Search Results (22)

To elucidate the mechanism underlying the changes in the bonding performance of reinforced reef limestone concrete under dry–wet carbonation cycles, and to establish a foundation for its durability analysis and design, experiments were conducted with varying dry–wet carbonation cycles (0, 20, 40, 60, and 80 cycles) and loading rates (0.01 mm/min, 0.1 mm/min, 1 mm/min, 2 mm/min, and 5 mm/min) through pull-out tests. The results demonstrate that as the number of dry–wet carbonation cycles increases, the damage to reinforced reef limestone concrete intensifies progressively, reaching a mass loss rate of 3.05% by the end of the cycles, while the ultrasonic wave velocity decreases by 17.4%. The effects of different loading rates and cycle counts on reinforced reef limestone concrete are primarily observed through alterations in peak bond stress. Utilizing the experimental data, this study established an equation to analyze the influence of dry–wet carbonation cycles and loading rates on the bond strength and slip behavior between steel bars and reef limestone concrete. This equation offers a theoretical framework for the durability analysis and design of reinforced reef limestone concrete. Full article

The influence of the carbonation of recycled coarse aggregates on the durability performance of the recycled aggregate concrete beams is still unclear. In this study, the corrosion characteristics and flexural performance of the carbonated recycled aggregate concrete (C-RAC) beams in corrosive environments were investigated. The results illustrated that the mass loss of the longitudinal tensile steel bars (LTSBs) in the corroded C-RAC beams decreased when the replacement ratio of the carbonated recycled coarse aggregate (CRCA) increased. Compared to the corroded non-carbonated recycled aggregate concrete (NC-RAC) beam, the mass loss of LTSBs in the corroded C-RAC beam was reduced by 37.91% when the CRCA replacement ratio was 100%. The average mass loss of the short limbs of the stirrups on the tensile side of the corroded C-RAC beam was lower than that of the corroded NC-RAC beam. As the CRCA replacement ratio increased, the flexural performance of the corroded C-RAC beams was enhanced. When the CRCA replacement ratio was 100%, the ultimate load and the displacement ductility coefficient of the corroded C-RAC beam increased by 14.04% and 25.82% compared to the corroded NC-RAC beam, respectively. During the service life, the concrete strains of the cross-section at the mid-span of the corroded C-RAC beams satisfied the assumption of plane section. The research results of this study can provide some reference for the durability design and engineering application of C-RAC beams. Full article

In corrosive environments containing chloride and sulfate, the corrosion of steel bars is common along the base of squat RC shear walls (SRCSW) due to problems such as construction quality, concrete stress concentration, local defects, and accumulation of water and corrosive media. In this paper, three SRCSWs are designed and constructed and their mechanical properties assessed. One side of each SRCSW was exposed to a corrosive environment for 70 days, while the other side was subject to the same conditions over different corrosion times (i.e., 0 day, 42 days, and 70 days). Then, the corrosion-induced cracking process, the mechanical properties of SRCSWs corroded along the base, the relationship between the mass loss of total steel bars (MLTSB) in the corroded area and the wall mechanical properties, and the relationship between the average width of corrosion-induced cracks (CICs) and the wall mechanical properties were studied through an accelerated corrosion test and a loading failure test. The results indicate that the area of corrosion-induced cracking on SRCSWs increased with the corrosion time, and the cracking area on the different SRCSWs was approximately identical when the SRCSWs were exposed to the same corrosion time. When the degree of corrosion was different, the loading failure characteristics of the SRCSWs were obviously different, but the failure mode always corresponded to shear failure. The load–displacement curves of the SRCSWs with different degrees of corrosion along the base basically coincided and were linear when the loading was in the elastic stage. Compared to SW-1, the peak load of SW-2 decreased by 4.0%, but that of SW-3 increased by 2.7%. Compared to SW-1, the yield loads of SW-2 and SW-3 decreased by 22.4% and 11.8%, respectively. When the MLTSB increased from 13.05% to 16.71%, the crack, yield, and peak loads of the SRCSWs corroded along the base decreased by 8.8%, 22.4%, and 6.8%, respectively. The cracking, yield, and peak loads of the SRCSWs corroded along the base decreased linearly with the increase in MLTSB and the average width of the CICs, and the corresponding fitting relations were established. The results of this study can serve as a reference for the durability design of SRCSWs in corrosive environments. Full article

