Wyniki wyszukiwania - Biblioteka Nauki

1

Wpływ plastyfikatora na dojrzewanie betonu w obniżonych temperaturach

100%

Bajorek G.

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2000

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tom z. 32[180], cz.1

11-18

EN

Concrete work in wintertime is always connected with the risk of disturbances in the process of hydration of cement. This may later slow down the process of reaching the planned strength of concrete, or even worse, it can permanently destroy its structure. This kind of concrete may never acquire the desired strength, or it may turn out to be vulnerable to the activity of the environment. This situation can be avoided by appropriate preparation of the concrete work in conditions of lower temperature, and by using proper types of admixtures. Besides the ones, which are labelled as anti-freeze, good protection results can be achieved by using plasticizer or superplasticizer. The paper presents the results of examination of continuous footing concrete, curing in natural conditions, with long term impact of freezing temperatures. As the initial protection of this concrete, KLUTAN P plasticizer was used in the amount equal to 0,7% of the cement mass. The designed class of concrete B15, at the indicator W/C = 0,53. The concrete mixture was produced in a mixer-plant 8 kilometres away, without heating the components. Concrete works was done with the use of pump on 22 December. The temperatures in the time of concrete works and in the time of curing were shown in chart 1 and, in a graphic form, in figure 1. As a result of doubts concerning the strength of concrete obtained, destructive tests were made on samples of 50 millimetres in diameter, cut out from three chosen elements, following the scheme presented in figure 2. This way 31 results of strength of concrete were obtained - depending on their distance form the edge of the element as well as its depth. The statistical analysis confirmed the B12,5 class concrete, without visible structural defects, with small fractures in the comers. Although the desired class of concrete was not obtained, the final level was 70-80% of the designed strength. This proves that the process of hydration was considerably slowed down, but in spite of the fact that the temperature fell much below 0°Celsius, it was not stopped altogether. The results of examination, in spite of their considerable dispersion, do not show any clear tendencies suggesting the occurrence of certain sections with better or worse parameters of strength. In spite of the unfavourable conditions of preparation, building-in and curing of the concrete, it achieved quite satisfying parameters of strength and obtaining the designed class would have been possible, but in a longer period of time and in better temperature conditions. This is the result of using the plasticizer, which lowered the freezing point for water in the cement paste so much, that, it did not allow the paste to freeze. The hydration processes were slowed down, nevertheless they did proceed. Each case of raised temperature, although it never reached 0°Celsius, caused their faster action. Using the admixture resulted in more gradual curing of the concrete, than would have been the case otherwise. The conclusions of the presented research may be useful in planning protective actions for concrete work in wintertime conditions.

2

Modelowanie efektów termiczno-wilgotnościowo-mechanicznych w masywach betonowych

84%

Majewski S. , Klemczak B.

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2007

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tom z. 111

293-304

PL

W artykule krótko omówiono możliwości modelowania efektów termiczno-wilgotnościowo-mechanicznych występujących w betonowych konstrukcjach masywnych. Przedstawiono autorski model fenomenologiczny, który może być wykorzystywany w ocenie ilościowej efektów zachodzących w konstrukcjach masywnych. Omówiono również możliwości rozbudowy modelu w ramach teorii lepkoplastyczności.

EN

The different approaches to modeling the thermo-moisture-mechanical effects specific for the massive concrete structures have been briefly presented in the paper. The original phenomenological model developed to estimate these effects in the massive concrete was presented. The possibilities of further development of the authors' model have been also discussed with respect to the viscoplasticity.

3

Szybkotwardniejące betony specjalne

84%

Bastian S.

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tom R. 4, nr 5

30-33

PL

W praktyce budowlanej powstaje niekiedy konieczność intensywnego przyspieszenia twardnienia betonu w celu uzyskania w czasie kilkunastu godzin jego wystarczającej wytrzymałości eksploatacyjnej, np. przy prowadzeniu prac remontowych takich obiektów jak mosty czy nawierzchnie drogowe, bądź też dla zapewnienia wykonanym elementom zdolności transportowych, co ma miejsce w przypadku produkcji wszelkiego rodzaju prefabrykatów.

4

Warunki betonowania w obniżonych temperaturach, na przykładzie Pomorza

59%

Pawelska-Mazur M.

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tom R. 82, nr 11

25-29

PL

Dynamiczny rozwój przemysłu budowlanego i związana z tym, realizacja coraz nowocześniejszych konstrukcji żelbetowych, wymusza stosowanie coraz bardziej zaawansowanych technologii betonowania. Napięte, krótkie terminy budowy wymuszają na wykonawcach niejednokrotnie prowadzenie robót budowlanych, bez względu na panujące warunki atmosferyczne. Przy wykonywaniu betonów w ujemnych temperaturach istotne znaczenie ma zabezpieczenie świeżej mieszanki betonowej przed zamarznięciem, aby mogły przebiegać reakcje chemiczne między cementem i wodą mające decydujący wpływ na wytrzymałość betonu. Zebrane informacje prezentowane w artykule, powinny stanowić cenne wskazówki dla wykonawców, podejmujących się realizacji obiektów budowlanych przypadających na okres niskich temperatur.

EN

The dynamic development of the construction industry, and the related use of ever more advanced reinforced-concrete structures, make it necessary to apply increasingly sophisticated technologies for concreting. Short completion deadlines often mean that contractors are compelled to proceed with construction works regardless of the weather conditions. When concrete is made at below-zero temperatures, it is important to protect the fresh concrete mixture from freezing, in order to enable the continuation of the chemical reactions between cement and water which have a decisive effect on the durability of the resulting concrete. The information presented in this article provides valuable guidance for contractors carrying out construction works in periods of low temperatures.