Rheoloji değiştirme ajanları : mikroorganizmalar ile geliştirilen anahtar teknoloji

Thesis (M.A.)--Özyeğin University, Graduate School of Sciences and Engineering, Department of Civil Engineering, August 2018.Recent development in concrete technology enabled the design of highly flowable mixes with improved workability. These advanced mixes require incorporation of fine materials or viscosity modifying agents (VMA) to reduce the possible segregation and bleeding due to the use of high range water reducers (such as superplasticizers). The VMAs used in concrete production are generally produced from acrylic polymers and polysaccharide-based biopolymers obtained from cellulose, starch or bacterial fermentation. Diutan gum, produced by fermentation of Sphinogomonas sp, and welan gum, which is a fermentation product of Alcaligenes sp, are the most commonly used polysaccharide VMAs. Similar polysaccharides can be obtained by fermentation of genetically modified bacteria or using plant cell walls. Most polysaccharide based VMAs are able to increase the viscosity of cement paste and exhibit shear thinning behavior such that increased shear rate results with a substantial decrease in apparent viscosity. This behavior is attributed to the long molecular structure of bio-based polysaccharides. Though highly effective bacterial fermentation products can resist the high PH environment of cement-paste, the ecological population of the species is not known. Thus, they are among the most expensive cement admixtures. Advances in construction technology and risen importance of sustainability initiatives reinforce the use of biological admixtures, however, their relatively high cost can be a major drawback in practical applications. Through the literature, nopal mucilage, brown algae, and bacterial cell walls were proposed as alternatives to these bacterial fermentation products. However, these alternatives also require extra processing which required bigger budget even compared to bacterial fermentation products. This project aims to incorporate bacteria cells to the cement-based mix as VMAs without any extra intervention. To achieve this goal, Sporosarcina pasteurii (S.pasteurii), Bacillus megaterium (B. megaterium), Bacillus subtilis (B. subtilis) and Paenibacillus polymyxa (P. polymyxa) were selected as suitable due to their abundant resource in nature. These Gram-positive bacterial cells include peptidoglycans and polysaccharides in their cell wall structure, which resembles the molecular structure of commercially used VMAs. In addition, these cells, particularly B. subtilis, can influence the viscosity of a suspension due to its motility. Throughout the study, these cells were grown in specified nutrient media and then harvested from the inoculum by centrifuging. Then, these cells were suspended in mixing water and their influence on the rheology of cement paste was evaluated. In addition, the influence of water to cement ratio, the dosage of cells added was evaluated along with the impacts of superplasticizers and fly ash on the performance of bacteria cells as VMAs. There are few established industrial and various small-scale companies that produce biological admixtures for cement-based materials. However, nationwide these biological admixtures (for instance chitosan) are