Jan Zatloukal

Development of Ultra High Performance Fiber Reinforced Concrete mixture

Formulation process of Ultra High Performance Fiber Reinforced Concrete (UHPFRC) is described in this paper. Materials locally available in the European Union were used throughout the optimization process. The mixture was also developed without any special curing, such as elevated temperature, pressure or vapor. The optimization process consisted of two steps. In the first step a cementitious matrix was optimized with respect to its maximal compressive strength, flexural strength and workability. The key element in the optimization process was to achieve maximal particles packing density, to choose efficient enough high-range water reducer (HRWR) and to decrease water binder ratio as much as possible. In the second step of the optimization process short, high tensile strength steel fibers were added into the matrix that showed highest workability and strength. The resulting compressive strength of UHPFRC mixtures exceeded 150 MPa after 28 days, average secant modulus of elasticity was in the range of 55 GPa and direct tensile strength in range of 10 MPa. During the optimization process mixtures with 1, 2 and 3% of fibers by volume were tested. It was found that with respect to acceptable workability and superior mechanical performance the optimal fiber content is between 2 and 3% by volume.

Concrete and cement composites used for radioactive waste deposition

This review article presents the current state-of-knowledge of the use of cementitious materials for radioactive waste disposal. An overview of radwaste management processes with respect to the classification of the waste type is given. The application of cementitious materials for waste disposal is divided into two main lines: i) as a matrix for direct immobilization of treated waste form; and ii) as an engineered barrier of secondary protection in the form of concrete or grout. In the first part the immobilization mechanisms of the waste by cement hydration products is briefly described and an up-to date knowledge about the performance of different cementitious materials is given, including both traditional cements and alternative binder systems. The advantages, disadvantages as well as gaps in the base of information in relation to individual materials are stated. The following part of the article is aimed at description of multi-barrier systems for intermediate level waste repositories. It provides examples of proposed concepts by countries with advanced waste management programmes. In the paper summary, the good knowledge of the material durability due to its vast experience from civil engineering is highlighted however with the urge for specific approach during design and construction of a repository in terms of stringent safety requirements.

Numerical analysis of projectile impact on cementitious composite

This paper describes the numerical modeling of projectile impact on cement based composite slabs. In the simulated experiment, local damage is inflicted by impact of defined projectiles on specimens made from normal strength concrete (NSC), ultra-high performance concrete (UHPC) and ultra-high performance fiber-reinforced concrete (UHPFRC). Deformable ogive-nose projectiles with diameter of 7.92 mm and mass of 8.0 g with impact velocity about 700m/s were used in the modeled experiment, hitting center of the specimens. Data from the measured and visual evaluation of specimen damage were used for comparison of specimen projectile impact resistance in relation to the used material and compared to the numerical prediction.

The Effect of Elevated Temperatures and Nuclear Radiation on the Properties of Biological Shielding Concrete

The paper reviews the so far known information about the properties of biological shielding concrete used in the containment vessel of nuclear power plants (NPP) and its behaviour when exposed to radiation. The damage of concrete caused by neutron and gamma radiation as well as by the accompanying generation of heat is described. However, there is not enough data for the proper evaluation of the negative impacts and further research is needed.

Evaluation of Crack Formation in Concrete and Basalt Specimens under Cyclic Uniaxial Load Using Acoustic Emission and Computed X-Ray Tomography

The paper discusses the use of acoustic emission, stress-memory effect, and X-ray computed microtomography (μST) to detect the onset of destruction of specimens of concrete and basalt which are widely used in construction. It is shown that the most informative parameter is acoustic emission activity based on which the onset of the formation of a main crack can be identified. The geometry of the crack is determined using computed X-ray tomography.

Relation between Parameters of Plasters Measured by Non-Destructive and Destructive Methods

Main target of this study is a comparison of material properties of plasters, which were obtained with use non-destructive methods and destructive methods and find out relation between them. These parameters were investigated on plasters. In this research the destructive methods were focused in obtain three parameters: the compressive strength, the tensile strength and the modulus of elasticity. For non-destructive testing was used pulse velocity method. Testing was carried out on specifically fabricated test specimens. With this study were obtained relations of the parameters for each type plasters measured with the non-destructive methods and with the destructive techniques. Obtained data were compared and then evaluated. These relations are very important and necessary for possibility to eliminate destructive methods in future.

Residual velocity of the non-deformable projectile after perforating the ultra-high performance fibre reinforced concrete

This contribution is focused on the optimal fibre content in the ultra-high performance fibre reinforced concrete (UHPFRC) mixture with respect to the residual velocity of the non-deformable projectile after perforating the UHPFRC slabs. Impact velocity of the non-deformable projectile was in the range of 700 m/s. The UHPFRC used in this study exceeded 150 MPa in uniaxial compression and tensile strength was around 10 MPa. In total 24 UHPFRC slabs with different fibre content were tested for impact loading. In addition, 8 slabs were tested for comparison including high strength concrete (HSC) and conventional fibre reinforced concrete (FRC). It was verified experimentally that UHPFRC had an excellent impact resistance compared to conventional materials such as FRC or HSC. Further it was found that optimal fibre content in UHPFRC for impact resistant structures is 2% by volume. Usage of less than 2% of fibre concrete by volume led to higher residual velocity of the projectile after perforating the slab and also to higher debris fragment mass.

Design of a novel horizontal impact machine for testing of concrete specimens

A novel design approach of an impact testing apparatus for concrete and highperformance cementitious composite specimens is described in this paper. To date, various approaches have been adopted when measuring the behaviour of concrete under impact loading. Most of the research teams used machines based on a guided drop-weight falling down freely on a concrete specimen. This paper describes the development process of a novel machine that is based on the pendulum principle. This experimental setup allows a horizontal placement of a specimen which has several advantages, such as easy elimination of a so called double hit, easy access to the sample and free space for the sensor mounting. The machine in the current setup is used for testing beam specimens, but, due to its modular concept it is also possible to rearrange the setup to test slabs utilizing a proprietary load transformer. The preliminary experimental results are shown in this paper as well as a description of the data acquisition system and adopted method of data filtration.

Possible Types of Degradation of Concrete in the Power Industry

This paper summarizes different types of degradation of concrete in the energy industry. There is described the most of important kinds of degradation and what effects they can cause. In conclusion, this article is formulated several points to prevent the degradation of building materials.

Identification of Thermo-Mechanical Parameters of Concrete Samples from Nuclear Plant

The civil structures of nuclear plants need to meet the most strict criteria in terms of safety and reliability not only during their design and construction, but during the duration of their life cycle. In addition, during the life-cycle of nuclear plant higher safety demands than the ones at the time of plant design may appear and the plant needs to prove meeting of such requirements. Validation of thermo-mechanical properties was required for the concrete structure of the containment building of Bohunice NPP in Slovakia. Identification of thermo-mechanical parameters of the material used in the containment structure was necessary to perform said analysis and detailed investigation on the concrete composition was performed. This paper describes the information that can be obtained using state-of-the art analytical methods – X-ray diffraction (XRD), X-ray fluorescence (XRF) and thermic analysis (TG/DTA).