Bond Behavior Of Reinforcement Research Articles

Experimental and analytical investigations on bond–slip behavior of steel reinforcement in UHPFRC considering yielding

AbstractThe bond behavior between ultra‐high‐performance fibre‐reinforced concrete (UHPFRC) and steel rebars plays an important role in the load‐bearing capacity and serviceability of structural members. A suitable bond–slip model is essential for predicting the load resistance and deformation capacity of members, after cracking of the UHPFRC. This paper studies the bond strength between ribbed steel bars and the surrounding UHPFRC before and after yielding of the steel reinforcement. To determine the corresponding bond–slip relationship, pull‐out tests, with varying embedment lengths of the reinforcement, namely 2 times and 10 times the rebar diameter, and diameter of reinforcing bars ranging from 10 mm to 16 mm were conducted. The bond stress, strain and slip along the embedment length of the steel rebars were measured by strain gauges and displacement transducers. Based on the test data, a bond stress–slip model was derived before (elastic stage) and after (inelastic stage) yielding of the reinforcement. The slip at the yield point is suggested through theoretical equations. The post‐yield bond–slip model is based on yield bond stress and frictional bond stress. The two‐part model was validated through iterative procedures and is able to predict the applied force, bond stress and strain distribution along the reinforcing bar. A comparison between the test data and analytical results demonstrates a good predictive capacity on the bond behavior of reinforcement in UHPFRC both before and after yielding of the reinforcement.

Bond Behavior of Low-Activated High Aluminate Concrete with Reinforcement under Cyclic Load

The bond behavior of reinforcement and low-activated concrete (LAC) was investigated in this study. The acoustic emission monitoring was also engaged while the specimen being loaded to figure out the inside fracture. Static loading and dynamic loading were applied for both of the LAC and normal concrete in the pull-out tests. The upper load was applied starting from 30% of the static ultimate load Pu with a 10% increment until the failure. The loading frequencies for the test were 0.5 Hz、1.0 Hz and 2.0 Hz. The bond stiffness after each stage of dynamical loads was examined. Test results reveal that the LAC performs higher compressive strength than normal concrete for a given W/C ratio. But, the bond strength of LAC seems not promotes correspondingly. It may be attributed to the conversion effect of high alumina contained in LAC, which leads to more voids inside the concrete.

Influence of Test Configuration on Bond Strength of GFRP Bars

It is well-known that test configuration affects bond behaviour of steel reinforcement, but this effect has not yet been sufficiently quantified when using FRP reinforcement. This paper presents partial results from an ongoing experimental programme that deals with the bond strength of GFRP bars with concrete, with regards to the effect of the surface treatment of the rebars and test configuration. A modified beam test is presented in this study along with a pull-out test with an eccentric bar placement. The bond strength of GFRP reinforcement with sand-coated treatment using silica sand and ribbed type with milled ribs was tested. The sand-coated bars exhibit different bond behaviour compared to the ribbed ones due to different forces transfer from the reinforcement to the concrete. Thickness of the concrete cover layer also has a significant effect on the bond behaviour of the reinforcement.

Effect of polypropylene fibers on bond performance of reinforcing bars in high strength concrete

Abstract Adequate bonding between reinforcement and concrete plays a vital role in the proper performance of reinforced concrete as a composite material. Hence it is important to evaluate the influence of various factors on the bond behavior of reinforcement and concrete. In this study, a total of 8 beam specimens with tension lap splice at the midspan and 12 concentric pullout specimens are fabricated to investigate the effect of polypropylene fibers on bond performance of reinforcement in high strength concrete (HSC). Fibers are added to concrete mixture by 0.15%, 0.30% and 0.45% volume fraction of concrete. The detrimental effect of polypropylene fiber on the workability of mixture restricts the use of a high amount of polypropylene fiber in mixtures. Splice specimens made of fiber reinforced concrete presented a greater number of cracks, higher failure loads and deflections and also larger crack width at their failure stage. Failure deflections of splice specimens made of fiber reinforced concrete are 20% higher than that of plain concrete specimens on average. After splitting failure, load carrying capacity of all beam specimens dropped to almost zero and the addition of polypropylene fibers did not provide residual capacity for the specimens. The slope of the bond stress-slip curves of specimens experiences a sudden change at the cracking load. Results indicate that existing prediction equations for bond strength are acceptable and even yield more accurate values when polypropylene fibers are added to concrete mixtures. The results of beam and pullout tests demonstrated that pullout test is not suitable to evaluate the effect of polypropylene fibers on bond strength.

