Tests for Chemical Reactivity Between Alkalies and Aggregate. Report 3. Further Investigation of the Mortar-Bar Test
Army Engineer Waterways Experiment Station VICKSBURG United States
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Tests were conducted to ascertain the effect of the differences between Corps of Engineers method CRD-C 123 and American Society for Testing Materials method ASTM C-227 for determining alkali-aggregate reactivity in mortar bars. Principal differences are grading of aggregate used in the mortar age of bars at time of initial measurement and number of times bars are measured. Test bars made of six cement-aggregate combinations were tested using CRD and ASTM gradings and measuring sequences. Also, blotting paper liners were placed in the exposure containers to improve the relative humidity of the air surrounding the bars in the containers. Results indicate a There was a significant difference, in some cases, between the 1-yr expansion of bars containing ASTM graded reactive aggregates that were measured according to the ASTM specified measuring sequence and bars containing CRD graded aggregate that were measured according to the CRD specified measuring sequence. Where there was a significant difference, the ASTM bars expanded more than the CRD bars. b There was no significant difference in the 1-yr expansion of bars measured initially at 24 plus or minus 2 hr. and those measured at 44 plus or minus 4 hr. age. c Subsequent measurement of bars after absorptive liners were placed in the exposure containers showed an abrupt increase in expansion of the bars in most cases. It is evident that the air surrounding the bars is not always of the desired relative humidity when bars are exposed in plastic containers of the type prescribed in CRD-C 123.