Reactive powder concrete (RPC) is widely used in large-scale bridges, and its durability in coastal areas has become a significant concern. Straw fibers have been evidenced to improve the mechanical properties of concrete, while research on their influence on the chloride corrosion resistance of RPC is deficient. Therefore, it is essential to establish the relationships between the quantities and parameters of straw fibers and the properties of the resulting concrete. In this study, the mass loss rates (MLRs), the relative dynamic modulus of elasticity (RDME), the electrical resistance (R), the AC impedance spectrum (ACIS), and the corrosion rates of steel-bar-reinforced RPC mixed with 0%–4% straw fibers by volume of RPC were investigated. A scanning electron microscope (SEM) and X-ray diffraction (XRD) were used to analyze the corrosion of steel bars. The reinforced RPC specimens were exposed to a 3% NaCl dry-wet alternations (D-As) and 3% NaCl freeze-thaw cycles (F-Cs) environment. The results show that, after adding 1%–4% straw fibers, the setting time and slump flow of fresh RPC were reduced by up to 16.92% and 12.89%. The MLRs were −0.44%–0.43% and −0.38%–0.42%, respectively, during the D-As and F-Cs. The relationship between the RDME and the fiber volume ratio was the quadratic function, and it was improved by 9.34%–13.94% and 3.01%–5.26% after 10 D-As and 100 F-Cs, respectively. Incorporating 4% straw fibers reduced the R values of the reinforced RPC specimens by up to 22.90% and decreased the corrosion rates after 10 D-As and 100 F-Cs by 26.08% and 82.29%, respectively. The impedance value was also increased. Moreover, a dense, ultra-fine iron layer and α-FeO(OH) were observed in the rust of rebars by SEM and XRD, as the corrosion resistance of rebars was enhanced. The results indicate that straw fibers improved the corrosion resistance of RPC, which can serve as a protective material to inhibit concrete cracking and thereby prevent rebar oxidation. This study provides theoretical support for the investigation of surface phenomena in reinforced RPC with straw fibers. Full article

The combined application of steel–FRP composite bars (SFCBs) and seawater sea-sand concrete (SSSC) in marine engineering not only solves the problem of resource scarcity and reduces the construction cost but also avoids the problems of chloride corrosion of steel reinforcement in seawater sea-sand concrete and the lack of ductility of FRP bars. At the same time, the addition of glass fiber (GF) and expansion agent (EA) in appropriate amounts improves the crack resistance and seepage resistance of concrete. However, the durability of SFCB with GF- and EA-reinforced SSSC in freezing–thawing environment remains unclear, which limits its potential application in cryogenic marine engineering. This study investigates the bonding properties between SFCB and GF-EA-SSSC interfaces using eccentric pullout experiments under different thicknesses of concrete protective cover and a number of freezing–thawing cycles. The results showed that the compressive strength and dynamic elastic modulus of SSSC decrease, while the mass loss increases with an increasing number of freezing–thawing cycles. Additionally, the bond strength and stiffness between SFCB and SSSC decrease, leading to an increase in relative slip. However, the rate of bond strength and stiffness loss decreases with an increase in the thickness of the concrete protective cover. Furthermore, formulas for bond strength, relative slip, and bond stiffness are established to quantify the effects of the thickness of the concrete protective cover and the number of freezing–thawing cycles. The experimental values obtained verify the accuracy of these formulas, with a relative error of less than 5%. Moreover, a bond stress–slip constitutive model is developed for SFCB and GF-EA-SSSC, and the fitting results closely resemble the experimental values, demonstrating a high level of model fit. Full article

