Cracking Moment Research Articles

Flexural behavior of GFRP and steel bars reinforced lightweight ultra-high performance fiber-reinforced concrete beams with various reinforcement ratios

The synergistic operating mode of the concrete matrix and the reinforcing bar determines the dependability of a structure in complicated environments. The objective of this research has been to provide a comprehensive analysis of the flexural behavior exhibited by lightweight ultra-high performance fiber-reinforced concrete (LUHPC) beams that have been reinforced with high-strength steel bars (HRB500) and glass fiber-reinforced plastic (GFRP) bars. LUHPC was used as the matrix material with a compressive strength of 120 MPa and a density of 2050 kg/m3. This study focused on examining the impact of different reinforcement ratios (0.59 %, 1.27 %, and 1.94 %) and reinforcement types (GFRP and HRB500 bars) about the flexural performance of LUHPC beams under four-point bend loading. As demonstrated by the results of experiments, GFRP-reinforced LUHPC (G-LUHPC) beams with higher reinforcement ratios have higher peak loads, flexural stiffness, and cracking loads but lower ductility. Compared with steel-reinforced LUHPC (S-LUHPC) beams, the bending strength of G-LUHPC beams was reduced by 18.2 %, 24.2 %, and 6.7 %, the peak deflection was increased by 166.5 %, 24.8 %, and 56.9 %, and stiffness degradation and crack development were rapid. After comparing the test results with the current commonly used specifications, it was seen that the codes could better predict the cracking moments and the deflections under service loads of G-LUHPC beams. However, it was noted that both the ultimate moments and the corresponding mid-span deflections were greatly underestimated.

Bending performance of lightweight aggregate concrete beam subjected to reinforcement corrosion: Experimental and numerical study

The application of lightweight aggregate concrete (LWAC) benefits the structural behavior of long-span and high-rise buildings. However, the corrosion-related durability issue of bending elements made of LWAC has remained unresolved for decades, and the bending performance of corroded LWAC beam, including load-bearing capacity, stiffness, cracking, and etc., has not yet been clearly defined due to limited knowledge in the available literature. This study aims to investigate the bending performance of LWAC beams subjected to reinforcement corrosion, and the test results provide valuable data for addressing the research gap relevant to the topic and contribute fundamental knowledge to the promotion of structural LWAC elements. Seven reinforced LWAC beams were tested to examine the cracking behavior, characteristic loads and deflections, deformation ability, and distribution of cross section strain at various moments. The modelling method considering the effect of rebar corrosion for LWAC beam was proposed. It was concluded that the corrosion of longitudinal rebar led to decreased cracking, yielding, and ultimate moment of LWAC beam, while the corrosion of stirrups increased the cracking moment and had little effects on the yielding and ultimate moments. The ductility of the tested specimens initially decreased and then increased with the raising corrosion level of the longitudinal rebar, which was attributed to the variation in bond performance between the rebar and LWAC. All tested beams exhibited a yielding deflection smaller than 1/235 of the span length. The strain distribution of the mid-span cross-section exhibited a nonlinear feature with increasing mass loss of the corroded longitudinal steel rebar. The proposed modelling procedure considering the corrosion effect showed good agreement with the test results, and a preliminary analysis of the bending performance of LWAC beams with different steel reinforcement corrosion ratios was completed. Data Availability StatementAll data, models, or code that support the findings of this study are available from the corresponding author upon reasonable request.

Experimental flexural investigation of RC beams with impeded steel truss using smooth steel angels

This paper emphasizes on testing the flexural capacity of Hybrid Steel Truss Reinforced Concrete Beam (HSTRCB), where a prefabricated steel truss is embedded into concrete beam instead of conventional rebars, forming a composite section. Five doubly reinforced concrete beams were designed, casted, experimentally tested and analyzed to investigate the flexural behavior of HSTRCB, in comparison to ordinary reinforced concrete beam. All beams were designed according to ACI 318, having same flexural capacity. First beam is ordinary reinforced concrete beam while the other four HSTRCB were designed having identical smooth steel angles, as compression and tension reinforcement, with different shear reinforcement alignment, and spacing. Different smooth truss typology were used as reinforced rebar replacement in the RC beams to determine the significant truss configuration that has highest flexural behaviour. The results showed that HSTRCB improves cracking moment, stiffness, energy absorption and effective cracked moment of inertia during the entire loading stages.

