on durability estimation. Comparative analysis with existing ML methods underscores the effectiveness of the framework. The findings highlight the dynamic evolution of feature importance rankings throughout the service life, shedding light on the continuous changes in the significance of different factors when predicting mechanical resistance.

Experimental study on improving the fire performance of the concrete beams with Fe-SMA

The conventional approach to satisfying the fire resistance requirements in designing reinforced concrete (RC) structures is to ensure enough concrete cover depth for the steel reinforcements. The objective is to prevent the temperature of steel reinforcements from rising too quickly. However, excessive concrete cover depth may increase the risk of concrete spalling during a fire and lead to a larger crack width. Fire is a natural heat source that can activate the shape memory effect of iron-based shape memory alloys (Fe-SMA) to generate recovery stress. This study proposes a new active approach for improving the fire performance of RC structures based on the Fe-SMA. The main objective is to investigate the feasibility of improving the fire performance of RC structures through the recovery stress generated by Fe-SMA under fire. The fire test of nine Fe-SMA RC beams was conducted. The temperature profile in the furnace was similar to ISO834, and the maximum temperature exceeded 800 °C. The flexural behavior of the concrete beams reinforced with Fe-SMA during and after the fire was tested. The experimental results demonstrate that the Fe-SMA has great potential in improving the fire performance of RC structures. The mid-span deflection of the Fe-SMA RC beams under fire is significantly lower than the conventional RC beams. The fire resistance of Fe-SMA RC beams increases from 97 min to 133 min at load level 0.3 and from 69 min to 103 min at load level 0.5. The residual deformation of Fe-SMA RC beams reduces from 46.3 mm to 27.6 mm at load level 0.3 and from 34.7 mm to 19.8 mm at load level 0.5. In addition, after 1 h of fire exposure, the Fe-SMA can develop permanent prestress after the beam cools to room temperature, improving the mechanical properties after fire. The residual bearing capacity and residual stiffness of the Fe-SMA RC beams are 21% and 86%–121% higher than the conventional RC beams, respectively. The prestress generated by Fe-SMA after 1 h of fire exposure was estimated using the equivalent section method.

Fire behaviour of reinforced concrete slab strips strengthened with prestressed NSM-CFRP laminates

Carbon fibre reinforced polymer (CFRP) composites are now widely used to strengthen reinforced concrete (RC) structures. Among the strengthening systems available, near-surface mounted (NSM)-prestressed CFRP laminates offer several advantages, as they significantly increase the load carrying capacity and also the serviceability performance of RC structures. However, as for other CFRP systems, there is a concern about their behaviour at elevated temperature and under fire exposure due to the glass transition process undergone by their polymeric components. Nevertheless, the fire performance of NSM-prestressed-CFRP strengthening systems has not yet been investigated. This paper presents an experimental study about the fire resistance behaviour of RC slab strips strengthened with prestressed NSM-CFRP laminates; the slabs were simultaneously subjected to a mechanical (fire) load and the ISO 834 fire curve, and the influence of the following parameters on their fire resistance behaviour was assessed: (i) the prestress level (0 %, 25 % and 50 % of the CFRP tensile strength), and (ii) the presence of passive fire protection, comprising up to 48 mm thick calcium silicate (CS) boards. The results obtained showed that: (i) without fire protection, the strengthening system remained effective during a very low period of fire exposure, which significantly decreased with the prestress level, from 16 min (0 %) to less than 5 min (50 %); (ii) with fire protection, even with 50 % of prestress, the strengthening system remained effective for more than 120 min; and (iii) the “critical” temperatures in the anchorages of the strengthening systems were found to be about 2.5Tg, 2.0Tg and 1.5Tg, for the prestress levels of 0 %, 25 % and 50 %, respectively, with Tg being the glass transition temperature of the adhesive.

