Jiří Kolísko

UHPFRC at high temperatures – Simultaneous thermal analysis and thermodilatometry

Simultaneous Thermal Analysis (STA) and Thermodilatometry Analysis (TDA) are done to reveal the structural and chemical changes in UHPFRC during its high-temperature load. Based on the measured results, several physical and chemical processes that studied material underwent at high-temperatures are recognized. In the temperature interval from 25 to 300 °C, the liberation of physically bound water from pores and the dehydration reaction of C-S-H take place. Additionally, AFt and AFm phases dehydrate at 110 – 156 °C. Endothermic peat at 460 °C corresponds to the portlandite decomposition. At 575 °C, the α → β transformation of quartz is found. This reaction is accompanied by a sharp endothermic heat flow peak and a volume expansion, whereas no change of mass is measured. In the temperature interval 580-800 °C, the calcite and C-S-H gels decomposition is monitored. At the temperature above 800 °C, there is one significant exothermal peak corresponding to a crystallization of wollastonite. In summary, STA and...

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.

The Effect of Elevated Temperature on High Performance Fiber Reinforced Concrete

High performance fiber reinforced concrete (HPFRC) became very popular material due to its high strength, elastic modulus, corrosion and fire resistance. However, detail description of HPFRC behaviour is necessary for its application and an effective building design and development. Here, also the fire safety of buildings must be considered. Therefore, the effect of elevated temperature on HPFRC is studied in the paper. For the reference material, experimental assessment of basic physical and mechanical properties is done. Then, the HPFRC samples are exposed to the temperatures of 600 and 800 °C respectively, and the effect of a high temperature exposure on material structure is examined. It is found that the applied high temperature loading significantly increases material porosity due to the physical, chemical and combined damage of material inner structure, and negatively affects also the pore size distribution.

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.

Application of UHPC Joints in Precast Structures

Acceleration of bridge construction requires the development of new construction methods. In composite steel concrete bridges the cast in situ bridge deck may be replaced by a precast deck. For fast assembly the joints have to be solved adequately. UHPC joints represent an alternative which can satisfy the requirements on mechanical properties of joints, on construction and economy. The function of the joints was experimentally verified using three different experiments. The performance of beams with precast and cast in situ slab was compared.

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.

Repeated Diagnostics of Maintained Prestressed Bridge Structure, Interpretation of Changes in Relation to Durability

General refurbishment of prestressed reinforced concrete bridge of Pavel Wonka in Pardubice was done in 2006. Within the preparation of refurbishment a full diagnostics of the structure was performed with the assistance of Klokner Institute, including diagnostics of longitudinal prestressed loose cables located in bridge boxes and the real condition of the corrosion was found. New inspection, including water-insulation system and condition of repaired concrete structures was held in 2015. Some of the findings and comparison of the condition before refurbishment and condition after about 10 years of operation are introduced in this article.

Design of an Experimental Prestressed Arch Pedestrian Bridge Made of UHPC

This paper presents the design of an experimental prestressed arch pedestrian bridge made of ultra-high performance concrete (UHPC). The structure is designed as a permanent single-span bridge with an intermediate deck. The span of the bridge structure is 58.5 m, the total width is 5.1 m, and the clearance width of the bridge is 4.5 m. The main structure of the bridge consists of two prestressed beams made of UHPC with dispersed steel fibers. The main beams are composed of prefabricated parts, subsequently prestressed.

Mechanical, Hygric and Thermal Properties of Flue Gas Desulfurization Gypsum

The reference measurements of basic mechanical, thermal and hygric parameters of hardened flue gas desulfurization gypsum are carried out. Moisture diffusivity, water vapor diffusion coefficient, thermal conductivity, volumetric heat capacity and linear thermal expansion coefficient are determined with the primary aim of comparison with data obtained for various types of modified gypsum in the future.

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.