Phase change material nanocomposites as an internal curing aid for nano-modified concrete under cold weather

Ultrafine nano-silica particles can improve the hydration process and concrete performance due to its high surface area and potent reactivity, which may be utilized to counteract the adverse effects of cold temperatures. In the current study, five nano-modified concrete mixtures were prepared to investigate the effect of a curing freezing temperature (-15 degrees C) on their mechanical and physical properties, durability, and microstructure features. All mixtures comprised calcium nitrate-nitrite as a cold weather admixture system (CWAS) to depress the freezing point of mixing water. In addition, nano-silica or nano-clay powders impregnated with phase change material (PCM) were added to the mixtures as internal curing nanocomposites. All mixtures were cured at - 15oC to simulate winter conditions in cold regions. The mixtures' performance was assessed based on setting times, 7 and 28 days compressive strengths, fluid absorption, and resistance to frost damage in water and salt solution. Furthermore, thermogravimetry, scanning electron microscopy associated with energy-dispersive X-ray spectroscopy, and mercury intrusion porosimetry were performed to assess the hydration, microstructural development, and pore structure features of the produced concrete, respectively. The coexistence of nano-silica and CWAS with the nanocomposites, especially in the case of nano-silica powder as a host for PCM, markedly improved the overall performance of concrete. This highlights the promising use of nano-modified concrete cured internally with nanocomposites for cold weather construction applications (down to -15 degrees C), without the need for heating practices.