Influence of steel reinforcement on the performance of an RC structure subjected to a high-velocity large-caliber projectile

The reinforcement setting in reinforced concrete (RC) protective structure should be optimized to resist the impact of high-velocity large-caliber projectiles (LCPs), which is yet to be clearly understood. This study adopts a high-fidelity finite element analysis (FEA) approach to examine the influence of steel reinforcement setting, including the diameter/spacing/strength of reinforcement, the number/spacing/distribution depth of the mesh layer, and the reinforcement ratio, on the performance of RC structure against the large-caliber projectile impact. The FEA approach utilizes an improved dynamic constitutive model of concrete recently proposed by the authors to capture the responses of concrete, i.e., the penetration resistance, cratering, scabbing, and cracking failure, and the *CONSTRAINED_BEAM_IN_SOLID coupling method to consider the bond-slip relation between steel reinforcement and concrete. By simulating the 64 mm-diameter projectile impact tests on the plain concrete (PC) and RC targets, it validates the established FEA approach in contrast to that using the existing concrete models in LS-DYNA, i.e., the Holmquist-Johnson-Cook, Riedel-Thoma-Hiermaier, and Karagozian & Case concrete models, and the full coupling method, i.e., the *CONSTRAINED_LAGRANGE_IN_SOLID. The performance of the RC target struck by a 154 mm-diameter LCP is further numerically studied using the validated FEA approach. Based on more than fifty simulation cases, it derives the optimal reinforcement setting for the engineering design: (i) increasing the mesh layer number should be given priority to increasing the reinforcement ratio; (ii) the optimal rebar diameter and spacing are 1/15 and 1/2 of projectile diameter, respectively; (iii) uniform distribution of reinforcement layer along target thickness is suggested; (iv) normal strength reinforcement is preferred; (v) the practical highest reinforcement ratio is 4% to reduce structural thickness.

A spike-shaped anchorage for steel reinforced polymer (SRP)-strengthened concrete structures

Steel reinforced polymer (SRP) composite has recently emerged as an effective and economical solution for strengthening of reinforced concrete (RC) structures. Premature debonding failure of unanchored SRP at low load levels generally governs the performance of RC structures strengthened with externally bonded SRP. Therefore, a novel yet simple spike-shaped anchorage system was proposed in this study to prevent the debonding failure of SRP and to improve the interfacial shear capacity. Experimental investigation through single-lap shear tests of SRP-concrete joints showed that the anchorage system changed the failure mode from composite debonding to fiber rupture. In addition, the anchorage system substantially increased the peak load and reduced the interfacial slippage of the SRP-concrete joint compared to the unanchored condition. A numerical procedure based on the finite difference method was developed to predict the full-range load response, and results matched well with the full-range experimental responses of anchored and unanchored specimens. Parametric study of the test results and numerical simulation based on finite difference method both showed that the fiber rupture failure mode could be achieved for anchors in various positions along the bonded length. The closer the anchor is to the loaded end, the less global slip was obtained when the load reached the peak value.

Assessment of seismic retrofitting interventions in reinforced concrete structures

Destruction of reinforced concrete (RC) structures, particularly non-ductile RC structures, in recent earthquakes demonstrate their vulnerability under lateral forces generated in an earthquake. Despite the extensive literature on the subject and the wide variety of strengthening techniques available, there is no consensus on the efficiency of these techniques in improving the seismic performance of RC structures. In this study, a five-storeyed RC-framed building is considered to evaluate its seismic performance through static non-linear pushover analysis. To examine the effect of various cases encountered in practice, the pushover analysis is carried out on the RC frame for various cases, i.e. a bare RC frame, an RC frame with masonry infills but with an open ground storey, and RC frames with shear walls with a variety of thicknesses and steel reinforcement ratios. Further, to investigate the effect of retrofitting, the RC frame is strengthened using local jacketing and bracings. From the results, it is observed that the initial stiffness and base shear of masonry infilled RC frame with an open ground storey exhibit an increase of 2.6%, and 19%, respectively, as compared to the bare frame. The use of shear walls increases the initial stiffness and base shears, and they increase by 6–14% and 8–20%, respectively, with an increase in the reinforcement ratio in the shear wall. Retrofitting with the use of both diagonal bracings causes the base shear to increase by a factor of 7.7 as compared to that of the open ground storey. Finally, the probability of damage to the RC frame in all cases was compared using seismic fragility curves.

