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Thermodynamic Stability of Ettringite Formed by Hydration of Ye’elimite Clinker
(Hindawi Publishing Corporation, 2016-09-08) Fridrichová, Marcela; Dvořák, Karel; Gazdič, Dominik; Pekárková, Jana; Kulísek, Karel
Although the stability of ettringite has been the subject of much research, the solution is not yet fully clear. Ettringite is generally considered to be stable up to a temperature of 110°C; however, some investigators claimed that ettringite may already decompose at even ambient temperatures. To prove these statements, ettringite was prepared by the hydration of ye’elimite, 3CaO·3Al2O3·CaSO4, and the system stored at laboratory temperature in two environments: in laboratory settings and in an environment of saturated water vapour.
Usability of alternative admixtures for the production of blended cements
(IOP Publishing, 2018-07-16) Sklenářová, Dorothea; Dvořák, Karel; Gazdič, Dominik; Hladík, Václav
This paper studies how pozzolan materials can be mechanically activated. For this, two major grinding technologies and different types of artificial pozzolans, such as red brick dust, granulated blastfurnace slag and sheet glass, were used. Observed properties were chemical and mineral composition, amorphousness, particle size and specific surface area. Pozzolan activity of selected materials was compared by evaluation of the reaction with lime using X-Ray diffraction (XRD) analysis and differential thermal analysis (DTA)
Development of grout for additional seal embankment dams
(Elsevier, 2015-06-25) Michalčíková, Magdaléna; Černý, Vít; Drochytka, Rostislav
The technology of sealing sand and gravel by chemical injection has been known and used for a long time. Chemical grouting is however expensive and sometimes the use of cement does not lead to the desired effect. That is why we are trying to find new materials and methods of injection. Clay and cement are added to a mixture save chemical products. Clay-cement mixes are used not only because they are better quality, but also because these mixtures have a tendency to penetrate better into incoherent sediments that would need an additional sealant of a chemical injection. In order to reduce cost in future, ordinary clay is replaces in the mixture secondary raw materials can be a suitable substitute for ordinary clay to a certain extent. This is true above all for fly ash. This paper deals with the appropriateness of using fly ash (secondary raw material), cement and lime (binders) and liquefying additives and examining their properties in the mixture. The aim of the paper is to propose the optimal injection mixture for additional sealing of earth dams.
Effect of steel fibres dosage in alkali-activated slag mortars on acoustic emission obtained during three-point bending tests
(EDP Sciences – Web of Conferences, 2017-05-24) Topolář, Libor; Šimonová, Hana; Schmid, Pavel; Rovnaník, Pavel
The acoustic emission phenomenon is directly associated with nucleation of cracks in structural materials during loading. This paper analyses acoustic emission signals captured during three-point bending fracture tests of alkali-activated slag mortar specimens with different amount of steel fibres. Typical parameters of acoustic emission signals were identified for different mixtures to further describe the under-the stress behaviour and failure development. The acoustic emission signals from crack growth were continuously monitored using acoustic emission sensors mounted on the specimen surface. Acoustic emission results are accompanied by selected mechanical fracture parameters determined via evaluation of load versus displacement diagrams recorded during threepoint bending tests
Rheological and mechanical properties of alkali-activated brick powder based pastes: effect of amount of alkali activator
(IOP Publishing, 2018-07-12) Vyšvařil, Martin; Vejmelková, Eva; Rovnaníková, Pavla
The rheological behaviour and mechanical properties of alkali-activated materials prepared by activation of a brick powder by alkaline solution (alkali + water glass) is presented in this paper. The effect of quantity of alkaline activator on the rheological and mechanical properties of brick pastes prepared from two types of brick dust was monitored. The rheological investigation included the characterization of flow properties and viscoelastic properties of the fresh mixtures. Compression and bending strengths were determined at 7, 28, 56 and 90 days. These materials have a low yield stress and a high viscosity strongly influenced by the amount of alkali activator. The fresh brick pastes become liquid more easily with increasing amount of alkali activator. The rising amount of alkali activator leads to a decrease of the material cohesion. The results of rheological and mechanical properties investigation showed considerable differences in behaviour of particular types of brick dust.

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