Mechanical and Microstructural Properties of Nanoconcretes Exposed to Low-Temperature Curing

Low-temperature curing significantly affects the performance of concrete. This study explored the mechanical and microstructural characteristics of concretes modified with three kinds of nanoparticles [i.e., nano-CuO (NC), nano-SiO2 (NS), and nano-TiO2 (NT)] at curing temperatures of -6 degrees C, -2 degrees C, 2 degrees C, and 6 degrees C. The results indicated that the compressive strength of concrete cured at positive temperatures was higher than that of concrete cured at negative temperatures. Variations in the stress-strain relationships for the specimens were similar, of which the strain of concrete modified with NT was higher than those modified with NC and NS. At positive curing temperatures, the peak stress of concrete specimens modified with NC and NT first increased and then decreased as the nanomaterial content was raised, and the peak stress reached its maximum value when the nanomaterial content was 2%. However, at negative curing temperatures, the peak stress reached a maximum value when the NC content was about 3%. Besides, in terms of the compressive strength of nanoconcretes, the optimum contents of the nanomaterials to resist external loads and the optimal contents for NC, NS, and NT cured at negative temperatures were 3.0%, 1.0%, and 3%, respectively. Moreover, compared with the controlled group of ordinary portland cement without nanomaterials, for concretes with added nanomaterials, the nanomaterials can significantly fill the internal pores of the concrete, which can inhibit the development of cracks. Furthermore, low-temperature curing can inhibit hydration reactions, and the resistance to negative temperatures for concretes modified with NT was better than that for concretes modified with other nanoparticles. This study will help us better understand the influence mechanism and degree of low-temperature curing on the behavior of nanoconcrete and provide guidance for engineering construction in cold regions.