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The reliability and durability of reinforced concrete structures depend on the amount of concrete cracking. The risk associated with cracks generates a need for diagnostic methods for the evaluation of reinforced concrete structures. This paper presents the results of a study of 10 single-span reinforced concrete beams to follow the process of crack formation and changes in their width. The beams were loaded to failure with two forces in a monotonic manner with unloading and in a cyclic manner. Continuous observation of the crack formation process was provided by the digital image correlation system. The simplified method for estimating the maximum crack width is proposed. The presented results confirmed the stochastic character of the process of crack formation and development. The maximum crack widths calculated on the basis of the proposed formula were on the safe side in relation to those calculated according to Eurocode 2. It was also confirmed that the distances between cracks do not depend on the loading manner. Hence the density function describing the distribution of distances between cracks can be used to assess the condition of reinforced concrete elements. The research has also shown the suitability of the DIC system (ARAMIS) for testing concrete elements.

This study aims to verify the adaptability of a crack width evaluation method for fiber-reinforced cementitious composite (FRCC) proposed by the authors to various combinations of fiber-reinforced polymer (FRP) bars and FRCCs. As this evaluation method requires bond constitutive laws between FRP bars and FRCC, bond tests between FRP and FRCCs were conducted. The FRP and FRCC combinations used in the bond tests were spiral-type CFRP and GFRP bars with PVA-FRCC, as well as strand-type CFRP bars with aramid–FRCC. The maximum bond stress tended to increase as the rib–height ratio of the spiral-type bars increased. When the rib–height ratio increased by 50%, the maximum bond stress of the CFRP and GFRP bars increased by 11% and 33%, respectively. For aramid–FRCC, the average maximum bond stress in the FRCC with a 0.25% volume fraction was 1.67 times that in mortar, and that in 0.50% was 2.01 times that in mortar. The bond constitutive laws were modeled using the trilinear model. Verifications of the method’s adaptability were conducted using tension tests on prisms made of spiral-type CFRP and GFRP bars with PVA-FRCC. As a result of the tension tests, when the FRP strain reached approximately 0.3%, the crack width was about 0.2 mm for CFRP bars and about 0.1 mm for GFRP bars. Verifications were also conducted using four-point bending tests on strand-type CFRP bar beams with aramid–FRCC. The crack width at the same FRP strain tended to become smaller as the fiber volume fraction of FRCC increased. When the FRP strain reached approximately 0.2%, the average crack width of the mortar specimen was around 0.25 mm, whereas it was about 0.15 mm in FRCC with a 0.25% volume fraction and about 0.10 mm at 0.5%. The test results for FRP strain versus crack width relationships were compared with the calculations using the crack width prediction formula. The test results and calculation results were in good agreement.

This study addresses the growing need for sustainable construction materials by investigating the mechanical properties and behavior of palm fiber-reinforced cementitious composite (FRCC), a potential eco-friendly alternative to synthetic fiber reinforcements. Despite the promise of natural fibers in enhancing the mechanical performance of composites, challenges remain in optimizing fiber distribution, fiber–composite bonding mechanism, and its balance to matrix strength. To address these challenges, this study conducted extensive experimental programs using palm fiber as reinforcement, focusing on understanding the fiber–matrix interaction, determining the pullout load–slip relationship, and modeling fiber bridging behavior. The experimental program included density calculations and scanning electron microscope (SEM) analysis to examine the surface morphology and diameter of the fibers. Single fiber pullout tests were performed under varying conditions to assess the pullout load, slip behavior, and failure modes of the palm fiber, and a relationship between the pullout load and slip with the embedded length of the palm fiber was constructed. A trilinear model was developed to describe the pullout load–slip behavior of single fibers, and a corresponding palm-FRCC bridging model was constructed using the results from these tests. Section analysis was conducted to assess the adaptability of the modeled bridging law calculations, and the analysis result of the bending moment–curvature relationship shows a good agreement with the experimental results obtained from the four-point bending test of palm-FRCC. These findings demonstrate the potential of palm fibers in improving the mechanical performance of FRCC and contribute to the broader understanding of natural fiber reinforcement in cementitious composites.

