THE SPECIFICATION OF CONCRETE STRENGTH. PART II, THE DISTRIBUTION OF STRENGTH OF CONCRETE FOR STRUCTURES IN CURRENT PRACTICE
THE QUALITY OF CONCRETE WHICH RESULTS FROM SPECIFICATIONS IS CONSIDERED. THE DATA WERE DRAWN FROM ABOUT 400 JOBS WHERE CONCRETE WAS PRODUCED FOR HIGHWAY STRUCTURES AND ABOUT 230 JOBS WHERE THE CONCRETE WAS USED FOR GENERAL STRUCTURAL WORKS. THE LATTER SERIES OF JOBS WAS INCLUDED TO EXTEND THE RANGE OF WORK COVERED AND TO PROVIDE SOME INFORMATION ON HOW THE QUALITY OF CONCRETE IN HIGHWAY STRUCTUES COMPARES WITH THE GENERAL RUN OF STRUCTURAL WORKS. IT IS NOTEWORTHY THAT, ALTHOUGH THE DATA COVERED A WIDE RANGE OF QUALITIES OF WORK, VERY LITTLE EVIDENCE WAS FOUND OF REJECTION OF CONCRETE EVEN WHEN THE STRENGTHS OF TEST CUBES DID NOT COMPLY WITH SPECIFICATION. IT HAS BEEN ESTABLISHED THAT THE AVERAGE PROPORTION DEFECTIVE IS SURPRISINGLY LOW, AND THE QUALITY OF STRUCTURAL CONCRETE CORRESPONDINGLY HIGH. THE QUALITY APPEARS TO BE INDEPENDENT OF THE PRECISE FORM OF SPECIFICATION USED; STRICT SPECIFICATIONS DO NOT IN FACT GIVE RISE TO A MUCH BETTER QUALITY THAN THOSE SPECIFICATIONS WHERE THE CONSUMER'S RISK IS THEORETICALLY MUCH LARGER. IT MUST BE CONCLUEDED THAT FACTORS SUCH AS ENGINEERING AND COMMERCIAL JUDGEMENT HAVE TAKEN PRECEDENCE OVER THE SPECIFICATION CRITERIA. THE AVERAGE QUALITY OF CONCRETE FOR HIGHWAY STRUCTURES EXPRESSED IN TERMS OF THE PROPORTION OF CONCRETE DEFECTIVE TO THE SPECIFIED STRENGTH IS APPROXIMATELY ONE PER CENT AND 90 PER CENT OF THE CONCRETE IS LESS THAN 10 PER CENT DEFECTIVE TO THE SPECIFIED STRENGTH. THERE IS SOME EVIDENCE THAT THE QUALITY OF CONCRETE WHEN SPECIFIED TO HAVE A HIGH STRENGTH, SUCH AS FOR PRESTRESSED WORK, MAY BE RATHER WORSE THAN THE OVERALL AVERAGE QUALITY FOR STRUCTURAL CONCRETE. ATTENTION IS DRAWN TO THE APPRECIABLE PROPORTION OF THE OVERALL VARIABILITY WHICH DERIVES FROM DAY-TO-DAY VARIATIONS AND IT IS SUGGESTED THAT THIS MUST BE BETTER CONTROLLED AS A FIRST STAGE IN IMPROVING QUALITY. /RRL(A)/
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Supplemental Notes:
- Rrl Rept Lr 300, 22 PP, 11 FIG, 1 TAB, 10 REF
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Authors:
- Metcalf, J B
- Publication Date: 1970
Media Info
Subject/Index Terms
- TRT Terms: Concrete; Concrete structures; Proportioning; Specifications; Statistical quality control; Strength of materials; Variables
- Subject Areas: Highways; Materials;
Filing Info
- Accession Number: 00213118
- Record Type: Publication
- Source Agency: Road Research Laboratory /UK
- Files: TRIS
- Created Date: May 3 1971 12:00AM