Comprehensive investigation of butyl stearate as a multifunctional smart concrete additive for energy-efficient buildings

Using of phase change materials (PCM) for increasing energy savings in sustainable buildings is receiving a lot of interest in commercial applications. Butyl stearate (BS), as PCM, can be used to maintain ambient temperature in the human comfort zone and prevent temperature fluctuations by enhancing the thermal properties of concrete. The long-term effects of BS on concrete are not well known. In this study, the applicability of BS, as a smart concrete additive, by direct incorporation in the concrete structure was investigated comprehensively including thermal, rheological, and corrosion behaviour. The thermal characterization of PCM was achieved using DSC, TGA, thermal conductivity, and thermal buffering experiments. Thermal storage capacity of BS was measured to be 134.2 J/g, which is high enough to be used for passive solar energy storage in buildings. The fresh concrete experiments revealed that workability and flowability of fresh concrete mixes were improved. The maximum hydration temperature was reduced, and a retarding effect was observed by the addition of BS. Moreover, the corrosion behaviour of steel embedded in concrete with BS as PCM was studied in a solution of NaCl (3.5 wt%) representing an aggressive environment by utilizing electrochemical impedance spectroscopy (EIS) for long-term corrosion tests that lasted for 1 year. The open circuit potential of steel in concrete with BS showed noble potential indicating low corrosion probability. The FESEM images and polarization resistance (R-p) values showed that the addition of BS in concrete decreases corrosion of the rebar in comparison with concrete without BS. Addition of BS not only enhances thermal capacity but also exhibits corrosion protection of rebar by hindering penetration of chloride ions into the concrete.