Concrete Repair Posts

Crack hiding tips (following epoxy injection)

Posted by John Bors on Tue, Apr 29, 2014 @ 12:04 PM

Can you make epoxy injection repaired cracks in concrete disappear? This is a difficult challenge, but you can take steps to reduce their visibility.

Architectural precast panel manufacturers as well as many concrete repair contractors have developed several techniques when a new surface coating is not the answer.

If the localized area around the crack is stained (from water leaks or dirt deposits), high pressure water blasting or light sandblasting might be the first thing to try. Be careful to avoid altering the surface texture or exposing the aggregate below the surface paste. An alternative stain removal procedure is to use a mild acid micro etch applied on the concrete surface. Although there are proprietary products formulated for this purpose, some specialists swear by a combination of dilute acetic acid (vinegar) and 1 % dish soap which can be sponged and scrubbed into the surface, allowed to soak and then rinsed off.

Assuming the crack requires epoxy injection, be sure to special order a non-tinted resin/hardener combination from us. Normally, our part B (hardener) of the epoxy injection resins is slightly tinted to help provide visual evidence that both components are delivered in proper proportions by the metering pump during crack injection.

ChemCo Systems StripSEAL™ is a great choice for a peelable (easily removed) surface seal (also callestripseal, removal epoxy injection surface seald capseal). It cures quickly and readily strips without leaving a residue. Occasionally, there may be a slight darkening of light surfaces—this can be fixed with a light application of dilute acetic acid as described above.

If the crack is relatively wide (you be the judge), you can pre-place a strip of 1/4” masking tape completely over the whole crack before sealing with StripSEAL. This prevents the StripSEAL from penetrating into the crack walls and allows the injection resin to fill to the level of the surface. This minimizes the shadow created by the indented seal. If masking tape is used, you will have to puncture it at the locations of each surface port in order to connect with the crack.

In concrete crack repair projects where appearance and esthetics are especially critical, you can try a modified dry sack technique. First, you will need to locate some of the smaller (fine) aggregate (suggested max. size 40-50 mesh) used in the original concrete mix or a similarly colored facsimile. Strip the seal no more than 30 minutes after the injection resin has gelled (long before cure, but while the epoxy is still tacky). Then take a small burlap sack filled with the small aggregate and dust the area of the crack until the still tacky glue line is covered. Or the dry aggregate can be scrubbed over the surface using a soft sponge rubber float. The fine aggregate should match the color of the surface and fill in the shadow of the crack as the fine grains are held in place by the tacky epoxy.

For large areas, or surfaces with other defects including bug holes, it may be more convenient to use a wet sacking or parging mix which contains Portland cement, fine aggregates and other admixtures similar to the constituents of the original concrete finish. Prior to performing this type of repair, it is highly recommended to practice on a small mockup placed in a non-visible location.

For more help, call us at ChemCo Systems (800-757-6773).

Tags: peelable injection seal, concrete crack repair epoxy, cracked concrete repair, concrete crack repair

Consider Lifecycle Costs for Concrete Restoration or Replacement

Posted by John Bors on Fri, Jun 15, 2012 @ 11:06 AM

It seems obvious on the surface that repair or restoration of cracked or spalled structural concrete in a stadium, parking deck, bridge, tunnel, dam, dock or runway will reduce ownership costs. But if the underlying damage is severe, it may be more cost effective to tear down and rebuild.

A critical element in this evaluation is an assessment of overall lifecycle costs. This is the time-honored method to determine the best course of action with regard to structural concrete repairs. By considering all aspects of the financial equation, an owner can achieve a fuller understanding of available options. Spending a little more today to fix an immediate problem correctly may considerably reduce the total cost of the structure over its lifespan.

“Life cycle costs (LCC) are cradle to grave costs summarized as an economic model of evaluating alternatives for equipment and projects,” said H. Paul Barringer, P.E. of Barringer & Associates. Inc. “The objective of LCC analysis is to choose the most cost effective approach from a series of alternatives to achieve the lowest long-term cost of ownership.”

Concrete Condition Survey epoxy plus steel for seismic upgrade

Identifying unseen conditions and the extent of damage is a key element in any LCC evaluation. Non Destructive Testing (NDT) is often used by engineers to obtain detailed structural information. NDT techniques include sounding, galvanic pulse testing, ground penetrating radar and in-situ load tests. When more upfront condition detail is available, the engineer can prepare a more accurate remedial cost estimate and it is less likely the owner will face costly change order surprises should he elect a repair option.

