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⩽0.20mm 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

The primary objective of this study was to assess freeze-thaw resistance of concrete whose structure was modified by varying the water/binder ratio and ground granulated blast furnace slag content, and by air entrainment. The innovative method of the polymer microspheres-based air entrainment was used to provide a stable pore structure.Test results show that the method is very effective both in providing adequate air entrainment and in improving freeze-thaw resistance of concrete. All air-entrained concrete specimens with polymer microspheres (the spacing factor of ≤ 0.25mm) had a good resistance to the action of frost, regardless of the W/S ratio and the slag cement content

The number of air voids, their size and disposition in cement paste,are important characteristics, which substantially affect the system of air voids that protects concrete from freezing and thawing cycles. The standard spacing factor L is based on the simplified Powers model, which assumes that all bubbles have the same diameter and are distributed in cube corners. A better solution is provided by Philleo, which determines the percentage content of protected paste (S*). The authors’ approach consists in determining the PPV factor, which is based on the concept of Philleo, and takes into account not onlythe actual structure of air voids, butalso of aggregate grains, which is often disregarded in analyses. In this article the results of analyzing the air void structure in air-entrained concrete on the basis on 2D image analysis are presented. Implementation of this research was possible thanks to the use of a special procedure of concrete samples preparation.Such an approach allows the separation of 4 phases of concrete: aggregate, cement paste, rings of the paste protected by air voids and air. The PPV results obtained from image analysis were compared with standard spacing factor L and with Philleo factor (S*).The authors are of the opinion that the 2D analysis proposed in the study will make it possible to describe more accurately the air-void system in air-entrained concrete

The purpose of the present study was to determine the impact of image quality on the results of air void system parameters determination in air-entrained concretes. The focus was on technical aspects related to the preparation of the scanned image of the concrete surface, which was then subjected to 2D surface analysis. Image processing aimed at separating joined voids and removing various types of defects in aggregate and cement mortar. The specific surface of the voids was determined with the air void equivalent diameter or perimeter as the calculation basis. Applying the Schwartz–Saltykov method, the 3D distribution of the air voids was reconstructed based on 2D measurements. On this basis, the micro-air content A300 was determined. The results of the 2D method were compared with the results of determinations carried out using the linear traverse (1D) method according to EN 480-11. The tests confirm the need to correct the image prior to measurements. Comparative tests showed good agreement between the air void system parameters determined using the 2D analysis and the EN 480-11 chord length counting method.

The European concrete standard EN 206 introduces the k-value concept as one of the three methods allowing the use of granulated blast furnace slag in the design of the freeze-thaw-resistant concrete mix. It is assumed that the freeze-thaw durability of the concrete, whose composition (w/c ratio) has been corrected by adopting a certain k-value, is the same as the freeze-thaw resistance of the reference concrete made with the cement containing no addition (CEM I). This article presents the results of freeze-thaw resistance analysis (modified with the ASTM C666A standard Class XF3) of 24 series of concretes made with a binder containing varied amounts of slag, with a w/b ratio ranging from 0.25 to 0.55. The aim of the study was to estimate the k-value as a parameter defined by the w/b ratio and the slag content in the binder. In this approach, the k-value is determined by trial and error in such a way that the deformation of the concrete specimens containing the slag corresponds to the deformation of the reference concrete. As shown by the analysis, the k-value decreases with increasing slag content in the binder.