Portland çimentosu ve süperakışkanlaştırıcı katkı uyumunun incelenmesi

Bu tezde, farklı C3A içeriğine sahip CEMI portland çimentoları ile süperakışkanlaştırıcı katkı uyumu incelenmiştir. Tez çalışması iki aşamalı olarak gerçekleştirilmiştir. Birinci aşamada, çok değişkenli regresyon programı ile çimento-katkı uyumunu etkileyen parametreler belirlenmiştir. Bu amaçla 9 adet normal portland çimentosu ve 3 adet polikarboksilat esaslı su azaltıcı katkı kullanılmıştır. 226 hamur karışımının Marsh-hunisi akış süresi ve mini-yayılması ölçülmüştür. Ayrıca, farklı katkı dozajında ve farklı S/Ç oranına sahip 243 hamur karışımının da reolojik özelikleri belirlenmiştir. Sonuçlar istatistiksel program ile analiz edilmiştir. İstatistiksel incelemede, çimentonun inceliği, C3A, C3S, C2S, C4AF ve eşdeğer alkali içeriği ile su azaltıcı katkı miktarı, katkı katı madde oranı ve karışımın su içeriği gibi parametreler dikkate alınmıştır. İstatiksel analizler 4 aşamada yapılmıştır. Birinci aşamada, faktör analizi ile etken parametreler belirlenmiştir. İkinci aşamada, doğrusal olmayan regresyon ile üçüncü aşamada ise yapay sinir ağları yöntemi ile girdi çıktı ilişkisi kurulmuştur. Son aşamada duyarlılık analizi ile etken parametreler belirlenmiştir. Sonuçta, çimento kaynaklı etken faktörlerin, etki şiddeti sırasına göre çimentonun inceliği ile C3A ve eşdeğer alkali içeriği olduğu saptanmıştır. Tezin ikinci aşamasında birinci aşmada belirlenen çimento-katkı uyumunu etkileyen parametreler hamur, harç ve beton karışımlarında detaylı olarak incelenmiştir. Bu aşamada, istatistiksel çalışma sonunda belirlenen faktörlere ilaveten, çimentonun alçı türü ve su azaltıcı katkı yan zincir yoğunluğunun etkisi de incelenmiştir. Bu bağlamda, çimento hamurlarının, mini-yayılması, Marshhunisi akış süresi ve reolojik özelikleri, harç karışımlarının ise, katkı ihtiyacı, zaman içerisinde yayılma kaybı, V-hunisi akış süresi, zamana bağlı akış kaybı, reolojik özelikleri ve basınç dayanımları incelenmiştir. Beton karışımlarında ise, hava içeriği, sertleşmiş ve taze birim hacim ağırlığı, çökme, yayılma, zamana bağlı çökme ve yayılma kaybı ile basınç dayanımı belirlenmiştir. Seçilen bazı hamur karışımlarında XRD analizleri yapılarak oluşan etrenjit ve monosülfoalüminat ürünleri hakkında daha detaylı bilgi elde edilmiştir. Su azaltıcı katkı içermeyen karışımlarda, çimento inceliğinin artışı ile karışımların taze hal ve reolojik özelikleri olumsuz etkilenmiştir. Ancak, süperakışkanlaştırıcı katkılı karışımlarda bu durumun tersi görülmüştür. Bu olumlu etki, çimento inceliğinin artışıyla birlikte, çimento taneleri üzerinde süperakışkanlaştırıcı katkının emiliminin artması, dolayısıyla, süperakışkanlaştırıcı katkının etkinliğinin artmasından kaynaklanmaktadır. Ayrıca, çimento inceliğinin artışıyla erken yaş dayanım değerleri artmıştır. İleri yaşlarda ise çimento inceliğinin artışı ile basınç dayanımları aralarındaki farklar azalmıştır. Çimento alkali ve C3A oranının azalmasıyla çimentolu sistemlerin taze hal özeliği iyileşmiştir. Dehidrat alçı içeren çimento hemihidrat içeren çimentoya kıyasla, taze ve reolojik özelikleri açısından hamur, harç ve beton karışımlarında kullanılan polikarboksilat esaslı su azaltıcı katkı ile daha uyumlu olmuştur. Kendiliğinden yerleşen beton karışımlarının çökme yayılması koruma potansiyeli katkı yan zinciri yoğunluğunun artmasıyla azalmıştır. Bu olayın, yan zincirlerin birbirine kenetlenmesinden kaynaklandığı düşünülmektedir.In this thesis, the compatibility between superplasticizeres and cements containing different amounts of C3A was investigated. The study was conducted in two steps. In the first step, the parameters affecting cement-admixture compatibility was obtained by using a multivariate regression program. For this purpose, 9 different CEM I portland cements and 3 polycarboxylate-ether based superplasticizer admixtures were used. Marsh-funnel flow time and mini-slump values of 226 cement paste mixtures were measured. In addition, the rheological properties of 243 paste mixtures having different W/C ratios and containing different amounts of admixture were determined. The results were analyzed statistically. In this analysis, cement fineness, C3A, C3S, C2S, C4AF and equivalent alkali content of cement as well as admixture utilization level, admixture solid material ratio and amount of mixing water were considered. The statistical analysis was carried out in four steps. In the first step, the effective parameteres were determined by factor analysis. The input-output relations were established by nonlinear regression and artificial neural networks methods in the second and third steps, respectively. In the last step, effective parameters were defined with sensitivity analysis. The cement-based factors that affect compatibility were determined as fineness, C3A and equivalent alkali content in order of decreasing severity. In the second step of the thesis, the effects of aforementioned parameters on the paste, mortar and concrete mixture characteristics were investigated in a more detailed manner. Moreover, the effect of cement-gypsum type and the admixture side chain density on the properties of cementitious systems were investigated. In this regard, the flow time, mini slump values, rheological parameters of the cement paste as well as admixture requirement, flow value, loss of flow, V-funnel flow time, loss of V-funnel flow time, rheological properties and compressive strength of the mortar mixtures were investigated. In the concrete mixtures, fresh and hardened unit weight, air content, slump, loss of slump, slump flow, compressive strength tests were performed. Besides, XRD analysis was carried out on some paste mixtures to obtain more information about the formation of calcium alumino sulfate hydrates. The fresh and reological properties of the control cementitious systems containing no water reducing admixture were negativly affceted by increasing cement fineness. The opposite effect was noted in the mixtures containing superplasticizer. Increasing the fineness of cement increased the superplasticizer adsorption level on cement pArticles, hence, increased the efficiency of the superplasticizer. In addition, increasing cement fineness led to an increase in the compressive strength of the mixtures at early ages. At later ages, the difference between the strength of the mixtures arisen from cement fineness reduced. The fresh and rheological properties of the cementitious systems were improved by decreasing C3A and equivalent alkali content of the cement. Compared to the hemihydrate-bearing cement, the cement containing dihydrate gypsum was more compatible with the polycarboxylate-ether based water reducing admixture in terms of fresh state and rheological properties of the paste, mortar and concrete mixtures. The slump retention of self consolidating concrete mixtures decreased with increasing side chain density of the superplasticizer admixture. The fact was attributed to the interlocking of the side chains of the admixture

