Polymeric microcapsules with switchable mechanical properties for self-healing concrete: synthesis, characterisation and proof of concept

Abstract

Microcapsules, with sodium silicate solution as core, were produced using complex coacervation in a double, oil-in-water-in oil, emulsion system. The shell material was a gelatin-acacia gum crosslinked coacervate and the produced microcapsules had diameters ranging from 300 to 700 μm. The shell material designed with switchable mechanical properties. When it is hydrated exhibits soft and 'rubbery' behaviour and, when dried, transitions to a stiff and 'glassy' material. The microcapsules survived drying and rehydrating cycles and preserved their structural integrity when exposed to highly alkaline solutions that mimic the pH environment of concrete. Microscopy revealed that the shell thickness of the microcapsules varies across their perimeter from 5 to 20 μm. Thermal analysis showed that the produced microcapsules were very stable up to 190°C. Proof of concept investigation has demonstrated that the microcapsules successfully survive and function when exposed to a cement-based matrix. Observations showed that the microcapsules survive mixing with cement and rupture successfully upon crack formation releasing the encapsulated sodium silicate solution.

A Review of Self‐Healing Concrete for Damage Management of Structures

“…Similarly, the investigation of more thermally stable materials like polyurea has led to the development of capsules ( Figure b) for survivability in elevated temperature environments . A different approach included the production of microcapsules with switchable mechanical properties to ensure survivability during the concrete mixing process. In this context, recent collaboration between universities and companies led to the design and production of microcapsules that exhibit ductile “rubbery” behavior when hydrated and when dried transition to stiff, brittle glass‐like behavior (Figure a) …”

“…Recent research activities in microencapsulation for self‐healing in cementitious systems: a) gum Arabic/gelatin shell microcapsules containing sodium silicate core, b) polyurea shell microcapsules produced containing semicrystalline sodium silicate, c) schematic of the microfluidics process including the photopolymerization process, d) a laboratory setup of double emulsion flow focusing microfluidics platform, e) optical microscope image of microfluidics produced monodisperse acrylate microcapsules and f) corresponding surface functionalized acrylate microcapsules . Reproduced with permission . Copyright 2017, IOP publishing.…”

Microcapsule‐Based Visualization Smart Sensors for Damage Detection: Principles and Applications

“…The results of thermalgravimetric analysis test showed that the mass loss of microcapsules is very small even at 180 °C and the morphology is intact, indicating the microcapsule can resist the high‐temperature condition during the mixing and compaction process after being added to the cementitious material. In 2017, Kanellopoulos et al investigated the geometry of microcapsules between wet and dry conditions. It was found that there was no effect on the structural integrity of the shell under the dehydration/rehydration cycles test.…”

Research Progress on Numerical Models for Self‐Healing Cementitious Materials

“…Alongside this work on autogenous healing has been a major research effort on autonomic (manufactured) healing systems . The three main techniques explored for delivering and releasing healing agents are as follows: i)The embedment of brittle vessels (normally tubes) into structural elements; ii)The addition of microcapsules into cementitious mixes; iii)The creation of interconnected channels or “vascular networks” within cementitious structural members …”