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

authors: Seifan, Mostafa

subjects: Concrete

abstract: 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.

text: 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.

year: 2018

title: Young male and female perceptions and experiences of physical activity in Apia, Samoa

authors: Tuagalu, Taauso Clark

subjects: young people

abstract: The purpose of the study was to investigate young people's perceptions and experiences of physical activity in Apia, Samoa.  Physical inactivity is one of the main risk factors contributing to the prevalence of obesity in Samoa.  Obesity and its health-related diseases are now the major causes of death in Samoa.  
Focus group interviews and a survey were adopted for this study and the findings were based on the data collected from young people between 16 and 24 years of age.  The findings indicated that a majority of young people have a positive attitude towards physical activity and recognize the link between physical activity and health.  A high percentage of young people indicated that physical activity is important to improve health including getting fit and losing weight.  However, there appears to be a significant portion of the respondents in the survey who think they are physically active while the reality is that they do not achieve the recommended national physical activity guidelines of 30 minutes a day over 5 or more days a week.  A key aspect that emerged in the study was the importance of daily living tasks in young people's physical activity.  Although not addressed in the survey, because it was based on a Western understanding of physical activity and daily life, the focus groups revealed that young people are regularly physically active through duties at home such as feeding the pigs, cooking meals on an earth oven and plantation work.  This finding suggests the importance of conducting research focused on a Pacific perspective and taking into account the specific national contexts in which young people live.
The study identified constraints on the ability of young people to be physically active.  A majority of the respondents cited cultural, environmental and discomfort factors related to physical activity as the main barriers.  For instance, the respondents indicated that family duties, lack of footpaths, troublesome dogs and boredom were barriers to physical activity.  
The evidence suggests that many young Samoans want to be more active and lose weight but they need help.  The findings show that young people could be more active if their sources of encouragement such as friends, school, church and village are involved in physical activity promotion campaigns.  A coordinated response engaging all health sector partners to establish and support youth physical activity and health initiatives is recommended.  More importantly, the Government of Samoa could play a key leadership role in coordinating the sector to ensure that everyone accepts the responsibility of preventing and controlling the prevalence of obesity and lifestyle diseases by encouraging more people to be active.

text: Young male and female perceptions and experiences of physical activity in Apia, Samoa The purpose of the study was to investigate young people's perceptions and experiences of physical activity in Apia, Samoa.  Physical inactivity is one of the main risk factors contributing to the prevalence of obesity in Samoa.  Obesity and its health-related diseases are now the major causes of death in Samoa.  
Focus group interviews and a survey were adopted for this study and the findings were based on the data collected from young people between 16 and 24 years of age.  The findings indicated that a majority of young people have a positive attitude towards physical activity and recognize the link between physical activity and health.  A high percentage of young people indicated that physical activity is important to improve health including getting fit and losing weight.  However, there appears to be a significant portion of the respondents in the survey who think they are physically active while the reality is that they do not achieve the recommended national physical activity guidelines of 30 minutes a day over 5 or more days a week.  A key aspect that emerged in the study was the importance of daily living tasks in young people's physical activity.  Although not addressed in the survey, because it was based on a Western understanding of physical activity and daily life, the focus groups revealed that young people are regularly physically active through duties at home such as feeding the pigs, cooking meals on an earth oven and plantation work.  This finding suggests the importance of conducting research focused on a Pacific perspective and taking into account the specific national contexts in which young people live.
The study identified constraints on the ability of young people to be physically active.  A majority of the respondents cited cultural, environmental and discomfort factors related to physical activity as the main barriers.  For instance, the respondents indicated that family duties, lack of footpaths, troublesome dogs and boredom were barriers to physical activity.  
The evidence suggests that many young Samoans want to be more active and lose weight but they need help.  The findings show that young people could be more active if their sources of encouragement such as friends, school, church and village are involved in physical activity promotion campaigns.  A coordinated response engaging all health sector partners to establish and support youth physical activity and health initiatives is recommended.  More importantly, the Government of Samoa could play a key leadership role in coordinating the sector to ensure that everyone accepts the responsibility of preventing and controlling the prevalence of obesity and lifestyle diseases by encouraging more people to be active.

