Uticaj različitih mineralnih dodataka na osobine samougrađujućih betona

Abstract

Over the last twenty years the two contradictory processes, connected to the durability of concrete structures, were observed: improvement of the quality of concrete mixtures, as a result of a continious growth of the knowledge in technology and of the improvement of codes and standards, led toward the potential durability of concrete structures, and a general decline of the quality of performance of the works, because of gradual reduction in the number of well skilled workers in concreting, affecting a decrease of actual durability of concrete structures. The exceed of the gap between these two mutual opposed processes can only result through a decisive increase of the industrialisation level of the construction process of works, i.e. through the elimination of the effect of „man – factor“ on the quality of performed structures. By use of Self–Compacting Concrete it is possible to achieve this aim. The durability of structures then exclusively depends on the achieved quality of concrete mixture. Developed during last decade of 20th century in Japan and continental Europe, today, Self-Compacting Concrete is applied in USA and United Kingdom as much as in the Middle East. By it’s nature, Self-Compacting Concrete does not need compaction by vibration. Compaction of this concrete, in every part, or in every corner of the formwork, including it’s hardly available parts, is done without any external forces except it’s own weight. These properties are achieved by adding superplasticizers, commonly with new Viscosity Modification Admixtures, or/and determened amount of powders. It is possible to use different mineral additions, where the use of those who are industrial by - product (like fly ash) has multiple environmental benefits. Concept of sustainable development, which beside sociological and economic aspects, include saving of energy, environment protection and preservation of an restorable natural resources, presents strategic determination of various economic sectors. In that way great contribution is expected from construction industry. Lack of natural aggregate in urban areas and increasing distance between deposits of high – quality natural aggregate and building sites, forced building contractors to analyze possibility of change of natural aggregate with recycled materials (masonry, slag, concrete, etc.). On the other hand, huge amount of old concrete exists in urban areas and it’s removal and deposition is a big ecological problem. Aim of this paper is analysis of properties and technology of Self-Compacting Concrete with different mineral additions (lime, fly ash and silica fume), natural and recycled aggregate, considering mixes without recycled aggregate, with third recycled fraction, and with second and third recycled fractions.