Iveta Hájková

Monitoring of Calcium Sulphate Phase Transformations Using High-Temperature X-Ray Diffraction

Within the task the so called high-temperature X-ray diffraction analysis (HT-XRD) was used in the field of sulphated binders. Gypsum or calcium sulphate CaSO4.2H2O is the basic raw material for the sulphated binder production. As it is known by gradual warming of gypsum its different phase transformations can be obtained which significantly differ in its properties. Using this analysis identifications of temperatures of particular phase transformations in the CaSO4·xH2O system can be performed.

Modification of Technological Properties of Laboratory Premixes

Sulfur binders belong to the group of airbrushes. They can therefore only harden and harden in the air. The main raw material, gypsum, can be mined in several places in the world. Even in the Czech Republic there is a deposit of natural gypsum in Kobeřice u Opavy. [5] In spite of this fact, we use mostly industrially produced gypsies, because the natural gypsum deposit has only very limited capacity. The Energogypsum, produced in the Czech Republic by ČEZ Energetické Produkty s.r.o., is the waste product of flue gas desulphurization using the wet limestone scrubbing method. Like the chemosynthesis, it is characterized by its high purity (the content of pure CaSO4 2 H2O is at least 90%). The one in the Czech Republic is manufactured by Precheza, a.s. in Přerov. The use of sulphate binders is varied. A better form in the form of alpha plaster is used to produce self-leveling floors and dentistry. Less-quality beta gypsum has a larger application. From it we can produce both gypsum and monolithic partitions. We can also use it for the production of plasterboard and gypsum fiber boards and, last but not least, as internal plasters for its good fire performance. [1] Plasters are being prepared today in two different ways. Firstly, they are still prepared in the original outpatient way directly on the building from individual raw materials, but they are also industrially produced in the form of dry mortar mixtures, which are mixed on the building only with water. The second way is more progressive with the fact that nowadays it is even more widespread. For many builders, however, it remains financially scarce. That is why we have recently begun to find a compromise solution that will satisfy both the technical and the economic ones. This is the development of the so-called binder premixes, ie the industrially produced mixed binder, which is mixed only with sand and water on the site. The situation on our market shows that the recently developed special premix for lime-cement plaster and mortar mixtures is very positive for the building public and therefore the effort is to generalize this mixed mortar in the production raw material base and, in addition, to develop its analogue based on sulphate binder. [2]

Water-Tight Concrete Constructions and Directives for their Design and Realization

The paper describes problems of water-tight concrete constructions, their design, manufacture and testing of quality in accordance with regulations and directives used in the Czech Republic and abroad. Current knowledge of water-tight constructions and water-tight concrete imply that main focus is on problems of use of water-tight concrete for construction of so-called white bath and preventing crack formation in concrete. Laboratory work is focused mainly on design of concrete based on individual regulations. Subsequently, influence of various types of cement and additions partly replacing cement on properties of water-tight concrete is examined. Research of heat development during hydration at early stages of maturing is and inseparable part of the experimental work, as well as development of compressive strength, water-tightness and frost resistance of concrete

Properties of Vibro Compacted and Pressed Concrete Products with Varnished Surface

Technology of so-called vibro compacted pressed concrete is currently used inter alia for manufacture of concrete products like concrete paving blocks, slabs, curbs or walling elements. Particularly wear layers of products for paving have recently been improved by special methods and technologies. The paper summarizes current knowledge of vibro compacted pressed concrete products with surface finish treated with hardened varnish. Main focus is on description of individual methods of finalizing wear layers of such products.

Quality Evaluation System for Description of Recycled Concrete Aggregates and Verification of its Functionality

Article presents quality evaluation system for description of recycled concrete aggregates (RCA), verification of RCA properties and subsequent application in to concrete mixtures as a partial or total replacement of natural aggregates (NA). Modernization and rehabilitation of constructions is accompanied by creation of demolition waste from old buildings and structures. The necessity of recycling is unavoidable, because volume of construction and demolition waste (C&DW) is increasing and the landfills are reaching their maximum capacity. Nowadays, there are numerous research teams focused on analysis of characteristics and application of RCA into new concrete as a replacement of NA. Test samples of RCA have always different source, grain composition and other physical and mechanical properties, which are variously described in each different paper. Up to now, there is no any uniform quality evaluation system for description of recycled concrete aggregates, which can easily describe their source and assumed properties. Our aim is to set up rules for description of RCA and simplify the evaluation of properties of various RCA. Qualification system will be applied on three different samples of RCA and verified by the selected properties tests. Tested samples of RCA will be than used as a replacement of natural aggregates in concrete mixtures. The replacement amount was set up on 20%, 40% and 100% according to the reviewed literature, to have a comparable replacement amount and valuable results for discussion. The results of RCA testing and testing of concrete with partial and total replacement of NA showed that the evaluation system is working properly. It can be concluded, that accuracy of the quality evaluation system for description of recycled concrete aggregates is sufficient, but more tests on RCA should be done to prove all connections in between description of RCA and their properties.

