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Hygric and mechanical parameters of ternary binder based plasters lightweighted by expanded perlite
(IOP Publishing, 2018-07-12) Čáchová, Monika; Koňáková, Dana; Vejmelková, Eva; Vyšvařil, Martin; Bayer, Patrik
This article is focused on modern plasters with improved thermal insulating ability. The studied plasters were composed of lime, cement, ceramic powder, expanded perlite and silica sand. Regarding the matrix, three kinds of binders were used. Lime was partially replaced by ceramic powder. These waste materials show good pozzolanic reactivity and thus bring economic and ecological benefits. Portland cement was added as a third component to the mixture for the purpose of improving mechanical performance of the studied plasters. In this article, mechanical properties of designed plasters are presented. It was proved that matrix strengthening brought positive effect and eliminated the deterioration of mechanical behaviour; the final values of compressive strength were over 3 MPa. Due to desired high porosity of the studied plasters, their durability can be strongly affected by presence of the water. Therefore, in this article, the hygric parameters were studied too. Namely, the water absorption coefficient, apparent moisture diffusivity, the water vapour diffusion resistance factor and sorption and desorption isotherms belong among studied hygric characteristics. In this article, pore size distribution curves, which affect the discussed parameters, are presented.
Method for the Accelerated Testing of the Durability of a Construction Binder using the Arrhenius Approach
(De Gruyter, 2016-05-02) Fridrichová, Marcela; Dvořák, Karel; Gazdič, Dominik
The single most reliable indicator of a material’s durability is its performance in long-term tests, which cannot always be carried out due to a limited time budget. The second option is to perform some kind of accelerated durability tests. The aim of the work described in this article was to develop a method for the accelerated durability testing of binders. It was decided that the Arrhenius equation approach and the theory of chemical reaction kinetics would be applied in this case. The degradation process has been simplified to a single quantifiable parameter, which became compressive strength. A model hydraulic binder based on fluidised bed combustion ash (FBC ash) was chosen as the test subject for the development of the method. The model binder and its hydration products were tested by high-temperature X-ray diffraction analysis. The main hydration product of this binder was ettringite. Due to the thermodynamic instability of this mineral, it was possible to verify the proposed method via long term testing. In order to accelerate the chemical reactions in the binder, four combinations of two temperatures (65 and 85°C) and two different relative humidities (14 and 100%) were used. The upper temperature limit was chosen because of the results of the high-temperature x-ray testing of the ettringite’s decomposition. The calculation formulae for the accelerated durability tests were derived on the basis of data regarding the decrease in compressive strength under the conditions imposed by the four above-mentioned combinations. The mineralogical composition of the binder after degradation was also described. The final degradation product was gypsum under dry conditions and monosulphate under wet conditions. The validity of the method and formula was subsequently verified by means of long-term testing. A very good correspondence between the calculated and real values was achieved. The deviation of these values did not exceed 5 %. The designed and verified method does not also consider the influence of other effects, for instance, chemical corrosion or corrosion caused by frost-thaw cycles. However, this method could be a supplementary tool applicable to the study of degradation processes and the estimation of a binder´s durability as well.
Effect of the preparation of lime putties on their properties
(Springer Nature, 2017-12-08) Soukupová, Eva; Tihlaříková, Eva; Neděla, Vilém; Rovnaníková, Pavla; Pavlík, Jaroslav
In the study of lime as the basic component of historical mortars and plasters, four lime putties prepared from various kinds of lime of various granulometry and by various ways of preparation were evaluated. The rheological properties and micro-morphologic changes, growing of calcite crystals, and rate of carbonation were monitored. The lime putty prepared from lump lime achieves the best rheological properties, yield stress 214.7Pa and plastic viscosity 2.6Pa·s. The suitability of this lime putty was checked by testing the development of calcium hydroxide and calcite crystals using scanning electron microscopy and environmental scanning electron microscopy. The disordered crystals of calcium hydroxide exhibit better carbonation resulting in the large crystals of calcite; therefore, the mortar prepared from the lump lime has the highest flexural strength and compressive strength 0.8/2.5MPa, its carbonation is the fastest and exhibits the longest durability. Also, thanks to the micro-morphological characterization of samples in their native state by means of environmental scanning electron microscopy, the new way of lime putty preparation by mixing was proven. The preparation consists in the mechanical crash of the lime particles immediately after hydration. This enables the properties of putty prepared from lump lime to be nearly reached.
Rheological and mechanical properties of lime-brick powder mortars with expanded clay aggregate
(IOP Publishing, 2018-07-16) Vyšvařil, Martin; Žižlavský, Tomáš; Rovnaníková, Pavla
The rheological behaviour and mechanical properties of lightweight lime-brick powder mortars with combined expanded clay-sand aggregates are presented in this paper. The rheological investigation included the characterization of flow properties and viscoelastic properties of the fresh mortars. Flexural and compressive strengths were determined at 7 and 28 days. These mortars are Non-Newtonian thixotropic liquids with conversion from shearthickening to shear-thinning behaviour depending on expanded clay aggregate (ECA) content. Yield stress and consistency coefficient of mortars significantly increase with decreasing amount of ECA; the mortars become more rigid and more viscous. Some of the mortars reached higher flexural strengths than similar lime mortars with metakaolin and higher compressive strengths than pure lime mortars. The lightweight lime-brick powder mortar with the mass ratio of 1:1 between gravelous sand and ECA was identified as the best among the analyzed mortars.
Study of hydration process of ternesite clinker
(IOP Publishing, 2018-07-16) Fridrichová, Marcela; Gazdič, Dominik; Dvořák, Karel; Pekárková, Jana; Kulísek, Karel
Currently ternesite, Ca5(SiO4)2SO4, is used in the cement production, is one of two key phases of calcium sulfoaluminate cement. Some investigators claim that this phase is nearly inert or very low reactive and it hydrates only after later age of hydration. In order to improve knowledge in this field, process of hydration of neat ternesite clinker under specific conditions of exposure was observed in this study. Ternesite was prepared by firing of raw meal consisting of high calcium limestone, microsilica and calcium sulfate hydrate. The resulting ternesite clinker was subsequently hydrated in four storage environments. Kinetics of hydration process was monitored in water and in environment of saturated carbonic acid, at two different temperatures of 5 and 40 °C. Mineralogical composition of hydrated samples was analyzed by X-Ray diffraction analysis (XRD) and by differential thermal analysis (DTA) in particular ages of hydration. Based on the results, it can be claimed that rate of decomposition of ternesite was related to conditions of storage. The rate of decomposition was significantly accelerated by the environment of carbonic acid and also by the elevated temperature. Presence of calcium carbonates in mineralogical forms of calcite, vaterite and aragonite, coupled with gypsum and thaumasite was identified.

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