The use of calorimetry for the tests of some mineral binders

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Inorganic binders, especially concrete, are the most widely used man-made material. The need for low cost, high durability, high strength, low specific weight, low hydration heat etc. leads to the development and utilization of inorganic or organic chemical modifying admixtures, such as air entraining agents, superplasticizers, accelerating and retarding agents etc. At present, more information on the properties, reactivity and dosage of these additives are urgently needed. The broad range of possible chemical composition of the admixtures evokes cross-compatibility problem. An instrument, which can be used for rapid simultaneous tests of several samples, the multi-cell isoperibolic calorimeter was developed on the Institute of Materials Chemistry, Faculty of Chemistry, Brno University of Technology. Isoparibolic calorimeter is convenient to study the influence of the main constituents as well as minor organic and inorganic admixtures, to estimate the start of setting and to calculate the partial heat of hydration evolved during the time of setting. The instrument is based on the measurement board plugged into the computer. Maximum number of samples measured is 32. The values measured are integral heats covering all the reactions proceeding during the setting and hardening of the pastes (mixtures): heat of wetting, heat of solvation, hydration, precipitation or crystallization, reactions of the new hydrates formed in the mixture etc. In spite of this versatility, calorimetry provides data indispensable in characterizing the chemical behaviour of cement, lime and other binders, especially in their mixtures with different constituents and additives. The values of hydration heats of individual clinker minerals are fundamental data in the thermochemistry of clinkers and cements. The effect of many main constituents of binders, such as slag, fly ash, silica fume, pozzolans etc. and minor additives studied by calorimetry contribute considerably to the optimisation of the composition of mortars and concretes produced form different, often unusual raw materials allowing to prepare tailored composites according to demand of the user.

KRÁTKÝ, J.; BRANDŠTETR, J.; HAVLICA, J.; HOLEŠINSKÝ, R.

13. 8. 2001

University of Miskolc

Miskolc

9636614806