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Although research has shown a considerable influence of the pre-cracking phenomenon on steel-congested concrete members, only normal concrete (NC) has been considered in the literature. The intention in this paper is thus to study the effect of the pre-cracking phenomenon on the bond response of pre-cracked NC with different slump flow values and self-consolidating concrete (SCC). Initial crack widths ranging from 0.0 to 0.5 mm are studied. Results show that initial crack widths larger than 0.10 mm have a significant influence on bond properties, such that reduction factors greater than 30% and 50% are obtained for the maximum bond strength of concrete specimens exposed to initial crack widths of 0.2 mm and 0.4 mm, respectively. Results show that concrete mixtures with higher workability are less sensitive to the pre-cracking phenomenon as compared to NC mixtures. The average bond stress of steel rebar in the pre-cracked SCC is found to be similar to that of the NC with a slump flow of 200 mm, which is considerably better than for NC with a slump flow of 97 mm. Moreover, results show that 65.8, 80.6, 88.5 and 93.1% fracture energy reductions are obtained for crack widths of 0.20, 0.30, 0.40 and 0.50 mm, respectively, as compared to the small crack width of 0.15 mm.

This study experimentally explores the effects of applying various types of fibres to concrete mixes on the flexural behaviour of longitudinal structural members with basalt fibre reinforced polymer (BFRP) bars. The main objective is to research the viability of using new advanced fibres of basalt to enhance the concrete response. Basalt fibre and basalt fibre reinforced polymer rebar and compared with the conventional concrete and with a 40 MPa compressive strength target, eighteen beams were fabricated and tested; twelve with basalt fibre reinforced polymer rebar concrete and six with conventional concrete Basalt fibre lengths 30 mm with 15 µm and BFRP bar length of 800 mm with 8 mm diameter were taken into account. Flexural tests were done using a four-point test setup on both of the BFRP- conventional concrete (CC) beams. The test matrix would include BFRP bar reinforcing beams and conventional steel rebar for comparative purposes. Results showed that the application of basalt fibres to concrete enhanced the ductility of these beams' curvature. Due to the delay in the concrete failure in the compression zone, a significant improvement in bending ability was also reported, which supported the BFRP bars achieved a higher ultimate strength. The opening and deep formation of a crack have been effectively limited by the aggregate interlock of basalt fibres, which maintained the crack widths lower than in the 0.7 mm permissible maximum in service. Basalt fibres of 4%, 6%, and 8% were done. Compared to conventional concrete 6% basalt fibre at 28 days of the curing period, the maximum compressive strength was attained 52.38 N/mm2, tensile strength was attained 5.55 N/mm2, Flexural strength increases to 7.45 N/mm2. However, basalt fibre reinforced polymer rebar concrete was larger than conventional concrete beams.

In this article, the outcomes from an experiential program aimed at investigating the effect of high- performance fiber reinforced cementitious composite (HPFRCC) layers and stirrups distance on flexural performance, ductility, moment redistribution, and plastic hinge length of two-span continuous concrete beams. The unique characteristics of reinforced HPFRCC continuous beams. Under flexural loading, such as high resistance to splitting cracks, less rebar slippage, damage localization in a single or few flexural cracks, inelastic strain concentration within a small region of rebar, and failure by the fracture of tensile longitudinal reinforcement in the plastic hinge region motivated this research study. The specimens have rectangular cross section of 250 mm (height) × 200 mm (width) and are continuous over two spans of 1800 mm each and two concentrated equal statically monotonic loads are applied at the mid-span of each beam. Eight beams specimens divided into three groups A, B and C were designed and cast due to the type of concrete and the stirrup spacing. Group A, consisted of two normal concrete beams with conventional stirrup spacing (d/2) (reference specimen) and compact stirrup spacing (d/4), and Group B consisted of four continuous beams made of high- performance fiber reinforced cementitious composite (HPFRCC) were layered with conventional stirrup spacing stirrups (d/2), and Group C, consisted of two continuous beams made of completely high- performance fiber reinforced cementitious composite(HPFRCC) with conventional (d/2) and compact stirrups spacing (d/4). The test results indicated that application of HPFRCC instead of conventional concrete in different section of beams with compact stirrups in critical length induced to increasing the ductility of Continuous beams. It can also be seen that increasing the transverse reinforcement, had a positive effect on the achieved moment redistribution compared with the reference beam with conventional spacing transverse reinforcement. In flexure, a highly nonlinear plastic strain distribution of the primary tensile reinforcement is observed at dominant crack locations, leading to significant differences in plastic hinge length and behavior as compared to ordinary reinforced concrete flexural members.

This paper presents the experimental results of bond and anchorage behaviours under Steel Strap Tensioning Technique (SSTT) confined high-strength concrete (HSC). The experimental tests consisted of pull-out test with short bond length and pull-out test with long bond length were performed to determine the bonding and anchorage capacity of SSTT-confined HSC. A total 36 specimens with short bond length and 16 specimens with long bond length were tested in this study. Three batches of concrete with compressive strength of 30 MPa, 60 MPa and 90 MPa were tested. Other parameter in this study was rebar diameter of 12 mm and 16 mm and different SSTT confinement ratios ranging from 0 to 0.2. To determine the effects of confinement on development bond and anchorage, an analytical expression was developed based on the parameters tested in this study. The equation is then verified with the bond strength proposed by the existing bond equations. The results from conducted tests indicated that the application of SSTT as an external confinement can increase the bond strength of confined concrete by up to 50%.