Influence of silica fume content on bond behaviour of reinforcement in HPSCC

The steel-to-concrete bond in high-performance self-compacting concrete (HPSCC) was investigated based on direct pull-out tests. The analysis was performed on specimens made from four different HPSCC mixes with varying contents of silica fume (SF) (0, 5, 10 and 15% by mass of cement). The specimens used allowed the determination of changes in bond at individual levels of elements with a total height of 160, 480, 800 and 1600 mm. The rebars in the elements were placed perpendicularly to the direction of concreting. A reference element, characterised by a parallel orientation to the direction of concreting, was also prepared. It was found that the modification of HPSCC using SF improved the quality of bond conditions, especially in the case of elements with substantial height. There was, however, no effect of rebar orientation with respect to this casting direction and to the change in bond stiffness.

Pull-out behaviour of recycled aggregate based self compacting concrete

The use of recycled aggregate in concrete is gaining much attention due to the growing need for sustainability in construction. In the present study, Self Compacting Concrete (SCC) is made using both natural and recycled aggregate (crushed recycled concrete aggregate from building demolished waste) and performance of recycled aggregate based SCC for the bond behaviour of reinforcement is evaluated. The major factors that influence the bond like concrete compressive strength (Mix-A, B and C), diameter of bar (Db=10, 12 and 16 mm) and embedment length of bar (Ld=2.5Db, 5Db and full depth of specimen) are the parameters considered in the present study in addition to type of aggregates (natural and recycled aggregates). The mix proportions of Natural Aggregate SCC (NASCC) are arrived based on the specifications of IS 10262. The mix proportions also satisfy the guidelines of EFNARC. In case of Recycled Aggregate SCC (RASCC), both the natural coarse and fine aggregates are replaced 100% by volume with that of recycled aggregates. These mixes are also evaluated for fresh properties as per EFNARC. The hardened properties like compressive strength, split tensile strength and flexural strength are also determined. The pull-out test is conducted as per the specifications of IS 2770 (Part-1) for determining the bond strength of reinforcement. Bond stress versus slip curves were plotted and a typical comparison of RASCC is made with NASCC. The fracture energy i.e., area under the bond stress slip curve is determined. With the use of recycled aggregates, reduction in maximum bond stress is noticed whereas, the normalised maximum bond stress is higher in case of recycled aggregates. Based on the experimental results, regression analysis is conducted and an equation is proposed to predict the maximum bond stress of RASCC. The equation is in good agreement with the experimental results. The available models in the literature are made use to predict the maximum bond stress and compare the present results.

Experimental investigation on bond of reinforcement in steel fibre-reinforced lightweight concrete

Bond behaviour of reinforcement is crucial parameter for load bearing reinforced concrete members. Many parameters like anchorage of reinforcement, lap splices, deflection or tension stiffening are influenced by the bond properties. It is well known that the ductility of bond can be improved by steel fibres. In this context almost innumerable experiments were performed for investigation of bond in normal weight concrete. However, the bond behaviour of reinforcement in steel fibre-reinforced lightweight concrete (SFRLWC) has received much less attention. For this reason, an experimental program dealing with bond in SFRLWC has been started at HTWK Leipzig/Germany. Main parts of the investigation were pull-out tests with various bar sizes and application of different steel fibre-reinforced lightweight and normal weight concretes. The paper reports the details of experimental investigations and evaluates the test results. As one of the most important outcomes that can be noted is that there is pronounced effect of bar size and steel fibre amount on bond properties in general. But those effects are more pronounced for SFRLWC in comparison to normal weight concrete with and without steel fibres.

