A capsule-based self-healing cementitious material, capable of autonomically repairing its own cracks, can extend the service life of concrete structures and decrease the costs associate with repair and maintenance actions. However, the size, shell thickness, shell material and mechanical properties of the capsules still need to be optimised to ensure self-healing performance. Thus, the objective of this research was to explore the controlled microfluidic encapsulation to investigate the production of microcapsules for physically triggered self-healing in cementitious materials. A flow-focusing microfluidic device was used to produce double emulsions to be selectively photopolymerised to generate a core-shell structure. Subsequently, the physical triggering was assessed by embedding the produced microcapsules in cement paste, fracturing it and observing the cracked surface in the SEM. The results showed the production of microcapsules with 80-140 μm of diameter with excellent control over size and shell thickness. Using water-in-oil-in-water (w/o/w) double emulsion, microcapsules were synthesised containing water, colloidal silica solution and sodium silicate solution as core material. In addition, an oil-in-oil-in-water (o/o/w) double emulsion was used to encapsulate mineral oil and emulsified healing agents. The formation of the core-shell structure with aqueous and organic cores was characterised using optical microscopy and SEM. It was demonstrated that the water is not retained inside of the capsule, resulting in the formation of dimples and buckled capsules, particularly for shells thickness ~7 μm. On the other hand, TGA confirmed the retention of mineral oil for shells thickness of ~2 μm and the encapsulation efficiency was demonstrated to be 66%. When the capsules were added to the cement paste, four key factors were observed to prevent physical triggering: (i) thick shells, (ii) buckling of thinner shells due to the loss of water core, (iii) mechanical properties and (iv) poor interfacial bonding. As a result, a mechanical characterisation of the shell material was performed, indicating brittle fracture at room temperature, reduced Young’s modulus when compared with cementitious matrix and stress at rupture of 15-36 MPa. In addition, an innovative methodology was proposed to functionalise the surface of the microcapsules with hydrophilic groups in order to increase the interfacial bonding between the cement paste and the microcapsules. Thus, microcapsules with low tensile strength, low shell thickness, organic core and good interfacial bonding were successfully synthesised and demonstrated to rupture upon crack formation. These results experimentally demonstrate the importance of reduced shell thickness, core retention and interfacial bonding as valuable guides during the design of microcapsules for physically triggered self-healing in cementitious materials.

Self-healing materials have received considerable development in the last decade. Recent results have demonstrated healing in polymeric materials via a chemical reaction using a healing agent or response to thermal treatment. The goal of this research is to develop a new composite material, for application in wire insulation, that can detect damage and heal itself using resistance heating. The composite material is composed of a conductive network embedded in a polymer matrix. The conductive network is used for damage detection and resistive heating. A matrix material is used that melts when heated and flows to fill damage. External electronic circuitry is used to implement a damage detection algorithm and apply current for resistive heating. Surlyn 8940 is chosen as the polymer matrix and carbon fibers are selected for the resistive heating elements. Methods for melt processing Surlyn are developed and used to produce Surlyn films and composite samples where carbon fiber is embedded in a Surlyn matrix. A finite element model of the resistive heating process is developed to predict the temperature distribution. Thermal imaging is used to characterize resistive heating while optical microscopy and tensile testing are used to characterize healing. Damage detection using capacitive measurements is demonstrated and characterized. The self-healing composite is placed on top of another conductive material such as in the wire insulation application. Capacitance measurements are made using the conductive network inside the composite is used as one electrode and the wide conductor as the second electrode. / Master of Science

The thesis showed preliminary evaluation of novel biodegradable and biocompatible agmatine-containing PAA crosslinkers. Hydrogels fabricated by this crosslinker can obtain controllable stiffness and excellent cell adhesion. The PAA contained thermo-sensitive hydrogel reported here is first employed as filler for depressed defects in rats. Results showed that such hydrogel can be injectable and biocompatible, might become a new material in plastic surgery in the clinic. The thesis also demonstrated a novel macro gels with self-healing capability and biocompatibility. The reversible photodimerization and photocleavage reactivity of coumarin has been successfully imparted to the polymer. / February 2015

Epoxy coatings are currently the most popular corrosion protection mechanism for steel reinforcement in structural concrete. However, these coatings are easily damaged on worksites, negating their intended purpose. This study investigates self-healing coatings for steel reinforcement to introduce an autonomous healing mechanism for damaged coatings. Coatings were applied to steel coupons, intentionally damaged, and introduced to a corrosive environment via aerated salt-water tanks. Performance of the experimental coatings was evaluated qualitatively and quantitatively. Adhesion strength and effects of coating thickness were also studied. Results from coated steel coupons subjected to damage and submerged in salt-water aeration tanks exhibited improved corrosion resistance performance with self-healing coatings. However, self-healing coatings have comparable poor adhesion to the substrate as do conventional coatings. This paper shows preliminary results demonstrating the potential benefits of self-healing coatings for steel reinforcement and identifies numerous avenues for future research.

