CORRELATION BETWEEN CHEMICAL AND MORTAR BAR TESTS FOR POTENTIAL ALKALI REACTIVITY OF CONCRETE AGGREGATES

CERTAIN SILICEOUS CONSTITUTENTS OF AGGREGATES CAN REACT WITH CEMENT ALKALIES TO CAUSE ABNORMAL EXPANSION AND CRACKING IN CONCRETE. THE ASTM MORTAR BAR EXPANSION TEST IS GENERALLY CONSIDERED TO BE THE MOST RELIABLE METHOD AVAILABLE FOR DETERMINING THE POTENTIAL ALKALI REACTIVITY OF SUCH AGGREGATES. BECAUSE THIS TEST REQUIRES CONSIDERABLE TIME, A QUICK CHEMICAL TEST WAS ALSO ADOPTED BY THE ASTM IN ORDER TO OBTAIN A RAPID EVALUATION OF CONCRETE AGGREGATES. THIS INVESTIGATION WAS MADE TO DETERMINE THE DEGREE OF CORRELATION BETWEEN THE TWO METHODS OF TEST. FIFTY-TWO CONCRETE AGGREGATES WERE EVALUATED BY MEANS OF THE RAPID CHEMICAL TEST FOR POTENTIAL ALKALI-AGGREGATE REACTIVITY AND THE RESULTS GENERALLY SHOWED GOOD CORRELATION WITH THE DATA OBTAINED IN THE MORTAR BAR TESTS. HOWEVER, THE CHEMICAL TEST DOES NOT ALWAYS GIVE RELIABLE RESULTS FOR SOME AGGREGATES BECAUSE OF THE INTERFERENCE OF CERTAIN CARBONATES. AN EMPIRICAL DIVISION OF THE CHEMICAL TESTS RESULTS IS PROPOSED WHICH WOULD SERVE TO ISOLATE THOSE AGGREGATES WHICH MAY CONTAIN SUCH INTERFERENCES, AND THEREBY INDICATE THE NEED FOR FURTHER TESTS. SOME AGGREGATES SHOWED A HIGH DEGREE OF REACTIVITY IN THE CHEMICAL TEST BUT DID NOT PRODUCE EXCESSIVE MORTAR BAR EXPANSION. AN ADDITIONAL EMPIRICAL DIVISION OF THE CHEMICAL TEST RESULTS IS SUGGESTED WHICH WOULD SEPARATE CHEMICALLY REACTIVE AGGREGATES INTO TWO GROUPS. SUCH A SEPARATION WOULD ELIMINATE THE NEED OF SUPPLEMENTARY MORTAR BAR TESTS ON MANY REACTIVE AGGREGATES. CHEMICAL TEST RESULTS WHICH FALL INTO ONE SUCH GROUP ARE INDICATIVE OF VERY HIGHLY REACTIVE, BUT NOT NECESSARILY EXPANSION-PRODUCING AGGREGATES. SPECIAL MORTAR BAR TESTS ARE NECESSARY FOR SUCH MATERIALS. THE GENERAL CHEMICAL TEST CRITERIA ESTABLISHED BY THIS STUDY FOR SEPARATING REACTIVE FROM NONREACTIVE AGGREGATES AGGREE FAIRLY WELL WITH THOSE PROPOSED BY ASTM SPECIFICATIONS AND THE CORPS OF ENGINEERS. THE PRESENT ASTM CHEMICAL TEST METHOD PERMITS TWO TITRATION PROCEDURES FOR THE DETERMINATION OF ALKALINITY REDUCTION. NEITHER PROCEDURE SHOWED ANY DISTINCT ADVANTAGE OVER THE OTHER AS A MEANS FOR EVALUATING THE POTENTIAL REACTIVITY OF AGGREGATES. /AUTHOR/

Media Info

  • Monograph Title: Physical and chemical properties of cement and aggregate in concrete
  • Serial:

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Filing Info

  • Accession Number: 00213212
  • Record Type: Publication
  • Files: TRIS, TRB
  • Created Date: Aug 19 1994 12:00AM