Determination of the Air-Void System Parameters in Hardened Concrete--An Error Analysis


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Title: Determination of the Air-Void System Parameters in Hardened Concrete--An Error Analysis

Author(s): B. W. Langan and M. A. Ward

Publication: Journal Proceedings

Volume: 83

Issue: 6

Appears on pages(s): 943-952

Keywords: air-entrained concretes; air entrainment; concrete durability; errors; hardened concretes; measurement; standard deviation; tests.

Date: 11/1/1986

ASTM Standard Practice C 457, "The Microscopial Determination of Air-Void Content and Parameters of the Air-Void System in Hardened Concrete," is extensively used in the assessment of the potential durability of concrete, particularly in the assessment of concrete that has failed in service. Unfortunately, little information is available concerning the accuracy of the air-void parameters obtained using this test method. In the current standard, the expected maximum single operator standard deviation is given for air content only and is based solely on theoretical calculations. To obtain an estimate of the magnitude of the total error, normal error analysis is applied to the equations used to determine the air-void parameters by the modified point count method. It is shown that the expected errors in the average chord intercept, specific surface, and spacing factor can be estimated if the errors in estimating the air and paste contents and number of voids per unit length can be established. Two methods are presented to predict the maximum theoretical errors in specific surface and spacing factor. Repetitive testing of standard surfaces is used to compare theoretical and measured errors for within-laboratory and interlaboratory data. It is shown that significant differences can exist between the air-void parameters determined, particularly in the interlaboratory data.