Wiesława Nocuń-Wczelik

Application of calorimetry in studies of the immobilization of heavy metals in cementitious materials

Cementitious systems based on blends of normal portland cement with different materials are used for the treatment and conditioning of toxic and hazardous wastes. The addition of waste material may interfere with the hydration reaction in the cement matrix and consequently with the setting and with hardening process. Some of the waste materials accelerate the hydration process, others act as set retarders. The progress of hydration can be monitored by heat evolution measurements and the calorimetric results are considered as indicators of the degree of hydration. In this study microcalorimetry was used to evaluate the heat output during the hydration of cement and of blends of cement and blast furnace slag treated with solutions of heavy metals.

Studies of cementitious systems with new generation by-products from fluidised bed combustion

The rate of heat evolution as well as total heat output are strongly affected by other components of hydrating mixture, apart from neat portland cement, such as slag, fly ash and other industrial by-products; among them the wastes from fluidised bed combustion (FBC) has been taken into account recently. In this study the calorimeter was applied to follow the early hydration of cements produced with these materials. They interact with cement paste in a few ways: as set controlling agent and as active pozzolanic admixtures. Thus the rate of heat evolution/hydration is modified, depending on the composition of clinker and percentage of waste in the mixture. After the series of measurements for clinker-waste mixture hydrated systems also some ‘model’ mixtures were investigated to separate the effects from particular waste components.

Application of calorimetry as a main tool in evaluation of the effect of carbonate additives on cement hydration

Calorimetry was applied to follow the hydration in the Portland cement–dolomite–limestone mixtures. In the experiments the limestone additive of various fineness (standard component of various common cements), as well as the dolomite additive (not a standard component) were used. The rate of hydration versus time for common cements reflects the proper setting and early hardening during the first days after mixing with water (two or three peaks and the induction period between them). The aim of measurements presented in this work was to show the course of heat evolution curve and the heat evolved values, equivalent to the acceleration/retardation of hydration, in case of the pastes produced from Portland cement and the carbonate additives mixed in variable proportions, as well as to verify the results by other methods. The rate of heat evolution accompanying cement paste hydration, total heat evolved, conductivity of hydrating suspension and rheological (flow) properties versus time are modified by the fine grained carbonate additives. This is due to the hypothetical nucleating effect of limestone and dolomite.

Calorimetry and other methods in the studies of expansive cement hydrating mixtures

In this study, the calorimeter was applied to follow the hydration of special cement mixtures exhibiting expansion or shrinkage compensation. The shrinkage-less and expansive binders were produced by mixing of Portland cement with an expansive additive produced by sintering and composed of calcium sulfoaluminate (yeelimite), calcium sulfate (anhydrite) and lime. The studies were focused on the synthesis of this aluminate—sulfate—lime additive (temperature of burning process as a parameter controlling the relative activity of components) from the materials being the by products and subsequently on the mixture proportions to ensure the hydration process resulting in non-shrinkage or expansion effect. In the experiments the proportions of expansive mixture and cementitious materials were variable. The investigations with aim to find the relationship between the volume changes and composition of initial mixtures in cement pastes and mortars (with sand) were also carried out. The phase composition and microstructure of products were characterized. The expansive additive in the environment of hydrating cement transforms into ettringite and gives an increase of volume when the plastic material transforms to the more rigid matter but before the ultimate hardening takes place. Proper, moderate setting and hardening in strongly modified mixtures is achieved when the calorimetric curve corresponding to the heat evolution on hydration is analogous to that for the basic Portland cement. The rate of heat evolution data are well compatible with the other results related to the other methods of hydration kinetics assessment (e.g. chemical shrinkage) and discussed in terms of the phase composition of hydration products.

Calorimetry in testing waste materials from the brown coal combustion

The calorimetric measurements were applied in testing the wastes collected from different furnaces in electric power plants as materials to be used in civil engineering. The fly ash materials were collected from two power stations based on different brown coal deposits and working with conventional and fluidized bed installation. The reactivity of high calcium fly ash from sub-bituminous coal combustion has been proved in calorimetric, conductometric, chemical shrinkage, and rheological measurements before their practical implementation on larger scale. Highly soluble components of fly ash contribute to the hydration products and structure formation, followed by setting and hardening of fly ash–cement mixture. These results have been the base of research project aimed in the innovative solutions dealing with the management of deposits of wastes generated as a result of coal combustion. The standardization and potential use on larger scale of these materials, necessary from the environmental point of view, seems to be the question of nearest future.

Production and use of by-product gypsum in the construction industry

Publisher Summary This chapter focuses on the production and the use of by-product gypsum in the construction industry. There are two groups of gypsum by-products that have been identified: chemical gypsum and desulphogypsum. The first by-product is produced by chemical processing and the second originates from the flue gas desulphurization installations in power stations. The compositions of the by-products differ substantially, primarily with respect to impurity content. Chemical gypsums are contaminated with the raw materials used in particular technologies, as well as the products of chemical processes. These contaminants affect the properties of by-product gypsum and subsequently formed binders. The desulphogypsum produced by the wet process is highly pure calcium sulphate dihydrate. Some impurities do not influence the reactions in the CaSO4–H2O system. However, if the SO2 sorbing agent is introduced to the flue gas stream without de-dusting or directly to the furnace, complex desulphurization products are formed.

The studies of the effect of sulfates added as chromium(VI) reducers in portland cement

The calorimetric measurements were applied in testing the effect of some sulfates, used as Cr(VI) reducers in cement, as setting and hardening modifiers. The iron(II) sulfate is most commonly added as Cr reducer to cement on grinding. This was taken as a reference in the studies of the other potential chromium reducers, such as tin(II) and manganese(II) sulfates on cement hydration. The high percentage of admixtures was reduced steadily from very high overdosage—to find the possible effect of non-homogeneity resulted from the hygroscopic character of compounds used and to detect the possible products which can be formed—to relatively small quantity, as used in practice. The progress of cement hydration was investigated by calorimetry and chemical shrinkage measurements. The rheological properties of cement paste admixtured with iron, tin, and manganese sulfates were investigated, as well as the phase composition of hydrated pastes was studies by XRD. The compressive strength of the small paste cylinders was measured. Finally, the hydrated samples were subjected to the SEM observations. The tin sulfate showed the strongest retarding action as it was proved by calorimetry and chemical shrinkage data, as well as by strength and rheological measurements; however, at small quantities, this compound has a positive impact on setting and hardening. The detrimental effect of overdosed Mn and Fe sulfates due first of all to the formation of higher amount of ettringite at very early age was found. This can be proved additionally by the change of rheological parameters—higher yield stress and viscosity.

Differential calorimetry as a tool in the studies of cement hydration kinetics with sulphate and nitrate solutions

The calorimetric measurements together with the experiments aimed in the characterization of pore solution and the other analyses relating to the interaction of cement paste with sulphate and nitrate solutions of various concentrations are reported. These salts modify the rate of cement hydration at early age. In the presence of sulphates, the formation of some well-defined calcium sulphates or calcium sulphoaluminates can be found. In case of nitrates, there are no additional products—the nitrate compounds are well soluble, and they do not crystallize in cement systems. However, one can observe that the concentration of ions in the liquid phase is modified and the properties of hydration product are changed, as the formation of products from the liquid phase is disturbed.

The reaction of calcium aluminates with some basic solutions

Abstract The calcium aluminates hydration in water and Na 2 CO 3 solutions have been studied using the microcalorimetry, DTA, TG and XRD methods. The composition of the liquid and solid phase products have been thereby established.