Crack control for slabs and beams in current design practices in Korea are based on the Frosch’s model, which is adapted in ACI 318. It is more difficult to have consistent quality control in underground construction sites, such as the RC box culverts used for electric power distribution built below the ground level. There are more discrepancies between the as-built dimensions and the design dimensions provided in drawings in these structures. Due to this variability in construction error, the crack widths measured in such structures have higher potential to have more differences than the calculated values. Although crack control is a serviceability concern, if the owner chooses to have a target crack width that needs better control, crack width estimations can be improved by considering such construction variability. The probability-based crack width model suggested in this study will allow minimizing the discrepancies between the measured and calculated crack widths and provide reliable estimations of crack widths. Typical size of slabs and beams ranging between 300 mm (12 in.) to 500 mm (20 in.) used in underground RC box culverts in Korea were tested under the four-point bending test program. The thicker specimens had smaller bar spacings which created more cracks with smaller crack widths. However, with smaller crack widths generated in these specimens, there were more errors between the measurements and calculated values. From site investigations in Korea, the thickness of slabs in underground box culverts varied the most among all parameters. As a result, the bottom concrete covers had the highest variability. Bottom concrete covers and bar spacings are the two most important parameters in concrete crack control. A probability-based crack width estimation model for flexural members was developed in this study to consider this construction variability. Monte Carlo simulations were performed to evaluate the probabilistic characteristics of the design surface crack widths with a target width of either 0.3 mm (12 mils) or 0.5 mm (20 mils). The probabilistic models of design variables included in the crack width estimation model were generated based on field-collected information from construction sites in Korea. Because the surface crack widths in RC flexural members are sensitive to the construction errors of concrete cover depths, and since there are differences between the assumed and actual stress distribution closer to the reinforcing bars, the probability of having surface cracks of 0.3 mm width (12 mils) is found to be quite high, such as 89% at the positive moment region (mid-span, bottom surface) of the top slab in RC box culverts and 45% for the negative moment region (support area, top surface) of the top slab with current design practice. In order to ensure crack widths to be smaller than the design target width, probability-based crack width factors are recommended in this study to improve estimations depending on the selected target reliability levels.

Crack patterns provide critical information about the structural integrity and safety of concrete structures. However, until now, there has been a lack of sufficient studies on using the Finite Element (FE) method to investigate the characteristics of the crack patterns of reinforced concrete (RC) beams. Therefore, this study aims to develop an FE model to analyze the load–displacement and crack characteristics of a beam under a four-point bending test using the concrete damaged plasticity (CDP) model that accounts for the influence of mesh size. The simulation results were validated against experimental results, including mesh convergence analysis, energy balance, load characteristics, and crack patterns. A parametric study was then conducted using this model to investigate the influence of the rebar’s diameter, number, and spacing on the RC beam’s load–displacement characteristics and crack behavior. The findings demonstrate that the FE model accurately simulates the working behavior of the RC beam, with a maximum deviation at a cracking load of 8.7% and crack patterns with a maximum deviation in the mean crack height of 12.1%. In addition, the results of the parametric study suggest that the rebar configuration significantly affects the RC beam’s loading carrying capacity. This study provides deeper insights into the use of FE modeling for analyzing the behavior of RC beams, which can be useful for designing and optimizing structures in civil engineering.

Various kinds of structures are made of premier construction material, concrete. Concrete is extensively used, only second for water; world consumption of concrete is staggering at 4.5 billion tons a year. All the constituent raw materials that go in the production of concrete are Ordinary Portland cement, coarse aggregate and sand which are valuable natural resources; these are facing fast depletion, as the demand for concrete is rising by leaps and bounds. In this context, conservation of concrete materials is inevitable at all costs. The world concrete industry consumes over ten billion tons of coarse aggregate annually. To conserve the natural coarse aggregate, industrial by-products must be increasingly substituted for natural coarse aggregate. In big and overpopulated cities, old and dilapidated structures are demolished for new constructions; the waste can serve as an alternative source, named recycled coarse aggregate (R.C.A). The current research is directed to investigate the suitability of R.C.A as natural coarse aggregate (N.C.A), in shear critical reinforced concrete beams.

