Characteristics of Entrained Air Voids in Hardened Concrete with the Method of Digital Image Analysis Coupled with Schwartz-Saltykov Conversion.

Teemu Ojala,Fahim Al-Neshawy,Jouni Punkki,Yanjuan Chen

doi:10.3390/ma14092439

Abstract

This paper presents the characteristics of air void systems in hardened concrete with the method of digital image analysis (DIA) coupled with Schwartz-Saltykov (SS) conversion. The results indicate that the DIA method coupled with SS conversion estimates the air content with more accuracy than it would without SS conversion; the correlation between air content obtained from the DIA method, and that from the thin section (TS) method is as good as the correlation observed between the pressure saturation (PS) method and the TS method. It was also found that the DIA method shows a better correlation with the TS method when the spacing factor without SS conversion is considered, while both methods show poor correlations when the corresponding specific surface is considered. In addition, it indicates that the peak of three-dimensional size distribution (3-DSD) of air voids after SS conversion falls in smaller voids, and 3-DSD of air voids shifts to a narrow size range, in comparison with the 2-DSD without SS conversion; the shape of the 3-DSD air voids remains constant irrespective of the class widths. Increasing the number of classes can minimise the standard deviation in the estimation, however, it also results in a leap in voids volume density, which will influence the estimation of air content.

Highlights

Since 1930, air-entrained concrete has been introduced to improve the resistance to freeze-thaw, and in 1954, various parameters were proposed by Powers to characterise the air void system in concrete [1]
This study demonstrated that image analysis provided a viable alternative to traditional lineal traverse and modified point count methods for characterisation of air void systems in hardened concrete; the lineal analysis consistently provided a higher value of total specific surface than areal analysis, despite that both methods provided a similar estimate of total air content
Conversion d is a non-parametric approach to reconstruct a sphere from a circle, and it does not assume an analytical function of size distribution

Summary

Introduction

Since 1930, air-entrained concrete has been introduced to improve the resistance to freeze-thaw, and in 1954, various parameters were proposed by Powers to characterise the air void system in concrete [1]. Many studies have appeared to describe the methods and calculate the air void parameters for the purpose of determining concrete resistance to freeze–thaw [2,3,4,5,6,7,8,9]. The most utilised methods for air voids analysis in concrete are the Chayes point method and the Rosiwal linear traverse method, which have been standardised by ASTM C457 [13], as well as EN 480-11. These techniques involve optical microscopic (OM) techniques and stereology science

Objectives

Methods

Results

Conclusion