only produced for the food industry. The product obtained by the end of this study is a novel and sustainable practice in Turkey, where the construction industry leads the economy.Günümüzde gelişen beton teknolojisi, yeni kuşak çimento esaslı malzemelerin gelişiminin önünü açmıştır. Akışkanlığı ve işlenebilirliği yüksek harç ve betonların kullanımı gittikçe artmaktadır. Bu tür malzemelerde dağıtma gücü çok yüksek akışkanlaştırıcı katkıların neden olduğu ayrışmayı (segregasyon) ve terlemeyi önleyebilmek için daha ince tanecikli malzemeler veya viskozite düzenleyici katkıların (VDK) kullanımı artmaktadır. VDK, akışkanlığı yüksek olan beton ya da harçların kararlılığını (stabilizesini) arttırmakta ve taze çimento hamuru performansını yükseltmektedir. Günümüzde beton üretiminde kullanılan VDK’lar suda çözünen polivinil alkol veya polimerlerden oluşmaktadır. VDK’lar akrilik polimerlerden, selülozdan, nişastadan veya bakteri fermantasyonu gibi polisakkarit bazlı biyopolimerlerden elde edilmektedir. Bakterilerden elde edilen polisakkaritlerden CP Kelco adlı şirketin Sphingomonas bakterisinin fermantasyonu ile elde ettiği diutan sakızı, Merck & CO adlı şirketin Alcaligenes bakterisini kullanarak ürettiği welan sakızı çimento esaslı malzemelerde VDK olarak sıkça kullanılmaktadır. Benzer şekilde piyasada bakterilerin genleri ile oynanarak ya da bitkilerin hücre duvarları kullanılarak farklı polisakkaritler elde edilebildiği bilinmektedir. Çimento esaslı malzemelerde VDK olarak kullanılan biyolojik polisakkaritler çimento hamurunun viskozitesini arttırdığı belirlenirken, yapılan testlerde kayma hızı arttırılırken malzemenin inceldiği (shear-thinning) gözlemlenmiştir. Bu özelliklerin biyolojik polisakkaritlerin uzun moleküler yapısı ile ilişkili olduğu bilinmektedir. Bu fermantasyonun ürünü olan polisakkaritler yüksek PH değerlerine dayanma özellikleriyle ön plana çıkarken, bunları üretecek mikroorganizmaların ekolojik olarak popülasyonu bilinmemektedir. Bu nedenle birim fiyat yükselmektedir. İlerleyen teknoloji ve sürdürülebilirlik bilinci biyolojik katkı malzemelerinin inşaat sektöründe kullanımının artmasını teşvik ederken, maliyetlerinin yüksek olması bir dezavantaj yaratmaktadır. Uluslararası literatürde bu fermantasyon ürünlerine alternatif olarak göllerden toplanan yosunlar ve bakterilerin, sadece hücre duvarlarının ayrıştırılarak kullanılması incelenmiştir. Ancak bu iki ürünün elde edilmesinde özel işçilik gerektirecek farklı işlemlerin uygulanması, maliyetlerin yine yükselmesine sebep olmuştur. Bu projenin amacı doğadan kolayca elde edilen mikroorganizmaları, hücre duvarını ayrıştırılması gibi özel işlemler gerektirmeden, çimento esaslı malzemelerde VDK olarak kullanarak reolojisi iyileştirilmiş bir çimento harcı (ürün) elde etmektir. Bu amaç doğrultusunda Sporosarcina pasteurii, Bacillus magetrium, Bacillus subtilis ve Paenibacillus polymyxa bakteri suşları seçilmiştir. Bu çalışma süresince, bakteriler besi yerlerinde büyütüldükten sonra santrifüj edilerek ortamdan ayrıştırılmıştır. Ardından bu hücreler çimento karışım suyuna eklenmiş ve çimento hamurunun reolojisine olan etkileri test edilmiştir. Ayrıca farklı su oranlarında ve bakteri dozajlarının test edileceği karışımlara, süperakışkanlaştırıcıların ve uçucu külün bakterilere olan etkisi incelenmiştir

