Report from 13th ICPIC and 7th ASPIC : new trends on concrete-polymer composites

The field of polymers in concrete is consolidated in the construction industry. The future of polymers in concrete is governed by the synergic interaction between these materials, in order to contribute significantly towards a more sustainable construction. Concrete-polymer composites (C-PC) have excellent mechanical and durability properties. Appropriate combination of polymers and classical construction materials provides opportunities for innovative applications and systems. This paper highlights the innovations and new approaches presented at the 13th International Congress on Polymers in Concrete in Madeira, Portugal, 2010 and at the 7th Asian Symposium on Polymers in Concrete in Istanbul, Turkey, 2012. The new trends presented are related with the micro and nanostructure, properties, test methods and applications of concrete-polymer composites

The effect of composition parameters on the rheological properties for self-compacting concretes

Kendiliğinden yerleşen beton (KYB), yeni nesil süperakışkanlaştırıcı katkılar ve değişik mineral katkılar kullanılarak geliştirilmiş yeni bir beton türüdür. Bu çalışmada, faktöriyel analiz yöntemi kullanılarak çimento hamuru, harç ve beton bileşenlerinin reolojik özelliklere etkileri araştırılmıştır. Su/bağlayıcı, mineral katkı/bağlayıcı, kimyasal katkı/bağlayıcı ve kum/bağlayıcı oranları değişken olarak seçilmiştir. Reolojik parametreler olarak, çökme-yayılma, viskozite ve kayma eşiği değerleri  ölçülmüştür. Uçucu kül ve silis dumanı, normal Portland çimentosu ile yer değiştirerek kullanılmıştır. Faktoriyel analiz sonunda reolojik özellikleri anlamlı olarak etkileyen bileşim parametreleri belirlenmiştir. Süperakışkanlaştırıcı katkılı çimento hamuru ve harç karışımlarının Bingham cismi gibi davranmasına karşılık, beton karışımlarında kayma eşiğinin sıfıra yakın değerler aldığı ve bu nedenle yaklaşık olarak  Newton cismi gibi davrandığı görülmüştür.  Anahtar Kelimeler: Kendiliğinden yerleşen beton, beton viskozimetresi, işlenebilme, reoloji, süperakışkanlaştırıcı, mineral katkı.Self-compacting concrete (SCC) has been developed using new generation superplasticizers and different mineral admixtures, and can be consolidated under its own weight without any vibration. It is suitable for high performance and densely reinforced structures as well as in most applications where traditionally vibrated concrete is used. The aim of this study is to investigate the effects of constituent materials on rheological properties of cement paste, mortar and concrete by application of factorial analysis method. Water/binder, mineral admixture/binder, chemical admixture/binder and sand/binder ratios were chosen as variables in the analysis. Slump-flow, viscosity (relative torque viscosity for concrete)  and yield shear (relative yield torque for concrete) were rheological parameters and their variations by time up to 90 minutes were recorded. A fly ash and a silica fume were used as fine materials for partial substitution of the normal Portland cement. By the factorial analysis the composition factors significantly influencing the rheological properties are determined. Test results show that, although the cement paste and mortar prepared with self-compacting superplasticizer, act as Bingham materials, the yield torque for the concrete approaches to zero indicating approximately a Newtonian-material behaviour.Keywords: Self-compacting concrete, concrete viscosimeter, workability, rheology, superplasticizer, mineral admixture

Effect of mixing proportions on the compressive strength and permeability of concretes containing mineral admixtures