The central pull-out tests were performed on C60 steel-fiber high-strength recycled concrete (SFHSRC) under the monotonic load. The failure mode characteristic of the specimens and the direction of the cracks were observed and described. The bond strength and slip displacement were measured. The effects of two parameters, replacement ratio of recycled coarse aggregate (RCA) and addition ratio of steel fiber, on failure mode and bond-slip mechanicals behaviors of SFHSRC were also analyzed. The experimental results showed that when the replacement ratio of RCA was kept unchanged, the slip displacement of rebar increased with the increase of addition ratio of steel fiber, but the bond strength increased first and then decreased; with the addition ratio of steel fiber was remained unchanged, the bond strength and slip displacement of rebar decreased with the increased of the replacement ratio of RCA. The bond strength and slip displacement mentioned above reached the maximum when the steel fiber addition ratio was 0.8%; that is, when the replacement ratio of RCA was 0 and the addition ratio of steel fiber was 0.8%, the bond strength reached the maximum. Based on the theoretical analysis of experimental data, a reasonable bond-slip constitutive model was established in this paper, which can help promote more extensive application of RAC and realize persistent development strategy of building, resources and environment to a certain extent.

The normal grouting material which has been widely used in traditional grouted sleeve connections has high brittleness and it often burst when broken. Moreover, these grouted sleeve connections required larger anchorage length and exhibited a worse cyclic load capacity than the steel bar. In this research, three kinds of fibers, including polypropylene fiber, polyvinyl alcohol fiber and basalt fiber, were selected as mixing materials in the grouting material. Their performance was tested in three areas: basic mechanical properties, toughness, and the optimal content and length of each fiber. Then, a total of 120 grouted sleeve connections with three selected optimal fiber grouting materials and five different anchorage lengths were manufactured. The mechanical performance of the grouted sleeves connections was tested under two loading schemes: cyclic loading at high stress (CH) and cyclic loading at large strain (CL). The compression test results of grouting materials demonstrated that fiber was an ideal material for improving the toughness of the grouting material. The optimal content of each fiber in grouting material was 0.5% (PP), 0.3% (BF) and 0.1% (PVA) and the optimal length was 9 mm (PP), 3 mm (BF) and 3 mm (PVA), respectively. Meanwhile, the minimum anchorage length of rebar in the grouted sleeves could be reduced by at least 1 d (d: diameter of rebar) when the fiber reinforced grouting material was adopted. According to the load–deflection curves under cyclic loading, the fiber reinforced grouted sleeve connections exhibited better residual deformation and stiffness degradation. Test results demonstrated that the fiber could clearly enhance the residual bond strength and ductility of the reinforced section, and the residual bond strength of the connections with the fiber grouting material could be increased by 3.8% ~ 22.8% when the steel bar was pulled out.

The mechanical properties of reinforced concrete (RC) structures are closely related to the bond stress-slip relationship of rebar-concrete interface. In this paper, a novel bond stress-slip model under monotonic and cyclic loading is proposed. For interfacial behaviour under monotonic loading, an innovative micro-element model, consisting of a spring element, a friction element and a switch element, is proposed to effectively characterize the interfacial micro-damage mechanical behaviours in a physical sense. By adopting a parallel system of micro-elements and setting the fracture threshold of individual spring element as a random variable, the expressions of the bond stress-slip relationship and interfacial damage variable are derived. Subsequently, succinct practical expressions for the bond strength, peak slip under monotonic loading are formulated. The bond stress-slip model for rebar-concrete interface under monotonic loading are further established. For cyclic constitutive model of rebar-concrete interface, a new method of cyclic correction factor for the degradation law of bond strength is developed. The bond strength degradation under cyclic loading affected by the number of cycles, maximum slip value and opposite loading can be reflected with reasonable accuracy. Furthermore, the predictions calculated by the proposed model under monotonic and cyclic loading are in favorable agreement with experimental results. All parameters in the model have clear physical meaning.

The effects and causes of different factors on the secondary tensile mechanical properties of corroded rebars (reinforcing bar) after yielding were investigated through experimental and simulation analyses to evaluate the secondary resistance performance of corroded rebar concrete members after stress and yielding. Different specimens were designed, and the rust depth, unloading level, and aging time of the rebars were used as influence variables in loading and unloading tests. The influence of each variable on the secondary tensile mechanical properties of corroded rebars after tensile yielding was studied, and reliability was verified by simulation analysis. The results showed that (a) when corroded rebars were in monotonic or secondary tension, the plastic deformation performance gradually decreased with the increase in corrosion depth, the engineering tensile strength decreased, and the pit section tensile strength increased; (b) the cold-draw hardening and aging properties of corroded rebars had no remarkable correlation with corrosion depth. (c) corrosion does not change the stress–strain constitutive relationship of the rebars during monotonic or secondary tension but affects the similarity of the stress–strain curve to the load–displacement (or average engineering stress–strain) curve of intact rebar.

The reinforcing bar (rebar) produced by Tempcore process had tempered martensite structure on its surface, owing to quenching and tempering, and ferrite–pearlite structure at the core owing to slow cooling rate. Bainite, a low-temperature transformation phase, was observed in the transition area. Mechanical properties of the rebar are significantly influenced by area ratio and hardness of the tempered martensite. In this study, microstructure and area ratio of the tempered martensite of the rebar produced by the Tempcore process were predicted using finite volume method and a continuous cooling transformation diagram. The area ratio of the tempered martensite was predicted with error range of ± 6%. Furthermore, association between the microstructure and hardness was determined by a non-isothermal tempering experiment. The hardness of the tempered martensite was successfully predicted using the tempering temperature with R-squared 98%. The proposed methodology can be effectively used to control the mechanical properties of the rebars.

Super ductile thermo-mechanically treated (SD TMT) reinforcing steel bars are commonly used these days for RC constructions given their excellent thermal and seismic resistant properties. The superior performance of SD TMT rebars is due to their distinct cross-sectional phase distribution (CSPD) of martensite, bainite, and pearlite, which impart better combinations of strength and ductility than conventional classes of steel. This paper presents an investigation carried out to study the influence of corrosion-induced damage to cross-sectional phase distribution (CSPD) on mechanical properties of SD TMT bars in comparison with the performance of conventional mild steel and ordinary TMT steel bars exposed to an aggressive environment. The influence of corrosion-induced damage to cross-sectional phase distribution (CSPD) on the stress–strain response of SD TMT bars has been investigated through tensile tests in a displacement controlled UTM. The study involved tensile tests carried out on SD TMT bars corroded to 25 different levels ranging from (0–45%) on five different rebar diameters (8mmO, 10mmO, 12mmO, 16mmO and 20mmO). The results suggest better characteristic performance of SD TMT steel bars over conventional hot-rolled rebars in mechanical behaviour's critical aspects. A correlation predicting the reduction of mechanical properties of corroded TMT bars' residual capacity concerning corrosion percentage has been suggested.

