Klára Křížová

Effect of High Proportion of Blended Cement in Concrete

The paper is concerned with assessment of blended cement high proportion in mix design of concrete. A long term development of concrete compressive strength and static modulus of elasticity were monitored. The cement proportion reached even 450 kg per m3 of concrete. The high proportion of blended cement was used with aim to obtain declared modulus of elasticity values for the given concrete strength class according to EN 1992-1-1. And just the blended cement influence was positively verified in the long-term development of both monitored parameters.

Verification of Rheological Properties of Self-Compacting Concrete with Reinforcement

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.

Effect of Combination of Admixture on the Development of Selected Properties of Concrete and their Comparison

The paper is involved with effects of admixtures (fly ash, slag) and their combination on selected properties of ordinary concrete. The set of concrete covers seven different containing of Portland cement and approximately 10% of admixed slag and concrete with fly ash and slag contents up to 42 %. At early age of the concrete balanced values of compressive strength were obtained except the concrete with admixture combinations. And on the contrary at 28-day age the concrete with admixture combinations obtained comparable values like concrete with only one type of admixture. The compressive strength was monitored together with modulus of elasticity to 180-day age of the concrete. In the last phase the obtained values were compared with guide value where the slower development of theses parameters with applied admixtures was pointed out.

Options of UHPC in the Czech Republic

This contribution describes the possibilities of UHPC concrete production. To begin with, the fundamental characteristic of this concrete, its development and composition are provided. An essential element for achieving the extraordinary properties of UHPC concrete is its composition. The experimental part describes the UHPC design, test examples and the testing of certain compressive strengths and tensile bending strength after 1 and 28 days. Simultaneously, basic UHPC buildings in the Czech Republic are mentioned.

Application of Alternative Fillers in the Cement-Bonded Particleboards Structure

Cement-bonded particleboards merge the good properties of wood and cement; they are board materials with properties which are pre-determined for use in many different cases in the case of construction of walls and partition walls, lower ceilings, facades, floors, etc. The disadvantage of the cement-bonded particleboards is the relatively high price which is mainly derived from the price of input materials. The main component creating the filler for cement-bonded particleboards is wood. Wooden chips are produced from tree trunks of cut trees which mean that, first of all, it is necessary to produce chips from the wooden substance. By using alternative fillers, it is possible to partially or wholly avoid this part of the production. The use of alternative raw materials in construction materials means there is the opportunity to decrease manufacturing costs and eliminate ecological loads. The content of this paper is the use of alternative fillers as an organic, as well as inorganic origin in the structure of cement-bonded particleboards. For the production of boards, technical hemp was selected, straw and jute as representatives of the most often used organic raw materials followed by a narrow fraction of Refaglas cellular glass, synthetic fibres and waste from the production of ORSIL mineral wool. In the board structure, this concerned 100% or 50% substitution of wooden splinter. For the valorisation of options for future use in board materials, physical-mechanical properties were monitored; in particular, attention was paid to bending strength, modulus of elasticity in bending and bulk density. Newly created boards must fulfil the technical parameters required for cement bonded particleboards stated by the standard EN 634-2.

The Influence of the Addition of Secondary Materials to the Thermal-Technical Properties of Filling Materials

The filling material is made up of technical Cannabis shives, hydraulic or air binders and other components. They are suitable for use as fillers in horizontal or vertical wooden structures such as rack systems. Thanks to its good thermal-insulating properties the filler may be used as thermal insulating filler in walls or floors. The article describes the behaviour of Cannabis padding materials used as secondary raw materials as the replacement part of the joiner component. The use of secondary raw materials (such as fly ash, fluid or classical slag), however, is conditioned by the maintenance of the same, or at least the best possible thermal-technical parameters of the resulting filling material.