Concrete Curing in North Carolina Summer Heat: Preventing Surface Crazing and Shrinkage Cracks

The Evaporation Rate Equation (ACI 305R)

Under American Concrete Institute guidelines, when the surface evaporation rate exceeds 0.2 lbs per square foot per hour (and 0.1 lbs/sq ft/hr for mixes containing silica fume), plastic shrinkage cracking is almost guaranteed unless preventative measures are taken.

Adding water to the ready-mix truck on-site ('watering the mix' to make it easier to rake) drastically lowers concrete compressive strength, increases total shrinkage, and produces a weak, dusty surface that will scale and pit during the first winter freeze.

AGCS Hot-Weather Concrete Protocols

AGCS protects summer concrete flatwork through proven field procedures:

• Early Morning Pours: Scheduling concrete trucks for 6:00 AM or 7:00 AM dispatch before ambient heat peaks.
• Moistening Subgrades: Thoroughly dampening the crushed stone subbase before placement so dry earth doesn't suck water from the bottom of the fresh concrete.
• Evaporation Retarders: Applying monomolecular film sprays (such as MasterKure ER 50 or SikaFilm) immediately after screeding to lock in surface moisture.
• Curing Compounds & Wet Curing: Spraying ASTM C309 membrane-forming curing compounds immediately following final broom finishing, or applying wet burlap covers.

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