Osvrt na samozaceljujući beton - biološki pristup

Concrete is one of the most used construction materials worldwide. It is known to be a strong and durable material at a reasonable price. The most well-known problem in concrete is the cracks, which affect the service life of the concrete structures and leads to consumes higher costs through maintenance. Cracks allow penetrating any ions into the concrete resulting in other big problems such as corrosion of steel reinforcement, sulphate attack, carbonation, alkali-aggregate reaction, etc. It is impossible to prevent the formation of cracks, therefore they can be controlled or repaired using a variety of methods. Nowadays, self-healing is one of the widely recognized techniques to improve concrete's long-term durability. Healing agents such as bacteria, chemical compounds, and polymers are utilized. In this method, with the help of a healing agent, the cracks start to heal autonomously during crack formation. Since Bacteria is the most used material for healing concrete, self-healing concrete is also known as bacterial-concrete or bioconcrete. This article provides an overview of self-healing concrete including describing the system, process, durability, and mechanical properties of healed concrete.

Revolutionizing concrete durability: Case studies on encapsulation- based chemical (autonomous) self-healing techniques and future directions – A critical review

Bacteria-based self-healing concrete is a construction material used to repair cracks in concrete, in which the bacterial spores are immobilized by bacteria carriers. However, the currently available bacteria carriers are not always suitable due to a complicated procedure or high cost. To develop a more suitable bacteria carrier as well as improve the anti-crack capability of self-healing concrete, in this study we evaluate the feasibility of using rubber particles as a novel bacteria carrier in self-healing concrete. Two types of self-healing concrete are prepared with rubber particles of different sizes to quantify the crack-healing effect. In addition, the fluidity and mechanical properties of the self-healing rubber concrete are compared with those of plain concrete and normal rubber concrete. The experimental results show that the self-healing rubber concrete with a particle size of 1~3 mm has a better healing capacity than the self-healing rubber concrete with a particle size of 0.2~0.4 mm, and the width value of the completely healed crack is 0.86 mm. The self-healing rubber concrete has a higher slump than the plain concrete and normal rubber concrete. According to the strength tests, the compressive strengths of the self-healing rubber concrete are low early on but they exceed those of the corresponding normal rubber concrete at 28 days. Moreover, the self-healing rubber concrete has higher splitting tensile strengths than the plain concrete and a better anti-crack capability. The results of a comparison to the other two representative bacterial carriers indicate that rubber particles have potential to be a widely used bacteria carrier for practical engineering applications in self-healing concrete.

Aim: This study’s objective is to determine how polypropylene fibre impacts self-healing concrete’s flexural strength. Materials and Methods: Investigation was divided into two groups, with each group preparing 18 samples with Gpower (80 percent). Group-1 denotes conventional self-healing bacterial concrete, while Group-2 denotes polypropylene fibre reinforced self-healing bacterial concrete. The number of samples was determined using clinical software and values taken from previous research publications. The independent sample T-test, performed using SPSS software version 21, demonstrates a substantial increase in the flexural strength of the fibre reinforced self-healing concrete. Result: In comparison to conventional self-healing bacterial concrete, polypropylene fibre reinforced self-healing bacterial concrete has a 19% higher flexural strength. The significance of the events was 0.354 (p>0.05), indicating that there was no significant statistical difference. The flexural strength of polypropylene reinforced bacterial concrete had a standard deviation of 0.79623. Conclusion: According to the findings of this experiment, M20 grade self-healing bacterial concrete reinforced with polypropylene fibre has a stronger flexural strength than regular self-healing bacterial concrete.

