An accelerated chloride threshold test for uncoated steel in highly resistive cementitious systems (hr-ACT test)

Currently, many supplementary cementitious materials are being used along with cement to reduce the CO₂ emissions. These cementitious systems exhibit very high resistivity due to pozzolanic reactions and the traditional test methods are inadequate to assess their durability performance related to corrosion, especially chloride threshold (Cl_th). This paper presents development of a test method (hr-ACT) for determining the Cl_th of such highly resistive systems with guidelines for identifying the same. The test specimen consisted of a mortar cylinder (lollipop) (cement:sand = 1:2.75) with steel embedded at the centre. Three binders, namely, OPC (w/b = 0.5), PC-FA (70% OPC + 30% Class F Fly ash) (w/b = 0.5) and Limestone Calcined Clay Cement (LC3 − 50% OPC clinker, 31% calcined clay, 15% limestone and 4% gypsum) (w/b = 0.4), and Quenched and Self-tempered (QST) steel were used in this study. The specimens were subjected to chloride in a cyclic wet-dry regime (2 day wet and 5 day dry) and the electrochemical impedance spectroscopy (EIS) test was conducted at the end of each wet period. Statistical analysis was done on the repeated polarization measurements (R_p) to detect corrosion initiation. Once corrosion initiation was detected, the total chloride content (acid soluble chlorides) in the mortar at the Steel–Cementitious binder (S-B) interface was determined using SHRP 330 and reported as Cl_th. The time required to complete hr–ACT test for an S–B system is about 3–4 months. The Cl_th was in the order OPC > PC–FA > LC3. Also, the synergistic effects of Cl_th and other parameters on service life are discussed.