1,721,010 research outputs found
Prediction of mechanical and penetrability properties of cement-stabilized clay exposed to sulfate attack by use of soft computing methods
No full textSimilar to its effects on any type of cementitious composite, it is a well-known fact that sulfate attack has also a negative influence on engineering behavior of cement-stabilized soils. However, the level of degradation in engineering properties of the cement-stabilized soils still needs more scientific attention. in the light of this, a database including a total of 260 unconfined compression and chloride ion penetration tests on cement-stabilized kaolin specimens exposed to sulfate attack was constituted. the data include information about cement type (sulfate resistant-SR; normal portland (N) and pozzolanic-P), and its content (0, 5, 10 and 15%), sulfate type (sodium or magnesium sulfate) as well as its concentration (0.3, 0.5, 1%) and curing period (1, 7, 28 and 90 days). Using this database, linear and nonlinear regression analysis (RA), backpropagation neural networks and adaptive neuro-fuzzy inference techniques were employed to question whether these methods are capable of predicting unconfined compressive strength and chloride ion penetration of cement-stabilized clay exposed to sulfate attack. the results revealed that these methods have a great potential in modeling the strength and penetrability properties of cement-stabilized clays exposed to sulfate attack. While the performance of regression method is at an acceptable level, results show that adaptive neuro-fuzzy inference systems and backpropagation neural networks are superior in modeling.Ege University Science and Technology Centre-Technology Transfer Office (EBILTEM)Ege University [113M202, 2014-BIL-009]; Scientific and Technological Research Council of Turkey (TUBITAK)Turkiye Bilimsel ve Teknolojik Arastirma Kurumu (TUBITAK) [113M202, 2014-BIL-009]The authors appreciate contributions of the Scientific and Technological Research Council of Turkey (TUBITAK) and Ege University Science and Technology Centre-Technology Transfer Office (EBILTEM) under grant numbers 113M202 and 2014-BIL-009, and the support provided by Cimenta Group, Denizli Cimento A.S. and Akcansa for providing cements used in the experimental part of this study
Effect of the addition of polypropylene fiber on concrete properties
No full textThe random distribution of polypropylene fibers in concrete mixtures leads to an increase in abrasion and freeze-thaw resistance, a decrease in volume expansions formed as a result of sulfate attack and alkali silica reaction (ASR). Since the addition of polypropylene fiber in appropriate ratios to concrete mixtures improves the durability properties of the elements, the total cost decreases. The energy absorption capacity of concrete mixtures increases and their plastic shrinkage cracks significantly decrease by polypropylene fiber utilization. This study presents a comprehensive literature review related to history, advantages and disadvantages, workability, mechanical properties, durability performance and dimensional stability of polypropylene fiber-bearing concrete mixtures. For this aim, compressive, tensile and flexural strengths, modulus of elasticity, flexural crack and post-cracking behavior, the resistance of freeze-thaw, sulfate, high-temperature and abrasion as well as alkali-silica reactivity, drying shrinkage-based length change and impact strength of fibrous concrete mixture are thoroughly discussed
Vibration analysis of steel fiber reinforced self-compacting concrete beam on elastic foundation