Betonda dayanıklılığın (dürabilite) en az dayanım kadar önemli olduğu son yıllarda daha iyi anlaşılmaya başlamıştır. Dayanıklı beton üretmek için düşük su/çimento oranının yanında puzolan (mineral katkı) kullanımının da gerekli olduğu bilinmektedir. Bu deneysel çalışmada farklı oranlarda uçucu kül veya silis dumanı mineral katkıları içeren iki seri beton üretilmiştir. ‘Merkezi Kompozit Tasarım’ adındaki deneysel tasarım ve analiz yapan istatistiksel yöntem kullanılarak her seride karışım parametrelerinden toplam bağlayıcı miktarı, su/bağlayıcı oranı ve puzolan/bağlayıcı oranı bağımsız değişken olarak seçilmiştir. Değişken sınırları puzolan özelliklerine ve betonların belirli bir kıvamda bulunması koşuluna göre belirlenmiştir. Her seride, kullanılan istatistiksel programın belirlediği 20 adet karışım hazırlanmıştır. Betonların basınç dayanımı ve klorür geçirimliliğini ölçmek üzere alınan numunelerin yarısı laboratuvar ortamında havada diğer yarısı da kirece doygun su içerisinde 90 gün boyunca saklanmıştır. Basınç dayanımının yanında ASTM C 1202 standardına uygun olarak hızlı klorür geçirimliliği deneyleri gerçekleştirilmiştir. Tüm deney sonuçları varyans analizi ile değerlendirilmiş ve her iki kür koşulu için ölçülen beton özelliklerinin karışım parametreleri cinsinde ayrı ayrı modelleri belirlenmiştir. Betonun seçilen bileşim parametrelerinin (toplam bağlayıcı miktarı, su/bağlayıcı oranı ve puzolan/bağlayıcı oranı) basınç dayanımı ve klorür geçirimlilği üzerine etkisi elde edilen istatistiksel modellere dayanılarak değerlendirilmiştir. Hızlı klorür geçirimliliği deneyinin havada saklanan betonların karşılaştırılmasında kullanılabileceği ancak su kürü uygulamasında mineral katkılı betonlarla katkısız betonların karşılaştırılmasında hatalı sonuçlara neden olabileceği belirlenmiştir.  Anahtar Kelimeler: Uçucu kül, silis dumanı, kür koşulları, istatistiksel analiz, merkezi kompozit tasarım.Concrete is a material which contains different amounts of pores in various sizes. On this account, penetration of liquid and/or gas into the concrete occurs by diffusion, absorption under pressure or capillary sorption through the pores. In no matter what way the transfer of liquid and gas occurs, the phenomenon is called as permeability. Permeability depends on amount, distribution, size and connectivity of pores within concrete for as much as rate of penetration of aggressive substances into concrete mainly related to the continuity of the pores and their shape and distance. It has been widely accepted for many years that mechanical strength of concrete is adequate enough for a structure and little maintenance would be sufficient to overcome any problem occurred during the service life. However, in recent years it is well known that in order to obtain a durable concrete, which shows the expected performance throughout its service life, selection of suitable materials in accordance with environmental conditions, the best proportion of concrete mixture and sufficient curing after casting are the most important steps to pay attention. Ingredients of concrete should be selected according to their participation in durability. Pozzolanic materials, most of which are by products of industries, are widely used in concrete production, especially to increase the durability properties. Pozzolanic materials react with Ca(OH)2, generated during the hydration of C3S and C2S components of cement, to form calcium silicate hydrate (C-S-H), hence reduce a weak part of concrete against durability. Furthermore, pozzolans improve the impermeability of concrete which is the main parameteraffecting the durability of concrete. In this experimental research, two series of concrete incorporated with fly ash and silica fume were produced. The statistical program of 'Central Composite Design' was used to design experiments and to analyze the testing results. In each series, total binder content, water/binder ratio and pozzolan/binder ratio were chosen as independent variables and the ranges of the variables were adjusted according to the properties of pozzolanic material and to obtain certain workability for all concretes. The range of the factors were selected between 300-400 kg/m3 for binder content, 0.48-0.58 (when silica fume was used) or 0.46-0.60 (when fly ash was used) for water/binder ratio and 0.03-0.12 for silica fume/binder ratio or 0.10-0.40 for fly ash/binder ratio. For each series of concretes, the total number of batches was 20. Lime saturated water curing was applied over the half of the specimens, cast to measure compressive strength and permeability, while the remaining ones were stored in air at laboratory conditions for 90 days. In addition to the compressive strength test, rapid chloride permeability test was conducted in accordance with ASTM C 1202. Test results were analyzed and evaluated by using ANOVA (Analysis of Variance). Statistical models are derived for each measured concrete property in two curing conditions by means of three independent components of concrete. Influence of selected mixture parameters on compressive strength and chloride permeability was evaluated by using the test results. It has been found that total binder content of fly ash added concretes was not influential on the compressive strength and chloride penetration. On the other hand, increasing binder content reduced the overall performance of silica fume added concretes because of the higher porosity of cement paste than that of aggregate. It was also seen that the optimum supplementary cementing material contents determined to obtain the minimum chloride permeability are shifted to higher values for the fly ash added concretes under the proper curing conditions rather than storing in air. However, the optimum percentages of the silica fume added concretes cured under both conditions are not changed. Besides, it is found that RCPT method can be employed to make comparisons for all of the air stored concretes produced with or without supplementary cementing material (SCM). However, for water cured SCM added specimens this method can be used for only internal comparisons, it is not appropriate to compare the chloride permeability of OPC concretes with those of pozzolan added concretes.  Keywords: Fly ash, silica fume, curing conditions, statistical analysis, central composite design

