A latex modified concrete (LMC) overlay delays the onset of corrosion by slowing movement of chlorides to the reinforcement. Slow LMC strength development, however, causes problems. Conventional LMC overlays must be cured 4 to 7 days before being opened to traffic. To avoid the slow cure problem, the Virginia Transportation Research Council developed a high early strength LMC (LMC-HE) that can be subjected to traffic in less than a day. Note the following differences between LMC and LMC-HE:
- The LMC-HE mix contains Type III cement and the LMC mix contains Type II cement.
- The LMC-HE mix uses more cement than the LMC mix.
- The LMC-HE mix has a lower water-cement ratio.
Test results showed that LMC-HE reached a compressive strength of 3000 psi within 24 hours, while typical LMC takes about 7 days to reach this level. The laboratory prepared LMC-HE mix had a higher permeability at early ages than the standard LMC. After about 26 weeks, high early strength latex modified concretes made in the laboratory have about the same chloride permeability as standard latex modified concretes.
The study results show that it is practical to accelerate LMC overlay construction by using Type III cement and a higher cement content. Under normal conditions, workers should be able to install the overlay on a weekend and open the road to traffic within a day.