It is well-known that concrete permeability is a good indicator of its expected durability until it remains uncracked. However, in various stages of its service life, different types of cracking in concrete can be developed due to exposure to different deterioration processes such as early plastic shrinkage or chloride-induced reinforcement corrosion. Although these cracks may not endanger concrete’s structural performance from the mechanical point of view, they create a pathway for aggressive ions that can initiate degradation processes, lead to increase in concrete permeability and thus reduce its durability. Cracking in concrete might not be preventable, but its capability to naturally seal small cracks, named autogenous self-healing (SH), provides an additional feature to manufacture more durable concrete structures. However, natural self-healing capability of concrete is limited and therefore it is typically omitted in the design of concrete structures. Hence, more attention has been recently paid to Engineered Self-healing Concrete (EShC) which is associated with artificially triggered healing mechanisms into the cementitious matrix by incorporating various substances such as crystalline products. EShC helps in reducing concrete permeability; thus, increasing its service-life and durability. Due to formation of needle-shaped pore-blocking crystals, Crystalline Admixtures (CA), as a candidate from the Permeability-Reducing Admixtures (PRA) category, can be implemented into concrete mixtures to fabricate EShC concretes. Crystalline waterproofing technology is not new, but still is unknown to many researchers, engineers, and construction industry professionals. The lack of knowledge of its microstructure and self-healing properties limits CA’s proper usage in the construction industry. The techniques to assess the self-healing capability of mortar and concrete are not well-standardized yet. No research work has been done to address certain durability characteristics of this material (i.e. electrical resistivity (ER) or chloride diffusivity) especially when combined with Supplementary Cementitious Materials (SCM) and Portland Limestone Cement (PLC). Since the resistance of concrete against ions’ penetration is a function of its permeability, it might be a straightforward and reliable parameter to rapidly evaluate concrete’s durability during its intended service life. Hence, electrical resistivity measurement is considered as an indirect and alternative tool for other time-consuming permeability testing techniques to examine the CA’s efficiency as it modifies the concrete’s microstructure by crystals’ deposition; thus, leads to permeability improvement. In comparison to previous studies, on a larger scale, this thesis aims to systematically study the effects of CA on the microstructural features, self-healing properties and long-term durability and resistivity of cement-based materials and in addition, draw some comprehensive conclusions on the use of CA in new and repair applications. This study is divided into three major phases to propose all-inclusive work on using CA in construction industry. To satisfy the goals of each individual phase, a test matrix consisting of a series of four mixes with variables such as use of PLC or presence of CA in powder form is considered. In order to address to the lack of research and industry knowledge discussed above, this PhD thesis includes the following phases: Phase (I) In this phase, the main focus is on the microstructural properties and the changes in the pore structure and chemical compositions of the cement phase of mortar mixes when treated with CA. These microstructural features are studied using Scanning Electron Microscope (SEM) and Scanning Transmission Electron Holography Microscope (STEHM). Moreover, physical and chemical characteristics of the hydration products are determined using image analysis and Energy Dispersive X-ray (EDX) Spectroscopy, respectively. Phase (II) This phase is allocated to macro-level investigation of durability characteristics such as chloride/water permeability and electrical resistivity of concrete structures containing CA and PLC cement. To non-destructively measure the chloride ion concentration in the field conditions, both changes in corrosion potential of rebars and concrete electrical resistivity in treated circular hollow-section steel reinforced columns exposed to simulated marine environment is monitored and compared over a 2-year period with control samples. In addition, laboratory-size concrete samples are studied to investigate the effects of CA presence on long-term resistivity, rapid chloride permeability, water permeability and chloride diffusivity of concrete. Later, a resistivity-based model is developed to predict long-term performance of concretes incorporating slag or metakaolin, studied in various environmental conditions. The long-term goal of this phase is to develop a standard design guideline and durability-based model. Phase (III) Using an innovative self-healing testing method [1], quantitative analysis of crack closure ability and self-healing potential of CA treated and control concretes with OPC or PLC cement is accomplished during this phase. The obtained results from first phase showed that