Effects of Changes in Total Aggregate Gradation on Portland Cement Concrete Properties, Phase 2 Durability: Fid-Bau Portal

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

S. M. Cramer / A. Carpenter

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