Title:
Reducing Shrinkage Cracking and Curling in Slabs-on-Grade
Author(s):
Johan Silfwerbrand and Jonatan Paulsson-tralla
Publication:
Concrete International
Volume:
22
Issue:
1
Appears on pages(s):
69-72
Keywords:
curling; desiccation; drying shrinkage; loading; shrinkage cracking; slabs-on- ground construction
DOI:
Date:
1/1/2000
Abstract:
The major distresses in concrete floors are not due to structural loads, but rather to restraint stresses, e.g., shrinkage stresses. Usually, these problems are either solved by use of numerous joints or by reinforcement meshes. Another problem is the slow drying process postponing application of surface materials. To find alternatives, a new technique to cast concrete slabs on grade has been developed. The novel approach is the use of airbags evenly spaced roughly 1 to 2 m (3.3 to 6.6 ft) apart and between concrete slab and subbase parallel to the short side of the slab. After 3 to 7 days of curing, the airbags are filled with compressed air and the slab is lifted, enabling the slab to dry in two directions and shrink without restraint. After a couple of weeks, the airbags are emptied and the slab is lowered again. The direct benefits are reduced cracking risk due to negligible shrinkage stresses, shorter drying times due to bilateral drying, and reduced curling due to equal upward and downward drying. Full-scale tests have been carried out on two concrete slabs.