Special Concrete and Composites 2017

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Authors: Jiří Němeček, Rostislav Šulc, Jitka Němečková, Jaroslav Kruis
Abstract: The paper summarizes utilization of nanoparticles (NP) in concrete for enhancing its mechanical, transport or other properties. The first part is devoted to review of NPs used in fresh concrete mixtures that have been reported previously in the literature while the second part shows original results from utilization of nanoparticles as healing agents for reparing of existing concrete structures. In the second case, nanoparticles are delivered to concrete via electrokinetic principle by using their surface charge provided in colloidal solutions. Particles are transported in the pore liquid of concrete due to electric field applied between the concrete surface and steel reinforcement. In this way, distressed concrete can be repaired, cracks sealed and risk of corrosion diminished. The injection of NPs can be complemented with extraction of chlorides that are the main deteriorating chemicals in reinforced concrete structures. Finally, the paper shows a framework developed for the electrokinetic transport of ionic species in concrete applied to chloride extraction from concrete and how it can be modified also for transport of nanoparticles.
Authors: Jiří Pazderka, Magdaléna Purkrtová, Clemens Hecht
Abstract: The paper deals with two problems in the field of cement-based crystalline coating: The uncertainties about the depth effect of crystalline coating and the influence of curing on resulting waterproofing effect. For coating depth effect investigation the authors used a method based on the analysis of surface hydrophobicity (contact angle method). The depth effect of crystalline coating can be detected on the basis of the different surface hydrophobicity in various distances from the coated surface. The results of measurement showed that the tested crystalline coatings affect concrete microstructure to depth of approximately 50 - 60 mm (measured 4 months after the coating application). But it turned out that used method is not appropriate for this purpose because the results can be affected by a lot of influences and it is necessary be cautious about the conclusions. Another part of experimental program showed that the curing of crystalline coating during its ageing is absolutely necessary for the consequent waterproofing effect. This fact is also the risk factor for the using of crystalline coatings because the waterproofing effect is dependent on a consistent technological discipline.
Authors: Dominik Gazdič, Jana Mokrá, Jan Hanáček
Abstract: This paper deals with the development and research of sulphate binder based on anhydrite for the industrial production of dry mortar self-leveling mixtures. As part of the experimental activity, selected plasticizers for the sulphate binders were tested. These additives were added in various weight ranges. The tests were carried out first on anhydrite pastes and then on anhydrite mortars of standard composition. Their influence was mainly observed on the achieved basic technological properties, such as the consistency, the initial setting time and the achieved strength.
Authors: Tomáš Žižlavský, Martin Vyšvařil, Patrik Bayer, Pavla Rovnaníková
Abstract: This paper studies the possibility of usage of the guar gum and its derivatives (carboxymethylhydroxypropyl guar (CMHPG) and hydroxypropyl guar (HPG)) as admixtures for aerial lime-based mortars. The influence on the properties of mortars was studied on the aerial lime –based mortars prepared with quartz fine grained sand and doses of admixtures ranging between 0,5 and 10‰. The hardened bulk densities, flexural and compressive strength, porosity, water absorption coefficient due to capillarity action and carbonation rate were studied. The addition of the hydroxypropyl guar lowered the bulk density (due to an air intake), improved workability, slightly increased the strength, slowed carbonation rate, and nobbled the water transport in the mortar. The addition of carboxymethylhydroxypropyl guar does not impact the bulk density, the strengths were increased similarly to HPG: it does not impact carbonation rate significantly, so the long term strengths were comparative with the HPG. The water transport was slightly better in lower doses and slightly worse in larger doses in comparison with the reference mortar. The pure guaran was found not to be beneficial for the lime mortars for its only advantage is in the water transport, where in any dose the transport was better than any other mortar, but the benefit of this is questionable.
Authors: Tomáš Jarolím, Jiří Brožovský, Dominik Šácha, Naděžda Pizúrová
Abstract: Frost resistance of concrete is one of the main durability parameter of Central European climatic conditions. Nanoparticles are the most worldwide examining in materials science. In Brno University of Technology has been interested in nanoparticles for years. First steps were dedicated in identification of nanoparticles (CNT), their dosage and dispersion. After solving before mentioned steps the CNT implementation to concrete could happened. In article was experimentally verify influence of CNT addition to concrete frost resistance after 100 frost cycles. Per results it could be said that addition small dosage of CNT increased frost resistance of concrete.
Authors: Karel Dvořák, Matěj Švéda
Abstract: This experiment describes the effects of the aging time since the moment of milling to Portland cements physico-mechanical properties. Possible mechanical activation effects to Portland cement particles has been found. For this experiment two kind of milling technology were used, the conventional milling in a ball mill and high-speed grinding technology in high speed disintegrator and influence of these technologies was also described. The aging period of the cement influences in particular physico-mechanical properties in the early stages of hydration but the final properties after 28 days were not influenced.
Authors: Martin Keppert
Abstract: Lead is an example of heavy metal, which influences the course of silicate cement hydration resulting to retardation of setting and hardening. This topic become of importance when a cementitious material is intended to be used as solidification/stabilization matrix for a waste or secondary product containing some lead species. There are literature data on the effect of Pb retarding action but they are incomparable each other due to uneven experimental conditions, used Pb salts, types of cement etc. The present paper aims to describe influence of various lead(II) compounds (nitrate, sulfate and lead(II) oxide) on setting course of Ordinary Portland cement (OPC). The setting was monitored by Vicat apparatus, the dosage of salts (expressed as wt. % of elementary Pb to OPC) was 0.5, 1, 2 and 5%. Obviously the present anions may also influence the setting time; the set of control experiments with sodium salts of above given anions was performed in order to eliminate the anion effect. The PbO was found to be most detrimental towards retarding of setting, while lead sulfate at higher dosages caused high instability of setting (oscillation). The effect of Pb was, in all cases, more important than influence of given anion.
Authors: Marcela Fridrichová, Dominik Gazdič, Jana Mokrá, Karel Dvořák
Abstract: This paper deals with the verification of the possibility of preparing synthetic ettringite in a way of direct addition of aluminum sulfate and calcium hydroxide as an alternative to the hydration of yeelimite. The stability of the resulting system was studied using the X-ray diffraction (XRD) and differential thermal analysis (DTA) in two different environments, namely in a laboratory environment and the environment of saturated water vapour. The evaluations of X-ray diffraction analysis and thermal analysis show that in the ettringite sample stored in the laboratory environment, evaporation of molecular water and subsequent transformation of ettringite into metaettringite or monosulfate can occur over time. Conversely, exposition of saturated water vapour environment can lead to saturation of the system by free calcium ions due to the slow dissociation of calcium carbonate, and thereby increase the amount of ettringite at the expense of gypsum and aluminum amorphous phase. To verify the above, it is recommended long-term monitoring of samples exposed in monitored environments.
Authors: Pavel Rovnaník, Ivo Kusák
Abstract: Alkali-activated slag is an alternative binder to the ordinary Portland cement. In order to improve its tensile properties steel fibres as dispersed reinforcement can be used. Since steel is very good conductor it changes the electrical properties of alkali-activated slag composite that can have a potential to be used as self-sensing material then. In this study up to 20% of steel fibres by mass of the slag was added to alkali-activated slag mortar and the mechanical properties, electrical resistance, capacitance and microstructure of the composites were investigated. The results showed that the best improvement of both the mechanical and electrical properties can be observed for the composite with 15% of steel fibres.

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