Maximum Crack Width Research Articles

RC beams strengthened by prestressed CFRP plate subjected to sustained loading and continuous wetting condition: Time-dependent prestress loss

Prestress loss of CFRP during prestressing and service stage is one of the critical technical issues in concrete structures rehabilitation. In this work, the prestress loss of reinforced concrete (RC) beams strengthened by a prestressed CFRP plate subjected to sustained loading and continuous wetting condition were experimentally studied. Eight RC beams strengthened by prestressed CFRP plate were prepared with different prestress levels of 20% and 40% respectively. The initial prestress loss was monitored up to 28 days and the loss ratios of all specimens were around 5%, which was dominated by slippage of the end anchorage system. Then, the specimens were sustainedly loaded at two levels under wet or dried environments for 170 days. The average prestress loss ratios during this period were all less than 2%, which indicates that the CFRP plate end anchorage system had good long-term performance. Moreover, the adhesive bonding was weakened by the moisture penetration, and the specimens with lower prestress levels were more susceptible to the wet condition. Nevertheless, regardless of the environmental exposure, the maximum crack widths of 40% prestressed specimens remained less than 0.2 mm even subjected to high sustained load level, which is within the limitation of the prestressed concrete structures.

Experimental and nonlinear finite element analysis of shear behaviour of reinforced concrete beams

This paper presents an experimental investigation and nonlinear finite element analysis (NLFEA), using the numerical analysis tool ANSYS©, carried out on the shear and diagonal cracking effect on the behaviour of reinforced-concrete (RC) beams made of normal strength concrete (NSC) and high-strength concrete (HSC), with and without transverse reinforcement. Beams were tested using four-point bending, by means of digital image correlation (DIC). In the experimental setup, the shear zone was digitised using a high-resolution camera to assess the deformation of concrete in the compression zone and to measure the diagonal crack widths. The results show that transverse reinforcement does efficiently control the diagonal crack width, increases the shear capacity of the beams, shifts the mode failure from shear to flexure, and significantly improves the ductility of beams in the ultimate state particularly when using HSC, given the better quality of the bond developed in the concrete with steel reinforcement. The values of ultimate shear strength obtained experimentally were compared to the corresponding empirical values available in the literature. Furthermore, detailed 3D finite element analysis (FEA) was used to predict the load–deflection response, the ultimate load, the cracking load, the ultimate deflection, the maximum diagonal crack widths and the cracks patterns in RC beams. The disparity in values between the numerical and experimental values is ranging from −11.08 to +0.6%, −2.02 to −0.52% and −13.27 to −1.01% for cracking load, ultimate load and ultimate mid-span deflection, respectively. While the ratio of the predicted to experimental maximum diagonal crack width for the beams ranged between 0.95 and 1.06. Also, a good agreement between the experimental and numerical crack patterns was achieved. Consequently, the FEA model is able to predict the shear response of RC beams with a good accuracy.

Experimental study on Early Desiccation Cracking Behabior of Short-cut Basalt Fiber Concrete

Early desiccation cracking of concrete would directly affect the durability of reinforced concrete structure. In order to improve the early desiccation cracking behavior of concrete, the concrete specimens mixed with basalt fibers were prepared. Based on the indoor and outdoor exposure test methods, the effects of short-cut basalt fiber content on early desiccation cracking of concrete and were analyzed by using initial crack time, crack number, maximum crack width and total crack area as evaluation indexes. The test results show that the total crack area of the basalt fiber concrete with a volume fraction of 0.05%, 0.1%, and 0.15% increased by -5.0%, 73.6%, and 86.5% respectively after the outdoor exposure test. The total crack area of reinforced concrete specimens with a volume fraction of 0.1% increased by 63.6% after the outdoor exposure test. The early desiccation cracking behavior of concrete and reinforced concrete could be improved by adding the content of short-cut basalt fiber.

Mechanical performance of concrete reinforced with polypropylene fibers (PPFs)

Fibers are one of the most prevalent methods to enhance the tensile capacity of concrete. Most researchers focus on steel fiber reinforced concrete which is costly and easily corroded. This study aims to examine the performance of polypropylene fiber reinforced concrete through different tests. PPFs were added into concrete blends in a percentage of 1.0%, 2.0%, 3.0%, and 4.0% by weight of cement to offset its objectionable brittle nature and improve its tensile capacity. The fresh property was evaluated through slump cone test and while mechanical strength was evaluated through compressive strength, split tensile strength flexure strength, and flexure cracking behaviors after 7-, 14-, and 28-days curing. Results indicate that slump decrease with the addition of PPFs while fresh density increase up to 2.0% in addition to PPFs and then decreases. Similarly, strength (compressive strength; split tensile strength, and flexure strength) was increased up to 2.0% addition of PPFs and then decrease gradually. It also suggests that Ductility; first crack load, maximum crack width, and load-deflection inter-relations were considerably improved due to incorporations of PPFs.

