Puzolanlı betonların ileri yaştaki mukavemetlerinin önceden belirlenmesi
Predetermination of the further age strength of the concrete with puzzolana
Yazar: ABDURRAHİM ADNAN KULAKOĞLU
Danışman: DOÇ. DR. HASAN YILDIRIM
İstanbul Teknik Üniversitesi / Fen Bilimleri Enstitüsü / İnşaat Mühendisliği Ana Bilim Dalı / Yapı Mühendisliği Bilim Dalı
Derece: Yüksek Lisans, 2017
Konu: İnşaat Mühendisliği = Civil Engineering

Özet:
Son zamanlarda inşaat sektörü çok hızlı gelişmektedir. Bunun yanında zaman kavramı büyük önem kazanmıştır. Planlama inşaat sektörünün vazgeçilmez bir parçası olmuştur. Yapıların zamanında teslimi firmaların prestiji ve müşterilerin mağdur olmaması açısından  büyük  önem  taşımaktadır. Bu durumdan dolayı üretim hızının yavaşlamaması için A'dan Z'ye her konuda pratik ve bununla birlikte güvenilir adımlar atılması gerekmektedir. Zaman önemli olduğu için inşaatın önemli malzemelerinden betonun daha ileri günlerde alacağı mukavemeti tahmin etmek önem kazanmaktadır. 28 günlük basınç mukavemeti süresi yaklaşık 1 aylık süredir. Barajlarda dökülen RCC (SSB, silindir ile sıkıştırılmış beton) betonlarında ise bu süre 270 gündür. Bu süreler inşaat işleri için azımsanmayacak kadar  uzundur. Oluşabilecek beton kalitesi riskini daha önceden öğrenmek çok yararlı olacaktır. Çünkü örnek verilecek olursa: Sektörde tünel kalıp sistemi ile yapılan inşaatlarda yaklaşık olarak 1,5 günde 1 kat betonu dökülmektedir. 28 günde bu durum yaklaşık olarak 18 kat beton imalatı demektir. Beton mukavemetinin istenilen düzeyden düşük olması durumunda 18 kat betonu dökülmüş olacaktır. Bu durum maliyet ve zaman anlamında çok büyük sıkıntılara ve geri dönüşlere sebebiyet verecektir. Bu süreyi kısaltmak için farklı özellikteki betonlarda pratik bir yaklaşıma ihtiyaç duyulmaktadır. Bu yaklaşım 'Hızlandırılmış Kür' olarak ifade edilir. Bu metod ile bu süre  60 ℃' de 7 günlere, 90 ℃'de ise 14 günlere indirilmiştir.
Hızlandırılmış kür; puzolanlı betonlara 20 derecedeki kür ortamından farklı olarak sıcak kür ortamında ısı sağlayarak betona erken dayanım kazandıran deneysel yöntemin adıdır. Buradaki amaç 28 günlük basınç dayanımını daha erken tahmin etmektir.
Hızlandırılmış kür çeşitleri;
•	Sıcak kür ortamında yapılan (Havada veya suda yapılan).
•	Kapalı boru içindeki sıcak buhar yada suyun taşıma yada ışıma yoluyla betonu ısıtması.
•	Beton yüzeyinin dış ortamdan izole edilerek elektrik kabloları ile ısıtılması.
Deneylerimizde çeşitli dozajlarda saf çimentolu, yüksek fırın cürüflu ve uçucu küllü betonlar kullanıldı. Bu betonlar dış ortam, 20 derecelik kür ortamı, 90 derecelik sıcak kür ortamı ve literatürden farklı olarak 60 derecelik sıcak kür ortamında 7, 14, 28 ve 45 günlerde bekletildi. Bu günlerin sonunda betonlar beton test cihazında kırılarak basınç dayanımları ölçüldü.
Deneylerin sonucunda saf çimentolu betonlarda hızlandırılmış kür ortamında erken dayanım elde edilemezken, 90 derecedeki ortamda 10-14. günlerde, 60 derecedeki ortamda ise 7. günlerde 28 günlük kür ortamındaki basınç dayanımları elde edilmiştir. Literatür çalışmasından farklı olarak 60 derecede 28 günlük beton dayanımı 90 dereceye göre daha erken elde edilerek, 90 derecelik ortama göre hem daha az enerji kullanılmış hemde daha kısa sürede sonuç elde edilmiştir.

