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|Title:||Concrete cores from Dry Dock No. 2, Charleston Naval Shipyard, S.C.|
|Authors:||United States. Bureau of Yards and Docks.|
United States. Navy.
Buck, Alan D.
Charleston Naval Shipyard, S. C.
|Publisher:||Concrete Laboratory (U.S.)|
Engineer Research and Development Center (U.S.)
|Series/Report no.:||Miscellaneous paper (U.S. Army Engineer Waterways Experiment Station) ; C-69-6.|
Abstract: Eight concrete cores from Dry Dock No. 2, Charleston Naval Shipyard, were examined to determine if alkali-silica reaction had occurred in the concrete and whether, if this reaction had occurred, it was continuing. Some of the concrete and of the associated white porcelaneous secondary reaction product (gel) indicated alkali-silica reaction had occurred. However, the quartz aggregate used in the concrete is not among types of material usually considered to be reactive. Also, the gel was definitely more crystalline than alkali-silica gel has usually been found to be. None of the tests and examinations made of the gel, aggregate, cement paste, and concrete suggested that the aggregate would be diagnosed as reactive by normal criteria. Apparently, only one source of aggregate had been used. Chemical analysis of a sample of gel from the reacted concrete showed it to consist of water, silica (Si02), lime (Cao), and potassa (K20); the last amounted to 19°/o. The approximate formula of this material, CaO.K20.5Si0.5H20, is reasonable as a generalized formula for impure alkali-silica gel; the microscopical examinations showed that the gel consisted of at least three crystalline phases. One ineluded amorphous material that is probably alkali-silica gel. It is concluded that alkali-silica reaction had occurred and that the effects of this reaction have essentially terminated. Since the alkali portion of the gel was high in K2o and low in Na2o, it is believed that the source of the alkali was the cement rather than the sea water to which the concrete was exposed. The environment of the dry dock with its unequal periods of wetting and drying probably resulted in moving concentration fronts or local concentrations of alkali from the cement which together with other environmental factors caused the reaction to occur. Not all of the concrete exhibited alkali-silica reaction; this may signify that two cements were used and reaction was confined to the concrete made with the one of higher alkali content, or it may be due to an undetermined environmental factor. It seems more probable that cements of different alkali contents were involved. Progress reports 1 and 2 are included as Appendixes A and B, respectively, and U. S Army Engineer Waterways Experiment Station TM 6-224 as Appendix C.
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