Cementitious based composite materials for thermal energy storage applications

Over the last century the exploitation of resources in the energy production generated clear and indisputable devastation in the ecosystem, such as global warming or combustion and dispersion of fossil fuels in the environment. The aim of the researches conducted in the last period is both to capitalize on renewable resources to avoid the diffusion of CO2 and both to cope with the mismatch of energy production and its demand. In this scenario, Sorption Thermal Energy Storage, even though still being a technology little known, appears to play a key role in the renewable energy sources system. This technology allows to stock an high amount of energy during the warm season and then releasing it when is needed, without significant losses. The sorption phenomena is based on the interaction between a sorbent and a sorbate that undergo a reversible adsorption-desorption reaction which allows to stock energy when the two substances are kept separated and to release it when they are brought together. The researches in the last period moved on the investigation of the suitable couple of materials sorbent-sorbate that grant the higher energy density release combined with the lower affordable cost. Composite materials result to be an adequate candidate that permit to store an elevate amount of energy without significant losses. The aim of this thesis is to produce a robust and low-cost composite material by using as host matrix the common Portland cement and accommodating inside some hygroscopic salts, precisely Magnesium Sulfate (MgSO4) and Calcium Chloride (CaCl2). The choice of the cement as matrix for the composite material is due to his porous morphology, which permit to accommodate salts inside it, to his uncomplicated availability on our planet and to his relative low cost with respect to the common sorbents employed so far as matrix. In the work are showed two methods to produce this composite material: a dry impregnation of saturated salt solution inside a white pure cement basis and a new proposed in situ synthesis where the powder cement is directed mixed with the saturated salt solution rather than pure water. The samples produced characterized by the higher estimated salt fraction within are tested thermally firstly assembling a preliminary thermal test in the university laboratory. The most promising ones are investigated at the National Institute of Metrological Research (INRiM) with the purpose of obtain the sorption parameters to classify the composite material. Two absorption isotherms are plotted after testing the sample respectively at 30°C and 50°C and the most important properties, i.e. water uptake, isosteric heat and energy density are calculated. Only the samples produced with sulfate magnesium allows a complete estimation of the properties, as a matter of fact the intrinsic deliquescence behaviour of calcium chloride inhibit a correct sorption test in the climatic chamber. The best sample results to be an in situ synthesized with sulfate magnesium and impregnated two times with the same salt. From the preliminary thermal test it reached an energy density of 0.15 GJ/m3 .