According to ACI 306R-10, cold weather exists when the air temperature falls below 40°F (4°C) during the protection phase. For shotcrete applications, this involves maintaining adequate thermal conditions from initial transport through the curing stage to prevent premature freezing.
In temperatures reaching –45°F (–43°C), shotcrete placement necessitates heat safeguards, thermal protective gear, and reduced work schedules. Safety hazards and material sensitivity intensify substantially, making preliminary discussion with the project owner or contractor vital to decide whether operations should proceed or temporarily cease during winter months.
Shotcrete requires a minimum temperature of 40°F (4.4°C) to initiate hydration. At 50°F (10°C), most formulations achieve 500 psi (3.5 MPa) within several hours to 48 hours. Elevated paste content and decreased water-cement proportions in wet-mix shotcrete frequently enable strength achievement within a single day.
Deploy heated formwork, hydronic heating systems, electric blankets, and forced air heat to preserve suitable placement environments. Revise the concrete composition using accelerating agents, elevated cement content, or Type III cement to expedite target strength attainment.
Rapid surface cooling or large temperature gradients (greater than 20°F or 11°C) can cause cracking before adequate strength develops. Methodical protection removal and continuous surveillance substantially diminish this hazard.
Cold weather need not halt shotcrete operations — but it does require detailed preparation, temperature control, and methodical execution. Following ACI guidelines and proven best practices ensures your shotcrete performs reliably through the most demanding conditions.
