Nano-Modified Concrete Incorporating Phase Change Material Under Cold Temperature

Stringent requirements (enclosures, temperature thresholds, etc.) are typically prescribed in codes for cold weather concreting, which entail substantial costs. Nano-silica has the capability of improving the hydration process and concrete performance due to its high surface area and vigorous reactivity, which may be utilized to counteract cold temperatures. In this study, five concrete mixtures were prepared to investigate the effect of a freezing temperature (-15 ℃) on their mechanical and physical properties. Combinations of ordinary cement and nano-silica sol were incorporated in concrete as the main binder components. All mixtures comprised calcium nitrate-nitrite as cold weather admixture systems (CWAS) to depress the freezing point of mixing water. In addition, nano-silica or nano-clay powders saturated with phase change material (PCM) were added to the mixtures as an internal curing aid. All mixtures were cured at -15ºC to simulate actual field conditions. The mixtures’ performance was assessed based on setting times, early- and late-age compressive strengths, fluid absorption, and hydration development. The coexistence of nano-silica and CWAS, with the addition of PCMs, especially in the case of nano-silica powder as a host, markedly improved the overall performance of concrete. This indicates the promising use of nano-modified concrete cured internally with PCMs for cold weather applications, without the need for heating practices.