Analysis of air-void system in hardened concrete from a three-dimensional perspective

Air-void analysis;three-dimensional;freeze-thaw;ASTM C457;American Society for Testing and Materials (ASTM)

Song, Yu ; Lange ; David A.

关键词: Air-void analysis;    three-dimensional;    freeze-thaw;    ASTM C457;    American Society for Testing and Materials (ASTM);   

Others  :  https://www.ideals.illinois.edu/bitstream/handle/2142/49671/Yu_Song.pdf?sequence=1&isAllowed=y

美国|英语

来源: The Illinois Digital Environment for Access to Learning and Scholarship

【 摘 要 】

The frost-resistance of concrete can be greatly enhanced by entrainment of small air bubbles in the cement paste.When the volume and distribution of the entrained air is properly controlled, the microstructure is protected from pressure exerted by freezing water. ASTM C457 “Standard Test Method for Microscopical Determination of Parameters of the Air-Void System in Hardened Concrete” is widely used for measuring the air void system. This manually conducted measurement is tedious and time-consuming, so automated methods have been explored.This study seeks to advance the technology for automating the measurement of air voids by using a flatbed scanner for image acquisition, applying new methods for segmenting the image, and using new ideas for the analysis of the image data. The cement paste is protected when an air bubble is close enough in proximity to relieve the stress created by freezing water. An ASTM C457 parameter – spacing factor – quantifies the proximity of paste to air bubbles in the microstructure.This study shows that parameters derived from one-dimensional measurements, such as the ASTM C457 method, or two-dimensional measurements, such as from images from flatbed scanner technology, can understate the true volume of paste protected by air voids during freeze-thaw cycles. A model developed in this study provides a statistical basis for inferring the true three-dimensional volume of protected paste from two-dimensional images. Based on statistics gathered from the two-dimensional scanned image, a method is developed to infer a true three-dimensional air-void distribution in hardened paste. Stereological principles and statistical concepts are introduced to establish a “conversion function” whereby the two-dimensional parameters can be used as input for a three-dimensional model. The quantity and sizes of air voids are characterized by the function, assuming the spatial distribution is isotropic uniform random (IUR). A function is generated based on this relationship, and it is expected that paste located beyond a certain range is poorly protected and vulnerable during freeze-thaw cycles. Compared with 1-D and 2-D approaches, the new method offers a more realistic sense of the degree of paste protected by entrained air which is needed for research of the mechanics of freeze-thaw damage.