High volume fly ash in portland cement concrete for bridge decks

The goal to be sustainable has driven the Tennessee Department of Transportation (TDOT) to question if high volume fly ash (HVFA) in portland cement concrete (PCC) is a viable option for use in bridge deck construction. The use of an industry byproduct to increase the durability of bridge decks is twofold; the use of a byproduct helps to decrease unit costs and the increase in durability lengthens the serviceability of bridge decks.;There were a total of 28 mixes made; 10 TDOT Class D mixes with three additional mixes at their maximum placement temperature of 90° F were compared to 10 HVFA Class C fly ash mixes with three additional mixes at TDOT's maximum placement temperature as well. One additional mix of both the TDOT Class D and HVFA were produced to compare shrinkage characteristics. TDOT 604.03 guidelines were followed for all mixes so an unbiased comparison of plastic and hardened properties, for their strength and durability, were determined.;The test results showed that HVFA Class C fly ash PCC is superior to the TDOT Class D PCC. HVFA Class C fly ash showed statistically lower absorption values and lower permeability results as measured by rapid chloride permeability testing (RCPT). The lower paste contents of HVFA did play a role in lower one day compressive strengths than the TDOT Class D PCC. With a lower water to cementitious ratio and Class C fly ash, HVFA rapidly gained strength, quickly overcoming the TDOT Class D PCC on compressive strength and static modulus of elasticity. Results at 7, 28, 56, 91, and 182 day testing showed an average compressive strength of 18% increase to TDOT Class D PCC and a 7% increase for static modulus of elasticity. TDOT's maximum placement temperature (90° F) was simulated for both mix designs which resulted in the hot HVFA mixes having an average increase in compressive strength and static modulus of elasticity of 31% and 11% respectively, over the hot TDOT Class D PCC. Restrained shrinkage testing was inconclusive, but no cracking occurred during the 28 days of testing.