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Uniaxial tension tests were conducted on 12 plain reinforced concrete (RC) and 48 large-scale steel fiber-reinforced concrete (SFRC) specimens, each containing conventional longitudinal reinforcement, to study their cracking and tension-stiffening behavior. The test parameters included fiber volumetric content, fiber length and aspect ratio, conventional reinforcement ratio, and steel reinforcing bar diameter. \"Dog-bone\" tension tests and bending tests were also performed to quantify the tensile properties of the concrete. It was found that the cracking behavior of SFRC was significantly altered by the presence of conventional reinforcement. Crack spacings and crack widths were influenced by the reinforcement ratio and bar diameter of the conventional reinforcing bar, as well as by the volume fraction and aspect ratio of the steel fiber. Details and results of the experimental investigation are provided and discussed.

Experimental and numerical studies have been carried out on reinforced concrete (RC) short tensile specimens. Double pull-out tests employed rectangular RC elements of a length determined not to yield any additional primary cracks. Tests were carried out with tensor strain gauges installed within a specially modified reinforcement bar and, alternatively, with fibre Bragg grating based optical sensors. The aim of this paper is to analyse the different experimental setups regarding obtaining more accurate and reliable reinforcement strain distribution data. Furthermore, reinforcement strain profiles obtained numerically using the stress transfer approach and the Model Code 2010 provided bond-slip model were compared against the experimental results. Accurate knowledge of the relation between the concrete and the embedded reinforcement is necessary and lacking to this day for less scattered and reliable prediction of cracking behaviour of RC elements. The presented experimental strain values enable future research on bond interaction. In addition, few double pull-out test results are published when compared to ordinary bond tests of single pull-out tests with embedded reinforcement. The authors summarize the comparison with observations on experimental setups and discuss the findings.

Structural members made of ultra-high-performance concrete (UHPC) have been attractive to engineers and researchers due to their superior mechanical properties and durability. However, existing studies were focused on the behavior of UHPC members reinforced with micro straight steel fibers at a volume fraction between 1 and 3%. There is a lack of studies on the influence of different types and amounts of fibers on the shear behavior of UHPC structural members. The objective of the study was to experimentally investigate the shear behavior of UHPC beams with macro hooked-end steel (MHS) fibers and polyvinyl alcohol (PVA) fibers, which are two of the most used fibers for high-performance fiber-reinforced cementitious composites. The shear behavior of ten large-scale non-prestressed UHPC beams was studied. The experimental parameters included the shear span-to-effective depth ratio, the fiber volume fraction, and the type of fibers. It was found that both MHS fibers and PVA fibers were effective in enhancing the shear performance of the UHPC beams whether the shear transfer mechanism was governed by arch action or beam action. Moreover, the measurement results of the average crack spacing imply the distinct difference in the fiber bridging effects of the MHS fibers and PVA fibers in the UHPC beams.

The Guide for Design of Pavement Structures (AASHTO 86/93) and Mechanistic Empirical Pavement Design Guide (MEPDG) are two common methods to design continuously reinforced concrete pavement (CRCP) published by the American Association of State Highway and Transportation Officials (AASHTO) in the USA. The AASHTO 86/93 is based on empirical equations to assess the performance of highway pavements under moving loads with known magnitude and frequency derived from experiments on AASHTO road tests. The MEPDG is a pavement design method based on engineering mechanics and numerical models for analysis. It functions by incorporating additional attributes such as environment, material properties, and vehicle axle load to predict pavement performance and degradation at the selected reliability level over the intended performance period. In order to evaluate the CRCP design procedure and performance, crack width (CW) and crack spacing (CS) from five examined test tracks in Europe with different climate condition, base layer, geometry, and materials were collected in this paper and compared with predicted distresses as well as CW and CS from AASHTO 86/93 and MEPDG design methods. The results show that the interactions between geometrics, material properties, traffic, and environmental conditions in the MEPDG method are more pronounced than in the AASHTO 86/93 and the prediction of CS and CW based on MEPDG matched closely with the recorded data from sections.

Crack monitoring is an important task in structural health monitoring. In this study, a procedure is developed to assess the crack width based on the strain curve of distributed fiber optic sensors (DFOS), taking into account of the strain redistribution of the structural substrate after cracking. Fifteen aluminum alloy plates with two or three pre-cut cracks spaced at varying intervals were installed with DFOS and subjected to a tensile test. During the test, the width of the cracks was measured using an optical microscope. The results revealed that cracks caused a peak value in the strain curve of DFOS, which is dependent on the spacing of the cracks. The peak strains overlap when the cracking spacing is less than 20 mm, as there is a significant strain interference between the two adjacent strain peaks. Depending on the number and location of cracks, thirteen scenarios are classified and a corresponding procedure is proposed to evaluate the crack width by considering the strain redistribution of the cracked substrate. Validation tests demonstrated that the proposed procedure reduced the relative measurement error to 6.64%. Therefore, the developed procedure improves the accuracy of crack width evaluation based on DFOS in practical engineering applications.