Substitution of only steel rebar with fiber-reinforced polymer (FRP) or in combination with steel rebar has been recommended to reduce corrosion effects in steel rebar. This paper has pursued the impact of hybrid concrete beams reinforced with High Strength Steel Bars (HSS) and Glass Fiber-Reinforced Polymer Bars (GFRP) manufactured employing High-Performance Fiber-Reinforced Cementitious Composites (HPFRCC) instead of conventional concrete through experimental tests. Seven concrete beams including conventional concrete and HPFRCC in three separate groups, having identical compressive strengths and longitudinal steel reinforcement ratios, have been tested following respected codes and regulations to supply sufficient development lengths using GFRP headed bars, under four-point loading tests. The first and second groups, each represented one conventional concrete beam and an HPFRCC model with GRFP or HSS; the third group included three HPFRCC beams using GRFP and Steel rebar to assess flexural behavior of beams under different reinforcement ratios. Experimental results indicated that HPFRCC beams demonstrated improvements in their load capacity, flexural strength, bending stiffness, ductility, and energy absorption compared to similar conventional concrete beams. Also, in hybrid beams compared to steel reinforced concrete beams both cast with HPFRCC, the more the effective reinforcement ratio of both single and hybrid bars increased, the more ductility was improved between 37 and 88 percent. Displacement ductility of hybrid beams having effective reinforcement ratios up to 1.35 and 1.25 times more than the balance ratio was increased 23 and 37.5 percent, respectively. Energy absorption for HPFRCC beams reinforced only with GFRP or steel rebar was increased 31 and 250 percent compared to identical conventional concrete beams, respectively. In hybrid compared to GFRP reinforced beams both cast with HPFRCC, the more effective reinforcement ratio increased, the more energy absorption was increased in a range of 51 up to 174 percent. Therefore, it can be concluded that using the hybrid of GFRP and HSS bars result in up to 30 percent improvement in flexural strength because of the effective performance of GFRP after steel rebar yielding and ductility increase due to HSSs yielding.

Concrete with the addition of polypropylene fibres is more cohesive and has better adhesion, deformability and tightness because the fibres “bind” the concrete matrix together and prevent large pores from forming in the concrete mix and limit the formation and spread of shrinkage cracks. Therefore, it can be assumed that polypropylene fibres affect the effectiveness of the concrete cover as a layer protecting steel bars against corrosion. This article presents the results of tests allowing us to estimate the effect of addition of polypropylene fibres on the reduction of reinforcing bars corrosion in concrete caused by the action of chlorides. Evaluation of the degree of corrosion of the reinforcement was analysed using the electrochemical polarisation galvanostatic pulse technique. The use of such a method allowed for the quantitative estimation of the effect of the addition of polypropylene fibre on the reduction of corrosion activity of the reinforcement in concrete.

In a comprehensive investigation, the simultaneous effectiveness of the factors of temperature (five temperatures), volume ratio of steel fibers (three volume ratios), and concrete cover thickness over the rebar (three covers) on the compressive strength, tensile strength, and concrete-steel rebar bond behavior was evaluated. 180 specimens comprised of 45 cubic specimens for the compression test, 45 cylindrical specimens for the splitting tensile strength test, and 90 prismatic specimens for the pull-out test were made. The results demonstrated raising the temperature reduced the compressive strength such that the strength of the plain specimens after exposure to 800 ℃ declined by 71.6%, compared to that of the corresponding non-heated specimens. Moreover, at a given temperature, the presence of steel fibers improved the tensile strength. After exposure to 800 ℃, the tensile strength of specimens with 1% steel fibers in volume was 127.9% higher than that of similar specimens without fibers. At a given temperature, the use and content of steel fibers had an effective role in compensating for losses in the tensile strength and bond strength induced by applying heat. Furthermore, as the concrete cover over the rebar increased, the failure mode became more ductile. The effect of steel fibers on increasing the bond strength of the specimens with a thinner concrete cover heated at elevated temperature was greater and more noticeable. Also, the concrete cover over the rebar had an effective role in compensating for the heat-induced bond strength loss, such that increasing the concrete cover from 25 to 65 mm easily compensated for the concrete-rebar bond strength reduction for every 200 ℃ increment in the exposure temperature.

Spliced region is a place where the concrete-rebar bond plays a significant role, and reduced bond strength in this region negatively affects the structure safety and integrity due to corrosion. This research has studied the combined corrosion effects of the main reinforcements and stirrups in the spliced region on the concrete-rebar bond strength in lap-spliced beams. A total of 15 lap-spliced RC beams with different stirrup spacing in the spliced region failed under 4-point bending; tensile bar and stirrup corrosions were the variables in this study. Finally, Response Surface Methodology (RSM) was used for estimating the relative bond strength of this beams. According to the results, adding corroded stirrups in the spliced region will cause negative effects on the bond strength in beam specimens via combined tensile bar-stirrup corrosion in the spliced region. Gradients in the descending part of the curve for relative bond strength versus corrosion were calculated at −0.0154, −0.016 and −0.017 when stirrups are 1, 2 and 3, respectively. Also, beams with 25% corrosion have the largest increase in the stirrup-induced bond strength. The results show that the model presented by RSM is in good agreement with the experimental results.