hydrated CA particle revealed fine, compact, homogenous morphology examined by STEHM and its diffraction pattern after water-activation indicated nearly amorphous structure, however, diffuse rings, an evidence for short-range structural order and sub-crystalline region, were observed which requires further investigation. The SEM micrographs taken from specimen’s fractured surface showed formation of pore-blocking crystals for all treated mixes while similar spots in un-treated sections were left uncovered. Although needle-shaped crystals were observed in the treated mortar specimens, but not all of them had shapes and chemical compositions other than ettringite (well-known to form needle-like crystals). Using backscatter SEM images and EDX spectrums, examination of polished mortar sections with and without CA also showed typical hydration phases, forming in the control system. Results from phase II showed that concretes treated with CA had almost 50% lower water penetration depth and thus smaller permeability coefficient when compared with the virgin OPC or PLC concretes. According to salt ponding test results, the use of CA helped in enhancing the resistance to chloride penetration compared to control concrete. This improvement increases with increasing in concrete age. Strong linear relationship between Surface Resistivity (SR) and Bulk Resistivity (BR) data was observed which indicates that these test methods can be used interchangeably. The presence of SCM in concrete indicated considerable increase in both SR and BR compared to control concrete. Concretes incorporating slag or metakaolin have tendency to react more slowly (or rapidly in MK case), consume calcium hydroxide over time, form more Calcium Silicate Hydrate (C-S-H) gel, densify internal matrix, and also reduce OH- in the pores’ solution; thus, increase concrete electrical resistivity. For laboratory specimens, environmental conditions such as temperature variation and degree of water saturation indicated considerable effects on electrical resistivity measurements. As temperature or water content of concrete decreases, its electrical resistivity greatly increases by more than 2-3 times from reference environmental condition. This is mostly because of variation or accessibility in electron mobility. Experimental results from field investigation showed that electrical resistivity readings were highly influenced by the presence of rebar and concrete moisture conditions. In addition, concrete cover thickness and CA addition into cementitious matrix had a negligible effect on its resistivity. In the last phase, an optical microscope was used to measure the average crack width. OPC samples had an average measured crack width of 0.244 mm as compared to 0.245 mm for OPC-CA, 0.251 mm for PLC, and 0.247 mm for PLC-CA. Self-healing test results also showed 90% self-healing ratio for CA modified mix within few days after starting experiment. Addition of CA into the mix led to higher rates of healing and full crack closure (width up to 250 µm) when compared to reference concrete. An empirical equation that relates water initial flow rate to the crack width (Q∝〖CW〗^3) was also proposed in this phase. Presence of PLC and CA in the mixture resulted in positive improvement in crack-closing capability and self-healing ratio. / Graduate / 2019-09-11

Los materiales autosanables son materiales con la capacidad de reparar sus daños de forma autónoma o con ayuda mínima de estímulos externos. En el campo de la construcción, el desarrollo de elementos autosanables aumentará la durabilidad de las estructuras y reducirá las acciones de mantenimiento y reparación. Los elementos de hormigón armado presentan frecuentemente pequeñas fisuras (< 0.3 mm), no relevantes mecánicamente, pero que pueden suponer un punto de entrada para agentes agresivos. El hormigón tiene una cierta capacidad de autosanación, capaz de cerrar pequeñas fisuras, producida principalmente por la hidratación continuada y la carbonatación. Estudios recientes han intentado mejorar dicha capacidad y diseñar productos específicos para conseguirla. Estos productos incluyen, entre otros, aditivos cristalinos, agentes micro o macroencapsulados, e incluso el uso de bacterias. Los aditivos cristalinos (CA) son un tipo de aditivo para hormigón que se considera que aporta propiedades de autosanación. No obstante, la falta de conocimiento sobre su comportamiento limita su uso. Además, los métodos para evaluar la autosanación en hormigones no están estandarizados todavía. Esto complica la realización de un análisis crítico de los diferentes productos y métodos de evaluación propuestos en la literatura. Para responder a esta falta de conocimiento, los objetivos de esta tesis son: 1) estudiar y proponer procedimientos experimentales para evaluar los fenómenos de autosanación en hormigón y, 2) evaluar experimentalmente las mejoras producidas al introducir aditivos cristalinos. Esta tesis incluye como ensayos para la determinación de la autosanación: la evaluación del cierre de fisuras, la permeabilidad al agua, flexión a tres puntos y absorción capilar. Además, se han realizado varias campañas experimentales para validar los ensayos propuestos. Posteriormente, estos ensayos se han utilizado para analizar la