THE CHLORIDE ION CONTENT OF CONCRETE AGGREGATES FROM SOUTHERN ONTARIO

The corrosion of reinforcing steel in concrete is a major cause of the deterioration of concrete bridge decks in Ontario. The concentration of chloride ions in concrete is one of the controlling factors of corrosion. Corrosion will not occur if the chloride content is below the threshold value of about 0.04 percent chloride ion by weight of concrete. The Amabel and Lockport dolomites which form the cap rocks of the Niagara Escarpment contain unusually large amounts of water-soluble chloride ions (0.041 and 0.026 percent by weight chloride ion respectively). These rocks are a major source of the crushed concrete aggregate used in Southern Ontario. The chloride ion content of these rocks exceeds specifications imposed in Europe for the chloride ion content of aggregates for use in reinforced and prestressed concrete. An investigation was conducted to find the source of the chloride ions contained in the rocks and to ascertain if the quantity of chloride ion found in the rocks was capable of causing the corrosion of reinforcing steel in concrete. It was found that the chloride ions had been introduced into the pores of the Amabel and Lockport dolomites by leaching of the overlying Salina Formation which contains beds of halite (NaC1). In order for chlorides in aggregate to cause corrosion of reinforcing steel there must be movement of chloride ions out of the aggregate into the cement paste and pore solutions in contact with the embedded reinforcing steel. Because of the extremely large pore size of the dolomites, resulting in a low degree of saturation even at high humidities, the transport of significant quantities of chloride ions into the pore solutions is difficult. This being the case, it is considered improbable that chloride ions from the Amabel and Lockport dolomites contribute significantly to the corrosion of reinforcing steel embedded in concrete. (Author)

• Corporate Authors:

  Ontario Ministry of Transportation & Communic, Can

  1201 Wilson Avenue
  Downsview, Ontario M3M 1J8,   Canada 
• Authors:
  • Rogers, C
  • Woda, G
• Publication Date: 1977-12

Media Info

• Features: Appendices; Figures; References; Tables;

Subject/Index Terms

• TRT Terms: Cement paste; Chloride content; Concrete aggregates; Corrosion; Crushed aggregates; Dolomite; Ions; Pore size distribution; Prestressed concrete; Reinforced concrete; Reinforcing steel
• Subject Areas: Geotechnology; Highways; I36: Aggregates;

Filing Info

• Accession Number: 00335493
• Record Type: Publication
• Report/Paper Numbers: Rpt. EM-17
• Files: TRIS
• Created Date: Sep 16 1981 12:00AM