Two-Part Bio-Based Self-Healing Repair Agent for Cement-Based Mortar

Factors affecting durability of concrete structures are generally associated with each other. Due to its brittle nature, concrete can crack under stress and these cracks are one of the main reasons for a decrease in service life in concrete structures. Therefore, it is crucial to detect and recover microcracks, then to repair them as they were developed to wider cracks. Recent research in the field of concrete materials suggested that it might be possible to develop a smart cement-based material that is capable of remediate cracks by triggering biogenic calcium carbonate (CaCO3) precipitaton. This paper summarizes a study undertaken to investigate the self-healing efficiency of Sporosarcina pasteurii (S. pasteurii) cells immobilized on both diatomaceous earth and pumice, to remediate flexural cracks on mortar in early ages (28 days after mixing). To obtain a two-phase bio additive, half of the minerals were saturated with a nutrient medium consisting of urea, corn-steep liqueur(CSL) and calcium acetate and the cells with immobilized to the other half without nutrients. Screening of the healing process was done with ultrasonic pulse velocity (UPV) testing and stereomicroscopy. With this approach, the cracks on mortar surface were sealed and the water absorption capacity of the so-called self-healed mortar decreased compared to its counterpart cracked mortar samples

IKEA Efect v Modelech Strojového Učení Založených na Pravidlech

Tato práce se pokouší vyhodnotit vliv vybraného kognitivního zkreslení na interpretovatelnost modelů strojového učení založeného na pravidlech. Tato práce se zaměřuje na zkreslení „efekt IKEA“, podle kterého lidé přiřadí vyšší hodnotu věcem, které vytvořili nebo částečně vytvořili. Při použití na modely opírající se o stroj je v této práci zkoumána hypotéza, že modely, které lidé měli šanci upravit nebo vylepšit, budou věrohodnější a srozumitelnější než ty, u nichž taková příležitost nebyla poskytnuta. K otestování této hypotézy byl proveden experiment crowdsourcingu. V těchto experimentech museli účastníci vyhodnotit věrohodnost pravidel automaticky generovaných algoritmem Apriori. Jedna skupina účastníků byla navíc vyzvána, aby pomocí pravidel vylepšila pravidla. V této předběžné studii nebyl pozorován žádný rozdíl v hodnocení vyvolané srozumitelnosti a věrohodnosti. Data pro statistickou analýzu poskytovaná platformou crowdsourcingu představují 120 odpovědí se stejným rozdělením velikosti vzorku mezi kontrolní a experimentální skupiny zpracované prostřednictvím výběrového řízení. Uplatnění t-testu a neparametrického testu ukazuje hodnoty p, které neumožnily odmítnout nulovou hypotézu. Test velikosti účinku však ukazuje malý účinek pro oba aspekty interpretovatelnosti. Doporučení pro budoucí práce je vytvořit více experimentů s použitím různých sad pravidel z různých témat a zapojit více lidí, aby dosáhli vyšší přesnosti ve statistice a získali spolehlivější výsledek.This thesis tries to evaluate the effect of a selected cognitive bias on the interpretability of rule-based machine learning models. This thesis focuses on the "IKEA effect" bias, according to which people assign a higher value to things that they created or partially created. Applied to machine leaning models, the hypothesis investigated in this thesis is that models that people had a chance to edit or improve will be more plausible and comprehensible than those where such opportunity was not provided. To test this hypothesis, the crowdsourcing experiment was carried out. In these experiments, participants had to evaluate the plausibility of rules automatically generated by the Apriori algorithm. One group of participants was additionally invited to use a rule editor to improve the rules. In this preliminary study, no difference in the elicited comprehensibility and plausibility ratings were observed. The data for statistical analysis provided by the crowdsourcing platform accounts for 120 answers with an equal sample size distribution between control and experimental groups processed through the selection procedure. Applying t-test and the non-parametric test shows the p-values that did not allow to reject the null hypothesis. However, the test of effect size shows a small effect for both aspects of interpretability. The advice for future works is to create more experiments using various rule sets from different topics and involve more people to achieve higher accuracy in statistics to obtain a more reliable result

Immobilization of bacterial cells on natural minerals for self-healing cement-based materials

