Influence of aggressive exposure on the degradation of nano-silica admixed cementitious mortar integrated with phase change materials

The objective of the present study is to evaluate the stability of cementitious mortar incorporated with phase change material (PCM, n-octadecane) at aggressive exposure conditions such as acid (1% H₂SO₄), alkali (5% Na₂SO₄) and chloride (5% NaCl). Thermogravimetric analysis (TGA) was performed to characterize and quantify the amount of deleterious compounds such as ettringite (Ca₆Al₂(SO₄)₃(OH)₁₂·26H₂O, AFt), gypsum (CaSO₄·2H₂O Gy) and Freidel’s salt (Ca₂Al(OH)6(Cl, OH)·2H₂O, Fs) formed due to the action of SO₄²⁻ (acidic and alkaline media) and Cl⁻ (chloride media) ions at the continuous exposure period of 180 days. Mass loss associated to the thermal degradation of n-octadecane PCM (CH₃(CH₂)₁₆CH₃) at various exposure solutions was also calculated at the temperature boundary of 250–300 °C. This study also highlights the introduction of optimized nano-silica dosage (3%) into the PCM based cementitious mortar to counteract the undesirable facets of PCMs on cementitious system.

Results revealed that incorporation of PCM in cementitious mortar augmented the amount of AFt, Gy (at acid and alkali exposure solution) and Fs (at chloride exposure solution) formation, responsible for the amplified rate of deterioration. It is important to be noted that after long term exposure of 180 days no traces of PCM was observed in PCM based cementitious mortar mixes, which signifies the mixes no longer holds the capacity to store energy. However, co-occurrence of nano-silica (3%) in PCM based cementitious mixes curtailed the negative impact of PCM on cementitious mortars exposed to aggressive conditions significantly. Further, differential thermogravimetric (DTG) curve shows an additional endothermic peak at 250–300 °C for 3% nano-silica modified PCM based cementitious mixes even after exposure to aggressive ions that implies the ability of the mix to sustain the thermal efficiency characteristics of PCMs.