How To Approach Concrete Structural Repairs
If a crack affects the performance of a concrete structure the goal is to restore it’s structural properties. Epoxy injection is typically the basis for this type of repair and may employ added reinforcement. The injected epoxy is actually stronger than the concrete and can restore the concrete strength, but if the key is to know of any underlying problems like an overloaded structure or movement conditions as the concrete will simply crack again in another location.
In using epoxy injection to repair a crack, the crack is first cleaned by vacuuming or flushing with water to get out any dust or contamination. The cracks on the surface are sealed with an epoxy gel to prevent the injected epoxy from running out. Injection and venting ports are installed and the epoxy is injected but high pressure is not used since that could widen cracks. After the cracks have been filled, the ports and surface seals are removed, typically by grinding the surfaces flush with the concrete matrix. Epoxy injection is also used to repair surface delamination of slabs.
When reinforcement corrodes and delaminates the concrete covering reinforced concrete can quickly lose strength. If concrete is too deteriorated for epoxy injection, then all failed concrete is removed and new concrete is applied. Obviously, serious caution must be taken to stabilize the structure prior to removing the damaged concrete. The key to successful repairs of this sort is in the preparation. No deteriorated concrete can remain and anyplace where reinforcing steel is corroded, the concrete must be removed completely around the bars, providing and at least ¾-inch clearance on all sides. The steel needs to be cleaned to remove any loose corrosion products like rust and new steel will be tied to the existing steel prior to replacing the concrete if the cross section of the steel has been reduced significantly. Full-depth repairs will need new steel to be installed and tied into the existing concrete.
For all repaired areas, the edges should be cut at a 90-degree angle and feather edges should be avoided at all costs. The configuration of the area to be repaired should be kept as simple as possible, and best as a aquare. An excellent and simple source of more information on this technique is ICRI’s Guide for Surface Preparation for the Repair of Deteriorated Concrete Resulting from Reinforcing Steel Corrosion, Guideline No. 03730.
For strengthening there are a variety of techniques which include simply increasing the size of the concrete member and external reinforcing. External reinforcing is often accomplished by bonding some a flexible reinforcement ,such as carbon or glass fibers, to the exterior of the concrete member then covering it with placed concrete, troweled-on concrete, or shotcrete.