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Membrane emulsification is a promising new technique that can be deployed as a scalable modular conduit for the consistent and continuous production of single and complex emulsions. This work reports on the development of a manufacturing platform based on membrane emulsification for the first time for microcapsule-based self-healing cementitious materials. The feasibility of single and double emulsion production with wall formation as a secondary step through UV radical polymerisation was explored using a discrete membrane emulsification dispersion cell. The operational parameters (pressure, dispersed phase flux, temperature, shear rate) were established for the specific phase characteristics (viscosity, density, interfacial tension) to achieve control of emulsion droplets and maintain a high encapsulation of core content (high payload). Microcapsules with sodium silicate core and an average diameter of ∼130 μm were produced. Microcapsules were shown to achieve high payload (∼89%). Moreover their thermal stability was characterised and their release performance in the cementitious matrix established. The results demonstrated the capability of membrane emulsification to produce microcapsules with an aqueous core for use in self-healing of cementitious materials.

Development and commercialization of self-healing concrete is hampered due to a lack of standardized test methods. Six inter-laboratory testing programs are being executed by the EU COST action SARCOS, each focusing on test methods for a specific self-healing technique. This paper reports on the comparison of tests for mortar and concrete specimens with polyurethane encapsulated in glass macrocapsules. First, the pre-cracking method was analysed: mortar specimens were cracked in a three-point bending test followed by an active crack width control technique to restrain the crack width up to a predefined value, while the concrete specimens were cracked in a three-point bending setup with a displacement-controlled loading system. Microscopic measurements showed that with the application of the active control technique almost all crack widths were within a narrow predefined range. Conversely, for the concrete specimens the variation on the crack width was higher. After pre-cracking, the self-healing effect was characterized via durability tests: the mortar specimens were tested in a water permeability test and the spread of the healing agent on the crack surfaces was determined, while the concrete specimens were subjected to two capillary water absorption tests, executed with a different type of waterproofing applied on the zone around the crack. The quality of the waterproofing was found to be important, as different results were obtained in each absorption test. For the permeability test, 4 out of 6 labs obtained a comparable flow rate for the reference specimens, yet all 6 labs obtained comparable sealing efficiencies, highlighting the potential for further standardization. ispartof: Science And Technology Of Advanced Materials vol:21 issue:1 pages:661-682 ispartof: location:United States status: Published online