The effect of additives on the performance, durability and multi-functional service sustainability of a novel self-compacting concrete (SCC) was investigated in this research. Constant partial replacement of cement with 40% fly ash and admixture of M25 grade conplast SP 430 were used to form the SCC. This was followed with the addition of varying amount (0–4%) of diethanolamine as an organic corrosion inhibitor, while one set of concrete was made without the additive, to act as a control. The effect of the additives on the compressive strength, split tensile strength, the corrosion rate of the reinforcement steel rebar and the ability of electrical energy being harnessed from the concrete were analyzed. It was observed that the amount of diethanolamine to be added for maximum enhancement of mechanical properties and corrosion resistance of SCC was 3.2%. The mechanical properties of the SCC and its corrosion resistance were found to be better. Also, the energy that could power some DC components and devices was harvested or generated from the concrete beam. Hence, the study concluded that diethanolamine is a good corrosion inhibitor for reinforced concrete steel rebar and that the presence of fly ash and admixture of M25 grade conplast SP 430, strengthened the concrete.

Combining fiber reinforced polymer (FRP) with seawater sea-sand concrete (SSC) can solve the shortage of river sand that will be used for marine engineering construction. The bond performance of BFRP bars and SSC specimens is researched by pull-out test in this paper. The effects of the parameters, such as bar type, bar diameter, concrete type and stirrup restraint, are considered. It is beneficial to the bonding performance by the reduction of bar diameter. The utilization of seawater sea-sand has a low influence on the bond properties of concrete. The bond strength of BFRP is slightly lower than the steel rebar, but the difference is relatively small. The failure mode of the specimen can be changed and the interfacial bond stress can be improved by stirrups restraint. The bond-slip curves of BFRP ribbed rebar include micro slip stage, slip stage, descent stage and residual stage. The bond stress shows the cycle attenuation pattern of sine in the residual stage. In addition, the bond-slip model of BFRP and SSC is obtained according to the experimental results and related literature, while the predicted curve is also consistent well with the measured curve.

A model is developed for moisture absorption by rebar made of basalt fiber-reinforced polymer composite (BFRP), taking account of Fick diffusion, structural relaxation, and the design features of the rebar in the initial stages of climatic aging. The model is experimentally confirmed. The analytical solution may be used for kinematic approximation of moisture absorption by other reinforced polymer composites.

The formation of open porosity in rebar made of basalt fiber-reinforced polymer composite (BFRP) is investigated during exposure tests in northern climates. A statistical model is proposed for pore formation in BFRP rebar.

Recently the application of self-compacting concrete (SCC) has emerging in construction structures due to its good abilities to improve durability and decrease bleeding with good bonding with rebar. On the other hand, large amount of aggregates is required for the production of SCC. However; replacing natural aggregate in SCC with waste materials can led to discover ecological building materials. Walnut shell (WS) is one of the agriculture waste materials which can be used as a substitution of aggregate in SCC. In this research, WS was used as a replacement of coarse aggregate for constructing SCC by employing ten different volume fractions from 5% to 50% with each increment of 5%. Fresh and hardened properties of SCC were investigated for all mixes and control one. The results showed that all tested properties decreased by increase WS volume fraction. However; the lightweight self- compacting concrete (LWSCC) can get at fraction volume of WS equal and or more than 35%. Where, slump flow diameter (SFD), compressive and bond strengths were 560 mm, 35 MPa and 6.55 MPa respectively achieved at 35% ratio of WS.

The present work deals with the investigation of core compressive strength in reinforced concrete column with the slip angle orientation and bond stress relationship using Magneto rheological fluid...

As part of ongoing research to validate the efficacy of a potentiodynamic polarization technique of determining the critical chloride threshold (CCRIT) value of steel reinforcing bars exposed to ch...

The aim of the current research is to investigate the structural behavior of steel-concrete-steel sandwich beams with a new suggested shear connectors. The shear connector was manufactured from deformed rebar in the form of stirrups. Four push out specimens were tested to obtain direct shear strength for the new type of shear connectors. Also four full size steel-concretesteel sandwich beams were tested under three points loading. All beams were simply supported. The experimental results showed three failure modes as follow: (1) flexural failure; (2) shearing of shear connectors; and (3) buckling in compression plate. The use of proposed shear connectors from deformed steel bars produces a good connection between steel plates and concrete core, where the load capacity of steel-concrete-steel beam with long leg stirrups (L. connector) is larger than other beams. The ultimate load of beam B1 (steel-concrete-steel sandwich beam with L. connector) is 0.125 greater than the ultimate load of beam B2 (steelconcrete-steel sandwich beam with J-hook connectors). http://dx.doi.org/10.30572/2018/kje/100303

Electro-chemical Chloride Extraction (ECE) is considered one of the most effective techniques used to extract chloride ions from reinforced concrete structures. The effectiveness of using ECE depends on some important factors such as anode type, current intensity, extraction duration, type of rebar, and chemical properties of concrete. On the other hand, ECE may cause some detrimental effects on some mechanical properties of concrete and steel such as a reduction in bond and compressive strengths of concrete, and embrittlement (i.e. reduction in ductility) ductility of reinforcing steel. The major aim of this research work was to investigate the effectiveness of ECE using locally available un-galvanized steel mesh with conductive cement paste anode as a new type of anode on a reinforced concrete slab as a structural element. The slab behavior before and after ECE was studied by determining compressive strength, water absorption rate, concrete chloride content, and steel corrosion potential. The slab behavior was studied taking into consideration the established steel arrangement with spacing 20 cm between re-bars. The effect of initial chloride content on chloride extraction efficiency was investigated. Effectiveness of ECE with small initial chloride content 0.4% and 0.8% was compared with that of high initial chloride content 2.5% to know whether the initial chloride content is an important factor in ECE effectiveness or not.

Earlier research efforts related to concrete-to-steel rebar bond behavior predominantly focused on common parameters such as concrete strength, rebar diameter, bonded length and concrete cover, disregarding the actual/real state of concrete that comprises tension cracked regions. This investigation aims to study the concrete-steel rebar bond behavior through bending stressed specimens, in order to evaluate the influence of concrete cracking coupled with other parameters to achieve a realistic simulation. Accordingly, beam-end specimen(s) have been modified to yield the possibility of conducting pull out testing under certain bending stress level. In this study, ten test specimens were prepared and tested to cover some parameters including concrete strength, rebar diameter, bonded length, concrete cover thickness and confining stirrups in conjunction with bending stress level. Test results proved remarkable influence for stress level on bond behavior whereas, unstressed specimens showed higher bond strength than partially and fully stressed specimens by 40 and 63%, respectively. New models are proposed to predict bond strength and describe bond stress-slip behavior for stressed members. The proposed models demonstate adequate agreement with the experimental results.