Uçucu küllü silindirle sıkıştırılmış betonlarda dayanıklılık

Silindirle sıkıştırılmış beton (SSB), sıfır çökme değerine sahip ve geleneksel beton ile benzer malzeme kullanılarak elde edilen bir özel betondur. Bu tezde maksimum agrega çapı 25 mm olan, bağlayıcı olarak sadece portland çimentosu içeren kontrol örneğine ek olarak farklı oranlarda çimento veya agrega yerine uçucu kül içeren SSB‘ler maksimum yoğunluk metoduna göre tasarlanmıştır. Üretilen kontrol karışımının çimento dozajı 250 kg/m3 olup, bir seri karışımda çimento yerine ağırlıkça %20, %40, %60 oranlarında, bir diğer seride ise ek bağlayıcı olarak agrega yerine çimento ağırlığınca %20, %40, %60 oranlarında uçucu kül kullanılmıştır. Farklı su/bağlayıcı oranlarında (0.30, 0.35, 0.40 ve 0.45) toplam 25 karışım hazırlanmıştır. Bunlar arasından optimum su muhtevasına sahip 7 karışım seçilerek devamındaki deneylerde kullanılmıştır. Deneysel çalışma iki aşamalı olup birinci aşamada basınç, yarmada çekme, eğilme dayanımı gibi mekanik özelikler belirlenmiş, ikinci aşamada ise su emme, boşluk oranı, geçirgenlik ve donma-çözünme direnci gibi dayanıklılık özelikleri incelenmiştir. Elde edilen sonuçlara göre, uçucu külün çimento yerine kullanıldığı karışımlarda, uçucu kül miktarı arttıkça dayanım değerlerinde düşüşler ve durabilite özelliklerinde olumsuzluklar gözlenmiştir. Uçucu külün ek bağlayıcı olarak kullanılmasıyla üretilen SSB‘lerin hem taze hem de sertleşmiş haldeki özelliklerinde iyileşmeler görülmüştür

Mechanical properties of high-volume fly ash roller compacted concrete designed by maximum density method

WOS: 000313767900041In order to study the effect of high volume fly ash on mechanical properties of roller compacted concrete, in addition to control mixture containing no fly ash, in two different series of mixtures cement or aggregate was partially replaced with fly ash. The maximum aggregate size was 25 mm in all of the mixtures which were designed using maximum density method. The cement content of the control mixture was 250 kg/m(3). In one series of the mixtures 20, 40 and 60 wt% of cement was replaced with fly ash. In another series, a part of aggregate (equal to 20, 40 and 60 wt% of cement) was replaced with fly ash. Totally 28 mixtures having four different water/binder ratios (0.30, 0.35, 0.4 and 0.45) were prepared. Among these, seven mixtures containing optimum water content were selected for further research. It was observed that in the mixtures where cement was substituted with fly ash, increasing the fly ash content caused reduction in compressive, splitting tensile and flexural strength values at all of the ages up to even 180 days. On the other hand, when aggregate was replaced with fly ash, increasing the fly ash content increased the strength values of the mixture at all ages compared to these of the control specimen. (C) 2012 Elsevier Ltd. All rights reserved