Investigation of the Structural Behaviors of One-way HVFA-SCC Slabs Reinforced by GFRP Bars

Background: The corrosion of steel bar leads to the deterioration of structural behaviors, high cost maintenance, shortened service life. The bridge deck structures constructed by Fiber Reinforced Polymer (FRP) bars and High-Volume Fly Ash-Self-Compacting Concrete (HVFA-SCC) can achieve low energy consumption, sustainable construction and high durability. However, the structural behaviors of this bridge deck are still unclear. Objective: The aim of this paper is to study the structural behaviors, including ultimate loads, failure mode, cracking behavior, deflection and strain of one-way HVFA-SCC slabs reinforced with Glass- FRP (GFRP). Experimental: Eleven full-scale HVFA-SCC slabs, varying in reinforcement diameter, reinforcement ratio, shear-span ratio, the type of reinforcing materials and concrete matrix materials, were tested by using a four-point bending load. Methods: The test results of tested specimens were compared with existing theoretical models, such as crack load, ultimate bearing capacity, maximum crack width, maximum crack space and deflection predicted model. Results: The GFRP reinforced HVFA-SCC slab exhibits similar structural behaviors to the GFRP reinforced NC slab. The maximum crack width of HVFA-SCC slab is significantly increased by using GFRP bars with a diameter of 19 mm. Conclusion: It is concluded that it is feasible to use HVFA-SCC instead of NC combined with GFRP bars in bridge deck structures. The stress limit of concrete materials (0.45fc) is the main governing factor for the service limit state (SLS) of GFRP reinforced HVFA-SCC slabs. The maximum crack width of GFRP reinforced HVFA-SCC slabs can be predicted by using EHE-08 and GB 50608-2010 models.

Prediction of crack width and intermediate-crackdebonding strain of FRP bonded two-way RC slabs a comparative and novel approach

This paper presents the confirmation study for the suitability of existing models to forecast the maximum crack width (MCW) and intermitted-crack-debonding (ICD) strain of fibre-reinforced polymer ...

Flexural analysis of transverse joints of prefabricated T girder bridge superstructure

Rapid construction of prefabricated bridges requires minimizing the field work of precast members and ensuring structural stability and constructability. In this study, we conducted experimental and analytical investigations of transverse joints of prefabricated T-girder bridge superstructures to verify the flexural performance and serviceability. In addition, we conducted parametric studies to identify the joint parameters. The results showed that both the segmented and continuous specimens satisfied the ultimate flexural strength criterion, and the segmented specimen exhibited unified behavior, with the flexural strength corresponding to that of the continuous specimen. The segmented specimens exhibited elastic behavior under service load conditions, and the maximum crack width satisfied the acceptance criteria. The reliability of the finite element model of the joint was verified, and parametric analysis of the convexity of the joint section and the compressive strength of the filler concrete showed that the minimum deflection and crack width occurred at a specific angle. As the strength of the filler concrete increased, the deflection and crack width decreased. However, we confirmed that the reduction in the crack width was hardly observed above a specific strength. Therefore, a design suitable for prefabricated bridges and accelerated construction can be achieved by improving the joint specifications based on the required criteria.

Self-healing of early-age cracks in cement mortars with artificial functional aggregates

Cracking seriously affects the functionality and durability of the concrete structure. Therefore, the development of robust self-healing concrete is important to extend the service life of the structure. In this study, artificial functional aggregates with fly ash, silica fume, metakaolin, limestone powder and sodium carbonate powder were designed and prepared by the powder granulation technology to promote the self-healing efficiency of concrete. Mortar specimens with artificial functional aggregates which partially replaced the sand were prepared to verify the feasibility of the approach. Crack self-healing efficiency was evaluated by visual observation and the water ingress test. In addition, healing products formed in the crack were analyzed with XRD, TG and SEM, respectively. Experimental results indicated that the artificial functional aggregates were well combined with the mortar matrix and could be intersected by cracking. The addition of artificial functional aggregates improved the self-healing capacity of mortar specimens. Mortar specimens with artificial functional aggregates exhibited higher closure ratio of surface crack and better regain of water tightness compared with the control specimens. The maximum crack width that can be healed was about 0.47 mm in the mortar specimen with artificial functional aggregates. Microstructure investigation showed that the major healing products in the crack mouth were calcite precipitations which firstly deposited on both walls of the crack and then gradually overlapped together to become denser and denser with the extension of healing time. More calcium carbonate precipitations were observed in internal crack of mortars with artificial functional aggregates compared to the control mortar due to the effective supply of carbonate ions from the artificial functional aggregates. Typical hydration product C-S-H gel was also detected by SEM observation in the internal crack wall.