A design methodology for fibre reinforced concrete elements in serviceability conditions integrating tension softening and stiffening effects

This paper proposes a design methodology to derive an analytical bilinear moment‒curvature diagram (Mana–χana) for the cross-section of fibre reinforced concrete (FRC) elements that also includes conventional steel flexural reinforcement (R/FRC). This bilinear diagram is obtained by determining the post-cracking tensile capacity of FRC (NtcFRC), which integrates not only the tensile stiffening capacity of the FRC surrounding the conventional flexural reinforcement due to the bond stress transference between this reinforcement and FRC, but also the tensile softening of the cracked FRC out of this zone. This Mana–χana is defined by two points, the first corresponding to the cracking moment and its corresponding curvature (Mcrana,χcrana), while the bending moment of the second point of this diagram (Muana) is a multiple of the analytical cracking moment (CuMcrana), where Cu is dependent on the fibre volume percentage (Vf). The curvature corresponding to Muana,χuana, is obtained by assuming the flexural stiffness of a fully cracked RC section. Therefore, the Mana–χana is determined by geometric and material properties of directly assessed by a designer.For demonstrating the applicability of the proposed design methodology, a database of beams of distinct cross-section aspect ratios and compressive strength classes, reinforced with different percentages of steel fibres and reinforcement ratios of conventional steel bars was established. By using the bilinear Mana–χana, and applying the principle of virtual work, the deflection of these beams was estimated with sufficient accuracy for design purposes, when compared to experimental records. Although the formulation has been applied to beams made by steel fibre reinforced concrete (SFRC), it is conceptually general and applicable to elements of concrete reinforced with other types of fibres.

Cracking performance in the hogging moment region of HSS-UHPC continuous composite girder bridges

To elucidate the cracking performance of concrete slabs at the negative bending moment region of high strength steel (HSS)-ultra high performance concrete (UHPC) continuous composite girder bridges, eight scale-reduced steel-concrete composite beams, constructed using HSS and UHPC that varying parameters of UHPC slab thickness and width and shear connection degree at the steel-concrete interface were prepared and tested. The composite beams' cracking pattern, bending stiffness, load-deflection curve, steel-concrete interfacial slippage, and strain history were presented and discussed. The test results show that the HSS-UHPC composite beams subjected to negative bending moments exhibited favorable cracking performance. With the UHPC slab width increasing from 450 mm to 550 mm, the composite beams' initial cracking moment, bending stiffness, and flexural ductility increased by 33.4%, 20.5%, and 39.8%, respectively. The utilization of a thick UHPC slab benefited the performance of the composite beams under negative bending moments. Replacing the 80 mm-thick slab with a 110 mm-thick slab improved the structure’s cracking moment and bending stiffness by 15.0% and 21.4%, respectively. Additionally, as the shear connection degree increases from 0.64 to 1.02, the initial cracking and ultimate failure moments of the composite beam were improved by 7.2% and 1.6%, respectively. In contrast, the bending stiffness of the beams with a shear connection degree of 1.02 was 12.4% smaller than those of 0.64. A comprehensive comparison between the formula-predicted cracking performance and current experimental results was performed to examine the capability of existing design approaches in calculating the HSS-UHPC composite beams. The flexural resistance algorithm proffered by Xu exhibits favorable alignment with test results, thereby providing a compelling methodology for designing HSS-UHPC continuous composite girder bridges.

Effect of Rebar Harsh Storage Conditions on the Flexural Behavior of Glass FRP Concrete

