Rethinking concrete: Proactive methods and materials for the 21st century

by Samantha Ashenhurst | July 16, 2018 10:24 am

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by Chris Bennett, CSI
In the classic 1967 film, The Graduate, the character Mr. McGuire famously tells Benjamin Braddock one word: Plastics. This iconic scene refers to a then-new material affecting all aspects of life. Plastic was everywhere; it wrapped food, replaced wooden toys, swapped out metal in automobiles, and displaced cotton thread in Fifth Avenue fashion.

This cultural change also manifested itself in the construction industry, not least among which was concrete. Acrylics, epoxies, and various ethylene-based materials began to enter the construction landscape in the 1960s. Even the marketing around concrete in construction was modified to encourage “plasticity.” Designers were influenced into employing high-range water reducers that went by the modern and keenly American-sounding name, “superplasticizer.”

At that time, construction methods gained a speed and flexibility with “plastic.” However, it is now apparent replacing cement, rock, and water with plastics has unanticipated negative effects, such as shorter life cycles as a result of deterioration and corrosion, which have affected buildings, bridges, and highways. (For more, click here[2].) The concrete of The Graduate’s era has not proven to be resilient, as is evidenced by the colossal budgetary allocations governments have requested for infrastructure repair. (For more, click here[3].) Building professionals compound this problem by adding even more plastic-based materials—epoxy skim coats above, vapor barriers below, and all manner of patch and repair materials in-between—when concrete fails.

In fact, tens of millions of acres of concrete are wrapped in “plastic bags” today, despite obvious negative effects to the environment (from using fossil fuels) and a property owner’s checkbook. Fears of failure and risk responsibility are partly to blame, but there are also those who have taken advantage of this fear to foster the continued use of 50-year-old slab designs that use plastic, now a billion-dollar commodity industry in concrete.

Fortunately, many discoveries have advanced the concrete sector in the last 50 years, with millions of square feet standing as evidence to post-1960s engineering and science. This article will briefly touch on a few technologies making a significant impact in lowering the use of plastic in the field of concrete: reactive copolymerizing solids (RCS), thinner control joints, hydro-demolition, and corrosion inhibitors.

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Reactive copolymerizing solids
Concrete’s strength comes from calcium silicate hydrate (C-S-H). It is sometimes referred to as the “glue of the built environment.” Traditional concrete is quite porous, allowing moisture, vapor, and contaminants through the open spaces in the C-S-H, and can necessitate the use of additional materials (e.g. plastic) to make up for this weakness. RCS describes a technology type that reacts with concrete to naturally close those spaces and encourage growth of additional C-S-H throughout the material’s life cycle. It is mostly employed in commercial applications but can be applied topically to any existing concrete surface or as an internal cure in new construction, eliminating the requirement for all additional curing methods and materials by making the concrete itself control water loss.

Builder Meyer Najem (CallisonRTKL and BSA Life Structures) employed integral RCS solutions to eliminate moisture mitigation products at the 11,334-m² (122,000-sf) Community Cancer Center North in Indianapolis, Indiana. This technology contributed to cost savings during initial construction. Additionally, due to less vapor transmission, early strength gains in the concrete allowed for mobilization of other trades on an accelerated schedule—tile installation began 72 hours after the slab was poured, and complete polished floor sections were finished within seven days. By taking eight weeks off the construction schedule the project team was also able to positively impact the environment by lowering the use of diesel generators for equipment and lighting. The cancer center will also operate with lower maintenance costs because of a stronger concrete matrix.

Brian Harlow, vice-president at Fiat Chrysler Automotive (FCA), decided to move away from epoxy-coated floors for both operational and sustainability considerations. With more than 18-million m² (200-million sf) of property under his care, this is understandable. By using an RCS technology at the award-winning Kokomo Casting Plant (KCP) in Indiana, FCA put an end to the need to routinely strip, prep, and repour epoxy, as the concrete itself can now be made to prevent hydraulic fluids, oils, and other contaminants from entering the automotive facility’s slabs.

