Kendiliğinden yerleşen betonlarda ince malzemeve en büyük agrega boyutunun beton özelliklerineve agrega kenetlenmesine etkisi
The effects of fine material content and maximumaggregate size on concrete properties and aggregateinterlocking for self-compacting concrete
Yazar: HAYATİ HİLMİOĞLU
Danışman: PROF. DR. MUSTAFA HULUSİ ÖZKUL
İstanbul Teknik Üniversitesi / Lisansüstü Eğitim Enstitüsü / İnşaat Mühendisliği Ana Bilim Dalı / Yapı Mühendisliği Bilim Dalı
Derece: Doktora, 2022
Konu: İnşaat Mühendisliği = Civil Engineering
Dizin: Agrega = Aggregate ; Basınç dayanımı = Compressive strength ; Beton özellikleri = Concrete properties ; Elastisite modülü = Modulus of elasticity ; Kendiliğinden yerleşen betonlar = Self compacting concretes ; Süreksizlik = Discontinuity ; Çekme dayanımı = Tensile strength

Özet:
Kendiliğinden yerleşen beton (KYB), dökümü esnasında vibrasyon ve sıkıştırma gerektirmeyen, segregasyona uğramadan kendi ağırlığı ile yoğun donatılı bölgelerde bile akma kabiliyeti olan, mekanik özellikleri yönünden normal vibrasyonlu beton (NVB) özelliklerine göre daha üstün özelliklere sahip olan bir betondur. Beton içerisine süperakışkanlaştırıcılarla birlikte çeşitli kimyasal ve mineral katkı maddeleri ilave edilerek, betonun doldurma, ayrışmaya karşı direnci ve geçiş yeteneği arttırılmış, akıcılık,  işlenebilirlik, yüksek mukavemet, durabiliteye sahip olma ve geçirimsizlik özelliği ile donma, çözülmeye karşı yüksek direnç özelliği yükseltilmiştir. Özellikle yeni nesil süperakışkanlaştırıcı katkılar yüksek oranda dispersiyon (dağıtma) ve sterik etkilere sahip olduklarından betonun yüksek akıcılık, yüksek geçiş yeteneği ve yüksek doldurma kapasitesi gibi özelliklerini arttırmaktadır. KYB'lerin inşaat teknolojisinde kullanılmaya başlanılmasıyla, inşaat kalitesi artmış,  inşaat yapım süresi kısalmış, kalifiye işçi ihtiyacı azalmış, vibrasyon gürültüsü ortadan kalkmış, mimari çizimlerde çok geniş bir alan yaratılmış, daha ince cidarlı beton dökebilme imkanı sağlanmış, yeni uygulamaların önü açılmış ve inşaat maliyetleri azalmıştır. Bu bakımdan KYB'ler beton teknolojisinde bir devrim yaratmıştır.
Bu çalışmada 350 kg/m3 sabit miktarda çimento, farklı miktarlarda uçucu kül (UK), kalker tozu (KT), süperakışkanlaştırıcı (SA) ve viskozite katkı maddeleri (VAK) kullanılarak, 10 mm, 16 mm ve 22 mm en büyük agrega boyutunda, KYB özelliğine sahip betonlar üretilmiş ve üretilen bu betonlar üzerinde taze ve sertleşmiş beton deneyleri yapılmıştır. EFNARC (2002) standardında KYB'lerde tasarım oranları ve miktarlarının belirlenmesinde hacımsal oranların kullanılması tavsiye edildiği için deneylerde kullanılan malzeme miktarlarında hacimsal değerler kullanılmıştır. Kalker tozlu karışımlarda, her bir karışım için 350 kg/m3 çimentoya, 100 kg/m3, 200 kg/m3 ve 300 kg/m3 KT ilave edilerek, 450 kg/m3 (350 kg/m3+100 kg/m3), 550 kg/m3 (350 kg/m3+200 kg/m3) ve 650 kg/m3 (350 kg/m3+300 kg/m3) KT'li KYB'ler üretilmiştir. Uçucu küllü karışımlarda ise, her bir karışım için 350 kg/m3 çimentoya, 82 kg/m3, 164 kg/m3 ve 246 kg/m3 UK ilave edilerek, 432 kg/m3 (350 kg/m3+82 kg/m3), 514 kg/m3 (350 kg/m3+164 kg/m3) ve 596 kg/m3 (350 kg/m3+246 kg/m3) UK'lı KYB'ler üretilmiştir. Hacimsal oranlar esas alındığından 100 kg/m3 KT hacım olarak 82 kg/m3 UK'ya karşılık gelmektedir. Bu değerler kullanılarak her bir karışımın sırasıyla  36 dm3, 72 dm3 ve 108 dm3 UK ve KT içermesi ve UK ve KT miktarlarının hacimsal olarak sabit tutulması sağlanmıştır.


