An accelerated chloride threshold test for uncoated steel in highly resistive cementitious systems (hr-ACT test). (25th October 2021)

• Record Type: Journal Article
• Authors: Rengaraju, Sripriya; Pillai, Radhakrishna G.
• Is Part Of: Construction & building materials. Volume 305(2021)
• Publication Date: 2021-10-25
• Subjects: Chloride threshold -- Quenched and Self-tempered steel -- Highly resistive cementitious binder -- Limestone calcined clay cement; Building materials -- Periodicals; 624.18
• DOI: 10.1016/j.conbuildmat.2021.124797
• Languages: English
• ISSNs: 0950-0618

Abstract

Highlights: A quantitative limit for highly resistive concrete system electrochemical studies. A novel test method using EIS technique to detect onset of corrosion & determine Clth . Advantages of EIS over LPR technique in corrosion initiation studies of S-B systems. Evidence of synergistic effects of Clth and Da on service life of reinforced concrete. Abstract: 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 ( Clth ). This paper presents development of a test method (hr-ACT) for determining the Clth 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 (Rp ) 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 Clth . The time required to complete hr–ACT test for an S–B system is about 3–4 months. The Clth was in the order OPC > PC–FA > LC3. Also, the synergistic effects of Cl th and other parameters on service life are discussed.