It's the second most common man-made material after potable water. There's about a cubic yard of it placed every year for every man, woman and child on the planet. It's hard to look anywhere and not see it. If you haven’t guessed, we are talking about concrete.
You would think we know everything we need to know about this ubiquitous, ages-old building material, but as technology and formulations continue to evolve, the regulations surrounding how we use and repair it evolve as well.
Which brings us to the recently updated ACI 563 specification for the repair of concrete in buildings. We got in touch with Fred Goodwin. A concrete guru and head of BASF’s Construction Chemicals Corrosion Competency Center. Goodwin also played a role in developing and writing the updated specification — who better to help us wrap our heads around how these changes affect the way we work?
BASF Insights: First off, what is the difference between a specification and a regulation or code?
Fred Goodwin: This is a reference specification so it's written in mandatory language. And it is intended as the instructions that a specifier would provide to the installer. Codes provide guidance from the building official to the specifier and address life safety issues.
BI: Is it mandatory to follow the specification?
FG: That's correct, if it is required by the specifier. There's a mandatory requirements checklist and an optional requirements checklist. The mandatory requirements indicate things like the owner-approved work areas schedule requirements, the required certifications and experience, specific repair procedures, and tests required to be performed by the owner's testing agency.
BI: Are there any optional components?
FG: The optional requirements are choices such as designated tool and equipment storage areas, the contractual requirement to submit a quality control plan and timing of the plans submission, if other testing services will be provided, and to indicate when compressive test specimens are to be tested if other than at 28 days.
BI: Why did this need to be created? Don’t we already have good specifications?
FG: ACI 563 was created as a companion document to existing specifications meant for new construction. ACI 318 the code and ACI 301 is the accompanying specification for structural concrete for new construction. Likewise, ACI 562 is the code for repair, and ACI 563 is the companion specification for repair. ACI 563 provides a series of steps that need to be performed in order to assure a minimum level of quality and acceptance of concrete repair.
BI: What does ACI 563 mean for a contractor?
FG: It tells the contractor the he must submit product data sheets and certifications to include performance data, including safety data sheets. He also must submit supplemental testing data indicating compliance with the specified requirements and that mock-ups can be used for verification of performance of the material. It has a provision for substitution of materials, so if the contractor does not want to use one product, it gives them the opportunity to change products. Chapter 8 states the product testing data must be documented in a fashion that can be verified for proprietary products.
BI: Why is this important for a contractor?
FG: If there's doubt as to the performance of the material, verifiable test results provide a level of assurance that the material is doing what it should. In-house methods and modifications that are not documented do not provide the opportunity to independently verify performance.
BI: If there is a problem with the work and a contractor hasn’t followed the standard, what can happen?
FG: This is often when lawyers get involved and everybody wants money or to tear it down and start over. If there is a specification that is accepted by the industry and it was followed, a contractor is on solid footing. If somebody's not following the rules, then they're liable. The code and specification define the rules.
BI: Do you expect 100 percent compliance with this specification?
FG: The construction industry is conservative, but this is a set of rules that, if required by the specifier, will assure a higher level of performance. There have been studies showing that as much as half of all concrete repairs are performing less than satisfactorily after a few years.
BI: Wow. That’s significant. What causes this subpar performance?
FG: It's several factors all working together. First, when a new structure is built there are two kinds of defects — patent defects and latent defects. Patent defects are immediately observable and addressed during the walkthrough inspection after completion. Latent defects are hidden defects. For example, the reinforcing steel is too close to the surface, or improper construction will produce cracking in a certain pattern, or the subsoil was not adequately compacted, resulting in settlement that will eventually occur.
BI: Which is more common?
FG: Both are common, but a lot of repairs are triggered by latent construction defects. We ignore the symptoms and deterioration progresses until it gets bad enough that we must do something. By then, the structure is already in distress and it's a whole lot harder and more expensive to fix.
Then there’s the quality of the repair itself. Is the correct material selected? Is the selected material compliant with industry specifications? Is the material installed and is it inspected correctly? And is it maintained? If all of those if statements are true, then a lot of good things happen but they often are not.
Concrete is an amazing material in that nothing usually happens dramatically or rapidly deteriorate. When a concrete structure fails dramatically, it makes the news, like a bridge collapse. That doesn't happen very often.
BI: If concrete has been around so long, and is still functioning, how is it that our newer concrete degrades?
FG: There's a nice synergy that happens between cementitious materials and steel. Cementitious materials are very alkaline, or have a high pH. Steel doesn't rust at a high pH, but that high pH will not remain high after decades of exposure. When it falls, the steel will start to rust. When the steel starts to rust, it creates an expansive force in the concrete, causing cracks to form. Once cracks form, everything goes downhill in a hurry.
FG: The other thing that causes corrosion are certain types of ions. The bad actor really is chlorides, the most common de-icing chemical. The public will not tolerate ice on bridges, and the cheapest way to remove ice from bridges is to put salt (sodium chloride) on them. We also call it “bridge eraser” because it makes the steel rust and the bridge to deteriorate.
BI: What about water? Concrete is made with water but we know water also degrades it. Why?
FG: You have to have it for the cement to hydrate but once the cement has cured (or reacted), the objective is to keep water out. That's why we have coatings and sealants and membranes and a lot of other products. We're just keeping the water out of concrete. The measure of the ability to keep water out is permeability. One has to keep water in the concrete as strength increases with time in the concrete. But once enough strength has developed, we need to keep water out because free water in concrete can expand and cause freeze-thaw deterioration. For corrosion to occur, you have to have moisture present in the concrete as well. When chlorides move into concrete, they move in with the water. Many other deterioration mechanisms in hardened concrete also involve the presence or movement of water.
Looking for help navigating your next round of concrete repairs? Connect with a BASF expert to find out how best to meet the ACI 563 requirements.