Uçucu kül inceliğinin yüksek dozajlı betonun özelliklerine etkisi

Abstract

Bu çalışmada, Seyitömer Termik Santrah'na ait üç farklı incelikteki uçucu kül kullanılarak, uçucu kül inceliğinin beton özelliklerine olan etkisi incelenmiştir. Üç farklı incelikteki uçucu kül, ağırlıkça üç farklı ikame oranında (% 10, % 20 ve % 30) PÇ 32.5 yerine ikame edilerek, 375 kg/m3 toplam bağlayıcı miktarına sahip, çökme hunisinde 12±1 cm. çökme yapabilecek şekilde sabit işlenebilirliği olan, herhangi bir katkı içermeyen betonlar üretilmiştir. Üretilen 10 betondan biri şahit, diğer 9 tanesi ise uçucu küllü betondur. Üretilen betonlar, 7x7x28 cm. ebadındaki prizmatik kalıplara dökülmüştür. Her seride, normal kür görmek üzere 8 adet, 20+2 "C'deki klima odasında, varil içindeki deniz suyunda haftalık ıslanma-kuruma çevrimine tabi tutmak amacıyla da 4 adet, her seride 12 ve toplam olarak 120 adet bu numunelerden üretilmiştir. Normal kür görmüş betonlarda, 28, 56 ve 91. günde ultrases hızı ölçülmüş, 3, 7, 28 ve 91 günde eğilme ve basınç deneyleri, 28 ve 91 günde ise kılcallık deneyleri yapılmıştır. Deniz ortamındaki numuneler üzerinde, 28 ve 56 günde ultrases hızı ölçülmüş, 28 ve 91 günde ise eğilme ve basınç deneyleri yapılmıştır. Yapılan deneyler neticesinde şu sonuçlara varılmıştır: TS 639'da yer alan puzolanik aktivite testi, öngördüğü su miktarı bakımından uçucu küllü harçların kalıplara homojen olarak yerleştirilmesine imkan vermediğinden, bu test açısından yetersiz görülmüştür. Bunun yerine, eşit kıvam için karışım hazırlanmasının daha uygun olacağı düşünülmektedir. İnce ve orta incelikte kül içeren betonlar, düşük ikame oranlarında, hem dayanım hem de kılcallık açısından şahite yakın, hatta aşan bir performans göstermişlerdir.

According to ACI 116R, fly ash is 'the finely divided residue resulting from the combustion of ground ör powdered coal that is transported from the fire box through the boiler by flue gases'. Fly ash possesses pozzolanic properties similar to naturally occurring pozzolanic materials, primarily of volcanic ör sedimentary origin. Fly ash is classified as an artificial pozzolan. Pozzolan is a 'siliceous ör siliceous and aluminious material, which in itself possesses little ör no cementitious value but will, in finely divided form and in the presence of moisture, chemically react with calcium hydroxide at ordinary temperatures to form compounds possessing cementitious properties'. Pozzolans, such as fly ash, are used as ingredients in portland cement concrete. ASTM 618 defines two classes of fly ash - Class F and Class C. Class F fly ash is usually produced by burning sub-bituminious coal ör lignite. The separation fly ash into two classes reflects difference in composition which affects cementitious and pozzolanic properties. Class C fly ash usually has cementitious properties in addition to pozzolanic properties, while Class F fly ash is rarely cementitious when mixed with water alone. Fly ash is used in concrete as a separately batched material and as an ingredient in blended cement. Fly ash is used in concrete for reasons including economics, improvements and reduction in temperature rise in fresh concrete, workability, and contribution to durability and strength in hardened concrete. When fly ash concrete is properly cured, fly ash reaction products help fiil in the spaces between hydrating cement particles in the cement paste fraction of the concrete, thus lovvering its permeability to water and aggressive chemicals. The slower reaction rate of many fly ashes is a real help in limiting the amount of early heat generation and the detrimental early temperature rise in massive structures. Using fly ash in concrete saves energy by reducing the amount of xiit/ portland cement (an energy intensive product) required to achieve the desired concrete properties. in Türkiye, 15 millions of tones of fly ash are obtained from coal-fired power plants annually. The production of cement, however is about 30-35 millions of tones. Fly ash is foirmed great potential whether in partially use instead of cement ör in the production of cement. Unfortunately, use of fly ash is nearly at zero level with respect to developed countries. Although Türkiye is not a wealthy country, not to use this potential is a big deficient. However, the concrete industry which is developing continuously has sufficient accumulation for use of fly ash. The necessary thing is to determine perfectly the properties of fly ash and the properties that arise from its use and to maintain their properties. in order to verify this, a good labor between university, concrete industry and other official and private associations ör a center that put fonvard studies including waste material, ete. is required urgently. in this study, the effect of fineness of fly ash has been investigated on the properties of concrete with high cementitious content. Having three different finenesses of fly ash corresponding to Seyitömer coal-fired power plants were used in experimental research. By using meşe ashes that have three different replacement ratios by weight instead of ordinary portland cement, 10 series of concrete has been produced. Cementitious content and amount of workability are kept constant at 375 kg/m3 and 12±1 cm in the production of concrete, respectively. No admixture was used. Some part of produced concretes was subjected to normal cure and the other part to weekly wetting-drying cycle in sea water kept in barrel waiting in climate room which has a temperature of 20±2 °C. Pulse velocities, flexural and compressive strengths and capillarity coefficients of concretes subjected to normal cure were determined at 28 th, 56 th, and 91 m days; and 3 rd, 7 th, 28 th, and 91 th days; and 28 th and 91 th days, respectively. Pulse velocities and flexural and compressive strengths of concretes subjected to wetting-drying cycle in sea water were determined at 28 th, 56 th and 91 th days; and 28 th and 91 th days, respectively. The mix proportions of produced concretes, the properties of fresh concrete and the result of experiments mentioned above are presented in tables just below. xiii t/î CD O e o.o. o 3 O t- O, <+, o a> O. o t- eu.s O § O C c/î. e O '?E o a. o x XIV XV XVI The conclusions derived from results of experiments can be summarized as follows: - Although Turkish fly ashes generally increase water demand of mortars, pozzolanic activity test carried out according to TS 639 reduces water amount for fly ash mortar compared to control mortar. T S 639 is inconvenient from the point of view of pozzolanic activity test. - As the replacement ratio and coarseness increase, water amount that is necessary for equal workability in concrete increases for used fly ashes. This phenomenon can be explained in such a way that as the fly ash gets coarser, it looses its spherical form and becomes rough and porous. - Concrete containing fine and medium fly ash shows good performance from the point of view of whether mechanical strength and capillarity at the low replacement ratios.