Projectile impact-induced spalling damage on carbon fiber reinforced polymer strengthened RC plates

As the most widely used material in protective structures, a better understanding of the resistance of reinforced concrete (RC) to high-speed projectile striking is needed. It has been accepted that concrete material possesses limited impact resistance in virtue of its poor energy absorption capacity. To improve the performance of RC structures under impulsive loading, affixing externally-bonded Fiber Reinforced Polymer (FRP) sheets on structural elements is a practical method. Due to the emphasis of most existing literature on the penetration behavior of projectiles, the studies of impact-induced spalling damage on normal and FRP strengthened RC plates are not sufficient and in-depth. In this paper, the local response of un-strengthened and FRP strengthened RC plates under projectile impact is systematically investigated with experimental approaches. In consideration of the complexity of transient behavior as well as multiply parameters involved, empirical approaches based on dimensionless analysis are proposed to predict the diameter and depth of spalling craters on normal RC plates and strengthened ones with frontal CFRP layers, which fill current research gap and are potential tools for damage assessment and repair. The validity of the proposed approaches is verified by test results from the present and published studies.

Seismic Performance Evaluation of Corrosion-Damaged Reinforced Concrete Columns Controlled by Shear Based on Experiment and FEA

It is extremely important to investigate the effect of the seismic performance of corrosion-damaged reinforced concrete (RC) members, in terms of strength and deformability, on the seismic performance of the entire building. This will allow a more accurate assessment of the seismic performance of RC structures with corroded members, including beams and columns. However, current methods of evaluating the seismic performance of RC structures fail to fully consider the influence of reinforcement corrosion and other performance deterioration of RC members. The main objective of this study is to propose a practical method of evaluating the seismic performance of RC structures with corrosion-damaged members, identifying factors contributing to structural performance deterioration based on strength and deformability for direct, quantitative evaluation of seismic performance. To achieve the aforementioned objective, the authors examined the effects of reinforcement corrosion on the structural behavior of RC beams and factors contributing to structural performance deterioration. Past experiments verified the strong correlation between the half-cell potential (HCP) before and after reinforcement corrosion and the reduction factor based on energy absorption capacity. However, current research evaluates the correlation between the extent of corrosion and structural performance deterioration of RC beam members, which are not members that resist lateral force. As such, the results cannot be directly applied to the evaluation of the seismic performance of RC structures containing corrosion-damaged members. To achieve this study’s main purpose of proposing a practical method of evaluating the seismic performance of RC structures comprised of corrosion-damaged members, analytical methods including structural experiments should be applied to corrosion-damaged lateral resisting members, namely, column members of the shear failure type with non-seismic details. This study performed cyclic loading tests on columns of the shear failure type having reinforcement corrosion to examine the correlation between HCP before and after corrosion and seismic performance deterioration. At the same time, finite element analysis (FEA) was carried out in consideration of the weakened bonding between steel and concrete, so as to analyze the correlation between structural performance deterioration before and after corrosion of shear columns. Through a comparison of the experimental findings and FEA results, this study proposed a seismic performance reduction factor in relation to the extent of corrosion of shear columns.

Temporal-spatial reliability analysis of RC bridges with corroded steel reinforcement bars

