Tereza Komárková

Design of Methodology for Non-Destructive Testing of Steel-Reinforced-Fiber-Concrete

Measuring instruments used for non-destructive testing of structures thanks to advances in electronics and electrical engineering are still more frequently applied. Among the building materials with which the ability to perform quality control using non-destructive testing methods would be most welcome is indisputably steel reinforced fibre concrete (SFRC). The paper deals with the design of new methods and methodologies that enable determination of the concentration and orientation of steel fibres in steel fibre reinforced concrete. Especially the distribution of steel fibres in concrete is the quintessential aspect of this construction material. Initial results of experiments have demonstrated the applicability of the proposed methods and methodologies and the objective of the article is to introduce it to the scientific community.

Testing an Impedance Non-destructive Method to Evaluate Steel-Fiber Concrete Samples

Abstract Steel-fiber reinforced concrete is a composite material characterized by outstanding tensile properties and resistance to the development of cracks. The concrete, however, exhibits such characteristics only on the condition that the steel fibers in the final, hardened composite have been distributed evenly. The current methods to evaluate the distribution and concentration of a fiber composite are either destructive or exhibit a limited capability of evaluating the concentration and orientation of the fibers. In this context, the paper discusses tests related to the evaluation of the density and orientation of fibers in a composite material. Compared to the approaches used to date, the proposed technique is based on the evaluation of the electrical impedance Z in the band close to the resonance of the sensor–sample configuration. Using analytically expressed equations, we can evaluate the monitored part of the composite and its density at various depths of the tested sample. The method employs test blocks of composites, utilizing the resonance of the measuring device and the measured sample set; the desired state occurs within the interval of between f=3 kHz and 400 kHz.

Methods Appropriate for Determination of the Prescribed Reinforcement of the Elements of Reinforced Concrete Structures - Nowadays Used Methods

The paper reacts to the contemporary situation in the field of determining the position of reinforcement in the reinforced concrete structures, in which the best method used so far – the Co 60 radiography – is significantly limited or even excluded due to the tightening of laws and regulations for management of radiation sources. In the article, the authors focus on the use of alternative NDT methods which, in an appropriate combination, can substitute the present radiographic method. They mention the advantages as well as technological and principle limitations of the methods of georadar and electromagnetic indicators, and on practical examples they demonstrate their usability when used separately or in a suitable combination.

Conclusive Determination of Compliance with the Prescribed Reinforcement Elements of Concrete Structures - The Appropriate Methods and their Capabilities

Despite efforts to maintain quality during the construction of reinforced concrete structures, it is relatively common for improper reinforcement to be used, contradicting the project, which can lead to serious structural defects. It is then up to non-destructive testing methods to prove these defects. The key is the choice of the appropriate method and equipment, both in terms of achieving the necessary results and the possibility of their documentation. In recent years, there has been a significant progress in the development of non-destructive methods for the diagnosis of reinforcement and modernization of the technologies used so far, especially in the field of GPR and electromagnetic methods. At the same time, however, for a number of reasons, major limitations appear in the area of a conventional method of radiography. This contribution focuses on the current state of the problem, and it demonstrates the applicability of individual methods and their limitations given by their physical principles and technical solutions on a set of practical examples.

Evaluation of Selected Physicomechanical Properties of SFRC according to Different Standards

Steel fiber reinforced concretes are currently very popular, especially in the construction of industrial floors of warehouses and other halls with relatively large floor areas. However, it is important to mention that despite the rapid development of steel fiber reinforced concretes, the standards and regulations for their designing and testing have not been unified yet. This paper presents findings about the physicomechanical parameters of the steel fiber reinforced concretes manufactured by adding steel fibers into the truck mixer on the building site. The experimentally obtained results from the performed tests of tensile strength in bending according to various procedures are compared, and the suitability of the methods used is assessed according to these procedures.

Influence of Dispersed Reinforcement on the Physico-Mechanical Properties of the SFRC

The article deals with steel fiber reinforced concrete (SFRC), specifically with its physical mechanical parameters which influence both design and reliable behavior of the building material in structures. The resulting physical mechanical properties of the SFRC depend on the properties of the individual components and also on their quantity. In the building practice, a common dosing of steel fibers that are added into fresh concrete mixture is ranging between 0.5% and 2%. The paper also describes the methodology of certain laboratory tests suitable for SFRC and the ways of data evaluation. The experiments proved a substantial influence of the quantity of steel fibers in the individual mixtures to the resulting mechanical properties.

Techniques of Non-Destructive Testing of Steel Fiber Reinforced Concrete

Non-destructive testing (NDT) is seeing increasingly frequent use in civil engineering thanks to the fact that the tests are repeatable and do not cause serious damage to the material. The requirements for the development and modernization of available testing devices and methodologies are ever increasing and the testing of existing structures often requires the use of NDT. Unfortunately, every measurement and methodology has its limits and the measurement devices for the evaluation of steel fiber reinforced concrete (SFRC) are no exception. In recent decades there has been an effort to modernize and develop existing measurement devices for SFRC testing. This building material is commonly used especially in large-scale structures. Nevertheless, the technology of SFRC could seem complicated when compared with ordinary concrete and the very nature of this composite material could lead to SFRC inhomogeneity during construction. This paper describes the assessment of SFRC by more or less available methodologies and measurements utilizing non-destructive principles.

Rock Joint Asperities and Mechanical Strength of Concrete

Mechanical interactions between concrete foundations of large civil engineering structures (tunnels, bridges or dams) and the asperity surfaces of rock masses represent a useful topic for investigation. It is obvious that such large objects exert huge pressures on bedrocks and this might result in surprising variations of mechanical properties of the materials used in foundations. The present contribution evaluates possible changes of the compressive strength of concrete caused by the invasive acting of asperity-like needles penetrating into the volume of this material. The experimental arrangement simulates mechanical interactions between sharp asperities of bedrocks and the cement-based materials placed in the foundations of large civil engineering structures.

Experimental Determination of the Influence of an Air Entraining Additive on the Resistance of Concrete to Chemical Defrosting Agents

The paper describes the results of an experiment performed as part of the GAČR 13-18870S project dealing with the durability characteristics of the surface layer of hardened concrete. The paper aims to evaluate the experimental determination of the influence of an air entraining additive on the resistance of cement concrete to water and defrosting chemicals. For the purposes of the experiment 4 mixtures were prepared which differed in the amount of air entraining additive and the amount of cement. The test results were evaluated using statistical analysis of experiment.

Experimental Determination of Concrete Resistance of Various Composition to Water and De-Icing Chemicals

The focus of the project GAČR 13-18870S is the research in concrete durability determined primarily by its surface layer quality. The surface layer can be difficult to assess for which reason the project makes use of available standardised and non-standardised test methods by means of which the concrete surface layer or its internal structure can be examined. One of these methods which is commonly used is Determination of resistance of cement concrete surface to water and defrosting chemicals. The paper presents the results of experiments performed with concretes differing only in w/c ratio and plasticiser content. Two more methods were used during the research based on the action of a thawing solution upon the surface of the specimen during freezing and thawing. The only difference between these methods is the direction in which the thawing agent acts on the test surface. The presumed experiment outcome was the existence of a strong dependence of the outcomes of the methods on the w/c ratio. The performed analyses confirmed the experiment presumption.