The California Department of Transportation (Caltrans) needed a concrete pavement that would deliver a surface ready for traffic in 4 hours. Different admixture manufacturers experimented with various combinations to try to achieve this. Finally, Master Builders came up with what they call "4x4 Concrete," an innovative mixture that develops 400-psi flexural strength in just 4 hours after placement. This material costs about half as much as current fast-setting hydraulic cement concrete and can be produced with standard locally available materials. Chumo Construction recently placed over 500 cubic yards of this new mix on a remove-and-replace job for the California Department of Transportation with great success. We asked Tom Pyle, chief, Office of Rigid Pavements & Structural Concrete with Caltrans, and James Anderson, engineering service western manager for Master Builders, to discuss this new development in high-early-strength concrete for paving repair.