92-MPa Air-Entrained High-Performance Concrete Using Tennessee Materials

An air-entrained high-performance concrete (HPC) mixture design for prestressed bridge beams was developed in an attempt to interest the Tennessee Department of Transportation. The mixture contained locally available, 19-mm maximum-size limestone as the coarse aggregate and a manufactured limestone fine aggregate. A dense, combined aggregate gradation was used to lower water demand and thus enhance durability. Type II portland cement, microsilica, and Class C fly ash were used as binder materials. The resulting w/(c + p) was 0.22. Twelve 0.028-m(3) batches of the HPC were mixed for the study. The mixture design produced an average air content of 4.1 percent and an average slump of 72 mm: Although it contained 4.1 percent air, the mixture remained very dense, with an average unit weight of 2422 kg/m(3). Average compressive strengths of 72.6, 63.3, 84.8, and 92.9 MPa were achieved at simulated release at 7, 28, and 56 days, respectively. Measured static modulus of elasticity at 28 days agreed with ACI 3638-92 equations within 2 percent. Further, after 600 freezing and thawing cycles, the average durability factor of two prismatic specimens was 100, and visible damage was minimal.