A STUDY OF CHERT AGGREGATE REACTIVITY BASED ON OBSERVATIONS OF CHERT MORPHOLOGIES USING ELECTRON OPTICAL TECHNIQUES

TWENTY-TWO VARIETIES OF CHERT FROM TEN DIFFERENT LOCALITIES IN OHIO REPRESENTING FOUR DEPOSITIONAL REALMS WERE INVESTIGATED TO RELATE SOME OF THE HARMFUL PROPERTIES OF THE CONCRETE AGGREGATES TO THE ELECTRON OPTICAL SURFACE MORPHOLOGIES OF CHERT. POROUS, SPONGY, INTERMEDIATE, POLYGONAL AND CRYSTALLITE MORPHOLOGIES OF CHERT WERE OBSERVED BY ELECTRON OPTICAL TECHNIQUES AND WERE COMPARED WITH ROUTINE ENGINEERING LABORATORY TESTS. POROUS, SPONGY AND CRYSTALLITIC CHERTS EXHIBITED (1) THE LEAST FREEZE-THAW DURABILITY, (2) THE HIGHEST SOLUBILITY, AND (3) THE GREATEST EXPANSION DUE TO ALKALI-CHEMICAL REACTIVITY, WHEREAS THE INTERMEDIATE AND POLYGONAL CHERT MORPHOLOGIES SHOWED THE LOWEST TOTAL POROSITY AND SMALLER PORE DENSITIES AND SUBSEQUENTLY THEY EXHIBITED BETTER CRYOTHERMAL DURABILITY AND LOWER CHEMICAL REACTIVITY. POLYGONAL CHERTS ARE MOST SUSCEPTIBLE TO FAILURE BY THERMAL SHOCK. THESE STRESSES ARE RELATED TO MICROFRACTURES THAT INORDINABLY EXPAND DUE TO CHANGES IN TEMPERATURE. LABORATORY TESTS DEMONSTRATE THAT CHERTS RICH IN CHALCEDONIC SILICA (SPONGY MORPHOLOGY) EXHIBIT ALKALI-AGGREGATE REACTIVITY. MORTAR-BAR TESTS MADE WITH CRUSHED CHERT AND HIGH-ALKALI CEMENT SHOWED HARMFUL EXPANSIONS DUE TO REACTIVITY WHENEVER THE PROPORTION OF CHERT, REGARDLESS OF SURFACE MORPHOLOGY, EXCEEDED 10 PERCENT. COMPARISON OF GEOLOGICAL OCCURRENCE, PETROGRAPHY, GEOCHEMISTRY, ELECTRON MICROSCOPY, X-RAY DIFFRACTION, DIFFERENTIAL THERMAL ANALYSES AND THE ORIGIN OF THE CHERTS STUDIED REVEAL MANY DIFFERENCES. THE MOST IMPORTANT DIFFERENCES ARE THE DEGREE OF STRUCTURAL DISORDER, AND CRYSTALLINITY, SURFACE MORPHOLOGY, SPECIFIC GRAVITY, PORE- SIZE DISTRIBUTION AND TOTAL POROSITY, GRAIN PACKING DENSITY, FIBROUS SILICA CONTENT, AND DEGREE OF WEATHERING AND MICROFRACTURING. IT IS CONCLUDED THAT THE CORRELATION OF HIGHWAY LABORATORY TESTS WITH THE TECHNIQUES OF ELECTRON MICROSCOPY AND X-RAY DIFFRACTOMETRY SHOWS GREAT PROMISE IN PREDICTING THE SERVICE RECORDS OF CHERTY AGGREGATES. /AUTHOR/

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Filing Info

  • Accession Number: 00237743
  • Record Type: Publication
  • Files: TRIS
  • Created Date: Jul 7 1994 12:00AM