Bond of deformed steel reinforcement in lightweight foamed concrete

Villiers, Johannes P. de; Zijl, Gideon van; Rooyen, Algurnon S. van

doi:10.1002/suco.201600019

Cited by 25 publications

(15 citation statements)

References 14 publications

(21 reference statements)

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“…The bond failure models include split and pull‐out. When the depth of the concrete protective layer exceeds a certain range ( c / d > 5–6) or it comes to hooped specimens, the failure model of bond between the deformed bar and the concrete is generally the shearing off of concrete keys between adjacent ribs, which is the main focus of this study. This paper has established the relationship between bond stress and the slip surface.…”

Section: Introductionmentioning

confidence: 99%

Theoretical model for the bond–slip relationship between ribbed steel bars and confined concrete

Zhao

Zhu

2017

Structural Concrete

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This paper conducts a theoretical research into bond-slip relationship between ribbed steel bars and concrete. According to whether the concrete is cracked or not, the ascending part of the bond-slip curve is divided into two sections which are calculated by two different mechanical models. Based on the wedging action mechanism, the slip is introduced as displacement boundary conditions into the model, which is the main innovation of this study. The boundary conditions of the model are changed by the changing slip, so the bond stress values corresponding to all levels of slip are obtained. According to the rebar geometrical parameters specified in National Standard GB1499-2007, the spacing of the adjacent ribs is fitted as a linear function of the rebar diameter. Then characteristic slip with the rib spacing as the main parameter is adopted in this study. Also, a negative exponential function is proposed for the descending part of the bond-slip curve. Specially, parameters of slipping path are therefore suggested for engineering applications. Comparison between calculated values and test results shows that the theoretical model can reasonably predict the local bonding problems with different steel bar diameters and concrete strength grades. K E Y W O R D S bond-slip, elasticity, reinforced concrete, ribbed bars, wedging action 1 | INTRODUCTIONReinforced concrete (RC) structures resist together external loads with the promise of reliable bond and anchor force between rebar and concrete. Research into the problem has demonstrated that bond between concrete and rebar is established through three mechanisms: chemical adhesion, friction, and mechanical interlock between the steel bar ribs and the concrete. 1 The effect of chemical adhesion is small and friction forces do not develop until adhesion has failed and relative displacement between reinforcement bar and concrete takes place. Both of the chemical adhesion and the friction force are important in the case of plain bars. For deformed bars, however, the mechanical interlock of the ribs of the bars embedded in concrete governs the bond stress deformation behavior. 2 During the 1970s, Tepfers treated this problem analytically as a thick-walled cylinder subject to internal radial pressure. 3 The outer radius of the cylinder is determined by the concrete cover depth and the inner radius by the bar size. Resistance to splitting was calculated on the assumption of plastic tensile behavior of concrete on the splitting surfaces, and expressions were developed for additional contributions from confining reinforcement. 4,5 Since then several researchers have developed theoretical expressions for bond strength based on Tepfers's methodology, dividing the thick-walled cylinder into an uncracked outer ring and a partly cracked inner ring. The important issue for the inner ring is the choice of softening model. 6 More refined approximation for the non-linear state of the inner ring was developed by Van der Veen, 7 Uijl et al, 8 and Nielsen and Bićanić, 9 extending Tepfers's mo...

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Section: Introductionmentioning

confidence: 99%

Theoretical model for the bond–slip relationship between ribbed steel bars and confined concrete

Zhao

Zhu

2017

Structural Concrete

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“…Interlock between steel ribs and concrete is highly dependent on the concrete strength (density of foamed concrete), bar diameter and ribs geometry. Tests performed by Villers [6] have shown that lightweight foamed concrete of 1200 kg/m 3 density ensures more than eight time lower bond strength than normal concrete based on similar mixture receipt. Poor bond behaviour of cellular concrete is associated with low fracture and stiffness causing premature crushing of concrete by steel ribs.…”

Section: Introductionmentioning

confidence: 99%

Application of fibre composite grids as reinforcement of foamed PC and GP concrete

et al. 2019

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Cellular concretes cannot be reinforced as easily as traditional ones. Generally porous materials do not ensure sufficient bond of reinforcement; additionally, due to limited amount of aggregate, interlock between aggregate particles and reinforcement ribs is not satisfactory. The idea of reinforcement presented in the paper incorporates bi-directional composite reinforcing grids placed in tensile zone of the cellular concrete slab where transverse fibres are ensuring anchorage for fibres located in the main direction of stresses. The concept is based on geotechnical applications where grids are commonly used as soil stabilization, but the grids adopted in this solution are much stronger thanks to introduction of high strength fibres as composite reinforcement.

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“…Besides, a low‐water–cement ratio of magnesium phosphate cement equates to a low‐binder–sand ratio and weak bonding strength with Portland cement . The addition of fly ash approximates the color of magnesium phosphate cement specimens to the color of Portland cement, thus reducing the cost of material, enhancing the fluidity of mortar, and reducing its bonding strength . However, repaired concrete is frequently eroded by acid rain, industrial wastewater, and other corrosive media during usage.…”

Section: Introductionmentioning

confidence: 99%

“…[12][13][14][15][16][17][18] The addition of fly ash approximates the color of magnesium phosphate cement specimens to the color of Portland cement, thus reducing the cost of material, enhancing the fluidity of mortar, and reducing its bonding strength. [19][20][21] However, repaired concrete is frequently eroded by acid rain, industrial wastewater, and other corrosive media during usage. In addition, the hydration of cement is eroded and thus damaged by corrosive ions.…”

Section: Introductionmentioning

confidence: 99%

Microstructure and property evolution of interfacial microregion of magnesium phosphate cement on mortar under various environments

Zhang

et al. 2018

Structural Concrete

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Portland cement specimens repaired with magnesium phosphate cement were soaked in Ca(OH)2 and Na2SO4 solutions for an extended period to test the bonding strength of the specimens. After the immersion, the fracture positions and surfaces of the specimens were observed and analyzed. Subsequently, the interfacial microregion of the specimens in different immersion periods was analyzed using an optical microscope and SEM. Besides, the microstructure and property evolution of the interfacial microregion of magnesium phosphate cement (MPC) on mortar under various environments were studied in erosion environment, which was compared with the interfacial microregion in natural environment. Results indicate that the bonding strength of the specimens is weaker in Ca(OH)2 solution than in the natural environment. At first, the bonding strength initially increases and then stabilizes with time. Moreover, the bonding strength of the specimens is weaker in Na2SO4 solution than that in the natural environment. The bonding strength initially increases and then decreases with time. In the natural environment, the crystal morphology in the interfacial microregion changes slightly, and the crystal structure becomes compact. In Ca(OH)2 solution, the crystal morphology in the interfacial microregion changes significantly, and the crystal structure becomes compact. In Na2SO4 solution, the crystal morphology in the interfacial microregion makes significant changes, and the crystal structure loosens.

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Bond of deformed steel reinforcement in lightweight foamed concrete

Cited by 25 publications

References 14 publications

Theoretical model for the bond–slip relationship between ribbed steel bars and confined concrete

Theoretical model for the bond–slip relationship between ribbed steel bars and confined concrete

Application of fibre composite grids as reinforcement of foamed PC and GP concrete

Microstructure and property evolution of interfacial microregion of magnesium phosphate cement on mortar under various environments

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