Technological Properties Testing of Blended Portland Cements with Fluidized Filter Ash

The work aims to study the behaviour of blended cement with fluidized filter ash (FFA) considering to formation of the increased proportion of ettringite and its eventual transformation into thaumasite. In part of an experiment there were prepared three cements, two of them served as a reference one-component and the reference blended cement with limestone, a third one was tested blended cement with a FFA. All three cements were put to determination of basic technological properties and next they were observed during hydration process.

Cement Based Heat-Insulating Materials for Use in Floor Constructions

Many architects, designers and builders struggle with the ongoing problem of how to fill the space between the load bearing foundations / ceiling land the flooring structure in the easiest and cheapest way while still retaining the optimum heating and sound insulating properties. In this age of hi-tech and plentiful amounts of construction materials, it is very difficult to focus on the market. On paper, very similar products from natural or artificially produced materials can be delivered to the construction site in a hardened state, most frequently in the form of boards or granulate or produced directly on-site or near a concrete plant and transported to for placement in a liquid state. This areas does concerns both new residential or industrial objects, as we as old objects which are waiting for reconstruction. During the project solution, various mixtures were designed that use the cement mortar and filler as a binder in the form of technical foam, expanded clay, vermiculite, perlite and hemp shives, so that when fresh the density does not exceed 1.400 kg / m3 and the materials can then be used as heat-insulating material in the flooring construction.

Testing of Technological Properties of Foam Concrete

At present the demand for thermal insulation materials is bigger than ever before. Also cement foam or foamconcrete, the mixture of cement mortar and technical foam can be one of such materials. Due to its liquid consistency this material can be simply applied in fresh status on uneven board surfaces where application of common thermal insulating materials would be very complex and time consuming.This work is involved in use of fly ash in foamconcrete and polystyrene-concrete compositions; these are very lightweight concretes produced from fine-grained cement mortars by its foaming using foamable admixtures. The objective of this work is to verify whether final physical and mechanical properties are improved when fly ash is applied within the mixture, in particular, the compressive strength thermal coefficient and stability after 12 hours from mixing.

Impact of Grinding Technology on Final Properties of Portland Cement

Portland cement got his name derived from the appearance of concrete that resembles sandstone located near city of Portland in England. In 1824, John Aspdin was granted a patent for the production of Portland cement.In the past, energy and economic demands on production of cement were lower than they are today. Production was characterized by a slower burning mode and coarser grinding. Product produced this way were reaching lower compressive strength.Currently there are several companies producing Portland cement. Main ones in Czech Republic are Holcim, Heidelbergcement group and Lafarge Cement a.s. Their production methods are very similar. The differences are mostly in the possibility of using local raw materials with different chemical composition and the technical equipment of factories. In the production, the main emphasis is on reducing energy and financial cost.One way to save energy and money is to use mechanical-chemical activation when grinding Portland clinker.

Nanosilica Activated High Volume Fly Ash Concrete: Effects on Selected Properties

By volume, there is no other material used as much as concrete. Its mechanical properties, durability and favorable price makes concrete the perfect construction material. In last few decades, we are seeing a growing trend of partial Portland cement’s replacement with secondary raw materials, most commonly with fly ash. So-called high volume fly ash (HVFA) concretes usually contains over 50% of it. While HVFA concrete’s long-term properties and price are improved over the classical one, its early age properties are often affected negatively. Here, a highly reactive pozzolans enters the scene. Materials like microsilica and metakaolin are known to accelerate concrete’s strength development and improve early age characteristics. In this paper, nanosilica is used for this purpose. These SiO2 nanoparticles possesses a much higher surface area and thus reactivity. Three mixtures with 0, 40 a 60% portland cement’s replacement with fly ash were prepared and tested with and without addition of small amount of nanosilica. Effects on compressive strength, static and dynamic moduli of elasticity and resistivity against water pressure were observed. Results clearly demonstrates that even with dosage in the range of tenths of percent, nanosilica can significantly improve concrete’s properties.