The deterioration of concrete can be due to: (1) the corrosion of reinforcement; (2) freezing and thawing, including frost damage; (3) chloride ingress; (4) carbonation of concrete; (5) sulphate attack; (6) acid attack; (7) alkali attack; (8) alkaliaggregate reaction; (9) salt attack; and (10) abrasion. Investigation of the durability of concrete generally consists of either the causes of deterioration or the extent of it. Usually, methods used to improve the durability of concrete aim to prevent the causes of deterioration; however, occasionally methods that limit the extent of damage are employed. In this context, and in order to propose test, which can assess the durability between the material properties and deterioration mechanisms, is carried out. Such an analysis should help to focus the attention of various investigators the key issues that ultimately determine the durability of concrete structures. Concerning the various deterioration mechanisms described above, one of the fundamental properties that influences the initiation and extent of damage of concrete is corrosion of reinforcement in the concrete structure. Environmental effects such as the freezing and thawing cycles have caused deterioration of the bridge decks and all other exposed reinforced concrete structures. Concrete is full of microcracks even when it is not loaded. When under vehicular traffic, some structural cracks form that can join the other already existing cracks, providing an easy route to reinforcing steel for the deicing salt. The presence of shrinkage and temperature cracks can also do the same. When chloride ions along with moisture reach the level of reinforcing steel, they start corroding the steel reinforcement. Corrosion of steel reinforcement in concrete bridge decks and parking structures is one of the most common types of deterioration, which has substantially reduced the useful life of such facilities. This widespread problem and the rapidly increasing cost of maintenance and repair have resulted in great economic and social repercussions. The rising rate of the use of chloride deicing salt is a major factor causing corrosion, and there is no feasible economic alternative to its use at present. Corrosion may occupy a greater volume than the parent steel reinforcement, thereby extending pressure on the upper concrete, causing it to spall off the main body of concrete. Common types of deterioration and corrosion mechanisms of reinforcement in concrete are reviewed with the view of effects of the concrete environment on the process. It is feasible to study the effect of the individual and combined causes on the onset and rate of reinforcement corrosion. The role of concrete design and construction practices is discussed as the first protection resort available against corrosion. The importance of concrete quality in providing protection to reinforcement cannot be overemphasized. Bleeding of concrete, which may happen during construction, can result in unfavorable consequences and lead to unfavorable consequences and also to premature corrosion of steel. The limitations and applicabilities of the various repair techniques and protective measures in existing structures, of course, have differential impacts on concrete in version environments. Cathodic protection is considered the most versatile and effective means of controlling the corrosion of steel and subsequent deterioration of the concrete.

The deterioration of concrete can be due to: (1) the corrosion of reinforcement; (2) freezing and thawing, including frost damage; (3) chloride ingress; (4) carbonation of concrete; (5) sulphate attack; (6) acid attack; (7) alkali attack; (8) alkaliaggregate reaction; (9) salt attack; and (10) abrasion. Investigation of the durability of concrete generally consists of either the causes of deterioration or the extent of it. Usually, methods used to improve the durability of concrete aim to prevent the causes of deterioration; however, occasionally methods that limit the extent of damage are employed. In this context, and in order to propose test, which can assess the durability between the material properties and deterioration mechanisms, is carried out. Such an analysis should help to focus the attention of various investigators the key issues that ultimately determine the durability of concrete structures. Concerning the various deterioration mechanisms described above, one of the fundamental properties that influences the initiation and extent of damage of concrete is corrosion of reinforcement in the concrete structure. Environmental effects such as the freezing and thawing cycles have caused deterioration of the bridge decks and all other exposed reinforced concrete structures. Concrete is full of microcracks even when it is not loaded. When under vehicular traffic, some structural cracks form that can join the other already existing cracks, providing an easy route to reinforcing steel for the deicing salt. The presence of shrinkage and temperature cracks can also do the same. When chloride ions along with moisture reach the level of reinforcing steel, they start corroding the steel reinforcement. Corrosion of steel reinforcement in concrete bridge decks and parking structures is one of the most common types of deterioration, which has substantially reduced the useful life of such facilities. This widespread problem and the rapidly increasing cost of maintenance and repair have resulted in great economic and social repercussions. The rising rate of the use of chloride deicing salt is a major factor causing corrosion, and there is no feasible economic alternative to its use at present. Corrosion may occupy a greater volume than the parent steel reinforcement, thereby extending pressure on the upper concrete, causing it to spall off the main body of concrete. Common types of deterioration and corrosion mechanisms of reinforcement in concrete are reviewed with the view of effects of the concrete environment on the process. It is feasible to study the effect of the individual and combined causes on the onset and rate of reinforcement corrosion. The role of concrete design and construction practices is discussed as the first protection resort available against corrosion. The importance of concrete quality in providing protection to reinforcement cannot be overemphasized. Bleeding of concrete, which may happen during construction, can result in unfavorable consequences and lead to unfavorable consequences and also to premature corrosion of steel. The limitations and applicabilities of the various repair techniques and protective measures in existing structures, of course, have differential impacts on concrete in version environments. Cathodic protection is considered the most versatile and effective means of controlling the corrosion of steel and subsequent deterioration of the concrete.