Antituberculosis drug resistance patterns in two regions of Turkey: a retrospective analysis

BACKROUND: The emergence of Mycobacterium tuberculosis strains resistant to antituberculosis agents has recently received increased attention owing largely to the dramatic outbreaks of multi drug resistance tuberculosis (MDR-TB). METHODS: Patients residing in Zonguldak and Kayseri provinces of Turkey with, pulmonary tuberculosis diagnosed between 1972 and 1999 were retrospectively identified. Drug susceptibility tests had been performed for isoniazid (INH), rifampin (RIF), streptomycin (SM), ethambutol (EMB) and thiacetasone (TH) after isolation by using the resistance proportion method. RESULTS: Total 3718 patients were retrospectively studied. In 1972–1981, resistance rates for to SM and INH were found to be 14.8% and 9.8% respectively (n: 2172). In 1982–1991 period, resistance rates for INH, SM, RIF, EMB and TH were 14.2%, 14.4%, 10.5%, 2.7% and 2.9% (n: 683), while in 1992–1999 period 14.4%, 21.1%, 10.6%, 2.4% and 3.7% respectively (n: 863). Resistance rates were highest for SM and INH in three periods. MDR-TB patients constituted 7.3% and 6.6% of 1982–1991 and 1992–1999 periods (p > 0.05). CONCLUSION: This study demonstrates the importance of resistance rates for TB. Continued surveillance and immediate therapeutic decisions should be undertaken in order to prevent the dissemination of such resistant strains

Investigation of properties of macro defect free (MDF) cements prepared with different polyvinyl alcohol copolymers and alumina cements

