Milan Rydval

Volumetric Changes of the UHPC Matrix and its Determination

Research in the Ultra-High Performance Concrete applications field is very important. Current experiences shows that the structure design should be optimize due to relatively new fine-grained cement-based Hi-Tech material with excellent mechanical and durability properties. It is not sure if some of the volumetric changes like creep or shrinkage has or has not an impact on an advantage for the construction and for the structure design. The effect of the shrinkage and creep of common used concretes are well known and well described at publications but the effect of volumetric changes of the UHPC is mostly unknown because of the fact that some of experimental tests are long term and the development of UHPC is still in its basics. A lot of works are focused on a basic mechanical properties and durability tests.

Impact of Steel Fibers on Workability and Properties of UHPC

This paper is focused on properties of fresh and hardened cement-based composite Ultra-High Performance Concrete with regard to different volume fraction of short brass coated steel fibers BASF MASTERFIBER® 482. Workability of fresh concrete and basic mechanical properties (tensile strength in bending, compressive strength) of hardened UHPC were found out. The workability of fresh concrete was measured by small mortar Haegermann cone. Percentage differences at cost were obtained at hardened concrete, too. The aim of the first experimental part of the research was the impact of volume fraction of steel fibers according to workability of fresh concrete and also according to mechanical properties of hardened UHPC with the same volume fraction of each component of the mixture, only the volume fraction of the steel fibers was different at each mixture. The mixture design of UHPC was changed to maintaining the workability of fresh concrete at the second part of the research. The workability at mixture with dosage of steel fibers of 300 kg/m3 measured by Haegermann cone was around 300 mm. In the framework of grant project GAČR 15-05791S the basic mechanical properties of hardened fine-grained cementitious composite material UHPC at small beams size of 160/40/40 mm and beams size 300/70/70 mm were determined. The aim of the research project was not only the determination of basic mechanical properties for each mixture design but also workability assessment and costs linked with higher amount of the volume fracture of steel fibers.

Material Properties of Ultra - High Performance Concrete in Extreme Conditions

The Ultra High Performance Concrete (UHPC) is a very promising material suitable for application in special structures. However, the knowledge of performance of this relatively new material is rather limited. The exceptional mechanical properties of UHPC allow for a modification of the design rules, which are applicable in ordinary or high strength concrete. This paper deals in more detail with impact of thermal stress on bond properties between prestressing strands and UHPC and an influence of high temperature to final material properties of different UHPC mixtures. Specimens in the first experimental part were subjected to the cycling freeze-thaw testing. The relationship between bond behavior of both type of material (UHPC and ordinary concrete) and effect of cycling freeze-thaw tests was investigated. The second part of experimental work was focused on mechanical properties of UHPC exposure to the high temperature (Tmax = 200°C to Tmax = 1000°C). Tested mechanical properties were compressive and flexural strengths, the fracture properties will be presented in the next paper. The obtained experimental data serve as a basis for further systematic experimental verification and more accurate information about the significantly higher material properties of UHP(FR)C and its behavior in extreme conditions.

UHPC Reinforced by Hybrid Fibers and its Resistance to High Temperature Loading

As part of the development and research of UHPC materials, the broad professional public deals mainly with the determination of the basic physical and mechanical parameters, in particular the compressive strength, that is considered as a determining parameter for these cement-based composites. The strength of the composite material is determined under normal laboratory conditions. Fine cement-based composite materials are increasingly used not only for academic purposes but also for practical applications. Therefore, it is necessary to focus on other parameters that determine these new Hi-Tech materials. The mechanical properties of materials at elevated temperatures belong to an area that is not properly defined not only in the Czech Republic but also in the world. Research into the behavior of these composite materials and their thermal loading can provide additional information and basics to expand these building materials such as France, USA, Japan and other countries around the world. In the Czech standards applicable to the design of concrete structures subjected to thermal stress, the values of the reduction coefficient Kc, θ are used only for commonly used dense concrete and also for expanded concrete. It is clear that these values cannot be used for fine-grained composite materials with cement binder reinforced hybrid reinforcements. The aim of the paper is to determine and describe the behavior of these materials in the temperature range of 20 ° C to 1000 ° C for two test modes that affect residual strength and high temperature strength.