year: 2009

title: How do colorectal cancer patients rate their GP: a mixed methods study

authors: Blackmore, Tania Louise

subjects: Science & Technology

abstract: Background: New Zealand (NZ) has a high incidence of colorectal cancer (CRC) and low rates of early diagnosis. With screening not yet nationwide, the majority of CRC is diagnosed through general practice. A good patient-general practitioner (GP) relationship can facilitate prompt diagnosis, but when there is a breakdown in this relationship, delays can occur. Delayed diagnosis of CRC in NZ receives a disproportionally high number of complaints directed against GPs, suggesting deficits in the patient-GP connection. We aimed to investigate patient-reported confidence and ratings of their GP following the diagnostic process. 
Methods: This study is a mixed methods analysis of responses to a structured questionnaire and free text comments from patients newly diagnosed with CRC in the Midland region of NZ. A total of 195 patients responded to the structured questionnaire, and 113 patients provided additional free text comments. Descriptive statistics were used to describe the study population and chi square analysis determined the statistical significance of factors possibly linked to delay. Free text comments were analysed using a thematic framework. 
Results: Most participants rated their GP as ‘Very good/Good’ at communication with patients about their health conditions and involving them in decisions about their care, and 6.7% of participants rated their overall level of confidence and trust in their GP as ‘Not at all’. Age, gender, ethnicity and a longer diagnostic interval were associated with lower confidence and trust. Free text comments were grouped in to three themes: 1. GP Interpersonal skills; (communication, listening, taking patient symptoms seriously), 2. Technical competence; (speed of referral, misdiagnoses, lack of physical examination), and 3. Organisation of general practice care; (appointment length, getting an appointment, continuity of care). 
Conclusions: Māori, females, and younger participants were more likely to report low confidence and trust in their GP. Participants associate a poor diagnostic experience with deficits in the interpersonal and technical skills of their GP, and health system factors within general practice. Short appointment times, access to appointments and poor GP continuity are important components of how patients assess their experience and are particularly important to ensure equal access for Māori patients.

text: How do colorectal cancer patients rate their GP: a mixed methods study Background: New Zealand (NZ) has a high incidence of colorectal cancer (CRC) and low rates of early diagnosis. With screening not yet nationwide, the majority of CRC is diagnosed through general practice. A good patient-general practitioner (GP) relationship can facilitate prompt diagnosis, but when there is a breakdown in this relationship, delays can occur. Delayed diagnosis of CRC in NZ receives a disproportionally high number of complaints directed against GPs, suggesting deficits in the patient-GP connection. We aimed to investigate patient-reported confidence and ratings of their GP following the diagnostic process. 
Methods: This study is a mixed methods analysis of responses to a structured questionnaire and free text comments from patients newly diagnosed with CRC in the Midland region of NZ. A total of 195 patients responded to the structured questionnaire, and 113 patients provided additional free text comments. Descriptive statistics were used to describe the study population and chi square analysis determined the statistical significance of factors possibly linked to delay. Free text comments were analysed using a thematic framework. 
Results: Most participants rated their GP as ‘Very good/Good’ at communication with patients about their health conditions and involving them in decisions about their care, and 6.7% of participants rated their overall level of confidence and trust in their GP as ‘Not at all’. Age, gender, ethnicity and a longer diagnostic interval were associated with lower confidence and trust. Free text comments were grouped in to three themes: 1. GP Interpersonal skills; (communication, listening, taking patient symptoms seriously), 2. Technical competence; (speed of referral, misdiagnoses, lack of physical examination), and 3. Organisation of general practice care; (appointment length, getting an appointment, continuity of care). 
Conclusions: Māori, females, and younger participants were more likely to report low confidence and trust in their GP. Participants associate a poor diagnostic experience with deficits in the interpersonal and technical skills of their GP, and health system factors within general practice. Short appointment times, access to appointments and poor GP continuity are important components of how patients assess their experience and are particularly important to ensure equal access for Māori patients.

year: 2021-04-08