|Dr. N. Subramanian
Joined: 21 Feb 2008
Location: Gaithersburg, MD, U.S.A.
|Posted: Tue Jan 21, 2020 10:19 pm Post subject: Repair Methods for Damaged Concrete Floors
|Repair Methods for Damaged Concrete Floors
By Constro Facilitator -January 10, 2020
Concrete Floors can be repaired using some common methods. All of these involve covering the existing concrete slab with a new coating of concrete or concrete-like topping and finishing the new layer as desired. Concrete floors should be repaired with a surface topping only when the concrete slab contains surface, or hairline, cracks or has cosmetic surface flaws. If the concrete floor to be repaired is heaving, has large or wide cracks, or is damaged due to freeze damage, then other alternatives should be considered instead of resurfacing.
Concrete Repair and Maintenance System
As a first step to increase the likelihood of a successful repair, it is paramount to use a consistent, systematic approach to concrete repair. Reclamation’s concrete repair and maintenance system consists of seven basic
1. Determine the cause(s) of damage
2. Evaluate the extent of damage
3. Evaluate the need to repair
4. Select the repair method and material
5. Prepare the existing concrete for repair
6. Apply the repair method
7. Cure the repair properly
Discussed below are a few methods of repair of concrete floors that could be used according to the necessity of the concrete floors.
Sealers and Coatings
Concrete sealing and coating compounds are applied to cured, dry concrete as a maintenance and repair procedure to reduce or prevent penetration of water, aggressive solutions, or gaseous media. They help to reduce or prevent associated deterioration such as corrosion of rebar, freeze-thaw, carbonation, or sulfate damage. These materials are not suitable for repairing badly damaged or deteriorated concrete, but they are suitable for sealing concrete surfaces and cracks in concrete that is in overall good condition.
Cracks in concrete are widely regarded as long-term durability and maintenance problems because they increase the permeability of the concrete. Cracks can allow the ingress of moisture and other compounds into concrete, leading to further deterioration. Cracking is a problem that occurs in most geographical locations and climates, and many types of concrete structures. Reclamation has a large inventory of aging concrete that is experiencing deterioration resulting in cracking or exacerbated by cracking. Effective sealing and coating compounds for smaller cracks could slow or halt deterioration in some cases.
Sealers and coatings comprises of four divisions;
1. High Molecular Weight Methacrylic Sealing Compounds
2. Low Viscosity Epoxy Sealing Compounds
3. Silane and Siloxane Sealing Compound
4. Coating Compounds for Concrete
Thin repairs are generally from about ¼- to about 2 inches deep and do not encompass any existing reinforcing steel. Typical examples of thin repairs include surface grinding, Portland cement mortar, some coatings and surface sealers, dry pack mortar, packaged cementitious and chemical repair mortars, and polymer mortars (including epoxy mortars). Unfortunately, insufficiently thick repairs to some concretes should not be considered permanent. In some circumstances, thin repairs my lead to accelerating deterioration behind or adjacent to the repair.
In general, thick repairs refer to repairs that are about 3 inches thick and that completely encompass at least some reinforcing steel from the existing structure. If the repairs do not encompass any steel from the existing structure, they are typically at least 6 inches thick. In such cases, consideration should be given to anchoring additional reinforcement (that will be embedded in the repair material) to the existing concrete. Typical examples of thick repairs include replacement concrete, preplaced aggregate concrete, shotcrete, and silica fume concrete.
This type of repair consists of the following materials;
1. Replacement Concrete
2. Preplaced Aggregate Concrete
4. Silica Fume Concrete
Crack and Water Leak Repairs
They are significantly different from methods for thin or thick repairs. In many ways, properly repairing cracks and leaks can be the most difficult type of repair. In many Reclamation structures, if the concrete cracks, there is also a water leak. Reclamation’s seven-step process should be followed for crack repairs. In other words, the cause and extent of the cracks or leaks should be determined, including whether the cracks are dormant or active (moving); exposure conditions should be considered, wetting and drying, etc.
There are two basic types of crack repair: (1) resin injection, and (2) adding additional reinforcement. These two methods can be performed separately or in combination. Additional reinforcement is typically added if the shear or tensile capacity of a structural element has been, or might be, exceeded.
