Repair & Restoration of Concrete
Failed Concrete Repairs Impact Restoration Success Rate
According to a 2004 research issued by the ACI Strategic Development Council, the yearly cost to owners in the United States to repair, maintain, and strengthen concrete structures is expected to be between $18-$21 billion.
Despite this significant investment by infrastructure owners, the success rate of concrete repairs still must be improved. For example, it has been claimed that just slightly more than half of the repairs completed on US Corps of Engineers facilities are working adequately.
However, there is some good news. Long-term concrete preservation, repair, and restoration IS POSSIBLE when qualified and experienced professionals apply appropriate concrete repair & restoration technology.
Acknowledging the Root of Concrete Problems
It takes time and effort to preserve and extend the life of concrete structures. Many factors can impact the expected life span of concrete structures, including freeze-thaw resistance, alkali-silica reactivity, carbonation, poor original construction, or unsuitable design. Successful concrete repairs begin with a condition evaluation to determine the underlying cause of the problem, with priority given to repair design and implementation.
If concrete damage is caused by reinforcing steel corrosion, the concrete restoration approach should include Type 1 discrete anodes or concrete cathodic protection. If the concrete damage was caused by a chemical attack, the concrete restoration approach should include removing all contaminated concrete and replacing it with acid resistant concrete or Portland cement concrete with chemical resistant coatings and linings.
Process of Concrete Preservation
It takes time and effort to preserve and prolong the service life of concrete structures. Many aspects must be addressed in order to achieve long-term service life extension.
Removal of Bulk Concrete
Concrete removal and surface preparation procedures are also essential parts in the restoration process and can have a significant influence on the lifespan of concrete repairs. Lightweight electric or pneumatic chipping hammers weighing 15 pounds are used to remove degraded concrete without damaging the sound concrete that will be left in position.
Another effective method for removing bulk concrete is hydro demolition, which utilizes high-pressure water blasting. If larger jackhammers or other methods such as concrete scarifies or roto milling are utilized, great care should be taken to remove any microcracked concrete substrate as well as concrete surrounding the reinforcing bars.
Unless a cathodic protection system or electrochemical treatment is applied, concrete removal should continue until the exposed steel no longer exhibits any significant corrosion, even if some sound concrete must be removed.
Simple Concrete Restoration' Geometry
Another significant factor to consider is the shape of the concrete patches. In order to reduce the formation of dying shrinkage cracks in the repair material, which might impact bonding or long-term durability, the repairs should be basic in geometry – rectangular, square, or any mix of both shapes. 1/2 inch to 1 saw cuts are utilized along the repair border to define the patch boundaries and reduce the possibility of thin repairs at the extremities, also known as featheredges.
Materials for Concrete Restoration
When choosing a concrete repair material, there are several aspects to consider. The qualities of concrete repair materials should be defined for the expected application and in-place service environment. To mention a few, repair materials include Portland cement mortars and concrete, polymer-modified Portland cement mortars, epoxy mortars, calcium aluminate mortars, Sulphur concrete, and silicate concrete.
The modulus of elasticity, thermal expansion properties, abrasion resistance, freeze-thaw and scaling resistance, chemical resistance, and setting times will differ for each of them. An epoxy mortar, for example, may have a different coefficient of thermal expansion than the parent Portland cement concrete. This might be a problem with outdoor repairs when temperature changes can put stress on the bond line.
The selected concrete repair material should have attributes equivalent to the parent concrete, such as compressive strength and modulus of elasticity, for structural restorations where the repair material will be loaded in-service.
When shoring is put around columns prior to the repair, this is an example of structural repairs. Most repairs, it might be claimed, are non-structural in character, with greater focus placed on the durability of concrete repair material than physical features. Cracking resistance (drying shrinkage and modulus of elasticity), permeability, and freeze-thaw endurance are all important features to consider.
Bond strength is one of the keys to long-term durability of repairs, regardless of the property required. Bond strength is affected by material qualities as well as application factors such as surface preparation and curing techniques.
Constructability Is Another Important Factor in The Selection of Concrete Repair Material
Constructability is a wide concept that includes handling characteristics, rheology, and cure durations. Pumpability, slump, flow, and hang / stickiness of concrete repair materials vary, and they can be designed for a specific installation procedure such as form-and-pour repairs, form-and-pump repairs, pre-placed aggregate repairs, tremie concrete repairs, dry pack repairs, trowel-applied vertical and overhead concrete repairs, low velocity wet sprayed repairs, and dry sprayed shotcrete repairs.
When there is a requirement for an early return to service, such as bridge deck or parking deck repairs, or to allow coatings and membranes to be changed sooner, a concrete repair material with a short set time might be useful. Ready-mix concrete from a nearby concrete factory is a popular material for concrete repair and major parking deck restorations.
Ready-mix concrete can have a variety of material properties, such as self-consolidating concrete, which provides a well-consolidated mix with a great formed surface finish. Repair materials can also be site batched concrete from a mobile mixer, and many companies provide a wide selection of designed pre-blended bagged repair mortars and concrete.
After installation, the repair material should be kept from severe temperatures. While in the plastic state, repair materials should be shielded from wind, dryness, and freezing temperatures. Curing concrete repair material properly is crucial for preventing moisture loss, drying shrinkage, cracking, and curling. Wet curing and curing chemicals, like new construction, will increase the durability of the repair material.
Implementing a quality control procedure guarantees that concrete repairs are done appropriately. Documenting the repairs with before and after photos, confirming that the surface preparation is acceptable by observing the cleanliness and surface amplitude or direct tension testing, material testing by a qualified testing agency, sounding the finished repair to detect voids or lack of bonding, and direct tensile bond testing of the cured repair material are some basic procedures.
Summary
Because concrete restoration differs from new construction, it is critical to engage with professional concrete repair contractors to guarantee the structural integrity of your building is preserved. A professional concrete repair contractor will have relevant experience in the project environment as well as a decent safety record.
Repairs of industrial plants, cooling towers, parking structures, concrete silos, railroad and DOT bridges, concrete dams, wind turbine foundation repairs, building façade repairs, and the repair and preservation of historic buildings can all have special access and safety needs.
The majority of the work required to preserve and prolong the service life of structures is self-performed by specialty concrete repair professionals. Concrete repair contractors can be general contractors as well as specialized contractors such as post-tensioned concrete repair contractors, structural strengthening specialists employing carbon and glass fiber composites, waterproofing contractors, and cathodic protection contractors.