Physio-mechanical and micro-structural properties of cost-effective waste eggshell-based self-healing bacterial concrete

Concrete which is vastly utilized in building materials has its own disadvantages, one being the phenomenon of crack formation which allows the passage of water, CO2 and other chemicals into the concrete. The incoming materials cause decrement in strength along with durability and ductility. These materials also have adverse effects on reinforcements. If the cracks are not healed as soon as they are formed, they might expand and become larger allowing passage of more amount of materials causing greater problems. That’s why the best solution is to prevent the formation of cracks from the very beginning. Self-healing concrete provides one such solution. In self-healing concrete, the concrete material is capable of healing the cracks formed beforehand, on its own. Microbial actions help in this. The basic principle of self-healing concrete is the formation of calcium carbonate precipitate by bacterial action. This introduction of bacterial concrete paves the way to the production of more durable, sustainable, crack-free and more efficient concrete. The usage of bacteria in concrete justifies its name, microbial concrete or biological concrete (in short bio concrete). The bio concrete causes less pollution and is economic as well. This paper aims at defining bacterial concrete and its effects on concrete properties and describing its merits and few demerits.

Concrete is the most broadly used construction material; thus, developing sustainable concrete is essential to decrease greenhouse gas (GHG) emissions from concrete production. Implementation of self-healing concrete technologies is a promising approach to enhance the durability and sustainability of the transportation infrastructure. Among these technologies, bacterial concrete has the potential to seal microcracks through microbial induced calcite precipitation (MICP). Bacterial protection is essential to ensure the viability of this technology due to concrete’s harsh environment. Additionally, the success of this technology depends on the presence of an adequate mineral precursor compound and nutrient for the bacteria. As such, the main objective of this study was to optimize the healing efficiency of bacterial concrete in subtropical climates through the vacuum impregnation of bacteria into a lightweight aggregate (LWA). To achieve this objective, mortar samples were prepared while incorporating different combinations of precursors (magnesium acetate, calcium lactate, and sodium lactate) and alkali-resistant healing agent Bacillus pseudofirmus bacteria (with and without). In addition, a control sample was prepared without bacteria or precursors for comparative purposes. For each sample, three mortar cubes and three mortar beams were cast and used to evaluate the compressive strength, crack healing efficiency, and flexural strength recovery. The morphology of healing products was also observed in bacteria-containing samples under scanning electron microscopy with energy x-ray dispersive spectroscopy (SEM/EDS). Results showed that self-healing bacterial concrete could be optimized (without significant reduction in mechanical properties) if Bacillus pseudofirmus bacteria at a concentration of 108 cells/ml and sodium lactate precursor at a concentration of 75 mM/l are impregnated into lightweight aggregate.

Fracture behavior study of self-healing bacterial concrete

Under extreme environmental conditions, concrete is often damaged, ranging from cracking to destruction caused by corrosion of steel reinforcement. Damage caused by steel corrosion must be repaired immediately to prevent the wider spread of steel corrosion. This study carried out grouting, jacketing, and self-healing concrete repairs. Encapsulated Bacillus subtilis bacteria were used to make self-healing concrete. The specimen was a reinforced concrete (RC) beam measuring 62x15x15 cm damaged by steel corrosion. The reinforcement in the concrete was subjected to accelerated corrosion with mass loss (corrosion levels) of 20%, 25%, and 30%. The concrete beams were subjected to pre-cracked loading to produce cracks, which were then repaired. This study utilised resistivity, one of the NDT methods, as a parameter to measure the quality of reinforced concrete. Additionally, flexural strength was tested to evaluate the quality of the repair. The results indicated a decrease in resistivity and flexural strength as the corrosion level increased. Grouting and jacketing repairs showed a positive correlation between resistivity and flexural strength, whereas self-healing concrete exhibited a negative correlation. Resistivity testing on these repairs is limited, making this research crucial.

