Effects of Changes in Total Aggregate Gradation on Portland Cement Concrete211 Properties, Phase 2 Durability

摘要

Transportation-related agencies are experimenting with increased control of211u001eaggregate gradation in their concrete pavement specifications. There is anecdotal 211u001eevidence that shows that total aggregate gradation can be optimized to yield 211u001eimproved concrete performance during construction and service life. Strong 211u001escientific data are less numerous in supporting this idea because of the 211u001evariability in aggregates that can occur and the practical considerations in 211u001eavoiding waste particle sizes. This laboratory study examined the influence of 211u001etotal aggregate gradation on the freeze-thaw durability of concrete test 211u001especimens that employed a variety of sedimentary and igneous aggregates common in 211u001eWisconsin. Optimized gradations consisted of increased amounts of aggregate 211u001eparticles in the No. 4 to No. 16 sieve size range and decreased amounts of fines 211u001ein the No. 50 to No. 200 sieve size range. A near-gap gradation was fabricated by 211u001eremoving some particles in the No. 4 to No. 16 sieve size range and increasing 211u001ethe amount of fine material in the No. 30 to No. 100 sieve size range. Several 211u001emethodologies and practical considerations were considered in establishing the 211u001eaggregate gradations. A control gradation utilized a 60-40 blend of coarse/fine 211u001eaggregate with gradiations determined by the naturally occurring particle sizes. 211u001eThe concrete specimens prepared in this study were subject to strength, 211u001eshrinkage, permeability and accelerated-freeze-thaw testing. All concretes showed 211u001eexcellent freeze-thaw durability. The optimized gradation mixed did not show 211u001econsistently improved performance compared to control mixes. The near-gap mixes 211u001eshowed reduced strength, reduced freeze-thaw durability and increased shrinkage.