Petr Misák

Determination and evaluation of the air permeability coefficient using Torrent Permeability Tester

A quality of a covercrete (covercrete = cover concrete) up to a depth of 20–50 mm practically decides about the durability of concrete of a structure. The covercrete prevents accessing of acid substances from the atmosphere to steel reinforcement. For evaluation of a state of the covercrete from the durability viewpoint is possible to use a relatively new NDT method for determination of concrete air permeability. The work of the team focuses on the determination of the quality of the surface layer of concrete using the TPT method and specification of the impact of humidity on the value of the air permeability coefficient.

Applying Method of Acoustic Emission for Monitoring of Different Concrete Mixture during Setting and Hardening

Non Destructive Testing is a powerful tool for determination of properties, durability and lifetime of concrete structures. Acoustic Emission Method is an unusual technique which describes only active defects or changes into structure arising as a consequence dangerous tension into structure. The method is appropriate to be used in homogenous structures as metal structures when cracks are highly active (generates sound). Its application in civil engineering is not so much used because building structures are inhomogeneous. This article shows possible application of Acoustic Emission Method for monitoring of concrete structure changes during its lifetime. The main aim of the article is to show the application of Acoustic Emission Method during the early age to 28 days after mixing. It is believed that early age of concrete structure is very important for its quality. Common concrete cube specimens have been tested after the production by Acoustic Emission Method with using waveguides. The results of acoustic emission method will be compared to classical parameters of fresh concrete e.g. the value water-cement ratio, air void content measured by different methods (pressure methods, AVA) and similar. In the results will be compared four mixtures when two mixtures were aerated and two mixtures were without aeration.

Comprehensive Testing Techniques for the Measurement of Shrinkage and Structural Changes of Fine-Grained Cement-Based Composites during Ageing

The paper deals with an experimental analysis focusing on the utilization of a specific measurement technique for determining the development of shrinkage and for monitoring structural changes in fine-grained cement-based composites during their ageing. Advanced measurement equipment and procedure allowing simultaneous measurement of length changes, mass losses, acoustic responses, and temperature development were designed and verified by the experimental investigation. The main scope of the experiments performed was focused on finding the relationships between the characteristics being investigated while maintaining a uniform test setup. For the purpose of the experimental measurement, three fine-grained cement composite mixtures were designed and manufactured. The mixtures differed in the water-to-cement ratio (w/c) and in the amount of plasticizer. The measurement outputs are presented in the form of diagrams showing the relations between the studied parameters, such as relative length changes, mass losses, temperature progress, and acoustic emission (AE) activity during solidification of the composites. The measurement results showed close relations between the examined characteristics. The progress of relative length changes together with the progress of mass losses and temperature development is reflected in the AE activity. The advanced measurement procedure and technique provided valuable information about the behaviour of cement-based composites during early setting and long-term hardening.

Experimental Analysis on Shrinkage and Swelling in Ordinary Concrete

The paper deals with the experimental determination of shrinkage development during concrete ageing. Three concrete mixtures were made. They differed in the amount of cement in the fresh mixture, 300, 350, and 400 kg/m3. In order to determine the influence of plasticiser on the progress of volume changes, another three concrete mixtures were prepared with plasticiser in the amount of 0.25% by cement mass. Measurements were performed with the goal of observing the influence of cement and plasticiser content on the overall development of volume changes in the concrete. Changes in length and mass losses of the concrete during ageing were measured simultaneously. The continuous measurement of concrete mass losses caused by drying of the specimen’s surface proved useful during the interpretation of results obtained from the concrete shrinkage measurement. During the first 24 hours of ageing, all the concrete mixtures exhibited swelling. Its magnitude and progress were influenced by cement, water, and plasticiser content. However, a loss of mass caused by water evaporation from the surface of the specimens was also recorded in this stage. The measured progress of shrinkage corresponded well to the progress of mass loss.

Possibilities of Experimental Determinations of the Modulus of Elasticity in the early Stage of Ageing of Cement Composites

This paper deals with the possibilities of experimental determination of the dynamic and static modulus of elasticity of fine-grained cement composites in the early stage of setting and hardening - up to 72 hours. Several cement pastes and cement mortars were produced for the purpose of this experiment. The measurement of the modulus of elasticity on the manufactured cement-based composites was carried out in the first 24 hours, each time only by the ultrasonic pulse velocity test using the innovative Vikasonic instrument. In the following 48 hours, the resonance method and the static load test were employed. The results of the pilot measurement and particularly the assessment of the possibilities of determination of the moduli of elasticity are presented in this paper.

Experimental Determination of how the Static Modulus of Elasticity is Influenced by the Value of the Upper Loading Stress

There is a large number of factors that have a strong influence on the elastic modulus of concrete. These are technological influences as well as issues connected with the testing methods for its determination, one of which is the choice of the upper loading stress of cyclic loading during testing the static modulus of elasticity of concrete in compression. The upper loading stress should be equal to 1/3 of the specimen’s compressive strength, however, its choice is often made incorrectly. This paper describes an experiment focused on discovering the impact that deviating from the 1/3 upper loading stress has on the measured value of the static modulus of elasticity.

Repeatability and Reproductibility of Results of Fresh Concrete Testing

The aim of this paper is to summarize the results of 11 experiments which focused on assessing the precision of results of fresh concrete testing. The observed characteristics are slump test, flow table test, density and air content. More than twenty participants (testing laboratories) took part in these experiments. The test results were evaluated with statistical methods used for evaluations of interlaboratory comparisons. The article deals especially with the values of repeatability and reproducibility, which provide further understanding of the interval within which it is possible to expect with the given probability the test results measured in one or more laboratories.

Repeatability and Reproducibility of the Static Elastic Modulus of Concrete Measurement

In recent years, the static modulus of elasticity is one of the most discussed property of hardened concrete. The aim of this article is to show results of 6 performed experiments focused on test results precision. The measurements were made according to the standards ISO 6784 and ISO 1920-10. More than 20 participants (laboratories) from Europe took part in these experiments. Test results were compared using the statistical methods for interlaboratory comparison. Repeatability and reproducibility, which provide more detailed information about range of expected values of elastic modulus, are the most discussed characteristics in the article.

Assessment of the Influence of Multiple Cyclic Loading on the Static Modulus of Elasticity of Hardened Concrete

This paper deals with determining the dependence of the value of the static modulus of elasticity of concrete in compression on the number of loading cycles. The deformation of specimens during multiple cyclic loading was measured in the elastic region of the stress-strain curve for concrete. The specimens were subjected to up to 1500 loading cycles. The main goal of the experiment was to ascertain whether the multiple cyclic loading causes significant changes in the static modulus of elasticity.

The Properties of Historical Wrought Iron Tie Rods

The preservation of brick masonry buildings and historically significant buildings is a very hot topic today. A problem that often occurs during reconstruction and modernization is an optimal solution between price and efficiency. First of all, it is necessary to view the object as a complex system, when it is necessary to ensure its spatial rigidity. Planning and progress of reconstruction is then derived from the correct assessment of the building. The spatial rigidity of buildings in the past was also ensured by means of reinforcing elements. For masonry buildings, wall and beamed ties have been used for this purpose until the end of the 19th century. Since these wrought ties are made of a completely different material so-called wrought iron, its properties are different from the currently used materials. They differ in both tensile strength and other properties just because of other processing technology and manufacturing. At the time of the construction of the buildings it was not possible to provide a variety of length of the ties, so that ties have been joined by forged connections or adjustable wedge relations. The article deals with determining the tensile strength of wrought ties obtained by destructive methods. The results of the experiment may serve to predict the behaviour of ties from a similar period.