(Received 30 September 1998; accepted 14 July 1999)
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Alkali-silica reactivity (ASR) was identified as contributing to premature failure of 12 concrete pavements in Minnesota. The available aggregate sources used in these distressed pavements were tested for potential ASR. Standardized tests result in conflicting information. The sands tested as potentially deleteriously expansive in the ASTM C 1260 Mortar Bar Test (expansion >0.2%), but tested as not deleteriously reactive in the ASTM C 1293 Concrete Prism Test (0.0295 to 0.042% expansions). Although expansions of these C 1293 prisms remained low, sand-sized opaline shales reacted to form gel, spalls, and cracks. Similar cracking and gel deposits are associated with these shales in field samples. The C 1260 mortar bars made with crushed quartzite aggregates exhibited moderate expansion values (average expansions ranging from 0.135 to 0.188%), but the C 1293 prisms made with quartzite coarse aggregates exceeded the 0.04% expansion limit (0.082 to 0.1137% expansion). Quartzite is reacting in several pavements but not as extensively as the high C 1293 test results imply. The sands are reacting in pavements and in test samples, but this reaction is not manifested as expansion in the C 1293 prisms.
Geologist, Office of Materials and Road Research, Minnesota Department of Transportation, Maplewood, MN
Stock #: CCA10427J