Incorporating crumb rubber (CR) as a substitution for aggregate in concrete is a strategy to mitigate environmental damages caused by this waste. Here, the bond behavior between the steel rebar and high-strength concrete containing CR after exposure heat was studied. Steel fibers (SF) was added in the mix design to evaluate its effect on improving the bond behavior. 108 specimens were fabricated, in which the variables were the volume percentage of CR (0, 5, and 10%), SF volume ratio (0, 0.5, and 1%), applied temperature (200, 400, and 600 °C). Three specimens were fabricated for each composite mixture. Afterward, the pullout test was performed on the hardened specimens to evaluate the bond strength, bond stress-slip behavior, failure mode, and bond strength-compressive strength relationship. The observations showed that incorporating CR lowered the bond strength, and with increasing temperature, this reducing effect increased. In this regard, at the applied temperature of 600 °C, the bond strength of specimens with 5% and 10% CR declined by around 24% and 40%, respectively, compared to that of the reference specimen at the same temperature. Moreover, after testing all the heated specimens, it was found that the reducing impact of temperature rise on the bond strength was negligible up to 200 °C (around 5%), significant up to 400 °C (around 20%), and destructive up to 600 °C (around 65%). Additionally, for the specimens failing in the splitting mode, the effect of incorporating SF was positive, and for the specimens failing in the pullout mode, this effect was negligible and, in some cases, even negative. The empirical results suggest that for the specimen incorporating CR, a greater embedment length must be applied compared to the same specimen without CR. In the end, soft computing methods including gene expression programming (GEP) and artificial neural network (ANN), as two promising techniques, were utilized to predict the bond strength and bond-slip behavior. Then, the experimental findings were compared with those of the equations proposed by ACI-408 and CEB-FIP codes. The developed model exhibits good agreement with experimental results and provides more accurate predictions in comparison with the investigated codes.

Corrosion reduces cross-section area of rebar and bond between the rebar and concrete, which leads to the degradation of durability of structure. In this study, a three-dimensional mesoscopic numerical analysis model was established to explore influence of localized corrosion on behavior of single-way RC slab. In the model, concrete was considered as a tri-phase composite consisted of coarse aggregate particles, mortar matrix and interface transition zones (ITZs). The effect of corrosion was simulated by reducing cross-section area of rebar and bond. Localized corrosion of reinforcement was taken into account and non-linear spring element was adopted to describe interaction between concrete and reinforcement. The simulation results for corrosion RC slab are in good agreement with test result in terms of ultimate flexural capacity and displacement. On this basis, the flexural behavior of corroded single-way RC slab under fourth-point bending condition was simulated and analyzed whilst the influence of corrosion level, concrete strength, rebar type and diameter was investigated. Simulation results indicate that flexural bearing capacity of corroded RC slab increases when reinforcement was minor corroded and decreases for a further increasing corrosion level. The effect of concrete strength on bearing capacity of slab is insignificant with the increase of corrosion level. The RC slabs with plain rebar break in brittle failure when corrosion level is over 7.5%. However, slab with deformed rebar fail in a ductile pattern in this case. Under fourth-point bending condition, energy dissipation of RC slabs with larger reinforcement ratio decreases faster. The influence of reinforcement ratio and bond at rebar-concrete interface caused by the variation of rebar diameter is still significant when the rebar is corroded.

The assessment of nonuniform corrosion of rebar is a key issue concerning the reliability of reinforced concrete structures. In this paper, the sectional nonuniform corrosion of plain rebar and the effect of corrosion on bond strength with concrete are studied. The plain rebar in concrete of 52 specimens were fast corroded by using electrochemistry method in a 5% sodium chloride solution. The bond strength of corroded plain rebar in concrete was measured by the central pull-out test. The sectional contour, diameter loss and sectional area loss of corroded plain rebar were detected within the bond length corresponding to the mass loss from 0.1 % to 11.9%. Based on the oretical analysis and test data, the predictive models of the corroded sectional contour line and the bond strength of corroded plain rebar to concrete are built up. The results indicate that the nonuniform corroded sectional contour of plain rebar is approximate elliptical shape, the bond strength can be predicted by using the diameter loss of corroded rebar. Finally, the adaptability of the predictive models is ascertained with the experimental results.

This study investigates the effects of fire, cooling methods, and cover thickness, on the behaviour (strength and ductility) of 12-mm diameter rebars embedded in mortars with river sand (RS) substitutes such as granite powder and manufactured sand, with 30 and 50 mm cover thickness. Beyond 500°C, thermal stress induced random spalling of mortar cover, and tension test results showed strength decrement and ductility increment of rebars for air cooling, while the vice versa was observed for water quenching.

The effect of long term immersion in seawater at different temperatures on the properties of pultruded glass fibre reinforced polymer (GFRP) composite rebar was investigated. Samples were conditioned in seawater and in dry at 23, 55 and 75 °C for 0, 8, 20, 30 and 36 months to analyse the changes in shear properties such as transverse shear strength (TSS) and short beam shear strength (SBSS). Both TSS and SBSS increased after conditioning in dry at 55 and 75 °C; on the other hand, TSS decreased gradually due to conditioning in seawater at 23, 55 and 75 °C, whereas SBSS decreased due to conditioning in seawater only at 75 °C. Microscopic analysis specified that the shear strength decreased due to fibre/matrix interfacial failure as a result of de-bonding and fibre pull-out. Compared to the short beam shear test, the transverse shear test was found to be a sensitive technique to measure the durability of pultruded GFRP rebar. FT-IR analysis indicated superficial hydrolysis reaction of polymer matrix occurred when the sample was conditioned at 75 °C. A reversible change in glass transition temperature (Tg) and in viscoelastic property of the polymer matrix was observed due to conditioning in seawater at 23 and 55 °C.