In New York City, constructing Adidas’ flagship location downtown on Fifth Avenue meant contending with build-outs as well as maintaining the original building’s existing finishes to reduce the need for new materials. RCS was applied topically on both new and existing slabs to create a sustainable floor in an aggressive “Big Apple” timeline. Adidas AG and architect Gensler NY received many awards for this project, including the 2017 Retail Week Interiors Awards for best international store. However, a more significant reward was realized by reducing the project’s carbon footprint with a decrease in material usage.

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Thin joints
Control joints are necessary in concrete slabs to control the cracking that occurs as the new slab moves due to thermal and volume changes while it cures. The 1960s-influenced concrete contracts or shrinks at a rate of nearly 25 mm (1 in.) per 31 m (100 ft) as it cures. While modern curing systems are less susceptible to volume changes, they are still at the mercy of thermal factors. Traditionally, most of the contraction happens in the first 90 days, but concrete continues to expand and contract with changes in temperature and humidity many years after being poured and placed.

Control joints are typically cut as soon as the slab can support the weight of the equipment and the saw operator to help reduce random cracking. However, the control joints raise additional maintenance considerations throughout a facility’s life cycle. With hard-wheeled traffic from pallet jacks, loading carts, and forklifts as well as foot traffic, control joints are subject to abuse, resulting in maintenance costs for owners. This is especially true in industrial and distribution warehouse facilities. It is not uncommon for some property owners to complain that more than 70 percent of their floor maintenance costs come from having to constantly clean and repair joints.

The standard control joint blade for many years was around 3 mm (¹⁄₈ in.) wide because the technology did not exist to make them thinner, but the late engineer Art McKinney, PE, SE, a fellow at the American Concrete Institute (ACI), pioneered the use of the now more common thinner control joint blade (around 1.6 mm [¹⁄₁₆ in.]) in North America. (The author worked with Art McKinney, PE, SE, on a number of large projects where “skinny” or “thin blade” technology was utilized.)

McKinney’s premise is thinner joints in a working facility better distribute the weight of rolling loads, thus reducing the amount of wear and tear on the joint areas. Minimal damage to joints means they last longer, so owners spend less time, materials, and money repairing these areas. Further, thinner joints require less joint filler material. This might not seem like substantial energy and material reduction to the carbon footprint of a facility, but hundreds of millions of acres of concrete slabs are being created. This change could influence millions and millions of lineal feet of joint space. The healthy impact to our environment by using half the “plastic” of current methods in this area of construction—achieved by simply making control joints half as wide as is currently being done—could be very substantial.

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Water
Concrete is the world’s second most used material in construction. Water is the first. Water reacts with cement and aggregate to create concrete but it is also essential for the material’s demolition or refinement. Hydro-demolition technologies use high-powered streams of water to remove concrete. Unlike mechanical demolition using tools like jackhammers, hydro-demolition removes material on a bridge, road, or building without creating micro-fractures in the surrounding matrix. This helps the concrete structure to remain intact longer while reducing the need for patch and repair materials.

Water is also essential in refining existing concrete surfaces. When the contracting firm Desco took on the task of surface preparation and architectural concrete floor installation at a 55,741-m² (600,000-sf) Rolls Royce facility, a wet refinement process was chosen to reduce material use and meet the client’s schedule. Polishing the floors dry would have meant using additional latex and epoxy grouts and potentially heavy coats of acrylic sealers as well as the extra time and labor necessary for installation.

There are additional benefits of a wet polishing. The accelerated installation means reducing the operation of diesel generators and their impact on our air while powering commercial grinding and polishing equipment. The air at the worksite is made safer in another way by trapping silica on the surface of the concrete in a slurry instead of letting it become airborne. (Click here[9] for Occupational Safety and Health Administration’s regulatory requirements.) Dry polishing requires specialized air filtration systems and frequent filter cleaning to reduce the amount of silica dust making its way into the air. Additionally, Occupational Safety and Health Administration’s (OSHA’s) new regulatory requirements can mean heavy fines for contractors and even jobsite shut downs.

