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.

Yes / Cracks in concrete composites, whether autogenous or loading-initiated, are almost inevitable and often difficult to detect and repair, posing a threat to safety and durability of concrete infrastructures, especially for those with strict sealing requirements. The sustainable development of infrastructures calls for the birth of self-healing concrete composites, which has the built-in ability to autonomously repair narrow cracks. This paper reviews the fabrication, characterization, mechanisms and performances of autogenous and autonomous healing concretes. Autogenous healing materials such as mineral admixtures, fibers, nanofillers and curing agents, as well as autonomous healing methods such as electrodeposition, shape memory alloys, capsules, vascular and microbial technologies, have been proven to be effective to partially or even fully repair small cracks. As a result, the mechanical properties and durability of concrete infrastructure can be restored to some extent. However, autonomous healing techniques have shown a better performance in healing cracks than most of autogenous healing methods that are limited to healing of cracks having a narrower width than 150 µm. Self-healing concrete with biomimetic features, such as self-healing concrete based on shape memory alloys, capsules, vascular networks or bacteria, is a frontier subject in the field of material science. Self-healing technology provides concrete infrastructures with the ability to adapt and respond to the environment, exhibiting a great potential to facilitate the creation of a wide variety of smart materials and intelligent structures.

Yes / The presence of cracks has a negative impact on the durability of concrete by providing paths for corrosive materials to the embedded steel reinforcement. Cracks in concrete can be closed using shape memory polymers (SMP) which produce a compressive stress across the crack faces. This stress has been previously found to enhance the load recovery associated with autogenous selfhealing. This paper details the experiments undertaken to incorporate SMP tendons containing polyethylene terephthalate (PET) filaments into reinforced and unreinforced 500 × 100 × 100 mm structural concrete beam samples. These tendons are activated via an electrical supply using a nickelchrome resistance wire heating system. The set-up, methodology and results of restrained shrinkage stress and crack closure experiments are explained. Crack closure of up to 85% in unreinforced beams and 26%–39% in reinforced beams is measured using crack-mouth opening displacement, microscope and digital image correlation equipment. Conclusions are made as to the effectiveness of the system and its potential for application within industry. / EPSRC for their funding of the Materials for Life (M4L) project (EP/K026631/1) and Costain Group PLC for industrial sponsorship of the project and author

<p>To make bacterial-based self-healing concrete, alkaline-resistant bacterial spores, nutrient sources, and a calcium source are incorporated into a concrete matrix. Two ureolytic spore-forming bacteria, <i>Sporosarcina pasteurii</i>, <i>Lysinibacillus sphaericus</i>, and two non-ureolytic spore-forming bacteria, <i>Bacillus cohnii</i>, and <i>Bacillus pseudofirmus</i>, which have been used in previous studies as bacterial concrete healing agents, were compared in this study. The four bacteria were compared for their (1) sporulation rates on different sporulation agar plates, (2) growth in five liquid media, (3) survival rates in light weight aggregates (LWA) and in mortar samples, and (4) calcium carbonate precipitation rates from either calcium lactate or calcium nitrate. Sporulation was successfully induced after three-day incubation at 30°C on an appropriate sporulation medium. High sporulation rates of <i>B. cohnii</i>, and <i>B. pseudofirmus</i>(93% and 99% respectively) were found on alkaline R2A medium (AR2A). A sporulation rate (89%) of <i>S. pasteruii</i>was observed on tryptic soy agar supplemented with 2% urea (TSAU)<i>.</i>The highest sporulation rate (60%) of <i>L. sphaericus</i>was found on R2A medium supplemented with 2% urea (R2AU). In the growth study, tryptic soy broth supplemented with 2% urea (TSBU) was a positive control which supported rapid growth of all four bacteria. <i>Sporosarcina pasteurii </i>and <i>L. pasteurii</i>showed rapid growth rates in alkaline yeast extract broth (AYE) and yeast extract with 2% urea broth (YEU) respectively. In contrast, <i>B. cohnii</i>, and <i>B. pseudofirmus</i>grew poorly in all media except in the positive control. Viable counts of the four bacterial spores reduced (1.8–3.3 logs) during the first 24 h in mortar samples and then remained stable for next 27 days testing period. Among the four, <i>S. pasteurii</i>showed the smallest reduction of viable counts (1.8–2.5 logs) in mortar after one day of incubation. Both <i>S. pasteurii</i>and <i>L. sphaericus</i>showed high CaCO₃productions (>80%) after 24 h incubation at 30°C in YEU containing either calcium nitrate or calcium lactate. However, <i>B. pseudofirmus</i>and <i>B. cohnii </i>showed<i></i>low calcite recovery rates (<11%) in AYE containing either<i></i>calcium nitrate or calcium lactate under the same incubation condition. Overall, <i>S. pasteurii</i>was the best bacterial concrete healing agent of the four. This bacterium had (1) rapid growth rate in AYE, (2) about 90% sporulation rate within 3 days, (3) highest survival rates after 24 h in mortar samples and, (4) high CaCO₃precipitation rates, 82 or 98%, in broth containing calcium nitrate or calcium lactate respectively.</p><p>In addition, two different lightweight aggregates (LWA), expanded shale (ES) and expanded clay (EC), which were used as bacterial carriers and protective materials, were compared in this study. Each type of LWA was separated into three sizes (<0.85 mm, 0.85– 2.0 mm, and >2.0 mm) and immobilized with spores of <i>B. cohnii</i>or <i>B. pseudofirmus.</i>Viable counts recovered from EC and ES reduced <1.0 log after the immobilization process and remained stable during the 150 days testing period. Neither the type nor the particle sizes of the two LWA significantly affected the survival rates of the bacterial spores. This result showed that both EC and ES could be used as carriers for bacterial healing agents. It was also found that when the spores were immobilized with nutrients in LWA, their survival rates in mortar samples can be improved slightly (<1.0 log).</p><p><br></p>

