Concrete Repair Charles Town WV can often help extend the life of an existing structure. However, damage during lift-out, chipping of the old concrete, and inadequate curing can significantly reduce the effectiveness of repairs.
A wide range of repair materials are available for repairing concrete structures. These can differ in their construction characteristics including shrinkage, modulus of elasticity, and freeze-thaw durability.
Contractors often rely on nondestructive evaluation techniques (such as radar, impact echo, and infrared thermography) to determine the severity of damage and how deep it goes. Using these techniques allows contractors to see how the concrete has degraded without breaking it open. However, when the damage is structural in nature it can be very difficult to get a good picture of how far the deterioration has progressed. A destructive core sample may be necessary to obtain more information, and a petrographer should be hired to examine the results of the testing.
It is very important to evaluate the quality of the existing concrete surface prior to the application of any repair material. Adequate soundness and a good bond are crucial to the durability of the repair work. The best repair materials would give unsatisfactory performance if applied to a weak or friable substrate.
To achieve a sound, good quality surface, it is recommended that a suitable cement or mortar be used for pre-repair, especially on very sour soils. The surfaces should be free of oil, grease, paints, and other chemicals that could act as a bond breaker. In addition, the cured surface should be kept moist and not allowed to dry out too soon.
Concrete mix manufacturers such as QUIKRETE, Sika, Master Builders and MAPEI offer a wide range of repair products for almost every situation. Contractors should consult with a representative to ensure that they are selecting the right product for the job at hand. They should also consider geometry and structural requirements to help them choose a product that will provide the durability they need for the project at hand.
Generally speaking, it is preferable to use a commercial-grade repair material that is designed for the intended application. It will have the proper mixture to withstand the intended stresses and be capable of bonding well with the existing concrete.
Ideally, a contractor should prepare a mock-up or pull-off test on-site to check how the chosen repair material works with the existing concrete. By using a metal dolly, the contractor can pull on the dolly to measure the failure psi. A lower psi means that the repair material will likely bond well with the existing concrete.
Repair Materials
The selection of a suitable repair material is a vital component in the successful repairing of concrete. The chosen repair material should be durable under the exposure conditions to which the repaired structure will be subjected and also have adequate resistance against chemical attack, in order to extend the life of the structure and prevent further deterioration.
Cement-based materials are currently the most commonly used repair materials for concrete structures. They have the advantages of good compatibility with the substrate, low cost and easy operation. To enhance the performance of cement-based repair materials, admixtures such as fly ash, blast furnace slag and silica fume are commonly added to the mixtures.
An important feature of the repair materials is their permeability, which should be low in order to avoid leakage of water and other substances into the existing concrete. This is particularly important when repairing cracked concrete, as the cracks will continue to move and eventually develop into shear (or tension) failure zones.
Another key factor for the selection of the repair materials is their coefficient of thermal expansion, which should be similar to that of the existing concrete to ensure that undue stresses are not transferred either at the interface or within the new material. Finally, the chosen repair material should have a modulus of elasticity which is adequate for the structural repairs that are being carried out.
For a quick and economical repair of small holes or cracks in concrete, a pre-mixed, viscous compound is available, which can be applied with a trowel, and will fill the voids immediately, and is capable of bonding to concrete. For larger gaps, a more heavy-duty product may be required that has a thicker formula so the user can pack the patch and sculpt it into the hole.
Many scholars have studied the interaction between the repaired concrete and the existing concrete, and different methods of testing the bond strength are utilized. The most common testing method is the pull-out test, although other tests such as shear and flexural test are sometimes used. It has been found that the quality of the bond between the repair material and the substrate depends on a variety of factors, including the surface preparation of the old concrete, the type of repair material and the moisture content of the repair material and the substrate.
Bonding
When repairing concrete, the most important thing is to ensure that the new repair material bonds well to the existing concrete. This is not easy to do. Contractors need to consider the properties of the concrete repair materials as well as application factors such as surface preparation and curing practices.
There are several tests to determine the bond strength of repair materials. These include flexural bond strength tests to measure the bend resistance of the repair; shear bond strengths, slant shear, and push-out test to evaluate shear strength; and pull-out bond strength, split-pull test, and core pull-put test to measure tensile strength.
The dimensional characteristics of the concrete repair material are also important. They should be similar to the original concrete, particularly in terms of drying shrinkage and modulus of elasticity. The coefficients of thermal expansion should be similar as well. This will minimize the formation of die shrinkage cracks at the interface that can debond the repair.
To improve the bond between the concrete repair materials and concrete substrate, some researchers have suggested that using a bonding agent prior to placing the concrete repair is a good idea. This can be a liquid or powdered product. The chemical bonding agent can help the concrete repair materials to penetrate into the pores and capillaries of the old concrete and adhere firmly to them.
Once the bonding agent has been applied, contractors can then begin the process of preparing the concrete substrate to accept the repair material. This includes cleaning the surface, removing any loose material, and sweeping or vacuuming the area to remove dust and other contaminants that can act as bond breakers. Contractors should also prepare the old concrete by spraying it down with water or use a power washer to rinse the surface clean.
Finally, the concrete repair contractor should perform a psi test or mock-up on-site to make sure the new repair will be able to withstand the required loads. The test involves gluing a metal dolly to the surface of the old concrete, letting it set, and then pulling it to see at what point the dolly fails. This will give the contractor a good idea of whether or not the proposed concrete repair will hold up under load, and allow them to make any necessary adjustments before beginning construction on the project.
Curing
Concrete derives its strength from hydration of the cement, which is why curing is so important. Curing maintains moisture in the concrete to complete this hydration process and ensure proper hardening to attain a desirable strength. It also reduces drying shrinkage cracking. This is especially important on jobs that are exposed to the elements after placement, such as road and airport pavements.
When preparing to apply a repair material, it is imperative that the concrete surface be clean and free of any loose particles that might interfere with bonding. Also, it is important to keep in mind that the type of repair material that is being used may require different curing conditions than the original concrete. The concrete mix, specified strength, mixture proportions, ambient weather conditions and future exposure conditions should be considered when determining appropriate curing conditions.
The best way to prepare a concrete surface for bonding is to sweep it with a stiff bristle broom or power broom to remove dirt, loose aggregate and oily residues. It is also important to wash the area with water to remove any excess concrete dust, grit and debris.
Once the concrete is clean, a bonding agent can be applied. This can be a liquid, powder or spray material. The product instructions should be followed closely when applying the bonding agent. It is important to follow the directions exactly so the bonding agent will adhere to the existing concrete and not peel or wash off.
Lastly, it is important to protect the concrete from extreme weather conditions until it has achieved its required strength. This is particularly important for concrete repairs because the new materials are likely to be subjected to more severe stress from loads and weather conditions than the original concrete. This stress can debond a concrete repair, even after the bonding agent has been applied.
Once the concrete is properly cured, it can be safely opened to traffic. However, it is important that the contractor test the strength of the concrete to determine if it is ready for traffic. Using a concrete temperature and strength monitoring system like SmartRock can help to ensure that concrete is not being damaged while it is still in a plastic state.
