This paper presents the findings of an experimental study on the corrosion performance of both conventional and corrosion-resistant steel reinforcements in normal-strength concrete (NC), high-performance concrete (HPC), and ultra-high-performance concrete (UHPC) columns in an accelerated corrosion-inducing environment for up to 24 months. Half-cell potential (HCP), linear polarization resistance (LPR), and electrochemical impedance spectroscopy (EIS) methods were used to assess the corrosion activities and corrosion rates. The reinforcement mass losses were directly measured from the specimens and compared to the results from electrochemical corrosion rate measurements. It was concluded that UHPC completely prevents corrosion of reinforcement embedded inside, while HPC offers higher protection than NC in the experimental period. Based on electrochemical measurements the average corrosion rate of mild steel and high chromium steel reinforcement in NC in 24 months were respectively 6.6 and 2.8 times that of the same reinforcements in HPC. In addition, corrosion-resistant steel reinforcements including epoxy-coated reinforcing bars, high chromium steel reinforcing bars, and stainless-steel reinforcing bars showed excellent resistance to corrosion compared to conventional mild steel reinforcement. There was no active corrosion observed for epoxy-coated and stainless-steel reinforcements during the 24 months of the accelerated aging; the average corrosion rate of high chromium steel was 50% of that of mild steel in NC based on the electrochemical corrosion measurements; the average mass loss of high chromium steel were 47% and 75% of that of mild steel in NC and HPC, respectively. The results also showed that the LPR method might slightly overestimate the corrosion rate. Finally, pitting corrosion was found to be the dominant type of corrosion in both mild steel and high chromium steel reinforcements in NC and HPC columns.

A reliable compressive stress–strain model was established for concrete with varying densities reinforced either using steel fibers alone or using a combination of steel fibers and micro-synthetic fibers. Moreover, a simple equation was presented to determine the compressive toughness index of fiber-reinforced concrete in a straightforward manner. The fiber reinforcing index was introduced to explain the effect of various parameter conditions of fibers on the enhancement of the concrete properties under compression. Numerical and regression analyses were performed to derive equations to determine the key parameter associated with the slope at the pre- and post-peak branches and compressive toughness index via extensive parametric studies. The proposed models are promising tools to accurately predict the stress–strain relationships of fiber-reinforced concrete with different densities, resulting in less scattered values between experiments and predictions, and reasonably assess the efficiency of fiber reinforcements in enhancing the compressive response of concrete.

One way to reinforce concrete is to use steel bars. It is essential to find substitute artificial materials because such bars are prone to corrosion, and reinforcing steel suffers from the penetration of hazardous substances into porous concrete. Several solutions have been proposed in recent years for reducing the pores and microcracks thus created. From these solutions, biological methods have attracted more attention due to their cost-effective and eco-friendly nature. On the other hand, fiber reinforcement may significantly improve concrete tensile strength, crack-related properties, and ductility. In the present study, Bacillus subtilis is used in specimens in which one of the three polypropylene, hooked-end steel, or barchip fibers (at volume percentages of 0.3%, 1%, and 0.75%, respectively) is considered as reinforcement. Moreover, bacterial strains in the culture medium are used in place of concrete mixing water, and bacterial spores in the culture medium are applied as a surface treatment gel. Cylindrical specimens were cast to be used for the compressive strength, water absorption, and electrical resistance tests. With a reduction of 36% in water absorption, the bacterial specimens outperformed their corresponding controls. The compressive strength test revealed an increase of 25.5% in compressive strength in surface-treated specimens relative to the corresponding control ones. The best performance of bacteria was observed in reducing electrical resistance in the concrete specimens reinforced with polypropylene fibers. Overall, the three applications of bacteria were found capable of forming calcite sediments, with greater deposits formed due to bacterial activity than by the spores used in the surface treatment.

The critical chloride threshold, C_{crit/, is a value of a reinforced concrete system and the critical parameter that is used to define the initiation of reinforcement corrosion and is used for service life predictions. The published Ccrit/ data in the literature shows significant variability due to the lack of a standardized laboratory test that can consistently be used by the industry and researchers. This paper reports data from a multi-laboratory validation study of a novel Ccrit/ test method, developed based on a framework established by ACI Committee 222. The study was conducted using the same set of materials in three different laboratories, and its repeatability and reproducibility were evaluated. Results indicated that the mean Ccrit/ values were not statistically significantly different. Exhibiting good repeatability and reproducibility, this test method should be further evaluated to be implemented as a standard laboratory Ccrit/ test method.}

This paper presents the findings of a systematic comparison of the corrosion behavior of corrosion-resistant steel reinforcements, including epoxy-coated steel, high-chromium steel, and stainless steel reinforcement in normal-strength concrete (NC) and high-performance concrete (HPC) columns in an accelerated chloride attack environment for 24 months. The corrosion potential and corrosion rate of the reinforcements were monitored using electrochemical methods, and the degradation of the axial compressive capacity of 40 corroded columns over time was obtained and discussed. Findings indicated that corrosion-resistant reinforcements showed significantly better corrosion performance: no corrosion was observed for intact epoxy-coated and stainless steel reinforcements, and less corrosion (54%) was found on high-chromium steel than conventional mild steel in NC, while similar corrosion rates were found for mild steel and high-chromium steel reinforcements in HPC. Results also indicated that HPC provided reliable protection to the embedded reinforcements, showing smaller corrosion rates than those in NC. The measured average corrosion rate of mild steel and high-chromium steel reinforcements in HPC was 17 to 37% of that in NC. In addition, an analytical model was synthesized to predict the axial load-axial shortening relationship of the corroded circular reinforced concrete columns.