In this research, two phases of work were conducted. First, an investigation into the durability concerns for precast prestressed concrete piles exposed to marine environments was conducted. The investigation characterized the durability concerns of chemical, biological, and physical deterioration mechanisms. The results of this study were used to develop potential high performance marine concretes (HPMC) that would be capable of 100+ year service lives in marine environments. Extensive durability testing and service life modeling of the HPMC was performed. Chloride ingress resistance was investigated using accelerated and long-term test procedures and the results used to perform service life modeling to predict the time before corrosion initiation. Sulfate resistance characterization was performed using multiple techniques to characterize the physical and chemical behavior of binder compositions containing binary or ternary mixes containing cement and supplementary cementitious materials (SCM's) subjected to a sulfate-laden environment. Accelerated carbonation testing and material characterization led to the finding of relationships in the chemical composition of mix designs and the observed durability and the results used to perform corrosion initiation service life modeling. An investigation into the influence of self-healing of cracked concrete led to fundamental findings on the behavior of chloride ingress for cracked concrete structures in marine environments. The results of this research led to the development of concrete mix designs capable of providing service lives over 100 years in Georgia's marine environments, as well as the advancement of the current state of knowledge on the durability characteristics of ternary mix designs.

<div> <p>The formation of the cracks in concrete materials can shorten the service life of the structure by exposing the steel rebar to the aggressive substances from the external environment. Self-healing concrete can eliminate the crack automatically, which has the potential to replace manual rehabilitation and repairing work. This thesis intends to develop a self-healing fiber-reinforced cementitious composite by the use of internal curing agents, such as lightweight aggregate, zeolite and superabsorbent polymer (SAP). This study has evaluated the crack width control ability of three different types of fiber, polyvinyl alcohol fiber (PVA), Masterfiber Mac Matrix and Strux 90/40 fiber. Mechanical performance and flexural stress-strain behavior of the fiber-reinforced cementitious composite were tested and compared. In order to investigate the feasibility of using internal curing aggregate to enhance autogenous healing performance, two types of porous aggregates, zeolite and lightweight aggregate (LWA), were used as internal curing agents to provide water for the autogenous healing. The pore structure of the zeolite and lightweight aggregate was examined by the scanning electron microscopy (SEM). Two replacement ratios of sand with internal curing aggregates were designed and the healing efficiency was evaluated by the resonant frequency measurement and the optical microscopic observation. To further understand the influence of the internal curing on the designed material, water retention behavior of the bulk sample and the internal curing aggregates was evaluated. Moreover, to study the self-sealing effect of the superabsorbent polymer (SAP), the robustness of the SAP under various environmental conditions was first evaluated. The influence of the superplasticizer, hydration accelerator and fly ash on the absorption behavior of the SAP was investigated by the filtration test and void size analysis. Afterward, the self-sealing performance of the SAP in cement paste was evaluated by a water flow test.</p> <p>The evaluation of three types of fiber indicated that the use of PVA fiber could produce a cementitious composite with stronger mechanical strength and crack width control ability. The result of the autogenous healing evaluation showed that the incorporation of the internal curing aggregates increased the self-healing recovery ratio from 12.6% to over 18%. The internal curing aggregate could absorb and store water during the wet curing and release it when the external water supply is unavailable. The comparison between the two types of internal curing aggregates indicated that finer pores in the internal curing aggregate can lead to a slower water release rate that is capable of continuously supplying water for the autogenous healing. In addition, the SAP was proved to be robust when various content of the additives and fly ash were used. And the self-sealing effect of the SAP is found to be effective in regaining the water tightness of cement paste. The result of this thesis can assist in the design of the fiber-reinforced cementitious composite with self-healing performance in civil engineering.</p> </div> <br>

No description available.