“Grinding wet means we know we will always maintain a safer worker environment and be able to meet OSHA’s new regulatory requirements on allowable airborne silica, and finish fast. We do not cut or polish dry anymore,” says Brandon Godbey, head of Desco’s polishing division.

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Cutting-edge technologies
At the National Center for Education and Research on Corrosion and Materials Performance (NCERCAMP) at the University of Akron in Ohio, David M. Bastidas, PhD, and his colleagues from the chemical and biomolecular engineering department are advancing another type of eco-friendly concrete science at the micro level. Although still in the early stages, studies related to smart micro-encapsulated corrosion inhibitors are investigating concrete corrosion, specifically in areas where steel rebar makes contact with the concrete matrix. Corrosion is reduced by using time-released “pills” containing natural colophony (rosin) from California pines. Rosin or “Greek pitch” is a solid state of resin made from pine and other coniferous trees. This system of limiting the corrosion and degradation of concrete comes from allowing the progressive and efficient release of resin inhibitors throughout the life cycle of the concrete.

Corrosion inhibitors are one of the most efficient methods to prevent corrosion in concrete, but historically they have been plagued by high cost as well as the contaminant nature of some of the compounds themselves. This upcoming technology is attractive because unlike concrete corrosion prevention from the 1960s the micro-encapsulation in the natural resin coating makes it environmentally sustainable as well as effective. The corrosion inhibitors consist of a core-shell structure containing combinations of hydroxides and nitrites from different metals, forming a microcapsule. The inhibitor releases according to the pH of the surrounding matrix and the presence of aggressive agents like chlorides and carbonates. This could mean substantially less “plastic” in many reinforced concrete structures while still enjoying the benefits of inhibitors. Since the pine resin is not soluble in water (it has a hydrophobic nature) it will only react with corrosion agents and not simply in the presence of moisture. (A more in-depth overview of this technology will be presented later this year at the concrete symposium at University of Akron’s NCERCAMP. Visit www.uakron.edu/ncercamp[11] for details.)

Conclusion
Concrete production makes up six to eight percent of total manmade greenhouse gasses (GHG). (For more, click here[12].) Further, many of the raw materials for several epoxies and resins used in coatings and patch material are largely derived from petroleum. The carbon footprint is substantial. The effect after 50 years of employing The Graduate-era concrete methods is bridges are falling apart and buildings are cracking. Building professionals understand replacing the elements creating C-S-H (water, aggregates, and cement) has a cost.

It is not to say plastics are not useful or do not have their place, for they have, of course, been helpful in many ways. When building a waste water treatment plant and designing spaces to house fluoride tanks, one must have epoxy coatings on the concrete floor or soon the facility will not have any concrete at all. The author is not questioning the function of plastic, rather if its use is necessary at all times, given the high stakes regarding construction costs and the environment and with successful alternative technologies being readily available. For example, the concrete in the lobby of the waste water treatment plant does not need the same coatings as the tank room.

All of us would like to see concrete last longer, enjoy a smaller carbon footprint, and require less material waste. This will not happen by maintaining the same 50-year-old benchmarks in construction documents. It will not happen by avoiding hard conversations or repeating mistakes of the past. However, it can happen by exploring new possibilities, beginning new conversations, and learning from each other. To paraphrase Mr. McGuire, there is a great future in concrete.

Chris Bennett, CSI, is a construction consultant specializing in contractor training, specification writing, and building technology development for MasterFormat Divisions 03, 07, and 09. Bennett can be reached via e-mail at chris@BennettBuild.US[13] or via Twitter @BennettBuild.

Source URL: https://www.constructionspecifier.com/rethinking-concrete-proactive-methods-and-materials-for-the-21st-century/

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