influencia de varios parámetros, incluyendo entre otros: presencia de aditivos cristalinos, nivel de daño, tiempo necesario para el sanado, composición del hormigón y condiciones de sanado. Finalmente, se analizan los efectos producidos al añadir aditivos cristalinos en hormigón en la fluidez, resistencia e hidratación. Los resultados muestran que el cierre de fisuras es un ensayo eficaz y sencillo para evaluar la autosanación. Sin embargo, la orientación de la fisura durante el sanado ha resultado ser de gran importancia, y no considerar este aspecto puede llevar a conclusiones engañosas. El ensayo de permeabilidad al agua propuesto en este trabajo presenta una buena estabilidad y es fácil de implementar en laboratorios. Además, las relaciones obtenidas entre los parámetros de fisura y la permeabilidad del agua han confirmado la relación cúbica indicada en la literatura. Este trabajo muestra que analizar la eficiencia de autosanado mediante el cierre de fisuras puede llevar a una sobreestimación de la capacidad de sanación, comparada con los resultados obtenidos mediante permeabilidad. Los ensayos de sorptividad resultaron fáciles de implementar, sin embargo, los resultados obtenidos mostraron una alta dispersión y sensibilidad a las variaciones en las fisuras producidas durante el proceso de prefisuración. En cuanto a la evaluación de la recuperación mecánica, los resultados muestran que la evolución de las propiedades del hormigón con el tiempo es un parámetro que debe considerarse, especialmente en fisuras de edades tempranas. En este trabajo se ha obtenido que los aditivos cristalinos potencian las reacciones de autosanación, pero tienen una capacidad limitada. La proximidad de los CA a la industria es un punto positivo para su inclusión como un nuevo tipo de aditivo de hormigón. Sin embargo, los resultados obtenidos en esta tesis indican que se necesitan más análisis para determinar sus efectos completos en hormigón, especialmente con respect / Self-healing materials are materials with the capability to repair their damage autonomously or with minimal help from an external stimulus. In the construction field, the development of self-healing elements will increase the durability of structures and reduce their maintenance and repair actions. Reinforced concrete elements frequently suffer small cracks (< 0.3 mm), not relevant mechanically, but they can be an entrance point for aggressive agents. Concrete has a natural self-healing capability able to seal small cracks, produced by the continuing hydration and carbonation processes. Recent studies have attempted to improve that healing capability and to design specific products to achieve it. These products include, among others: crystalline admixtures, micro- or macro-encapsulated agents, and even the use of bacteria. Crystalline admixtures (CA) are a concrete admixture that is claimed to provide self-healing properties. However, the lack of knowledge on their behavior and self-healing properties limits their usage. In addition, the methods to evaluate the self-healing capability of mortar and concrete are not standardized yet. This complicates the performance of a critical analysis of the different self-healing products and evaluation methods found in the literature. In order to answer to this lack of knowledge, the objectives of this thesis are: 1) to study and propose experimental procedures in order to evaluate self-healing in concrete and, 2) to evaluate experimentally the self-healing enhancements produced when introducing crystalline admixtures. This thesis includes the following tests for the determination of the self-healing: the evaluation of crack closing, water permeability, three point bending tests and capillary absorption test. In addition, several experimental campaigns have been performed with the objective of validating the proposed tests. Afterwards, these methods have been used to analyze the influence of several parameters, including among others: the presence of crystalline admixtures, the damage extent, healing time needed, concrete composition and healing conditions. Finally, the effects that crystalline admixtures produce in concrete are analyzed in terms of slump, strength and hydration. The results show that crack closing is an effective and simple method to evaluate self-healing. However, the orientation of the crack during healing is of great importance, and disregarding this aspect may lead to misleading conclusions. The water permeability method proposed in this work has good stability and it is easy to implement in concrete laboratories. Moreover, the relations obtained between crack parameters and water permeability confirmed the cubic relation, as reported in the literature. This work shows that analyzing healing efficiency by means of crack closing tends to overestimate self-healing if compared with the results obtained by means of water permeability. Sorptivity analysis tests were easy to implement, however, the results obtained in this work showed high dispersion and sensitivity to the variations of the cracks introduced during the precracking process. Regarding the evaluation of mechanical recoveries, the results show that the evolution of concrete properties with time is a parameter of importance that, therefore, should