Influence of ground pumice powder on the bond behavior of reinforcement and mechanical properties of self-compacting mortars

he aim of this study is to investigate the effect of the bond strength of self-compacting mortars (SCMS) produced from ground pumice powder (GPP) as a mineral additive. In this scope, six series of mortars including control mix were prepared that consist of 7%, 12%, 17%, 22% and 27% of ground pumice powder by weight of cement. A total of 54 specimens of 40x40x160 mm were produced and cured at the age of 3, 28 and 90-day for compressive and tensile strength tests and 18 specimens of 150x150x150 mm mortar were prepared and cured at 28 days for bond strength tests. Flexural tensile strength and compressive strength of 40x40x160 mm specimens were measured at the curing age of 7, 28 and 90-day. Mini V-funnel flow time and mini slump flow diameter tests were also conducted to obtain rheological properties. As a result of the study, it was observed that the SCMs containing 12% of GPP has the highest bond strength as compared to control and GPP mortars. Compressive strength slightly increased up to 12% of GPP.

Bond behavior of reinforcement in Lightweight Aggregate Self-Compacting Concrete

An investigation of the steel-to-concrete bond in Lightweight Aggregate Self-Compacting Concrete (LWASCC, comprising exclusively pumice aggregates) is presented based on direct pull-out and beam tests. Experimental parameters include: rebar diameter, bond length and type of additive used in the LWASCC mixture. The results are compared with those obtained from identical specimens made of: (i) pumice aggregate self-compacting concrete (PASCC) with normal-weight sand and (ii) normal-weight SCC (NWSCC). The majority of specimens exhibited failures due to splitting (at relatively low slips) and rebar pull-out for direct pull-out and beam tests, respectively. Empirical formulations are used to predict experimentally derived bond strengths.

Bond Behavior of Reinforcement in Conventional and Self-Compacting Concrete

Self-compacting concrete (SCC) can be placed under its own weight without compaction. In addition, it is cohesive enough to be handled without segregation and bleeding. Modification in the mix design of SCC can have a significant influence on the material's mechanical properties. Therefore, it is important to investigate whether all of the assumptions about conventional concrete (CC) design structures also valid for SCC construction. Bond behavior between concrete and reinforcement is a primary factor in the design of reinforced concrete structures. This study presents a bond strength model based on the experimental results from eight recent investigations of SCC and CC. In addition, the proposed model, code provisions, and empirical equations and experimental results from recent studies on the bond strength of SCC and CC are compared. The comparison is based on the measured bond between reinforcing steel and concrete utilizing the pullout test on the embedded bars at various heights in the mock-up structural elements to assess the top-bar effect on single bars in small prismatic specimens by conducting beam tests. The investigated varying parameters on bond strength are the: steel bar diameter, concrete compressive strength, concrete type, curing age of the concrete, and height of the embedded bar along the formwork.

Influence of Cracks on the Durability of RC Structures

To carry out maintenance and assessment of reinforced concrete (RC) structures, a good understanding of the effect of the change in bond behaviour of reinforcement during service life is essential. Steel reinforcement is subjected to corrosion due to carbonation and chloride attack. The former ordinarily induces uniform corrosion, the latter induces generally localised corrosion at cracks level. The existence of cracks and the crack width affect the starting points of corrosion, as indicated by the results of the exposure test carried out by Shiessl et al.[1]. Corresponding techniques, such as non-destructive in-situ testing for concrete cover thickness, permeability and the positions of the reinforcing bars, are helpful to model the real behaviour. Cracked portion around the tensile reinforcement in a flexural member can be considered to be equivalent to a concrete member having a single reinforcement subjected to pull-out force at both ends. In this paper a damage process model is proposed based on slip crack propagation in order to evaluate the effective load capacity.

Bond behaviour of reinforcement in self-compacting concretes

This experimental work examines the bond strength between reinforcement steel and concrete, and the top-bar effect in self-compacting concretes. Eight different concretes were used, four self-compacting (SCC) and four normally-vibrated (NVC). Tests were conducted on 200 mm cube specimens and 1500 mm high columns. It was found that, at moderate load levels, SCC performed with more stiffness, which resulted in greater mean bond stresses. The ultimate bond stresses are also somewhat greater although, due probably to the negative effects of the bleeding having less impact on failure, the differences between SCC and NVC are reduced considerably, and even disappear completely for concretes of more than 50 MPa. On the other hand, the top-bar effect is much less marked in SCC, and therefore a change in the factor that takes into account this effect in the formulas used for calculating the anchorage length of the reinforcement is proposed for these concretes.