Geri Dön

Çimento ve kimyasal katkı uyumunun işlenebilme, terleme, erket rötre ve ayrışma üzerindeki etkileri

Effects of cement and superplasticizers interaction on workability, bleeding, early shrinkage and segregation of concreters

  1. Tez No: 66872
  2. Yazar: CENK BAŞEĞMEZ
  3. Danışmanlar: PROF. DR. SÜHEYL AKMAN
  4. Tez Türü: Yüksek Lisans
  5. Konular: İnşaat Mühendisliği, Civil Engineering
  6. Anahtar Kelimeler: Belirtilmemiş.
  7. Yıl: 1997
  8. Dil: Türkçe
  9. Üniversite: İstanbul Teknik Üniversitesi
  10. Enstitü: Fen Bilimleri Enstitüsü
  11. Ana Bilim Dalı: İnşaat Mühendisliği Ana Bilim Dalı
  12. Bilim Dalı: Belirtilmemiş.
  13. Sayfa Sayısı: 85

Özet

ÖZET Yüksek, çökme değerine sahip akıcı-plastik kıvamlı, taze haldeki betonların önemli sorunları İşlenebilme yeterliği, işlenebilme kaybı, segregasyon (ayrışma), terleme ve erken rota çatlaklarının oluşumudur. Bununla beraber günümüz beton teknolojisinde önemli yerleri olan süperakışkanlandırıcı katkıların kullanılmasının bu problemler üzerinde yadsınmayacak etkileri vardır. Çeşitli çimentolarla bu katkıların kullanılması çimento-katkı ikilisinin uyum sorununu da beraberinde getirmektedir. Yapılan çalışmada farklı çimento-katkı ikilisi uyumlarının işlenebilme, işlenebilme kaybı, terleme, segregasyon ve erken rötre çatlaklarının üzerindeki etkileri incelenmiştir. Bu incelemeler yapılırken aynı sınıfa sokulan süperakışkanlaştırıcıların veya çimentoların farklı fabrikalar tarafından üretilmesinin oluşturduğu içerik farkının yarattığı değişimler de gözlenmiştir. Bunun için Türkiye'de yaygın olan iki ayrı katkı firmasından süperakışkanlaştırıcı ve geciktirici içeren türü (ASTM Tip F ve Tip G) temin edilmiştir. Ayrıca farklı fabrikalarca üretilmiş 3 farklı sınıf çimento (PÇ42.5, KÇ 32.5 ve TÇ 32.5) olmak üzere toplam 7 çeşit çimento, deneylerde kullanılarak uyum sorunu araştırılmıştır. İşlenebilme kayıplarını bulabilmek için çökme ve çökmede yayılma deneyleri yapılmış daha sonra 67 dakika boyunca her 10 dakikada bir çökme ve yayılma değerleri ölçülerek çökme kaybı ve çökmede yayılma kayıpları bulunmuştur. Çökme değerleri 5 cm nin altına indiğinde Ve-Be deneyleri yapılmıştır. Diğer yandan ASTM C232-87 standartına göre terleme deneyleri yapılmıştır. Bu deneylerden alınan sonuçlar incelenerek 60 dakikalık peryotlar halinde terleme hızlan ve terleme miktarları hesaplanmıştır. Daha sonra terlemenin erken rötre üzerindeki etkilerinin incelenmesi amacıyla 50 x 50 x 10 cm boyutlarında bir kalıp hazırlanın üst tarafına yakın 8'lik demir donatı konmuş, daha sonra içine beton dökülmüş, üstü malayla düzeltilmiştir. 24 saat sonra sertleşmiş beton üzerinde yapılan gözlemlerde çatlak oluşup oluşmadığına bakılmış eğer çatlak oluşmuşsa boylan ve ortalama genişlikleri ölçülmüştür. Segregasyon ölçümü için 15 x 15 x 60 an boyutlarında kalıp hazırlanmış daha sonra bu kalıba kürekle beton doldurulmuştur. 24 saat sonra sökülen kalıplar oda sıcaklığında bırakılmış, 28. günde enleri doğrultusunda 4 eşit parçaya kesilerek 15 x 15 x 15 cm boyutunda numuneler elde edilmiştir. Bu numuneler üzerinde basınç deneyleri yapılarak basınç mukavemetleri bulunmuş ve değişimleri incelenmiştir. Deneyler her çimento-katkı ikilisi için yapılmışta-, çimento katkı ikilisinin problemdeki esas değişken olması amacıyla çalışma boyunca üretilen betonlarda, çimento dozajı, su/çimento oranı, karışım granulometrisi ve karışım oranlan sabit tutulmuştur. Değişen sadece katia-çimento ikilisi ve 18 cm çökmeyi sağlayacak katkının miktarıdır. Yapılan deneylerde şu sonuçlar bulunmuştur. Geciktirici içeren süperakışkanlaştırıcı eklemek, çökme kaybını azaltmakta, terleme miktarını arttırmaktadır ve Traslı çimentolan minimum derecede etkilemektedir. Farklı fabrikalar tarafından üretilen aynı sınıf çimentolar arasında içerik farkı en az Portland çimentolarda en fazla Trash çimentolardadır. Çimentodaki C3A ve C4AF miktarı arttıkça çökme kaybı artmakta, terleme azalmaktadır. Terleme hızının ve terleme miktarının artması erken rötre çatlaklarının oluşmasını önlemektedir. En az çatlak oluşumu geciktirici süperakışkanlaştırıcı kullanılan, terleme değerleri yüksek betonlarda oluşmuştur. Plastik rötre çatlakları, en az terlemeyi gösteren Traslı çimentolarda oluşmuştur. Terlemenin fazla olması segregasyonu arttıran bir faktördür fakat tek faktör değildir. Katkı çimento ikilisinin bireysel uyumlarından doğan farklı segregasyon değerleri genelleme yapmayı engellemektedir. Bununla beraber Trash çimentoların segregasyon değerleri düşük çıkmıştır. xtii