Secondary aluminum ash (SAA) is a type of common solid waste which leads to pollution without treatment. Due to its chemical reactivity, the application of SAA to reactive powder concrete (RPC) may help solidify this solid waste while increasing its performance. However, RPC is usually in active service when used with steel bars. NaCl can corrode the steel bars when reinforced RPC is used in a coastal environment. In this study, the corrosion resistance of reinforced RPC was investigated. The specimens were exposed to an environment of NaCl with freeze–thaw cycles (F-Cs) and dry–wet alternations (D-As). The corresponding mass loss rates (MRs), the electrochemical impedance spectroscopy (EIS) curves and the dynamic modulus of elasticity (DME) were measured. The results show that the MR and the DME of reinforced RPC decrease with increasing values of F-C and D-A. F-C and D-A increases lead to increased electrical resistance (R). The real part value corresponding to the extreme point of the EIS curve is increased by 0~213.7% when the SAA is added. The relationship between the imaginary part and the real part of the EIS fits the quadratic function. The equivalent circuit of the reinforced RPC is obtained from the EIS curves. The R of the rust is calculated by using the equivalent circuit. The rust’s R decreases in the quadratic function with the mass ratio of the SAA. After 200 NaCl F-Cs, the MR, the DME and the R vary within the ranges of 23.4~113.6%, −2.93~−4.76% and 4.92~13.55%. When 20 NaCl D-As are finished, the MR, the DME and the R vary within the ranges of 34.7~202.8%, −13.21~−14.93% and 120.48~486.39%. The corrosion area rates are 2.3~68.7% and 28.7~125.6% higher after exposure to 200 NaCl F-Cs and 20 NaCl D-As. When the SAA is mixed, the MR is decreased by 0~13.12%, the DME increases by 0~3.11%, the R of the reinforced RPC increases by 26.01~152.43% and the corrosion area rates are decreased by 21.39~58.62%. This study will provide a novel method for solidifying SAA while improving the chlorine salt resistance of RPC. Full article

Straw fiber, as a kind of waste if not properly treated, will pollute the environment. It can be used in cement-based materials as a plant fiber material. Agricultural solid-waste straw fiber has good tensile properties and is expected to be used as a fiber-reinforced material for reactive powder concrete (RPC) and to improve the corrosion resistance of RPC. In this paper, the ultrasonic velocity through specimens, the electrical resistance, the AC impedance spectroscopy and tafel curve were analyzed. The corrosion resistance of the steel bar under the chloride salt freeze–thaw cycles and dry–wet alternations was systematically studied. The result shows that adding a certain content of straw fiber can improve its corrosion resistance. Under the action of two chloride salt environments, the lowest mass loss rate was 0.82% for the sample with 3% straw fiber content and the mass growth rate of the specimens with 4% straw fiber is the highest aqt 0.9%. In terms of ultrasonic velocity, the lowest loss rate was 5.68% for specimens with fiber content of 2%. The specimens were subjected to 0 dry–wet alternations and freeze–thaw cycles; the highest electrical resistance is 19.96 kΩ when the fiber content is 1% and the lowest electrical resistance is 11.105 kΩ when the fiber content is 2%. Under the dry–wet alternations, the content of straw fiber and its corrosion resistance are: 1% > 4% > 0% > 3% > 2%. Under freeze–thaw cycles, the content of straw fiber and its corrosion resistance were as follows: 1% > 0% > 4% > 3% > 2%. Full article

In this study, the influence of CO₂ curing on the corrosion resistance of reinforced alkali-activated compounds is investigated. Fly ash (FA) and blast furnace slag powder (BFS) are used as mineral admixtures. The specimens were subjected to dry–wet alternations with 3% NaCl, used to simulate a concrete structure under a corrosion environment. The ultrasonic velocity, mass loss rate, and electrical characteristics (such as electrical resistance, AC impedance spectra, and corrosion area rates determined by Tafel curves) are utilized to determine the degree of corrosion. Scanning electron microscopy (SEM) and X-ray diffraction (XRD) are used to analyze the corrosion mechanism. Results show that the corrosion resistance is decreased by the addition of FA but improved by CO₂ curing. When CO₂ curing is provided, the addition of BFS shows a higher enhancing effect on the corrosion resistance than that of FA. The equivalent circuit diagram of reinforced alkali-activated compound mineral admixtures obtained by AC impedance spectra is composed of three electrical elements (electrical resistance and capacitance in parallel) in series. The X-ray diffraction results show that adding BFS and CO₂ curing can decrease the rust’s iron oxides on the steel bars’ surface. Finally, as found in the SEM photos, BFS and CO₂ curing can effectively improve the compactness of specimens. Meanwhile, the roughness of hydration is increased by CO₂ curing. Full article

