Minnesota Department of Transportation
Study goals included: 1) identify mechanisms causing premature failure in Minnesota concrete pavements; 2) evaluate the accuracy of existing tests of aggregate freeze-thaw durability using Minnesota aggregate sources and pavement performance records; 3) develop a new methodology for quickly and reliably assessing aggregate freeze-thaw durability; and 4) evaluate techniques for mitigating D-cracking. Research results indicate that the poor durability performance of some Minnesota PCC pavement sections can often be attributed to aggregate freeze-thaw damage. However, secondary mineralization, embedded shale deposits, poor mix design and alkali-aggregate reactions were also identified as problems. Petrographic examination can help to differentiate between these failure mechanisms. A reliable and universal method for quickly identifying D-cracking aggregate particles was not identified. A test protocol was developed for improved aggregate durability evaluation. It includes several tests which are selected for use based on aggregate geological origin and composition and the results of previous tests. Further validation of the proposed test protocol is recommended. Several techniques appear to be effective in improving the freeze-thaw durability of concrete prepared using marginally durable aggregate: mix design modifications, reductions in aggregate top size, and the blending of durable and nondurable aggregates. Some chemical treatments showed promise, but may not be economical.
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