Özet (Çeviri)

SUMMARY EFFECTS af CEMENT and SUPERPLASTICIZERS INTERACTION m WORKABILITY, BLEEDING, EARLY SHRINKAGE md SEGREGATION tf CONCRETES Nowadays, superplasticizers or high range water reducers have an important place in concrete technology. Superplasticizers are used to increase the workability and high range water reducers to decrease the water/cement ratio. In high performance concretes these two aims should be realized at the same time with the same admixture, so we can indifferently use superplasticizers or high rang© water reducer terminology for these admixtures. Flowing concretes produced with superplasticizers which have high slump values have also Bome serious problems in fresh and green stages such as workability loss, segregation, bleeding and early shrinkage. On construction sites, the slump values of the concrete decreases while the fresh concrete is poured into the mould. In supeiplasticizered concretes, this slump loss generally occurs within 30 minutes. Therefore, the concrete needs more energy in order to be placed and it is also not possible to place this concrete without voids. There are few methods to prevent workability loss in superplasticized concretes. These methods are to dose superplasticizers at the job site, to delay the addition of superplasticizers, to split dosing of superplasticizers» to use retarders, to use other polymeric supplementary admixtures. Retarding type of superplasticizers are commonly using in our country, Turkey, by ready mixed concrete producers. Cohesion is an unavoidable property of the fresh concrete. Without cohesion coarse aggreagates may easily be scattered. Separation of coarse aggregates from the fresh concrete mass is called segregation. Concretes without segregation are defined as stable concretes, but water in stable concrete does not bleed either. These segregation of aggregates and bleeding of water should be at a minimum level in stable concretes. Segregation of coarse aggregates may be prevented if the mix composition is modified to ensure that there exist sufficient quantity of fine particles in tjie mix. In flowing fresh concrete one may proclaims that coarse aggregates will precipitates due to their quantity and expell water. On the other hand at the beginning of mixing cement particles absorb more water than the quantity necessary for their hydration. Following the flocculation, cement particles bleed the excess of water which is rising up to the surface. There are several experimental studies about these problems. In literature, it is stated that the compositions of cements have an important role in these problems. The composite oxides of Portland Cements such as C3A and C4AF adsorb quickly water molecules and the superplasticizers molecules dispersed in mixing water are also adsorbed simultaneously by these elements. But the main efficiency of the xfrsuperplaşticizers on workability is on the calcium silicates such as C3S and C2S. Therefore in the case of the adsorption of superplaşticizers molecules by C3A and C4AF, C3S and C2S can not find sufficient quantity of superplactieizer. As a result and demonstrated in some researches when the ratio of C3A and QAF in cement increases, slump loss increases and bleeding decreases. Another experimental study states that when the fineness of cement and its hydratation heat have higher values, the bleeding decreases also. Early shrinkage cracks occur at a green concrete stage. After bleeding, the water collected on the surface evoparates by the atmospheric effects such as high temperature, low relative humidity, high speed of wind. If the rate of evaporation is greater than the rate of bleeding, the surface shrinks and few cracks appear. These cracks are called early shrinkage cracks. The causes of these cracks are not only superficial plastic shrinkage but also settlement of aggregates. In fact, there is no difference between plastic shrinkage cracks and settlement cracks except their dimensions. Plastic shrinkage cracks have a thickness of less than 0.10 mm and it is difficult to measure their length due to their mesh-like shapes. Settlement cracks have a thickness between 0.10 mm and 1.00 mm and their lengths vary with the lengths of rigid materials like steel rods, coarse aggregates nearby the surface. These rigid materials affect the direction and dimension of the early shrinkage cracks. Early shrinkage cracks are influenced by many parameters. Among them interaction of cement and admixture, thickness of concrete, cover on reinforcement steel, cement type, composition and hydratation type, proportion of the mix, water/cement ratio, speed of bleeding, (etc.) may be cited. Chemical formulas of admixtures of course play an important role in workability. The well-known and preferred supetplasticizers are Naphthalene sulfonate- formaldehyde polycondansate (NSF), melamine sulfonate-formaldehyde polycondansate (MSF). hi some publications, the NSF group superplaşticizers, are admitted as better water reducers and having some retarding effect Superplaşticizers containing retarder are especially preferred for diminishing the slump loss but they can also increase the bleeding. Increased bleeding can affect fresh concrete in a negative way by impairing the stability, but it has also positive function by preventing plastic shrinkages. There are standard tests for measuring the workability of concrete. These tests are accurate and applicable for limited region of consistency. For example, V@~Be test İs used for dry concretes, slump tests for plastic and flow test for flowing concretes. Slump test which is the simplest and preferred test may give some opinion for workability of the flowing concretes but this information is not comprehensive enough. It is proved that the concretes which have same slump may have different cohesion and fluidity ; therefore it is more correct and realistic to evaluate the workability by basing it on rational characteristic parameters of viscous materials. These parameters are rheological constants. Bingham model is the most suitable for cement paste, mortar and concrete. Bingham model may be defined with two rheological constants, plastic viscosity and yield value,. They constitute characteristic parameters of the viscous suspensions. It is difficult