Which action helps prevent crusting when placing concrete in cold weather?

Which action helps prevent crusting when placing concrete in cold weather?

• A. Heating the subgrade and keeping the concrete near the specified minimum temperature
• B. Cooling the subgrade and keeping the concrete near the maximum temperature
• C. Finishing immediately after placement
• D. Using minimal curing water

Answer: (A)

Preventing crusting in cold weather comes from keeping the concrete and its foundation warm enough so hydration proceeds smoothly and the surface doesn’t dry out too quickly. Heating the subgrade helps transfer heat into the concrete, reducing the surface temperature drop that causes a hard, skin-like crust to form while the interior is still plastic. Keeping the concrete near the specified minimum temperature ensures the cement continues to hydrate at a steady rate without becoming too cold or freezing, which would promote crust development and weaker hardening. Cooling the subgrade would pull heat away and encourage rapid surface drying and stiffening, increasing crust risk. Finishing immediately after placement can disrupt the surface while it’s still plastic and doesn’t address moisture loss or uniform curing. Using minimal curing water reduces moisture available for hydration and accelerates surface drying, also promoting crust formation.

Preventing crusting in cold weather comes from keeping the concrete and its foundation warm enough so hydration proceeds smoothly and the surface doesn’t dry out too quickly. Heating the subgrade helps transfer heat into the concrete, reducing the surface temperature drop that causes a hard, skin-like crust to form while the interior is still plastic. Keeping the concrete near the specified minimum temperature ensures the cement continues to hydrate at a steady rate without becoming too cold or freezing, which would promote crust development and weaker hardening.

Cooling the subgrade would pull heat away and encourage rapid surface drying and stiffening, increasing crust risk. Finishing immediately after placement can disrupt the surface while it’s still plastic and doesn’t address moisture loss or uniform curing. Using minimal curing water reduces moisture available for hydration and accelerates surface drying, also promoting crust formation.