Treballs Finals de Grau d'Enginyeria de Materials, Facultat de Química, Universitat de Barcelona, Any: 2015, Tutor:
Dr. Joan Formosa Mitjans
Magnesium Phosphate Cements (KMgPO4·6H2O; k-struvite), that are known as
MPC, part of the family of Chemically Bonded Phosphate Ceramics (CBPC), widely
used in the field of biomaterials. These cements are obtained from the acid-base
reaction on an aqueous medium between pure MgO and mono-potassium phosphate. It
is a spontaneous and highly exothermic reaction that leads to a very fast setting of the
material.
The main disadvantage of these cements compared with others such as Portland is
the high cost of raw materials that are necessary to elaborate the MPC. In the present
study we use a by-product called LG-MgO (low magnesium oxide), supplied by the
company Magnesitas Navarras, S.A., with the aim to reduce the final cost of MPC and
promote aspects such as sustainability and green environment as a consequence of the
reduction of the pure MgO mining activity.
The research presented here consists in the exhaustive characterization of different
dosages of MPC elaborated with magnesium by-product that incorporate air entraining
additive and Phase Changing Materials (PCM) to improve the thermal behavior of
material when there are thermal oscillations, and thus reduce the use of cooling and
heating systems helping to the decrease of CO2 emissions and increasing energy
efficiency on the buildings. Moreover, mechanical properties such as elastic modulus,
compressive strength and flexural strength are analyzed to test the feasibility of the use
of these cements as a passive cooling and heating system. Finally, the degradation of MPC when subjected to thermal cycles is analyzed (thermal durability). Results show that k-struvite is the major product formed in the MPC, although there
are also inert phases of magnesium by-product that act as reinforcement. It is verified
that the increase of PCM and additive in the content reduces the mechanical properties
due to their contribution to increase the porosity and decrease the density. Moreover,
we demonstrated that MPC and PCM do not suffer degradation after 750 thermal cycles
equivalent to a year.