Nowadays, fiber-reinforced polymer (FRP) has become a widely accepted alternative reinforcement to steel bars in concrete members due to its many sustainability traits, as represented by its high strength-to-weight ratio, corrosion resistance, non-conductive properties, and electromagnet neutrality. However, FRP bar exposure for an extended period of time to harsh environmental conditions and chemicals can have an adverse effect on their mechanical properties. In this investigation, glass FRP bars were exposed to indoor controlled temperature, outdoor direct sunlight, outdoor shade, seawater, and alkaline solution for six months prior to using them as reinforcement in concrete flexural members. This research involves the fabrication and testing of five pairs of 3 m-long concrete beams with 200 mm by 300 mm cross-sections embedded in the tension zone with the exposed GFRP bars. The 10 beams were instrumented with strain gauges and tested following a four-point loading scheme using a hydraulic jack attached to a rigid steel frame. Crack width records from the tests showed the inferior serviceability of the beams that contained rebars stored in an outdoor environment relative to the control beams. GFRP bar exposure to an alkaline solution or outdoor direct sunlight slightly affected the cracking and ultimate moment capacities, reducing them by 5% and 3% in terms of the same parameters as the controlled indoor exposure, respectively. The influence of GFRP bar exposure to open-air shade or sunlight decreased the pre-cracking stiffness by 25% and flexural ductility by 10–20% when compared with the control specimens. The predicted ultimate flexural strength using the ACI 440 provisions gave comparable results to the experimentally obtained values. A simple mathematical equation that envelops the moment–deflection relationship for GFRP over-reinforced concrete beams and only requires information about initial cracking and ultimate flexural conditions is proposed.

Improvement of the Cracking Moment-Based Asphalt Mixture Splitting Test Method and Splitting Strength Research

The asphalt mixture splitting test is one of the most important methods for measuring asphalt’s tensile properties. To characterize the limitations of the traditional splitting test and the influence of the specimen size and loading conditions on the accuracy of the test, the factors affecting the strength of the splitting test were analyzed to reveal the splitting failure state and establish a unified representation model between the splitting and direct tensile tests. Initially, the moment of specimen cracking was taken as a key indicator, combined with image processing technology, to establish a set of criteria to judge the splitting test. Subsequently, standardized splitting tests were conducted and compared to tests of different specimen sizes and loading methods. Based on the octahedral strength theory, the stress points before and after the improved test were compared to the existing failure criteria. Direct tensile and splitting tests were conducted at different rates, and a unified strength–rate function model was established, realizing the unified representation of direct tensile and splitting tests. The research results indicate that the standardized splitting test is prone to the phenomenon wherein the specimen end face cracks before the center, affecting the accuracy of the test and potentially leading to redundant material strength evaluations. Using a loading method with a “35 mm specimen thickness” and a “0.3 mm rubber gasket + 12.7 mm arc-shaped batten” can essentially achieve the test hypothesis of “cracking at the center first”, resulting in less discrete outcomes and closer alignment to the three-dimensional stress failure state. The tensile and splitting strengths are both power function relationships with the rate as the independent variable, establishing a unified function model of the tensile and failure strengths. The research provides a more reliable testing method and calculation model for asphalt pavement structure design, and it also provides an effective basis for the improvement of splitting tests on materials such as concrete and rock.

An innovative prestressing system of prestressed carbon fiber sheets for strengthening RC beams under flexure

An innovative prestressing system was developed in this study, which can effectively anchor the prestressed carbon fiber sheets as well as conveniently apply prestress to the carbon fiber sheets. Tensioning tests of the carbon fiber sheet-anchor assemblies were first conducted to verify the anchorage behavior of anchors. Then this prestressing system was used for strengthening reinforced concrete (RC) beams to further verify its feasibility and investigate the effect of the impregnation and curing conditions of the carbon fiber sheets on the flexural strengthening efficiency. The results indicated that the tested ultimate capacity of the carbon fiber sheet-anchor assembly reached 72.1∼97.9% of the theoretical ultimate capacity of the carbon fiber sheet based on different impregnation and curing conditions. The concrete crushing failure and rupture failure of prestressed carbon fiber sheets occurred in the strengthened RC beams. The cracking and yielding loads of the RC beams with prestressed sheets were increased by 56.7∼68.5% and 21.7∼30%, respectively, while those with non-prestressed sheets were increased by 27.3% and 13.7%, respectively. The ultimate load was significantly affected by the impregnation and curing conditions. The prestressed carbon fiber sheets with the uncured full impregnation condition were not superior to the non-prestressed sheets in terms of the ultimate load, whereas the cured full impregnation and partial impregnation conditions were more effective than the uncured full impregnation condition. Finally, theoretical equations were used to calculate the cracking, yielding, and ultimate moments of RC beams strengthened with prestressed carbon fiber sheets.

