| Abstract: | Conclusion The reported results of chemical tests for potential reactivity of concrete aggregates from some of the largest hydraulic
structures showed that the virtur of the chemical method lies in its practicality and adequate reliability. An evaluation
of the chemical test results for potentially reactive aggregates must take into account both the amount of dissolved silica
SC, and the extent of reduced alkalinity RC. This is corroborated by comparative experiments on test bars and by a sufficiently close correlation function between SC and RC values. When carbonaceous rocks, clays, magnesium silicates (serpentines), and gypsum are present in aggregates, distorting
the chemical test results, additional bar test of aggregates are necessary.
From the Editors. In hydrotechnical construction, instances are encountered of craks appearing in concrete as a result of
alkaline chemical reactions. This not uncommon reaction is usually explained by the interaction of portland cement alkalis
with amorphous silica, occasionally present in gravel and crushed rock, concrete aggregates. When parts of the aggregates
are dampened, a gel film is formed which, as it grows and hardens, ruptures the cement rock in the concrete. Until now there
has been no accurate test for the degree of reactivity of aggregates and cement; likewise, there is no suitable procedure
for determining the potential reactivity of aggregates. This leads to an erroneous evaluation of aggregate usefulness. Planners
of hydraulic structures are investigating new roneous evaluation of aggregate usefulness. Planners of hydraulic structures
are investigating new methods for determining potential reactivity, to avoid an unwarranted increase in the cost of concrete,
and complications in quarry economy. New methods for determining the potential reactivity of aggregates and cumulative data
from studies of alkaline reactions in concrete are of great interest, especially for researchers and planners of hydraulic
structures. Consequently, the editorialboard has found it useful to publish research material on this problem of several years’
standing.
Translated from Gidrotekhnicheskoe Stroitel’stvo, No. 7, pp. 29–31, July, 1974. |
