In order to make more energy efficient buildings it is important to reduce the energy consumption used for heating and cooling. While the daytime temperature can be too hot for comfort, the temperature at night can be too cold. The resulting need for cool ing during the day and heating during the night results in an unnecessary energy consumption that can be greatly reduced by storing the energy from the excess heat during the day and releasing it back at night.
A substance that melts will absorb energy (heat) during the melting process while keeping the temperature constant until it is completely melted. This energy will be released again when the substance solidifies. This process can be used to reduce the unwanted temperature fluctuation inside building s, utilizing a phase change material (PCM) that melts at a comfortable indoor temperature. Bulk quantities of PCMs are subject to problems that can be avoided by encapsulating the PCM into microcapsules. These microcapsules can then be added to building m aterials, such as concrete, in order to create a "smart" material suitable for passive house construction. It is however important to solve the problem of reduced material strength due to the incorporation of the PCM.
Unencapsulated PCM can adversely affect the properties of concrete. It is therefore important that all PCM is encapsulated when synthesizing the microcapsules, and that the microcapsules are not easily broken. It is also essential that there is good interaction between the microcapsule shell and the concrete matrix. A poor interaction has been found to create air voids between the microcapsules and the surrounding concrete, which will reduce the concrete compressive strength. The air voids may also impede the heat transfer to the microcapsules.
Whether the encapsulated PCM is in a solid or liquid state has little effect on the compressive strength of geopolymer concrete, while Portland cement concrete becomes weaker when it is heated to temperatures above the melting point of PCM.
Addition of microcapsules results in a significant change of the flow properties of the pre-set concrete. In addition, it affects the setting times.Microcapsules with a hydrophilic shell have a much more pronounced effect on the flow properties than microcapsules with a hydrophoboc shell, since much more water is adsorbed onto microcapsules with a hydrophilic shell. The microcapsules also affect the reaction rates of the concrete. However, the reaction products formed in the concrete does not seem to be affected by the addition of microcapsules.
Addition of microcapsules containing PCM to concrete can reduce the power consumtion for heating/cooling with up to 30% while keeping good enough strength for structural purposes.However, it is important to develop fire-resistant microcapsules, since concrete constructions containing microcapsules might start to burn when exposed to a fire.
Vi har opparbeidet oss en betydelig kompetanse angående faseovergangsmaterialer (PCM), og hvordan mikrokapsler som inneholder disse påvirker egenskapene til forskjellige betongtyper. Vi har også etablert oss innen området geopolymerbetong (som har et mye lavere CO2-avtrykk enn vanlig sement). Dette har ført til at vi nå jobber på et prosjekt sammen med ESA (European Space Agency) for å utvikle geopolymerbetong som kan 3D-printes på månen.
3 stipendiater har tatt sin doktorgrad innen dette prosjektet, og en fjerde stipendiat forventes å disputere i løpet av våren 2020.
Prosjektet har ført til et betydelig internasjonalt samarbeid, også med institusjoner vi ikke har hatt slikt samarbeid med tidligere. Vår betydelige publiseringsvirksomhet innen faseovergangsmaterialer har ført til at vi har blitt invitert inn som samarbeidspartner på 5 H2020-søknader.
Resultatene fra forskningsprosjektet er lovende, og vi ser nå på muligheter for å videreutvikle dette til noe som kan kommersialiseres.
Micro-encapsulated phase change materials can be added to concrete in order to minimize the temperature fluctuations inside buildings, and thereby reduce the need for heating and cooling. The thermal properties of these materials have been found to be ver y efficient. However, the few studies that have tested the strength of concrete that contains this kind of microcapsules have shown that the addition of microcapsules reduces the compressive strength of concrete. Although some speculations regarding the r eason for this reduced compressive strength has been put forward, very little is actually known about the mechanisms behind this. In this project we aim to discover these mechanisms, and thereby be able to optimize the combined mechanical and thermal prop erties of the concrete. This will be achieved by producing microcapsules with various sizes, shell thickness, shell compactness and shell materials, and characterize how these parameters affect both the other properties of the microcapsules (such as softn ess and tendency to rupture) and the compressive strength and thermal properties of concrete. This knowledge can be used to build more energy efficient buildings without adversely affecting their structural integrity.
In addition, the through characteriz ation of the microcapsules will give us valuable new information about the interplay between the different particle characteristics and the properties of the microcapsules. This new knowledge will also be important for other fields where microcapsules are utilized, e.g., medical and pharmaceutical applications, and the food and cosmetic industry.