Yüksek fırın cürufu içeren betonlarda sıcak kür yöntemi ile erken dayanım elde edilmesi
Obtaining early strength of blast furnace slag concretes by hot curing method
Yazar: MUHAMMET TEKİNGÜNDÜZ
Danışman: DOÇ. DR. HASAN YILDIRIM
İstanbul Teknik Üniversitesi / Lisansüstü Eğitim Enstitüsü / İnşaat Mühendisliği Ana Bilim Dalı / Yapı Mühendisliği Bilim Dalı
Derece: Yüksek Lisans, 2021
Konu: İnşaat Mühendisliği = Civil Engineering

Özet:
Beton temel olarak çimento, su ve agregadan oluşan bir yapı malzemesi olup
Türkiye'de kullanılan en yaygın yapı malzemesidir. Bunun sebeplerinden bazıları,
düşük maliyetli olması, bileşenlerinin kolay bulunabilirliği, taze haldeyken istenilen
şeklin verilmesi ve yüksek basınç danayımı şeklinde sıralanabilir. Artan inşaat
sektöründeki faaliyetlerin karşılanmasında önemli bir rol sahibi olan beton yapı
malzemesinden temel olarak üç ana özellik beklenmektedir. Bunlar işlenebilirlik,
dayanım ve çevresel etkilere karşı dayanıklılıktır.
Bu tez çalışmasında betonun temel özelliklerinden olan basınç dayanımı konusu ve
dayanıma etki eden kür koşulları ele alınacaktır. Betonun en önemli mekanik
özelliklerinden olan basınç dayanımı, son yıllardaki teknolojideki gelişmeler ve inşaat
sektöründeki artan talepler sonrasında yaklaşık 250 MPa'ı aşacak şekilde beton
tasarımları üretilmesini sağlamıştır. Buna ek olarak, yürütülen projelerideki zaman
darlığından ötürü bu yüksek dayanımlara kısa sürede ulaşmak önem kazanmıştır.
Artan inşaat sektöründeki taleplerin karşılanması için betonda dayanım kazanma
hızına etki eden kür yöntemini geliştirme çalışmaları yapılmaktadır. Bu çalışmalar
arasında en yaygın olan uygulama sıcak kür uygulamasıdır. Beton basınç dayanımının
planlanan dayanıma erken ulaşması, inşaat projelerinin kısa sürede tamamlanmasına,
kalıp söküm zamanlarının kısalmasına ve bu sayede maliyet ve işçilik bakımından da
fayda sağlanacağı görülmektedir. Buna ek olarak bu yöntemle birlikte prefabrik yapı
üretiminde de proje zamanına ek olarak üretimin gerekli dayanımı kazanana kadar
bekletilmesi gereken depolama yeri konusunda kolaylık sağlanacaktır. Beton priz
süresinin kısalması kalıp çıkarma süresini kısalttığı gibi soğuk hava şartlarında da
betonun istenilen dayanıma sahip olmasını sağlamaktadır.
Yaygın olarak bilinen betondaki standart kür uygulamasında 20+2°C'de kirece
doygun suda bekletilme uygulaması yapılmaktadır. Bu standart uygulama sonrasında
betonun 28.günde basınç dayanımı ölçülmektedir. Bu tez çalışmasında bu yönteme ek
olarak üretilen numunelerin laboratuvar koşullarında hava kürü ve bunun yanında
tezin asıl konusu olan ve erken dayanım alınması amacı ile uygulanan kirece doygun
60 ve 90 derecelik sıcak su kürleri uygulanmıştır.
Bu çalışmada, saf çimentolu ve belirli miktarlarda çimento ile değiştirilen yüksek fırın
cüruflu betonlar üç farklı dozaj grubu altında incelenmiştir. Üretilen numuneler her bir
ayrıtı 10 cm olan küp kalıplarda 7, 14, 28 ve 56 gün bekletilmiştir. Standart kürde tüm
günlerde, sıcak kürlerde erken dayanım amaçlandığından sadece 7. ve 14. günlerde,
dış ortamdaki numunelerde ise dayanım düşüşü beklendiğinden dolayı sadece 28. ve
56. günlerde üçer adet numune üzerinde basınç dayanımı deneyleri yapılmıştır.