Concrete, a composite material consisting of aggregates bound together with cement paste, is the most widely used construction material. Concrete is relatively cheap, very versatile and has excellent compressive strength. However, its tensile strength is limited and for this reason steel rebars are often added to create reinforced concrete (RC). Cracking inevitably occurs in all RC materials and associated structures due to a variety of mechanical and environmental actions. The generation of tiny microcracks within concrete facilitates the flow of potentially aggressive fluids that can corrode the embedded steel rebars and, in extreme cases, lead to premature structural failure. Concrete, along with all cement-based materials, does possess some inherent self-healing capacity and is able to heal certain-size cracks autogenously. This self-healing capability is very limited and therefore researchers have attempted to improve upon it by using a variety of techniques. In particular, the use of engineered additions for autonomic self-healing has gained significant interest in the past two decades. An example is the addition of microcapsules that disperse throughout the hardened material subsequently providing reservoirs of healing agents. When cracks arise within the material, they rupture the embedded microcapsules causing a release of their contents into the crack volume. The released material then reacts to provide filling, sealing and healing of the crack. The primary aim of this research project was to investigate the autonomic self-healing performance of concrete containing microencapsulated sodium silicate. The effect of microcapsule addition on the fresh, hardened and self-healing properties of cement, mortar and concrete were all explored. Self-healing was monitored using a variety of techniques and results reveal the increased self-healing ability of microcapsule-containing cementitious materials as well as the efficacy of sodium silicate as a healing agent. Furthermore, the self-healing concrete field trial displays the great potential for microcapsules to be incorporated into large-scale self-healing concrete applications.

Recent interest in environmentally friendly alternatives to chromate-based corrosion inhibitors has led to the development of a range of novel coating formulations. The work described in this thesis has been aimed at investigating the mechanism of self-healing and active corrosion protection of the new coatings by searching for active components that have migrated from the coating to a controlled defect. The use of glow discharge optical emission spectroscopy (GDOES) has been investigated as a tool for both the generation of a reproducible controlled defect and for elemental depth profiling of the coatings and corroded substrates. Conclusions drawn from the elemental depth profiles have been validated by a range of characterisation techniques including optical microscopy, scanning electron microscopy, energy-dispersive X-ray spectroscopy (EDX) and electrochemical techniques. The work has focused particularly on a comparison of hybrid coatings doped with inhibitors encapsulated in nano-containers, as compared with the direct addition of inhibitor species to the coating matrix. The work also investigates the effects of inhibitor addition to sol-gel coatings or primer systems or both, highlighting possible synergistic effects of mixed inhibitor systems (for example, sol-gel coating doped with strontium aluminium polyphosphate (SAPP)) supporting primers doped with benzotriazol (BZT) or mercaptobenzothiazol (MBT). The various coatings have also been studied in the absence of inhibitor species to assess the effectiveness of the coatings as barriers between the substrate and the corrosive environment. This aspect of the study has highlighted minor inhibitive effects of some of the reagents used in the coating formulations and a major inhibitive effect of the nano-containers. The work therefore concludes with recommendations for a possible coating formulation combining the most beneficial elements of the various coatings investigated.

No description available.

