How To Repair Precast Concrete Steps

What to practice when things don't plough out perfectly.

By Evan Gurley

Perfect: "Being complete of its kind and without defect or blemish."

Even the most experienced precaster who follows all the proper mix design procedures and production steps cannot produce a "perfect" piece every time. This is true in well-nigh every industry, not just in precast physical manufacturing. Repair is therefore an inevitable function of nigh every industry.

When something doesn't turn out perfectly, the imperative question is this: When a correction or repair is needed, what advisable action should be taken? The respond should be in two parts: one to address the crusade of the problem, and i to address the trouble itself.

Get to the root of the problem

It is almost always obvious to the naked eye when a trouble is occurring with your concrete structure. Cracking and honeycombing, for example, are easy to spot. But the existent concern is the underlying cause of the problem. Recognizing that a problem exists is not the same as determining its cause. For instance, peachy is seen as a problem, but the crusade of the cracking (improper design, improper stripping/storage, drying shrinkage) will require a more in-depth analysis of the construction.

Earlier attempting any repairs, identify the cause and take corrective measures at the appropriate stage of production. This will increase the likelihood that the problem will not occur again.

In one case you take found and stock-still the crusade of the problem, it's fourth dimension to turn your attention to the problem itself. The b ottom line is to make up one's mind whether to repair the piece or scrap it, merely this requires intelligent evaluation of the cause and severity of the problem, blazon of repair needed, power to accomplish it correctly, available time to properly complete the repair, and price comparisons of repair versus replacement.

Consider these questions:

• Is it possible to repair the product without compromising the effective structural life, performance and integrity of the production?
• Will the price of repairing the product exceed the price of casting an entirely new replacement?
• Will the repaired concrete product meet the artful expectations?
• Will the time constraints allow for proper analysis and an appropriate repair?
• If you lot were purchasing this product for your projection, would you lot be satisfied with the quality of the production?
• Will this repaired product upon delivery affect your company's relationship with the buyer and negatively influence futurity work? What cost do you lot put on that?

After you have considered these questions and decide that repair is the all-time alternative, stride through your standard repair procedure. If you don't have a standard repair process in identify, you are probably non alone – merely it'due south a good idea to develop i. Here is a synopsis of what a standard repair procedure may contain:

• Make up one's mind what is causing the problem.
• Evaluate the severity of harm (classification, major/minor).
• Determine your repair method.
• Set older concrete for repair.
• Utilize repair to the product.
• Let for proper curing of the repair.
• Inspect the repaired concrete.
• Plant a database of files for repaired products and document repairs.

With a standard repair procedure, you tin can consistently evaluate concrete repairs on a case-past-instance basis. Information technology can be used for major too as pocket-sized defects. It is also highly recommended that you have an up-to-engagement physical repair manual.

Major or minor?

Determining whether the defect is classified as major or minor is your next step in the repair process. A qualified person should gauge which defects are minor and which are major. This person must be thoroughly familiar with the production's role and the environment in which information technology will exist.

The classifications of major and small defects are stated in the NPCA 2008 Quality Control Manual for Precast Concrete Plants:

Minor Defects. "Defects not impairing the functional employ or expected life of a precast concrete production shall exist considered minor defects. Minor defects may be repaired past any method that does not impair the product. Repairs of minor defects are essentially cosmetic; in other words, the production would deport as intended without the repairs."

Major Defects. "Defects in precast concrete products that impair the functional employ or the expected life of products shall exist considered major defects. Unless major defects are repaired the product shall be rejected. Major defects shall be evaluated past qualified personnel to determine if repairs are feasible, and if so to plant the repair process. Proper repairing procedures and curing shall be inspected."

Determine your repair method

With sufficient information determining the cause and the classification (major or minor) of the problem, you are now ready to determine your repair method, depending on the type of repair needed.

Major and minor defects require different repair procedures and therefore should be approached differently. Whichever method is used, make the repairs as shortly equally possible subsequently the defect has been noted to minimize the differential shrinkage between the original concrete and the repair concrete. The concrete repair should become an integral part of the production with no delaminations or cracks.

Set up older physical for repair

Thorough, clean and moist – this is the condition that you desire your existing concrete to be in earlier repair. Training of the existing physical for the application of repair materials is an important issue.

If the repair involves some bad concrete, remove the weak materials thoroughly and firmly into sound concrete; stone must fracture and not pull out. Even if you apply the finest repair materials to a concrete production, if the existing concrete is not prepared correctly the results could be substandard. It is essential that the repair material bonds to the existing concrete.

The shape of the repair is also of import. Don't feather the edges; instead, saw cut some depth at an bending to develop a wedge activity for the new material. Dig out enough material behind exposed rebar to allow the new mix to fully envelop the bar (see Figure 1). Make a program to get the cloth where it is needed and to keep it in that location (repairing an underside or vertical side requires different consistency, forming, placing and possibly curing than a peak surface – assuming you can't rotate the piece).

One time the existing concrete has been properly prepared, it must remain make clean and protected from harm until the repair materials tin can be placed and cured. Echo the grooming process if a repair becomes contaminated or damaged. Also, if information technology involves whatever exposed steel, clean any rust or adhered concrete. If you are required to reconstitute galvanized or epoxy rebar surfaces, consult with your bar supplier for specific recommendations; you lot may need to cut out extra concrete to allow more than piece of work space behind the bar.

Epoxy-bonded materials generally piece of work amend when the mating surface is kept dry. For normal repair mixes, the mating surface needs to be well-saturated but free of all continuing or excess water. Mating surfaces that will be repaired with cementitious materials should be in saturated surface dry (SSD) status. The repair cloth should be as dry as possible for workability, just you don't want the substrate pulling moisture abroad from information technology. Think that the moisture is there to hydrate the cement, so keep the surface moist.