Self-Healing Biogeopolymers Using Biochar-Immobilized Spores of Pure- and Co-Cultures of Bacteria

A sustainable solution for crack maintenance in geopolymers is necessary if they are to be the future of modern green construction. This study aims to develop self-healing biogeopolymers that could potentially rival bioconcrete. First, a suitable healing agent was selected from Bacillus subtilis, Bacillus sphaericus, and Bacillus megaterium by directly adding their spores in the geopolymers and subsequently exposing them to a precipitation medium for 14 days. Scanning electron microscope with energy-dispersive X-ray (SEM-EDX) analysis revealed the formation of mineral phases for B. subtilis and B. sphaericus. Next, the effect of biochar-immobilization and co-culturing (B. sphaericus and B. thuringiensis) on the healing efficiencies of the geopolymers were tested and optimized by measuring their ultrasonic pulse velocities weekly over a 28-day healing period. The results show that using co-cultured bacteria significantly improved the observed efficiencies, while biochar-immobilization had a weak effect, but yielded an optimum response between 0.3–0.4 g/mL. The maximum crack width sealed was 0.65 mm. Through SEM-EDX and FTIR analyses, the precipitates in the cracks were identified to be mainly CaCO3. With that, there is potential in developing self-healing biogeopolymers using biochar-immobilized spores of bacterial cultures.

Restricted Effect of Two Plant Root Systems on the Crack Expansion of China Yunnan Laterite under Dry-wet Cycle

In order to research the restricted effect of hedera nepalensis root systems and heteropogon contortus root systems on the crack expansion of Yunnan laterite under dry-wet cycle, this paper prepares Yunnan laterite with certain moisture content, and makes the compacted samples of pure laterite and composite soil mixed with root systems by adopting hedera nepalensis root systems and heteropogon contortus root systems respectively, and then simulates the dry-wet cycle of laterite in engineering (i.e., rainfalls and evaporations), measures the crack width of samples experiencing different cycles, and makes statistical analysis on the average maximum crack width of samples in all groups by adopting the method of indoor spraying and natural drying. The result indicates that, 10% and 20% mixed hedera nepalensis root systems can exert obvious restrictions on the crack expansion of Yunnan laterite after dry-wet cycle, while 30% mixed hedera nepalensis root systems and 10% mixed heteropogon contortus root systems can also restrict the crack expansion of Yunnan laterite, but the restricted effect is weaker. As for 20% and 30% mixed heteropogon contortus root systems, composite soil samples will disintegrate after the 2nd dry-wet cycle.

Numerical Evaluation of Bond Behavior of Ribbed Steel Bars or Seven-wire Strands Embedded in Lightweight Concrete

The bond-slip relationship between concrete and steel is significant in evaluating the nonlinear behavior of reinforced concrete structures. The force transmitted by the bond in reinforced concrete structures was studied numerically in high-strength, lightweight concrete with ribbed reinforcing steel bar or seven-wire strand, using ATENA 3D software. The first part of the study was a validation of the model based on the actual results of standardized pull-out tests using the software. Subsequently, the bond behavior was studied, where a four-point static bending test was modeled based on the real bond-slip relationship of the pull-out test. It was deduced that the ATENA 3D software can simulate the experimental tests and provide meaningful results. In addition, inferred from the numerical modeling, the maximum crack width and the mid-span deflection of the reinforced concrete beam increased when the bond stress between the concrete and the reinforcing steel bars was decreased. When a high amount of reinforcement (two strands) was used, concrete failure occurred before the strands yielded. However, further increase of the bond stress also decreased the maximum crack width and mid-span deflection. The failure occurred due to the increase in the strand yielding point by using one strand as a reinforcement of the beam.