Deney sonuçlarında referans üretim olarak kullanılan saf çimentolu betonlarda sıcak
kür uygulanması erken dayanım kazancı sağlayamamış, standart kür ile kürlenen
betonlara göre daha düşük dayanımlar vermiştir. Yüksek fırın cüruflu numunelerde isexviii
90 derece sıcak kürde bekletilen numuneler 14 günde 28 gün dayanımı değerine
ulaşabilmiş, 60 derecelik ortamda ise bu 14 günlük süre 7 güne kadar inmiştir. Böylece
90 dereceye göre hem enerji hem zaman tasarrufu sağlanmıştır. Laboratuvar ortamında
hava küründe bekleyen numunelerde ise su kaybından dolayı tüm günlerde ve tüm
numunelerde basınç dayanımlarının 28 günlük standart kürlü dayanımlardan daha
düşük olduğu gözlemlenmiştir.
Elde edilen bu sonuçlara göre cüruflu betonlarda 60 derece sıcaklık ve 7 günlük kür
süresi erken dayanım ve zaman yönetimi açısından en uygun koşul olarak
belirlenmiştir. Katkı içermeyen referans betonlarında ise sıcak kür işlemi araştırmada
kullanılan sıcaklıklar için beton dayanımını olumsuz etkilediği için standart kür
koşullarının kullanılması daha uygun olacaktır.

Abstract:
Concrete is basically a building material consisting of cement, water and aggregate
and is the most common building material used in Turkey. Some of the reasons for this
are low cost, easy availability of components, giving the desired shape when fresh, and
high compressive strength. Three main characteristics are expected from concrete
building material, which has an important role in meeting the activities in the
increasing construction sector. These are workability, strength and resistance to
environmental influences.
When the binding elements in concrete are mixed with water, they perform hydration
reactions. These reactions are exothermic reactions and cause hydration reactions to
occur faster under the influence of high temperature and form the concrete mass.
Hydration reactions consist of four main stages.
- In the first 30 minutes, surface reactions take place on the cement grains, giving
heat to the environment and forming the cement gel;
- The rate of hydration slows down for several hours because the diffusion of
water into the unhydrated cement grains is somewhat obstructed by the gel;
- After about 20 hours, water reaches the anhydrous cement grains remaining in
the gel, resulting in strong hydration reactions and an increase in temperature (at the
same time the hardening of the concrete occurs at this stage).
- Hydration reaction rate will continue declining for years.
Curing should be applied to the concrete to ensure that these hydration reactions
continue, especially on the surface. The curing process provides the recovery of the
amount of water that the concrete will lose from its surfaces, preventing the
interruption of hydration reactions and creating a strong and smooth structure in the
concrete. In case of insufficient curing, effects such as water loss in concrete and
stopping of hydration are observed. As a result, the concrete cannot reach its maximum
strength, cracks may appear in the concrete and the durability of the concrete may be
adversely affected.
The effect of using technology in concrete technology has been observed to a great
extent from past to present. For example, the process of mixing traditional concrete by
hand has been almost completely replaced by ready-mixed concrete today. However,
even if there are some new developments in cure, traditional methods are still used in
general and these projects extend the completion time. Sometimes plastic shrinkage
cracks occur due to rapid drying and insufficient early curing due to the fact that the
curing process is not carried out for the required time in large projects. This situation
causes the hardened concrete surface to have a bad structure. Today, various chemicalsxx
are used for curing, but skilled labor is required to implement these processes, and
these processes can bring various dangers
In addition, the production of portland cement has a high percentage of emissions from
industrial sources worldwide, and environmental damage is a concern. An effective
way to reduce this environmental damage is to use mineral additives as cement
substitutes in concrete production. The use of mineral additives in concrete provides
additional benefits such as reducing production costs, saving energy, and reducing the
volumes of some industrial wastes. Mineral materials such as ground blast furnace
slag, fly ash and silica fume contribute to the formation of hydration products in
concrete and can partially replace Portland cement. Moreover, another reason why
such mineral additives are a good alternative as a cement substitute is that they are
beneficial in terms of strength and durability in hardened concrete, and also in terms
of properties such as air entrainment, bleeding, reducing hydration heat, segregation
and plastic shrinkage in fresh concrete. This admixture created by mineral additives
can be explained by the pozzolanic effect. Although pozzolanes have binding
properties in concrete, they do not harden like cement when mixed only with water.
