Carbonation and electrochemical chloride extraction from concrete

✍ Scribed by N.M. Ihekwaba; B.B. Hope; C.M. Hansson

• Publisher: Elsevier Science
• Year: 1996
• Tongue: English
• Weight: 861 KB
• Volume: 26
• Category: Article
• ISSN: 0008-8846
• DOI: 10.1016/0008-8846(96)00076-2

✦ Synopsis

Chloride ingress into steel reinforced concrete (r.c.), and the subsequent application of electrochemical chloride extraction (ECE) are shown to be considerably retarded by the presence of a carbonation front. Four concrete blocks each reinforced with two layers of steel mats in two different configurations were electrochemically treated. One block of each type was initially carbonated to a depth of about 30 mm, and subsequently ponded with saturated chloride solution (as NaCl) for 18 months. Electrochemical treatment using an applied current density of 1 A/m2 of concrete surface was applied after sampling the concrete's chloride ion profiles. Carbonated concrete specimens operated at about twice as much polarizing voltage at the same applied current density as the non-carbonated concrete specimens. Higher chloride extraction was obtained in non-carbonated concrete than in carbonated concrete blocks irrespective of the configuration of the reinforcement system. Accumulations of alkali ions were greater in the non-carbonated concrete specimens in addition to higher initial chloride ion concentrations, and this was significantly greater in the specimens reinforced with different rebar mats at the top and lower sections. The changes in alkali ion accumulations followed a similar trend as chloride ion profiles. Hence, any softening effect due to these alkalies on the cement silicate hydrates is expected to be more pronounced in the non-carbonated than carbonated concrete. It is predicted that chloride contaminated concrete which has its cover considerably carbonated will likely show an inefficient ECE performance.