CT scanning of internal crack mechanism and strength behavior of cement-fiber-tailings matrix composites

This paper deals the relationship between compressive strength and internal crack formation (e.g., crack width and volume) of cement-fiber-tailings matrix composites (CFTMC) using an industrial computed tomography system and scanning electron microscopy. Two types of fibers (polypropylene PP and polyacrylonitrile PAN) were used to manufacture CFTMC with a constant cement-to-tailings ratio, solid content and curing time of 1:6, 75 wt% and 14 days, respectively. The results showed that strength gaining of CFTMC increased remarkably with fiber additions which effectively improve its toughness. When compared to samples without fibers, the compressive strength of CFTMC was the highest because of the reduced interconnection between pores and high particle packing density. The internal structure analysis showed that the maximum crack widths of CFTMC increased when the fiber content increased from 0.3 to 0.6 wt%, regardless of fiber type, growing the crack volumes of samples. The failure pattern of all CFTMC samples was mainly tensile, shear and mixed failure (tensile/shear), and a high strength value accompanies with a big volume of crack. At last, the findings of this study may offer a key reference for fiber-reinforced backfills, which can lift their strength, stability and integrity behavior under extreme conditions, such as rock burst, squeezing ground, blast or seismic event.

A Critical Review of Methods for Determining the Damage States for the In-plane Fragility of Masonry Infill Walls

ABSTRACT We subjected nine full-scale masonry infilled reinforced concrete frame specimens to quasi-static cyclic loading to critically review the methods for determining the damage state of masonry infill walls to develop reliable in-plane fragility functions. Among the three methods, the method based on maximum crack widths gave the smallest dispersion, whereas the skeleton curve-based methods generated excessive dispersions and the phenomena-based method was shown to be self-contradictory in certain circumstances. If the damage states were determined by maximum crack widths, neither the brick type nor the plaster had a significant influence on the fragility functions.

Structural Performance Under Monotonic Static Loading of Reinforced Concrete Gable Roof Beams with Multiple Web Openings

In the present study, an attempt has been made to experimentally investigate the flexural performance of ten simply supported reinforced concrete gable roof beams, including solid control specimen (i.e., without openings) and nine beams with web openings of different dimensions and configurations. The nine beams with openings have identical reinforcement details. All beams were monotonically loaded to failure under mid-span loading. The main variables were the number of the created openings, the total area of the created openings, and the inclination angle of the posts between openings. Of interest is the load-carrying capacity, cracking resistance and propagation, deformability, failure mode, and strain development that represent the behavior of reinforced concrete gable beams. Test results showed that the total concrete weight consumed for the tested gable beams with openings was lower than the solid gable beam by (14.9–26%). This reduction in weight led to a reduction in the flexural stiffness and, in turn. in the load-carrying capacity by (6.2–17.9%). The percentage of the decrease in the concrete consumption to the reduction in the load-carrying capacity for the tested beams with openings attained (140–240%). It was recorded that the maximum crack width depended on the total area of the created openings rather than the number of these openings.

Prediction of maximum thermal crack width of RC abutments utilizing actual construction data and study on influential parameters using neural networks

In this study, an attempt was made to predict the maximum width of thermal cracking in RC abutments using field data. The data was obtained from Japanese Yamaguchi prefecture database which is a database of concrete structures in the prefecture constructed with appropriate concreting work. Reliable data was chosen carefully to avoid incorporation of possible human errors. Feed-forward multilayer perceptron neural network was used for prediction. k-fold cross validation was performed to avoid overfitting. By using the trained NN, several parametric studies were conducted to observe the influences of different parameters. Main idea of this research was to solve the complex problem of predicting the maximum crack width by using the parameters which are easier to obtain in the field. The results have shown the potential of predicting the crack width and observable influence of several parameters. The results will be helpful in proposing countermeasures to mitigate harmful thermal cracks.

Application of ureolysis-based microbial CaCO3 precipitation in self-healing of concrete and inhibition of reinforcement corrosion

Cracking is inevitable in concrete due to its quasi-brittle nature. The presence of micro-cracks will not only impair concrete, but induce reinforcement corrosion by providing paths for the ingress of harmful species. In the past decades, a new technique to repair cracks automatically based on microbial induced carbonate precipitation has become attractive. This paper explored the crack healing potential of reinforced concrete incorporated with ureolytic type microbial self-healing agents immobilized in porous ceramsite particles. Effects of healing on the mechanical and electrochemical performances of reinforced concrete were investigated. The maximum crack width that could be healed completely by bacteria was up to 450 μm in 120 days. The highest regain ratios of flexural strength and modulus were achieved by bio-based healing when the initial damage degree was taken into account. As indicated by the Tafel polarization results, reinforcement corrosion was successfully inhibited by the crack closure from microbial precipitation without any side-effects.