Corrosion of steel bars is one of the most significant causes of deterioration of reinforced concrete (RC) structures. The performance of RC structures is affected by many factors such as materials, environments, and load conditions, which usually possess uncertain features. Some of uncertainties may be time- and space-dependent, and the corresponding reliability problems become more challenging. To address these issues, this paper studies the temporal-spatial reliability analysis of RC bridges with corroded steel reinforcement bars. At first, a compound corrosion model is developed in which the combined effects of carbonation (general corrosion) and chloride penetration (pitting corrosion) are considered. In the reliability analysis, both the temporal and spatial variability are accounted through a stochastic process and a random field, respectively. An extended instantaneous response surface (t-IRS) method is then proposed to evaluate the temporal-spatial reliability. Unlike the original t-IRS method, in addition to the original variables, the random variables transformed from the random fields and the space variable are also used as the input variables of the extended surrogate model. When generating sample points, both the time variable and the space variable are treated as uniformly distributed random variables within given intervals. Finally, the proposed method is applied to a RC bridge example with corroded steel reinforcement bars and the results are compared with that of Monte Carlo simulation (MCS) method, demonstrating the effectiveness of the extended t-IRS method.

Seismic assessment of irregular RC frames with tall ground story incorporating nonlinear soil–structure interaction

This paper is dedicated to evaluate the nonlinear Soil–Structure Interaction (SSI) impact on the earthquake-based response of vertically irregular reinforced concrete (RC) moment resisting frames. The main contribution of this paper is to evaluate the seismic performance of RC structures with 5 and 10 stories considering a number of key parameters including irregularity ratio, soil type and the vertical safety factor (FSv) of the foundation. In this regard, the beam on nonlinear Winkler foundation (BNWF) scheme is used for the modeling of shallow foundations resting on a semi-infinite sandy medium. Vertical irregularity is considered by using a tall ground story in the RC frames. The models are subjected to 15 earthquake ground motions for conducting nonlinear dynamic time-history analyses to capture the seismic demands of soil–structure systems. The results demonstrate that considering SSI influence reduces the seismic demands in the lower stories, which is more evident in the case of soft soils (site class E). Moreover, a rational relationship between the maximum inter-story drifts and the response of the foundations is observed. It is also concluded that for both regular and irregular structures, lower values of the FSv lead to a considerable decrease in the structural demands (story drifts) and an impressive growth in transient and residual foundation settlements.

Seismic Performance of Full-Scale Circular Reinforced Concrete Columns Constructed with TRCC Permanent Formworks

ABSTRACT The structural systems should maintain their strength, stiffness and ductility capacity under seismic effects. In reinforced concrete (RC) structures, the confinement effect provides these important features in the presence of the lateral reinforcements. Textile reinforced cementitious composites (TRCCs) have very good tensile, flexural and long-term performance. By using these multilayered composites as permanent formwork, the confinement effect can occur in RC columns. Moreover, thanks to the permanent formworks, the performance of RC structure will be increased during earthquake and service life will be extended against the drawbacks of structural defects. In this study, TRCC circular permanent formworks were produced by using a newly developed PPR (Pull-Pour-Roll) technique and machine. A cementitious mortar was designed and four and six layers of Ar glass (Alkali Resistant Glass) and four layers of basalt textiles were selected for the production of composite permanent formworks. The most important features of permanent formworks are hollow, thin section and three-dimensional structural elements. Five full-scale circular column specimens were tested in the laboratory under the combination of constant axial load and reversed cyclic lateral load. Three of the columns were constructed as permanent formwork, while others were reference specimens built by temporary formworks. All composite formwork columns and one of the reference specimens include insufficient lateral reinforcement. Whereas the other reference column has adequate lateral reinforcement. This study was carried out to evaluate the effect of TRCC permanent and conventional temporary formworks in RC columns on key parameters of confinement. These parameters are, respectively, the hysteretic response, strength, displacement ductility, stiffness degradation, energy absorption capacity, damping ratio, residual displacement, crack pattern and failure mechanism. The comprehensive experimental investigations have shown that TRCC permanent formwork improves confinement efficiency. Consequently, there is great potential for use of TRCC permanent formworks as an alternative for conventional formworks in the RC columns.

The effect of different earthquake ground motion level on performance of reinforced-concrete structures

Four different earthquake ground motion levels with different probabilities of exceedance were expressed with the current seismic design code. In this study, earthquake-structural parameters were obtained by taking into account four different ground motion levels for four different provinces with different earthquake hazards. Structural analyses were carried out using different earthquake ground motion levels obtained for each province. In the structural analysis, a sample reinforced-concrete structure with the same structural characteristics was selected. The results were obtained by using both ground motion levels and design spectra for four provinces. With this study, both the earthquake hazard and the ground motion level change were examined separately. It was determined that the two variables significantly changed the target displacement values expected from the structure.

