Some precast, prestressed beams can reach heights of 2.4 m or more necessitating special considerations for lateral pressure to ensure formwork tightness. In order to investigate the initial form pressure of the precast, prestressed self-consolidating concrete (SCC), an experimental program was undertaken. Sixteen non air-entrained and four air-entrained SCC mixtures with a slump flow of 680 ± 20 mm were evaluated. These mixtures were made with 440 to 500 kg/m3 of binder, Type MS cement or HE cement and 20% Class F fly ash, 0.34 to 0.40 water-cementitious material ratio (w/cm), viscosity modifying admixture (VMA) content of 0 to 100 mL/100 kg of binder, and 0.46 to 0.54 sand-to-total aggregate (S/A) volume ratio. Two high-performance concrete (HPC) mixtures with 0.34 and 0.38 w/cm and slump of 150 mm were also investigated. Moreover, decay in lateral pressure with time was also determined in order to evaluate the rate of pressure drop and the time required for pressure cancellation. Test results indicated that SCC proportioned with higher binder content developed higher relative initial pressure for the 2.0-m deep section. For a given binder content, the more viscous mixtures made with 0.34 w/cm exhibited lower relative initial pressure and longer duration before pressure cancellation. It is worthy to note that air-entrained SCC exhibited higher initial pressure. Finally, a good correlation was established between the final setting time and pressure cancellation time.