to measure them in a construction site, special devices are needed. Standard slumptest results are mainly related to yield value but do not give clear information about the plastic viscosity. The yield value gives information about the fluidity and the energy necessary for the placement, the plastic viscosity inform us about the fluidity but it also gives valuable information for the cohesion of the concrete. Japanese scientists suggest slump spread test to solve economically this problem. In this test, after classical slump test, the horizontal spreading of the concrete in two directions are measured and the mean value is computed. The time between the raising of the cone and the measurement of the spread is also determined. It is accepted that the speed of the spreading values is relatively proportional to the plastic viscosity. In this study slump spread tests are also applied. In our research w/c ratio, cement content, mix proportion and gradation of aggregates were constant. Simple superplacticizers (ASTM C 494 Type F) and retarded superplacticizers (ASTM C 494 Type G) were all SNF types Portland cements were used PÇ42.5, KÇ32.5 TÇ 32.5 according to T.S. 19. They correspond respectively to ASTM Type III and Type Ip. They were purchased from three different factories near Istanbul. The concretes had different amounts of superplacticizer admixtures to ensure 18±1 cm slump value, Üıey all had w/c ratio of 0.54 and cement content of 350 kg/m3. To investigate workability, workability loss, bleeding, early shrinkage cracking and heterogeneity due to segregation Hie following tests were carried on concrete specimens. Slump values and spreads of slump were measured every 10 minutes during 70 minutes and the slump and spread losses were calculated from these test result. Ve-Be times were also measured for the concretes which had slump values less than 5 cm. Bleeding rates and total bleeding were obtained by applying ASTM C 232-87, bleeding test To observe effects of interaction of cements and chemical admixtures on early shrinkage cracking, wooden plates moulds of 50 x 50 x 10 cm were prepared, reinforcement steel of 8 mm diameter were placed near the top of the moulds, concrete was poured and trowelled, the concrete cover on the reinforcement was 15 mm. After 24 hours, the samples were examined for the formation of early shrinkage cracks. The length and width of the formed cracks were measured. For segregation investigation, the concretes were freely placed into prismatic moulds of 60 cm height, having 15x15 cm cross section. The prismatic specimen sawn after 28 days of hardening in 4 cubes of 15 cm size from four different level. Compressive strength of these cubes were measured at 28th day. In that way the heterogeneities caused by segregation were investigated. Ail these experiments were carried out for every combination of cements and chemical admixture series in order to search their interactions The thesis consists of five parts:In the first part, an introduction is given, it contains the objective of the investigation and relevant general information. The aim and scope of the present work are also presented. The second part explains the experimental studies. The properties of ingredients, e.g. aggregates, cements and chemical admixtures the principles assumed, the mix composition, the methods of mixing and curing, are described. In the third part the experimental results are gathered. These results are discussed and evaluated in the fourth part. The fifth part summarizes the general conclusions and some suggestions for Anther researches. The conclusions obtained from this experimental work can be outlined as follows: 1. Addition of a retarded type superplasticizers (ASTM Type G) in concretes generally reduces slump loss. This effect was at minimum level in the case of TÇ32.5 cements. (Pozzolan blended Portland cement). 2. Superplasticizers generally loose their efficiency on fluidity of the mix within 40 minutes. This trend is general and not related to the trademark of the admixtures and cements. 3. Speed and amount of bleeding water, increase with all the superplacticizers, but this increase is pronounced in the case pf retarded superplacticizers. 4. Speed and amount of bleeding water of concretes manufactured with pure Portland Cement (PC 42.5) are relatively high even without superplacticizers, but these values are very reduced for pozzolan blended Portland Cements, (in our research TÇ 32.5), are relatively high even without superplacticizers, but these values are very reduced for pozzolan blended Portland Cement concretes. This reduction is not observed for the (KÇ 32.5) cement concretes. KÇ 32.5 cement is also a pozzolan blended Portland Cement, but contains less pozzolan than TC 32.5. 5. Among same types (ASTM Type F) of superplasticizers, only one gave stable bleeding values with all kind of cements. It is interesting to note that this superplacticizers can give high bleeding values as retarding type superplasticizers (ASTM Type G) give. 6. Using retarding type superplasticizers (ASTM Type G) reduced early shrinkage cracks. The formation of these cracks are also prevented for die concretes which had high bleeding values and produced without addition of chemical admixtures. From these observations one may pretend that die plastic shrinkage cracks occur in the cases of concretes which have restricted values of bleeding. 7. If the concrete cover on steel reinforcement is thick enough, early shrinkage cracks are reduced and this observation is general and not influenced by die cement and admixture type and cement - admixture interaction. XVtt8. Occurrence of segregation is affected by the interaction of cement and admixture, but this effect can not be expressed by some analytical formulation. However the minimum compressive strength of sawn cubes were always obtained at ttw highest level of prisms. This its the consequence of the bleeding. The compressive strengths at the bottom of prisms were also low due to the interlocking of the segregated coarse aggregates. One may assume that the cemenf-admixture combination which induce high bleeding may give rise to segregation risk. Therefore bleeding is an efficient factor on segregation but not the only factor on it. xviii