Effect of Cement C3A Content on Properties of Cementitious Systems Containing High-Range Water-Reducing Admixture

The effect of cement tricalcium aluminate (C3A) content on the properties of cement paste, mortar, and concrete mixtures containing high-range water-reducing (HRWR) admixture was investigated. Three commercial Type I cements prepared with the same raw material and same gypsum rock interground with clinker, but with different C3A contents (by changing mixture proportions), were used. The fresh state, rheological properties, and compressive strength of the mixtures were studied. Moreover, X-ray diffraction (XRD) patterns of 6-h-age paste mixtures from each cement were obtained. By reducing the C3A content of the cements, the fresh state, rheological, and consistency retention properties of the mixtures improved; however, the strength of the mixtures at early ages decreased. The difference between strength of the mixtures closed at later ages. The XRD analysis of the pastes revealed the formation of more ettringite in the paste prepared from high C3A content cement

Effect of false set related anomalies on rheological properties of cement paste mixtures in the presence of high range water reducing admixture

felekoglu, burak/0000-0002-7426-1698WOS: 000561439400001There are many studies related to the fresh state properties of the cementitious systems in the literature. However, there is no specific study about the effects of false set formation on fresh state properties of these systems. in this study, the effect of false set formation on fresh state and rheological properties of the cement paste mixtures containing high range water reducing (HRWR) admixture was investigated experimentally. For this aim, two different commercial CEMI 42.5 R. type cements produced by different companies were used. in order to investigate the effect of false set formation related anomalies on fresh state properties, paste mixtures were prepared with different mixing times. in the mixtures where false set related anomaly was the case, rheological properties were positively affected by prolonging the mixing time.Turkish Cement Manufacturers AssociationTurkish Cement Manufacturers Associatio

EFFECT OF POLYMER/CEMENT RATIO AND CURING REGIME ON POLYMER MODIFIED MORTAR PROPERTIES

WOS: 000582670600010Cement is the most consumed building material in the world. However, cement manufacture is responsible for 5-7% of the world CO2 emissions. in this paper, cement was partially replaced by styrene-butadiene rubber (SBR) polymeric latex in order to reduce cement consumption. Besides, effects of SBR addition on the strength and physical properties of plain mortar exposed to three different curing regimes are presented. Three different curing regimes were applied to the 40 x 40 x 160 mm prismatic mortar specimens: (I): Specimens were cured in water until the test age (CW), (II): after demoulding, specimens were immersed in water for 2 days and kept in ambient temperature until the time of the test (2DWA) and (III) involved 2 days of water curing followed by 1 day in an oven at 50 degrees C and subsequentely placing in ambient temperature until the test time (2W1OA). Results showed that combining 2 days of water curing followed by ambient temperature curing (2DWA) along with 3% SBR polymer content showed good performance in terms of compressive strength, water absorption and void content. Moreover, a good performance in terms of flexural strength was observed by combining 2W1OA curing regime with 2% SBR content. However, the detrimental effect of water curing regime (CW) in terms of compressive and flexural strength was also observed with the increase of SBR ratio

THE ROLE OF NA(2)O(EQ )RATIO ON THE FLOWABILITY AND STRENGTH DEVELOPMENT OF CEMENTITIOUS SYSTEMS IN THE PRESENCE OF A POLYCARBOXYLATE ETHER-BASED ADMIXTURE

###EgeUn###In this study, the effect of equivalent Na2O(Na2Oeq) ratio of cement on fresh properties and compressive strength of paste and mortar mixtures containing polycarboxylate ether-based high range water reducing (HRWR) admixture was investigated. A low and a high alkali cement were used. Five mixtures having five different Na2Oeq ratios were prepared with increasing alkali content of the cement by incorporating three different amounts of NaOH solution to the low alkali cement-bearing mixtures. Irrespective of the absence or presence of HRWR, Na2Oeq content of the mixtures was found to have a considerable adverse effect on the fresh properties of the mixtures, particularly on their flow loss. NaOH addition increased 1-day compressive strength of the mortar mixtures, however, reduced the compressive strength at later ages. In spite of having a lower fineness and a longer setting time, low alkali cement showed slightly higher 1-day strength than high alkali cement. This seems to have occurred, to some extent, from the higher HRWR admixture demand (0.4 wt.%) of the high alkali cement-bearing mixture than that of the mix containing low alkali cement (0.25 wt.%). At later ages, both of the cements showed equivalent strength values.Turkish Cement Manufacturers AssociationThe authors would like to thank Baticim and Oyak cement plants for their kind assistance in providing the cements and determining the chemical composition of the cements. The first author would like to acknowledge the scholarship provided by Turkish Cement Manufacturers Association during his PhD study