be considered, especially for early age cracks. In this work, crystalline admixtures have been reported as an enhancer of self-healing reactions, but with a limited capacity of enhancement. The proximity of CA to the industry is a positive point to their inclusion as a new type of admixture for concrete. However, the results obtained in this thesis indicate further analyses are needed to determine their full effects on concrete, especially regarding self-healing. / Els materials autosanables són materials amb la capacitat de reparar els seus danys de forma autònoma o amb ajuda mínima d'estímuls externs. En el camp de la construcció, el desenvolupament d'elements autosanables augmentarà la durabilitat de les estructures i reduirà les accions de manteniment i reparació. Els elements de formigó armat presenten freqüentment fissures menudes (< 0.3 mm), no rellevants des del punt de vista mecànic, però poden suposar un punt d'entrada per a agents agressius. El formigó té una capacitat de autosanació capaç de tancar fissures menudes, produïda principalment per la hidratació continuada i la carbonatació. Estudis recents han intentat millorar eixa capacitat i dissenyar productes específics per aconseguir-la. Aquests productes inclouen, entre d'altres, additius cristal·lins, agents micro- o macroencapsulats, i fins i tot l'ús de bacteris. Els additius cristal·lins (CA) són un tipus d'additiu reductor per formigó que es considera que proporciona propietats de autosanació. No obstant, la manca de coneixement sobre el seu comportament limita el seu ús. A més, els mètodes per avaluar la autosanació de formigons encara no estan estandarditzats. Açò complica la realització d'una anàlisi crítica dels diferents productes i mètodes d'avaluació proposats a la literatura. Per respondre a aquesta manca de coneixement, els objectius d'aquesta tesi són: 1) estudiar i proposar procediments experimentals per avaluar els fenòmens d'autosanació en formigó i, 2) avaluar experimentalment les millores produïdes en introduir additius cristal·lins. Aquesta tesi inclou com assajos per a la determinació de l'autosanació: l'avaluació del tancament de fissures, la permeabilitat a l'aigua, flexió a tres punts i absorció capil·lar. A més, s'han realitzat diverses campanyes experimentals per validar els assajos proposats. Posteriorment, aquests assajos s'han utilitzat per analitzar la influència de diversos paràmetres: presència d'additius cristal·lins, nivell de dany, temps necessari per a la sanació, composició del formigó i condicions de sanació. Finalment, s'analitzen els efectes produïts en afegir additius cristal·lins en formigó en fluïdesa, resistència i hidratació. Els resultats mostren que el tancament de fissures és un assaig eficaç i senzill per avaluar l'autosanació. No obstant això, l'orientació de la fissura durant la sanació ha resultat ser de gran importància, i no considerar aquest aspecte pot portar a conclusions enganyoses. L'assaig de permeabilitat a l'aigua proposat presenta una bona estabilitat i és fàcil d'implementar en laboratoris. A més, les relacions obtingudes entre els paràmetres de fissura i la permeabilitat a l'aigua han confirmat la relació cúbica de la literatura. Aquest treball mostra que analitzar l'eficiència de l'autosanació amb el tancament de fissures pot sobreestimar la capacitat de sanació, comparada amb els resultats obtinguts-dues mitjançant permeabilitat a l'aigua. Els assajos de sorptivitat van resultar fàcils d'implementar, però, els resultats obtinguts en aquest treball van mostrar una alta dispersió i sensibilitat a les variacions en les fissures produïdes durant el procés de prefissuració. Pel que fa a l'avaluació de la recuperació mecànica, els resultats mostren que l'evolució de les propietats del formigó amb el temps és un paràmetre d'importància que, per tant, s'ha de considerar, especialment per fissures primerenques. En aquest treball s'ha obtingut que els additius cristal·lins potencien les reaccions d'autosanació, però tenen una capacitat limitada. La proximitat dels CA a la indústria és un punt positiu per a la seva inclusió com un nou tipus d'additiu de formigó. Tanmateix, els resultats obtinguts en aquesta tesi indiquen que calen més anàlisis per determinar els seus efectes complets en formigó, especialment pel que fa a l'autosanació. / Roig Flores, M. (2018). Self-healing concrete: efficiency evaluation and enhancement with crystalline admixtures [Tesis doctoral no publicada]. Universitat Politècnica de València. https://doi.org/10.4995/Thesis/10251/100082 / TESIS

Reactive powder composites (RPC) have been recently a subject of many researches of modern concrete technology. This type of concrete is very fine and its behaviour exceeds the other types of concrete, therefore there are new possibilities of its use. The design and production of RPC is complex technology process which needs to gain new results in RPC research to get the best features regarding its higher price. This thesis is focused on design of reactive powder concrete (RPC200), which compressive strength is between 200 – 300 MPa. Next goal is to prove the influence of curing regimes like high temperature or pressure, and also check the possibilities of production of low cement reactive powder composite (LCRPC).

