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The article describes the results of an experiment that was done to develop a technique of reinforcement strength characteristics determination by using method of “thread cut”, after various temperature effects on it.

Steel corrosion is major reason of the deterioration of reinforced concrete structures. Decreasing the transportation of erosion ions in concrete is one of effective methods to protect the steel from corrosion. In the present work, a novel nano-hydrophobic admixture is introduced to improve the ion-diffusion properties and the corrosion resistance of reinforced steel. Compared with unmodified concrete, the nano-hydrophobic admixture effectively decreases the water adsorption, water evaporation, and chloride ions transport in a concrete structure, and then improved the concrete’s durability. The concrete’s water adsorption decreased more than 78%, and the initial corrosion time of reinforced steel is prolonged more than one time by treatment with the nano-hydrophobic admixture. The inhibition penetration of the medium in concrete modified by hydrophobic nanoparticles is the key to provide the protective properties of steel reinforcement from chloride erosion.

Crack control remains important even if corrosion-resistant reinforcement (chromium-containing or -chromium-coated bars) is used because cracking of the concrete can lead to durability concerns such as freezing-and-thawing damage. Considering that the surface roughness is different for various corrosion-resistant bars even without coatings, differences in both crack widths and spacing are expected. Twelve slabs were tested to 1) identify how cracking is affected by various types of bars; 2) investigate if current crack width calculations are adequate for these bars; and 3) evaluate crack widths at higher stress levels considering that chromium-containing bars (for example, stainless steel andASTM A1035) have higher strengths that may be used in design. Primary variables considered included the bar type and bar spacing. The influence of bar stress was also of primary interest as high service stresses are possible with the use of higher strength reinforcement. Keywords: bridge deck cracking; corrosion-resistant reinforcing steel; crack control; crack width; high-strength reinforcing steel; stainless steel reinforcing steel.

Reinforcing steel (RS) is mainly used in building construction and many industries, but it suffers from corrosion problems, especially in acidic environments. Biopolymers are characterized by their unique chemical composition, as they contain a variety of functional groups that are capable of binding strongly to the metal surface and forming a protective layer on it. Herewith, two biopolymers, viz. dextrin (Dex) and inulin (Inu), were tested as eco-friendly inhibitors for the corrosion of RS in 1.0 M HCl medium at different temperatures. Various experimental tools were utilized in this research. The inhibition efficiencies (% IEs) of the tested polymeric compounds were improved by increasing their doses while reducing with rising temperature. The % IEs of Dex and Inu at a dose of 500 mg/L reached 85% and 93%, respectively. The examined biopolymers displayed cathodic/anodic behavior (mixed type) with a foremost anodic one. The acquired higher % IEs were demonstrated by intense adsorption of Dex and Inu on the RS surface fitting the Langmuir isotherm. The influence of rising temperature in the range of 288–318 K on the corrosion behavior was examined, and the evaluated thermodynamic and kinetic parameters sustained the mechanism of physical adsorption of the polymeric inhibitors. Additionally, the kinetics of corrosion, as well as its inhibition by Dex and Inu, were also investigated. The SEM micrographs of the RS surfaces were accorded with all utilized experimental tools. The results gained from all used tools were discovered to be in good agreement with each other.

Chloride threshold values for steel reinforcing bars in reinforced concrete under the effect of varying temperatures and extended long-term conditions in hot climate are investigated. This investigation covers a gap in the current codes, including ACI 318, where the effect of temperature on the chloride threshold is not addressed. A total of 96 concrete specimens reinforced with carbon steel reinforcing bars sourced from two manufacturers were cast with different chloride contents and exposed to four temperatures of 20, 35, 50, and 65°C (68, 95, 122, and 149°F) for a period of more than 2 years. The chloride threshold values were determined based on corrosion potential, corrosion rate, and mass loss at the end of the exposure period. The results of the three techniques showed a consistent trend of significant dependency of the chloride threshold value on temperature. The average water-soluble chloride threshold values based on mass loss were found to be 0.77%, 0.72%, 0.47%, and 0.12% by weight of cement for temperatures of 20, 35, 50, and 65°C (68, 95, 122, and 149°F), respectively. These findings are significant as they showed a dramatic drop in the chloride threshold values at high temperature. This research highlights the need for reassessment of ACI Code limits considering hot climate.

