Kimyasal katkı malzemelerinin biyomineralizasyon ile kendiliğinden iyileşen çimento-esaslı malzemelerin performansına olan etkisi

Year 2019, Volume: 2 Issue: 1, 38 - 49, 15.06.2019

Zeynep Başaran Bundur , Ali Amiri

Abstract

Beton yapıların servis ömrünü etkileyen faktörler birbirleriyle genellikle bağlantılıdır. Beton gevrek ve kırılgan doğası yüzünden, gerilmeler altında çatlayabilir. Son yıllarda yapılan araştırmalar kendiliğinden iyileşen çimento esaslı malzemelerin üretiminin mümkün olduğunu göstermiştir. Kendiliğinden iyileşme özelliği, betonun oluşan çatlakları kendiliğinden kapatabilmesidir ve bu amaçla kullanılabilecek yenilikçi yöntemlerden biri biyomineralizasyondur. Biyomineralizasyon mikroorganizmaların metabolik aktiviteleri sonucu ürün olarak kalsiyum karbonat (CaCO₃) oluşmasıdır. Bu oluşan ürün/CaCO₃çökeltisinin çatlakları doldurması ile kendiliğinden iyileşme elde edilir.Bu çalışmanın amacı, çimento-esaslı malzemelerde kendiliğinden iyileşmenin sağlanabilmesi için çimento hamuru içine katılan bakterilerin malzemenin performansına olan etkisinin incelenmesidir. Bu amaç doğrultusunda bakteriler sulu besi yerinde büyütüldükten sonra hiçbir işlem uygulanmadan çimento harcı içine katılmış ve performans değerlendirmesi priz süresi, basınç dayanımı, karbonizasyon ve kendiliğinden iyileşme kabiliyeti incelenerek belirlenmiştir. Bakterilerin harç içine eklenmesi kimyasal yapıyı ve basınç dayanımını olumsuz yönde etkilemez iken, priz süresinde belirgin bir artış olmuştur. Bu artış, bakteri ile beraber çimento içine katılan besi yeri ile ilişkilendirilmiştir. Çimento harcı içine karıştırılan bakteriler eğilme altında oluşturulan çatlakları kapatabilmiş, ürün/CaCO₃çatlakları doldurmuştur. Son olarak, süperakışkanlaştırıcı ve hava sürükleyici katkı (HSK) gibi sıkça kullanılan katkı malzemelerinin biyomineralizasyona olan etkileri incelenmiştir. Süperakışkanlaştırıcı kullanımı bakterilerin kendiliğinden iyileşmeyi sağlamasında olumlu  bir etki sağlarken, HSK’nın çatlak içinde CaCO3 çökelmesini kısmen azalttığı gözlemlenmiştir.

Keywords

Kendliğinden iyileşme, priz süresi, biyomineralizasyon, basınç dayanımı, çimento harcı

Influence of chemical admixtures on performance of biomineralized self-healing cement-based materials

Abstract

Factors affecting the durability of concrete structures are generally associated with each other. Due to its brittle nature, concrete can crack when stress is applied.  Recent research in the field proposes that it might be possible to develop a smart, cement-based material that can self-heal itself. Self-healing is the ability of concrete to heal the cracks without any external application. Self-healing property of concrete can be obtained via different approaches. Use of biomineralization is a novel technique to provide self-healing in cement-based materials. Biomineralization is a biochemical process in which microorganisms stimulate the formation of minerals. In this system, calcium carbonate (CaCO₃) is induced by leveraging the metabolic activity of microorganism and self-healing is obtained by sealing of the cracks with CaCO₃.The goal of this study to investigate the influence of bacterial self-healing agent on performance of cement-based materials. In this study, the bacteria will be introduced to cement paste with its growth media without any additional manipulation such as encapsulation. Performance of cement-based mortar was evaluated by Vicat needle test, compressive strength test, thermogravimetric analysis and crack healing ability. While incorporation of bacterial cells did not affect the compressive strength and chemical composition, there was a significant delay in initial setting time. This was attributed to the nutrient medium added along with bacterial cells. With this approach, the flexural cracks on the mortar surface were sealed with the CaCO₃. At last but not the least the influence of superplasticizers and air entraining agents (AEA) on self-healing was investigated. While the superplasticizers improved the self-healing efficiency of the bacterial cells, AEA relatively educed the amount of CaCO₃precipitation within the cracks.

Keywords

Self-healing, cement-based mortar, biomineralization, compressive strength, initial settin time

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