Macro-Defect Free (MDF) Cements, which are cement-polymer composites, had been developed and patented by the scientists from Imperial Chemical Industry (ICI) in order to increase especially the flexural strength of cementious materials by decreasing large voids at the early 1980?s in London. These new composite materials were produced by adding small amount of polymer and water into the cement and processed in a different method inspired by rubber production. The most important property of this composite is its unusually high flexural strength. Although, generally more than 80% (by weight) of this composite is cement, it has 20-30 times higher flexural strength than conventional cement paste. 150-300 MPa flexural strengths are easily achieved which are close to the strength of ordinary steel and it was a very important development if we compare it with ordinary cement paste which has only 5-10 MPa flexural strength. Inventors of the MDF cements attributed this high flexural strength to the elimination of macro voids in the material during processing and they thought that polymer was a rheological aid and inert filler. However, further studies have proved that crosslinking reactions between the ions of cement and polymer chains are also very important to obtain such high flexural strengths. In addition, pressing the material under moderate temperature after production is another reason for improving mechanical properties. Different cement and polymer types can be used for the production of this composite material. However, highest flexural strengths are always obtained when Calcium Alumina Cements (CAC) as cement and Poly (Vinyl alcohol) Acetate (PVAc) copolymers as polymer were used. On the other hand, this composite has serious durability problems under water effect. Significant amount of swelling are observed and the strength of this composite decreases in water storage even in very short time. In this study, MDF cements were produced by using CAC-PVAc copolymers and effects of ingredients on the water sensitivity were investigated. In the first part of the experimental studies, MDF cements were produced with different type of PVAcs which differ in their hydrolysis degrees. Secondly, MDF cements were also produced with four different types of CACs which differ in their Al2O3 content and their effects on water sensitivity were investigated. Biaxial flexural strength tests were conducted on the specimens after storing in both dry and humid conditions. Purpose of these tests was finding the most suitable PVAc and CAC type with respect to both mechanical and durability properties. Seven different types of PVAc were used in the first step. Their hydrolysis degrees were changing between 79.6 to 99.1%. MDF cements were successfully produced with 5 of 7 different PVAcs, except those with fully hydrolyzed PVAc (98.4%) or carboxylated PVAc (96.0%). All mixtures were affected from moisture in different rates between 45% and 80% depending on PVAc type. However, the PVAc at the lowest hydrolysis degree (79.6%) gave the lowest strength loss (45%). Increasing the degree of hydrolysis of PVAc increased the strength loss of MDF specimens stored in water.In the second step, MDF cements were produced with 4 different types of calcium alumina cement, which their alumina contents were changing between 42 to 79%. Water/cement ratio was changing between 0.09 and 0.19 while the polymer/cement ratio was kept constant at 0.07. Twenty five different batches were prepared in order to produce MDF cements, which differ in their water contents. Production was successful with all 4 different types of calcium alumina cements. The highest biaxial flexural strength was obtained as 257 MPa on CAC 70 composite, which was prepared by cement with 70% Al2O3 content and water/cement ratio of 0.15. The lowest biaxial flexural strength was 70 MPa and belongs to the CAC 79 composite, which was prepared with 79% Al2O3 content cement and water/cement ratio of 0.19. Although, the production of MDF becomes harder for highest level of Al2O3 (79%) than those with lower Al2O3 content there is a slight increase on properties with the increasing content of Al2O3 up to 70%. As conclusion, MDF cements, which were produced with low hydrolysis degrees PVAcs, and alumina cements, which have highest Al2O3 content up to 70%, showed higher flexural strength and better durability properties under water effect. Keywords: MDF cement, calcium alumina cement, polymer, polyvinyl alcohol acetate. composite.Literatürde Macro-Defect-Free (MDF) cement olarak adlandırılan büyük boşluklarından arındırılmış çimento-polimer kompozitleri veya kısaca MDF çimento olarak adlandırabileceğimiz malzeme 1980’li yılların başında çimento bazlı malzemelerin özellikle eğilme dayanımlarının artırılması amacıyla geliştirilmiştir. MDF çimentolar, ağırlıkça % 80’den fazla oranda çimentonun az miktarlarda polimer ve su ile karıştırılması ile elde edilir. Bu karışıma yüksek eğilme dayanımları elde edebilmek için kauçuk endüstrisinde de kullanılan kalenderleme işlemi uygulanmaktadır. Bu esnada çimento ve polimer arasında çapraz bağların olduğu düşünülmekte ve bu durum yüksek eğilme dayanımlarının temel sebebi olarak açıklanmaktadır. Ayrıca, bu malzemeyi üretimden sonra bir miktar basınç ve sıcaklık altında küre tabi tutmanın da eğilme dayanımının artırılmasında önemli etkisi vardır. Öyle ki normal çimento hamuru ile ancak 5-10 MPa eğilme dayanımı elde edilebilirken, MDF çimento ile 200 MPa’ı aşmak rahatlıkla mümkündür. Hatta bazı araştırmacılar 300 MPa’ın da üzerine ulaşarak çeliğin dayanımına yaklaşmışlardır. En yüksek dayanımlar alüminli çimento ve polivinil alkol-asetat (PVAc) kopolimerleri kullanılan kompozitlerde elde edilmektedir. Öte yandan, bu kompozitlerde çok önemli dürabilite problemleri söz konusudur. Özellikle bu malzemenin suyla temas etmesi halinde dayanımı büyük oranda düşmektedir. Bu çalışmada farklı PVAc ve alüminli çimentolar kullanılarak üretilen çimento-polimer kompozitlerinin dayanım ve dayanıklılık özellikleri incelenmiştir. Çalışmanın 1. bölümünde hidroliz dereceleri farklı PVAc’ların kullanılmasının MDF üzerindeki etkisi incelenirken, alüminli çimentoların Al2O3 yüzdesindeki değişimin etkilerinin incelenmesi 2. bölümü oluşturmaktadır. Bu sayede MDF çimento üretimi için en uygun malzemeler belirlenmeye çalışılmıştır.  Anahtar Kelimeler: MDF çimento, alüminli çimento, polimer, polivinil alkol-asetat, kompozit

