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Self-healing of cracks in cementitious composites is of great significance to improve the serviceability of concrete structures. In this study, poly urea–formaldehyde (PUF) microcapsules enclosing epoxy resins were synthesized. The damage- and healing process of cement paste incorporating microcapsules was in situ detected by acoustic emission (AE) technique, in which passive AE and active AE were combined to provide complementary information about the damage and crack formation. The two representative AE signals, i.e., matrix cracking and debonding of the interface, were used as calibration for further AE post-processing analysis. The effects of the concentration of microcapsules and the level of pre-damage were investigated. The results revealed the distinguished cracking mechanisms according to the differentiated feature of the signals in terms of the temporal and spectral AE descriptors. The plot of average frequency (AF) versus RA index (rise time/amplitude) confirms that the cracking modes contribute to the characteristic spectrum. [ABSTRACT FROM AUTHOR]

The effects of the addition of minerals of various compositions (i.e., silica-based materials, chemical expansive agents, swelling minerals and crystalline components) on the self-healing performances of cementitious materials were investigated. The self-healing capabilities were assessed by performing water permeability tests, quantifying the widths of the surface cracks and studying the water absorption of mortars that were pre-cracked by either splitting or compression. The results showed that the cracks that appeared early on healed more efficiently when they were cured in still rather than flowing water. High pHs and high temperatures accelerate crack healing. The healing efficiency can be further improved by utilizing a combination of minerals rather than a single mineral. A self-healing mechanism was discussed by combining these results with micro-observations. The precipitation of calcium carbonate, which is aided by higher pH values and higher calcium ion contents, was found to be the main contributor to the healing of surface cracks. [ABSTRACT FROM AUTHOR]

This work proposes a novel insight into the autolytic mineral self-healing strategies for cementitious materials. The autolytic mineral microsphere (AMM) was prepared via the fluidization technique with cement clinker/calcium oxide as the healing substances and amino trimethylene phosphonic acid as the autolytic coating film. The basic characteristics of AMM and its hydration influence on the cementitious composite were analyzed by the laser particle analyzer, calorimetry, X-ray diffractometry and scanning electron microscopy. The autogenous self-healing capacity of the cementitious composite incorporating AMM was assessed by the crack closure, flexural property restoration and electrochemical impedance spectroscopy. Through the autolytic procedure, AMM regulated the hydration evolution and enhanced the self-healing performance of cementitious composite. The AMM containing cement clinker steadily healed the crack, leading to a well regeneration of fractured structure and restoration of flexural property. The partial substitution of cement clinker by calcium oxide in AMM further increased the crack filling, but induced a volume instability of the cement matrix as well, resulting in the strength decrease under a long-term secondary hydration. The structural alteration of cementitious composite was predominately impacted by the self-healing effect in the first 28 d re-curing, whilst the volume instability effect played a dominant role subsequently. [ABSTRACT FROM AUTHOR]

Secondary hydration is the main driving force of autogenous self-healing and directly impacts the closure of cracks in damaged cementitious materials. In fiber-reinforced cement composites, secondary hydration also dominates the regeneration of the fiber-matrix interface during the self-healing processes. As an important factor influencing the cement hydration, silica fume (SF) addition can be crucial to the self-healing performance of cementitious materials and composites. In this paper, the effect of SF on the autogenous self-healing of ultra-high-performance fiber-reinforced concrete was investigated. With a ≥20% SF addition, the secondary hydration the cement matrix adjacent to the cracks was accelerated. The dissolution of amorphous silica and the formation of Si-containing healing phases was observed. These effects predominated the closure of the mouth and the inner part of the cracks. SF addition also enhanced the regeneration of fiber-matrix interface by promoting the growth of self-healing products in these areas. The closure of cracks and the regeneration of fiber-matrix interface are both responsible for the restoration of flexural properties. • The secondary hydration acceleration of the cement matrix after cracking was found with a ≥20% SF addition, which promoted the self-healing of the cracks in UHPFRC. • The effect of SF on the structural regeneration of the cracks in UHPFRC was elucidated with a self-healing mechanism of the amorphous Si dissolution. • The self-healing of the deep matrix crack and fiber-matrix interface together induced the flexural property restoration of the SF-containing UHPFRC. [ABSTRACT FROM AUTHOR]