Abstract
Spherical polymeric microcapsules, carrying liquid sodium silicate, were used for autonomic self-healing of mortars. Microcapsules were added at varying volume fractions (Vf), with respect to the cement volume, from as low as 4% up to 32% and their effect on fresh, mechanical and self-healing properties was investigated. For this purpose a series of techniques were used ranging from static mechanical testing, ultrasonic measurements, capillary sorption tests and optical microscopy. A detailed investigation was also carried out at the microstructural level utilising scanning electron microscopy (SEM) and energy-dispersive X-ray spectroscopy (EDX). Results showed that although increasing Vf resulted in a ∼27% reduction in the mechanical properties, the corresponding improvement in the self-healing potential was significantly higher. Areal crack mouth healing reached almost 100%. Also, the measured crack depth and sorptivity coefficient reduced to a maximum of 70% and 54% respectively in microcapsule-containing specimens. SEM/EDX observations showed that the regions in the periphery of fractured microcapsules are very dense. In this region, high healing product formation is also observed. Elemental analysis revealed that these products are mainly ettringite and calcium-silicate-hydrate (C-S-H).
Highlights
Amongst the self-healing techniques developed in the last twenty years the microencapsulation approach is by far the most studied
This study has shown that microencapsulated sodium silicate solution can undoubtedly be successfully used for autonomic selfhealing of cement-based materials
It demonstrated the effect of using a large spectrum of volume fractions of microcapsules on the fresh, mechanical and self-healing properties of mortars
Summary
Amongst the self-healing techniques developed in the last twenty years the microencapsulation approach is by far the most studied. The two techniques have many similarities, but the use of microcapsules alleviates the manufacturing related issues associated with the incorporation of hollow tubes in matrices. Are containers that envelope a healing compound keeping it protected from the manufacturing processes as well as from the surrounding host matrix. The most fundamental principle of selfhealing via microencapsulation is that the microcapsules are homogeneously dispersed in the bulk volume of the host material and the release of their healing compound is triggered by the formation of cracks that rupture their shell. Consequent chemical interactions between the encapsulated material(s) and the host matrix heal the crack. In this way, bulk material properties can be partially, or fully, restored
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