State-of-the-art review on advancements of eco-friendly bacterial-infused self-healing concrete for sustainable constructions

In recent decades, the durability of concrete has become a significant area of research and continues to be a key concern in the construction field. Issues such as cracking and spalling are widespread and often stem from environmental influences, substandard construction practices, insufficient oversight, design flaws, and other contributing factors. This paper explores the latest developments in concrete durability research, addressing common issues like alkali-aggregate reactions, sulfate attacks, corrosion of steel reinforcement, and freeze-thaw cycles. These problems can lead to structural degradation or a loss of strength within just a few years. Accurately identifying the location and size of cracks can also be quite difficult. Recent advancements in deep learning have introduced highly accurate methods for crack detection. In this study, over 60 research papers published in top-tier journals and conferences within the past three years were collected through a systematic literature review. These studies were then categorized into 10 key topics based on the accuracy of their crack prediction results: trial-and-error methods, Transfer Learning (TL), Encoder-Decoder (ED), Generative Adversarial Networks (GAN), YOLO V5, LeNet-5, Mask R-CNN, Artificial Neural Networks (ANN), Support Vector Machines (SVM), Binarization, YOLO V3, 3D-SM, IPZ, and VGG-16. This survey aims to analyze the strengths and weaknesses of the models within each category, with a particular focus on the latest advancements in Convolutional Neural Networks (CNNs) and YOLO V5. Third, the study identifies the commonly used evaluation metrics and loss functions applied to CNN and YOLO V5 datasets. Finally, it examines several recurring challenges in the fields of CNN and YOLO V5, analyzes existing solutions, and offers recommendations for future research directions.

Self-healing concrete is an innovative solution to improve durability issues in traditional concrete structures. The review focuses on a novel approach in self-healing concrete technology by partially replacing cement with agro-industrial waste, which has received less attention in existing literature. The use of agro-industrial waste aims at increasing the environmental sustainability of concrete production, it also introduces unique properties that contribute to the self-healing process. The literature of various agro-industrial waste materials like coffee husk ash (CHA), rice husk ash (RHA), sugarcane bagasse ash (SCBA), fly ash, and ground granulated blast furnace slag (GGBS), as a potential replacement for cement. The waste materials that act as supplementary cementitious materials and possess inherent healing properties due to their chemical composition. To evaluate the processes governing this precipitation, this paper discusses the impact of incorporating agro-industrial waste on bacterial concrete's mechanical, durability, and self-healing performance. The present work sheds a light on various factors of bacterial concrete such as types of bacteria and dosage, mix proportion and the outcome of mechanical and durability tests. Furthermore, the study emphasizes the need for comprehensive investigations on self-healing concrete's long-term performance and scalability with agro-industrial waste. The limited availability of studies on use for future research to explore deeper into the connection between agro-industrial waste and self-healing concrete, opening the door to more durable and sustainable building materials.Graphical abstract

Polyhydroxyalkanoate (PHA) production is a promising opportunity to recover organic carbon from waste streams. However, widespread application of waste-derived PHA as biodegradable plastic is restricted by expensive purification steps, high quality requirements, and a fierce competition with the conventional plastic market. To overcome these challenges, we propose a new application for waste-derived PHA, using it as bacterial substrate in self-healing concrete. Self-healing concrete is an established technology developed to overcome the inevitable problem of crack formation in concrete structures, by incorporating a so-called bacteria-based healing agent. Currently, this technology is hampered by the cost involved in the preparation of this healing agent. This study provides a proof-of-concept for the use of waste-derived PHA as bacterial substrate in healing agent. The results show that a PHA-based healing agent, produced from PHA unsuitable for thermoplastic applications, can induce crack healing in concrete specimens, thereby reducing the water permeability of the cracks significantly compared to specimens without a healing agent. For the first time these two emerging fields of engineering, waste-derived PHA and self-healing concrete, both driven by the need for environmental sustainability, are successfully linked. We foresee that this new application will facilitate the implementation of waste-derived PHA technology, while simultaneously supplying circular and potentially more affordable raw materials for self-healing concrete.