Explicitly Assessing the Durability of RC Structures Considering Spatial Variability and Correlation

The durability design of reinforced concrete (RC) structures that are exposed to aggressive environmental attacks (e.g., corrosion due to chloride ingress in marine environment) plays a vital role in ensuring the structural serviceability within a reference period of interest. Existing approaches for the durability design and assessment of RC structures have, for the most part, not considered the spatial distribution of corrosion-related structural properties. In this paper, a closed-form approach is developed for durability assessment of RC structures, where the structural dimension, spatial variability, and correlation of structural properties such as the concrete cover thickness and the chloride diffusion coefficient are taken into account. The corrosion and crack initiations of an emerged tube tunnel segment that was used in the Hong Kong-Zhuhai-Macau bridge project were assessed to demonstrate the applicability of the proposed approach. The accuracy of the method was verified through a comparison with Monte Carlo simulation results based on two-dimensional random field modeling. The proposed method can be used to efficiently assess the durability performance of RC structures in the marine environment and has the potential to become an efficient tool to guide the durability design of RC structures subjected to corrosion.

Modelling Strategies for the Numerical Simulation of the Behaviour of Corroded RC Columns under Cyclic Loads

Rebars corrosion phenomena can modify the structural behaviour of reinforced concrete (RC) members and consequently the seismic performance of RC structures. Since many existing RC structures are affected by this phenomenon, the influence of the reinforcement corrosion on the seismic performance is still under examination, especially when the corrosive attack is localized in the dissipative areas of the plastic hinges. In this work, the effect of localized corrosion is numerically investigated, through the adoption of a suitable finite element model, object of validation with the outcomes of an experimental campaign carried out in the Laboratory of the University of Rome “Tor Vergata”, on un-corroded and corroded RC columns subjected to axial load and cyclic horizontal actions. Particular attention has been paid to the definition of the three-dimensional model and to the modelling of the corroded rebars and their corrosion morphology. Indeed, different modelling strategies are proposed with the aim to properly simulate the cyclic behaviour of the corroded columns. The main results show how more refined strategies taking into account the morphological aspects of the corrosion phenomenon produce a better fit with the experimental results for both Damage Control and Life Safety limit states performance.

Low-cycle fatigue properties of bimetallic steel bars after exposure to elevated temperature

The BSB (bimetallic steel bar) has a broad application prospect in RC (reinforced concrete) structures servicing in corrosive environment. To determine seismic resistance of RC structures, it is important to clarify the low-cycle fatigue properties of reinforcement. Fire has lasting effects on mechanical properties of BSB. To value the service performance of RC structures after fire, the low-cycle fatigue properties of BSB are investigated experimentally. After elevated temperature, the substrate and cladding layer are still tightly bonded. When exposure temperature is relatively high (800 °C and 900 °C), there is martensite formed because of the quenching treatment. When the exposure temperature is lower than 700 °C, the hysteresis curves perform the full rhombus. When the exposure temperature ranges from 700 °C to 900 °C, the hysteresis curves become slender and the maximum tensile and compressive stresses increase. The models for predicting the cycles to failure and total dissipated energy density are proposed, which can predict the low-cycle fatigue properties of BSB after exposure to elevated temperatures. The comprehensive discussion between metallographic structures and low-cycle fatigue properties is performed. When the exposure temperature ranges from 300 °C to 700 °C, BSB specimens perform the ductile fracture failure. The intergranular embrittlement of martensite leads to the intergranular failure of BSB specimens exposed to 800 °C and 900 °C.

