Rudolf Hela

The Effect of Metakaolin and Silica Fume on the Properties of Lightweight Self Consolidating Concrete

This paper is concerned with the development of lightweight self-consolidating concrete, especially with the comparison of the effect of metakaolin and that of silica fume on the properties of this concrete. The use of metakaolin for improving the durability and for achieving better physico-mechanical properties of concrete is relatively new approach in concrete technology. The experimental works which are described in this paper are used for the manufacture of lightweight self-consolidating concrete of different fractions of the expanded clay lightweight aggregate Liapor with different fractions of normal weight aggregate. The metakaolin used of Czech production.

Utilization of Lightweight Aggregate from Expanded Obsidian for Advanced Thermal Insulating Plasters Production

The thermal insulating of new and existing buildings is of a key influence in reduction of their energetic demand factor resulting in reduction of emissions of gases, carbon particles and dust which directly improves the environment. At development of light thermal insulation plasters with very low thermal conductivity the foam-plastic matters or light porous aggregates are frequently used at present. The foam-plastic materials do not appear as convenient ones in view of the environment and sustainable development as well. In the given case the thermal insulation plasters based on light cellular aggregates appear as more suitable. However a majority of light aggregates (for example expanded perlite) do not show a good ratio of insulation and mechanical properties. The paper describes a design and development of thermal insulation plasters based on expanded obsidian that can be used for thermal insulating of building constructions and for moisture sanitation. Considering the applied type of aggregates the materials show better ratio of thermal insulation and mechanical properties while in practice the plasters can be used as a full- value alternative for classical thermal insulation systems.

Selected Properties of Cementitous Composites with Portland Cements and Blended Portland Cements in Extreme Conditions

The paper is focused on research of physico-mechanical properties of concretes with Portland-limestone cement, Blastfurnace cement and Portland-composite cement in comparisom with concrete with Portland Cement CEM I. Following physico-mechanical properties of concretes exposed to extreme conditions were tested: compressive strength, flexural strength, tensille splitting strength, velocity of propagation of ultrasonic pulse, dynamic elasticity modulus and density of hardened concrete. Following environments were used in tests: sulphates, magnesic ions, nitrates, gaseous CO2, high temperatures.

Evaluation of Degradation of Concrete Exposed to High Temperature by Means of Ultrasonic Pulse Method

Ultrasonic pulse method is a non-destructive testing method used for testing materials. For concrete, it is used mostly for determination of dynamic elasticity modulus, compressive strength, homogeneity, to determine depth of cracks or as a supportive method for testing frost resistance. Applicability of using ultrasonic pulse method for evaluation of degradation of concrete exposed to high temperature was proved. This method is unambiguously utilizable for rationalization of experimental work focused on optimization of composition of concrete resistant to high temperatures. Ultrasonic pulse method can be also used for mapping the degree of degradation of concrete elements and structures, which can be measured by means of direct sounding. Appropriateness of the use of ultrasonic pulse method for evaluation of degradation of concrete exposed to high temperature was proved. This method is unambiguously applicable for rationalization of experimental work focused on optimization of composition of concrete resistant to high temperatures. Ultrasonic pulse method can be also used for mapping degree of degradation of concrete elements and structures, which can be measured by means of direct sounding.

Carbon Nanotubes in Cementitious Composites: Dispersion, Implementation, and Influence on Mechanical Characteristics

For effective utilization of nanoparticles in cementitious composite materials, their perfect dispersion is necessary. Appropriate quantity of ultrasonic energy (US energy), as well as usage of proper and compatible surfactant, is a prerequisite for carbon nanotubes’ (CNT) suitable deagglomeration. US energy was supplied by Bandelin Sonopuls HD 3200 ultrasonic homogenizer. Influence of US energy’s amount on CNT’s dispersion in aqueous medium was monitored in two steps: at first roughly by an optical microscope and in the next step precisely by the measurement of absorbance via UV/Vis spectrophotometry. After the appropriate amount of US energy was found, cement mortars with CNT were prepared and tested. Their physical and mechanical properties were examined and compared to the reference specimens.

Study of Effect of Various Types of Cement on Properties of Cement Pastes

This article studies the effect of various types of cement on rheological properties of cement pastes. Rheological properties are significantly related to workability of concrete and to requirements of mixing water amount and thus affect the development of strength, durability of concrete and resistance of concrete to extreme conditions and to high temperature. This article describes the influence of cement type, type and dose of superplasticising admixtures on development of torque in time. Torque was monitored by the rotational viscometer Viskomat NT. Theoretical part of the article briefly describes the phenomenons that can accompany mixing and processing of cement pastes. Experimental part is focused on monitoring the rheological behaviour of cement pastes of different formulas by monitoring the evolution of torque in time.

Elimination of Negative Influence of Fluidized Bed Combustion Fly Ash on Viscosity of Cement Mix

Use of fluidized bed combustion fly ash as an admixture for manufacture of cement based composite materials is not quite common now, however, there are real ways of utilizing its potential. The most important negative feature of this fly ash is its variable chemical composition, which supports formation of new forms growing within the structure with negative impact of durability of the composite material. The morphology of this type of fly ash is also not very favorable as it has negative influence on consistency. Fluidized bed combustion fly ash considerably deteriorates consistency of cement mixture, which results in higher water-cement ratio and consequently worsening of physico-mechanical and durability parameters of the whole composite. Therefore the question arises how to eliminate this negative influence on consistency without the necessity of increasing water cement ratio.

Determination of Properties of Concrete Floor after a Fire and Renovation

Concrete exposed to high temperature considerably changes its properties down to total destruction. The paper describes renovation of concrete floor damaged by a fire of a factory building. Individual steps of determination of damage of concrete floor structures caused by high temperatures are described. Structure of damaged floor was technically analyzed, redevelopment was designed and renovation works were carried out.

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.

Mixing of Different Particle-Size Fractions of Fly Ash to Increase its Activity in Cement Composites

Fly ash residue from coal burning process in power plants have been used as an active additive in concrete since middle of nineteenth century. Nowadays, we are trying to maximize its reactivity in cement composites by several methods. One of the methods is mechanical activation by mixing several size fractions to reach ideal particle size distribution. Ideal particle size distribution of fine components in cement composites helps to reach maximal compactness and thus increases strength and durability. In this paper we present results of compressive and tensile strength of cement-fly ash mortars with mixing 3 size fractions origins in 3 electrostatic precipitators from power plant Tušimice. Fly ashes from 1st precipitator, 2nd precipitator and 3rd precipitator were mixed with ration 10:4:1, 5:4:1 a 0:4:1.