Deney sonuçları değerlendirildiğinde, taze betonlar üzerinde yapılan birim ağırlık değerlerinin, ek ince malzeme miktarı (EİM) artışına bağlı olarak istikrarlı bir eğilim göstermediği, UK ve KT'li karışımların birim ağırlıklarının birbirine yakın değerler aldığı, çökme-yayılma değerlerinin EİM miktarı ile birlikte arttığı, V-hunisi akış sürelerinin KT'li KYB'lerde daha uzun olduğu, elekte ayrışma değerlerinin sınırlar içinde kaldığı gözlenmiştir. Plastik viskozitenin, KT'li karışımlarda daha büyük değerler aldığı, ancak kayma eşiğinde belirli bir eğilim bulunmadığı anlaşılmıştır. 
Her iki agrega boyutu için de EİM miktarı artarken basınç dayanımlarının yükseldiği ve UK'lı betonların KT'li ve NVB'lere göre daha yüksek dayanım verdikleri belirlenmiştir. Tüm yarmada-çekme dayanımlarının NVB'lere göre daha yüksek değerler aldığı gözlenmiştir. Tüm KT'li karışımlarda elastisite modülü değerlerinin EİM  miktarı artışına bağlı olarak kendi aralarında artan değerler aldığı görülmüş ancak UK'lı karışımlarda belirli bir eğilim gözlenmemiştir. Poisson oranı değerleri  KT'li karışımlarda, UK'lı ve NVB'li karışımlara göre biraz daha yüksek elde edilirken süreksizlik sınırı ve çözülme sınırı değerlerinin UK'lı karışımlarda KT ve NVB'lere göre daha yüksek değerler aldığı görülmüştür. Gevrek davranış konusunda önemli parametreler olan süreksizlik sınırı/ basınç dayanım oranlarının tüm karışımlarda % 56-69 sınırları arasında kaldığı, çözülme sınırı/basınç dayanım oranlarının ise % 90'ın üzerinde elde edildiği gözlenmiştir. Bu haliyle tüm karışımların gevrek olarak değerlendirilebileceği sonucuna varılmıştır.
Bu çalışmanın ana konusu, NVB'lerde görülen iri agrega kenetlenmesinin KYB'lerdeki etkisini incelemektir. Bilindiği gibi NVB'lerde kesme dayanımı üzerine etki eden faktörlerden birisi de iri agrega kenetlenmesidir. KYB'lerde hem toplam agrega miktarı hem de karışım içindeki iri agrega oranı azaltılmaktadır. Yapılan çalışmada, KYB'lerdeki ince malzeme miktarı (dolayısıyla iri agrega miktarı) ve iri agrega boyutunun kesme (kayma) dayanımına etkisi incelenmiştir. Eğilmede-kesme dayanımı değerleri göz önüne alındığında, tüm KT'li karışımlar eğilmede-kesme değerlerinin UK ve ek ince malzemesiz (EİM*) karışımlara göre daha yüksek değerler aldığı, doğrudan kesme dayanımı değerleri karşılaştırıldığında ise 10 mm agregalı UK'lı betonlarda % 11'e ulaşan düşüş, 10 mm agregalı KT'li betonlarda ve 16 mm agregalı KT ve UK'lı betonlarda ise aynı mertebede veya daha yüksek oranlarda dayanımlar elde edilmiştir. Bu durum, iri agrega oranı azaltılmış, EİM miktarı artırılmış KYB'lerde agrega kenetlenmelerinin genel olarak azalmadığını (10 mm iri agregalı UK'lı doğrudan kesmede % 11 azalma) göstermektedir. Bunun nedeninin artan EİM ile birlikte hem matrisin dayanımının artmasından hem de ara yüzeyin iyileşmesinden kaynaklandığı söylenebilir.

Anahtar Kelimeler: 
Kendiliğinden yerleşen beton, Taze beton özellikleri, Agrega kenetlenmesi, Basınç dayanımı, Yarmada- çekme dayanımı, Eğilmede- çekme dayanımı, Elastisite modülü, Poisson oranı, Süreksizlik sınırı, Çözülme sınırı, Doğrudan kesme dayanımı.

