What are Phase Changing Materials?
Phase Changing Materials (PCMs) are a combination of sensible-and-latent thermal energy storage materials which can store energy and emit it in the form of heat based on its solidifying and melting temperatures.
Potential Benefits of PCMs in Construction
- PCMs are novel technique that can control the temperature increase and fall of concrete, if they are embedded into it.
- Since PCMs can store and release thermal energy, they to have the potential to mitigate the risk of thermal crackingand increase concrete freezing and thawing resistance.
How to incorporate Phase Changing Materials in Concrete?
There are several ways to produce concrete with PCMs like:
- Direct incorporation and microencapsulation which can be added directly during the mixing process of concrete.
- Macro encapsulation through the saturation of lightweight aggregates pores, nano-silica (if used), and carbon nanotubes (if used) with liquid PCMs.
Classification of PCMs
PCMs fall into two categories: organic and inorganic.
The Organic PCMs, Paraffin or non paraffin, are preferable to be used with concrete because of their noncorrosive nature and applicability (melting and solidifying temperatures range).
The inorganic PCMs are mainly metallic or salt hydrates.
Metallic PCMs require extremely high temperatures for melting and crystallisation that are outside the range of concrete’s service temperatures.
The salt hydrates PCMs may react with cement hydration products causing deterioration in addition to their instability leading to thermal properties change after being exposed to freeze-thaw cycles due to the continual release/gain of water.
Drawbacks of PCMs
Although PCMs have a significant effect on mitigating concrete thermal cracks, there might be a negative effect on the mechanical performance of concrete such as a reduction in compressive strength and elastic modulus. Increasing the drying shrinkage can also happen.
Thus, when choosing to use a phase changing material to be implemented in concrete, care should be taken to the type. Also, trial batches of concrete containing PCM should be done to verify its good applicability.