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Title: MONITORING MORTAR BAR ALKALI-AGGREGATE REACTIVITY
Accession Number: 00625708
Record Type: Component
Availability: Find a library where document is available Abstract: Extensive and progressive pattern cracking was observed in four recently constructed North Carolina bridges. Petrographic examination (ASTM C-295 and C-856) showed the presence of alkali-silica gel in concrete cores, but a quick chemical test (ASTM C-289) on the suspect aggregate proved inconclusive. To establish the alkali-aggregate reactivity potential of the aggregates used in these bridges and to identify the nature and extent of reactivity of selected aggregates in North Carolina, a series of mortar bar tests (ASTM C-227) was conducted. Mortar bar specimens were prepared with combinations of a high-alkali cement and several different aggregates. In addition to length and weight measurements, two different compression wave velocity measurements were made over a 1-year period. The standard ultrasonic pulse velocity (ASTM C-597) was determined in addition to a velocity determination referred to herein as a cycle velocity. The cycle velocity is obtained by striking one end of a mortar bar to initiate a compression wave that reflects back and forth through the bar. An oscilloscope measures the output of an accelerometer attached to the opposite end, displaying a peak for each arrival of the compression wave at the accelerometer. The compression wave velocity is then determined from this fundamental mode of vibration. In these mortar bar tets, the cycle velocity measurement was more repeatable than for the ultrasonic pulse velocity. However, both ultrasonic and cycle velocity measurements are good laboratory indicators for monitoring the progress of alkali-aggregate reaction. Pulse and cycle velocities are inversely related to expansion, while weight changes of the mortar bar specimens are poorly correlated with expansion. The tests revealed that some North Carolina aggregates are reactive and should not be used with high-alkali cements.
Supplemental Notes: This paper appears in Transportation Research Record No. 1362, Aggregate and Pavement-Related Research. Distribution, posting, or copying of this PDF is strictly prohibited without written permission of the Transportation Research Board of the National Academy of Sciences. Unless otherwise indicated, all materials in this PDF are copyrighted by the National Academy of Sciences. Copyright © National Academy of Sciences. All rights reserved
Monograph Title: Monograph Accession #: 01405044
Language: English
Authors: Hearne Jr, Thomas MCowsert, Jack ECordle, V OwenPagination: p. 44-50
Publication Date: 1992
Serial: ISBN: 0309054028
Features: Figures
(13)
; References
(2)
; Tables
(4)
TRT Terms: Uncontrolled Terms: Geographic Terms: Old TRIS Terms: Subject Areas: Geotechnology; Highways; Materials; I32: Concrete; I36: Aggregates
Files: TRIS, TRB, ATRI
Created Date: Jan 8 1993 12:00AM
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