In recent years, HRB400 and HTRB600 steel bars have become the mainstream standard reinforcing steel used in concrete structures in China. However, significant controversy still exists regarding the selection of material constitutive models and the determination of model parameters for buckling, fatigue, hysteresis, and other material characteristics. In this article, an automated process of multi-parameter calculation of the constitutive model for reinforcing steel – simulation accuracy evaluation of the constitutive model – selection of the constitutive model of reinforcing steel is established based on the hybrid programming method using MATLAB and OpenSees software. First, tensile and low-cycle fatigue tests were carried out on HRB400 and HTRB600 steel bars. Second, based on the constitutive model in OpenSees software and the skeleton curve and characteristics such as yielding, fatigue, and hysteresis, the constitutive model parameters of HRB400 and HTRB600 steel bars are determined using indirect and direct fitting methods. Finally, the five similarity parameters of the simulated normalized cumulative hysteretic energy dissipation coefficient are compared with the test results. The results indicate that the simulation accuracy of the Reinforcing Steel model exceeds 72%, which is higher than other four models, making it the best choice for reinforcing steel in numerical simulation.

The crevice corrosion of the reinforcing steel in the carbonated simulated concrete pore solutions (SCPSs) containing 0.04 mol/L chloride was investigated. In comparison, the steel without crevice covered on its surface was also studied. Results showed that the crevice corrosion in the uncarbonated SCPS was not triggered and the steel remained passivity by suppressing the anodic dissolution in the crevice interior. As SCPS was carbonated to have pH values of 10.5 and 11.5, the crevice corrosion was easier to be activated than the widely reported pitting corrosion owing to the rapid oxygen depletion within the crevice, but the crevice corrosion damage might be alleviated to a certain extent due to the relative compact surface film formed inside the crevice. The further carbonation led to the activation dissolution of both the crevice interior and exterior, causing the more serious corrosion damage. Corrosion process of the crevice corrosion was systematically analyzed by combining the electrochemical measurement results and Evens polarization diagram.

The main shortcomings associated with using high-strength steel (HSS) bars in concrete beams are related to the cracking behavior of these beams at service load and the possibility of concrete crushing prior to steel yielding. This paper investigates the effect of using high-strength concrete (HSC), fiber-reinforced concrete (FRC), and compression reinforcement to enhance the flexural behavior of HSS-reinforced concrete (RC) beams. Plain concrete, steel-fiber, and synthetic FRC were used to cast 24 beams of singly and doubly reinforced concrete sections. In addition, concrete compressive strengths of 7.25 and 11.6 ksi (50 and 80MPa) were used in the investigation. Four-point bending tests were conducted on all beams. The experimental results showed that increasing the concrete compressive strength contributes the most to the flexural capacity in steel FRC specimens. Results also indicated that highest curvature ductility was achieved by synthetic FRC beams with [f'.sub.c] = 11.6 ksi (80 MPa). The crack widths and deep propagation of cracks were noticeably restrained at service and steel yielding load in fiber-reinforced specimens. In addition, the applicability of ACI ITG-6R-10 recommendations was evaluated using the results of plain concrete specimens then extended to cover fiber-reinforced concrete beams. Keywords: cracking behavior; fiber-reinforced concrete; flexural strength; high-strength concrete; high-strength reinforcing steel.

Bar diameter is one of the basic factors affecting bond behavior, which is still of interest due to opposing opinions regarding its effect on bond behavior in the pull-out test. This paper presents an experimental and numerical bond analysis of ribbed reinforcing bar in concrete. The aim was to experimentally evaluate the effect of bar diameter on the bond behavior in the pull-out test and to perform numerical simulations of the conducted experiments in ABAQUS to verify their convergence to the obtained experimental results. The experiments used concrete of C35/45 grade and B500SP reinforcing steel bars of three diameters: 10, 12, and 16 mm. FEA simulations employed the Concrete Damaged Plasticity (CDP) material model and the Contact Cohesive Behavior (CCB) method to model the concrete–bar interface. The study shows that bar diameter significantly affects the bond, both on the bond stress–slip relationship and the type of bond failure, as well as on the bond strength. FEA simulations correctly reflected the bond behavior observed in the specimens. The analytical models presented estimates that were too conservative regarding the maximum bond stress relative to the experimental results.

In this study, the ability of lithium nitrite and amino alcohol inhibitors to provide corrosion protection to reinforcing steel was investigated. Two types of specimens—reinforcing steel and a reinforced concrete prism that were exposed to chloride ion levels resembling the chloride attack environment—were prepared. An autoclave accelerated corrosion test was then conducted. The variables tested included the chloride-ion concentration and molar ratios of anti-corrosion ingredients in a CaOH2-saturated aqueous solution that simulated a cement-pore solution. A concentration of 25% was used for the lithium nitrite inhibitor LiNO2, and an 80% solution of dimethyl ethanolamine ((CH3)2NCH2CH2OH, hereinafter DMEA) was used for the amino alcohol inhibitor. The test results indicated that the lithium nitrite inhibitor displayed anti-corrosion properties at a molar ratio of inhibitor of ≥0.6; the amino alcohol inhibitor also displayed anti-corrosion properties at molar ratios of inhibitor greater than approximately 0.3.