Yes / The paper presents a new healing system that uses pre-tensioned hybrid tendons to close cracks in cementitious structural elements. The tendons comprise an inner core, formed from aramid fibre ropes, and an outer sleeve made from a shape memory PET. During the manufacturing process, the inner core of a tendon is put into tension and the outer sleeve into compression, such that the tendon is in equilibrium. A set of tendons are then cast in a cementitious structural element and heat activated once cracking occurs. This triggers the shrinkage potential of the PET sleeve, which in turn releases the stored strain energy in the inner core. The tensile force thereby released applies a compressive force to the cementitious element, in which the tendons are embedded, that acts to close any cracks that have formed perpendicular to the axis of the tendons. Details of the component materials used to form the tendon are given along with the tendon manufacturing process. A set of experiments are then reported that explore the performance of three different tendon configurations in prismatic mortar beams. The results from these experiments show that the tendons can completely close 0.3 mm cracks in the mortar beams and act as effective reinforcement both before and after activation. A nonlinear hinge-based numerical model is also described, which is shown to be able to reproduce the experimental behaviour with reasonable accuracy. The model is used to help interpret the results of the experiments and, in particular, to explore the effects of slip at the tendon anchorages and the amount of prestress force that remains after activation. It is shown that, with two of the tendon configurations tested, over 75% of the prestress potential of the tendon remains after crack closure. / UK-EPSRC (Grant No. EP/P02081X/1, Resilient Materials 4 Life, RM4L).

Nos últimos anos, as indústrias têm mostrado muito interesse em procurar sistemas de pinturas que possam ser mais eficientes na proteção do substrato metálico. Os sistemas comuns de pinturas criam uma barreira passiva sobre substrato que evita o contato com a água e outras espécies agressivas. No entanto, a degradação do revestimento pode ocorrer como consequência de fatores externos como radiação UV, temperatura ou ação mecânica. Por este motivo, pesquisadores têm buscado sistemas de pintura com proteção ativa que sejam capazes de se autorreparar (self-healing), levando o substrato a um tempo de vida em serviço mais prolongado. Uma maneira para atingir este efeito ativo é a incorporação de sistemas de nanocontainers ou nanorreservatórios com material ativo encapsulado (inibidores de corrosão) na matriz do revestimento. O objetivo deste trabalho é avaliar o efeito na resistência à corrosão do aço carbono ABNT 1020 numa solução de NaCl 0,01 mol/L quando seja submetido a um prétratamento com camada de tinta alquídica aditivada com nanocontainers contendo o inibidor de corrosão dodecilamina. Três tipos de nanocontainers foram avaliados: 1) nanocontainers a base de nanopartículas de sílica revestida com diferentes camadas de polieletrólitos. 2) nanocontainers a base do mineral haloisita. 3) nanocontainers a base de uma sílica mesoporosa com arranjo ordenado hexagonal tipo SBA-15. Também foi estudada a cinética de liberação do inibidor dodecilamina dos diferentes tipos de nanocontainers usando a técnica de impedância eletroquímica. Os métodos eletroquímicos utilizados para avaliar a resistência a corrosão e o efeito de autorreparação ou self healing foram a técnica de varredura do eletrodo vibratório (SVET) e espectroscopia de impedância eletroquímica (EIS), obtidas em solução aerada de NaCl 0,01 mol/L para chapas de aço carbono revestidas. Testes acelerados de corrosão numa câmara de névoa salina (SSC) foram realizados seguindo a norma ASTM B 117-11. As imagens de microscopia ótica, microscopia eletrônica de varredura e microscopia eletrônica de transmissão foram obtidas para conhecer a estrutura e morfologia dos nanocontainers e o aspecto dos corpos de prova pintados. A caracterização da sílica mesoporosa foi realizada por termogravimetria (TGA), adsorção e dessorção de nitrogênio e difração de