Semi-rigid base is widely used in asphalt pavement construction, because they provide the potential to reduce rutting and lower pavement construction budgets. However, questions remain about the long-term performance of asphalt pavements with a semi-rigid base in terms of their propensity for transverse cracking. This study presents the results of a long-term field investigation of transverse cracking. The study collected 202 field cores extracted from 14 field test roads, and covers different pavement ages, traffic volumes, and recycled asphalt pavement (RAP) content across eastern China. Data regarding crack spacings, lengths, and propagation over time were obtained, while crack widths, depths, and patterns were analyzed using the field cores. The results show that crack spacings tend to be dense over the years until reaching an extreme value and the crack propagation can be clearly divided into three stages (0–4 years for initiation, 4–8 years for steady development, and a boost after 8 years) for the projects evaluated. The transverse crack can be categorized into four categories: surface-initiated cracking, reflective cracking with small area unpenetrated, reflective cracking, and thermal cracking. Surface-initiated cracking is the primary crack pattern found in asphalt pavements constructed with a semi-rigid base. A finite-element model was constructed, and the simulation results indicate that the surface-initiated crack tends to appear if the modulus of the base layer is higher, the asphalt top layer is more aged, the thickness above the base layer was thicker, or the cooling rate was faster.

A system of edge cracks was applied to polished (010) surfaces of K-rich gem-quality alkali feldspar by diffusion-mediated cation exchange between oriented feldspar plates and a Na-rich NaCl–KCl salt melt. The cation exchange produced a Na-rich layer at and beneath the specimen surface, and the associated strongly anisotropic lattice contraction lead to a tensile stress state at the specimen surface, which induced fracturing. Cation exchange along the newly formed crack flanks produced Na-enriched diffusion halos around the cracks, and the associated lattice contraction and tensile stress state caused continuous crack growth. The cracks nucleated with non-uniform spacing on the sample surface and quickly attained nearly uniform spacing below the surface by systematic turning along their early propagation paths. In places, conspicuous wavy cracks oscillating several times before attaining their final position between the neighboring cracks were produced. It is shown that the evolution of irregularly spaced towards regularly spaced cracks including the systematic turning and wavyness along the early propagation paths maximizes the rate of free energy dissipation in every evolutionary stage of the system. Maximization of the dissipation rate is suggested as a criterion for selection of the most probable evolution path for a system undergoing chemically induced diffusion mediated fracturing in an anisotropic homogeneous brittle material.

Rock failure, which causes instability in rock engineering, is an engineering accident that generally occurs through the coalescence of the preexisting cracks in rocks. Therefore, it is very important to research the coalescence of rock cracks to prevent rock engineering accidents. Based on the mechanical theories of elastoplastic mechanics and fracture mechanics (the generalized Drucker–Prager (D-P) yield criterion and the core concept of the Kachanov method), the propagation of the plastic zones at rock crack tips affected by far-field uniform pressures is theoretically researched considering the interaction of two collinear cracks of unequal length. Moreover, for two cases of two cracks of equal length and unequal length in rocks, the basic laws of crack coalescence by the propagation of the plastic zones at rock crack tips are first studied, and the suggested threshold values of crack spacing for crack coalescence in rocks are provided. The results show that, for equal-length cracks, as the crack spacing decreases, the cracks propagate by a quadratic polynomial function, and the threshold is 0.2 of the ratio of crack spacing to crack length. Moreover, for unequal-length cracks, as the crack spacing decreases, the cracks propagate by a linear function, and the threshold is 0.3 of the ratio of crack spacing to secondary crack length. Finally, using the numerical simulation of a rock slope including equal-length and unequal-length cracks, and a laboratory test with a rock-like material specimen including unequal-length cracks, the main conclusions of the abovementioned theoretical studies have been verified. In this study, although the basic law of crack coalescence is first studied and the threshold value of crack coalescence is suggested first, the researched crack morphology and rock properties are relatively simple.

Overlaying a reinforced concrete beam (RCB) with polymer cement mortar (PCM) is a strengthening method that improves flexural stiffness by the increasing sectional force. However, the reduction between bond strength and the reinforcement in PCM overlay at high temperatures results in an increase in flexural crack spacing. Therefore, the pullout force must be taken into account when estimating the flexural capacity of PCM-overlay RCBs. The experimental study aims to assess the flexural performance of PCM-overlay RCBs under three different environmental temperature conditions: 20, 40, and 60°C. Seventeen beams with varying reinforcement ratios in PCM are tested at the mentioned temperature levels. Experimental results indicate a decrease of approximately 6 to 13% in strength at elevated temperatures, which can be attributed to the reduction in bond strength of the reinforcement caused by the degradation of the PCM. Analytically, the strength reduction is calculated by determining the average crack spacing in the flexural zone. Therefore, the proposed average crack spacing method (CSM) predicts that the flexural strength is within ±10% limits of experimental observations. This method is more conservative than the conventional sectional analysis method (SAM). The average CSM can contribute to a safer design of PCM-overlay RCBs by preventing overestimated prediction of the ultimate strength at high environmental temperatures.

Considering the influence of the visible load-induced transverse cracks on chloride ion diffusion in cracked concrete of the in-service reinforced concrete (RC) elements under marine environment, a typical concrete volume with one transverse crack was taken to establish the governing equation. Assuming the crack widths at the outer lateral and bottom surfaces were equal, a model to predict the equivalent chloride diffusion coefficient in cracked concrete was put forward to consider the influence of the average transverse crack width, crack spacing and crack extending lengths in beam height and width directions on chloride diffusion. Results show that the proposed model can better reflect the variation trend of the equivalent chloride diffusion coefficient with different crack widths in in-service RC elements under marine environment.