Efficiency study of superplasticizers to ensure durability of concrete placed by pump.

Production of contemporary, high-performance concrete is almost impossible without chemical admixtures, particularly when plastic concrete is placed by pump or when adequate consistency has to be kept from manufacturing to placing of concrete in most environmental conditions. This was the starting point of my diploma work: to choose a chemical admixture - superplasticizer that will be sufficiently effective, practical to use and compatible with available basic materials. I obtained the basic proportion of concrete mix in the laboratory of a concrete plant, where I carried out experiments and, according to the results obtained, developed and adapted it to each type of superplasticizer. I made 59 different mix proportions, with 11 different superplasticizers. I carried out tests of consistency with most of the mixtures immediately after mixing of the concrete, as well as half an hour and an hour later. Then I made standard concrete cubes for compressive strength determination at the age of 1, 3, 7 and 28 days. In the diploma work I describe in detail properties of concrete mixtures made by the best 4 superplasticizers. As it turned out, the influence of used superplasticizers on properties of concrete mixtures differs substantially. Some require a large quantity of fine particles in the mixture (I used limestone filler), others cause a large percentage of air bubbles in fresh concrete. I found out that it is necessary to start from the requirements regarding the properties of concrete in fresh and hardened state and to adjust the composition of the concrete to meet the requirements. It also means selection of adequate superplasticizer, which has to be compatible with the basic materials for concrete that are available in concrete plant. I