Crack remediation in mortar via biomineralization: effects of chemical admixtures on biogenic calcium carbonate

Due to copyright restrictions, the access to the full text of this article is only available via subscription.Limited research on biomineralization in cement-based systems suggested that self-healing of surface cracks could be obtained by triggering biogenic calcium carbonate (CaCO3) precipitation within the cracks. While this is encouraging, there is not enough information regarding the influence of admixtures on crack remediation and durability of the biogenic CaCO3 against weathering conditions. In this study, the microorganisms were introduced to mortar with their growth medium, which included corn steep liquor (CSL) and urea. With this approach, the cracks on mortar surface were sealed with the CaCO3 and the water absorption capacity of the so-called self-healed mortar decreased compared to its counterpart cracked mortar samples. The biogenic CaCO3 precipitate was found to be durable against freeze-thaw; however the precipitate was unstable under rain water and light. While the addition of air entraining agents (AEA) did not influence the self-healing ability of cells, use of superplasticizers improved the self-healing ability in terms of crack sealing, water absorption, and durability of the precipitate.TÜBİTA

Rheological measurements of printable mortars containing calcium sulfoaluminate cement

The introduction of digital fabrication in the construction field presents a significant advantage over conventional production methods. As the material itself shoud fulfill some of the requirements that used to be imposed on the formwork, improving the mix-design for the new technique remains a challenge. Although many approaches exist to adjust the rheological properties of printable mortars by modifying mix designs, combining the appropriate rheological properties of the fresh printable material with an optimized setting rate, can introduce a suitable mix-design for the construction industry. Meanwhile, the main objective of digital fabrication, namely to increase the environmental and economic sustainability should be taken into account. This experimental study represents the rheological behaviour of printable mixture composed of two different types of cement : Ordinary Portland Cement (OPC) and Calcium Sulfo-Aluminate cement (CSA). This investigation considered a steady stress sweep method to analyze the rheological behavior of pastes composed of CSA (20% OPC replacement). The behavior of the cement pastes with OPC and CSA cement was studied in specific time intervals to determine the open time. Then, mortars were made from selected mix designs and printed in the same time gaps, to investigate the time that the deposited first layer can be stable with fewer surface defects. Automated Laser Measurements (ALM) were performed to compare the shape stability and surface quality of printed layers. The results showed that the replacement of OPC by CSA increased the yield stress in the mixtures. Moreover, when including CSA cement, mixtures were extrudable and also printable, with a reduced but efficient open time. The increasing amount of sulphoaluminate clinker resulted in higher yielding point in a shorter period of time

Combination of Portland cement and calcium-sulfoAluminate cement : the highroad for durable 3D printing ?

3D printing of cementitious materials opens new horizons for the construction industry. This newly developed technique uses a layer-by-layer fabrication process, inducing a higher porosity at the interface between the printed filaments. Consequently, this interface zone offers an ideal ingress path for chemical substances and affects the durability in a negative way. This in combination with a high content of ordinary Portland cement (OPC) in the composition of printable mixtures counteracts the many advantages of the construction type and decreases the eco-friendliness of the material drastically. To improve the "green" character of 3D printed cementitious materials, combinations of OPC and Calcium-Sulfoaluminate (CSA) cement are often made. This combination shows advancements regarding the evolution of cement hydration, but the expansive character of CSA cement also leads to the formation of additional voids which will affect the microstructure in a significant way. For the purpose of this research, 4 different mix compositions with OPC replacements up to 20% have been prepared and their effect in fresh state is investigated through measurements and isothermal calorimetry (TAM AIR). Scanning Electron Microscopy (SEM) analysis was performed on two layered printed specimens to examine the effect on the microstructure in hardened state and correlate the results with the mechanical performance, measured by compressive test and inter-layer bonding tests. These results showed that the setting time is lower for every combination of OPC and CSA, creating mixtures with a higher buildability. Due to the low amount of anhydrite, the expansive character of CSA is most pronounced in case of 10% and 15% OPC replacement, resulting in a higher amount of capillary pores and affecting the mechanical performance in the most negative way

Neutron radiography to study the water ingress via the interlayer of 3D printed cementitious materials for continuous layering

info:eu-repo/semantics/publishe

Neutron radiography to study water ingress via the interlayer of 3D printed cementitious materials

3D printing of cementitious materials is a newly developing technology in which structural elements are built via a layer-by-layer process. Among the many advantages of this technique, it is also expected to lead to more sustainable structures due to a reduced waste generation nd more efficient structural design, placing materials only where needed. However, the result of this technique is a layered and anisotropic specimen, creating weak interlayers which will not only endanger the structural behaviour, but also affect the durability as they form a preferential path for the ingress of aggressive substances. For the reason, this research study focuses on the transport of water through printed elements, fabricated with different print velocities (i.e. 1.7 cm/s and 3.0 cm/s) and with special attention for the interlayer interface. Water transport was visualised by means of neutron radiography, performed at the Paul Sherrer institute in Villigen. The effect of an increased print velocity is investigated through qualitative and quantitative analyses of the obtained radiographs. First qualitative results showed that for samples printed with a lower printing speed, the water uptake occurs in a more uniform way compared to specimens printed with a higher velocity. In case of a higher printing speed, the water ingress starts more at he sides and this effect becomes more and more pronounced due to the non-uniform distribution of sand particles through the sample. These results are confirmed by representing the water profile at the interface in a quantitative way. Calculation of the amount of water in a specifed zone at the interface shows that, independently from the water distribution, the water uptake after 60 minutes of exposure is higher in case of a low printing speed