Abstract: Hybrid cements represent a relatively new type of binders which combine some of the advantages of Ordinary Portland Cement (OPC), the application of mineral admixtures and alkali activation. Hybrid cements represent blends containing a low portion of OPC and a high proportion of mineral additions (such as blast furnace slag, fly ash, metakaolin ....). The paper is focused on the study of properties of mortars prepared from hybrid cements. Mortars with hybrid cements were prepared for an evaluation of the effects of the dosage and the composition of alkali activator, the dosage of OPC and the ratio between ground granulated blast furnace slag and fly ash. The results make it possible to optimize the composition of hybrid alkali activated concretes.
Abstract: Conventional high temperature fly ash has been used for manufacturing of construction materials, concrete in particular, for quite a long time. Fluidized bed combustion fly ash, however, has little use in this area, mainly for its chemical composition and morphology. Current efforts are directed towards the development of new technological processes and building materials that would allow the use of this industrial waste and its qualities. One possible way of fluidized bed combustion fly ash’s utilizing in construction industry is the production of cold balled lightweight aggregate. Production of this material is economically advantageous and enables processing of large volumes of raw materials. This paper describes possibilities of using this aggregate for production of lightweight concrete of lower compressive strength classes and consequent testing of durability and resistance to various types of aggressive environment and cyclical freezing and thawing. Physico-mechanical properties and microscopic defects were also studied
Abstract: The article is involved with study of fire resistance of concrete for tunnel linings. It summarises the problems of present knowledge of concrete resistance in tunnels and deals with behaviour of concrete particular parts at exposure to high temperatures. Further possibilities of fire resistance improvement for production of concretes together with fire prevention are described in this paper.
Abstract: The article deals with theme of high fly ash content concretes intended for long life constructions. Considering the still growing consumption of fly ash in construction concretes it is a live theme in the Czech Republic and abroad as well. The emphasis will be laid namely on characteristics and requirements for fresh concrete intended for construction of these specific concrete constructions. They are for instance waterproof constructions, tunnel linings, concretes for bridge and road constructions etc. Also the hardened concrete properties like compressive strength, resistance to pressure water, durability and further necessary parameters for obtainment of required properties of these concretes will be monitored.
Abstract: The use of fibre reinforcement in normalweight concrete technology is commonly used in practice. In the area of lightweight concrete, for example with use of expanded clay aggregate, there is not widely used this type of technology. The paper describes the experimental verification of various doses of steel fibres in two types of bulk and compressive class of lightweight expanded clay aggregate concrete and its influence on the physical and mechanical properties of hardened concrete – compressive and flexural strength, stress-strain diagram.
Abstract: The subject of the article is to inform the experts about results of a set of fire resistance tests of light concretes designed for traffic and tunnel structures. In addition to commonly used recipe C 30/37 FX4, corresponding version of light concrete class LC 35/38/XF 4 was tested. One of the goals of the tests was verification of behaviour of “road” (XF4) concretes under the most demanding conditions of fire, especially in road tunnels. In addition to standard curve, the hydrocarbon and Eureka curves were used for the fire tests. The loading curves differ from normally used standard curve especially in the temperature rise speed (temperatures over 1,000°C are reached within a couple of minutes). In this case, real concrete moisture and possibility to remove water steams from a component are substantially important for the fire safety (integrity).
Abstract: The paper presents results of mechanical and physical tests of self-compacting concrete with fibre reinforcement. Self-compacting concretes belong to special types of concretes with filling ability without invoking external dynamic forces. Especially high storage rate and concrete access even in densely stored reinforcement, high homogenisation, low water-cement ratio and exclusion of external vibrations are benefits of SCC concretes. The highest risks that must be considered when designing this type of the concretes are their resistance to segregation, sedimentation, blocking and bleeding. Several SCC formulas with two types of fibres (steel, polypropylene) were designed and compared and the effects of fibres reinforcement on concrete selected properties were monitored in fresh and hardened condition, too.
Abstract: Gas permeability of concrete is a property, which is recognized as one of the basic indicators of its durability. Measuring of the air permeability is mostly carried out on samples, which are not exposed (before or during the tests) to any certain external loads, which could cause microcracks in hardened cement matrix. However, in the case of real structures there is always some stress level and thus the concrete permeability is usually affected by microcracks. To know both, permeability of sound concrete and the permeability of concrete containing certain amount of microcracks, is the basic assumption for correct evaluation of its durability. Our paper deals with the permeability of loaded specimens made of high performance fibre reinforced concrete (HPFRC). This type of concrete is in Slovakia used for the construction of containers for a low and medium level radioactive waste storage and thus their properties in loaded conditions are of primary concern. Permeability was measured with Torrent Permeability Tester on cube specimens at different loading levels and after unloading. Specimens were 10 years old and varied in the amount of fibre reinforcement.
Abstract: In this paper, the effect of different kind of glass fiber on hydric properties of ultra-high performance concrete and normal strength concrete is determined. It was the use several types of micro fine high-dispersible alkali resistant fibers that prevent the formation of shrinkage cracks caused by tensions. Comparative measurements with both concrete without glass fibers are done as well. The main aim of this experimental work is to obtain sufficiently accurate input data for the estimate of durability surface layers of concrete which are connected with water transport and its accompanying effects such as biological degradation, water soluble salt transport or degradation by rainwater absorbing oxides of sulfur and carbon from air.