THE CONCEPT OF HARDNESS AS APPLIED TO MINERAL AGGREGATES

AGGREGATE HARDNESS, AS JUDGED BY THE SCRATCH HARDNESS TEST , IS A QUALITY REQUIREMENT FOUND IN MOST CONCRETE AGGREGATE SPECIFICATIONS. SOFTNESS OR SCRATCHABILITY, IS VIEWED AS A CHARACTERISTIC DELETERIOUS TO THE BEHAVIOR OF PORTLAND CEMENT CONCRETE. THE HISTORY, INTENT, AND PHILOSOPHY BEHIND THE SOFT PARTICLE REQUIREMENT ARE REVIEWED IN DETAIL AND DATA ARE PRESENTED WHICH DEMONSTRATE THE INVALIDITY OF THE CURRENT INTERPRETATION OF AGGREGATE SOFTNESS AND THE PRESENT SCRATCH TEST. THE AUTHORS WERE UNABLE TO LOCATE A SINGLE REFERENCE IN SUPPORT OF THE CURRENT INTERPRETATION OF EITHER THE SOFT PARTICLE REQUIREMENT OR THE SCRATCH HARDNESS TEST. A SERIES OF TESTS PERFORMED ON AN AGGREGATE RECENTLY REJECTED FOR NON-COMPLIANCE WITH THE PROVISIONS OF THE SCRATCH TEST DEMONSTRATE QUITE DRAMATICALLY THE FALLACY OF CURRENT INTERPRETATIONS. SOFTNESS, PER SE, IN THIS INSTANCE DID NOT PROVE CRITICAL TO THE BEHAVIOR OF THE CONCRETES UNDER TEST CONDITIONS. THE INADEQUACY AND POOR REPRODUCIBILITY OF THE SCRATCH TEST IN THE 3 TO 4 MOHS HARDNESS RANGE IS CLEARLY DEMONSTRATED AND THE QUESTION OF APPLICABILITY TO AGGREGATES IN GENERAL IS AMPLY SUPPORTED. IT IS CONCLUDED THAT THE SCRATCH HARDNESS TEST AND AGGREGATE SOFTNESS WHEN ASSOCIATED WITH A TRULY DETRIMENTAL QUALITY CHARACTERISTIC MAY HAVE MERIT AS A QUICK FIELD ESTIMATE OR UNDER LOCAL CONDITIONS. THE UNIVERSAL APPLICATION OF THE TEST OR THE SOFT PARTICLE REQUIREMENT, HOWEVER, IS CLEARLY IN CONFLICT WITH THE BASIC PHILOSPHY OF MATERIALS EVALUATION . /AUTHOR/

• Record URL:
  http://onlinepubs.trb.org/Onlinepubs/hrr/1967/196/196-002.pdf
• Supplemental Notes:
  • Paper sponsored by Committee on Mineral Aggregates and presented at the 46th Annual Meeting. Distribution, posting, or copying of this PDF is strictly prohibited without written permission of the Transportation Research Board of the National Academy of Sciences. Unless otherwise indicated, all materials in this PDF are copyrighted by the National Academy of Sciences. Copyright © National Academy of Sciences. All rights reserved
• Authors:
  • Gray, J E
  • Renninger, F A
• Publication Date: 1967

Media Info

• Media Type: Print
• Features: Figures; References; Tables;
• Pagination: pp 15-24
• Monograph Title: Aggregates and concrete durability
• Serial:
  • Highway Research Record
  • Issue Number: 196
  • Publisher: Highway Research Board

Subject/Index Terms

• TRT Terms: Aggregate gradation; Concrete aggregates; Hardness; Hardness tests; Materials; Mineral aggregates; Portland cement concrete; Soil particles; Specifications
• Uncontrolled Terms: Aggregate particles; Requirement; Scratches
• Old TRIS Terms: Materials specifications
• Subject Areas: Geotechnology; Highways; Materials;

Filing Info

• Accession Number: 00210617
• Record Type: Publication
• Files: TRIS, TRB
• Created Date: Feb 2 1994 12:00AM