raios-X. Os estudos de cinética de liberação do inibidor foram realizados numa solução de NaCl 0,1 mol/L a diferentes valores de pH (2, 9 e 6.2) e contendo 1% m/m de nanocontainers carregados com inibidor dodecilamina, onde foi possível demonstrar que a pH 2 a velocidade de liberação do inibidor foi maior para os três tipos de nanocontainers estudados. Com relação aos resultados de espectroscopia de impedância eletroquímica (EIS) e técnica de varredura com eletrodo vibratório (SVET) para os corpos de prova revestidos com uma tinta alquídica contendo 10 % m/m de nanopartículas de sílica obtidas por Lb-L ou haloisita e 15 % m/m de sílica mesoporosa foi comprovado o efeito selfhealing da tinta pela liberação do inibidor dodecilamina encapsulado dentro da estrutura do nanocontainer. Este efeito também foi notado nos testes de névoa salina, onde o inibidor de corrosão é liberado pelo abaixamento do pH nas regiões anódicas ou de corrosão retardando o processo de corrosão na região do defeito. / In the last years, the industries have shown much interest in searching painting systems that may be more effective in protecting the metallic substrate. Common painting systems create a passive barrier over the substrate that avoids contact with the water and other aggressive species. However, degradation of the coating may occur as a result of external factors such as UV radiation, temperature or mechanical action. For this reason, researchers have sought paint active protection systems that are able to self-repair (self-healing) leading to a longer lifetime of the substrate. One way to achieve this active effect is the incorporation of nanocontainer systems with encapsulated active material (corrosion inhibitors) to the coating matrix. The objective of this study is to evaluate the effect on corrosion resistance of carbon steel ABNT 1020 in aerated 0.1 mol/L NaCl solution when it is subjected to a pretreatment with alkyd paint layer doped with nanocontainers containing dodecylamine as corrosion inhibitor. Three types of nanocontainers were evaluated: 1) SiO2 nanoparticles coated with polyelectrolytes multilayers. 2) halloysite nanoparticles. 3) type SBA-15 mesoporous silica particles of. The kinetics of release of the inhibitor dodecylamine from the different types of nanocontainers was also determined indirectly using electrochemical impedance spectroscopy technique. Electrochemical measurements were performed to evaluate the self-healing effect of coated carbon steel panels after a provoked defect with scanning vibrating electrode technique (SVET) and electrochemical impedance spectroscopy (EIS), all measurements were performed in an aerated NaCl 0.01 mol/L solution. Accelerated corrosion tests in salt spray chamber (SSC) were also carried out following the prescriptions of ASTM B 117-11 standard. The images from optical, scanning electron and transmission electron microscopy were obtained to show the morphology and structure of the nanocontainers and the aspect of coated samples. The characterization of mesoporous silica was made by transmission electron microscopy, thermogravimetry (TGA), adsorption/desorption of N2 and X-ray diffraction. Kinetic studies of the release of encapsulated corrosion inhibitor were performed in NaCl 0.1 mol/L solution at different pH values (2, 9 and 6.2) containing 1 wt. % of dispersed nanocontainers loaded with dodecylamine inhibitor, and it was possible to confirm that at pH 2 condition the release of inhibitor was more efficient in comparison to other pH conditions (9 and 6.2). On the other hand, the results obtained by electrochemical impedance spectroscopy (EIS) and scanning vibrating electrode technique (SVET) of the coated carbon steel panels with alkyd paint loaded with 10 wt. % (SiO2 nanoparticles or halloysite) and 15 wt. % (mesoporous silica) has proven the self-healing effect by the release of corrosion inhibitor from nanocontainers on the defect area triggered by the pH decrease typical of anodic or corroding areas. This self-healing and protective effect was also noticed in salt spray tests, where the corrosion inhibitor was released slowing down the corrosion process on the defective region.

