Monday, December 12, 2011

Should I use injection sealing to repair my slab?

Injection sealing is a technology where a grout material is injected into a leaking crack to prevent leakage. While there are many circumstances where this is an excellent repair method, there are some circumstances where it is simply not appropriate. It is important for building owners to understand these circumstances so they can be sure that injection-sealing is properly deployed.

If the leaking water is generally free from chlorides, then injection sealing is a cost-effective and appropriate repair. This would be the case for most foundation walls, on the underside of suspended slabs which are covered in plants (below a lawn for example) and generally in southern climates where de-icing salts are not used. The goal in these locations is to prevent the annoyance of water dripping into the facility below.

If the leaking water is chloride-contaminated, then injection sealing may cause more harm than good. Chloride-contaminated leakage would occur in northern climates below parking decks, parking lots and driveways.  This is because de-icing salts are applied in these areas, adding chlorides to the melt water.  The goal in these instances is two-fold: to prevent the annoyance of water dripping into the facility, and to protect the reinforced concrete structure from chlorides.

Why do chlorides matter?  When chlorides penetrate concrete, they depassivate the embedded reinforcing steel.  If oxygen and water are also present (and they usually are), then the embedded reinforcing steel starts to corrode.  The corrosion products take up more space than the original steel and therefore typically cause the concrete cover over the reinforcing steel to break off (this is also known as delamination or spalling).

Concrete Delamination - Copyright Halsall 2011

Injecting a leak in an area with chloride contaminated leakage can actually trap the chloride contaminated water in the crack or on the top surface of the slab. Injection sealing is usually completed from below.  Ports are drilled on an angle to intersect the leaking crack. The injection material is injected under pressure.  Done well, the injection material should completely fill the crack from the top of the slab to the bottom of the slab.  However, this injection does not fix the fundamental defect in the waterproofing system above the slab.

Water trapped in the depth of the crack, or on top of the slab (below the waterproofing membrane) can hasten the chloride-related corrosion and deterioration. In locations exposed to chlorides it is far better to excavate from above and properly repair the defect in the waterproofing membrane.  This not only stops water from dripping on occupants below, but also protects the slab from the chlorides, minimizing structural deterioration over time. The repair costs more in the first instance than injection-sealing, but less in the long-term because it reduces the risk of structural deterioration.

A proper condition evaluation and specifications should ensure that the appropriate repair methodology is used in the appropriate locations.

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