00215219

Monograph

http://onlinepubs.trb.org...ubs/nchrp/nchrp_rpt_69.pdf

FOUR INDIVIDUAL STUDIES CONCERNED WITH THE GRADATION OF AGGREGATES USED IN HIGHWAY CONSTRUCTION WERE CONDUCTED ON: (1) EFFECT OF VARIATIONS IN GRADATION OF COARSE AGGREGATE ON CHARACTERISTICS OF PORTLAND CEMENT CONCRETE. (2) VARIATION IN GRADATION OF AGGREGATES IN BITUMINOUS HOT-MIX PLANTS, (3) EFFECT OF INCREMENT SIZE ON SAMPLING ACCURACY, AND (4) MATHEMATICAL STUDY OF THE PATTERN OF VARIATIONS IN GRADATION OF AGGREGATES. A STATISTICALLY DESIGNED EXPERIMENT WAS USED TO DETERMINE THE EFFECT OF GRADATION VARIATIONS ON THE WORKABILITY AND COMPRESSIVE STRENGTH OF THE RESULTANT CONCRETE. INVESTIGATION WAS MADE OF VARIATIONS IN GRADATION OF BOTH FINE AND COARSE AGGREGATES AND ASPHALT CONTENTS AT SEVERAL POINTS IN THE PRODUCTION PROCESS OF BITUMINOUS HOT- MIX PLANTS. AN EXPERIMENT WAS CONDUCTED TO ESTABLISH THE PRACTICAL RELATIONSHIP BETWEEN MAXIMUM PARTICLE SIZE AND MINIMUM INCREMENT SIZE FOR DETERMINING THE GRADATION OF A LOT OF AGGREGATE. SEVERAL LOTS OF KNOWN GRADATION WERE PREPARED AND SAMPLED WITH SAMPLING SCOOPS OF PREDETERMINED CAPACITY. IT APPEARED THAT VARIATIONS IN THE GRADATION OF AGGREGATES FOLLOWED AN INHERENT PATTERN. DATA WERE ANALYZED TO DETERMINE THE POSSIBILITIES FOR SELECTING A SINGLE SIEVE FOR USE AS A QUICK CHECK ON COMPLIANCE WITH GRADATION SPECIFICATIONS. THE CONCRETE STUDY INDICATES THAT SAVINGS IN MANPOWER AND TESTING TIME CAN BE EFFECTED BY REDUCING THE SAMPLING FREQUENCY OF COARSE AGGREGATES FOR CONCRETE. THE MOST SIGNIFICANT FINDING WAS THAT COMPRESSIVE STRENGTH REMAINED SUBSTANTIALLY CONSTANT, REGARDLESS OF LARGE VARIATIONS IN THE GRADATION OF THE COARSE AGGREGATE, PROVIDED THE SLUMP WAS MAINTAINED AT A UNIFORM LEVEL. RESCREENING OR RESIZING COARSE AGGREGATES IS CONTRAINDICATED, AND IT IS RECOMMENDED THAT RESTRICTIVE GRADATION SPECIFICATIONS BE BROADENED TO ACCOMMODATE GRADATION VARIATIONS ACTUALLY FOUND TO EXIST. THE HOT-MIX BITUMINOUS PAVING PLANT STUDY FOUND THAT INDICATED VARIATIONS IN THE GRADATION OF BINNED AGGREGATES WERE LARGELY DUE TO WITHIN-BATCH VARIATION. IT IS RECOMMENDED THAT COMPLIANCE WITH JOB-MIX FORMULA GRADATION REQUIREMENTS BE BASED ON QUALITY HISTORY CHARTS RATHER THAN ON THE RESULTS OF INDIVIDUAL TESTS. THE USE OF USUAL SAMPLING TOOLS DOES NOT SEEM TO SERIOUSLY BIAS THE RESULTS. THE MATHEMATICAL STUDY CONFIRMED THAT THERE IS A TYPICAL PATTERN TO VARIATIONS OF AGGREGATE GRADATION. GRADATION SPECIFICATION SHOULD HAVE THE GREATEST TOLERANCE ON THOSE SIEVES THAT PASS 50 TO 70% OF THE AGGREGATE. THE REQUIRED SIZE OF TEST PORTIONS DEPENDS ON BOTH THE MAXIMUM PARTICLE SIZE AND THE GRADATION OF THE AGGREGATE.

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. 58 PP, 39 FIG, 43 TAB, 17 REF, 5 APP

1969

NCHRP Report

Digital/other

Aggregate gradation; Asphalt content; Asphalt plants; Coarse aggregates; Compressive strength; Construction management; Evaluation; Fine aggregates; Mixing plants; Portland cement concrete; Road construction; Sieves; Specifications; Workability

Particle size distribution

Construction; Geotechnology; Highways

TRIS, ATRI

Jan 12 1970 12:00AM