No description available.

Yes / Considering the continuous development of sustainable development, energy saving, and emission reduction concepts, it is very important to reduce concrete's cement content in order to improve its environmental impact. Using reactive admixture to replace part of the cement in ultra-high performance concrete (UHPC) can effectively improve the overall performance of the concrete and reduce carbon dioxide emissions (CO2), which is an important aspect of environmental protection. Here, industrial waste residue (fly ash and slag), sea sand (SS), and manufactured sand (MS) were used to produce UHPC under standard curing condition, to reduce the material cost and make the it more environmentally friendly and sustainable. The effects of water-binder ratio, contents of cementitious materials, types of sands, and content of steel fibers on the mechanical performance of UHPC under standard curing were investigated experimentally. In addition, the effects of various factors on the depth under hydraulic pressure and electric flux of UHPC, mass loss, relative dynamic modulus of elasticity, flexural, and compressive strengths of UHPC specimens after freeze-thaw cycles were conducted to evaluate the impermeability, chloride, and freeze-thaw resistance of various UHPCs produced. The obtained experimental results show that the SS-UHPC and MS-UHPC prepared by standard curing exhibit high strength, excellent impermeability, and chloride resistance. The frost resistant grade of all groups of UHPCs prepared by standard curing are greater than F500 and had excellent freeze-thaw resistance, including those produced with local tap water or artificial seawater. The investigation presented in this paper could contribute to the production of new UHPCs of low cost and environmental-friendly and accelerate the application of UHPC in engineering structures.

Three epoxy-coated reinforcing steel (ECR) types removed from job sites, one shipped directly from the coater's plant, three commercial corrosion inhibitors, and one ECR plus a corrosion inhibitor were evaluated as reinforcing steel corrosion protection systems against chloride induced corrosion. The three corrosion inhibitors were calcium nitrite, an aqueous mixture of esters and amines, and a mixture of alcohol and amine. The ECR was tested in two groups, 0% and 1% coating damage. Corrosion protection performance was evaluated by the amount of visually observed blister surface area, for the ECR, and corroded surface area, for the tested corrosion inhibitors. Results of the ECR testing demonstrated that coating debondment and corrosion of ECR is directly related to the amount of damage present in the coating, as well as coating thickness. For the bare steel tested with and without corrosion inhibitors, the results showed that corrosion increases with increasing chloride concentrations. Corrosion inhibition characteristics were demonstrated only by the calcium nitrite corrosion inhibitor. A corrosion protection evaluation test was developed for concrete corrosion inhibitor admixtures. The test solution is a simulated concrete pore water. Corrosion is accelerated by evaluating the temperature to field conditions of 40 C. The test consists of a 7 day pretreatment period followed by a 90 day test period. The corrosive sodium chloride is added to the solution containing the bare or epoxy-coated reinforcing steel specimens after the 7 day pretreatment period. In addition, the solution is periodically saturated with oxygen. / Master of Science

Concrete experiences volume changes throughout its service life. When loaded, concrete experiences an instantaneous recoverable elastic deformation and a slow inelastic deformation called creep. Creep of concrete is composed of two components, basic creep, or deformation under load without moisture loss and drying creep, or deformation under drying conditions only. Deformation of concrete in the absence of applied load is often called shrinkage. The deformation due to creep is attributed to the movement of water between the different phases of the concrete. When an external load is applied, it changes the attraction forces between the cement gel particles. This change in the forces causes an imbalance in the attractive and disjoining forces. However, the imbalance is gradually eliminated by the transfer of moisture into the pores in cases of compression, and away from the pores in cases of tension. Designs typically use one of the two code models to estimate creep and shrinkage strain in concrete, ACI 209 model recommended by the American Concrete Institute or the CEB 90 Eurocode 2 model recommended by the Euro-International Committee. The ASSHTO LRFD is based on the ACI 209 model. Three other models are the B3 model, developed by Bazant; the GZ model, developed by Gardner; and the SAK model developed by Sakata. The development of concrete performance specifications that limit the amount of compressive creep of concrete mixtures used by the Virginia Department of Transportation, specifically concrete mixtures used for prestressed members (A-5 Concrete) were assessed, along with determining the accuracy and precision of the creep models presented in the literature. The CEB 90 Eurocode 2 model for creep and shrinkage is the most precise and accurate predictor. The total strain for the VDOT portland cement concrete mixtures discussed in this study were found to be between 1200 ± 110 microstrain at 28 days, and 1600 ± 110 microstrain at 97 days, at a five percent significant level. / Master of Science