Nos últimos anos, as indústrias têm mostrado muito interesse em procurar sistemas de pinturas que possam ser mais eficientes na proteção do substrato metálico. Os sistemas comuns de pinturas criam uma barreira passiva sobre substrato que evita o contato com a água e outras espécies agressivas. No entanto, a degradação do revestimento pode ocorrer como consequência de fatores externos como radiação UV, temperatura ou ação mecânica. Por este motivo, pesquisadores têm buscado sistemas de pintura com proteção ativa que sejam capazes de se autorreparar (self-healing), levando o substrato a um tempo de vida em serviço mais prolongado. Uma maneira para atingir este efeito ativo é a incorporação de sistemas de nanocontainers ou nanorreservatórios com material ativo encapsulado (inibidores de corrosão) na matriz do revestimento. O objetivo deste trabalho é avaliar o efeito na resistência à corrosão do aço carbono ABNT 1020 numa solução de NaCl 0,01 mol/L quando seja submetido a um prétratamento com camada de tinta alquídica aditivada com nanocontainers contendo o inibidor de corrosão dodecilamina. Três tipos de nanocontainers foram avaliados: 1) nanocontainers a base de nanopartículas de sílica revestida com diferentes camadas de polieletrólitos. 2) nanocontainers a base do mineral haloisita. 3) nanocontainers a base de uma sílica mesoporosa com arranjo ordenado hexagonal tipo SBA-15. Também foi estudada a cinética de liberação do inibidor dodecilamina dos diferentes tipos de nanocontainers usando a técnica de impedância eletroquímica. Os métodos eletroquímicos utilizados para avaliar a resistência a corrosão e o efeito de autorreparação ou self healing foram a técnica de varredura do eletrodo vibratório (SVET) e espectroscopia de impedância eletroquímica (EIS), obtidas em solução aerada de NaCl 0,01 mol/L para chapas de aço carbono revestidas. Testes acelerados de corrosão numa câmara de névoa salina (SSC) foram realizados seguindo a norma ASTM B 117-11. As imagens de microscopia ótica, microscopia eletrônica de varredura e microscopia eletrônica de transmissão foram obtidas para conhecer a estrutura e morfologia dos nanocontainers e o aspecto dos corpos de prova pintados. A caracterização da sílica mesoporosa foi realizada por termogravimetria (TGA), adsorção e dessorção de nitrogênio e difração de raios-X. Os estudos de cinética de liberação do inibidor foram realizados numa solução de NaCl 0,1 mol/L a diferentes valores de pH (2, 9 e 6.2) e contendo 1% m/m de nanocontainers carregados com inibidor dodecilamina, onde foi possível demonstrar que a pH 2 a velocidade de liberação do inibidor foi maior para os três tipos de nanocontainers estudados. Com relação aos resultados de espectroscopia de impedância eletroquímica (EIS) e técnica de varredura com eletrodo vibratório (SVET) para os corpos de prova revestidos com uma tinta alquídica contendo 10 % m/m de nanopartículas de sílica obtidas por Lb-L ou haloisita e 15 % m/m de sílica mesoporosa foi comprovado o efeito selfhealing da tinta pela liberação do inibidor dodecilamina encapsulado dentro da estrutura do nanocontainer. Este efeito também foi notado nos testes de névoa salina, onde o inibidor de corrosão é liberado pelo abaixamento do pH nas regiões anódicas ou de corrosão retardando o processo de corrosão na região do defeito. / In the last years, the industries have shown much interest in searching painting systems that may be more effective in protecting the metallic substrate. Common painting systems create a passive barrier over the substrate that avoids contact with the water and other aggressive species. However, degradation of the coating may occur as a result of external factors such as UV radiation, temperature or mechanical action. For this reason, researchers have sought paint active protection systems that are able to self-repair (self-healing) leading to a longer lifetime of the substrate. One way to achieve this active effect is the incorporation of nanocontainer systems with encapsulated active material (corrosion inhibitors) to the coating matrix. The objective of this study is to evaluate the effect on corrosion resistance of carbon steel ABNT 1020 in aerated 0.1 mol/L NaCl solution when it is subjected to a pretreatment with alkyd paint layer doped with nanocontainers containing dodecylamine as corrosion inhibitor. Three types of nanocontainers were evaluated: 1) SiO2 nanoparticles coated with polyelectrolytes multilayers. 2) halloysite nanoparticles. 3) type SBA-15 mesoporous silica particles of. The kinetics of release of the inhibitor dodecylamine from the different types of nanocontainers was also determined indirectly using electrochemical impedance spectroscopy technique. Electrochemical measurements were performed to evaluate the self-healing effect of coated carbon steel panels after a provoked defect with scanning vibrating electrode technique (SVET) and electrochemical impedance spectroscopy (EIS), all measurements were performed in an aerated NaCl 0.01 mol/L solution. Accelerated corrosion tests in salt spray chamber (SSC) were also carried out following the prescriptions of ASTM B 117-11 standard. The images from optical, scanning electron and transmission electron microscopy were obtained to show the morphology and structure of the nanocontainers and the aspect of coated samples. The characterization of mesoporous silica was made by transmission electron microscopy, thermogravimetry (TGA), adsorption/desorption of N2 and X-ray diffraction. Kinetic studies of the release of encapsulated corrosion inhibitor were performed in NaCl 0.1 mol/L solution at different pH values (2, 9 and 6.2) containing 1 wt. % of dispersed nanocontainers loaded with dodecylamine inhibitor, and it was possible to confirm that at pH 2 condition the release of inhibitor was more efficient in comparison to other pH conditions (9 and 6.2). On the other hand, the results obtained by electrochemical impedance spectroscopy (EIS) and scanning vibrating electrode technique (SVET) of the coated carbon steel panels with alkyd paint loaded with 10 wt. % (SiO2 nanoparticles or halloysite) and 15 wt. % (mesoporous silica) has proven the self-healing effect by the release of corrosion inhibitor from nanocontainers on the defect area triggered by the pH decrease typical of anodic or corroding areas. This self-healing and protective effect was also noticed in salt spray tests, where the corrosion inhibitor was released slowing down the corrosion process on the defective region.