The corrosion of reinforcing steel in concrete has been reported as one of the main durability problems of reinforced concrete (RC) structures exposed to chloride, carbonation or both. To investigate the structural performances of RC structures subjected to corrosive exposure, the corrosion of rebars embedded in concrete is accelerated to induce a targeted degree of reinforcement corrosion in a short time duration. Several earlier researchers have attempted to develop a setup to induce the accelerated corrosion of steel bars in concrete structures. However, the induced corrosion has not been simulative of the naturally occurring corrosion of steel in concrete, causing a lack of accuracy in the test results. In this study, an attempt was made to develop a novel approach that could be utilized to induce required degrees of reinforcement corrosion following a natural pattern. To demonstrate the efficacy of the proposed setup and procedure of introducing uniform reinforcement corrosion, RC beam specimens were designed, cast, and corroded to three different corrosion levels. After inducing reinforcement corrosion, the beams were tested under flexural stress, and then the corroded bars were extracted to measure the mass loss due to corrosion. The visual inspection and gravimetric and flexural test results showed the capability of the proposed corrosion setup and procedure to induce the targeted uniform corrosion of steel bars, simulating a real-life scenario and facilitating the evaluation of the effect of reinforcement corrosion on the flexural performances of RC beams with very high accuracy. Full article

Corrosion of steel bars is of great significance for safety and service life of reinforced concrete structures. This work develops a prediction method for steel corrosion mass loss rate before the crack of concrete structure based on a spiral distributed fiber optic sensor. Reinforced concrete sample instrumented with a spiral distributed fiber optic sensor were prepared. The mathematic relationship between the corrosion mass loss rate of steel bar and the spiral distributed strain is theoretically derived. Meanwhile, numerical analysis by MATLAB shows that these parameters such as the protective layer thickness, corrosion mass loss rate, bar diameter, corrosion expansion coefficient have a remarkable influence on spiral distributed strain. Additionally, electrical accelerated corrosion experiment was performed on the reinforced concrete specimens. The helix strain along the distributed sensor was used to evaluate the corrosion mass loss of steel bar. Further, the influencing factors on the corrosion sensitivity are illustrated here and the corrosion mass loss rate before concrete crack is also quantified. This research provides insights into the corrosion deteriorate mechanism. Full article

In order to evaluate the influence of freeze–thaw action on the durability of concrete structures, this paper presented an experimental study to investigate the effects of freezing–thawing cycles and concrete strength on the bond behavior between steel bars and concrete confined with stirrups. Through freeze–thaw cycles and center pullout tests, the failure mode of pullout specimen, concrete strength, mass loss, dynamic elastic modulus, and bond–slip curves were analyzed. At last, the bond–slip constitutive model was proposed for specimens with stirrup confinement under freeze–thaw action. Main test results indicate that the failure mode and shape of bond–slip curves are affected by stirrups. The bond strength hasa certain increase after 100 freeze–thaw cycles owing to the constraining force from stirrups, whereas the splitting tensile strength significantly declines. After 100 freeze–thaw cycles, the splitting tensile strength of C20 and C40 decreased by 40.8% and 46.5%, respectively. The formula was provided to calculate the bond strength of constrained concrete after freeze–thaw cycles, and the damage coefficient and other related parameters in the formula were suggested. The predicted bond–slip curves are close to the experimental results, which could provide reference for the related research of bond performance after freeze–thaw action. Full article

