Šárka Nenadálová

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.

Study of Corrosion Damage of Glass Fibers in Textile Fiberglass Reinforcement under Expositions Simulating Concrete Environment

The main point of this paper is to assess the level of corrosion damage of the composite textile fiberglass reinforcement in environments that simulate the concrete pore solution by the techniques of FT-IR (Fourier transform infrared spectroscopy), SEM (scanning electron microscopy) as well as EDS (scanning electron microscopy). Effect of corrosion on the tensile strength segmented textile glass fiber was tested and also it was investigated specific type of protective organic coating on glass fiber. The results express the evidence of local corrosion damage on the examined samples just at pH 13.5, and on the contrary high stability in the environment simulating carbonated concrete and concrete contaminated by chloride anions. The thesis also points on the unevenness of the excluded protective organic coating with localized porosity which relates to the above mentioned corrosion damage.

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.

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.

Diagnosis of Myslinka Stone Railway Bridge

Within the solution of the research project GAČR P105/12/G059 a detailed diagnosis of the stone railway bridge on the railway line Plzeň - Tachov was performed. The bridge is created by two parallel vaulted tubes made from sandstone where a frequented road of second category goes through under one of them and Myslinsky brook flows under the second. The bridge was built approximately in 1978 and in 2006 a reinforced concrete frame structure was built to the bridge portal. Length of both tubes is about 45.5 m, width about 5.7 m, height of the tube above the road is about 6.0 m and above the brook 7.8 m. The arch is made as an annular vault. On the basis of the diagnostic works the structure is evaluated from the point of view of moisture, amount of water soluble salts, strengths of sandstone and there is also a visual observation of a condition of the structure itself performed. In the end there recommendations for a consequent procedure in case of the revitalization are stated.

Water Vapour Resistance Factors of Three Wall Surface Finishing

There are results of water vapour resistance factors of three compositions commonly used for wall finishing in the paper. The compositions are: basic adhesive diffusion mortar; basic adhesive diffusion mortar with silicate plaster; basic adhesive diffusion mortar with acrylic plaster. There are not only the results of water vapour resistance factors but there are also the discussions as well as the impacts of the border conditions, it means temperature, relative humidity and barometric air pressure in the paper.

Impact of Increased Temperature on Cohesiveness of Textile Glass Reinforcement with UHPC Matrix

The contribution is focused on research results of thin elements with UHPC matrix reinforced by textile glass reinforcement. A set of three test samples with size of 1100 x 120 x 20 mm were produced in laboratories of the Klokner Institute. Using accompanying tests the material characteristics of the concrete matrix and the textile glass reinforcement were determined. This reinforcement is modified by a protective epoxy surface layer, co called coating. The reason of the coating is to prevent a formation and a development of corrosive processes on the reinforcement texture. The samples were tested at four-point bend test in a thermal chamber. The thermal chamber is a space where it is possible to gradually regulate the temperature up to 75 °C under a constant value of a loading. In the course of the temperature increasing is using a measuring unit measured mainly bend in the middle of the span in time and the course of an inner and outer temperature. The impact of the increased temperature on the cohesiveness of the non-conventional reinforcement and the UHPC matrix is evaluated from the monitored data.