Geopolymer composites represent promising alternatives to ordinary Portland cement materials, whose properties can be improved by mixing polyvinyl alcohol (PVA) fibers and nano-SiO2 (NS). In this study, bond tests and numerical modeling were conducted to investigate the effects of PVA fibers and NS on the rebar-matrix bond behaviors of geopolymer composites. A modified mathematical model derived from the Harajli model and a finite element numerical model based on the Mori-Tanaka homogenization and the Tsai-Hill failure criterion were proposed. The prediction results of the numerical and modified mathematical models were compared to those of an existing model and the experiment. The results showed that PVA fibers and NS can effectively improve the bond strength and toughness of the geopolymer composites and that the bond behavior is optimized when the PVA fiber content is within 0.6%–0.8% and the NS content is 1.5%–2%. The numerical and modified mathematical models can effectively reflect the rebar-matrix bond behaviors of the NS and PVA fiber reinforced geopolymer composites. The proposed numerical model exhibits high prediction accuracy, providing an effective guide and reference for predicting the bond behaviors of rebar and geopolymer composites.

An inorganic anticorrosive coating, merging wollastonite into Chemically Bonded Phosphate Ceramic (CBPC) binders, was prepared to protect rebar from corrosion. In order to evaluate the corrosion resistance behavior of Wollastonite-based Chemically Bonded Phosphate Ceramic (WoCBPC) coatings, the electrochemical measurements were applied. The experiment results showed that the value of corrosion potential (Ecorr) and polarization resistance (Rp) is the largest and the value of corrosion current density (Icorr) is the smallest among all WoCBPC coatings, when the content of wollastonite reaches 20% of the ceramic filler (WoCBPC20). Moreover, the resistance of WoCBPC20 coating (Rc) value was much higher than that of other WoCBPC coatings, which means the best anticorrosion properties. The structure formation of WoCBPC coatings was identified by using XRD as well as SEM/EDS techniques. The intensity of berlinite phase reaches the maximum with the introduction of wollastonite in WoCBPC20 coatings. Meanwhile, the fibrous wollastonite particles with high modulus can inhibit the spread of cracks in CBPC matrix. Therefore, the WoCBPC coatings show a barrier effect to prevent aggressive substances from contacting the rebar effectively.

This study investigated the flexural performance of steel fibre beams reinforced with smooth and deformed reinforcement, both experimentally and numerically. As part of the experimental investigation, five full-scale reinforced concrete beams were constructed with plain and steel fibre concrete and were tested under 4-point flexural monotonic loading. The amount of fibre and the condition of the rebar were the main parameters studied. The test’s outcome built up a numerical model to simulate the actual performance of the reinforced concrete beams under tested loading. Afterward, a parametric study was conducted to get a better understanding of the behaviour of the steel fibre concrete beams. The experimental results show that the cracking load was not affected by the steel reinforcement conditions, whether smooth or deformed. Moreover, 9% of the ultimate deflection was caused by tension stiffening and 3% due to the steel fibre content in steel fibre concrete beams. Finally, the concrete compressive strength was found to have less of an effect on the ultimate deflection than the ultimate load.

This paper describes the role of epoxy resin in the development of advanced building materials. It reviews in brief the growth of epoxy resin-based high-performance concrete and masonry mortar technology, and epoxy resin as protective coating on mild-steel bar (rebar) for concrete reinforcement. Literature survey reveals that the properties of concrete could be improved significantly with the variation of concentration of the epoxy resin in the composition of polymer-modified concrete (PMC), and that makes the PMC very versatile in applications. Challenges on the use of epoxy resin in the concrete and masonry mortar composition and contribution of the resin on the mechanical and physical properties of building materials have been described. Some ambiguous results on epoxy resin-based concrete available in the literature have been verified in the laboratory, and the confusions have been diffused. Performance of the epoxy resin as a protective coating on rebar has also been discussed. Experimental results show that epoxy resin-based concrete exhibits high compressive strength, less chloride-ion permeation and high chemical resistance to the corrosive environment. Finally, the perspectives of epoxy resin for overall use in building materials and also in specific applications such as repairing of building, the protection of constructions from flood, saline water, and prevention of liquid from penetration into interior of materials have been discussed.

A cerium film was prepared on the surface of rebar by chemical conversion method to enhance its corrosion resistance. The film in the simulated concrete pore solution was measured by electrochemical method, transmission electron microscope (TEM) and X-ray photoelectron spectroscopy (XPS). The effect of temperature on film formation was studied, and the optimum temperature was determined at 35 °C. The film produced by too high formation temperature has more defects, resulting in the lower corrosion resistance. The Ce film resistance increased with time evolution until 800 h, then decreased and stabilized. The Ce film layer has a double-layer film structure, the upper layer is an oxide of cerium, and the underlayer is an oxide of iron. Results revealed that after being immersed in the simulated concrete pore solution, the corrosion resistance of the Ce film was enhanced by self-densification.

Preflex beam composite girders are widely used in the bridge industry. Understanding the post-cracking behavior of preflex beam girders under cyclic loading is essential to improve monitoring and maintenance. The aim of this study was to evaluate the relationship of the deterioration of the lower flange concrete under cyclic loading to the resulting changes in stiffness, neutral axis location, reinforcement bar stress, and steel-lower-flange stresses of the preflex beam. The study also compared the preflex beam behavior with a conventional girder without prestress under cyclic loading. The experimental study included two specimens of the same details, of which one was preflexed and the other was a conventional non-preflexed specimen. The cracking and post-cracking behavior of the specimens were investigated under multiple cyclic loading stages. The study concluded that changes in the concrete crack width can be used to fairly estimate changes occurring in the neutral axis location, rebar stress, and steel-lower-flange stress of the preflex beam under cyclic loading. The smaller width and shorter length of concrete cracks, implying smaller changes in the preflex beam girder, improved its behavior remarkably compared with the non-preflexed girder with wider and longer concrete cracks under cyclic loading. Furthermore, the study concluded that a closer spacing of the shear ribs reduces the crack width. However, the number of cracks would be larger.

