Isıl işlem uygulamanın yüksek dozajlı beton özelliklerine etkisi

Gülseren, Hakan
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Fen Bilimleri Enstitüsü
Bu çalışmada betonun ilk yaşlardaki mukavemet gelişi mini hızlandırmada yararlanılan ısıl işlemlerin, yüksek dozajlı yani hidratasyon ısısı yüksek betonlara uygulanması durumunda, betonun ilk ve ileri yaşlardaki mukavemetine ve diğer fiziksel özelliklerine ne şekilde etkidigi araştırılmıştır. Bu çalışmada beton agregası karışımının granülometri eğrisi TS 706 şartnamesine güre (A16-B16) referans eğrileri arasında kalacak şekilde ayarlanmıştır. En büyük agrega boyutu, granülometri si ve su/çimento oranları sabit, dozajları sırasıyla 300, 350, 400, 450 ve 500 kg/m olan beş farklı bileşimde beton üretilmiştir. En düşük dosajlı beton karışımının kıvamını kuru-plastik, en yüksek dozajlı beton, karışımının kıvamını akıcı hale getiren su/çimento oranının 0.50 olduğu tesbit edilmiş ve tüm beton karışımlarında bu oran sabit tutulmuştur. Üretildikten hemen sonra 20°C'de havada bekletilen numunelere "20 C 'de saklanmış" adı verilmiştir. Uygulanan ısıl işlem çevrimlerinin ön bekleme süreleri, ısınma ve soğuma hızları, ısıl işlem sıcaklıkları, bu sıcaklıkta bekleme süreleri birbirinden tamamen farklıdır. Bunlar dan ısıl işlem sıcaklıkları 40 C olana "yumuşak çevrim", 60 C olana "ılımlı çevrim", 80°C olana "sert çevrim" adı verilmektedir. Deneyler sonucunda çalışmada elde edilen sonuçlar aşağıda özetlenmiştir. Betonlara uygulanan kürün işlem sıcaklığı arttıkça, 1 günlük numunelerin basınç mukavemeti, eğilme mukavemeti ve ultrases hızı da artmıştır. Betonun her üç özelliğine de ılımlı ve sert çevrim uygulamaları 1. günde, diğer kür uygulamalarına oranla en olumlu sonuçları vermiştir, ileri yaşlarda uygulanan Üç ısıl işlem çeşidi de, 20°C 'de saklanan betonlara oranla basınç mukavemetini düşürmezken, eğilme mukavemetine basınç mukavemetine oranla daha olumsuz etki yapmıştır. Beton ultrases hızı değerleri ise ileri yaşlarda, işlem sıcaklıkları yüksek ılımlı ve sert çevrimlerden, 20 C 'de saklanan numunelere oranla olumsuz etkilenmiştir. Su/çimento oranı sabit tutulduğundan dozaj arttıkça ısıl işlem uygulanmış ve uygulanmamış betonlarda basınç mukavemeti, eğilme mukavemeti ve ultra ses hızı olumsuz yönde etkilenmiştir. Betonun difüzyon katsayısı da dozaj arttıkça yükselmiştir. 350 dozdan sonra dozajın artmasıyla porozite değerleri ısıl işlenmiş betonlarda şahit betonlardan daha büyük çıkmıştır.
Heat treatments are used to increase the early strength of concrete. The productivity of a from can be considerably increased at comperatively little cost. In addition it makes casting in the precast works and the construction site largely independent of the weather. No modern concrete works should therefore be without a heating system for concrete hardening. Different systems are in the mean time available on the market so that an optimal solution can be found for every application. The proper heating system can thus only be selected following thorough analyses at the intendet location and comprehensive consultation. The increasing utilisation of concrete in industrial and private building projects is due in no small measure to the increase of the early strength of concrete that was achived during the past few decates. Efforts to attain increasingly higher early strengths are aimed at raising the productivity in concrete construction still further. Through the acceleration of the development of strength at an early concrete age, contunious production processes are possible in particular in the manufacture of serial parts. In this way, the major part of all concrete production activities at the conctruction site and in the precast works will become independent of seasonal temperature fluctuations. An increase of early strength of concrete can be achived through. - Utilisation of rapid hardening cements - as low as possible water/cement ratios - use of accelerators - heat application The most widely used method among these is steam curing under atmospheric pressure, in other say "Application of Heat Treatment". Steam curing causes some reduction in strength of concrete at later ages, XI while increasing the early strength. This observable fact was explored by many researchers for normal content cemented concrete. By this study» it was tried to find out the influence of steam curing on the properties of high content cemented concrete at early and later aqes. This study is presented in 5 chapters. In the first chapter general knowledge about the subject» deginations, related literature» the purpose and the necessity of the study are given. The experimental work is handled in the second chapter. The characteristics of the concrete compositions, the preportlons of concrete mixes, the methods of prepartions and curing of concretes are given in this chapter. The types of heat treatment cycles and the experimental techniques used in tests are also given in the second chapter. The test results obtained of hardened concrete are listed and necessary explications are given in the third chapter. Appraisals of test results and their discussion on the effect of the heat treatment are the subjects of the fourth chapter. The conclusions evolved from