Juraj Bilčík

Numerical Modeling of Reinforcement Corrosion on Bond Behaviour

Chloride-induced steel corrosion is one of the major deterioration problems for steel reinforced concrete structures. Its effects on RC structures include cracking of the concrete cover, reduction and eventually loss of bond between concrete and corroding reinforcement, and reduction of cross-sectional area of reinforcing steel. The accumulated corrosion products on the bar surface cause longitudinal cracking of the concrete cover. Loss of concrete cover leads to reduction in bond strength at the interfacial zone between the two materials. In addition, the deterioration of the ribs of the deformed bars causes a significant reduction of the interlocking forces between the ribs of the bars and the surrounding concrete keys. This deteriorates the primary mechanism of the bond strength between deformed bars and concrete, and hence, the bond strength decreases significantly. In this paper the effect of reinforcement corrosion on the bond strength between reinforcement and concrete was investigated for different corrosion levels. The effect of corrosion was simulated by the nonlinear numerical analysis with the FEM program using the 3D models.

Effect of Chloride-Induced Steel Corrosion on Working Life of Concrete Structures

The reinforcing steel embedded in concrete is generally protected against corrosion by the high alkalinity (pH = 12.5 to 13.5) of the concrete pore solution. The structural degradation of concrete structures due to reinforcement’s corrosion has an impact on the safety, serviceability and durability of the structure. The corrosion of reinforcements in the construction of a transport infrastructure (especially bridges), parking areas, etc., is primarily initiated by chlorides from de-icing salts. When corrosion is initiated, active corrosion results in a volumetric expansion of the corrosion products around the reinforcing bars against the surrounding concrete. Reinforcement corrosion causes a volume increase due to the oxidation of metallic iron, which is mainly responsible for exerting the expansive radial pressure at the steel–concrete interface and development of hoop tensile stresses in the surrounding concrete. When this tensile stress exceeds the tensile strength of the concrete, cracks are generated. Higher corrosion rates can lead to the cracking and spalling of the concrete cover. Continued corrosion of reinforcement causes a reduction of total loss of bond between concrete and reinforcement.

Screw Anchors Used as Post-Installed Shear Reinforcement in Flat Slabs

More restrictive requirements of new codes, increasing of imposed loads connected with usage change of the existing structures, errors in design process or during execution can lead to necessity of the strengthening of the existing buildings. In paper, the new and modern strengthening system of flat slabs against punching shear using screw anchors is presented. Screw anchors are installed from lower face of the slab into vertically drilled boreholes. After the installation, the screw anchors operate as punching shear reinforcement. The advantages of the system are significant resistance and deformation capacity increment of the flat slab as well as easy and fast installation with no need to drill through the whole slab thickness and access the upper face of the slab. System is suitable for strengthening of office buildings, since removal of the flooring is not needed or in parking garages, where the water resistance is not disturbed by the system. Moreover, paper deals with special problems that are connected with design of the presented strengthening system e.g. considering of load (deformation) level of the slab at the moment of strengthening, performance of the screw anchors in cracked and non-cracked concrete and anchorage conditions improvement of the screw anchors by application of glue or mortar into the borehole prior the screw installation.

Bond Behaviour between GFRP Reinforcement and Concrete Using a Pull-Out Test

Corrosion of steel reinforcement is one of the most often deterioration reasons of RC structures. At present, the corrosion of steel reinforcement can be avoided by using non-metallic reinforcement from composite materials, especially in structures that are exposed to extreme environmental environment. These materials are durable and non-conductive. They are composited from two materials: fibres and matrix. The most commonly used FRP (Fiber Reinforced Polymers - FRP) reinforcement are glass fibre reinforced polymers (GFRP). The bar surface can be e.g. sanded, wrapped, with helically wound ribs. The bond between concrete and reinforcement is one of the basic requirements for the composite action of both materials. The transfer of forces between the steel reinforcement and the concrete is provided by the following mechanisms: adhesion, friction and mechanical interlocking. The bond between GFRP reinforcement and concrete is different and it is ensured by friction and mechanical interlocking of the rebar surface. The chemical bond does not originate between GFRP reinforcement and the surrounding concrete, so adhesion does not contribute to transfer of the bond forces. Some few test methods are used to determine the bond between GFRP reinforcement and concrete. The pull-out test were used to determine the bond behaviour between GFRP rebars and concrete. This paper describes the preparation, process, results and evaluation of the pull-out tests.