Benzer Tezler

  1. Tez No

    406375

    Kimyasal katkı-biyopolimer uyumunun çimento harcı özelliklerine etkisinin kitin özelinde incelenmesi

    Investigation of chitin effect on the properties of cement slurry as an example of chemical additive-biopolymer compatibility

    ORTAÇ MORALIOĞLU

    Yüksek Lisans

    Türkçe

    Türkçe

    2015

    Polimer Bilim ve TeknolojisiCelal Bayar Üniversitesi

    İnşaat Mühendisliği Ana Bilim Dalı

    DOÇ. DR. ALİ UĞUR ÖZTÜRK

  2. Tez No

    467260

    Nano silika kullanımının kendiliğinden yerleşen betonların reolojik, mekanik ve içyapısal özellikleri üzerine etkilerinin araştırılması

    Investigating the effects of nano silica usage on rheological, mechanical and microstructural properties of self-consolidating concretes

    MUHAMMED YASİN DURGUN

    Doktora

    Türkçe

    Türkçe

    2017

    İnşaat Mühendisliğiİstanbul Teknik Üniversitesi

    İnşaat Mühendisliği Ana Bilim Dalı

    DOÇ. DR. HAKAN NURİ ATAHAN

  3. Tez No

    600361

    Kıvam koruma performansı açısından kalsiyum alüminat çimentosunun akışkanlaştırıcı kimyasal katkılarla uyumunun incelenmesi

    Investigation of compatibility of calcium aluminate cement with plasticizing chemical admixtures from the view point of consistency retainig performance

    ŞEBNEM ALPASLAN

    Yüksek Lisans

    Türkçe

    Türkçe

    2019

    İnşaat MühendisliğiDokuz Eylül Üniversitesi

    İnşaat Mühendisliği Ana Bilim Dalı

    PROF. DR. KAMİLE TOSUN FELEKOĞLU

  4. Tez No

    462945

    Kendiliğinden yerleşen betonlar'da kimyasal katkı ve çimentoların beton özelliklerine etkisi

    The effects of chemical additives and cement on self-compacting concretes

    BURAK İNAN

    Yüksek Lisans

    Türkçe

    Türkçe

    2017

    İnşaat Mühendisliğiİstanbul Üniversitesi

    İnşaat Mühendisliği Ana Bilim Dalı

    PROF. DR. FAHRİYE KILINÇKALE

  5. Tez No

    330667

    Değişik dispersif ajan ve çimento ile stabilize edilen kilinserbest basınç dayanım özellikleri

    Unconfined compressive strength properties of various dispersing agents and cement stabilized clay

    AYŞEGÜL GÖREN

    Yüksek Lisans

    Türkçe

    Türkçe

    2013

    İnşaat MühendisliğiGazi Üniversitesi

    İnşaat Mühendisliği Ana Bilim Dalı

    DOÇ. DR. YÜKSEL YILMAZ

Geri Dön