Chloride Permeability and AC Impedance of High Performance Concrete

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Title: Chloride Permeability and AC Impedance of High Performance Concrete

Author(s): M. R. Hansen, M. L. Leming, P. Zia, and S. Ahmad

Publication: Special Publication

Volume: 140

Issue:

Appears on pages(s): 121-146

Keywords: AC impedance; chlorides; coulombs; durability; pavements; high performance concretes; mechanical properties; mix proportioning; highways; permeability; quality control; silica fume; strength; tests; Materials Research

Date: 9/1/1993

Abstract:
Three types of High Performance Concrete (HPC) for highway applications were investigated: Very Early Strength (VES), High Early Strength (HES) and Very High Strength (VHS). Two of the objectives of the research were to measure the chloride permeability of these concretes and explore an alternate method using AC impedance. Many of the concretes had coulomb values of 4000 and higher, placing them in the "high permeability" category as specified by AASHTO T 277 - Rapid Chloride Permeability Test (RCPT). Coulomb values were also found to decrease with concrete age and with increased silica fume content. Coulomb values were found not to vary significantly with dosage of calcium nitrite used as accelerator, up to 6 gal/yd 3 (29.7 l/m 3). The AC impedance test results (ohms) were found to correlate well with the RCPT results (coulombs) and were sufficiently accurate to place the concretes in the proper chloride permeability category. The advantages of the AC impedance test are that it is faster and less expensive than the RCPT and it avoids the potential heating problem sometimes encountered in the RCPT. AC impedance was found to increase with concrete age and with increased silica fume content and decrease with increased calcium nitrite dosage.