CALCIUM NITRITE AS A CORROSION INHIBITOR IN REINFORCED CONCRETE BRIDGE DECKS

Abstract

The use of calcium nitrite as a corrosion-inhibiting admixture in reinforced concrete has been studied on two bridges - the Kentucky 152 Bridge in Washington County and the Gose Road Bridge in Boyle County. Calcium nitrite was added to concrete used in the slabs, diaphragms and barriers of the KY 152 bridge and only in the slab of the Gose Road bridge. Construction of both structures was monitored in the fall of 1986. Placement of concrete on both bridges was satisfactory; however, problems were experienced in finishing the concrete. The finishing problems were related to: 1) concrete stickiness; 2) use of spinning-drum screed; 3) use of tyning for deck grooving; and 4) contractor inexperience with the concrete. The finishing problems included: 1) pulled or exposed aggregate; 2) pull cracks; 3) unclosed surface voids; and 4) irregular grooves. Compressive strength of the calcium-nitrite admixed concrete for both bridges exceeded 6,000 psi at 28 days. Freeze-thaw tests of specimens from the Gose Road bridge concrete (that incorporated a super water reducer) indicated no deterioration at 360 freeze-thaw cycles. Half-cell, corrosion-potential tests were conducted on both bridge decks in March 1987. Those tests revealed no active corrosion in either bridge. In July 1987, corrosion-potential and polarization-resistance tests were performed using stainless-steel reference electrodes buried in concrete across the deck of the Gose Road bridge. Those tests revealed that reinforcing steel in the bridge was in a passive state and that no active corrosion was occurring. Recommendations are included on remedying concrete-finishing problems. It is recommended that other experimental bridges be constructed using calcium nitrite.