Filip Vogel

TRIAXIAL COMPRESSIVE STRENGTH OF ULTRA HIGH PERFORMANCE CONCRETE

The aim of this work is to describe the strength of Ultra High Performance Concrete (UHPC) under triaxial compression. The main goal is to find a trend in the triaxial compressive strength development under various values of confinement pressure. The importance of triaxial tests lies in the spatial loading of the sample, which simulates the real loading of the material in the structure better than conventional uniaxial strength tests. In addition, the authors describe a formulation process for UHPC that has been developed without using heat treatment, pressure or a special mixer. Only ordinary materials available commercially in the Czech Republic were utilized throughout the material design process.

Basic and Hygric Properties of Concrete Containing Fine Ceramic Powder

The motivation for utilization of active admixtures in concrete lies primarily in a positive effect on properties of hardened concrete with regard to its durability. Fine parts complement the grain size distribution curve, but also due to subsequent hydration arise phases with better resistance to aggressive substances from surrounding environment. Process of pozzolanic reaction is also associated with a reduction in open capillary porosity, causing a gradual reduction of the permeability of concrete. The paper presents an experimental program focused on the monitoring of evolution of basic and hygric properties of concrete with fine ceramic powder addition.

Time Progress of Compressive Strength of High Performance Concrete

Development in the field of concrete engineering is increasingly focused on the practical application of high performance concrete (HPC) or ultra-high performance concrete (UHPC) in construction practise. Newly developed kings of concrete are newly using in transport and building structures. The process of hydration of hydraulic binders based on Portland cement doesn ́t stop after 28 days, when the test of compressive strength take place, but it ́s a long time process that takes for many months. For design we use the values of strength of 28 days. This paper explorers how does the long-term development of compressive strength of HPC runs. The composition of HPC is significantly different from the common concrete lower strength classes. The question of the influence of additives, filler on microsilica based, silica flour to the time development of compressive strength is being explored in this paper. There is also recorded the influence of curing condition of the test specimens to the compressive strength. The age of testing samples starts at a very early ages 1, 3, 7, 21, 28, 45, 90 and 180 days. The strength in uniaxial compression was measured on cubes with dimension 100 mm.

ANALYSIS OF MECHANICAL PROPERTIES OF HYDROTHERMALLY CURED HIGH STRENGTH CEMENT MATRIX FOR TEXTILE REINFORCED CONCRETE

The main objective of this article is to describe the influence of hydrothermal curing conditions in an autoclave device (different pressure and temperature), which took place at various ages of a fresh mixture (cement matrix – CM, and fibre-reinforced cement matrix – FRCM), on textile reinforced concrete production. The positive influence of autoclaving has been evaluated through the results of physical and mechanical testing – compressive strength, flexural strength, bulk density and dynamic modulus of elasticity, which have been measured on specimens with the following dimensions: 40×40×160mm 3 . In addition, it has been found that increasing the pressure and temperature resulted in higher values of measured characteristics. The results indicate that the most suitable surrounding conditions are 0.6MPa, and 165 °C at the age of 21 hours; the final compressive strength of cement matrix is 134.3MPa and its flexural strength is 25.9MPa (standard cured samples achieve 114.6MPa and 15.7MPa). Hydrothermal curing is even more effective for cement matrix reinforced by steel fibres (for example, the compressive strength can reach 177.5MPa, while laboratory-cured samples achieve a compressive strength of 108.5MPa).

Comparison of Stress-Strain Diagrams in Different Age of the Cement Matrix for Textile Reinforced Concrete

This article deals with cement matrix for the textile reinforced concrete. It is necessary to know maximum of the mechanical properties of cement matrix for using textile reinforced concrete. The main topic of this article is to determine stress-strain diagrams at various age of the cement matrix. The compressive strength of the cement matrix was determined by using cube specimens (100 x 100 x 100 mm). The cement matrix, steel fibre reinforced cement matrix and ordinary concrete C 30/37 were tested at age 12 and 18 hours and 1, 7, 28 and 45 days. Cubes were tested in one-axial press. Loading of cubes was controlled by increase of deformation. Speed of loading was 0.008 mm/s. Time, load force and deformation were recorded for determination stress strain diagrams. The results of the experimental program and stress-strain diagrams were compared with each other in conclusion of this article.

