Advanced Materials Research Vol. 897

Abstract: Ultra High Performance Concrete (UHPC) and High Strength Concrete (USC) are because of the high density of their matrices very susceptible to spalling during fire exposure. By aid of a heat treatment with maximum temperatures of about 450°C a network of capillaries and micro cracks could be formed, which leads like a porous medium to a relief of water vapor already at harmless low pressures and could prevent the materials from spalling. In the framework of the presented study on UHPC some orientating tests have been performed to obtain knowledge concerning alterations of the microstructure during thermal treatment at 150°C, 250°C, 350°C and 450°C and the subsequent storage in air with 100% relative humidity at 20°C as to allow water uptake and rehydration. The tests have shown that by aid of the said treatment generation of a respective porous system was achieved, which remained open for the transport of water vapor at high temperatures, also after water uptake and rehydration of the dehydrated cementitious matrix. However further studies are needed to get information about effects of the treatments on the mechanical properties and the durability of members.

Abstract: The use of the alkali activated cements for the manufacture of perlite concrete pressed and vibro-pressed products for heat insulation intended for various purposes was studied. The interfacial transition zone perlite grain cement stone was examined in order to reveal features of its formation. These features allow to create a dense and strong shell/caging around the perlite grain which helps to avoid its corrosion and produce perlite concretes with high durability.

Abstract: Though, concrete in general is a non-combustible building material, modern High Performance Concrete (HPC) is very susceptible to violent explosive spalling during a fire attack. This requires protective measures for fire safety design of concrete structures. The current most worthwhile method to prevent explosive spalling is the addition of monofilament Polypropylene fibres (PP-fibres). However, since it has become common knowledge that PP-fibres are suitable for fire safety design, a variety of theories concerning the mode of action of PP-fibres have been suggested. The present article summarizes the most important hypothesis and presents an innovative method for the analysis of micro structural processes in heated specimens. The results show that due to the thermal decomposition of PP-fibres capillary channels are created. Simultaneously, a netlike micro crack formation occurs, which connects these capillary channels. This enables the relief of internal stresses (mechanical effect) and the formation of a permeable transport system for the escaping water vapour (permeation effect).

Abstract: The paper focuses on exploring the correlation dependence between the physical-mechanical properties of concretes and alternatively concretes with concrete recyclate and silicate admixtures and the susceptibility of concretes to carbonation. Determining the susceptibility of concretes to carbonation by testing the permeability of their surface layer using the TORRENT, ISAT, or GWT methods is relatively lengthy and requires expensive instrumentation. The first estimate of durability or susceptibility of concretes to carbonation can be easily made on the basis of standard physical-mechanical tests. It seems that the values of volume masses and tensile splitting strengths of concretes could be a good basis for the estimate of their durability.

Abstract: 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 1^st precipitator, 2^nd precipitator and 3^rd precipitator were mixed with ration 10:4:1, 5:4:1 a 0:4:1.

Abstract: The fly ash aerated concrete is a modern material combining high use value with environmental aspects of its production. It is mainly an utilisation of secondary raw materials with related minimum consumption of natural resources. The resulting properties the aerated concrete product obtains by autoclaving during which a complete line of calcium hydro silicates are formed due to occurring hydrothermal reaction and tobermorite mineral is the most important one. This mineral has a significant influence principally on aerated concrete strength. This article thus verifies the autoclaving time influence on tobermoritic phase developments and to this related compressive strength of the fly ash aerated concrete.

Abstract: The reconstruction of the historical buildings needs the replacement of the original and damaged materials using possible compatible materials that closely replicates the original ones in its appearance, chemical, physical and mineralogical properties, strength and durability. Thus, a complex approach based on advanced analytical methods is needed to identifying of the suitable materials. The paper is aimed at the study of the chemical and mineralogical properties of the historical stones of the medieval castle in the East Slovakia in order to replacement the original materials by the new ones with similar composition. The carbonates and silicates were confirmed as the main components of the stones by X ray fluorescence (XRF) and Fourier transformation infrared (FTIR) methods. The mineralogical analysis confirmed the presence of the calcite as the dominated carbonate minerals as well as the presence of the quartz and muscovite representing the silicate forms.

Abstract: The article focuses on the observation of the quality of polymer-modified mortars, where through the use of appropriate types of by-products the amount of C-S-H phase registered an increase. Specifically, it was waste shale and waste diatomaceous earth because these two by-products displayed pozzolana reaction. Tests were performed which showed that the increased content of C-S-H phase contributes to the improvement in monitored properties, particularly increase in the values of adhesiveness.

Abstract: The paper discusses the possibilities of production of external thermal insulation material from technical hemp bonded mixture of cement, hydraulic lime and secondary raw materials. To verify the applicability of this material as a heat-insulating, it was necessary to test its properties. The basic characteristics are to be determined bulk weight and heat conductivity factor. Additionally was also tested the tensile strength in bending and compressive strength. Based on the measured properties was decided to evaluate the applicability of this material as an additional thermal insulation.

Abstract: 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.