Protected Paste Volume (PPV) as a parameter linking the air-pore structure in concrete with the frost resistance results

A new description is proposed of the air void structure in air-entrained concretes using a PPV (Protected Paste Volume) parameter. The PPV is determined as a ratio of the paste area protected by air voids to the total paste area, obtained from the 2D surface measurements. This approach, although constitutes a development of the Philleo concept, takes into account the number, size and distribution of not only air voids but also aggregate grains, often disregarded by other researchers. The obtained results show that the standard spacing factor L ⩽ 0.20 mm fails to guarantee that 100 percent of the paste volume is protected against the harmful effects of frost, which is the basic assumption in the Powers spacing factor model. The preliminary verification was carried out of the relationships between the parameters L and PPV and the results of freeze-thaw experiments. According to the authors, at this stage of the study the PPV provides better correlation with the frost resistance results than the standard spacing factor L. Unlike other indicators representing a statistical estimation of the average spacing of air bubbles, the PPV much better reflects the spatial displacement of the air pores in concrete and can thus be considered as an improved factor of air voids spatial dispersion.