Karel Kolář

Multi-Functional High-Performance Cement Based Composite

The paper introduces development of new type of high-performance Portland cement based composite applicable for number of practical utilization. The fundaments of performed research was to design mixture with controlled process of hydration, easy production, suitable time of setting, good workability and rapid evolution of mechanical properties as well as satisfactory long-term stability of hardened composite. Selected mixture were evaluated by means of mechanical properties and volume changes determination.

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.

Measurement of Volume Changes of High Performance Cement Based Composites

Performed research work is focused on the experimental determination of volume changes of high-performance concrete. Studied topic is an essential problem of all cement based composites because of its influence to mechanical and durability properties due to crack formation. Special high-performance cement based mortars are often used for quick rehabilitation and renovation of current concrete structures where minimal level of total volume changes is required. Interpretation of final results is highly dependent on the way of measuring, as it is documented in the present experimental program.

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.

Dynamic Stability of Multi-Functional Composite Developed for Application in Permanent Way of Prague Underground

There are described properties of hardening multi-functional silicate composite during its long-term dynamical loading in the paper. Studied composite was developed for special application in permanent way structure in Prague underground. Dynamic loading was carried out on the laboratory model, in which the composite was applied as a bench of the rail anchoring. Due to loading in early ages was also studied the option of steel fibers addition. Results obtained confirmed impressive potential for practical use during new tracks construction, and quick repairs as well, because of rapid evolution of mechanical properties and sufficient resistance to dynamic loading. Silicate composite with fibers addition had better mechanical properties, however significant improvement during dynamic loading was not recorded in comparison with the reference mixture without fibers. Generally, new composite material confirmed great potential for practical use in transportation industry.

Controlled Hardening of Silicate Binders for the Optimization of High Performance Composites

This paper describes the fundamental principles for the development of high performance composites applicable in severe condition. Studied composite is based on the advanced silicate matrix consisted of cement and suitable addition modifying mineral additives. Experimental work was focused on the study of the evolution of mechanical properties and determination of frost resistance of developed composite at early age, what is crucial parameter for quick reconstruction. Obtained results confirmed that the action of frost did not interrupted the process of hydration of developed binding system, because index of frost resistance determined on the base of studied mechanical properties had increasing trend during the freeze/thaw cycling. Present paper declares high potential of silicate binders for difficult application.

Application of Laser Microscope System for Evaluation of Separation Agents

This paper demonstrates application of laser confocal scanning microscope system for fair-face concrete surface evaluation. Measure system presents a new generation optical system for identification and description of esthetical imperfections of various building materials. System enables 3D observation and high-precision 3D measurement in real time.