A unified shear strength equation for slabs and beams longitudinally reinforced with FRP or steel bars based on simplified cracked elastic properties

At service load conditions, deflections and stresses in reinforced concrete (RC) slabs and beams are typically calculated using the properties of the transformed cracked cross section. For more than eighty years, the depth of compression zone factor k in cracked singly-reinforced rectangular RC sections has been calculated using k=2ρn+ρn2-ρn where ρ is the reinforcement ratio and (n) is the modular ratio. It is shown that in slabs and beams with a wide range of concrete compressive strength fc′ that are reinforced longitudinally with steel or FRP bars, ρn ranges from 0.005 to 0.16. Within this range, k can be accurately calculated using k=0.95ρn0.43 or simply k=ρn0.44. The error between the former equation and the exact equation ranges from –2% to + 3 %. This equation is used to show that the shear strength of concrete vc in the ACI–440.11-22 code for GFRP–reinforced members depends effectively on ρ, fc′ and d, just like the strength of steel–reinforced members in the ACI–318-19 code equation. It is proposed to apply to the factor Er/Esteel1/3 where Er and Esteel are the moduli of elasticity of the FRP and the steel bars respectively to the ACI–318 equation to make it suitable also for FRP–reinforced members. This unifies the equation for the two types of reinforcement and provides a better correlation with the experimental results from 233 FRP–reinforced members available in the literature than the current ACI–440.11 code equations. On the other hand, the transformed cracked moment of inertia Icr can be related solely to ρn and approximated using Icr=0.36ρn0.81bd3 where b and d are the sectional width and effective depth respectively. This equation is used to show that the cracked flexural stiffness is effectively related to the modulus of elasticity and the area of the reinforcing bars raised to the power 0.8, to d2.2 and to modulus of elasticity of the concrete raised to the power 0.2.

Structural performance of fiber-reinforced SCC beams containing Stalite lightweight aggregates

This study intends to investigate the structural performance of large-scale fiber-reinforced lightweight self-consolidating concrete (LWSCC) as well as lightweight vibrated concrete (LWVC) beams made with Stalite aggregates under flexure loads. A total of fourteen reinforced concrete beam specimens were tested under a four-point bending configuration until failure. Two different binder contents (550–600 kg/m3), two types of lightweight aggregates (coarse and fine Stalite aggregates), two PVA fiber lengths (8–12 mm), and three fraction volumes of fibers (0.3%, 0.5%, and 1%) were considered in this study. The structural performance of the tested beam specimens was assessed in terms of load–deflection response, cracking behavior, energy absorption, displacement ductility, cracking moment, and ultimate flexural strength. This study also investigated the performance of design code provisions in predicting the cracking and ultimate moment capacities of all tested specimens. The results indicated that using shorter PVA fibers seemed to better improve the structural performance of LWSCC beams in terms of deformability, energy absorption, ductility, and ultimate flexural capacity than using longer PVA fibers. Using up to 1% PVA8 fibers in lightweight concrete beams made with Stalite aggregates proved to completely compensate for the drop in ultimate flexural strength that resulted from the use of low-density aggregates and further helped the beams to experience much higher rates of deformation. The results also showed that the model proposed by Henager and Doherty well predicted the ultimate moment capacity of LWSCC/LWVC beams reinforced with PVA fibers.

Comparative Studies of the Confined Effect of Shear Masonry Walls Made of Autoclaved Aerated Concrete Masonry Units.

Confined walls are popular in areas exposed to seismic action. The advantage of such structures is increased load-bearing capacity, ductility, and energy dissipation. Confined masonry walls are also used to restrain the intensity of cracking and improve load-bearing capacity in areas exposed to seismic action. This paper describes the research on 18 confined walls and presents a comparison with research on unconfined walls (referenced models). The confined models were classified into three series: HOS-C-AAC-without openings and with confining elements around the perimeter; HAS-C1-AAC with a centrally positioned opening and circumferential confinement; and HAS-C2-AAC with a centrally positioned window opening and additional confinement along the vertical edges of the opening. The area of the window opening was 1.5 m2. All walls were made of autoclaved aerated concrete (AAC) masonry units of the nominal density class of 600. The walls were tested under initial compressive stresses σc = 0.1; 0.75; and 1.0 N/mm2. The reference models without confinement (six models of the series HOS-AAC without openings and the series HAS-AAC with openings) were prepared from the same masonry units, had almost the same outer dimensions, and were tested under the same initial compressive stresses σc. The analysis was performed for the morphology of cracks, stress values at the moment of cracking and failure, stiffness, and angles of shear strain. The morphology of cracks was found to depend on initial compressive stresses and the presence of an opening. A significant increase in compressive stress leading to cracks and failure stresses was observed with increasing values of initial compressive stresses. As the wall behavior was clearly non-linear, the bilinear relationship described by energy dissipation E, stiffness at the moment of cracking Kcr, and maximum displacement uu was proposed to be included in the engineering description of the relationship between horizontal load and displacement of confined walls. Confinement along the vertical edges of the opening having an area of 1.5 m2 (acc. to EN 1996-1-1) increased the maximum forces Pmax by ca. 45% and marginally affected the ductility of the wall when compared to the elements with circumferential confinement.