A huge repair bill may tilt the balance towards replacement as is the case with some older hospitals in California where state regulations require emergency buildings to meet current more stringent earthquake codes. A major healthcare provider in Los Angeles, for example, recently demolished two large buildings erected around 30 years ago and is rebuilding. The high cost of improving the structural elements of these facilities to meet current seismic standards was one of several factors which led management to select the replacement path.

In some cases, replacement may prove to be the better option for an older structure with only a few years left before the design life ends. In all instances, it is prudent to hire an engineer for a structural lifecycle evaluation and condition survey. If the damage is not disruptive to the entire structure, often the best option is to repair.concrete spall repair testing

Take the case of San Francisco Airport, which has taxiway lights embedded in concrete structures. When the concrete collars for these lights began to fail, the airport tried a quick setting cementitious repair material which failed to eliminate the problem. Faced with a live heavily used aircraft taxi lane, it considered all options for further repair or complete replacement. In this case, it chose a proven solution capable of being injected in harsh loading conditions: a customized epoxy formulated specifically to cope with the difficult working conditions and without compromising concrete integrity. “The ChemCo epoxy stabilized our taxiway lights and eliminated further deterioration,” said Charlie Freas, a civil engineer at San Francisco International Airport. “This proved to be the right decision in the long term, both financially and structurally.”

The airport has since used similar epoxy formulations to repair cracking in parking structures, service tunnels below groundwater level, and the airport’s light rail system, as well as for concrete spalling on taxiway aprons and ramps.

With regards to pavement concrete spall repair, the airport is constantly inspecting its runways, aprons, and the surrounding concrete infrastructure for any signs of degradation in order to avoid flying object damage (FOD) which can cause catastrophic damage to jet engines. “As concrete spalling can be substantial at times and the consequences so significant, we would rather replace an entire concrete section than be faced with the possibility of having to buy a new airplane engine,” said Freas. “However, we have confidence that effective epoxy spall repairs provide the flexibility and strength to support our planes without further spalling.”

Factors to Consider for Concrete Restoration

Freas pointed out that lifecycle costs may not be the only factor to take into account when it comes to the repair versus replace question. In some instances, the airport needs to realign a runway or change the grade, at which point all associated concrete areas may be completely removed and replaced.

concrete crack repairSimilarly, the Port of Oakland in California has to look beyond the subject of lifecycle costs for certain structures. One tenant, for instance, utilized an 80-year-old wharf complex for container crane operations. While the wharf clearly needed to be rebuilt, the port had no temporary site available. Repair was the only possibility.

Another time a tenant dropped a 60-ton piston from a height of 100 feet onto a wharf resulting in severe damage. In this case, lifecycle costs favored repair. The port harnessed epoxy injection for concrete crack repair of the wharf deck and soffit (underside). “I’ve inspected the wharf below sea level and the ChemCo Systems customized epoxy prevented any corrosion of the rebar, returned the structure to its original strength and extended its lifespan,” said Bill Morrison, Manager of Harbor Facilities for the Port of Oakland. “After many years, these wharves are still operating as designed.”

Repurpose for Changing Times

A recent fast-growing trend is to find and adapt new uses for vacant buildings or structures that have remaining useful life. Governments world-wide are passing new regulations and may offer monetary incentives to recycle or adaptively reuse existing buildings rather than choosing demolition. This is already happening widely in the U.S. where the practice is often referred to as brownfield redevelopment. In China’s large cities, owners are rewarded with financial incentives if they agree to convert an old hotel into condos or an aging office structure into a warehouse. Several former parking decks have been transformed into computer server farms in Beijing after exterior shells were revamped.

This repurposing trend for existing buildings is a high growth element of the sustainable construction movement and is beginning to eclipse new construction in urban areas of North America due to architectural preservation, environmental and waste disposal concerns.

 Whether you elect to repair, restore or replace concrete, do it right, select the correct materials and consult an engineer who can help you evaluate your options from a lifecycle perspective. Call or email us at ChemCo Systems if you need help with concrete restoration, repair or protection.

Tags: cracked concrete repair, concrete restoration, runway epoxy, concrete spall repair