The degradation of road pavements due to environmental factors is a pressing issue in infrastructure maintenance, necessitating precise identification of pavement distresses. The pavement condition index (PCI) serves as a critical metric for evaluating pavement conditions, essential for effective budget allocation and performance tracking. Traditional manual PCI assessment methods are limited by labor intensity, subjectivity, and susceptibility to human error. Addressing these challenges, this paper presents a novel, end-to-end automated method for PCI calculation, integrating deep learning and image processing technologies. The first stage employs a deep learning algorithm for accurate detection of pavement cracks, followed by the application of a segmentation-based skeleton algorithm in image processing to estimate crack width precisely. This integrated approach enhances the assessment process, providing a more comprehensive evaluation of pavement integrity. The validation results demonstrate a 95% accuracy in crack detection and 90% accuracy in crack width estimation. Leveraging these results, the automated PCI rating is achieved, aligned with standards, showcasing significant improvements in the efficiency and reliability of PCI evaluations. This method offers advancements in pavement maintenance strategies and potential applications in broader road infrastructure management.

It is generally recognized that cracks provide easy access to ingress of chlorides in concrete and hence, the initiation of corrosion of steel in cracked concrete occurs at early stage. However, wide variety of results on the effect of crack widths on corrosion of steel in concrete are reported in many studies. Apart from crack width, the crack depths, cracking frequency and healing of cracks also influence the corrosion of steel in concrete. This paper presents a comprehensive review and summarised the results on the effect of cracking on corrosion of steel in concrete. The effect of crack widths on the diffusion of chlorides ions and carbon-dioxide is also discussed in this paper. Among all available results, a correlation between the corrosion current and the crack widths up to 0.3 mm can be established, however, no distinct trends are observed beyond that crack width. Conflicting results on the effect of crack widths on chloride ion diffusion are also reported. The longitudinal crack causes more severe corrosion of steel in concrete than transverse cracks of same width. Cracked concrete containing supplementary cementitious materials exhibited superior corrosion resistance than cracked ordinary Portland cement concrete of same width of transverse as well as longitudinal cracks. The same is also true in the case of lower water–binder ratios of cracked concrete. The increase in crack depth increased the chloride diffusion; however, the corrosion test shows an opposite trend. Conflicting results on the effect of crack frequency on corrosion of steel are also reported.

Addition of superabsorbent polymers (SAPs) to cementitious mixtures promotes the self-healing ability of the material. When cracking occurs; SAPs present inside the crack will swell upon contact with water and subsequently release this water to stimulate the further hydration of unhydrated cement particles and the calcium carbonate crystallization. However; the inclusion of SAPs affects the mechanical performance of the cementitious material by the creation of macro-pores as water is retracted from the swollen SAP. To counteract the reduction in strength, part of the cement is replaced by nanosilica. In this research, different mixtures containing either SAPs or nanosilica and a combination of both were made. The samples were subjected to wet–dry cycles simulating external conditions, and the self-healing efficiency was evaluated by means of the evolution in crack width, by optical measurements, and a water permeability test. In samples containing SAPs, an immediate sealing effect was observed and visual crack closure was noticed. The smaller influence on the mechanical properties and the good healing characteristics in mixtures containing both nanosilica and SAPs are promising as a future material for use in building applications.

The accuracy measurement of rock fracture toughness is one of the basic tasks of rock fracture mechanics. In order to study the influence of the width of the prefabricated crack on the fracture toughness of rock, the failure process of notched semi-circular bend (NSCB) specimens with four sizes and five different width of the prefabricated crack was studied by experimental and numerical methods. The influence of the width of the prefabricated crack on the peak load, crack initiation position, dimensionless stress intensity factor and fracture toughness is analyzed and discussed. The results show that the peak load and fracture toughness of NSCB increase with the increase of the width of the prefabricated crack, and the smaller the specimen size is, the larger the increase is. When the width of the prefabricated crack is less than 1.3 mm, the crack initiates at the dichotomy of the prefabricated crack tip; when the width of the prefabricated crack is greater than or equal to 1.3 mm, the crack initiates near the corner of the prefabricated crack tip. If NSCB specimen is adopted to determine the fracture toughness of limestone, it is recommended that the width of prefabricated crack should be less than 1.3 mm. The conclusions provide a reference for the fabrication of NSCB specimens and the accurate measurement of limestone fracture toughness.