Title: Quantifying Fluid Absorption in Air-Entrained Concrete Using Neutron Radiography
Author(s): M. Khanzadeh Moradllo, C. Qiao, M. Keys, H. Hall, M. T. Ley, S. Reese, and W. J. Weiss
Publication: Materials Journal
Appears on pages(s): 213-226
Keywords: absorption; air entrainment; formation factor; freezing-and-thawing resistance; neutron radiography; performance specification
The absorption of fluid in concrete is often useful in the prediction of durability. Studies on the influence of entrained air voids (air content and quality) on fluid absorption in concrete are unfortunately very limited. This paper investigates fluid (water) absorption in air-entrained concrete mixtures with three water-cement ratios (w/c = 0.40, 0.45, and 0.50) and a range of air contents (2.5 to 9.0%) with and without high-range water reducer. Neutron radiography is used to measure the time-dependent depth of water penetration, water absorption, and the degree of saturation. In addition, water absorption is related to the apparent formation factor, which is determined from electrical resistivity measurements on concrete samples immersed in a simulated pore solution. Results show that air content has a minimal impact on the rate of water absorption of the matrix. However, the air content significantly alters the degree of saturation, with higher air contents having a lower degree of saturation. As the w/c decreases, the rate of water absorption is reduced due to the refined microstructure. For the given w/c, the addition of the high-range water reducer has a slight reduction in the rate of water absorption. Results indicate a linear relationship between sorptivity (initial and secondary) and the reciprocal of the square root of the apparent formation factor. This relationship can provide a powerful tool in quality control to obtain the apparent formation factor.