Flexural cracks in steel fiber-reinforced lightweight aggregate concrete beams reinforced with FRP bars

Fourteen plain and steel fiber-reinforced lightweight aggregate concrete (LWC) beams with two types of fiber-reinforced polymer (FRP) reinforcing bars were tested under a four-point bending load with different reinforcement ratios, bar diameters and clear span lengths to evaluate their cracking behavior. The test results showed that using steel fiber-reinforced lightweight aggregate concrete (SFLWC) and increasing the clear span length mitigated the maximum crack width at low load levels, while increasing the reinforcement ratio tended to decrease the maximum crack width during the entire loading period. At service load, all CFRP-reinforced beams satisfied the crack width criteria of 0.7 mm, while more than half of the GFRP-reinforced specimens exhibited unconservative crack widths. Crack width prediction equations in the current design codes in the US, China, and Canada were compared based on the experimental results. The original average crack spacing equation recommended by GB 50608 was modified considering the effect of bar position. Furthermore, using the method of probability and statistics, the relationships between the maximum crack width and the average crack width for the tested beams were investigated. Accordingly, a rational alternative crack width model was proposed for CFRP- and GFRP-reinforced beams incorporating the effects of lightweight aggregates and steel fibers.

Structural performance of concrete bridge decks reinforced with Grade-830 steel bars

High-performance reinforcement, which is known by its high-corrosion resistance and high-strength, is advantageous in the design and construction of concrete bridge decks. This research investigates the structural behavior of concrete bridge decks reinforced with either high-performance A1035M (Grade 830) or ASTM A615M (Grade 420) reinforcing steel at both the service and strength limit states. The tensile strain of the reinforcing steel, the compressive strain of the concrete, and the deflection of the specimens were monitored continuously during testing. A crack width microscope was used to measure the maximum crack width and the number of cracks. The results indicated an increased serviceability and flexural strength for the decks containing Grade 830 reinforcing steel.

Bending performance of unbonded prestressed basalt fiber recycled concrete beams

This study investigated the influences of volumetric basalt fiber dosage and recycled coarse aggregate replacement rate on the flexural performance of unbonded prestressed basalt fiber recycled concrete beams. A symmetric loading test was conducted on nine specimens based on their variety of volumetric basalt fiber dosages and aggregate replacement rates. Failure modes, bearing capacities, deformation characteristics, and crack widths were observed, and the influences of volumetric basalt fiber dosage and recycled coarse aggregate replacement rate on flexural performance are discussed. The bending process of unbonded prestressed recycled concrete beams and unbonded prestressed basalt fiber recycled concrete beams exhibits an elastic stage, a cracking stage, and a failure stage, which is similar to that of conventional unbonded prestressed concrete beams. The addition of basalt fiber can effectively enhance the adhesion between mortar and recycled coarse aggregate, inhibiting crack development, increasing the cracking load, and enhancing ductility. After verifying the applicability of plane-section assumptions via testing, and referring to methods for calculating the bearing capacity of unbonded prestressed conventional concrete beams, formulas for calculating the flexural capacity and maximum crack width of unbonded prestressed recycled concrete beams and unbonded prestressed basalt fiber recycled concrete beams were established. These provide a simple and feasible method for the calculation of flexural capacity and crack width.

Study on the destructive test of T-beam strengthened by external prestressing

Three T-beams with severe cracks in the operation were selected for the approach bridge of the Yellow River Bridge of a national highway. Three pieces of external T-beams were used for reinforcement and the destructive tests were carried out on the strengthened T-beams. The test results of the T-beam test of the approach bridge are analyzed to evaluate the bearing capacity. The main conclusions are as follows: The strengthened T-beam has greatly improved the mechanical performance, improved the cracking load of the T-beam, and slowed the crack development. The change of beam deflection is divided into three stages: 0~30t, 30~66t, 66~134t. The deflection value increases gradually, and the turning point of deflection changes basically corresponds to the crack development. The stiffness and ultimate load carrying capacity of the T-beam are greatly improved, which greatly improves the safety of the T-beam. Due to the lack of space at the bottom of the beam, the test beams of the three pieces of reinforcement were loaded to the final failure, and the maximum crack width has reached the loading termination condition. This indicates that the elastic stress stage of the T beam is increased after the reinforcement, and the T beam has a strong T-beam. Deformation recovery capability. It provides some reference for the reinforcement and transformation of similar T-beams and the evaluation of bearing capacity.