Effect of Moisture Content on the Air Permeability of Concrete


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Title: Effect of Moisture Content on the Air Permeability of Concrete

Author(s): T. Hassan and P. Zia

Publication: Special Publication

Volume: 228


Appears on pages(s): 1417-1434

Keywords: air permeability; concrete; durability; moisture content; nondestructive testing

Date: 6/1/2005

Low permeability is an important characteristic of durable concrete. Concrete of low permeability minimizes the entry of moisture and aggressive chemicals. It provides better corrosion protection of steel reinforcement and limits freezing/thawing damage of concrete. A variety of test methods using gas or liquid have been developed to measure the permeability of concrete, but most of them are costly and suitable for use only in the laboratory. A simple device and test method developed by Zia and Guth at North Carolina State University measures air permeability of concrete. The Zia-Guth device, consisting of two concentric cylindrical chambers, is adhered to the concrete surface by vacuum and measures the rate of pressure increase in the inner chamber as air flows from the outer chamber through the concrete and into the inner chamber. The device is economical, and its compactness and quick response time make it suitable for nondestructive testing of in-place concrete in the field. Permeability of concrete depends not only on the microstructure of the concrete but also on the moisture content in the concrete. This paper presents the results of an experimental study undertaken to evaluate the effect of moisture content on the air permeability of concrete using the Zia-Guth testing device. Three different types of concrete varying in w/cm ratio and admixture content were tested. The influence of moisture content of the concrete on airflow was examined by testing slab specimens (400 x 400 x 75 mm) for each type of concrete under different moisture contents and at different concrete ages. Test results showed that the measured permeability index could vary by 10 to 300 percent depending on the moisture content and the type of concrete. Based on test results, a general methodology is proposed to account for the effect of the moisture content of concrete on the air permeability of different types of concrete.