In cold regions, concrete practitioners face challenges to achieve target performance criteria of concrete produced under low temperatures. There is still dearth of knowledge on how to alleviate the heating requirements for cold weather concreting. Nano-silica has the potential to produce concrete mixtures with dense microstructure and improved hardened properties under cold temperatures. This thesis applied the response surface method to assess the effect of multiple parameters on 40 concrete mixtures cast and cured under freezing temperatures down to -5℃. In addition, a comprehensive study was conducted to further understand the behavior of these mixtures and suitability for repair applications under cold temperatures. Also, this thesis explored the efficacy of using a hybrid protection system (insulation blankets + Phase change material (PCM) mat) on hydration development, mechanical properties and bonding behavior with steel of nano-modified concrete cured under lower freezing temperatures (-10 and -20℃), without heating, using experimental and numerical studies. The results suggested that the incorporation of at least 2% nano-silica with single or blended binders (maximum of 15% fly ash), especially with low w/b and calcium nitrate-nitrite (CNAI), achieved satisfactory performance when cured under freezing temperatures down to -5℃. This was substantiated by the complementary investigation which proved the applicability of nano-modified concrete, especially with a higher nano-silica dosage (4%) without and with fly ash (15%), for repair applications. Hence, it achieved satisfactory performance and compatibility with parent concrete. Furthermore, the experimental and numerical results showed that nano-modified concrete comprising CNAI, without or with fly ash (20%) and protected using the hybrid system achieved adequate hydration development, mechanical properties and bonding with steel re-bars due to the nucleation, pozzolanic and filler effects of nano-silica. Moreover, the developed thermal analysis and mechanical models showed an adequate generalization capability to predict concrete-steel interfacial temperature evolution, as well as bond strength with less than 10% error between predicted and experimental results. The synoptic outcomes of this thesis suggest that nano-modified concrete mixtures and hybrid protection system may provide an integrated strategy for alleviating heating requirements and improving the quality of concrete for various cold weather concreting applications down to -20℃.