Title: Evaluation of Chloride Limits for Reinforced Concrete Phase A

Author(s): Karthik Obla, Colin Lobo, Rongjin Hong, National Ready Mixed Concrete Association, Neal Berke, Tourney Consulting Group

Publication: CRC

Volume:

Issue:

Appears on pages(s):

Keywords: corrosion, steel, steel reinforcement, stain, crack, chloride, ACI 318, prestressed

DOI:

Date: 7/1/2017

Abstract:
The corrosion of steel reinforcement in concrete is a major cause of deterioration to concrete structures. Corrosion of steel results in the formation of rust that occupies a larger volume than the original steel and causes staining, cracking, and spalling of the cover concrete. The highly alkaline environment in concrete protects steel from corrosion. However, when chlorides in solution reach the reinforcement, corrosion initiates and propagates damage. Chloride ions present in deicing chemicals and seawater are the primary source of external chlorides that can migrate to the reinforcing steel in concrete to cause corrosion of steel in concrete. Depending on the cover and quality of concrete, it can take a period of time before external chlorides reach a certain level of concentration (threshold) adequate to initiate corrosion at the level of the reinforcement. In contrast, internal chlorides are available to initiate corrosion when concrete is cast. Internal chlorides in concrete mixtures originate from concrete-making materials when concrete is produced. The scope of this study is on the internal chlorides in concrete. The ACI 318 Building Code Requirements for Structural Concrete establishes limits on water-soluble chloride ions in concrete mixtures used for reinforced and prestressed concrete based on assigned exposure class of structural members under the durability provisions. The chloride limits in ACI 318 are provided in Table 1.