No abstract

Cement-based materials possess an inherent autogenous self-healing capability allowing them to seal, and potentially heal, microcracks. This can be improved through the addition of microencapsulated healing agents for autonomic self-healing. The fundamental principle of this self-healing mechanism is that when cracks propagate in the cementitious matrix, they rupture the dispersed capsules and their content (cargo material) is released into the crack volume. Various healing agents have been explored in the literature for their efficacy to recover mechanical and durability properties in cementitious materials. In these materials, the healing agents are most commonly encapsulated in macrocontainers (e.g. glass tubes or capsules) and placed into the material. In this work, microencapsulated sodium silicate in both liquid and solid form was added to cement specimens. Sodium silicate reacts with the calcium hydroxide in hydrated cement paste to form calcium-silicate-hydrate gel that fills cracks. The effect of microcapsule addition on rheological and mechanical properties of cement is reported. It is observed that the microcapsule addition inhibits compressive strength development in cement and this is observed through a plateau in strength between 28 and 56 days. The improvement in crack-sealing for microcapsule-containing specimens is quantified through sorptivity measurements over a 28 day healing period. After just seven days, the addition of 4% microcapsules resulted in a reduction in sorptivity of up to 45% when compared to specimens without any microcapsule addition. A qualitative description of the reaction between the cargo material and the cementitious matrix is also provided using x-ray diffraction analysis.

Please check the manuscript for details of any other licences that may have been applied and it is a condition of accessing publications that users recognise and abide by the legal requirements associated with these rights. You may not engage in further distribution of the material for any profitmaking activities or any commercial gain. You may freely distribute both the url (http://uhra.herts.ac.uk/) and the content of this paper for research or private study, educational, or not-for-profit purposes without prior permission or charge. Take down policy If you believe that this document breaches copyright please contact us providing details, any such items will be temporarily removed from the repository pending investigation.

Several different healing agents and mechanisms have been put forward for use in autonomous healing of small cracks in cementitious composites. While the existing research on this topic focuses mainly on the use of polymeric materials as encapsulated healing agents, this study aims at assessing the efficiency of inorganic silica precursors as potential healing materials. This work investigated the effect on self-healing of different types of polymeric microcapsules containing silica precursors. The microcapsules were embedded in three different types of cement-based matrix, namely mortar, paste and grout. The results in all cases showed that the inclusion of microcapsules resulted in a marginal reduction of compressive strength in more cases for low volume fraction additions. Increasing the microcapsules concentration increased the reduction in the compressive strength. However, the observed crack healing % and durability recovery were substantially larger than any reduction on the mechanical properties. In addition, the incorporation of polymeric microcapsules in the cementitious matrix resulted in slight improvement of the composites' fracture toughness.

No abstract