Final Report an Evaluation of New Inhibitors for Rebar Corrosion in Concrete

ii DISCLAIMER The contents of this report reflect the views of the authors, who are responsible for the facts and the accuracy of the data presented herein. The contents do not necessarily reflect the official views or policies of the Virginia Department of Transportation, the Commonwealth Transportation Board, or the Federal Highway Administration. This report does not constitute a standard, specification, or regulation. ρ Density A Cross-sectional area AMA Aminoethylethanolamine ATP 2-aminothiophenol or orthoaminothiophenol BGP Di-sodium β-glycerophosphate Cl-Chloride ion CN Calcium nitrite CPE Constant phase element DCI Calcium nitrite commercial mix from W.R. Grace DS Din -butyl sulfoxide EIS Electrochemical impedance spectroscopy L Length LN Lithium nitrate LP Linear polarization m Mass mpy Mils (one-thousandth of an inch) per year NA Sodium metasilicate NO 2 Nitrite ion ORR Oxygen reduction reaction PA Phosphonic acid (also known as aminotrimethylenephosphonic acid (AMP) and nitrilotrisphosphonic acid) R Resistance RCM Resistance change method SEM Scanning electron microscope SSD Saturated surface dry condition of aggregate TCRUs Temperature Corrected Resistance Ratio Units W air Weight of mortar or concrete in air W water Weight of mortar or concrete in water w/c Water to cement ratio XPS X-ray photoelectron spectroscopy iv v ABSTRACT The corrosion of reinforcing steel in concrete is estimated to affect more than 50 percent of the 575,000 bridges in the United States. One approach to mitigating this problem is to use corrosion-inhibitive compounds admixed into the concrete paste. This study sought to examine the corrosion-inhibition performance of a series of compounds admixed into high-quality concrete and to delineate the effects of these compounds on the concrete with regard to the corrosion process. A series of eight compounds were admixed into Type A4 concrete. The compounds tested were aminoethylethanolamine, aminothiophenol, di-sodium β-glycerophosphate, calcium nitrite, din -butyl sulfoxide, lithium nitrate, sodium metasilicate, and nitrilotrisphosphonic acid. Concrete blocks were cast, into which were placed 0.009-in-diameter 1040 steel wires. The corrosion rate was assessed via a resistance change measurement (RCM) of these wires over time using a temperature-corrected four-point resistance measurement. The time-to-open circuit for the wires was also monitored. RCM was compared to (1) electrochemical impedance spectroscopy results of tests conducted in a simulated pore solution, and (2) chloride permeability measurements of the concrete as per ASTM C 1202. The effect of the admixtures on the compressive strength and density of the concrete was also assessed. RCM and time-to-open circuit results showed that four test inhibitors …