The complete replacement of faulty concrete should always be a last consideration. Although there are still occasions where removal is necessary, such as an old, badly broken sidewalk, for example, most concrete structures are rarely beyond repair. Because of the more recent introduction of specialized repair products and their methods of application, problem concrete can be restored and made stronger and more durable than the original.
The unlimited selection of repair products available makes choosing the right one for the individual problem important. These products are sold in a wide range of prices, and it is not always necessary to purchase the more costly product when a less expensive one will solve the problem.
How long a repaired area will remain serviceable will depend on the exposure to which it will be subjected. Also the location of the problem will determine, to a large degree, the product for best results. One material used by Concrete Salt Lake City to repair a honeycombed area on a vertical surface may be a poor choice for a scaled floor. It is for this reason that there is such a wide selection of manufactured materials formulated for special purposes.
The repair of concrete cracks is probably the most common. They are caused by a variety of factors. There are two classes of cracks: active and dormant. A dormant crack, such as a drying shrinkage crack, is one not likely to change in character, and may well be ignored. Cracks that increase in length and width or show movement under loads are considered active. Such cracks should be repaired as soon as they are noticed, to prevent their development of a serious problem at a later age.
Unfortunately, cracks are caused by so many different conditions that the reasons for their appearance are not readily determined. Some are created while the concrete is in the plastic state or during the initial set, as a result of one or more of the following:
1. Settlement due to unstable subgrade
2. Subbase paper rupture
3. Poor form construction
4. Lack of, insufficient, or improper placement of reinforcement
5. Rust on reinforcement steel
6. High-slump concrete
7. Improper or insufficient vibration
8. Lack of curing
9. Volume change due to settlement of solids in plastic concrete
10. Heavy ground vibration nearby, such as from a pile driver
11. Stripping forms before the concrete has cured sufficiently
12. Lack of or insufficient expansion and control joints
The decision on whether or not to repair some of these cracks will depend, to some extent, on the subsequent use of the faulty concrete area. A dormant crack on a concrete floor which is to be covered by tile or a carpet requires little or no attention. This same type of crack appearing outdoors should be repaired to prevent its becoming active under adverse weather conditions. Indoor surface cracks are less likely to become more serious under normal conditions than would outdoor cracks that are subjected to greater changes in volume. Call Concrete Salt Lake City for any concrete repair needs.
Although some cracks develop during or shortly after concrete placement, others appear weeks, or months, after the concrete has hardened.
Frequently, these cracks are due to loads applied before the concrete has gained sufficient strength to sustain the imposed stress. When 3500-psi concrete is placed, it is not expected to reach that compressive strength until a month later under normal conditions. In cold weather, which is unfavorable to proper curing, it may be 6 weeks or longer before that strength is reached. Concrete has low flexural strength, seldom above 650 psi, which is related, to some degree, to the compressive strength. If both the above factors are kept in mind, it is easy to see that a load on a concrete floor before it has reached its full required strength may well cause cracking. After the initial volume change in plastic concrete, which results from some settlement of solids, and the loss of some of the mixing water due to evaporation, concrete will continue to change in volume in the hardened state. Changes in temperature, freezing and thawing, exposure, and wetting/drying cycles create concrete volume change. The lack of or improper placement of control and expansion joints where volume changes are excessive will create unnecessary cracks. Concrete placed on frozen subgrade, nearby blasts, improper vibration, and other influences in combination cause problems in hardened concrete.
When the concrete crack presents a serious structural defect, the cost of the repair product should not be considered if the material chosen can permanently cure the problem. Here, one might consider epoxies. One epoxy product, specially manufactured for such a problem, has worked very successfully over the years. Concrete cores taken from a repaired section of the crack had strengths higher than cores taken from a nearby sound section of the same area. The particular epoxy mentioned here is a two-component system, which produces a 100 percent solid, modified epoxy resin which is injected into the crack and is self-bonding. True, the process is more expensive than some others, not only because of the cost of the material but also because of the method of application. Special entry ports for the injection of the material are installed, where required, along the line of crack. The port-free areas are sealed on the surface of the crack with a special hydrostatic cement paste to prevent leakage. After the crack has been prepared, the resin is injected into the ports, under pressure, until the entire crack has been filled. Later, the ports are removed, and the crack area is ground to an even surface. A big advantage in the epoxy systems, as with magnesium phosphate cements, is the ability of these repair products to be applied in temperatures below freezing. Some epoxies permit their application to moist, wet, and dry surfaces. They harden rapidly and have been used successfully underwater in the repair of dams. However, the use of most epoxy products requires the employment of knowledgeable concrete contractors familiar with the various products, the proper preparation of the problem surface, and the correct method of application.
PREPARATION OF REPAIR AREA
Regardless of the repair product selected, the success of the project will depend not only on the material used but also on the preparation of the area to be repaired. Both improper surface preparation and failure to follow the manufacturer’s recommendations for the use of the product are sure to guarantee a short life of the cure. Recommended procedures for proper surface preparation are listed:
1. All loose material in small areas, such as chuckholes, should be removed with the use of pneumatic hand tools. Broom and vacuum the hole for the bonding agent to follow.
2. On large areas, such as worn or scaled surfaces, the old surface can be cleaned by sandblasting or water blasting, by using a jackhammer, by being scarified, or by scabbling.
3. All dust and debris must be removed to assure good bond of the repair material. The use of brooms, water blasting, and/or air blasting will usually produce the desired result. When brooms are used, however, it is a good additional insurance to vacuum the area for the removal of very fine dust particles.
4. The problem area must be cleaned of any old existing coatings. Remove all oils, greases, dirt, and wax solutions. If the old surface is only slightly soiled, the use of chemical surface-cleaning agents may be sufficient. These surface cleaners should be washed off thoroughly after use with soap and water, then hosed down.
5. Paint deposits or bituminous materials are best removed by Flame-treating.
For any needed concrete repairs in the salt lake city area please call Concrete Salt Lake City.