In addition to general shear loading, perfobond shear connectors (PBLs) also undertake tensile uplift forces at the interfaces between steel parts and concrete components. The tensile behavior of PBLs is as significant as the shear behavior to the safety of composite bridge structures. For further evaluating the combined shear-tensile response of PBLs, it is necessary to first investigate the tensile mechanism of PBLs. Accordingly, uplift tests with three specimens under static and cyclic loading were performed to investigate the tensile behavior of PBLs. The test results showed that the breakouts of concrete blocks dominated the failure of PBLs in tension. The residual separation was negligible when the tension force was below 30 percent of the capacity. Subsequently, a detailed finite element (FE) model for the uplift test was established and validated based on the test results. The strain path inside concrete blocks was presented as a cup shape, whose dimension was relevant to the embedded depth of holes and the boundary conditions. Further, 360 FE models with varying hole diameters, perforated rebar diameters, embedded depths, and concrete strength were conducted to explain the tensile mechanism and provide databases for the theoretical analyses. The results showed that the diameter of perforated rebars was irrelevant to the tensile capacity and stiffness of PBLs, while both the tensile capacity and stiffness increased with the embedded depth and concrete strength. Besides, the tensile stiffness was also related to the hole diameter. Consequently, according to the forms of existing tensile capacity expressions for headed studs and Mindlin’s solution, the equations for the tensile capacity and stiffness of PBLs were derived.

In this research paper, results are obtained from Reactive Powder Concrete (RPC) push-off specimens - double L shape subjected to direct shear loading. Different parameters considered are compressive strength, percentages of steel fiber, presence of aggregate and shear reinforcement. The results show that increasing in steel fiber content starting from 0.0% and ending with 1.5% leads to increases in the shear strength by (261%) and attempt to decrease its brittleness. The presence of steel fiber content enhances and improves the tensile strength and the shear strength. Using RPC in constructing the specimens enhances the shear strength by 29.6% compared with NSC specimen. Shear strength increased by 25% when the compressive strength increased from 75 to 90MPa. The presence of transverse steel rebar in the direction of shear line increased the shear strength by (108.3%) as compare with the specimen without shear rebar. The presence of small aggregate in RPC mix creates an increase in the shear strength by (9.1%).

Electro-mechanical impedance (EMI) is among the many types of gauges that can be used for structural health monitoring (SHM) of concrete structures. The bond strength between concrete and planted rebar plays an important role in the integrity of concrete structures strengthened by post-installed anchors. This paper presents a method to monitor the development of epoxy bond strength between concrete and a planted rebar by the EMI technique. Three concrete cubes each with a planted rebar were fabricated and used for a set of monitoring experiments. To conduct experiments, a lead zirconate titanate (PZT) patch was attached to the polished side surface of the planted rebar. During the monitoring test, conductance spectra signals from three PZT patches were acquired at the 0th, 20th, 40th, 60th, 80th, 100th, and 120th min of the experiment. Furthermore, a pull-out test was conducted on two concrete beams with three planted rebars each. The root mean square deviation (RMSD) and mean absolute percentage deviation (MAPD) were applied to compare instantaneous conductance signatures with the initial, baseline conductance signature across different frequency ranges to ascertain the growth of bond strength during the curing process of epoxy. The results of the monitoring experiments and the pull-out test demonstrate the effectiveness of EMI technique in monitoring bond strength development between concrete and planted rebars. The results also show potential application prospects of the EMI technique in the SHM of reinforced concrete structures.

This study investigates the influence of steel slag (SS) and steel fibers on the electrical resistivity and electromagnetic (EM) shielding effectiveness of high-strength concrete (HSC). It was found that the electrical resistivity of mixtures were mainly influenced by free water. Thus, the EM shielding effectiveness was evaluated without the effect of free water. HSC with 20% replacement ratio of SS exhibited slightly improved EM shielding, lower electrical resistivity, and reduced strength (compressive and flexural) compared to HSC without SS. However, HSC with steel fibers exhibited significantly improved EM shielding, lower electrical resistivity, and higher strength and toughness compared to HSC without steel fibers. An increase in the steel fiber content in the HSC significantly decreased the electrical resistivity and increased the shielding effectiveness, strength, and toughness. Regardless of the fiber content in the fiber volume fraction of mixture, the shielding effectiveness is similar for cases with and without SS whose electrical resistivity values differ only slightly. This proves that the EM shielding effectiveness was mainly affected by the electrical resistivity and these properties are significantly correlated when the electrical resistivity values differ noticeably. HSC reinforced with rebar with 50 mm spacing exhibited a 23.5–75.6% increase in the shielding effectiveness in the 600–1,000 MHz frequency region compared to pristine HSC.

Corrosion of steel reinforcement bars is a crucial issue for the reinforced concrete structures. Being one of the most common deterioration mechanisms, corrosion severely affects the serviceability and durability of the structure as the steel reinforcement suffers from a reduction of the cross section and deterioration of the mechanical properties. Additionally, due to the steel oxidation process, residual material is formed, and the volume occupied by the reinforcement increases, leading to cracking and spalling of the concrete cover. A predictive model coupling concrete carbonation process and phase-field approach for brittle fractures is proposed to simulate the carbonation induced corrosion of rebar and the subsequent cracking phenomenon. First, a Fick diffusion law is used to describe the carbon dioxide (CO2) diffusion within the concrete which leads to a generalized corrosion process. As the corrosion evolves, the steel mass loss is converted into expansion strain due to the formation of residual material, and the damage evolution within the concrete cover is determined. After validation against examples from the literature, numerical simulations are performed, presenting a phase-field strategy capable to describe the cover cracking of corroded RC beams.