[ES] El hormigón es considerado como uno de los principales materiales de construcción más ampliamente utilizado en obras de infraestructuras. Su consideración como material de gran durabilidad y su ventajosa relación calidad-precio en comparación con otros materiales le ha hecho indispensable en la era moderna. Sin embargo, las fisuras son prácticamente inevitables en las estructuras de hormigón armado y se consideran como uno de sus puntos débiles, ya que comprometen la durabilidad de las infraestructuras y pueden generar condiciones inseguras. Hay muchas técnicas de reparación para sellar y sanar las fisuras, pero suelen ser costosas y requieren tiempo de intervención. Por esta razón, en los últimos años, se han realizado muchas investigaciones buscando alternativas para resolver estos problemas desarrollando una nueva generación de hormigones que se han denominado hormigones auto sanables. Se ha demostrado que las tecnologías de auto sanado cierran eficazmente las fisuras parcial o totalmente en un sistema cementoso. Sin embargo, los estudios a nivel del hormigón son todavía bastante limitados y en la mayoría de los casos las dosificaciones de la mezcla no fueron optimizados para la introducción de agentes de autosanado. Del estudio amplio de la literatura se aprecia que la incorporación de agentes de autosanado no siempre conllevan efectos positivos en las propiedades del hormigón. En consecuencia, según el tipo de agente de sellado/sanado, será necesario optimizar la dosificación para garantizar que no reduce en alguna medida las prestaciones del hormigón colocado. Se analiza un amplio espectro de agentes de sanado/sellado: bacterias (BAC), adiciones cristalinas (CA), biomasas y agentes incorporados en micro o macro cápsulas. Previamente a su introducción en el hormigón se evaluó su compatibilidad con los materiales cementosos, como información básica para el diseño de las mezclas. La optimización del diseño de las mezclas de hormigón se llevó a cabo dependiendo del agente elegido y los objetivos de la investigación. Al utilizar CA, se encontró que aumentar su dosis y el contenido en cemento conducía a mejorar la eficiencia de curación (HE) y la de sellado (SE). La variación de la relación agua-cemento (a/c) no produjo una mejora notable de HE y SE. Se profundizó el conocimiento sobre las propiedades de adherencia entre las armaduras y la matriz de hormigón. La inclusión de agentes de sanado (BAC, CA, biomasas) conllevó la mejora de la adherencia con un crecimiento del 57% cuando se adiciona CA. Aunque la presencia de fisuras longitudinales redujo críticamente la adherencia, se logró una recuperación importante gracias a los efectos del auto sanado. Se encontraron efectos contrapuestos del uso de microcápsulas. Se confirma una reducción significativa de la resistencia mecánica y una mejora significativa del sellado. Los parámetros de diseño de mezcla se optimizaron para compensar la reducción de resistencia, con un programa experimental con diseño factorial completo. Por la estructura inerte, las macrocápsulas tiende a perturbar el empaquetamiento de los áridos. Para la optimización de la mezcla se desarrolló un modelo de empaquetamiento de partículas modificado para predecir la proporción de huecos de las mezclas de áridos y cápsulas. Con todo, el resultado de esta investigación puede servir como guía para comprender la contribución de los parámetros de diseño de mezclas que afectan las propiedades de auto sanado, que potencialmente ayudará a investigadores e ingenieros a formular mezclas de hormigón para aplicaciones de auto sanado. / [CA] El formigó és considerat un dels principals materials de construcció més àmpliament utilitzat en obres d'infraestructures. La seua consideració com a material de gran durabilitat i la seua relació qualitat-preu avantatjosa en comparació amb altres materials l'ha fet indispensable en l'era moderna. Tot i això, les fissures són pràcticament inevitables en les estructures de formigó armat i es consideren com un dels seus punts febles, ja que comprometen la durabilitat de les infraestructures i poden generar condicions insegures. Hi ha moltes tècniques de reparació per segellar i curar les fissures, però solen ser costoses i requereixen temps d'intervenció. Per aquesta raó, en els darrers anys, s'han realitzat moltes investigacions buscant alternatives per resoldre aquests problemes desenvolupant una nova generació de formigons que s'han anomenat formigons auto sanables. S'ha demostrat que les tecnologies de auto curat tanquen eficaçment les fissures parcialment o totalment en un sistema de ciment. Tot i això, els estudis a nivell del formigó són encara força limitats i en la majoria dels casos les dosificacions no van ser optimitzades per a la introducció d'agents d'auto curat. De l'estudi ampli de la literatura s'aprecia que la incorporació d'agents d'auto curat no sempre comporta efectes positius en les propietats del formigó. En conseqüència, segons el tipus d'agent de segellat/curat, cal optimitzar la dosificació per garantir que no redueix en alguna mesura les prestacions del formigó. S'analitza un ampli espectre d'agents de curat / segellament: bacteris (BAC), addicions cristal·lines (CA), biomassa i agents incorporats en micro o macro càpsules. Prèviament a la seua introducció al formigó es va avaluar la