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This paper brings a new insight into understanding the influence of macrocapsules in packing systems, which can be useful in designing the inert structure of self-healing concrete. A variety of tubular macrocapsules, in terms of types and sizes, was used to assess the capsules' effect in the packing, together with various aggregate types and fractions. The voids ratios (U) of aggregate mixtures were evaluated experimentally and compared with the prediction via the particle packing model of Dewar. The packing of coarse particles was found to be considerably affected by the presence of macrocapsules, while no capsules' effect on the packing of fine particles was attained. A higher capsule dosage and capsule aspect ratio led to a higher voids ratio. In the formulation of the inert structure, the packing disturbance due to capsules can be minimised by increasing the content of fine aggregates over coarse aggregates. Dewar's model showed a good compatibility with experimental results in the absence of capsules. However, the model needed to be upgraded for the introduction of tubular macrocapsules. Accordingly, the effect of macrocapsules was extensively analysed and a 'U model' for capsules (with some limitations) was finally proposed, offering a high predicting accuracy. [ABSTRACT FROM AUTHOR]

Concrete is one of the world's most used and produced materials, based on its dominant role in the construction sector, both for the construction of new structures and for the repair, restoration, and retrofitting of built ones. Recently, research has been focused on the development of innovative solutions to extend the service life of reinforced concrete structures, specifically by introducing self-healing properties aimed at reducing the necessary maintenance interventions and, consequently, the environmental impacts. These solutions imply costs and financial feasibility impacts, which must be measured and evaluated to support the ranking of preferable alternatives. Thus, this paper proposes a methodology capable of supporting the selection of material/product options from the early design stages in the construction sector. Assuming a life-cycle perspective, the Life-Cycle Costing (LCC) approach is proposed for comparing three material solutions applied to the case study of a wall component hypothesized to be used in building construction in Turin, Northern Italy. Namely, traditional standard concrete and two different self-healing concrete types were evaluated using the Global Cost calculation of each solution. The focus is on the material service life as a crucial factor, capable of orienting investment decisions given its effects on the required maintenance activities (and related investments) and the obtainable residual value. Thus, according to a performance approach, LCC is combined with the Factor Method (FM). Assuming the capability of the lifespan to affect the Global Cost calculation, the results give full evidence of the potential benefits due to the use of self-healing materials in construction in terms of the reduction in maintenance costs, the increase in the durability of buildings and structures and related residual values, and consequently, the reduction in the environmental impacts. [ABSTRACT FROM AUTHOR]

Alkaline solutions, such as sodium, potassium or lithium silicates, appear to be very promising as healing agents for the development of encapsulated self-healing concretes. However, the evolution of their mechanical and acoustic properties in time has not yet been completely clarified, especially regarding their behavior and related kinetics when they are used in the form of a thin layer in contact with a hardened cement matrix. This study aims to monitor, using linear and nonlinear ultrasonic methods, the evolution of a sodium silicate solution interacting with a cement matrix in the presence of localized cracks. The ultrasonic inspection via linear methods revealed that an almost complete recovery of the elastic and acoustic properties occurred within a few days of healing. The nonlinear ultrasonic measurements contributed to provide further insight into the kinetics of the recovery due to the presence of the healing agent. A good regain of mechanical performance was ascertained through flexural tests at the end of the healing process, confirming the suitability of sodium silicate as a healing agent for self-healing cementitious systems. [ABSTRACT FROM AUTHOR]

Self-healing concrete has the potential to optimise traditional design approaches; however, commercial uptake requires the ability to harmonize against standardized frameworks. Within EU SARCOS COST Action, different interlaboratory tests were executed on different self-healing techniques. This paper reports on the evaluation of the effectiveness of proposed experimental methodologies suited for self-healing concrete with expansive mineral additions. Concrete prisms and discs with MgO-based healing agents were produced and precracked. Water absorption and water flow tests were executed over a healing period spanning 6 months to assess the sealing efficiency, and the crack width reduction with time was monitored. High variability was reported for both reference (REF) and healing-addition (ADD) series affecting the reproducibility of cracking. However, within each lab, the crack width creation was repeatable. ADD reported larger crack widths. The latter influenced the observed healing making direct comparisons across labs prone to errors. Water absorption tests highlighted were susceptible to application errors. Concurrently, the potential of water flow tests as a facile method for assessment of healing performance was shown across all labs. Overall, the importance of repeatability and reproducibility of testing methods is highlighted in providing a sound basis for incorporation of self-healing concepts in practical applications. [ABSTRACT FROM AUTHOR]

Additive manufacturing (AM) can produce complex vascular network configurations, yet limited testing has been done to characterize the damage and healing behavior of concrete with embedded networks for self-healing. In this study, different AM methods and network wall materials were used to produce vascular networks for self-healing concrete prisms, where their load-response behavior, healing efficiency and microstructure were evaluated using non-destructive techniques: acoustic emission (AE), ultrasonic pulse velocity (UPV), digital image correlation (DIC), and X -ray computed tomography (CT). The types of healing agent release mechanisms that were studied include a ductile-porous network that supplies fluid from its pores and a brittle network that fractures under load to release fluid. DIC coupled with AE verified debonding of ductile-porous networks from the cementitious matrix, and was able to track damage progression as well as healing for all networks with load regains up to 56 % and stiffness regains up to 91 % using polyurethane. [ABSTRACT FROM AUTHOR]

The use of capsule-based technology for self-sealing and self-healing cementitious systems has been extensively investigated for both macro- and microencapsulated additions. In this study, macrocapsules, produced using a novel technique were characterised and compared, evaluating mechanical triggering, bonding with the cementitious matrix, and self-sealing efficiency upon integration into cementitious mortar specimens. Macrocapsules containing a commercially available water repellent agent were produced in two ways. Stereolithographic additive manufacturing (3D printing) was used to produce novel rigid acrylate macrocapsules as well as alumina ones. Cementitious macrocapsules produced with a rolling technique were also used as a comparison. The capsules were characterised in terms of watertightness, water uptake, and shell morphology. Following this, the capsules were integrated into cement mortar prisms and subjected to controlled cracking by three-point bending to evaluate the triggering and subsequent self-sealing effect. The results highlighted influential process parameters that can be optimised and explored for further capsule-based self-sealing in structural applications. [ABSTRACT FROM AUTHOR]