Cement (and derivatives thereof) is one of the materials most commonly used in construction, given its good performance at low cost. Over recent years, one part of scientific and technological research is aimed at incorporating additional functions into these materials. Specifically, Doctor Idurre Kaltzakorta studied the possibility of adding capacities to the cement such as self-repair of cracks as well as storing latent heat energy.
Her PhD thesis, undertaken at Tecnalia's Construction Unit, was presented at the University of the Basque Country (UPV/EHU) and entitled: Synthesis of silica microcapsules encapsulating different organic compounds for addition in the cement paste.
As the title of her research suggests, Dr Kaltzakorta created silica (it is, for instance, the base of glass) microcapsules with organic material inside, the idea being to provide the cement with new functions. She opted for two types of organic materials, each corresponding to one of the two added features mentioned above. Thus, on the one hand, the microcapsules were filled with various epoxy resins (used in the manufacture of adhesives), to provide the cement with the capacity for the self-repair of cracks. On the other, phase change materials were encapsulated. These are materials which absorb or free a great quantity of heat on the phase of the material changing (from solid to liquid or liquid to gas and vice-versa), and enable the storage of latent heat energy in the cement material.
Sol-gel and emulsion
Ms Kaltzakorta studied the synthesis of the encapsulated material, opting for synthesising microcapsules by combining sol-gel chemistry with emulsion technology. This route enabled the encapsulation of organic material, difficult with other routes, under mild temperature and pressure conditions.
Once the microcapsules were obtained, the thesis analysed the effect of the addition of these to the cement matrix, to verify the viability of the technique. With this in mind, Ms Kaltzakorta used a number of techniques with which the features of the new cement material could be studied, techniques such as X-ray tomography, scanning electron microscopy, mechanical testing and differential scanning calorimetry.
In conclusion, the thesis shows the viability of the development of a new generation of cements capable of the self-repair of cracks as well as storing latent heat energy, based on the application of silica microcapsules with various organic materials. In fact, the research for developing the new cement with the capacity for self-sealing of cracks has given rise to a patent. Moreover, according to Ms Kaltzakorta, the proposal presented in this thesis is a commitment to sustainability. On the one hand, getting the cement material to self-repair increases the useful life of the structures. On the other, using a material capable of regulating the temperature within the buildings will enhance their energy efficiency.
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