Vit Černý

Usability of Fly Ashes from Czech Republic for Sintered Artificial Aggregate

Artificial sintered aggregate produced by self-firing is one of the few building materials, which can be produced with only fly ash. If the character of the fly ash is optimal, no other additions are needed. However, not every fly ash has optimal composition. Quality of fly ash then influences composition of the mix, technological parameters and quality of produced aggregate. Parameters influence the process of self-firing, strength of granules during the phases of drying process, ignition and burning under given underpressure on an agglomerating bed. This often influences correct setting of proportion of combustion material and reduces quality of aggregate. The paper evaluates fly ash produced in the Czech Republic by both high temperature and fluidized bed combustions. Their granulometry, specific surface, bulk weight, structure, chemical composition and behavior at higher temperatures up to the melting point are evaluated.

Experimental Testing of Hydroinsulating Injection Screens

One of the most widespread method of redevelopment of wet masonry is additional creating of hydroinsulating screen in the material. This method has many advantages. The biggest advantage is fact, that building can be repaired from inside without damaging its statics and saving it from being demolished, thus sparing the environment. In comparison to other procedures its application is quick, easy and has excellent final efficiency. Main object of this article is testing of application and total functionality of individual screens in masonry.

The Influence of Sulfates on Tobermorite Formation in Lime-Ash Composite

Autoclaved aerated concrete is an ecological building material with suitable properties and long-time tradition. The research of secondary raw materials usage and technology optimization is needed in order to increase the efficiency and sustainability of its production. It is important to focus on development of mineralogical composition while studying the influence of input materials and the parameters of hydrothermal synthesis on the properties of final product. This is especially important in case of tobermorite formation as the bearer of strength in the structure. Main focus of this paper is applicability of fly ash (silica component) and admixture of energo-gypsum (sulfate component) in production of lime-ash composite in hydrothermal conditions. The research was focused on autoclaving of samples at temperature of 170°C in three various isothermal sustains. Final samples were analyzed by XRD and SEM in order to proof the influence of input materials. Results show that 5% admixture of energo-gypsum had positive influence on tobermorite formation.

Content of Aluminium Hydroxide in Lime-Silica Composite and its Influence on Tobermorite Formation

Aerated concrete is lightweight building material with excellent thermos-technical properties compared to its strengths, easy workability and economic efficiency. It is material with long tradition of manufacturing since 1924 but its potential is yet possible to be extended. Since the beginning pure ingredients such as lime and silica sand has been used. Nowadays we are looking for ways to replace these expensive raw materials with cheaper alternatives. One of the most important mechanical properties of each material is its strength. In case of aerated concrete the bearer of strength is mineral tobermorite. It is created by reaction of silicon oxides and lime at hydrothermal conditions. It belongs to the group of calcium hydrosilicates with chemical formula Ca5Si6O16(OH)2·4H2O. Main goal of this paper is proposal for modification of the raw materials composition and autoclave regime of aerated concrete using aluminium hydroxide in order to improve final mechanical properties and mineralogical composition.

Use of Computed Tomography for the Evaluation of Autoclaved Aerated Concrete Structure

This paper deals with the use of computed tomography (CT) images and analytical software for the nondestructive evaluation of the texture of autoclaved aerated concrete (AAC) with 20% fluidized bed combustion fly ash as a substitute for quartz sand. The samples of AAC, made in the laboratory with the same composition but different ways of curing in the fresh stage (before autoclaving), were subjected to observation of the differences in the texture of the silicate matrix, such as inhomogenity, defects, and pore size distribution. The curing conditions with limited drying resulted in formation of larger, locally-connected pores and additional cracking after autoclaving, which led to a decrease in compressive strength up to 1.32 MPa, compared to samples cured in conditions that allowed complete drying reaching 1.95-1.96 MPa. Also there were problems identified related to imperfect laboratory preparation of the samples, such as agglomeration of individual mixture compounds and larger air void formation, due to the absence of vibrating, cracking and weak spots formation. CT provided sufficient contrasting images for consequent software evaluation of pore size distribution, however a higher resolution of the images is needed for determination of pores smaller than 0,125 mm.

Lightweight Aggregate Produced with Cold-Bonding of Fly Ash and Binder

Main object of this paper are results of ash usage in order to create artificial aggregates. Ashes are mineral residue of coal burning in thermal power stations. Fly ashes (high temperature ashes) are highly used in practice as supplement of cement and silicate components of silica materials. FBC ashes are not used such great scale. They can be used for restoration, mounds or for example also for production of ash autoclaved aerated concrete. [1] Production of artificial aggregate from sintered ash is possible mainly because of the fly ashes. [2] Focus of this paper is to compare various types of ashes for lightweight aggregate produced with cold-bonding. Apart from the fly ashes and FBC ashes are also tested bottom ashes from FBC technology. From the results could be assumed, that bottom ashes compared to their granularity could be used only very hardly. Fly ashes splendidly react with cement and reach higher strengths. But they need more than 10 % of binder in order to reach quality results. FBC ashes better cooperate with quicklime, but in order to reach suitable parameters they need smaller portion of binder.

Effect of Artificial Lightweight Aggregate on Resistance of Polymer Cement Mortars to Extreme Temperatures

This paper presents the results of research focused on the modification of composition of the polymer-cement mortars. The use of these materials is quite wide. The greatest use can be found in the production of reinforced concrete repair materials. Specifically, the article analyzes problems of lightweight aggregate effect on the resistance of polymer-cement mortars to extremely high temperatures. The link is particularly evident with the risk of fire. Attention was given to the two different types of aggregates - from primary raw materials (Liapor) and alternative sources of raw materials (fly ash aggloporite). The study was carried out by the laboratory analyzing the basic material characteristics of prepared samples which were exposed to temperatures up to 1200 ° C.

Effect of Modification of Cement-Bonded Particleboards Composition on their Frost Resistance

The article deals with the study of the effect of modification of composition of cement-bonded particleboards on their frost resistance. Powder waste from the line for production of cement-bonded particleboards was used for preparation of test units. Conditions of storage under alternating freezing and defrosting in combination with effect of water were specifically created. Subsequently, the fundamental physical-mechanical parameters were assessed.

Production Possibilities of Concrete Based on Artificial Fly Ash Aggregates

Production of artificial aggregates is one of the suitable ways how to use the maximum ratio of fly ash in construction materials. Subsequent use of aggregates is directed in addition to various embankments, filter layers and also for lightweight concrete. Concrete can be used wherever required low weight while maintaining the necessary strength. The contribution is geared to verify the applicability of newly produced artificial aggregates from different types of fly ash for standard concrete.

Study of Influence of Fly Ash Character on its Behaviour during Clinkering Process

Fly ash is currently secondary raw material, which is produced in huge quantities and its applicability is still not optimal. Even though it is used in cement, concrete, mortars, aerated concrete, ceramics, etc., it is still used, more than 80 % of it, for the reclamation of industrial areas and open cast mines. The production of artificial aggregate by clinkering fly ash utilizes at least 90 % of fly ash in the mixture and it is, together with aerated concrete, one of the ways to make the most of the potential of this raw material. This article deals with the description of the nature of individual fly ash types produced in the Czech Republic and the study of its influence on the behaviour during the thermal process. Chemical composition is the decisive parameter; it indicates the ratio of silicon, iron and aluminium oxides, and thus affects the melting point of the entire complex. This article points out the differences among the various fly ash types and it directly shows, using a picture-analysis, the changes in a sample cross-section during annealing.