Corrosion of reinforcing steel in concrete exposed to chloride-laden environments is a well-known and documented phenomenon. The need for cost effective systems for protection against corrosion has become increasingly clear since the first observations of severe corrosion damage to interstate bridges in the 1960's. As one potential solution to the mounting problem of corrosion deterioration of structures, corrosion-inhibiting admixtures have been researched and introduced into service. This report conveys the results of a three-part laboratory study of corrosion inhibiting admixtures in concrete. The commercial corrosion inhibiting admixtures for concrete have been analyzed by three evaluation methods, including: • Conventional concrete corrosion cell prisms under ponding, • Black steel reinforcing bars immersed in simulated concrete pore solutions, • Electrochemical screening tests of special carbon steel specimens in electrochemical corrosion cells containing filtered cement slurry solution. The purposes of the study include: • Determining the influence of a series of commercially available corrosion inhibiting admixtures on general concrete handling, performance and durability properties not related to corrosion. • Determining the effectiveness of corrosion inhibiting admixtures for reduction or prevention of corrosion of reinforcing steel in concrete, relative to untreated systems, under laboratory conditions. • Conducting a short-term pore solution immersion test for inhibitor performance and relating the results to those of the more conventional long-term corrosion monitoring techniques that employ admixtures in reinforced concrete prisms. • Determining whether instantaneous electrochemical techniques can be applied in screening potential inhibitor admixtures. Concrete properties under test included air content, slump, heat of hydration, compressive strength, and electrical indication of chloride permeability. Monitoring of concrete prism specimens included macro-cell corrosion current, mixed-cell corrosion activity as indicated by linear polarization, and ancillary temperature, relative humidity, and chloride concentration documentation. Simulated pore solution specimens were analyzed on the basis of weight loss and surface area corroded as a function of chloride exposure. Electrochemical screening involved polarization resistance of steel in solution. Results include corrosion potential, polarization resistance and corrosion current density. / Master of Science

The diploma thesis describes admixtures for concrete. It deals with the influence of admixtures on the properties of cement composites in the fresh and hardened state. The theoretical part described the individual components of concrete, where the main attention was focused to inert admixtures and their effect on mechanical properties, shrinkage, resistance of cement composites to aggressive medium. Furthermore, the effect of admixtures on concretes with recycled aggregates was described. In the first stage of the practical part, cement mortars with 25, 35 and 50% replacement of cement admixtures were created. In the second stage, concretes with admixtures and a minimum strength class of C30/37 and C50/60 were created. Finely ground granulated slag, micronized limestone and granite stone dust were used as admixtures in mortars and concretes. The change of properties in the fresh and hardened state was observed on cement composites.

Volume changes are one of the priority characteristics of concrete that plays an important role place mainly in the durability of structures as such. These low volume changes are required especially for structures as: industrial concrete floors, massive structures and waterproof structures. One of the possibilities in reducing these changes is the use of mineral admixtures with suitable grain curve of aggregate. Another possibility is the use of shrinkage reducing admixtures. There can occur problem with efficiency (long term age) with other components of the mixture. Therefore, the effort of this work is to use the avaible processes for maximum reduction of shrinkage and hydration temperatures.