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AGGREGATES AND CEMENTS FOR READY-MIX CONCRETE

THE SPECIFIC GRAVITY OF COARSE AGGREGATES IN CONCRETE VARIES CONSIDERABLY, DEPENDING ON THE CHEMICAL COMPOSITION OF THE AGGREGATE, ITS CONSOLIDATION AND POROSITY. LIMESTONE IS CONSIDERED TO BE A GOOD QUALITY ROCK FOR THE PRODUCTION OF CONCRETE BECAUSE IT CAN BE FOUND WITH A SPECIFIC GRAVITY OF 2.5 OR MORE. WHEN VERY HIGH STRENGTH CONCRETE IS REQUIRED, A VERY FINE GRAINED GRANITE IS PERHAPS THE BEST AGGREGATE. COARSE GRAINED GRANITE MAKES A VERY HARSH CONCRETE. MOST IGNEOUS ROCKS ARE EXCELLENT AGGREGATE MATERIAL. THE CAVITIES OF BASALT MAY BE FILLED WITH SECONDARY MINERALS WHICH MAY REACT INJURIOUSLY WITH THE CONSTITUENTS OF CONCRETE, PARTICULARLY WITH THE CEMENT. BASALTS AND OTHER VOLCANIC ROCKS MAY PRESENT GREAT DIFFERENCES IN SPECIFIC GRAVITY AS WELL AS FUNDAMENTAL VARIATIONS IN THEIR POROSITY AND ABSOPRTION QUALITIES. ECONOMY AND AVAILABILITY OF MATERIAL WILL USUALLY GOVERN THE CHOICE OF THE COARSE AGGREGATE FOR ANY PARTICULAR STRUCTURE OF PROJECT. GRAVEL INVOLVES A RELATIVELY LOW COST OF PREPARATION, PLUS A REDUCTION OF CEMENT. IF THERE ARE NO GRAVEL SOURCES AVAILABLE, CRUSHED STONE CAN BE USED. CRUSHED GRAVEL INVOLVES AN ECONOMIC PROBLEM, SINCE IT REQUIRES SPECIAL EQUIPMENT FOR CRUSHING. SAND OR CONCRETE GRIT IS PERHAPS THE SECOND MOST IMPORTANT MATERIAL IN THE PRODUCTION OF GOOD CONCRETE. FINE AGGREGATE PERFORMS TWO MAJOR FUNCTIONS IN CONCRETE: (1) AS AN INEXPENSIVE FILLER, AND (2) AS A LUBRICANT TO UNIFORMLY DISTRIBUTE THE LARGER MATERIAL THROUGHOUT THE MASS OF CONCRETE. FINE AGGREGATES MAY BE DIVIDED INTO TWO MAJOR CATEGORIES (1) THOSE CONSISTING PRINCIPALLY OF NATURAL SANDS OR ROCK FRAGMENTS, RESULTING FROM NATURAL PROCESSES OF WEATHERING BY DISINTEGRATION OR BY GLACIAL ACTION, (2) THOSE CONSISTING OF FINES PREPARED BY THE CRUSHING OF NATURAL ROCKS, AND THE SUBSEQUENT SCREENING OF THE CRUSHED MATERIAL INTO DESIRED SIZES. NATURAL SANDS ARE USED TO A GREATER EXTENT THAN ANY OTHER KIND OF FINE AGGREGATE. PARTICLE SHAPE AND SURFACE TEXTURE OF SAND ARE MORE IMPORTANT THAN THOSE OF COARSE AGGREGATE. CONCRETE COMPRESSIVE STRENGTH, HOWEVER, IS ONLY AFFECTED BY PARTICLE SHAPE TO THE EXTENT THAT PARTICLE SHAPE AFFECTS THE REQUIREMENTS OF MIXING WATER. PROPER GRADATION OF SANDS IS A MATTER OF PRIMARY IMPORTANCE. VARIOUS TYPES OF SANDS ARE DISCUSSED. THE UNIFORMITY OF CONCRETE STRENGTH IS AFFECTED BY CEMENT. THE VARIOUS TYPES OF PORTLAND CEMENTS ARE DESCRIBED AND DISCUSSED. GOOD MIXING IS ONE OF THE MOST IMPORTANT FACTORS IN PRODUCING UNIFORM CONCRETE.

  • Supplemental Notes:
    • Vol 20, No 10, PP 31-33, 2 PHOT
  • Authors:
    • Carbonell, C A
  • Publication Date: 1967-10

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  • Accession Number: 00212545
  • Record Type: Publication
  • Files: TRIS
  • Created Date: Mar 12 1994 12:00AM