In slab lifting projects, many customers worry whether injecting polyurethane foam will damage the original structure and cause concrete cracks. In fact, PU foam itself does not cause cracks , but if the construction method is not standardized, it may bring structural risks.
Material properties of polyurethane foam
Polyurethane foam is widely used in the fields of slab lifting and foundation reinforcement. Its advantages are:
- It has good elasticity and stress dispersion ability and can adapt to a certain degree of deformation;
- The expansion is controlled and usually does not cause concrete cracking due to its own reaction;
- It cures quickly and is lightweight , making it suitable for rapid repairs of uneven settlement areas.
Where does the risk of cracking come from? Three common construction misunderstandings
The base layer is not properly treated
and the concrete surface is not thoroughly polished and cleaned, and there are oil stains or loose layers, it will affect the adhesion of the foam, causing uneven lifting and further cracking of the local structure.
Improper injection control and
excessive injection of polyurethane foam will cause excessive local internal stress and easily cause cracks in the concrete. It is recommended to cut expansion joints (generally at intervals of 4-6 meters) to help release expansion stress.
Insufficient curing and maintenance
If the polyurethane foam is not moisturized or the temperature is too low during the curing process, the water will evaporate quickly, causing the foam volume to shrink, and indirectly leading to structural deformation.
How to prevent concrete cracking?
In order to avoid structural problems during construction, the following measures are recommended:
- Clean the base : thoroughly grind and clean the concrete surface to ensure there is no floating dust or oil stains; the base concrete strength is recommended to be ≥ C25.
- Reasonable injection and setting of expansion joints : control the amount of foam injection, and cut expansion joints with a spacing of 4-6 meters according to the on-site structure , and fill the joints with elastic sealing materials.
- Pay attention to the maintenance stage : After construction, the material should be covered with plastic film for maintenance for no less than 7 days. In winter, insulation measures should be strengthened to prevent material shrinkage or brittle cracking.
Summarize
Polyurethane slab lifting is essentially a low-interference, fast-repair, and structurally friendly reinforcement method. As long as the construction is standardized and the material dosage and maintenance conditions are strictly controlled, it will not cause concrete cracking.
If you need more information about construction techniques or material parameters, please contact us for professional advice.