It is well known that the most important parameters for predicting the frost resistance of pavement concrete are the air pore spacing factor, L, and the micropore content, A300. The A300 parameter requires complex calculations with the estimation of the air-void size in a 3D space. The procedure is based only on one-dimensional chord lengths. The air-void distribution is used only to determine the content of micropores and has no other practical application. Based on the results of the analysis, it was found that there is a simpler way to estimate the A300 parameter without the tedious calculations described in the EN 480-11 Standard. The presented approach is based on the existing linear correlation between the A300 parameter and the number of chords in 28 length classes. The developed function includes only a few coefficients (eight classes) because only chord lengths of 10-350 µm are statistically significant. This fact is important not only for the simplification of calculations but may also have consequences for the methodology of testing parameters characterizing the structure of air-entrained concrete using the 2D method. The presented function allows the estimation of A300 with a standard error not exceeding 0.02%, so it is useful for practical use.
Keywords: A300 micropore content; air entrainment; air-void distribution; concrete; frost resistance; spacing factor.