Effect of Temperature Increasing on Deformation Properties of TRC

This paper presents a description of the changes in the deformation properties of TRC under a gradual increase in temperature. TRC [1, 2] is a composite material consisting of a fine-grained UHPC matrix and textile glass fibres, known as AR-Glass. A very high load-bearing composite can be produced by combining the high compressive strength of UHPC (approximately 150 MPa) and the high tensile strength of textile glass fibres (about 2200 MPa). Samples 1100 x 120 x 20 mm in size were produced for the experiment. The samples were placed in a thermal chamber and were submitted to a constant load. In the next step, a gradual increase in temperature up to 75oC was simulated using heating cables located on the bottom of the chamber. We monitored the changes in bending in the middle of the span. Since the experiments are very time-consuming, the experiment was also simulated using a numerical model. Finally, there is a qualitative comparison of the two methods.

Residual Material Properties of High Strength Fibre Reinforced Concrete Exposed to Elevated Temperatures

This paper is focused on the research of material characteristics of high performance concrete reinforced with a combination of steel and hybrid fibers exposed to the extreme temperatures. In the performed experiments it was examined several types of mixtures (HPFRC, UHPFRC) exposed to the extreme temperatures up to 200-1200 °C. Outside residual parameters of each examined mixtures (tensile bending strength, compression strength, fracture parameters) was investigated the dependence of porosity of the matrix, sample damage and chemical analysis of samples exposed to extreme temperatures, to the resulting mechanical parameters. Part of the initial results of the research described base material and physical properties of the examined mixes and shows the effect of high temperatures on these properties. The results presented in the current paper are the basis for further research and the preparation of numerical models for the design of HPC exposed to extreme temperatures.

Functionally Layered Thin Slabs Made from UHPC and ECC Composites

Corrosion of short steel fibers is one of the limit factors for using cement based UHPC material like an architectural concrete. The steel fibers corrosion is undesirable effect. PVA fibers and TRC reinforcement are nowadays used for facade elements. Structural elements reinforced by non-conventional reinforcement have lower tensile strength, also modulus of rupture is lower, due to low tensile strengths and deformation modulus of PVA and TRC. The tensile strength is determined by properties of mixture design. The potential of functionally layered thin slabs consist on the high ductility and tensile strength of UHPC matrix reinforced by short steel fibers. The load bearing part of functionally layered slabs is made by UHPC reinforced by steel fibers and the covering part is made by ECC reinforced by PVA fibers. Ductile and durable elements should be prepared by acceptable ratio between load bearing part and covering part of functionally layered thin slab. Functionally layered slabs should be used for architectural facade elements.

Development of Cement Based Composites with PVA Fibers

This paper is focused on a mechanical properties of fine-grained cement based composite materials reinforced by short PVA fibers. Cementitious materials are characterized by their fragile matrix. Reinforcing by fibers (e.g. steel fibers, PVA fibers, PP fibers, glass fibers) increase the tensile strength. The behavior of the elements after developing and spreading of micro cracks under load should be described as a strain-softening, strain-hardening, etc. The multiple cracking under load is typical deformations of composite materials reinforced by short PVA fibers, that is worldwide known as a ECC.

Experimental Tests of I Profile Made from UHPC Reinforced with Textile Glass Fibres

This abstract is summarizing production and subsequent experimental testing of 3D profile of the symmetrical I shape concrete from UHPC matrix and reinforced with textile glass fibres. Upper and bottom covering strips of this profile are at the outside fibres reinforced with textile glass reinforcement. Position of this reinforcement is fixed in the distance of about 3 mm from outside fibres and is connected with reinforcement of the profile stem located in its axis. Such prepared beams were tested with four-point flexure evenly loaded until fracture. Course of the measurement was continuously recorded by the automatic logger, where mostly increase of the force in relation to deflection in the middle of the span and change of position of supports were recorded. From the recorded data were prepared graphic outputs compared with the same experiments performed on I profile which is not reinforced, i.e. only UHPC matrix, and for comparison also on the profile made from UHPC matrix with use of metal wires. In the conclusion were compared achieved test results. Mainly suitability and loading capacity of individual beam types was compared. Within the experiment were performed supporting tests based on which were determined material characteristics of tested matrix and textile glass reinforcement. Tests were performed in the Klokner Institute within solution of the grant project GACŘ 13-12676S.

Experimental Tests of Water Vapour Permeability of Plasters

In the paper there are summarized results of diffusion properties of mortars. Water vapour permeability represented by diffusion thicknesses and water vapour resistance factors are except mechanical properties the most important physical parameters of historic buildings. These parameters are influenced by border conditions among that mainly temperature, relative humidity and barometric air pressure belong. It is necessary to know these parameters to understand a material behaviour after a flood. They are decisive for a determination how quick a diffusion speed rate will be and a drying process will take. Everything depends on a type of binder, a material of a structure itself and primarily on properties of mortar and plaster and finishing. After a flood it is necessary to know when users of buildings can start to make rehabilitations and which of them are proper for particular material and when can return to their homes.