However, if there is slaked lime in the environment with water, then they react like
cement and form CSH gel. The calcium hydroxide they need when used in concrete
comes from cement.
The idea of using blast furnace slags in cement and concrete emerged in the 19th
century with the binding properties of these slags. Blast furnace slags are used as raw
materials in Portland cement or as mineral additives in concrete. Slags are used in
different ways in the cement and concrete industry today. While crystalline slags can
be used as aggregates in concrete, glassy blast furnace slags with a self-binding feature
can be used in concrete in cement or as a substitute for cement. In concrete as a result
of the replacement of blast furnace slag with cement at certain rates;
- Production costs are reduced;
- Increased workability;
- Concrete has relatively low strength at early ages but higher strength at further
ages;
- It does not affect shrinkage much compared to normal portland cement;
- By reducing the heat of hydration, it decreases the maximum concrete
temperature and the time required to reach this temperature;
- It increases the abrasion resistance a little if appropriate curing is applied, but
decreases it if not applied;
- Sulphate resistance is increased;
- It has been observed that the freeze-thaw effect does not change much when
the appropriate amount of air is entrained.
In this thesis, the issue of compressive strength, which is one of the basic properties of
concrete, and curing conditions that affect the strength will be discussed. Compressive
strength, which is one of the most important mechanical properties of concrete, has
enabled concrete designs to be produced in a way that exceeds approximately 250
MPa, following the developments in technology and increasing demands in the
construction sector. In addition, it has become important not only to obtain high
compressive strength but also to reach these high strengths in a short time. In order toxxi
meet the increasing demands in the construction sector, studies are carried out to
develop the curing method that affects the strength gaining speed in concrete. The most
common application among these studies is the hot curing application. It is seen that
the concrete compressive strength reaches the planned strength early, the construction
projects will be completed in a short time, the mold dismantling times will be
shortened, and thus, cost and labor will be beneficial. In addition to this, with this
method, in addition to the project time in the production of prefabricated buildings, the
storage area where the production must be kept until the required strength will be
facilitated. The shortening of the concrete setting time shortens the mold removal time
and ensures that the concrete has the desired strength in cold weather conditions.
In the standard curing application in concrete, which is widely known, it is applied in
water saturated with lime at 20 ± 2 °C. After this standard application, the compressive
strength of concrete is measured on the 28th day. In this thesis study, in addition to
this method, air cure and lime saturated 60° C and 90° C hot water cures were applied
in the laboratory conditions of the samples produced in addition to this method.
In this study, blast furnace slag concretes with pure cement and modified with certain
amounts of cement were examined under three different dosage groups. Samples with
each side of 10 cm were produced and the compressive strengths of these samples were
measured after they were kept for 7, 14, 28 and 56 days. Standard cure samples were
tested on all the days indicated. As early strength was aimed in hot curing samples,
these samples were tested on the 7th and 14th days. In the outdoor samples
compressive strengths were measured only on the 28th and 56th days, since a general
decrease in strength was expected.
In the test results, the application of hot curing did not provide an advantage in terms
of early strength in pure cement concrete used as reference production, and even gave
lower strengths on all test days compared to concretes cured with standard curing. In
blast furnace slag samples, samples kept at 90 degrees hot curing reached 28 day
compressive strength value in 14 days. 60 degrees hot curing reached 28 day
compressive strength value in 7 days. Thus, both energy and time savings were
achieved at 60 degrees compared to 90 degrees. Serious decreases were observed in
compressive strengths due to water loss in the concrete in the air-cured samples in the
laboratory environment.
According to test results, 60 degrees temperature and 7-day curing time were
determined as the most suitable conditions in terms of early strength and time
management in blast-furnace slag concretes. For reference concretes, it would be more
appropriate to use standard curing conditions, because hot curing process adversely
affects the concrete strength for the temperatures used in the research.