Long term follow up results of sequential left internal thoracic artery grafts on severe left anterior descending artery disease

<p>Abstract</p> <p>Purpose</p> <p>Several alternative procedures have been proposed to achieve complete revascularization in the presence of diffuse left anterior descending coronary artery (LAD) disease. With the extensive use of internal thoracic artery grafts in coronary artery bypass procedures, sequential anastomosis of the left internal thoracic artery (LITA) to LAD has gained popularity in these challenging cases. The long term results of sequential LITA to LAD anstomosis were examined in this study.</p> <p>Patients and Methods</p> <p>In order to determine the long term results of the sequential revascularization of LAD by LITA graft, 41 out of 49 patients operated between January 2001 and December 2005 were selected for control coronary arteriography. The median period for control coronary arteriography was 64 months.</p> <p>Results</p> <p>Seventy five anastomoses were found to be fully patent (91,46%) among the 82 sequential LITA anastomoses (41 LITA grafts) on the LAD at a median follow-up period of 64 months (53 to 123 months). Among the 41 LITA grafts used for this purpose, 36 were found intact (complete patency of the proximal and distal anastomoses) (87,8%). Two LITA grafts (4 anastomoses) were found to be totally occluded (4,87%). The proximal anastomosis of the LITA graft was observed to be 90% stenotic in one patient (1,21%). In one patient tight stenosis of the distal anastomosis line was observed (1,21%), while in another patient 70% narrowing of LITA lumen after the proximal anastomosis was detected (1,21%).</p> <p>Conclusion</p> <p>We strongly beleive that sequential LITA grafting of LAD is a safe alternative in the presence of severe LAD disease to achieve complete revascularization of the anterior myocardium with patency rates not much differing from conventional single LITA to LAD anastomosis.</p

A Comparative Study on Colloidal Nanosilica Incorporation in Polymer-Modified Cement Mortars

Nanosilica and polymers are both well-known admixtures of cementitious mixtures, changing their properties differently upon employment. However, having them incorporated simultaneously, and their possible interactions in the mixtures, is yet to be studied. In this research, mortar mixtures, modified by one type of polymer latex (Styrene butadiene acetate) and two types of nanosilica colloids (different average particle sizes), were investigated for their flowability and long-term mechanical properties. Interesting observations were made in both fresh and hardened state; in the fresh state, the high water demand of nanosilica incorporating mixtures was moderated at the presence of the polymer, and in the hardened state, improvements were observed, especially in terms of flexural strength. Mortar mixtures were produced with different amounts of polymer and colloidal nanosilica, and, accordingly, numerical analyses and simulations have been conducted to model and gain a better understanding of the investigated properties