Co-authors​ :

 Carmelo SANFILIPPO (ITALY), Emanuele PREVITI (ITALY), Emanuela MASTRONARDO , Vincenzo FIORE (ITALY), Luigi CALABRESE (ITALY), Candida MILONE (ITALY), Antonino VALENZA (ITALY) 

Globally, the building and construction sector accounted for 36% of the total energy consumption and 39% of energy and process-related CO2 emissions in 2018. Hence, this sector will have to play a major part in the vision of achieving the carbon neutrality by 2050. The development of new building envelopes and construction materials that boost energy savings, save resources and decrease carbon emissions, both during construction and operation of the buildings, is fundamental for reaching this goal. From here, the necessity to develop innovative and sustainable building insulation materials. Some attempts have been reported in literature to replace Portland cement with geopolymer concrete (GPC)[1,2], which is synthesized by alkali activation of materials rich in silica and alumina from industrial waste materials such as fly ash (FA), coal ash, rice-husk ash, red mud and ground granulated blast furnace slag[3], thus reducing the impact on the concrete manufacturing processes. Recently, several research efforts focused on the integration of a thermal energy storage medium into building materials (concrete or mortars) for increasing its overall thermal storage capacity, resulting in higher energy efficiency and reduced power consumption for heating and cooling. Indeed, a ThermoChemical heat storage material (TCM) is able to store and release heat though a reversible chemical reaction:
A·mH2O(s) ⇄ A·(m·n)H2O(s)+nH2O(g); (m≥n) (1)
In a typical cycle, during the day, the material stores the excess of heat and dehydrates. While during the night, when the temperature decreases, the TCM reacts with the ambient humidity and re-hydrates, releasing the previously stored heat into the environment. To this chemical heat (QC), it is added the sensible one stored by the concrete (QS). Hence, the total heat storage capacity is defined by the following equation:
Qtot = Qc + Qs = ΔH + CpΔH (2)
being ΔH the reaction enthalpy associated to the dehydration/hydration reaction, cP the specific heat capacity of the concrete, and ΔT the temperature variation associated to the storage/release phase.
While the external conditions vary, the temperature inside the building is kept constant, guaranteeing the environmental comfort, and thus reducing the global energy consumption due to a better isolation and the reduction of heating/cooling demand.
The goal of this study is to disperse a not toxic TCM in a porous geopolymer concrete that acts as matrix. The selected TCM is an organic salt hydrate which can dehydrate/hydrate under various temperatures and relative humidity typically achieved during days and nights. The synthesis and mechanical properties have been evaluated. The purpose is to undertake a preliminary evaluation aimed at defining its use as a functional material for the daily thermal storage of energy, allowing an improvement in the energy efficiency of buildings.