compatibilitat amb els conglomerants, com a informació bàsica per al disseny de mescles. L'optimització del disseny de les mescles de formigó es va dur a terme depenent de l'agent elegit i els objectius de la investigació. En utilitzar CA, es va trobar que augmentar-ne la dosi i el contingut en ciment conduïa a millorar l'eficiència de curació (HE) i la de segellat (SE). La variació de la relació aigua-ciment (a/c) no va produir una millora notable de HE i SE. S'aprofundí el coneixement sobre les propietats d'adherència entre les armadures i la matriu de formigó. La inclusió d'agents de curació (BAC, CA, biomassa) va comportar la millora de l'adherència amb un creixement del 57% quan s'hi afegeix CA. Tot i que la presència de fissures longitudinals va reduir críticament l'adherència, es va aconseguir una recuperació important gràcies als efectes del auto curat. S'han trobat efectes contraposats de l'ús de microcàpsules. Es confirma una reducció significativa de la resistència mecànica i una millora significativa del segellat. Els paràmetres de disseny de mescla es van optimitzar per compensar la reducció de resistència, amb un programa experimental amb disseny factorial complet. Per la seua estructura inert, les macrocàpsules tendeixen a pertorbar l'empaquetament dels àrids. Per optimitzar la mescles es va desenvolupar un model d'empaquetament de partícules modificat per predir la proporció de buits de les mescles d'àrids i càpsules. Amb tot, el resultat d'aquesta investigació pot servir com a guia per comprendre la contribució dels paràmetres de disseny de barreges que afecten les propietats de auto curat, que potencialment ajudarà investigadors i enginyers a formular barreges de formigó per a aplicacions de auto curat. / [EN] Concrete has been widely used as a major material for infrastructure works. The durable character and the advantageous price-quality ratio compared to other materials have made concrete indispensable in the modern era. However, cracks in concrete structures are inevitable and are known as one of the inherent weaknesses of concrete, thereby making a threat to the durability of infrastructure which can lead to unsafe conditions. There are many repair techniques to seal and heal the cracks, but these approaches are costly and time-consuming. Therefore, during past years, many researchers searched for alternatives to solve these problems by developing a new generation of concrete namely self-healing concrete. Self-healing technologies have proven to effectively close cracks partially or fully in the cementitious system. However, studies on the concrete level are still rather limited and in most cases, the mix designs were not optimized for the introduction of healing agents. Based on a comprehensive literature, it was revealed that not all healing/sealing agents induce positive effects to the concrete properties. Consequently, an optimization of the mix designs is necessary to guarantee that these agents do not negatively affect the concrete properties to some extent. In this PhD dissertation, a wide range of healing/sealing agents were utilized such as bacteria (BAC), crystalline admixture (CA), biomasses, micro- and macro-encapsulated agents. Prior to the introduction of these agents into the concrete, the compatibility between healing/sealing agents and cementitious materials was evaluated to serve as a basic input for designing the concrete mixtures. The optimizations of concrete mix designs were carried out depending on the choice of the agents and the research objectives. When using CA, it was found that increasing the CA dosage and cement content in the mix design improved the healing efficiency (HE) and sealing efficiency (SE). Varying the water-cement ratio (w/c) did not give a remarkable improvement of HE and SE. A deep insight in the bond properties between the steel reinforcement and the self-healing concrete matrix was achieved. The inclusion of healing agents (i.e., BAC, CA, biomasses) possessed a bond strength improvement with the highest enhancement of 57% attained by the CA addition. Although the presence of a longitudinal crack critically reduced the bond strength, a bond restoration was achieved due to self-healing effects. Dual effects of using microcapsules were found, confirming a significant reduction of mechanical strength and a significant sealing improvement. Therefore, the mix design parameters were optimized to compensate the strength reduction via full factorial designs. With respect to the inert structure, the incorporation of macrocapsules tended to disturb the packing of aggregates. Hence, a modified particle packing model was developed to predict the voids ratio of aggregate-capsules mixtures. All in all, the outcome of this PhD research can serve as a guidance to understand the contribution of mix design parameters affecting the self-healing concrete properties. This potentially helps researchers and engineers to formulate their concrete mixtures for self-healing application. / This project has received funding from the European Union’s Horizon 2020 research and innovation programme under the Marie Skłodowska-Curie grant agreement No 860006. / Hermawan, H. (2023). Optimised Mix designs for Self-Healing Concrete [Tesis doctoral]. Universitat Politècnica de València. https://doi.org/10.4995/Thesis/10251/202610