Abstract:
Self-compacting concrete (SCC) is a concrete that does not require vibration and compression during compacting, has the ability to flow under its own weight without segregation even in densely reinforced areas, and has superior mechanical properties compared to normal concrete placed in the mold with vibration. By adding superplasticizers together with various chemical and mineral admixtures to the concrete, the filling, resistance to segregation and flowing ability of the concrete have been increased, and its fluidity, workability, high strength and impermeability properties and resistance to freezing and thawing have been increased. Especially, new generation admixtures increase the properties of concrete such as high fluidity, high passing ability and high filling capacity since they have high dispersing capacity and steric hindrance effect. With the use of SCCs in construction technology, the construction quality has increased, the construction period has been shortened, the need for qualified workers has decreased, the vibration noise has disappeared, a wide area has been created in architectural drawings, it has become possible to pour concrete with thinner walls, new applications have been opened, In addition,  more secure working environment is provided and construction costs are reduced. In this respect, SCCs have created a revolution in concrete technology. SCCs have important differences from normal concretes with respect to composition, fresh and hardened state properties. 
The innovation of self-compacting concrete (SCC) can be regarded as a revolution in concrete technology. SCC was originally developed in 1988, to improve the durability of concrete structures (Okamura and Ouchi 2003). In recent years, it has found wide applications in construction due to its ability to fill molds without vibration. The production of SCCs requires a powerful superplasticizer, usually polycarboxylate-based, as well as a powder, mostly limestone filler (LS), fly ash (FA), granulated blast furnace slag or silica fume, or a viscosity modifying agent (VMA), such as polysaccharides, or both (Shindoh and Matsuoka 2003). The maximum aggregate size, grading, shape and angularity are important properties of aggregates which affect the fresh state behavior of SCC (Koehler and Fowler 2007a). In the production of SCCs, crushed stone, crushed gravel or uncrushed gravel can be used as coarse aggregate (CA), and river sand, crushed sand or dune sand (or combinations of them) can be used as fine aggregate, in a similar way to those used for normal vibrated concretes (NVC). Khaleel et al. (2011) used gravel, crushed gravel and crushed limestone as CA in SCC, obtaining the best performance on fresh concrete with gravel, followed by crushed gravel and then crushed limestone because of the differences in the particle shape and surface texture. 

