The increasing concern for safety and sustainability of structures is calling for the development of smart self-healing materials and preventive repair methods. The appearance of small cracks (<300 µm in width) in concrete is almost unavoidable, not necessarily causing a risk of collapse for the structure, but surely impairing its functionality, accelerating its degradation, and diminishing its service life and sustainability. This review provides the state-ofthe-art of recent developments of self-healing concrete, covering autogenous or intrinsic healing of traditional concrete followed by stimulated autogenous healing via use of mineral additives, crystalline admixtures or (superabsorbent) polymers, and subsequently autonomous self-healing mechanisms, i.e. via, application of micro-, macro-, or vascular encapsulated polymers, minerals, or bacteria. The (stimulated) autogenous mechanisms are generally limited to healing crack widths of about 100-150 µm. In contrast, most autonomous self-healing mechanisms can heal cracks of 300 µm, even sometimes up to more than 1 mm, and usually act faster. After explaining the basic concept for each self-healing technique, the most recent advances are collected, explaining the progress and current limitations, to provide insights toward the future developments. This review addresses the research needs required to remove hindrances that limit market penetration of self-healing concrete technologies.

The aim of this study is analyzing the self-healing effect of a crystalline admixture in four types of 11 environmental exposure comparing with a reference concrete. Healing was studied by means of permeability tests on 12 cracked specimens and physical closing of the crack was observed by optic microscope and quantified through crack 13 geometrical parameters. The studied crack openings were under 300 μm and the time set for healing was 42 days. The 14 results show a different healing behavior depending on the exposure and the presence of the crystalline admixture, 15 demonstrating that the presence of water is necessary for the healing reactions. 16

This paper analyzes the self-healing properties of early-age concretes, engineered using a crystalline admixture (4% by the weight of cement), by measuring the permeability of cracked specimens and their crack width. Two concrete classes (C30/37 and C45/55) and three healing exposure conditions have been investigated: water immersion at 15 °C, at 30 °C and wet/dry cycles. Specimens were pre-cracked at 2 days, to values of crack width in the range of 0.10–0.40 mm. The results show almost perfect healing capability for specimens healed under water at 30 °C, better than for specimens healed under water at 15 °C, while insufficient for the wet/dry exposure

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This paper presents the results are shown of a thorough characterization of the selfhealing capacity of High Performance Fibre Reinforced Cementitious Composites (HPFRCCs). The capacity of the material will be investigated to completely or partially re-seal the cracks, as a function of its composition, maximum crack width and exposure conditions. The analysis will also consider different flow-induced alignments of fibres, which can result into either strain-hardening or softening behaviour, whether the material is stressed parallel or perpendicularly to the fibres, respectively. Beam specimens, initially pre-cracked in 4-point bending up to different values of crack opening, were submitted to different exposure conditions, including water immersion, exposure to humid or dry air, and wet-and-dry cycles. After scheduled exposure times, ranging from one month to two years, specimens were tested up to failure according to the same test set-up employed for pre-cracking. Outcomes of the self-healing phenomenon, if any, were analyzed in terms of recovery of stiffness, strength and ductility. In a durability-based design framework, self-healing indices quantifying the recovery of mechanical properties were also defined and their significance crosschecked.

Autogenous healing is mainly produced by continuing hydration or carbonation. The aim of this research is to quantify the crack closing produced by autogenous healing for early-age concrete. This healing was evaluated for two crack size levels, 0.1 mm and 0.4 mm, under three healing conditions: water immersion, a humidity chamber, and wet/dry cycles. Crack closing was evaluated after 7, 14, 28 and 42 days under healing conditions. The internal status of the cracks was verified visually and using phenolphthalein. The results show that specimens stored in the humidity chamber did not experience healing, while specimens under wet/dry cycles and water immersion achieved the complete closing of small-sized cracks (under 0.15 mm). Autogenous healing showed higher speed under wet/dry cycles but higher final efficiency under water immersion. However, the inspection of the interior of the specimens showed that self-closing occurred mostly on the surface, and carbonation in the crack faces was only noticed very near the specimen’s surface. Additionally, this study proposes a preliminary strategy to model autogenous healing in concrete in terms of crack closing.

A Jaime, por el ingenio que le define y por estar siempre ahí. A Iván y su carácter inconformista, por perseguir sus sueños y, en especial, por ayudarme con los códigos de MATLAB de esta tesis. A mis padres, Mª Victoria y Martín, por inculcarme valores y por demostrar que con esfuerzo y constancia se puede llegar adonde quieras. Porque solo puedes ir más rápido, pero acompañado llegarás más lejos. Porque para poder crecer, debes tener buenos apoyos y el vuestro lo tengo siempre. Aunque no lo diga, os quiero mucho.Gracias a todos de corazón. The show must go on.Other research merits • T. Lucio-Martin, "Almacenamiento de calor sensible en materiales de base cemento para infraestructuras de centrales termosolares". Thesis Talk 2019. Present your research in 3 minutes, Universidad Carlos III de Madrid, June-July 2019. o Role: Speaker. o Contribution: T. Lucio-Martin presented the research developed in the thesis before a non-specialist audience in 3 minutes. T. Lucio-Martin was classified in the second semifinal (28 th June 2019) for participating in the final session that took place on 12 th July 2019. o URL semifinal: https://media.uc3m.es/video/5d25adc48f4208ecb18b456e o URL final session: https://media.uc3m.es/video/5d2ed2a08f420881a08b4568 This page has been intentionally left blank.

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