Presentation of phase change materials in concrete
A new article published in the journal Materials by a group of researchers demonstrated the potential and challenges of using concrete embedded in phase change materials (PCM) in buildings.
To study: Phase Change Materials in Concrete: Opportunities and Challenges for Sustainable Construction and Building Materials. Image Credit: Bannafarsai_Stock / Shutterstock.com
Concretely, the incorporation of PCM has shown significant potential in clean zone storage. However, the large-scale application of concrete incorporated in PCM has been hampered by the negative impacts of PCM on the durability and mechanical properties of concrete. So, researchers are trying to develop different techniques for incorporating PCM into concrete that can overcome these challenges.
Why use PCM-Incorporated Concrete?
Currently, the building sector uses a substantial amount of conventional energy and natural resources across the world, thus contributing to environmental degradation and increasing demand for energy. The energy consumption of buildings is expected to increase in the coming years due to the construction of new buildings, which will further stimulate energy demand.
Therefore, these developments are not in line with the United Nations Sustainable Development Goals (SDGs). The SDG intervention encourages the transition from fossil fuels to renewable energies to achieve sustainability.
Importance of concrete incorporated in PCM for durability
Currently, the focus has shifted towards passive cooling strategies that are sustainable over the long term. Passive cooling strategies such as the use of concrete incorporated into PCM can promote a sustainable future by helping to achieve net zero carbon emissions from buildings. Over the past decade, thermal energy storage (TES) has emerged as a promising technology for a low carbon future.
Various active and passive cooling techniques. Image Credit: Sharma, R et al., Materials
TES is a practical method that adheres to the principles of the United Nations SDGs regarding the use of clean energy for thermal comfort. Despite some deficiencies in mass and heat transfer, TES still exhibits the higher heat storage density than sensible heat storage (SHS) and latent heat storage (LHS) methods.
Studies have shown that the use of PCM can increase the TES needed for thermal comfort, which can reduce projected energy demand and fossil fuel consumption in the future.
PCMs can release and absorb heat at constant temperature. PCMs can also store a much higher amount of heat per unit volume than SHS materials used in buildings such as rock, masonry, and water. Therefore, LHS-based PCMs were considered the most relevant TES material for practical building applications.
PCM and its types
In the construction industry, eutectic, inorganic and organic PSMs are the commonly used types of PCMs. 20-32o is the accepted temperature range for passive cooling of buildings with PCM. Organic PCMs are either of the non-paraffinic type or of the paraffinic type. Paraffin is suitable for passive cooling and energy storage PCMs.
However, organic PCM has lower heat release rate / storage capacity due to low thermal conductivity. Inorganic PCMs are referred to as metallic materials, nitrates and salt hydrates. Properties such as non-flammability and high volumetric capacities of LHS make them suitable for construction applications.
However, segregation and phase separation and corrosion are the notable drawbacks of inorganic PCMs. Eutectic PCMs are called mixtures of organic and inorganic compounds. A unique melting temperature and a higher density than organic materials are the main properties of eutectic PCMs.
Techniques used for the incorporation of MCP in concrete
Microencapsulation, macroencapsulation, porous inclusion, and shape stabilization are the four common methods of incorporating MCP into concrete. Low strength and stiffness are the main drawbacks of microencapsulated PCM. Macroencapsulation is similar to microencapsulation with minor differences. However, poor heat transfer and leakage are the major drawbacks of the technique.
Although the shape stabilization technique can solve the leakage problem, the shape stabilized PCM has lower thermal conductivity. The porous inclusion technique is mainly used to improve thermal inclusion. However, the use of all of these techniques can increase the porosity and decrease the density and strength of concrete, despite improved thermal performance.
Techniques for improving the properties of concrete incorporated into PCM
Neutralizing or minimizing the effect of PCM on the mechanical properties of concrete is the only way to promote the field application of concrete incorporated in PCM. The negative impact on mechanical properties can be limited by depositing PCM in lightweight aggregate and embedding additional cementitious materials on the exterior surface.
The use of nanomaterials in the PCM, the filling of the pipes with PCM, the impregnation of the PCM in the pores of the concrete from the surface and the addition of carbon nanotubes and silica fume during the pasty phase have gave better results than direct PCM incorporation techniques.
The future of concrete incorporated in PCM
Efforts are underway to improve the thermal conductivity of concrete incorporated into PCM using materials such as foamed metal and layered clay minerals.
This study focuses on different PCMs, their adverse effects on the properties of concrete and ways to minimize the effects. Observations from studies have shown that the use of additional nanomaterials and cementitious materials can increase the strength of concrete incorporated into PCM. However, achieving a balance between thermal storage and mechanical properties remains a challenge for researchers. Thus, more research is needed to eliminate the adverse effects of PCM on concrete.
Sharma, R. Jang, J.-G. Hu. J.-W. Phase Change Materials in Concrete: Opportunities and Challenges for Sustainable Construction and Building Materials. Materials 2022, 15, 335. https://www.mdpi.com/1996-1944/15/1/335