Bioconcrete: next generation of self-healing concrete

Concrete is one of the most widely used construction materials and has a high tendency to form cracks. These cracks lead to significant reduction in concrete service life and high replacement costs. Although it is not possible to prevent crack formation, various types of techniques are in place to heal the cracks. It has been shown that some of the current concrete treatment methods such as the application of chemicals and polymers are a source of health and environmental risks, and more importantly, they are effective only in the short term. Thus, treatment methods that are environmentally friendly and long-lasting are in high demand. A microbial self-healing approach is distinguished by its potential for long-lasting, rapid and active crack repair, while also being environmentally friendly. Furthermore, the microbial self-healing approach prevails the other treatment techniques due to the efficient bonding capacity and compatibility with concrete compositions. This study provides an overview of the microbial approaches to produce calcium carbonate (CaCO₃). Prospective challenges in microbial crack treatment are discussed, and recommendations are also given for areas of future research

The effect of real and virtual construction field trips on students’ perception and career aspiration

To adequately prepare students for engineering practices, it is imperative that institutions adopt innovative methods of teaching, learning, and assessment. One such approach is the use of real field trips (RFT) to construction sites, which can enhance students’ perceptions of related careers. Although virtual field trips (VFTs) have emerged as a viable alternative—or supplement—to traditional field trips, little is known about their potential to provide the same or similar career exploration advantages. Using responses from a self-reported questionnaire administered to university students who participated in an RFT, this study sought to examine the usefulness of site visits in developing essential skills required for civil engineers. It also examines student perceptions on the use of VFTs as part of their university experience and the extent to which it could replace RFTs. The results indicate that students consider VFT as an enjoyable way to learn, given the possibilities facilitated by the new technology. However, notwithstanding its success, the students commonly opined that VFT was not a substitute for a RFT. From a holistic perspective, the issue is not whether VFTs can replace traditional field trips or not; it is rather the focus on identifying an integrated approach that combines lectures, and virtual and real field trips in a manner that supports a social constructivism mode of learning. Ultimately, this combination will enable students to effectively construct multiple links between lectures given in a hall and the real world outside

Induced calcium carbonate precipitation using Bacillus species

Microbially induced calcium carbonate precipitation is an emerging process for the production of self-healing concrete. This study was aimed to investigate the effects and optimum conditions on calcium carbonate biosynthesis. Bacilluslicheniformis, Bacillus sphaericus, yeast extract, urea, calcium chloride and aeration were found to be the most significant factors affecting the biomineralization of calcium carbonate. It was noticed that the morphology of microbial calcium carbonate was mainly affected by the genera of bacteria (cell surface properties), the viscosity of the media and the type of electron acceptors (Ca²⁺). The maximum calcium carbonate concentration of 33.78 g/L was achieved at the optimum conditions This value is the highest concentration reported in the literature

Microbially induced calcium carbonate precipitation: a widespread phenomenon in the biological world

Biodeposition of minerals is a widespread phenomenon in the biological world and is mediated by bacteria, fungi, protists, and plants. Calcium carbonate is one of those minerals that naturally precipitate as a by-product of microbial metabolic activities. Over recent years, microbially induced calcium carbonate precipitation (MICP) has been proposed as a potent solution to address many environmental and engineering issues. However, for being a viable alternative to conventional techniques as well as being financially and industrially competitive, various challenges need to be overcome. In this review, the detailed metabolic pathways, including ammonification of amino acids, dissimilatory reduction of nitrate, and urea degradation (ureolysis), along with the potent bacteria and the favorable conditions for precipitation of calcium carbonate, are explained. Moreover, this review highlights the potential environmental and engineering applications of MICP, including restoration of stones and concrete, improvement of soil properties, sand consolidation, bioremediation of contaminants, and carbon dioxide sequestration. The key research and development questions necessary for near future large-scale applications of this innovative technology are also discussed

THE INFLUENCE OF GEOMETRIC PARAMETERS AND MECHANICAL PROPERTIES OF ADHESIVE ON STRESS ANALYSIS IN ADHESIVELY BONDED ALUMINUM SINGLE LAP JOINT

The aim of this study was to investigate adhesively bonded joints, and the influence of geometric parameters and mechanical properties of the adhesive in single lap aluminum structures under tensile load. A finite element model has been constructed in the ANSYS FE package and the effects of adhesive thickness, rigidity, strength and geometry have been studied in order to adjust peel stress. Various paths have been defined and obtained along the length of the adhesive and aluminum joint overlap. The results indicate that by increasing the adhesive thickness, the stress concentration decreases in the areas prone to yielding if a flexible adhesive is used instead of a rigid one, and effective stresses along the overlap length are also reduced. In addition, for a given tensile force, three different adhesive area geometries are defined. Considering the variation of peel and shear stress along the corners, the amount of adhesive used according to the introduced geometries is saved without sacrificing joint strength