This paper dealt with the flexural behaviour study on reinforced concrete beams with conventional steel and basalt rebar using Portland Pozzolana Cement. Conventional steel bars are vulnerable to various environmental attacks and aggressive attacks such as corrosion. Basalt rebar can effectively overcome this problem due to the enhanced properties like inhibiting corrosion, high tensile strength, low young’s modulus, lightweight and resist electrical conductivity. In this paper, flexural behaviour of conventional Steel Reinforced Beam (SRB) and Basalt Fiber Reinforced Polymer beam (BFRB) were investigated experimentally and test results arrived were elaborately discussed. It has been noticed that BRB shows significant greater deflection when compared to SRB due to lower elastic modulus, whereas flexural load carrying capacity of BRB increases due to enriched tensile strength property in basalt rebar, significant increase of tensile strength in BRB. The results revealed that basalt rebar can be effectively used in construction as a replacement of conventional steel reinforcement for sustainable development.

Helix concrete consists of twisted steel wires of star shape and size approximately 1 mm2 areas with 25 mm, 35 mm, 50 mm, 65 mm & 80 mm long added to cement concrete. Replacing the rebar to some extent is to achieve higher crack resistance and structural strength throughout the concrete mass in all directions. In the present research, the analytical studies have been carried-out using MSC Nastran. The analytical studies have been carried-out on star cross sections of helix. It was observed that the shape and number of twists of steel wires maximizes the bond between the steel and cement based concrete matrix. Helix steel wire, with its twisted profile is a more superior reinforcement and is a substantial improvement over fibers of any time. When concrete is stressed or bent the fibers which are straight will slide out smoothly with minimal possible friction, so the force required to pullout is generally small. Adding deformation like a hooked end or corrugations adds friction and increases pullout force substantially.

Современные приборы для испытаний на «вырыв» не комплектуются специальными захватами для связей и арматуры периодического профиля. Предложен новый тип захвата для испытаний муфта-захват. Проведены лабораторные испытания химических анкеров с арматурой периодического профиля с применением новых типов захватов (муфт-захватов). Выполнен сравнительный анализ полученных результатов испытаний анкеров с применением четырех типов захватов. Сформулированы предложения по применению захватов при проведении натурных испытаний на объекте и в лабораторных условиях.

The use of indirect electrical techniques is gaining interest for monitoring the corrosion of steel in concrete as they do not require any connection to the rebar. In this paper, we provide insights into the physical aspects of the indirect galvanostatic pulse (GP) method in the Wenner configuration. Considering uniform corrosion, the instantaneous ohmic drop is decreased due to the presence of the rebar, which acts as a short-circuit. However, we observed that this phenomenon is independent of the electrochemical parameters of the Butler&ndash, Volmer equation. They are, however, responsible for the nonlinear decrease of the current that polarizes the rebar over time, especially for a passive rebar due to its high polarization resistance. This evolution of the resulting potential difference with time is explained by the increase of the potential difference related to concrete resistance and the global decrease of the potential difference related to the polarization resistance of the rebar. The indirect GP technique is then fundamentally different than the conventional one in three-electrode configuration, as here the steady-state potential is not only representative of polarization resistance but also of concrete resistance. Considering non-uniform corrosion, the presence of a small anodic area disturbs the current distribution in the material. This is essentially due to the different capability of anodic and cathodic areas to consume the impressed current, resulting in slowing down the evolution of the transient potential as compared to uniform corrosion. Hence, highly corroding areas have a greater effect on the transient potential than on the steady-state one. The use of this temporal evolution is thus recommended to qualitatively detect anodic areas. For the estimation of their length and position, which is one of the main current problematic issue when performing any measurement on reinforced concrete (RC) structures with conventional techniques, we suggest adjusting the probe spacing to modulate the sensitivity of the technique.

The aim of the work - experimental investigation on crack propagation and deformation in high-strength fiber reinforced concrete beams with round cross-sections under combined bending and torsion for the development of practical methods of crack resistance, deformation and strength analysis of such structures, and also for the accumulation of new experimental data on resistance under combined loading. Method is experimental-theoretical. Results. Deflection plots and force-deformation relationships for high-strength fiber reinforced concrete beams with round cross-sections under combined bending and torsion are determined experimentally. Principal deformations in terms of elongation and compression of concrete for the experimental beam structures with high torsion to bending moment ratio are determined. It is established that for high-strength fiber reinforced concrete structures of circular cross-section, generally, development of one-two discrete cracks is observed, therefore the circular shape of the cross-section slightly reduces the concentration defined by the material structure of high-strength concrete. On the basis of the conducted investigation on high-strength fiber reinforced concrete structures with circular sections, new experimental data on the combined stress-strain state in the studied areas of resistance is obtained, such as: values of generalized cracking, and failure, load, its level relative to the ultimate load; distance between the cracks at different stages of crack propagation; crack widths at principal reinforcement axis level, at a double diameter distance from the principal rebar axes and also along the entire crack profile at various stages of loading; coordinates of nonplanar crack formations; patterns of crack formation, development and opening in reinforced concrete structures under combined bending and torsion.

The concrete industry is one of the main consumers of natural resources. On the other hand, one of today’s major environmental problems is non-decaying waste tires left in the environment. This study utilizes the waste tires in C-25 concrete grade and investigates its behavior with rebar. An experimental study was carried out on the basic mechanical properties of concrete. A modified concrete was prepared by replacing sand in concrete with rubber aggregate by varying the replacement proportion from 4% to 16% with an increment of 4% by volume. After having the mechanical property, an effective finite element model was developed in ANSYS workbench. The stress-strain diagram from the experiment was described by command and used as input data in ANSYS simulation to analyze and determine the impact of resistance and deformation of rubberized concrete. From the experiment, it was found that the optimal rubber improves the strain capacity and its stress-strain curve shows more nonlinear behavior than normal concrete (NC). From all percentages, 8% crumb rubber concrete (CRC8) shows best relative performance it improves impact resistance, energy absorption and ductility of concrete by decreasing the weight of the structure. At failure, crumb rubber concrete (CRC) exhibited more ductility with large ultimate deflection and more uniform crack distribution. The bond behavior of CRC8 with the deformed bar is only slightly lower than NC. ANSYS output result shows that the structural behavior like maximum stress is comparable except the reduction in compressive strength. The results of FEA positively verified that rubberized concrete could absorb more impact energy before failure.