a Petrographic Examination . Petrographic examination 

 provides a recommended practice for the petrographic examination of aggre- 

 gates. Recommendations are available which show the amounts of reactive 

 minerals that can be tolerated. The reactive rocks and minerals that have 

 been more frequently encountered since 1960 appear to have larger potassium 

 proportions and are harder to recognize in petrographic examination. 

 Highly deformed quartz with an angle of undulatory extinction of 35 

 to 50 or more and with deformation lamellae appear characteristic of the 

 reactive quartz-bearing rocks. Relatively coarse-grained micas have also 

 been regarded as reactive constituents; fine-grained micas are reactive in 

 argillites (Dolar-Mantuani, 1969). 



b Mortar Bar Test for Potential Reactivity . This 

 test is the method most generally relied on to indicate potential alkali 

 reactivity. Acceptance criteria are given by ASTM Standard C33 for evaluat- 

 ing these test results. The procedure is useful not only for the evaluation 

 of aggregates, but also for the evaluation of specific aggregate- cement 

 combinations. However, criteria have not been developed for the metamor- 

 phic siliceous and silicate rocks. 



£ Chemical Test for Potential Reactivity . This test 

 is the method used primarily for a quick evaluation of natural aggregates. 

 The results are obtainable in a few days as compared with 3 to 6 months or 

 more with the mortar bar test. Acceptance criteria for this test are given 

 in ASTM Standard C33. Care must be exercised in interpreting the results 

 of this test. This test method has given questionable results when evaluat- 

 ing lightweight aggregates; therefore, it is not recommended for this 

 purpose (Ledbetter, 1973) . 



2^ General Criteria for Judging Reactivity . When avail- 

 able, the field performance record of a particular aggregate, if it has been 

 used with cement of high alkali content, is the best means for judging its 

 reactivity. If such records are not available, the most reliable criteria 

 are petrographic examination with corroborating evidence from the mortar bar 

 test (U.S. Army, Corps of Engineers, 1971c), sometimes supplemented by tests 

 on concrete although these have not been standardized. The chemical test 

 results should also be used in conjunction with results of the petrographic 

 examination and mortar bar test. It is preferable not to rely on the 

 results of only one kind of test in any evaluation (U.S. Army, Corps of 

 Engineers, 1971c). 



3 Recommended Procedures with Alkali-Reactive Aggregates . 

 If aggregates are shown by service records or laboratory examination to be 

 potentially reactive, they should not be used when the concrete is to be 

 exposed to seawater or alkali environments if nonreactive aggregates are 

 available (Highway Research Board, 1958) . When reactive aggregates must be 

 used, this should be done only after thorough testing, and preferably after 

 service records have established that, with appropriate limits on the alkali 

 content of the cement, or with the use of appropriate amounts of an effective 

 pozzolan, or both, satisfactory service can be anticipated. In cases where 

 seawater or alkaline soil environments are not involved, and there are no 

 sound materials available economically, reactive materials may be used 

 provided certain limits are set in the specifications: 



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