No full textIn this study, the effect of steel fiber utilization, boundary conditions, different beam cross-section, and length parameter are investigated on the free vibration behavior of fiber reinforced self-compacting concrete beam on elastic foundation. In the analysis of the beam model recommended by Euler-Bernoulli, a method utilizing Stokes transformations and Fourier Sine series were used. For this purpose, in addition to the control beam containing no fiber, three SCC beam elements were prepared by utilization of steel fiber as 0.6% by volume. The time-dependent fresh properties and some mechanical properties of self-compacting concrete mixtures were investigated. In the modelled beam, four different beam specimens produced with 0.6% by volume of steel fiber reinforced and pure (containing no fiber) SCC were analyzed depending on different boundary conditions, different beam cross-sections, and lengths. For this aim, the effect of elasticity of the foundation, cross-sectional dimensions, beam length, boundary conditions, and steel fiber on natural frequency and frequency parameters were investigated. As a result, it was observed that there is a noticeable effect of fiber reinforcement on the dynamic behavior of the modelled beam
Uçucu küllü silindirle sıkıştırılmış betonlarda dayanıklılık
No full textSilindirle 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
Sülfat etkisine maruz çimento ile stabilize edilmiş zeminlerin mikroyapısının incelenmesi
No full textÇimento ile zeminlerin stabilizasyonu, son yüzyılda kullanılan ve zeminlerin mühendislik
özelliklerinin geliştirilmesinde oldukça faydalı yöntemlerden biridir. Dayanımda sağladığı
artışın yanı sıra, geçirimlilikte sağladığı azalma ve hacimsel stabilitede artış bu yöntemin
sağladığı faydalardan birkaçıdır. Öte yandan, çimento stabilize zeminlerin sülfat etkisinde
kalması veya zeminin içinde sülfat bulunması halinde oluşan kimyasal reaksiyonlar sonucu
dayanım azalmakta ve hacimsel stabilite bozulmaktadır. Bu kapsamda, sülfat etkisi altındaki
kil zeminlerin stabilizasyon sonucu iyileşen mühendislik özelliklerinin değerlendirilmesi için,
sistematik bir yaklaşım yapılmıştır. Değişik tipte ve içerikte çimento kullanımının, sodyum ve
magnezyum sülfat tuzlarının, tuz konsantrasyonunun ve kür süresinin etkileri ayrı ayrı
değerlendirilmiştir. Kil zemin, iki tip çimento (normal portland ve sülfata dayanıklı)
kullanılarak stabilize edilmiştir. Çimento içeriği ağırlıkça % 0, 5, 10 ve 15 olarak seçilmiştir.
Öngörülen karışımlar Standart Proktor deneyleri sıkılığında hazırlanmıştır. Karışım suyu
hazırlanırken, sodyum sülfat ve magnezyum sülfat olmak üzere iki tip sülfat kullanılmış,
konsantrasyonları %0.3, 0.5 ve 1 olarak öngörülmüştür. Hazırlanan karışımlar 1, 7, 28 ve 90
günlük süre ile kürlenirken sodyum ve magnezyum sülfat etkisine maruz bırakılmıştır. Bu süre
sonunda serbest basınç dayanımları belirlenmiştir. Deneysel olarak elde edilen sonuçlar,
karşılaştırmalı olarak ortaya konulmuştur. Ayrıca, sülfat etkisinin çimento stabilize kil zeminin
içyapısında oluşturacağı etkiler, seçilen örnekler üzerinde SEM ve EDS analizleri ile
araştırılmıştır. Elde edilen sonuçlar, çimento içeriğinin ve kür süresinin artışı ile birlikte
dayanımın arttığını göstermiştir. Ortamda sülfat bulunduğunda ise etrenjit oluşumu ile oluşan
mikro çatlaklar dayanımın azalmasına neden olmuştur. Sülfat etkisine karşı koyan bir çimento
stabilize zeminin çimento içeriğinin %10 oranında olması gerektiği gözlemlenmiştir.
Mikroyapısal incelemeler ve dayanım deneyleri, betonda olduğu gibi, sülfata dayanıklı çimento
kullanımının çimento stabilize zeminlerde de sülfat etkisinin yarattığı hasara karşı bir direnç
gösterdiğini kanıtlamıştır.Widely used in the last century, stabilisation of soils with cement is known to provide benefits
in promoting the engineering properties of soils. In addition to its positive effects on strength,
additional advantages of this stabilisation method can be counted as the reduction in
permeability as well as the increase in volumetric stability. On the other hand, chemical
reactions occurring in cement stabilised soils either including sulfate salt or under sulfate attack
cause reduction in strength and loss in volumetric stability. In this scope, a systematic approach
was carried out to evaluate the improvement of the engineering properties of clays exposed to
sulfate attack. Effects of cement type, cement content, sodium/magnesium sulfate salts, salt
concentration, and curing period as well were individually investigated. Clay was stabilised
using two types of cements, namely, normal portland cement and sulphate resistant cement.