Apply repair to the product

Repair of Small Defects. Every bit stated in the NPCA QC Manual, minor defects are essentially cosmetic and are likely to occur more than oft. All the same, if minor defects are routinely seen in your concrete products, you haven't fully addressed the root of the problem.

• Cracking – Small cracks that practice not penetrate down to the steel reinforcement are cosmetic in nature and can be fixed past filling in the cracks with dry cement. The wet in the concrete and in the air will hydrate the cement and make full the cracks.
• Honeycombing – Small honeycomb areas can be cleared of any unsecured stone past chipping or sawing down to solid concrete, bravado or brushing the area clean, and filling in with standard repair materials (see Effigy two). Saw cut the existing concrete is more effective than chipping it out, because the cut lines create a well-defined retaining boundary in which the repair material tin can easily be compacted and consolidated. This standard repair material is what you list on your standard repair procedure. Information technology tin be the same alloy of materials used in the product, or information technology may be your favorite proprietary repair fabric.
• Chipping and Spalling – Chips and spalls are handled in the same routine manner. Spalled corners or edges from rough stripping or treatment are common problems. Spalling is normally a minor defect, but it should serve as a signal that additional training and instruction on production handling may be necessary. When repairing spalling, like the repair of honeycombing, the broken area must be properly prepared before applying repair textile. The nature of these defects well-nigh often involves angular breaks, which have outer edges tapering to thin edges. Since a repair material tin can't be tapered to a sparse edge (it will shrink abroad or fleck off), it is better to saw cutting at the edge of the pause, then cut out a minimum thickness of material to let the repair to have some substance.

Surface defects, whether honeycombing, sand streaking, form joint offsets or spalling, are among the easiest and near common repairs to make. Even though these are minor defects, they must be competently applied and finished. This includes proper preparation of the lacking area, placing the repair material, adequately curing the repair and passably finishing the exposed surface.

Unless you are using a proprietary textile that does not call for information technology, the area to exist repaired must be thoroughly dampened to proceed it from pulling moisture from the freshly applied fabric. Placing a damp burlap sheet or cover with a larger sheet of plastic on superlative and taping the edges to go along in the wet should suffice. The bond force of new physical to old physical develops much more slowly, and the tendency to compress and loosen is reduced by a long, moist curing period. Applying heat to the repaired areas may also be necessary to ensure hardening and strength proceeds.

Later the repair has cured, evaluate the finished surface for appearance. Appearance holds more significance than it should; even if the repair is structurally sound, it won't exist looked upon as a quality production if the repair doesn't look flush and like in advent as the residue of the product.

Repair of Major Defects. Repairs for major defects require the aforementioned training, material selection, workmanship and curing as for small defects. However, according to the NPCA QC Manual, major repairs must exist analyzed by a qualified person; they crave the repair procedure to exist established and written out; they oftentimes crave approval by an exterior agency before work begins; and they must exist inspected (witnessed) and documented. This is another reason to have a standard repair procedure in place.

Repair materials

Many different repair products are on the market, and in fact several businesses are making repair materials specifically for the precast manufacture. Consider several cloth backdrop when selecting a particular repair product. These include permeability, strength, adhesion, corrosion resistance and application method. Base of operations your choice of a repair textile on its intended purpose. If the customer is a land DOT, always make certain that the supplier uses materials that are state canonical for all states in which you supply products.

For nearly applications it is adequate to use the same ingredients from your original mix, but proceed with caution. Concrete used in repairs should be essentially the same as the original concrete, except that the repair concrete should incorporate less h2o. You should employ less water if the repair area is not cut into a nice formed area, and typically it is non. Also, the reduction of water will help reduce shrinkage. The repair batch acts more than like a dry-pack textile that you lot force and hammer into place to gain full compaction (encounter Effigy iii). Another cistron to consider is the size of the aggregate. The maximum size of aggregate should be equally large as possible merely not greater than one-one-half the minimum dimension of the repair.

Consider using a materials supplier that specializes in physical repair. These suppliers have the newest and all-time products bachelor and tin provide you lot with valuable information pertaining to your specific awarding. The repair fabric'due south strength, adhesion, shrinkage, colour and appearance need to exist compatible with the original physical, and this is where concrete suppliers tin help.

A new production that precast concrete repair suppliers are now offering is called "carvable" (shapeable) cement mortar. This production is used for structural and cosmetic repairs. Formerly these cement mortars either fix too fast or likewise tiresome, or they were too light or too night. Now they are offered in iii different fix times of v, fifteen and thirty minutes to meet the needs of a specific project. These mortars also come in different shades of grey to match the color of the existing concrete. They contain no gypsum cement and therefore volition not great when exposed to rain, snowfall and sleet.

Many repair products can obtain high strengths, some at a very early historic period, which is frequently a selling point. Keep in mind that typically the higher the early strength gain, the lower the service life of the repair. This is because the ingredients used to obtain loftier early strengths (Type III cement, accelerators, h2o-reducing agents, etc.) tin can cause shrinkage cracking and can be more than breakable than the concrete it is repairing. As a general dominion use a material with the forcefulness appropriate for the repair.

Later on you lot accept made all the corrections associated with concrete repair, how will you know whether it'due south adequate? Depending on the book of textile prepared, you could make and cure cylinders with the production just as you unremarkably do. Most plants have a cylindrical impact hammer, which evaluates hardness by measuring rebound inside the instrument. This can be used to compare the repair expanse with the base concrete.

The bottom line is that concrete products can't be perfect every time. But the manner in which these bug are handled will reverberate on the integrity of your company and the industry as a whole.

Source: https://precast.org/2010/05/concrete-repairs/

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