Question

An intern performed the resistivity test according to AASHTO T358 on two sets of 4 × 8 in. cylinder specimens at 28-day of concrete age. One set of specimens (ASTM) were wet cured through the testing ages. Other sets of specimens (Field) were wet cured for seven day following specimen fabrication, then dry cured. The average resistivity results of two sets of specimens are 89.8 and 14.9 kΩ – cm. However, the intern forgot to document the curing conditions. What is the result of average resistivity for the ASTM and Field specimens? Justify your answer. What is the likely corrosion rate for both sets of specimens according to the recommendation of CEB-192?

Answer 1

Answer----Electrical Indication of concrete's ability to resist cloride ion penitration test (AASTHO , ASTM), more commonly reffered to as rapid cloride permiability test (RCPT)

RCRT has larger variability in test results , per ASTM the result may differ as much as 51%.

Relationship between the two methods RCPT ( ASTM) and field specimen is very good at 56 days.

Corellation usually exist between both 14 days and 28 days SR value and 56 days RCPT.

Since surface resistivity test results as stated above for 4X8 in cylinder are 89.8 and 14.9 respectively hence cloride ion penitration is classified as very low.hence majority specimen are clasisified under moderate or low permeability category.

Surface resistivity results are genreally 1.9 times bulk resistivity results.

Corrosion of reinforcement and subsequent reduction in strength is directly praportional to permeability, since permiability is low corrosion rate will also be low .