Investigation of Cracking in Reinforced Concrete Structures by Means of Standardized Deformation Models

In this study, a detailed analysis of the use of standardized deformation models is carried out to calculate the design characteristics of reinforced concrete elements, such as crack resistance. For theoretical verification of the values of the moment of cracking, calculation methods based on the use of a nonlinear deformation model are used.A theoretical study of cracking moment using a non-linear deformation model shows that the application of a two-line diagram of concrete deformation allows to obtain the most accurate values of cracking moment.

Shear behavior and construction method of steel shear keyed joints in precast segmental beams

The joints between segments represent weak points and introduce discontinuity into structures, therefore they are particularly significant in precast concrete segmental bridges. In this study, a new steel shear key was designed, and 6 full-scale tests were conducted. Various shear keys and joint types were taken as experimental parameters to study crack propagation, failure mode, shear slip, ultimate bearing capacity, and the residual bearing capacity of various joints under direct shear loading. The results show that the stiffness and shear capacity of steel shear keyed joints were higher than concrete key joints, and the structural system was more stable than concrete keyed joints at the moment of cracking. Both the concrete key and steel key epoxied joints suffered direct shear failure. However, different to the concrete epoxied joints which experienced brittle failure, steel key epoxied joints demonstrated a large residual capacity. Based on traditional segmental bridges construction, construction methods involving steel shear keyed joints included short-line match, long-line match, and modular methods are introduced. Finally, the feasibility of steel shear keyed joints construction was verified via engineering tests.

Calculation Method for the Cracking Resistance and Bearing Performance of SFRAC Beams.

The utilization of recycled aggregate (RCA) in preparing recycled concrete (RAC) is an effective measure to solve the increase in construction waste. Furthermore, applying RAC to flexural members is a viable practice. The addition of steel fiber to RAC to prepare steel fiber recycled concrete (SFRAC) solves the performance deterioration caused by the recycled aggregate, so it is necessary to study the effects of the recycled aggregate replacement rate and fiber-volume ratio on the crack resistance and bending performance of SFRAC beams. In this study, 13 beams were designed and manufactured, with the water-cement ratio, recycled aggregate replacement rate, and fiber-volume ratio as the primary variables, and the cracking moment and ultimate moment of the SFRAC beams were systematically studied. The results show that the cracking and ultimate moments of the SFRAC beams increased with decreases in the water-cement ratio or with increases in the fiber-volume ratio and were unaffected by the replacement rate of recycled aggregates. Based on the experimental results and theoretical analysis, a calculation model and formula for the cracking moment were established. The ultimate bearing capacity of SFRAC beams can be accurately determined using the ACI 318 and ACI 544 standards. The research results serve as a valuable reference for the design of SFRAC beams, effectively address the issue of performance degradation in RAC structural members, and promote the use of green building materials.

Development of sustainable concrete using recycled polyethylene terephthalate (PET) granules as fine aggregate

Solid waste management has become a significant environmental challenge globally. This study aims to examine the performance of sustainable concrete incorporating polyethylene terephthalate (PET) granules as partial (0%, 10%, 30%, and 50%) volumetric replacement of sand. The mechanical properties including compressive strength, tensile strength and elastic modulus were examined. The flexural and cracking performance of the reinforced concrete (RC) beams, as well as bond behaviour of concrete mixes with steel reinforcement were investigated. Incorporating 10% PET granules demonstrated positive impact on the mechanical properties, flexural strength and cracking behaviour of RC beam, as well as bond strength. A theoretical model was proposed for predicting bond strength of concrete containing PET granules and the results corresponded well with both experimental and previous research findings. The American and Australian standards conservatively predicted cracking and flexural moments of the RC beams. Finite element modelling was conducted on the RC beams and the results corresponded well with the experimental findings.

