Accelerated quantification of critical parameters for predicting the service life and life cycle costs of chloride-laden reinforced concrete structures

Abstract

The use of corrosion resistant steels (instead of conventional carbon steels) and/or high performance concrete can increase the overall service life and can reduce the life cycle cost (LCC) of reinforced concrete (RC) structures exposed to chloride environments. At present, no accelerated standardized test procedures are available to directly evaluate critical parameters affecting the service life of RC systems and current test methods can take years or decades to indirectly evaluate these critical parameters for high performance construction materials. This prevents the engineers, designers, and owners from using new high performance materials, especially, the corrosion resistant steel reinforcement. This thesis evaluates the Accelerated Chloride Threshold (ACT) test procedure developed to determine the critical chloride threshold value of uncoated steel reinforcement embedded in cementitious materials. Using the ACT test procedure, the critical chloride threshold values of the ASTM A706, ASTM A615, microcomposite, SS304, and SS316LN reinforcement types were determined to be 0.2 kg/m³ (0.3 lb/yd³), 0.5 kg/m³ (0.9 lb/yd³), 4.6 kg/m³ (7.7 lb/yd³), 5.0 kg/m³ (8.5 lb/yd³), and 10.8 kg/m³ (18.1 lb/yd³), respectively. Using these values, the time to corrosion initiation of chloride-laden RC systems can be determined. The Accelerated Cracking and Spalling Threshold (ACST) test procedure has been developed to determine the amount of steel corrosion required to cause cracking and spalling of concrete cover. From preliminary experimental data, the critical cracking and spalling threshold thickness for a 19 mm (0.75 inch) concrete cover with 0.45, 0.55, and 0.65 water-cement ratios has been determined to be 20.64, 16.85, and 37.46 mils, respectively. Preliminary results indicate that for a cover depth of 19 mm (0.75 inch) the critical cracking and spalling threshold value (mils) is equal to 10 [⁻²⁴̇+(¹²⁵̇xw/c)⁻¹¹⁶̇x(w/c)²]⁻¹ [⁻¹ and can be used to determine the time of corrosion propagation in chloride-laden RC systems. A parametric study with different steel reinforcement, water-cement ratios, and chloride exposure conditions indicated that the use of corrosion resistant steels will increase the overall service life and can reduce the LCC of RC structures exposed to severe chloride environments.