Likewise, Kraenkel et al. (2009) prepared SCCs by using gravel, crushed granite or crushed basalt as CA and they observed that the concretes with crushed aggregates had longer V-funnel and J-ring times than those of the former due to the difference in surface roughness. Maximum aggregate size is reduced in SCC, compared to that of NVC, in order to obtain passing ability and segregation resistance (Koehler and Fowler 2007b). Workability properties measured as T50, V-funnel flowing time, U-box and L-box (for passing ability and filling ability) showed improvement for a maximum size of 10 mm compared to that of 20 mm (Khaleel et al. 2011). Mueller and Wallevik (2009) measured the rheologic properties of SCCs by using a BML viscometer and found that, although the plastic viscosity showed a slight change with an increase in maximum aggregate size, the yield stress increased significantly. Bouzian (2013) used river sand (RS), crushed sand (CS) and dune sand (DS) as fine aggregate in SCCs and observed that CS and DS in binary and ternary systems with RS should be lower than 65 and 24%, respectively, in order to obtain sufficient flowability. Similarly, Zeghichi et al. (2014) used DS and CS in the production of SCCs; they observed that the addition of DS into CS lowered the viscosity of the SCC and also improved the flowability due to the rounded shape of the dune particles. The most widely used filler in SCC is LS, followed by FA and granulated blast furnace slag (GBFS). The grading, fineness, amount, particle shape and surface roughness of the filler are important factors for the performance of SCCs in their fresh state. Skender et al. (2021) found decreased slump flows with increasing LS content in the case of cement substitution, while T500 and V-funnel flow times increased. On the contrary, LS was used as a cement replacement; larger amounts of filler caused lower yield stress and, as a result, higher slump values were obtained but plastic viscosity increased (Varhen et al. 2016). Askarian et al. (2018) used a natural pozzolan, pumice powder, as cement replacement in SCCs and obtained higher SP dosage to reach the target slump flow, however; the slump flow retention was improved compared to the mixtures with fly ash or slag. Barbhuiya (2011) used dolomite powder and FA in binary and ternary mixtures, and although the slump-flow results fell into the SF1 class (EFNARC 2005), SCCs with a high amount of dolomite powder showed lower spreads than those of the latter. SCCs were designed by using F-type FA up to 15% cement replacement; higher slump-flow and lower T500 and V-funnel times than those of the concrete without FA were reported (Jalal et al. 2013). It seems that the spherical shape of the FA particles gives more deformability to the SCCs than the angular particles of the cement. Class F type FA was used at cement replacement rates of 10 to 50% and yield stress decreased by up to 30% (Laskar and Talukdar 2008). Plastic viscosity showed an initial increase for the 10% rate, and then gradually decreased up to 30% rate. Both yield stress and plastic viscosity showed insignificant changes beyond the 30% level. Likewise, the rheological properties, yield stress and plastic viscosity increased with a high-calcium FA content (Ponikiewski and Golaszewski 2013). In this study, 2 different fine materials (LS and FA) were used to produce SCCs at 3 different volumes (36, 72 and 108 dm3 /m3 ) and with different aggregate sizes (10 and 16 mm). The effects of concrete composition on flowing, passing ability through the barriers, segregation, and blocking were investigated.
In this study, SCCs were prepared with 10 mm, 16 mm and 22 mm coarse aggregate sizes using limestone powder (LS) and fly ash (FA) as fine material. For each mix, the amount of cement and the water/cement (W/C) ratio were kept constant at 350 kg/m3, and 0.50 % respectively. LS mixes were prepared from 350 kg/m3 to 650 kg/m3 changing with 100 kg/m3 increments (100 kg/m3, 200 kg/m3, and 300 kg/m3 of LS additions). (The total powder contents including the cement: 450 kg/m3, 550 kg/m3, 650 kg/m3).  
FA mixes were prepared from 350 kg/m3 to 596 kg/m3 changing with  82 kg/m3 increments (82 kg/m3, 164 kg/m3, 246 kg/m3 of  FA) to keep the volume constant. (The total powder contents including the cement: 432 kg/m3, 514 kg/m3, 596 kg/m3). As a volume, the amount of fines materials in concrete with FA and LS was increased in 36 dm3 increments up to 108 dm3 (36 dm3, 72 dm3, 108 dm3).
Experimental results indicated that slump flow increases with increasing powder content. Opposite to this, V-funnel times increased with increasing powder content, however, they were shorter for FA than those of LS. For both types of powders, the segregations remained within the limits. The SCCs with LS showed higher plastic viscosity than those of FA concretes but no trend was obtained for yield stress.The compressive and splitting tensile strengths and modulus of elasticity of SCCs were compared with those of normal vibrated concrete (NVC). For all SCCs, higher compressive strengths were obtained than NVC. Compressive strength increased with increasing powder content; however, the SCCs with FA exhibited higher strengths than the others due to the pozzolanic effect. The splitting tensile strengths of all SCCs tested were higher than that of NVC, due to the better packing and enhanced compacting of the former concretes. The splitting tensile strengths of SCCs with LS addition and aggregate size of 10 mm and those containing FA and 16 mm aggregate were higher than the others. The moduli of elasticity of SCCs without additional powder and NVC are at the same level in general. However, when the powder content is increased, up to a 10.8% increase in modulus was obtained. The effects of powder type and aggregate size on the modulus are negligible. The Poisson ratios of SCCs and NVC remained in the range of 0.188-0.228. Test results showed no significant effect of type and content of powder and aggregate size on the Poisson ratio of SCCs. The relative initiation stresses of SCCs remained under that of NVC, showing a more inelastic behavior. For FA-added SCCs, those with the 10-mm size showed slightly higher relative initiation stress than those with the 16-mm size, which may be attributed to the more uniform and homogeneous behavior the former concretes have. However, for the LS addition, the opposite trend was obtained: The larger the aggregate size, the higher the relative initiation stress, maybe due to the difference in the additions. The relative critical stresses of SCCs remained over that of NVC, indicating a more brittle behavior for the former concretes. The relative critical stresses showed no significant trend with the type and amount of powder and aggregate size, and the change is slight, ranging from 0.93 to 0.98. The SCCs with LS showed higher modulus of elasticity for 10 mm aggregate size.
As it is known, one of the factors affecting the shear strength of normal concrete compacted by vibration is the interlocking of coarse aggregate. In self-compacting concretes, both the total aggregate amount and the coarse aggregate content in it are reduced. Therefore, the main purpose of this study is to investigate whether the coarse aggregate interlocking observed in normal concretes compacted by vibration is seen with the same effectiveness in SCCs. For this purpose, the effect of fine material amount (hence the coarse aggregate amount) and size on shear strength in self-compacting concrete was investigated. When the bending-shear strength values are taken into consideration, it was observed that the shear strengths of the mixtures with a high amount of fine material were higher for both fine material types and both aggregate sizes compared to the mixtures without additional fine material (350-0). 



When the direct shear strength values are compared, a decrease of 11% was obtained in the concrete with FA with a maximum aggregate size of 10 mm, and the same order or higher strengths were obtained in 10 mm concrete with LS and 16 mm concrete with LS and FA. This situation shows that aggregate interlocking of self-compacting concretes with reduced coarse aggregate content and increased fine material content does not generally decrease (11% reduction in direct shearing in 10 mm coarse aggregate FA). It can be said that the reason for this is both the increase in the strength of the matrix and the improvement of the interface with the increasing fine material. 

Keywords: 
Self-compacting concrete, Limestone powder, Fly ash, Aggregate interlocking, Fresh concrete properties, Slump flow, Shear strength, Initiation stress, Critical stress, Modulus of elasticity, Poisson ratio, Flexure without shear reinforcement.