The feasibility of using ultra-high performance concrete (UHPC) to strengthen RC beams in torsion

To explore the feasibility of using ultra-high performance concrete (UHPC) to strengthen reinforced concrete (RC) beams in torsion, pure torsion tests on 9 specimens have been conducted in this study, including one RC beam without strengthening (referred as control beam) and 8 UHPC-strengthened beams. The variables considered for investigation included the wrapping form of UHPC layer, thickness of UHPC layer, shape of steel fibers added in UHPC layer, UHPC-RC interfacial treatment, and reinforcement ratio of UHPC layer. The overall torsional behavior, torque–twist curves, torque-principal strain curves, cracking pattern and UHPC-RC interfacial slippage for all specimens were obtained based on the torsion tests. Results show that the cracking and ultimate torsional moments of all strengthened beams were higher than those of the control beam, with maximum increases of 488.5% and 593.2%, respectively. When the RC beam cannot be fully wrapped, which is the preferred strengthening scheme, 3-sided wrapping form is also an acceptable choice, but the 2-sided strengthening scheme should be avoided. The determination of the thickness of UHPC layer should comprehensively consider the strengthening effect, cost for strengthening and requirements for RC beam's dimensions after strengthening. RC beam surfaces should be fully roughened before casting UHPC to ensure that the UHPC layers and the RC beam persistently act together as a whole to resist torsional loads. The UHPC layers are recommended to be equipped with steel bars, which could substantially improve the torsional capacity and ductility of the strengthened beam on the premise of limited increase in the cost. Finally, the effectiveness of torsional strengthening using UHPC was compared with that using fiber reinforced polymer (FRP) in terms of increase in cross-sectional area, increases in cracking and ultimate torsional moments, increase in torsional stiffness, failure mode and long-term performance.

Experimental and analytical studies on the flexural behavior of steel plate-UHPC composite strengthened RC beams

In view of the excellent mechanical property of Ultra-High Performance Concrete (UHPC), a new method of using steel plate and UHPC (SP-UHPC) composite to strengthen damaged reinforced concrete (RC) beams was proposed. Four-point bending tests were conducted to investigate the failure modes, deformation characteristics, crack resistance, and bearing capacity of five SP-UHPC strengthened beams (SPUB), one reinforced UHPC strengthened beam (RUB), and one reinforced concrete beam (RCB). Additionally, the impacts of different strengthening techniques, the thickness of steel plate and UHPC on the flexural performance of the strengthened beams were investigated and discussed. The effects of the shear strength of UHPC-RC interface on the bearing capacity of the strengthened beams were analyzed. The test results show that the failure mode of strengthened beams is interface peeling failure. Compared with RCB, the cracking moments of SPUBs and RUB increased by about 214.5%-271.5% and 43.7%, respectively. The bearing capacity of SPUBs and RUB increased by 53.1%-73.7% and 53.4%, respectively. The flexural stiffness of strengthened beams increased by nearly one time on average. Compared with RUB, the SPUBs showed a superior crack resistance and interface slip resistance. The increase in the thickness of the steel plate and UHPC can improve the flexural stiffness and the strain behavior of strengthened beams significantly. Based on the test results, the calculation formulae of UHPC cracking moments and bearing capacity of SP-UHPC strengthened beams were proposed considering the effective anchorage length of interface, the strain hardening behavior of UHPC, and the residual strain in RC beam. The calculation results of UHPC cracking moments and bearing capacity coincide with the test results, demonstrating the accuracy of proposed calculation formulae.

Experimental study on cyclic flexural behaviour of GFRP-reinforced seawater sea-sand concrete slabs with synthetic fibres