Abstract:
Compressive strength of concrete mainly depends on the composition, size of the components, water content ratio, curing conditions etc. The 28 days strength is usually taken as reference strength. So, the strength of concrete in construction works is determined at its 28 days compressive strength.  To find this, a moist curing of concrete specimen for 28 days is required. 
The 28 days of waiting time is too long period for any corrective measure in case the strength is not desirable. That is after 28 days, by the time the quality of concrete is found to be not sufficient, the concrete would have hardened significantly and might be buried by subsequent construction. This makes the replacement of concrete mass of sub-quality concrete very difficult, costly and time consuming. Suppose if the concrete is of greater strength than the required, the uneconomical mix is just a waste of costly material. These indicate a necessity for finding the 28 days characteristic strength for real good quality control. Hence, for better quality control, an accelerated concrete curing procedure is needed which facilitates identifying the 28 days strength in 7 days. Hence, accelerated curing techniques  are becoming important. For economical construction, the 28 days strength is required well in advance and accelerated curing techniques are helpful to some extent. In the conventional accelerated curing, conduction of heat takes place from surface to the core of the concrete specimen and hence there exist a temperature gradient, leading to thermal stress in concrete. The concrete cubes were cured with the oven after 3, 7, 4, 28, 45 days. The compressive strength developed after the accelerated curing is compared with the 28 days strength estimated with the  usual procedure. The results obtained were suitably plotted as graphs so that the graphs can be used to estimate the 28 days strength from the early strength obtained by accelerated curing.
Recently, the construction sector has developed fast. In addition,The time concept gained the big importance. Planning has been essential part of the construction sector. The completion of the buildings are crucial with regard to the prestige of the companies and not to be wronged of the customers. Thus, we need to take a practical and confidential steps from A to Z. As the time is important, the estimation of the compressive strength of the concrete, which is one of the important materials of the construction has gained great importance. We are going to mention about the compressive strength of the concrete at 28 days. This duration approximately takes 1 month that is very long time for the site works. As it comes to RCC (SSB) concrete, this duration is average 270 days. It will be useful to know in advance the quality of concrete. For instance, we are pooring 1 floor concrete in a 1,5 days. In 28 days it means average 18 floors. In case of  the compression strength of concrete is lower, 18 floor has already been poured when we got the results. So, that will cause return period and big problems with regard to the cost and time. We need to take the pratical approach to minimize that time for the concrete having different charecteristics. This approach called Accelerated Curing. In that method we can reduce the time to 7 days at 60 °C and 14 days at 90 °C.

Accelerated curing is the name of the experimental method which gives heat to the pozzolanic concrete in the hot curing environment unlike the 20 degree curing environment and gives the concrete early strength earlier than 28 days. This purpose is to estimate the 28 day compressive strength earlier.
Three heating methods are commonly used to accelerate curing:
•	Discharging steam or hot air or water directly into the curing environment puts the heating (In the hot air or water).
•	Enclosing steam or hot water in pipes heats the concrete by convection and radiation.
•	Attaching electrical resistance wires to the forms and covering them with insulation
In summary , we will try to show by testing different concrete, whether we catch that time or not in acceletared curing condition (60°C, 90 °C). By doing that tests,we will add the Blast Furnace Slag and Fly Ashes seperately to the concrete. Third test will be without puzzolans to compare them with eachother. 
Fly ash is a fine powder which is a byproduct from burning pulverized coal in electric generation power plants. Fly ash is a pozzolan, a substance containing aluminous and siliceous material that forms cement in the presence of water. When mixed with lime and water it forms a compound similar to Portland cement. Typically, Class F fly ash is used at dosages of 15 to 25 percent by mass of cementitious material, and Class C fly ash at 15 to 40 percent. 
Blast furnace slag is formed during the production of hot metal by thermo-chemical reduction in a blast furnace. During this continuous process, iron ore or pellets as well as fluxes (lime[stone] and/or dolomite) are heated under reducing conditions in the presence of heated air. Coke and other reducing agents (e.g. injected coal) are combusted to produce carbon monoxide which reduces the iron ore or pellets to liquid hot metal. Granulated blast furnace slag exhibits cementitious properties and is thus used as hydraulic binder for cement, concrete, mortar and grout. For this purposes, it is ground, separately or together with Portland cement clinker and calcium sulphate and is referred to as ground granulated blastfurnace slag.
In these experiments ,If we add these puzzolans ,we will obtain 28 days compressive strength of the concrete by accelerated methods between 7 and 14 days. If we test the concrete without puzzolans by accelerated methods, we can not get the 28 days compressive strength of concrete in 14 days. So, we have to use fly ashes or blast furnace slags in our experiments to catch the true results.
As a result of our experiments, it is not possible to obtain early strength in accelerated curing environment in pure cementitious concrete at 90 ° and 60 °. In the 60. degree on the 7th day, the compressive strengths of the 28 day curing environment were obtained. In the 90. degree on the 14. day, the compressive strengths of the 28 day curing environment were obtained. Unlike the literature study, 28 day concrete strength at 60 degree was obtained earlier than 90 degree, and less energy was used and shorter time was obtained compared to 90 degree hot curing environment.