Experimental Study of Primary Lining Tunnel Concrete after Thirty Years of Operation

This article shows the acquisition and testing of concrete from tunnel primary lining. The main objective of this article was to describe the mechanical properties of primary lining tunnel concrete at higher age. The primary lining was made from dry mixture sprayed concrete. The primary lining concrete was in contact with the surrounding rock continuously. The surrounding rock could be dry or with ground water. Some surrounding rocks could produce a highly aggressive environment for concrete. The question was, whether the sprayed concrete is still in service after 30 years in this environment.

Fracture and Mechanical Properties of Fire Resistant Fibre Composites Containing Fine Ground Ceramic Powder

Significant advances in the field of building materials leads to increasingly frequent enforcement of these high performance materials in real constructions. Efforts to maximize the efficient use of non-renewable resources and especially energy-intensive materials lead to efforts to achieve maximum efficiency and usability [. Paper presents results of an experimental program focused on development of fire-resistance composites based on aluminous cement with fine ground ceramic powder (FGCP). Studied fibre composites were loaded by temperature 600 °C and 1000 °C. The influence of applied thermal load on composites was evaluated by means of fracture energy, compressive strength, bending strength and modulus of elasticity in bending.

Permeability and Basic Physical Properties of Concrete with Metakaolin Addition

Surfacing, concrete mixture composition and curing are of great importance for the concrete surface resistance. Thats the reason, why many leading experts agree on the importance of monitoring the concrete skin as the most loaded area affected by the external environment. Many research works demonstrate that application of metakaolin improves properties of concrete as freeze-thaw resistance and resistance against de-icing salts with freeze-thaw cycles combination. A very important role in concrete performance in such severe environment is played by porous system and surface of hardened concrete. The paper introduces an experimental program focused on the monitoring of water transport in surface layer of fair-face concrete aimed at monitoring the permeability of concrete, since concrete permeability is a property uniquely affecting durability of concrete. These methods are complemented by experimental results and other traditional tests. These findings will serve to further optimization of the structure being created, thus ensuring its better aesthetic and functional characteristics.

Experimental and Numerical Analysis of Tensile Properties of Textile Reinforced Concrete with Steel Fibres

The topic of this article is the experimental and numerical testing of tensile strength of glass textile reinforced cement-based composites with steel fibres. Cement-based composite is similar to high-performance concrete, with its maximal compressive strength higher than 100 MPa. We used thirty six dogbone-shaped specimens for uniaxial tensile loading with three different kinds of textile reinforcement. The difference between reinforcement was in its weight of 1 m2 of textile. We focused on maximal tensile stress in specimens and the ductile behaviour after first cracking occurred. We will compare results from experimental testing made on different types of reinforcement and results from numerical computer model. Tensile stress was generated by loading with constant increase of displacement.

Bond Properties of Concrete Beams Strengthened by AR-Glass Textile and Basalt Textile Reinforced Concrete

This paper deals with advanced application of textile reinforced concrete for strengthening and stabilization of existing load-bearing structure elements. Slim layer of fine grain concrete with compressive strength over 100 MPa was applied on one year old concrete beams with dimension 100 x 100 x 400 mm. Different number of layers of two types of textile fabrics was applied into concrete layer. One textile fabric was made from alkali-resistant glass fabric with surface density 585 g/m2 and the second was made from basalt fabric with surface density 260 g/m2. One layer of basalt textile fabric (surface density 120 g/m2) was applied on the top of strengthening layer to prevent shrinkage cracks of high strength cement matrix. Evaluation of destructive four points bending test of strengthened and reference specimens provided the efficiency of performed strengthening solution. Continual load and deflection measurement during bending test enables to create load-deflection diagram, where the action of textile can be observed.