It seems a no-brainer on the surface: Repairing cracked or spalled concrete in a stadium, parking deck, bridge, tunnel, dam, dock, or runway is an obvious solution to keep ownership costs down. But if the underlying damage is severe, it may be cheaper over the long term to tear everything down and rebuild.
The missing element, in many cases, is an assessment of overall life-cycle 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 reduce considerably 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,” says H. Paul Barringer, PE, Barringer & Associates Inc., Humble, Texas. “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
Identifying unseen conditions and the extent of damage is a key element in any LCC evaluation. Non destructive testing (NDT) often is 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 toward replacement—as is the case with some older hospitals in California where 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 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 that led management to select replacement.
In some instances, replacement may prove to be the better option for an older structure with a few years left before the design life ends. In all cases, it is prudent to hire an engineer for a structural life-cycle evaluation and condition survey. If the damage is not disruptive to the entire structure, often the best option is to repair.
Take the case of San Francisco International Airport, located on the Bay, which featured some taxiway lights embedded in concrete structures. When the concrete collars for these lights began to fail, the airport tried a quick setting repair material, which failed to eliminate the problem. Faced with a live and important aircraft taxilane, it considered all options: 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 epoxy stabilized our taxiway lights and eliminated further deterioration,” says Charlie Freas, a consulting 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. Groundwater infiltration is a constant challenge as it increases pumping costs and wear. With regard to pavement spalling, the airport frequently inspects 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 engine,” says Freas. “However, we have confidence that effective epoxy repairs provide the flexibility and strength to support our planes without further spalling.”
Factors to consider
Freas pointed out that life-cycle 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 redone.
Similarly, the Port of Oakland in California sometimes has to look beyond the subject of life-cycle costs for certain structures. One tenant used an 80-year-old wharf complex for container crane operations. Although 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, life-cycle costs favored repair. The port harnessed epoxy injection for the wharf deck and soffit (underside).
“I’ve inspected the wharf below sea level and the customized epoxy prevented any corrosion of the rebar, returned the structure to its original strength and extended its lifespan,” says 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
Another important trend: Governments worldwide passing regulations and offering monetary incentives to recycle or adaptively reuse existing buildings rather than choosing demolition. This is already happening widely in China’s large cities where owners are rewarded if they agree to convert an old hotel into condos or an aging office structure into a warehouse. Parking decks have been transformed into computer server farms in Beijing. 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 or replace, do it right. Use the correct materials and consult an engineer who can help you evaluate your options from a life-cycle perspective.
John Bors is vice president of ChemCo Systems, Redwood City, Calif.