Resin injection is used to repair concrete that is cracked or delaminated, as well as to seal cracks or joints in concrete that is experiencing water leakage. Epoxy resins are used to structurally rebond cracks that are dormant and relatively dry, while various polyurethanes and some methacrylic acrylates are used to seal cracks or joints that leak water. It is usually not possible to structurally rebond cracks that are leaking water, are dirty, or are very wet. Also, due to the high cost of resin injection, it is not normally used to repair shallow cracks, drying shrinkage cracks, or pattern cracking. Therefore, if repairs are needed for these types of cracks, a sealing approach is usually more effective.
Polyurethane and Methacrylic Acrylate Resins
These resins are used to seal and eliminate or reduce water leakage from concrete cracks and joints. They can also be injected into cracks that experience some degree of movement. Such systems, except the two-part solid polyurethanes, have relatively low strengths and should not be used to structurally rebond cracked concrete. Cracks to be injected with polyurethane resin should not be less than 0.005 inch in width, while cracks smaller than that can be injected with methacrylic acrylates. Using methacrylic acrylates requires special mixing procedures and stainless steel pumping equipment; however, in some applications, it is very effective at sealing very small leaking cracks, due to its very low viscosity.
Resins can be injected with many types of equipment. Small repair projects can be performed using caulk cartridge-type equipment and several firms make their products in cartridges for such application. Airless paint sprayers, paint pressure pots, and a variety of specialized pumps are examples of the available equipment.
Small projects that employ epoxy resin can use any system that will successfully deposit the epoxy in the required area. For these systems, the epoxy components are mixed together and then poured into the injection equipment. Once mixed, the epoxy must be injected before it starts to thicken. Longer pot life epoxies should be used for this technique.
Large epoxy injection projects generally require a single-stage injection method by which the two epoxy components are pumped independently from their separate reservoirs to the mixing nozzle. At the mixing nozzle, the epoxy components are mixed and then injected. The epoxy used with this injection technique must have a low initial viscosity and a closely controlled set time.
Stitching the Cracks
It is the easiest and long-lasting method of repairing concrete cracks. In this method, a number of the hole drilled along the crack surface and stitched with metallic wire. This metallic U-shaped wire is then passed through holes and anchored strongly in the holes with grout or an epoxy-based system.
Routing and Sealing
Routing and sealing isolate your non-structural crack, extinguishing any risk of deeper damage. Whilst it can be used on walls too, it is perfect for floor and ceiling work.
When it comes to choosing your product, consider your environment carefully- How much load-bearing do I need?/ How heavy is my foot traffic?/ Would it better suit medium use or heavy duty?
A v-shaped trough needs to be created at the root of the cause. Ideally, the trough should be twice as wide as it is deep. This will allow the flexible sealant to tolerate any future movement and mould into it. If you go for a 1:1 width and depth this is also okay, but a trough much deeper than it is wide will limit what the sealant can do. Where possible, the trough should be two inches in width and one inch in depth. If that large a funnel shape is not possible, then the same scale should be observed.
Gravity filling method
Gravity filling is the simplest filling method. The uncomplicated construction and operation of gravity filling machines permit them to run with a minimum of maintenance. The supply tank (more properly called the filler bowl) is the upper, central part of the machine. Filling stems are attached to the bottom surface of the bowl at each container filling point. A vent tube extends upward into the filler bowl to a point above the liquid level. To begin the filling operation, the container is raised by the platform until it contacts the filling stem. The platform then continues to raise the container against the stem, opening the filling valve. Low viscosity monomers and resins can be used to seal cracks with surface widths of 0.03 to 2 mm by gravity filling. High-molecular-weight methacrylates, urethanes, and some low viscosity epoxies have been used successfully. The lower the viscosity, the finer the cracks that can be filled.
Micro-topping treatments are made with very thin layers, no thicker than 1/8 inch, of polymer-modified concrete containing sand and are applied with trowels or brushes, depending on the final look desired. Because micro-toppings are so thin they are not self-leveling. They also dry very quickly, so the final texture is limited to how the micro-topping is applied over the concrete floor. The treated surface can cure in a day, and usually can be walked on within 36 to 42 hours of being applied.
It is important to seal micro-topping finishes, as they are porous and tend to collect dirt that is difficult to remove once embedded in the material. Micro-topping treatments may include two or more base coats and, in some cases, a very thin top coat without sand, if a very smooth finish is desired.
Once a small crack or chip appears, future wear and tear will only cause it to expand. Methods for concrete repair helps to fight the issues. The methods harden and bind the surface, trapping the lime inside the structure, hence, preventing further crumbling and delamination of the concrete floor. Analyse the defect and select the method that serves your repair needs.
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