Seawater and sea-sand (SWSS) concrete is a new type of concrete with many economic and environmental benefits. However, chloride-induced corrosion of steel reinforcement is a major problem associated with this type of concrete. Due to its excellent resistance in chloride environments glass fibre reinforced polymer (GFRP) reinforcement could be utilized in SWSS concrete as an alternative to steel Adding fibres can also improve the concrete properties reinforced with GFRP bars. Fibres can affect the post-crack response and failure mode of GFRP reinforced concrete and also improve the bond between rebar and concrete. This study focused on the flexural behaviour of GFRP reinforced SWSS concrete slabs with or without fibre incorporation which has not yet been fully addressed in the literature. Polypropylene (PP) and polyvinyl alcohol (PVA) fibres were used for the concrete reinforcement. Under-reinforced (ρ < ρb) and over-reinforced (ρ > ρb) GFRP reinforced concrete (RC) slabs were prepared and subjected to four-point cyclic bending loads. The results show that GFRP bar is a promising alternative to steel for SWSS concrete reinforcement. The GFRP RC slabs with plain SWSS concrete had a cracking moment which was 13% lower than the values predicted by the ACI 440.1R-15 provisions. However, adding fibres, particularly PP fibres, could successfully compensate for this reduction. Variation in GFRP reinforcement ratio had almost no effect on cracking moment. With the addition of fibres, the cracking moment and ultimate strength of the slabs were both improved. Crack width and crack spacing were reduced in fibre-reinforced SWSS concrete slabs compared with the plain concrete counterparts. Fibres reduced the residual deflection of the slabs at the end of each cycle. Comparing experimental deflection results with the values predicted by different models revealed that there is no available model could satisfactorily predict deflection for all the GFRP reinforced SWSS slabs.

Safety Analysis of Rebar Corrosion Depth at the Moment of Corrosion-Induced Cover Cracking

Concrete cover cracking induced by reinforcement corrosion is an important indication of the durability limit state for reinforced concrete (RC) structures and can be used to determine the structural service life. The process of rebar corrosion from the beginning of rusting to the occurrence of cover cracking due to corrosion expansion can be divided into two phases: the phase of the free expansion of the corrosion product and the phase of cover cracking. Based on the assumption of the uniform corrosion of the reinforcement, one model for predicting the reinforcement corrosion depth from corrosion initiation to cover cracking was established according to the cylindrical cavity expansion theory. The main factors affecting the reinforcement corrosion depth were analyzed. The main factors affecting the corrosion depth of reinforcement were analyzed. The quantitative sensitivity analysis of the factors influencing the calculation formula shows that the depth of reinforcement corrosion and the thickness of the concrete protective layer are approximately linearly increasing, with a growth rate of 0.2366 μm/mm; the diameter of the reinforcement is approximately linearly decreasing, with a decrease rate of 0.2122 μm/mm; the volume expansion rate of rust is approximately power function decreasing; the overall influence range of the yield criterion selection parameter is 0.15 μm; for the concrete strength grade, the overall influence range is 0.1 μm. The coefficient of determination R2 is 0.87, and the overall accuracy of the calculated formula is high, which can be used to predict the service life of reinforced concrete structures and guide the durability design in combination with the research results on the corrosion rate of reinforcement under different environments.

Flexural Behavior of GBFS-Based Geopolymer-Reinforced Concrete Beams

Geopolymer concrete (GC) is an emerging alternative construction material due to it being eco-friendly in production with considerably low carbon emissions. Despite being an alternative material, the structural behavior of GC is a rarely studied subject in the literature. The studies concerning the mechanical behavior of structural members made from GC have established the foundations of its practical usability. The current structural codes are exclusively for ordinary Portland cement concrete (OPCC), and the utilization of these for GC constitutes an open question. In this study, 12 GC beams with different shear span-to-effective depth ratios of 2.5, 3.5 and 4.5 were manufactured and tested in a three-point bending test setup. The effect of the shear reinforcement ratio was also taken into account (0, 0.34, 0.45 and 0.67%). The results were compared with the predictive capabilities of four structural codes and two equations in the literature (all for OPCC). In addition, comparisons were made with a very limited number of studies, which included predictive tools for the strength of GC. All specimens’ cracking moments were calculated with flexural tensile strength predictions and compared with experimental cracking moments. Moreover, particularly for the beams that failed in flexure, the ultimate bending moments were compared with the predictions of two structural codes for OPCC. It was observed that the best predictions of the cracking moment could be made by the equation of Diaz-Loya et al. (2011), which resulted in the lowest coefficient of variation (COV) and consistently predicted on the safe side, whereas, even with a lower COV, EC2 consistently overestimated the cracking moment. For the ultimate moment capacity, it was observed that both ACI318 (2019) and TS500 (2000) delivered relatively good predictions and could be employed confidently.