Abstract: Basalt fiber fly ash concrete conforms to the concept of green and economically viable development. To improve the reliability of its practical application in engineering, this paper presents a study on the characterization of its pore structure, frost resistance by the formation of pores, pore physical phase distribution, and fractal dimension, through the hydration process of fly ash and cement under the conditions of different basalt fiber lengths (6, 12, and 18 mm) in single mixing and blending scenarios. The results show that after 300 freeze-thaw cycles, the degree of freeze-thaw damage to fly ash concrete from high to low is unadulterated basalt fiber, single-adulterated basalt fiber, and mixed-adulterated basalt fiber. From pore structure characterization, basalt fiber admixture refines the pore space, that is, the maximum pore diameter and porosity both are reduced. From pore phase distribution and fractal dimension, the pore space of single admixture is mainly concentrated around the fiber, so that the internal pore space forms a linear concentrated distribution, causing the concrete to be prone to frost stress concentration. In the blending case, pore concentration is reduced significantly, and the small pore dispersion effect is conducive to reducing the role of frost stress. The fly ash component improves the pore structure through delaying the hydration micro-filling effect, and the fibers’ bridging effect prevents radial cracks in the pore space from further development, thus improving the frost resistance of concrete.

Key words: basalt fly ash concrete, single admixture, hybrid, pore structure characterization, frost resistance