Katarína Gajdošová

Experimental Evaluation of Properties of 120 Years Old Concretes at Two Concrete Bridges in Slovakia

Currently there are two bridges older than 120 years under reconstruction in Slovakia. One of them is the Old Bridge in Bratislava, which has been built in 1891 and has a steel superstructure supported by concrete piers. The other one is the Monier Arch Bridge in Krásno nad Kysucou, which has been built in 1892. Since only limited information about the properties of such an old concrete is available, it was almost impossible for the designer to verify the load bearing capacity of these bridges and to design their reconstruction efficiently. To verify the properties of these concretes drill cores were made on both bridges, some of them being more than 20 meters long [17]. After that the measured concrete properties were used to confirm or modify the reconstruction method proposed in the preliminary design. Our paper deals with some mechanical properties measured on these more than 120 years old concretes.

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.

Application of GFRP Reinforcement in the Design of Concrete Structures and its Experimental Evaluation

Abstract In the past, research on the use of FRP in civil engineering has been focused on strengthening existing structures where FRP reinforcements were applied to the surface of concrete elements. Recently, the application of FRP reinforcements has been studied to replace steel reinforcements for use in areas of increased environmental loads, with a need to exclude the corrosion of the reinforcement or to ensure the electromagnetic neutrality of the individual elements of the load-bearing structure. The GFRP reinforcement ratio was verified considering failure modes in flexure and the bond of the GFRP reinforcement with concrete. Besides classical reinforcements, GFRP has also been used in prestressed variants, and the possibility of its use as permanent formwork has been verified. In terms of extending the use of non-metallic reinforcements, it is important to note the long-term exposure and possible degradation of the mechanical properties.

Nonlinear Response of Approach Slab on Cyclic Loading

The approach slab is in the terms of structural behaviour an area element with interaction with a subsoil, where one of its edge is connected thru the hinge on the abutment of the bridge. In a simplified structural schemes it is possible to model this slab element with a hinged connection to the abutment and the subsoil interaction is represented by a spring area under the approach slab. More difficult approach of modelling the reinforced concrete slab and the subsoil interaction is by 3D soil elements with the properties of soil embankment. In both cases of those linear approaches exists few imperfections, which does not represent the real behaviour. Load from the traffic acts on the slab cyclic. Therefore special problems occur in modelling of those transition areas. By crossing vehicles and its acting in time, continuous consolidation of the soil under the approach slab is being in progress. It can possibly cause creation of the void and consequently loss of a contact between the slab and subsoil. The paper deals with modelling of the reinforced concrete approach slab and the soil interaction with a nonlinear soil element, and also response of the slab on the cyclic load. All these effects can cause changes in structural scheme, and therefore changes in a strain of the slab member. The model is trying to describe the subsoil consolidation in time. In a connection with that fact, the fatigue failures of the approach slab are examined too.

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.

Reinforcement Corrosion and its Effect on Bond Behaviour

The corrosion of reinforcement is one of the predominant reasons for loss of reliability of reinforced concrete structures. This has an impact on safety, serviceability and durability of the structure. The corrosion of steel in concrete reduces the cross sectional area of the reinforcement and decreases the bond between reinforcement and concrete. Corrosion products have a higher volume than steel, which produces internal stresses that lead to the cracking and spalling of the concrete cover. Additionally, corrosion of steel changes the mechanical properties of reinforcement. In this paper, the relationship between crack widths and bond strength between reinforcement and concrete was investigated.