Některé problémy při aplikaci chemických modifikujících přísad do betonu

Some problems arising during the application of the chemical modifying admixtures

článek ve sborníku ve WoS nebo Scopus

čeština

Massive introduction of chemical modifying additives in the concrete production in last decades in not accompanied by comfortable amount of necessary information. The chemical composition and effect of the admixtures for the same purpose is often principally different, the compatibility with the other constituents of the concrete mixture is poorly declared or was not tested, the optimal doses for the purpose and binder in question are not always known or maintained. The most important chemical admixtures are superplasticizers, the introduction of which improved markedly the properties of tailored fresh and/or hardened concretes, but their utilization is very often not professional. The producers do not publish the composition of their chemical admixtures, sometimes these products are mixtures of the more chemicals, which makes the research as well as the tests of compatibility difficult. To intensify the grinding of cement, different organic grinding aids are added, which are adsorbed on the surface of the grains preventing agglomeration during grinding, but consequently they influence in different way the robustness and compatibility of used superplasticizer, which are at present indispensable admixture in concrete production. The producers bring every year many novel products, which - if used properly - can improve markedly not only the properties of the tailored composites prepared, but also a financial effect. Very important, but rather insufficient thus far are the recommendations on the type of cement (binder) together with mineral and chemical admixtures for the given purpose, the composition of the tailored concrete mixture is not always optimized, the importance of the consequence of adding the separate constituents into the mixer is poorly tested and maintained. The published results of application research do not often reach the proper specialists and users. The best opprortunity to get essential and indispensable information are different workshops and conferences. In this presentation, some comments refer to most common problems in the chemistry and effect of reactions bringing about various complications in setting and hardening of tailored high-performance concretes of different composition and admixtures and the furure trends in the development of novel composites for the building industry.

BRANDŠTETR, J.; KRÁTKÝ, J.; SZKLORZOVÁ, H.

12. 5. 2004

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