Effects of nano-alumina on Portland concrete at low temperatures (5 ℃)

The purpose of this research is to solve the problem of concrete performance deterioration caused by low temperatures in cold regions. Based on the theoretical method of improving the performance of concrete with nanomaterials, the effect of nano-alumina (NA) on the properties of concrete under low- temperature curing is studied from the macro and micro scales. Through the compressive strength test, it is found that low-temperature curing reduces the compressive strength of concrete by more than 15%. Additionally, the incorporation of NA can make up for the adverse effects of low temperatures. Nevertheless, with the increase in the amount of inclusion, the compensation effect is decreasing, and 1% is the optimal amount of NA in concrete. Microscopic test methods such as mercury intrusion porosimetry (MIP), X-ray diffractometry (XRD), thermogravimetric analysis (TGA), and scanning electron microscopy (SEM) are used to explore the improvement mechanism of NA on concrete. The test results show that under low-temperature curing conditions, NA can still reduce the total porosity of the mortar in concrete, promote the hydration reaction of cement, consume more calcium hydroxide, generate more calcium silicate hydrate, thereby optimizing the microstructure and improving the performance of the concrete. In the future, the results and methodology of this study will provide guidance and reference for the scientific construction of concrete engineering in cold region environments.