The primary goal of the construction industries worldwide is to improve material durability and achieve sustainability. In recent years of sustainable cement industry innovation, alkali-activated cement has emerged as one of the most promising alternatives to ordinary Portland cement (OPC). In terms of durability, corrosion of steel is a significant problem and has become a major cause of deterioration of reinforced concrete structures worldwide. Thus, structural health monitoring techniques are essential to monitor the corrosion in real-time to avoid unexpected failure since civil engineering structures serve as a crucial pillar of the economy. This paper presents through an experimental campaign a novel method of automatically monitoring the performance of alkali-activated concrete (AAC) and ordinary Portland cement concrete (OPCC) under chloride-induced corrosion conditions using an embedded piezo sensor (EPS) based on the electro-mechanical impedance (EMI) technique. AAC was produced using alkali silicate-activated fly ash and ground granulated blast furnace slag. The accelerated corrosion tests were conducted on reinforced AAC and OPCC specimens in which the EPS was attached to reinforcing steel bars inside the specimens to monitor the changes in the EMI signature during the corrosion progression. To quantify the damage due to chloride-induced corrosion, statistical damage indices such as root mean square deviation were calculated. Further, the deterioration in structural parameters was identified by extracting the equivalent structural parameters (ESPs) such as stiffness, mass and damping from the raw EMI signatures. Based on qualitative and quantitative results, it can be seen that the changes in raw signature and damage in AAC were lower than OPCC. The deterioration in term of stiffness loss was found to be 39.35% in OPCC and 12.73% in AAC. Hence, it is demonstrated that the AAC exhibits a superior corrosion resistance to OPCC. Full article

Freeze–thaw cycles (FTCs) and steel bar corrosion (SBC) are the most common service conditions of hydraulic concrete and have significant impacts on its durability. Using pullout and microscopic tests of different FTC and SBC rates, we selected the mass loss rate, ultrasonic velocity, bond strength and bond slip in order to describe the changes in the macro-properties, and also selected the porosity and pore size distribution as micro-parameters in order to explore the influence of FTCs and SBC on the mechanical properties of hydraulic concrete. The results showed that the bond strength decreased as the FTCs increased due to the microstructure damage caused by FTC and SBC, which affects the mechanical properties. A corrosion rate of ≤3% offset the damage caused by 50 FTCs. FTCs and SBC resulted in superimposed damage effects on the concrete. In addition, we established a bond strength damage model based on the joint FTCs and SBC and quantitatively described the degradation law of the macro-mechanical properties. The analysis shows that the influence of FTCs on the bond strength was greater than that of the SBC. These research results can provide a reference and experimental support for the frost-resistant design and durability prediction of hydraulic concrete structures in cold environments. Full article

As it is widely known, corrosion poses a real threat for reinforced concrete structures, especially when they are located in coastal areas. This phenomenon, in conjunction with repeated loads, such as intense seismic events, adversely affect their useful service life. Several experimental studies have presented the magnitude of degradation of steel reinforcement due to corrosion in the presence of fatigue, which affects either the serviceability or durability of steel reinforcement. As a result, the current experimental study presents the results of the shot blasting process of steel reinforcement at various times of exposure to a corrosive environment and the influence on their dynamic response after the execution of low cycle fatigue tests at different constant strain amplitudes. The findings show the beneficial effect of the shot blasting process in terms of percentage mass loss and the improvement of mechanical performance of steel bars in terms of service life and energy dissipation capacity. Moreover, the assessment performed with a quality material index demonstrates the improved mechanical performance of shot blasted specimens vs. bare specimens, in the long term for medium range-imposed deformation. Full article

In this paper, the influence of Nano-silica (NS) and Polyvinyl alcohol (PVA) fibers on the corrosion behavior of steel rebar embedded in high-volume fly ash cement mortars under accelerated chloride attack was studied by using an impressed voltage technique. The PVA fibers used were 1.0 vol.%, and two mass fractions of cement (50 and 60 wt.%) were replaced by fly ash. Four NS mass fractions (0, 0.5, 1.0, and 1.5 wt.%) were utilized in this paper. In addition, the mono and hybrid effects of NS and PVA on the mechanical properties and water absorption of mortar were also studied. The results showed that the incorporation of PVA and nano-SiO₂ can improve the flexural and compressive strengths of high-volume fly ash mortar. Generally, the flexural and compressive strengths increased with the increase of nano-SiO₂ content. Moreover, the incorporation NS can also reduce the capillary water–absorption rate of cement mortar. The impressed voltage corrosion test indicated that the composite incorporation of nano-SiO₂ and PVA can significantly delay the deterioration process of steel bars in mortar, effectively reducing the steel rebar’s corrosion level and increasing the exposure time of the surface crack. With hybrid-incorporation 1.0 vol.% PVA and 1.0 wt.% nano-SiO₂, the steel rebar had the lowest corrosion degree, which exhibited a mass loss of 49% and increased the broken time by 71% as compared to the control mortar. Full article