The Effect of Cell Immobilization by Calcium Alginate on Bacterially Induced Calcium Carbonate Precipitation

Microbially induced mineral precipitation is recognized as a widespread phenomenon in nature. A diverse range of minerals including carbonate, sulphides, silicates, and phosphates can be produced through biomineralization. Calcium carbonate (CaCO₃) is one of the most common substances used in various industries and is mostly extracted by mining. In recent years, production of CaCO₃ by bacteria has drawn much attention because it is an environmentally- and health-friendly pathway. Although CaCO₃ can be produced by some genera of bacteria through autotrophic and heterotrophic pathways, the possibility of producing CaCO₃ in different environmental conditions has remained a challenge to determine. In this study, calcium alginate was proposed as a protective carrier to increase the bacterial tolerance to extreme environmental conditions. The model showed that the highest concentration of CaCO₃ is achieved when the bacterial cells are immobilized in the calcium alginate beads fabricated using 1.38% w/v Na-alginate and 0.13 M CaCl₂

Recycling of waste glass as aggregate in cement-based materials

Glass is a common material made from natural resources such as sand. Although much of the waste glass is recycled to make new glass products, a large proportion is still being sent to landfill. Glass is a useful resource that is non-biodegradable, occupying valuable landfill space. To combat the waste glass that is heading to landfill, alternative recycling forms need to be investigated. The construction industry is one of the largest CO₂ emitters in the world, producing up to 8% of the global CO₂ to produce cement. The use of sand largely depletes natural resources for the creation of mortars or concretes. This review explores the possibilities of incorporating waste glass into cement-based materials. It was found waste glass is unsuitable as a raw material replacement to produce clinker and as a coarse aggregate, due to a liquid state being produced in the kiln and the smooth surface area, respectively. Promising results were found when incorporating fine particles of glass in cement-based materials due to the favourable pozzolanic reaction which benefits the mechanical properties. It was found that 20% of cement can be replaced with waste glass of 20 μm without detrimental effects on the mechanical properties. Replacements higher than 30% can cause negative impacts as insufficient amounts of CaCO₃ remain to react with the silica from the glass, known as the dilution effect. As the fine aggregate replacement for waste glass increases over 20%, the mechanical properties decrease proportionally; however, up to 20% has similar results to traditionally mixes

Self-healing concrete: a novel nanobiotechnological approach to heal the concrete cracks

