# Methodological Basis for Reliable Evaluation of Air Void Structure Parameters Using the 2D Method

## TL;DR

This paper evaluates methods for measuring air void structures in concrete to improve frost resistance predictions.

## Contribution

The study defines optimal measurement frame parameters for reliable 2D evaluation of air void structures in concrete.

## Key findings

- Three 50 × 50 mm or four 40 × 40 mm measurement frames with 3 µm/px resolution yield satisfactory results.
- 2D and 1D methods show good agreement when analyzing air void structures.
- Pores over 1000 µm may not need to be considered in frost resistance evaluations.

## Abstract

Frost resistance of pavement concrete is closely related to air void structure. Traditionally, such a structure is assessed by measuring chord lengths according to the guidelines provided in the PN-EN 480-11 standard. In recent years, increased attention has been given to analyzing pore diameters (2D) on the surface of concrete samples. The measurement procedure employed in the surface method should enable accurate identification of small pores formed by modern air-entraining admixtures. Researchers suggest only pores under 300 µm significantly impact frost resistance, raising the question of whether pores over 1000 µm should be considered in measurements. This study attempts to define the measurement frame parameters required to obtain satisfactory results. Additionally, a comparative analysis of air void structure parameters from 2D and 1D methods was conducted. Geometrical models of air voids distributed within cement paste using the Monte Carlo method based on air void structure data derived from real concrete were created. Analysis of these models demonstrated good agreement between the 2D and 1D results. It was concluded that satisfactory results require the analysis of either three measurement frames of 50 × 50 mm or four frames of 40 × 40 mm, with a resolution of at least 3 µm/px.