Dealing with ambient conditions when placing concrete toppings

Toppings are subject to the same general industry recommendations for hot- and cold-weather concreting practices as any other concrete. Proper planning and execution are essential for minimizing the negative effects of weather extremes on topping placement, consolidation, finishing, curing, and strength development.


When planning around the effects of ambient conditions on topping construction, a key factor to consider is the mass of the existing slab. In hot and cold weather extremes, the topping and base slabs will normally be at different temperatures when placed but will come to a thermal equilibrium during curing. Typically, the base slab accounts for the bulk of the composite slab (bonded or unbonded) so conditioning of the base slab prior to construction cannot be overlooked.

Thinner toppings may be more susceptible to temperature-related issues. A cold base slab can cause finishing problems due to delayed set, retarded strength gain, or even freezing of the topping if not properly conditioned. A hot base slab can lead to rapid stiffening that negatively affects workability, consolidation, finishing, and bond. A research found that the rain, heat, and cold can all have a negative impact on a topping slab, the thin bonded topping placed in cold weather is susceptible to damage from freezing.


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