Control of Early-Age Cracking in Watertight Concrete Structures

Abstract Considering the importance of leaking cracks in terms of serviceability and durability of watertight concrete structures, emphasis is placed on thermal movements and their effect on foundation slabs and walls. Both members are usually restrained to some degree externally and/or internally. The results indicate that restrained thermal stresses are the primary cause of early-age cracks in concrete members. This paper offers a discussion of mitigation strategies to prevent the formation and propagation of early-age separating cracks. A FEM-based analysis was used to determine the development of stresses in walls on mat foundations in relation to the crack risk assessment.

Causes of Early-Age Thermal Cracking of Concrete Foundation Slabs and their Reinforcement to Control the Cracking

Abstract This paper focuses on the causes and consequences of early-age cracking of mass concrete foundation slabs due to restrained volume changes. Considering the importance of water leaking through cracks in terms of the serviceability, durability and environmental impact of watertight concrete structures, emphasis is placed on the effect of temperature loads on foundation slabs. Foundation slabs are usually restrained to some degree externally or internally. To evaluate the effect of external restraints on foundation slabs, friction and interaction models are introduced. The reinforcement of concrete cannot prevent the initiation of cracking, but when cracking has occurred, it may act to reduce the spacing and width of cracks. According to EN 1992-1-1, results of calculating crack widths with local variations included in National Annexes (NAs) vary considerably. A comparison of the required reinforcement areas according to different NAs is presented.

Design and Execution of Watertight Concrete Constructions

For various underground concrete structures (basements, tunnels), which remain permanently in the groundwater, watertight concrete is of increasing importance. Watertight concrete structures have several advantages over structures with exterior waterproofing membrane. The design and execution of watertight concrete structures is regulated by guidelines. Although these principles and procedures are widely used, it can be problematic to make them failure-free. The causes of this situation are manifold, but primarily related to the lack of designer’s knowledge and contractor’s technological indiscipline. Considering the importance of leaking separation cracks in terms of serviceability and durability of watertight structures, the contribution analyses constructional, technological and execution measures to reduce the occurrence of failures. Perhaps the paper can contribute to a better understanding of the behaviour and reasons of failures of this advanced technology.

Parameter Analysis of the Reinforcement for the Width and Spacing Control of the Early-Age Cracks in Concrete

Early-age volume changes in concrete induced by temperature change, hydration, autogenous and drying shrinkage can lead to concrete cracking and this can have lasting effects on serviceability, durability or aesthetics of the structure. The restraint to thermal movement is the product of the coefficient of the temperature fall from a peak level during cement hydration and a restraint factor. In most cases it is not necessary and also not economical to avoid cracks. In these cases, crack widths are limited due to water tightness, durability or aesthetic reasons. If early-age thermal cracking cannot be prevented, crack width can be controlled with reinforcement. The reinforcement distributes cracks and consequently reduces their widths and spacing. As a result, there forms a large number of smaller cracks instead of a few through-cracks. This means, that due to the formation of fine cracks, the strain capacity of a reinforced concrete element before the occurrence of through cracks can be increased with the help of skin reinforcement. This paper discusses the parameters of reinforcement affecting the width and spacing of early-age cracks in concrete. The effect of reinforcement on early-age cracking in concrete was investigated on numerical simulation and in full-scale experiments. The test variables were the reinforcement ratio and the cover thickness of the longitudinal reinforcing bars.

Bond of GFRP Reinforcement with Concrete

Corrosion of steel reinforcement is the major cause of deterioration of existing RC structures. Combined effects of moisture, temperature, and chlorides reduce the alkalinity of concrete and exacerbate the corrosion of steel reinforcement, especially for concrete structures subjected to aggressive environments, such as marine structures and bridges and parking garages exposed to de-icing salts. Glass fiber reinforcement polymer (GFRP) bars are suitable alternatives to steel bars in reinforced concrete applications if durability, electromagnetic transparency, or ease of demolition in temporary constructions is sought, that have to be demolished partially by tunnel boring machines (TBMs). The bond of GFRP reinforcement is different from steel reinforcing bars. This paper presents factors affecting the bond strength between GFRP reinforcement and concrete.