Corrosion-Resistant Steel Reinforcing Bars Initial Test

Abstract

The initial portion of the first phase of a five phase research effort to evaluate a corrosionresistant steel for reinforcing bars is descnoed. Rapid corrosion potential and time-to-corrosion (macrocell) tests are used. The test specimen consists of a No. 5 reinforcing bar embedded in a 30 mm diameter, 102 nnn long cylinder of mortar. The mortar is made using portland cement, graded Ottawa sand, and deionized water. Four different steel types are evaluated: hot-rolled regular steel, Thermex treated (quenched and tempered) regular steel, hot-rolled corrosion resistant steel, and Thermex treated corrosion resistant steeL Corrosion potential tests are perlbrmed to determine the tendency of a steel to corrode. The results for these tests are fuirly consistent, with little scatter. There is no significant difference in potentials for the four steels. The use of different test solutions did not influence the potential of the four steels. The macrocell tests are perlbrmed to determine the time-to-corrosion and the corrosion rates. The results for some of these tests are not consistent and show considerable scatter. The macrocell test is sensitive to the quality in the specimen fabrication. Because the initial tests in Phase I did not perform as intended, it is difficult to determine for certain which steel has the best corrosion resistance based on the resUlts reported here. However, the hot rolled regular steel specimens consistently exluoit the highest corrosion rate. The test solutions used at the anode and cathode in the macrocell tests appear to influence the corrosion rate and the difference in rates between the four steels. When the difference in pH of the anode and cathode solutions is decreased, the corrosion rates are reduced and the difference between the rates for the four steels is more pronounced. Based on the results of the Phase I initial tests, some modifications to the specimen fabrication procedure are reconnnended. The epoxy band should be applied in two coats. The reinforcing bar lengths should be heated after cleaning and after applying each coat in order to improve the bond between the reinforcing bar and the first epoxy coat as well as between the two coats of epoxy. Special care should be exercised when applying the epoxy band. Addition work in Phase I includes an evaluation of the effects of changing the ratio of the number of cathode to anode specimens from 3:3 to 2:1. Special care should also be exercised in the oversight of the corrosion potential and macrocell tests.