Browsing by Author "Azima, Mahzad"

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Crack remediation in mortar via biomineralization: effects of chemical admixtures on biogenic calcium carbonate
(Elsevier, 2018-11-30) Amiri, Ali; Azima, Mahzad; Bundur, Zeynep Başaran; Civil Engineering; BUNDUR, Zeynep Başaran; Amiri, Ali; Azima, Mahzad
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.
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Influence of Sporasarcina pasteurii cells on rheological properties of cement paste
(Elsevier, 2019-11-20) Azima, Mahzad; Bundur, Zeynep Başaran; Civil Engineering; BUNDUR, Zeynep Başaran; Azima, Mahzad
Nowadays with the developments in the concrete materials technology, researches started to focus on highly flowable mixes with improved rheological properties. These highly flowable mixes generally require use of viscosity modifying agents (VMAs) to reduce bleeding and segregation. VMAs are water-soluble polymers that can be produced from acrylic polymers and polysaccharide-based biopolymers obtained from cellulose, starch or bacterial fermentation. Through the literature, nopal mucilage, brown algae and bacterial cell walls were proposed as alternatives to these bio-based admixtures. However, these alternatives also require extra processing which results again with a higher unit cost. This paper summarizes the rheological properties of a cement paste including bacterial cells. The main goal of this study was to investigate the influence of Sporasarcina pasteurii (S. pasteurii) cells on viscosity and yield stress of cement-based materials. The bacterial cells were directly incorporated to the mix water and influence of cells on viscosity and yield strength was evaluated by rheological tests. In addition, the influence of bacteria dosage, water to cement ratio (w/c), use of superplasticizers and fly ash on performance of biological VMA were investigated. Our results showed that the apparent viscosity and yield stress of the cement-paste mix were increased with the addition of the microorganisms. Moreover, the provided biological VMA was found to be compatible with the use of fly ash and superplasticizers depending on the w/c of cement paste.
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Rheology modifying agents : a key technology developed by using microorgsnisms
(2018-08) Azima, Mahzad; Bundur, Zeynep Başaran; Bundur, Zeynep Başaran; Fındıkçı, İlknur Eruçar; Zihnioğlu, N. Ö.; Department of Civil Engineering; Azima, Mahzad
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.