Concrete is one of the world’s most versatile and widely used construction materials due to its unique properties, including high compressive strength, versatility, availability, affordability, simple preparation, fire resistance, excellent thermal mass, compatibility with steel reinforcement bar and the possibility of casting in desired shapes. Despite these advantages, crack formation is the main issue associated with the concrete structures. Low tensile strength, coupled with internal and external stresses, are recognized as the key causes of crack formation in a structure. Although the embedment of reinforcement bars limits the rate of crack growth, it cannot prevent crack initiation in concrete. The initiated cracks accelerate the structure degradation by allowing aggressive fluids and gasses to seep into the matrix. This phenomenon brings about a reduction in concrete service life, increases maintenance costs and, in severe cases, leads to structural failure. With the help of biotechnological pathway, concrete can be designed to have self-healing characteristics to address the above mentioned problems. In this novel approach, a bio-concrete is made by the addition of microorganisms and nutrients into the matrix during the concrete preparation. Once a crack occurs in the concrete structure, the healing agent is activated and the precipitated calcium carbonate (CaCO₃) fills the initiated crack. The resulted CaCO₃ is recognized as the most compatible material with the concrete composition which has efficient bonding capacity with the crack surface. The main goal of this research was, therefore, to design a new generation of viable self-healing mechanism for application in bio self-healing concrete structures. Initially, an investigation was performed to screen the most effective factors, including bacteria, nutrients and operating conditions, on CaCO₃ precipitation and to maximize the production of CaCO₃. Considering the different mechanical and physical properties of CaCO₃ polymorph (calcite, vaterite and aragonite), a morphological qualification based on X-ray diffraction (XRD) was conducted. Since the concrete has a high pH (~12), the capability of microorganisms to produce CaCO₃ in such a condition was investigated. To evaluate the ability of the preliminarily designed bio-agent to induce CaCO₃ in high pH, the concrete environment was simulated using a laboratory fermentor. The results indicate that the proposed bio-agent is able to withstand high pH while decreasing the microbial viability. It was also found that the proposed CaCO₃ production mechanism significantly depends on the presence of air and its effectiveness enhances at a higher level of aeration. This observation shows that the efficiency of the bio self-healing mechanism decreases in the oxygen-limiting areas such as deeper cracks and interior parts of the matrix. To address this issue, possible use of oxygen releasing compounds (ORCs) was investigated. The effects of different ORCs on the concentration and morphology of CaCO₃ were screened, and an optimization study using response surface methodology was performed to further enhance the efficiency of the designed bio-self-healing mechanism in oxygen-limiting conditions. The results demonstrate that the presence of key ORCs at their optimum level can increase CaCO₃ production. Considering the pore size of the concrete matrix, there is a high risk for microorganisms to squeeze and damage upon cement hydration. Furthermore, the exerted shear stress on the bio-agent during the concrete preparation and drying shrinkage as well as the concrete pH can adversely affect the performance of the bio-concrete. Therefore the topic was further explored to minimize the negative effects of direct incorporation of bio-agent into the concrete matrix. It has been proven that the addition of proper nano scale-size metallic particles can improve the properties of the concrete. Considering the unique characteristics of nanoparticles, magnetic iron oxide nanoparticles (IONs) were proposed as a protective vehicle for the bio-agent. Naked and amine-modified IONs were successfully synthesized and characterized by different techniques, including XRD, transmission electron microscopy (TEM), scanning electron microscope (SEM) and Fourier transform infrared spectroscopy (FTIR). The results indicate that the presence of naked IONs has a positive contribution to the production of CaCO₃ and can serve as the carrier for the bio-agent. In the final part of this work, the performance of the designed bio self-healing concrete was investigated using various laboratory tests, including compressive strength, water absorption, drying shrinkage and crack healing observation. The results show that the presence of proposed bio-agents in concrete not only contributes to improving the compressive strength but also results in decreasing the water absorption. To evaluate the self-healing behavior of this technology, several cracks were created in the concrete specimens. The microscopic observation revealed that the bio-concrete possesses a superior crack healing characteristic. The bio-concrete could effectively sense the concrete cracks and the resulted CaCO₃ sealed the damages. This study uncovered several limitations of using bio self-healing mechanism in concrete. Most importantly, it elucidated the potential of applying this novel technology to enhance the concrete durability and mechanical properties by addressing the uncovered issues

The Effect of Real and Virtual Construction Field Trips on Students’ Perception and Career Aspiration

To adequately prepare students for engineering practices, it is imperative that institutions adopt innovative methods of teaching, learning, and assessment. One such approach is the use of real field trips (RFT) to construction sites, which can enhance students’ perceptions of related careers. Although virtual field trips (VFTs) have emerged as a viable alternative—or supplement—to traditional field trips, little is known about their potential to provide the same or similar career exploration advantages. Using responses from a self-reported questionnaire administered to university students who participated in an RFT, this study sought to examine the usefulness of site visits in developing essential skills required for civil engineers. It also examines student perceptions on the use of VFTs as part of their university experience and the extent to which it could replace RFTs. The results indicate that students consider VFT as an enjoyable way to learn, given the possibilities facilitated by the new technology. However, notwithstanding its success, the students commonly opined that VFT was not a substitute for a RFT. From a holistic perspective, the issue is not whether VFTs can replace traditional field trips or not; it is rather the focus on identifying an integrated approach that combines lectures, and virtual and real field trips in a manner that supports a social constructivism mode of learning. Ultimately, this combination will enable students to effectively construct multiple links between lectures given in a hall and the real world outside

Fermentation of Menaquinone-7: The Influence of Environmental Factors and Storage Conditions on the Isomer Profile

Menaquinone-7 (MK-7) provides significant health gains due to its excellent pharmacokinetic properties. However, MK-7 occurs at low concentrations in mainstream foods, heightening the demand for nutritional supplements. MK-7 exists as geometric isomers, and only all-trans MK-7 is bioactive. Exposure to certain environments impacts the isomer profile. Knowledge of these factors and their influence on the isomer composition is important, as the efficacy of fermented MK-7 end products is solely determined by the all-trans isomer. This investigation aimed to evaluate the short- and long-term effect of atmospheric oxygen, common temperatures, and light on the isomer profile. From the short-term study, it was ascertained that MK-7 is moderately heat-stable but extremely light-sensitive. The stability of all-trans MK-7 was then examined during 8 weeks of storage at a low temperature with minimal oxygen exposure in the absence of light. Negligible change in the all-trans MK-7 concentration occurred, suggesting it is reasonably stable during prolonged storage in this environment. These findings will aid the development of optimal storage conditions to preserve bioactive MK-7 in fermented nutritional supplements, the large-scale availability and consumption of which will help compensate for the dietary deficit of this essential vitamin and provide consumers with better health outcomes