the study and proposals for further investigations are given in the last chapter. Granulation curve of aggregate mixture belong concrete samples had been regulated so as to be between of (A16-B16) curves according to T.S. 706 list of conditions. The maximum aggregate size and grading of aggregate and effective water/cement ratios were kept- constant. The cement content of mixes was chanqed from 3 3 300 kg/m up to 500 kg/m and the increasing step was 50 kq/m. The optimum water/cement ratio was obtained as 0.50 for all mixes. This ratio occured with acceptable consistency of fresh concretes. Normal portland cement (PC 400 > was used. The following different heat treatment cycles have been applied: the presteaming period-holding» preset- temperature rise period, maximum temperature period-heat treatment temperature-and cooling period and also total cycling period were varied. When presteaming period is 4 hours, heating and cooling rate is 10°C/h, maximum temperature is 40 C and the total cycle time is 20 hours that cycle has been called "Long or smooth cycle". When presteaming periods are 2 and 1 hour» heating and cooling rates are 20°C/h and 30°C/h, maximum temperatures are 60 C and 80 C and the total cycle times are 12 hours and 8 hours those cycles were called "moderate" cycle and "short-hard" cycle. Control mixes cured on the air at temperature 20 °C ;;ii and %70±5 percentage of humidity. And they were tested in order to demonstrate the relative influence of the heat treatment cycles on the properties of high content cemented concrete; with respect to normal dose concrete. The parameters of the heat treatment cycles, have been collected and shown in the Table 1. In addition the functions of the cycles which variate by the temperature and time are shown in Figure i. Table 1- Properties of Cycle Parameters * TEMPERATURE (°C) Figure 1- Applied Heat Treatment Cycles >; m On the hardened concrete specimens, the same testing program has been repeated for some experiments at the ages of 1, 28 and 90. 9 piece of 7x7x28 cm. prismatic specimens had been manufactured for each of mixes. The ultrasonic velocity was measured at the ages of 1, 28 and 90 on prismatic specimens in the same manner. After which simple beam flexure test has been performed on the same prismatic specimens, and the modified compressive strength tests where conducted on their broken pieces. Just at the age of 28, after beam flexure test has been performed, the durability and water absorbation trials were applied on the half of broken pieces. The variation of concrete properties mentioned above with the change in cement content of concrete and heat treatment applies were shown on the graphs and the evaluations and discussions were based on these graphs. Important results obtained in the study can be grouped as follows: 1) Results related to compressive strength a) The highest strength values were obtained when the short cycle applied at the first day. It had seen that when the heat treatment temperature was increased, strength has developed at the first day. b) It's known that rapid hydration may cause a reduction in the strength usually attained at later ages when steam curing-heat treatment -applied. But in this study, later age strength of heat treatment applied concrete was not lower than control concrete. The reason can be explained due to keep the specimens on the air. c) While keep constant water/cement ratio, to extend the dose of cement caused reduction in the strength of" concrete both at early and later ages. d> The most effectual results were obtained in content of 350 and 400 and by the way of applications short and moderate cycles. 2> Results related to flexural strength a> In general, the way of effecting of heat treatment siv the flexural strength of concrete is similar to that of the compressive strength. b) The 1 day relative bending strength of concrete was influenced in positive direction from heat treatment. c) While keep constant water/cement ratio s to extend the content of cement caused reduction in the flexural strenqth of concrete. d> It's also the most effectual results were obtained in content of 3S0 and 4ÖÖ and by the way of applications short and moderate cycles. 3) Results related to ultrasound velocity a> The 1 day real t ive ultrasound velocity of concrete was influenced in the same manner with comprehensive and flexural strenqth of concrete from heat treatment. b) The ultrasound had decreased as long as increase amount of cement content. c ) At the later ages the relative ultrasound velocity of concrete was influenced in negative direction by the way of hard and moderate heat treatment applications. As a conclusion to apply high temperatured heat treatments have increased the ultrasound velocity of concrete at early ages» but at the later ages it's influence became neqative. 4> Results related to capilarity a) Heat treatments and to rise up the cement content had increased to capilarity at the age of 28. B> Results related to water absorption a> Heat treatments and high volume cement had caused to rise up the water absorption.
Tez (Yüksek Lisans) -- İstanbul Teknik Üniversitesi, Fen Bilimleri Enstitüsü, 1993
Anahtar kelimeler
Beton, Isıl işlem, Concrete, Heat treatment