Jiří Brandštetr

Possibilities of the use of isoperibolic calorimetry for assessing the hydration behavior of cementitious systems

Abstract The possibilities of a new multicell isoperibolic–semiadiabatic calorimeter for the measurement of the hydration heat evolution of binders in pastes, mortars and concretes of different composition during setting and early hardening are presented. Up to 32 samples can be tested simultaneously. The measurements enable to study the influence of the main constituents as well as minor organic and inorganic additives on hydration, to estimate the start of setting and to calculate the partial heat of hydration during a given time of curing. Due to the simple construction, no special service is demanded.

The synthesis and characterization of an expansive admixture for M-type cements I. The influence of free CaO to the formation of ettringite

The hydration process of expansive admixtures for M-type of expansive or shrinkage compensation cements was studied by thermal analysis supplemented by infrared spectroscopy and X-ray diffraction. The main attention was focused on ettringite formation and on the influence of lime content upon the process. The behaviour of expansive admixture during hydration is significantly affected by the content of lime. The increasing content of lime slows down the rate of ettringite formation and supports the formation of monosulphate (AFm phase) that can be transformed afterwards into ettringite during hardening process. This process may produce better expansion effect because of better transfer of expansion stress after the setting of the paste.

Influence of superplasticizers on the course of Portland cement hydration

A multicell isoperibolic — semiadiabatic calorimeter was used for the measurement of temperature and the determination of the hydration heat evolution at earlier period of cement pastes setting and hardening. The measurements were aimed at the determination of the effect of superplasticizers (SPs) on the course of the Portland cement hydration. Commercial polycarboxylate SP was added to the mixtures and the heat effect was measured. With the increasing content of SP, the hydration temperature increased up to a certain value and then decreased. In case of a sufficient amount of water in the mixture to achieve complete hydration of cement, samples with the highest values of the maximum hydration temperature reached the highest values of the released total heat. If there is not a sufficient amount of water to achieve complete hydration, the samples with the highest values of the maximum hydration temperature reach the lowest values of the released total heat.

Calorimetric determination of the effect of additives on cement hydration process

Possibilities of a multicell isoperibolic-semiadiabatic calorimeter application for the measurement of hydration heat and maximum temperature reached in mixtures of various compositions during their setting and early stages of hardening are presented. Measurements were aimed to determine the impact of selected components’ content on the course of ordinary Portland cement (OPC) hydration. The following components were selected for the determination of the hydration behaviour in mixtures: very finely ground granulated blast furnace slag (GBFS), silica fume (microsilica, SF), finely ground quartz sand (FGQ), and calcined bauxite (CB). A commercial polycarboxylate type superplasticizer was also added to the selected mixtures. All maximum temperatures measured for selected mineral components were lower than that reached for cement. The maximum temperature increased with the decreasing amount of components in the mixture for all components except for silica fume. For all components, except for CB, the values of total released heat were higher than those for pure Portland cement samples.

Investigation of Subterranean Termites Nest Material Composition, Structure and Properties

Termites (Isoptera1) are colourless or white insect sometimes called “white ants2” but they are intimate relatives of cockroaches. The organization of termite community definitely belongs to the most complicated in the nature hence termites are described as the eusocial3 insect. Termites are distributed all over the world from the 47° Northern latitude to the 47° Southern latitude, but they are extremely abundant in the tropical rainforest4. Until today there are recognized about 3 000 termite species in the 9 families but two of them became extinct (Fig. 1). Only species of the genera Archotermopsis, Hodotermopsis, Zootermopsis and Reticulitermes can be found also in the temperature regions. Only two species5 are native of the temperature region of Europe. Besides the known kinds of termites an existence of other more than 1000 species is supposed [1-6]. The foundations of thermite taxonomy were established by Holmgren [7-9]. The following studies provided by Snyder [10], Grasse [11] and Emerson [12] define seven families of termites which are today generally accepted. Many of the conventional phylogenetic reconstructions

The synthesis and characterisation of an expansive additive for M-type cements

The expansion effect of laboratory-prepared expansive additives for M-type expansive cement was investigated at the early stage of hydration by the multicell isoperibolic calorimeter and volumetric technique based on Archimedes’ principle. The relative volume changes and heat released during hydration are strongly affected by the content of lime in the expansive additive due to the influence of CaO on the kinetics and mechanism of formation of ettringite. The increasing content of lime favours the formation of monosulphate and its later transformation to ettringite generating expansion stress. The effect of expansive additive on the behaviour of mortar samples was measured as linear elongation of test blocks using Graf-Kaufman dilatometer. Lower or higher content of lime in expansion additive slightly decreases the 7th-day compressive and flexural strength of samples while this effect is negligible for expansive additive with nominal composition of ettringite.

The synthesis and characterization of an expansive additive for M-type cements Part III. the influence of gypsum and water-to-cement ratio on the formation of ettringite

The expansive admixtures for M-type expansive cements were prepared by mixing of aluminate cement and gypsum. Hydrated samples were investigated by thermal analysis, infrared spectroscopy, and scanning electron microscopy. The main attention was focused on the formation of ettringite and the influence of water-to-cement and water-to-gypsum ratio on the process. The results of thermal analysis and infrared spectroscopy indicate high water-to-cement ratio and high water-to-gypsum ratio as the most proper condition for the formation of ettringite. It was observed that the value of water-to-gypsum ratio close to 1.76 supported the formation of monosulfate phase in the expansive mixture. The SEM indicates an oriented crystal growth of ettringite crystals that produces the expansive stresses.

Activation of Bentonite and Talc by Acetic Acid as a Carbonation Feedstock for Mineral Storage of CO2

The average global temperature has been slightly increasing by 0.76 °C over last 150 years. If the current state will continue, average Earth temperature will increase at the end of this century for about 1.1 – 6.3 °C according to applied emission scenario. Main reason of the observed global warming is the increasing contents of greenhouse gases (GHG), such as carbon dioxide (CO2), methane (CH4) a nitrous oxide (NO2), in the Earth atmosphere. The most important greenhouse gas is CO2. Carbon dioxide is considering as responsible for about two-third of the enhanced “greenhouse effect”. Its atmospheric concentration has risen from the pre-industrial levels of 280 ppm to 380 ppm in 2005. Human emissions of greenhouse gases are very likely responsible for global warming of the planet surface (IPCC, 2007). The increasing carbon dioxide content in the atmosphere and its long-term effect on the climate has led to increasing interest and research of the possibilities of capture, utilization and long-term storage of carbon dioxide (Yang at al., 2008; Jiang, 2011) Fossil fuels have been used as the world’s primary source of energy upon over the 20th century and this trend is expected to continue throughout the 21st century (Yang at al., 2008; Maroto-Valer at al., 2005). There is a direct link between emissions of carbon dioxide (Ce), human population (P), economic development that is indicated by gross domestic product (GPD), production of energy (E), amount of carbon-based fuels used for production of energy (C) and CO2 sinks (SCO2):

Recent development in thermochemical solution analysis

Abstract A review of techniques used in thermochemical analysis (TCHA) is given with regard to the available instruments. A survey, of versatile applications of this mode of calorimetry in solutions (measuring of heats of liquid-liquid, or solid-liquid reactions) in analytical, physical, organic etc. chemistry is outlined.