Study on the mechanical performance of TRC-strengthened RC beams under a salt freeze–thaw environment

The issue of the freeze–thaw has significantly affected the safety of reinforced concrete (RC) structures. Strengthening is an effective method to improve the safety performance of RC structures. To investigate the freeze–thaw resistance of RC beams strengthened with textile-reinforced concrete (TRC), the crack pattern, failure mode, load–deflection behavior, and bearing capacity of TRC-strengthened RC beams under a salt freeze–thaw environment were studied. The test parameters included the number of freeze–thaw cycles, installation method (cast-in-place versus precast), and sustained loading. The test results showed that the failure mode of the TRC-strengthened beam changes from flexural failure to shear failure due to freeze–thaw cycles. The installation method also affected the failure mode of the beams. The beam prepared using the precast method exhibited debonding failure, whereas the beam prepared using the cast-in-place method exhibited shear failure. When the freeze–thaw cycles exceeded a certain number or the sustained load surpassed a certain value, the crack control ability of the TRC weakened. The freeze–thaw cycle changed the load–deflection curve of the TRC-strengthened beam from a typical three-stage form to an approximate line. The ultimate load of the TRC-strengthened beam decreased with an increase in the number of freeze–thaw cycles. The ultimate load was also affected by the sustained load: the greater the sustained load, the greater the decrease in the ultimate load.

Time Scale of Chloride-Induced Corrosion on Circular Section RC Linked Accelerated Test to Natural Corrosion

The time scale in accelerated decay is essential for studying the durability of reinforced concrete (RC) structures exposed to the chloride corrosion environment. An accelerated corrosion test (ACT) was carried out on RC specimens were conducted under different chloride concentrations and applied voltages, with the information of steel measured. A novel prediction model of the complete corrosion process is proposed to evaluate the time correlation between accelerated decay and natural corrosion. The corrosion process of RC is divided into two stages: corrosion initial stage and corrosion stage of reinforcement. For the first stage, the coefficient of circular section members is presented. For the second stage, the accelerated factor of the test for the natural environment is proposed based on the Arrhenius-type and Faraday’s law. It is calculated by making regressions among some values of parameters, while moving to natural corrosion are extrapolating. The accelerating effect of applied voltages increases in the low-chloride environment, which is better than that in the high-chloride environment. This study provides calibration of the time scale for laboratory tests to analyze the performance of RC structures after corrosion.

Impact of Laboratory-Accelerated Aging Methods to Study Alkali-Silica Reaction and Reinforcement Corrosion on the Properties of Concrete.

This study focuses on two separate investigations of the main aging mechanisms: alkali–silica reactivity (ASR) and the corrosion of reinforcing steel (rebar) concrete, both of which may result in a premature failure to meet the serviceability or strength requirements of a concrete structure. However, these processes occur very slowly, spanning decades. The impact of direct chemical additives to fresh concrete to accelerate ASR and the corrosion of reinforcing steel on the fresh and hardened properties of the ensuing material are investigated to inform the potential use of chemicals in large-scale studies. The deterioration of reinforced concrete (RC) is determined by means of expansion, cracking, bulk diffusivity and surface resistivity measurements, and compressive, split tensile and flexural strength tests. The results indicate that the addition of sodium hydroxide and calcium chloride can effectively accelerate the crack formation and propagation in concrete due to ASR and the corrosion of rebar, respectively. The ASR-induced cracks maintained a constant crack width from 0.05 mm to 0.1 mm over the measurement period regardless of the intensity of aging acceleration. Adding 4% chloride by weight of cement for accelerating rebar corrosion resulted in an average crack that was 82% larger than in the case of ASR accelerated with the addition of sodium hydroxide. The addition of alkali resulted in an increase in early-age (7-day) strength. At a total alkali loading of 2.98 kg/m3, 3.84 kg/m3 and 5.57 kg/m3, the 28-day compressive strength of concrete decreased by 3%, 10% and 24%, respectively. Similarly, a higher early-age strength and a lower later-age strength was observed for the concrete in the presence of corrosive calcium chloride. The results from this research are expected to inform future studies on the long-term performance of RC structures under accelerated ASR and corrosion.