Pieter Desnerck

Bond Behaviour and Shear Capacity of Self-Compacting Concrete

In this paper the bond mechanism of steel reinforcement to concrete and the shear capacity are examined. Tests have been conducted on conventional vibrated concrete (CVC) and self-compacting concrete (SCC). The results from pull-out tests on 200 mm cube specimens show that for the same compressive strength the maximum bond stress for SCC is as high or higher than for CVC and this for all tested diameters (8, 12 or 16 mm). The bond stress increases with increasing bar diameter. The specimens were loaded at constant rate and during testing the slip of the bars and the applied load were recorded. The four-point loading tests point out a slightly decreased shear capacity of SCC in respect to CVC with the same compressive strength. The shear capacity decreases with increasing shear span-to-depth ratio a/d (2 to 3) for all the tested concrete types. During the testing the maximum applied load was recorded and the crack and failure mechanism were observed.

Bond properties of self-compacting concrete

Proper force transfer between the reinforcement and surrounding concrete is one of the most significant factors affecting the structural behaviour of reinforced concrete structures. Due to the importance of this issue, there is lots of research devoted to investigating the bond properties of conventional vibrated concrete mixtures. This chapter presents a comprehensive review of different aspects of bond properties of self-compacting concrete (SCC). In the first part of this chapter, bond strength to reinforcing bars and prestressing strands is reviewed, including the top-bar effect for various types of SCC mixtures. The effect of using chemical admixtures, such as viscosity-modifying admixtures (VMAs), to reduce the top-bar effect is discussed. The effect of using supplementary cementitious materials (SCMs) and fillers on bond strength characteristics of SCC is reviewed. Bond strength between successive lifts of SCC in multi-layer casting is reviewed highlighting the effect of elapsed time between the castings of different layers and the thixotropy of the lower lift on bond in multi-layer casting. Finally, bond strength characteristics between SCC mixtures used in repair applications and existing hardened concrete are discussed. The bulk of the literature agrees that bond properties of SCC to embedded reinforcement, pre-stressing strands, and hardened concrete is higher than that of vibrated concrete (VC). The rheological properties of the SCC, including the yield stress, plastic viscosity, and hence static stability play a key role in achieving the desired bond properties for SCC mixtures.

Chapter 2 - Mechanical properties

The State-of-the-Art Report of RILEM Technical Committee 228-MPS on Mechanical properties of Self-Compacting Concrete (SCC) summarizes and extensive body of information related to mechanical properties and mechanical behaviour of SCC. Due attention is given to the fact that the composition of SCC varies significantly. A wide range of mechanical properties are considered, including compressive strength, stress-strain relationship, tensile and flexural strengths, modulus of elasticity, shear strength, effect of elevated temperature, such as fire spalling and residual properties after fire, in-situ properties, creep, shrinkage, bond properties, and structural behaviour. A chapter on fibre-reinforced SCC is included, as well as a chapter on specialty SCC, such as light-weight SCC, heavy-weight SCC, preplaced aggregate SCC, special fibre reinforced SCC, and underwater concrete.

Shear Friction of Reinforced Self-Compacting Concrete Members

This paper describes how aggregate interlock along inclined cracks is one of the basic mechanisms that contribute to the shear resistance of reinforced concrete members. In self-compacting-concrete (SCC) the amount of coarse aggregates is lower than in conventional vibrated concrete (CVC). This different grading could have an influence on the aggregate interlock. To study this effect, push-off tests are carried out. The shear plane of the specimen is crossed by steel bars resulting in reinforcement ratios ranging between 0.45 and 2.68%. It follows that the experimentally determined shear friction of self-compacting concrete is slightly higher than the shear friction of CVC. However, the vertical displacement corresponding with the ultimate shear strength is larger.

Impact of Material Deterioration on the Strength of Reinforced Concrete Half-Joint Structures

Summary During the 1960’s and 1970’s a number of reinforced concrete (RC) bridges were constructed with ‘half-joints’ introduced into bridge decks. A half-joint is a particular type of RC structure that was introduced into bridge decks as a means of simplifying the design and construction operations. However, a major disadvantage is that there are problems associated with leakage of water through the joint leading to concrete deterioration and corrosion of the reinforcement. When assessing the integrity of existing half-joint structures, determining the influence of material deterioration and/or repair works is a challenge as current code provisions or guidelines do not pro-vide guidance on how to take any associated strength losses into consideration. This paper focusses on the impact of changes in the material properties (such as compressive strength, yield strength of the reinforcement, reinforcement bar diameter, etc.) on the load bearing capacity of reinforced half-joint structures. The vulnerability of a typical half-joint design to these changes is analysed using finite element models. The results allow designers, assessors and decision makers to better quantify the impact of observed deterioration phenomena on the predicted strength of the studied half-joint.

External Strengthening of Continuous RC Beams with CFRP

The structural behaviour of reinforced beams strengthened in flexure with externally bonded FRP (Fibre Reinforced Polymer) reinforcement has been extensively investigated with respect to isostatic beams. Design methods are given in guidelines and standards, and failure modes are described. However, limited information is available on the behaviour of continuous beams, strengthened with composite reinforcement. For flexural strengthening of a 2-span continuous beam, the FRP reinforcement can be applied on top of the central support, at the bottom-side of the two spans or at both locations. By means of an analytical study, the non-linear behaviour of this type of beam is investigated. The failure modes are studied and it is verified to which degree moment redistribution is still present when applying this strengthening technique which makes use of a linear elastic polymeric material.