Kris Sisomphon k.sisomphon@tudelft.nl
Oguzhan Copuroglu o.copuroglu@tudelft.nl
The development of a self-healing cement is the main objective of this proposal. Emphasis is to come to a cement which exhibit a long-term self-healing capacity. The basic idea is to blend a regular cement with a predefined fraction of dissoluble encapsulated cement particles (DEP). Individual DEP particles are to be encapsulated by a viscous agent that acts as a membrane in high pH-conditions and dissolves whenever coming into contact with air. If a crack develops and air and/or water penetrates into this crack, the pH will drop, urging the membrane to dissolve and activate the DEP particles to commence hydration. The self healing material, developed in the form of a blended cement, will enhance an easy implementation into the market. Introducing a new product that remains as closely as possible to the basic ingredients of a regular concrete should encourage this approach.
Within the scope of this research proposal, micro-level modelling and advanced experimental studies of the self healing potential of dissoluble encapsulated particles, blended within regular cement systems, will be performed. The main research questions are: Firstly, what should be the thermodynamical/chemical conditions of the encapsulation membrane in order to comply with the self healing requirements. Secondly: what is the mechanism behind the moisture movement and what are the main potential moisture sources in order to establish self healing?
With the aim to answer these research questions it is important to combine the advanced facilities of TU Eindhoven and TU Delft. In Eindhoven the Nuclear Magnetic Resonance (NMR) scanning facility can be used for non destructive testing and imaging of the moisture transport in porous media like cement based materials, whereas in Delft, the ESEM and Nano-indenter can be used to analyse the local properties of the healed material at the nanoscale. The experimental results will provide the necessary data to validate a HYMOSTRUC-based numerical model, development for this self healing cement. As such, this model will give the possibility to predict under which circumstances which blended cement gives the best self healing properties.
The project is carried out by CiTG, Section Material and Environment of Delft University of Technology. Industrial partners who have shown their interest are ENCI BV, BAM Infraconsult and Strukton Civiel BV.
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Ye Guang g.ye@tudelft.nl
Haoliang Huang h.huang@tudelft.nl
Self-healing IN cement-based materials by liquid capsules: Mechanism and application
Cracks, caused by shrinkage and external loading, are unavoidable in concrete structures. These cracks facilitate the ingress of aggressive and harmful substances into concrete and reduce the durability of the concrete structures. Fortunately, cement-based materials have the potential to heal the cracks under certain conditions. In this research, two mechanisms of self-healing in cement-based materials are proposed.
The first mechanism is self-healing by further hydration of unhydrated cement. The cracks can be healed by further hydration when extra water and unhydrated cement are available. It is well known that even after long time service, a large fraction of unhydrated cement remains in the concrete matrix, especially in high performance concrete. Therefore the main criterion for the self-healing by further hydration is the supply of extra water in the system. In this research, the extra water will be stored in capsules which will be pre-mixed in the concrete mixture. When the concrete cracks, the cracks pass through the capsules because of its low strength. In this way the water can be released from the capsules and induces the further hydration of unhydrated cement particles.
The other mechanism of self-healing is reaction of blast furnace slag (BFS) activated by sodium silicate solution in slag cement-based materials. BFS is a by-product in the manufacture of pig iron, and it is the main cement replacement material in the Netherlands
However, because of the low strength of capsules, mechanical properties of concrete are expected to decrease. Taking into account self-healing efficiency and mechanical properties of concrete, the amount of capsules mixed will be optimized by modeling and experiments.