The cement contents were considered to be 0, 5, 10 and 15%, by weight. The mixtures were
compacted using Standard Proctor effort. Two sulphate solutions were used: sodium sulphate
and magnesium sulphate solutions. The concentration of the salts in mixture water were
designated as 0.3, 0.5 and 1%. Specimens listed above were exposed to magnesium and sodium
sulphate attack during 1, 7, 28 and 90 days curing. Experimental results were comparatively
discussed. Moreover, the effect of sulfate attack on microstructure of cement stabilized clay
was investigated by carrying out SEM and EDS analyses on selected specimens. The results
obtained from experimental this experimental study revealed that, increase in cement content
and curing period caused increase in strength. Micro cracks caused by ettringite formation
induced strength loss. A cement stabilized clay resisting sulfate attack should include 10% of
cement, by weight. As previously observed in concrete, microstructural investigations and
results of strength tests revealed that use of sulfate resistant cement provide resistance against
sulfate attack in cement stabilized soils
Investigation of cement-superplasticizer Admixture compatibility
No full textBu 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
Effect of gypsum type on properties of cementitious materials containing high range water reducing admixture
No full textIn this study, the effect of cement gypsum type on properties of the properties of cement paste, mortar and concrete mixtures containing high range water reducing admixture (HRWR) was investigated. Two different types of cement prepared from the same clinker but containing either calcium sulfate hemihydrate or dihydrate as retarder were used. The fresh and hardened (compressive strength and drying shrinkage) properties as well as static and dynamic rheological behavior of the mixtures were investigated. Compared to the mixtures containing dihydtate, the fresh and rheological properties of mixtures were negatively affected when cement-containing hemihydrate was used. However, hemihydrate utilization had a positive influence on the early compressive strength. The adverse effects on fresh properties were more significant in paste mixtures. These negative effects decreased in the mortar and concrete mixtures. The presence of hemihydrate in cement was found to increase the drying-shrinkage. (C) 2016 Elsevier Ltd. All rights reserved.Turkish Cement Manufacturers AssociationThe authors would like to thank Izmir-Cimentas cement plant for their kind assistance in providing the cement and determining the chemical composition of the cement. The first author would like to acknowledge the scholarship provided by Turkish Cement Manufacturers Association during his PhD study
Sustainable materials: A review of recycled concrete aggregate utilization as pavement material
No full textIn this paper, a comprehensive literature review was conducted on the utilization of recycled concrete aggregate (RCA), which is the dominant construction and demolition waste material, in base and subbase layers and its comparison with natural aggregate (NA). The effects of crushing on the particles as a result of the compaction on the resilient modulus, permanent deformation, and California Bearing Ratio are analyzed. The paper also contains the NA consumption and waste disposal policies of different countries, RCA standards, and the environmental-economic reasons for its use. This literature review mainly focuses on pavement layers as this is the main application of RCA in the use of recycled materials. Developing integrated construction and demolition waste management will help achieve the primary goal of preventing and reducing the generation of these wastes, both locally and globally. In this way, not only is the main purpose of preventing the increase in the production of construction and demolition waste achieved, but also the reuse and recycling of the waste materials produced are encouraged. Results show that RCA has equivalent or better performance than virgin aggregate for almost any application with proper care and process control, and can be used in unbound pavement layers or other applications requiring compaction. But it is always recommended that its mechanical properties and durability performance be evaluated with full-scale tests before use. The information provided will be useful for contractors and engineers to evaluate alternative solutions and to explore the rational use of such sustainable materials in applications
Properties of self-consolidating concrete incorporating coarse recycled concrete aggregate
No full textIn this study, the effect of recycled concrete coarse aggregate on properties of self-consolidating concrete was examined. This aggregate was replacing 25%, 50%, 75%, 100% of limestone coarse aggregates. RC aggregate was used in SCC mixtures after 24 hours water saturation and surface dry (SSD). The results have shown that replacement of limestone coarse aggregate with RC aggregate caused the compressive strength decrease. However, the effect on tensile splitting and flexural strength was lower. As a result of this study it was found that it is possible to produce SCC compatible with EFNARC 2002. Moreover; it was observed that the use of RC aggregate in SSD state positively affected the fresh properties of SCC
Mechanical properties of high-volume fly ash roller compacted concrete designed by maximum density method
No full textIn 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
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