Recent research in the field of concrete materials showed that it might be possible to develop a smart cement-based material that is capable of remediating cracks by Microbial-induced calcium carbonate precipitation (MICP). The early remediation of microcracks enables the design of cement-based systems with an elongated service life with a sustainable approach. However, the main challenge of the application is to extend the viability of the cells against the restrictive environment of cement-paste. These cells have to tolerate the highly alkaline conditions of cement paste, survive the mixing process, and remain viable even when access to nutrients is limited. This paper summarizes a novel study undertaken to investigate the self-healing efficiency of Sporosarcina pasteurii (S. pasteurii) cells immobilized on zeolite and sepiolite minerals having the same particle size. This manuscript reports an extensive experimental study to understand the factors influencing the efficiency of immobilization barriers, such as composition and reactivity. To obtain the bio-additive, the bacterial cells were immobilized without nutrients and additional nutrients were only provided during the curing stage after crack initiation. Screening of the healing process was done with ultrasonic pulse velocity (UPV) testing and stereomicroscopy. Further evaluation on performance was done by evaluating the decrease in water absorption capacity. The healing precipitate was characterized through Environmental Scanning Electron Microscope (ESEM) and Fourier-Transform infrared spectroscopy (FTIR). With this approach, the cracks on mortar surface were sealed and the water absorption capacity of the so-called self-healed mortar decreased compared to its counterpart cracked mortar samples. Sepiolite was found to be a more suitable bedding for the microorganisms compared to zeolite, therefore samples containing sepiolite exhibited a higher performance in terms of crack healing. The results showed that while vegetative cell immobilization on locally available materials is a simple and economically feasible approach the healing capacity of bacterial cells can be hindered due to the reactivity of the mineral

Use of corn-steep liquor as an alternative carbon source for biomineralization in cement-based materials and its impact on performance

Due to copyright restrictions, the access to the full text of this article is only available via subscription.Early age microcracks are generally the primary cause for a decrease in service life of cement-based structures. Recent studies suggested that it might be possible to develop a smart cement-based material that could self-heal microcracks. The use of microbial induced calcium carbonate precipitation (MICP) in cement-based materials is a novel approach to trigger self-healing and it has become an interesting field of research. MICP is a biochemical process where calcium carbonate (CaCO3) precipitation is obtained via metabolic pathways for microorganism and MICP via urea hydrolysis is the most common approach used in cement-based materials. Through the literature the most commonly used nutrient media for urea hydrolysis was composed of yeast extract and urea. However, use of yeast extract as a carbon source not only resulted with a severe retardation of initial setting and it increases the cost of the application. This study investigates the suitability of corn steep liquor (CSL) as an alternative replacement of yeast extract. CSL was found to be a suitable alternative for MICP applications without compromising bacterial growth, ability to promote CaCO3 precipitation. In addition, use of a nutrient medium including CSL and urea did not have such an adverse effect on initial set and compressive strength as compared to a urea and yeast extract medium. (C) 2018 Elsevier Ltd. All rights reserved

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

Biomineralized cement-based materials: impact of inoculating vegetative bacterial cells on hydration and strength

Due to copyright restrictions, the access to the full text of this article is only available via subscription.Biomineralization in cement-based materials has become a point of interest in recent years due to the possibility that such an approach could be used to develop a self-healing cement-based system. The objective of this study was to investigate the impact of vegetative cells of Sporosarcina pasteurii on the hydration kinetics and compressive strength of cement-based materials. The hydration kinetics were greatly influenced when a bacterial solution consisting of urea-yeast extract nutrient medium and vegetative cells was used to prepare bacterial cement pastes; specifically, severe retardation was observed. In addition, an increase in calcium carbonate precipitation, particularly calcite, occurred within the bacterial pastes. Furthermore, after the first day of hydration, the bacterial mortar displayed compressive strength that was similar to or greater than the compressive strength of the neat mortar

The performance evaluation of protection barriers in bacterial self-healing mortar

The early age microcracking is a significant problem in concrete structures resulting in increased permeability and decreased durability. The previous work showed that Sporasarcina pasteurii cells immobilized on natural minerals such as bentonite, diatomaceous earth, sepiolite, and pumice effectively remediated early-age microcracks in the cementitious systems by triggering microbial-induced calcite precipitation (MICP). This promising approach can solve early-age shrinkage cracking in cementitious systems. Therefore, it is essential to assess the impact of self-healing additives on drying shrinkage. This study investigates the influence of mineral-based biological additives on the drying shrinkage capacity of cement-based mortar and the possible self-healing of cracks if any occur. To achieve this goal, the free shrinkage in control (containing only minerals) and bacterial (containing bio-based additive) samples were measured based on ASTM 596-18 norms. Moreover, the performance assessment of developed self-healing additives was done by determining compressive strength and initial setting time of bacterial self-healing mortar