July 8, 2022
By Bill DuBois, CSI, CCS, AIA, and Chris Bennett, CSI, AIA
Construction documents need to be clear, concise, correct, and complete—but is this enough to fend off the twists and turns of executing the contract for construction? One may begin with the very best in design intent, but it is the responsibility of the entire project team to understand and adhere to this for it to become a reality. Too often, team members will alter the intended design from lack of understanding the material or even to accommodate their own business advantage. Construction administration is critical to ensure the design intent is achieved and owners are properly protected.
To demonstrate the humanistic aspect of construction, this article makes an analogy between two complex assemblies of infrastructure—the human body and a constructed facility. Both exist to support life, have a life cycle of their own, and require planning and nurturing before they can take on productive roles. With a little creative flexible thinking, Figure 1 shows the comparisons, while Figure 2 (page 24) offers another analogy—CSI’s facility life cycle process and a possible life cycle of a human being. Similarly, a facility and certainly its concrete must be well-configured with a healthy foundation to increase the chance for a successful, long life.
While the authors could go on examining how buildings compare to biology, that is another story being developed by the field of biomimicry. Instead, this article focuses on the facility’s design intent around Division 03, one of the “muscular/skeletal” systems. To start off on the path of being strong and healthy, and living a long, prosperous life, a person requires a strong foundation of bones and muscles to carry them through. In the built environment, concrete and concrete flooring systems are essential in maintaining a strong facility life.
One of the unforeseen gifts that came with the popularity of polished concrete was the realization of how poorly concrete is built. With the demand of polished concrete floors growing, finishes like carpeting, tiles, and epoxies were removed in many buildings—in frequent cases, this enabled project teams to see right underneath the skin, the building was an infected, unhealthy environment. Suddenly, questions arose:
Many ideas have been offered to resolve these problems, but they have proved only to be temporary solutions, merely addressing the symptoms of a chronically unhealthy system and not the root cause. To make matters worse, industries have sprouted up around creating such stopgaps, taking away the incentive for suppliers and contractors to meet a healthy, sustainable design intent. This includes a variety of clear coating topical finishes which mimic polished concrete, but do not provide the same performance.
One of the first places to see these problems was flooring, which takes the most physical abuse in most spaces. With the help of gravity, it collects the most dirt and debris, requiring the most routine maintenance. The traffic atop the slab from hard-wheeled equipment or children’s snow boots crusted with rock salt on school floors compounds the abuse.
|Project conception||Parents think about starting a family|
|Project delivery||Approach the method of birth|
|Design||A child develops through stages of growth and elementary education|
|Construction documents||A young adult matures in high school to learn the basic skills and get a sense of direction|
|Procurement||College selection and settlement on cost|
|Construction||College education to build a career|
|Facility management||Healthy adult lives, filled with purpose|
Concrete should be able to address these issues for flooring. When done correctly it is durable and long lasting and there are the additional esthetic benefits that should also be built to last. Concrete can be dyed, stained, integrally coloured, textured, or polished. Broken glass, seashells, marble chips, and other media can also be introduced into the concrete matrix to expand the visual possibilities.
However, for a concrete floor to be as maintenance friendly as possible and maintain its original appearance, it must be non-absorptive to resist moisture, dirt, and movement from changes in volume. A facility cannot maintain its clean and healthy status when the floor is dirty or unable to be resilient to abuse.
Verification and definitions (or lack thereof)
The Ancient Romans figured out how to make concrete resilient and sustainable—the evidence remains standing today (Figure 3, page 26). However, specifying the physical properties of exposed concrete flooring seems to remain a nebulous challenge. This is primarily because the industry has not had a clear way of quantifying the exact definition of polished concrete.
According to the International Polished Concrete Institute (IPCI):
Polished concrete is a process which enhances the natural beauty of existing concrete by hardening and applying a sheen to the concrete. There are two primary methods to create this sheen: Topical or Mechanical.
However, this can be vague. Traditionally, it has been entirely up to the contractor to deliver a shiny floor by means of a prescribed process, but polished concrete is not simply “a shiny floor.” There are inherent understandings in polished concrete’s performance such as abrasion resistance, stain resistance, coefficient of friction, and life cycle maintenance. The owner is not only expecting a shiny floor. Who is to argue, given a vague specification focused only on esthetics which prescribes a process rather than a quantifiable and verifiable result? Polished concrete also requires more than esthetic benchmarks to protect against substitutions.
Defending design intent
The goal is an esthetically pleasing, durable, easily maintainable, slip-resistant, sustainable, and resilient floor. Taking the steps explored in the following section, these attributes can be established by way of the specifications and verified in the field.
It takes a good slab that has been placed correctly to get controlled results. Flatness is important—one will not be able to get an even and consistent appearance if the slab is wavy and improperly cured. This is particularly true when a “cream” finish with minimal aggregate exposure is desired.
Aggressive grinding, at additional expense, to expose more aggregate can even out the appearance, but does not guarantee the desired look. In fact, it forces the owner to accept another level of aggregate exposure. Sheen is also an esthetic that can be achieved ranging from a dull/matte finish to a highly polished/mirror-like glossy finish. Of course, the shinier the finish, the more noticeable the flatness. However, it is important to keep in mind “shiny” is not the definition of polished (or refined) concrete; in many cases, a highly reflective finish is inappropriate. For example, a highly reflective floor in a restroom compromises privacy between stalls.
By specifying the industry standard for floor flatness and floor levelness, ASTM E1155, Standard Test Method for Determining FF Floor Flatness and FL Floor Levelness Numbers, an appropriate degree of flatness may be specified to suit the function and esthetic of a space. Higher flatness/levelness numbers are easier to achieve with better concrete curing, and for polished concrete, this generally means wet curing or internal curing with nano silica-based supplementary cementitious materials (SCMs) (hydro cements, nano infused cements [NIC], certain colloidal solutions, etc). Using a standard cast-in-place specification will also potentially land a project in trouble, as those slabs are not generally built to maintain higher standards in Ff/Fl. Specifiers may also want to expand their approach with Ff/Fl benchmarks by expanding language to account for smoothness.
Early methods of specifying exposed concrete surfaces were based on “grit levels,” and then later measuring reflected light (and its clarity) from the floor. However, this has proved too subjective, often unintentionally distorting original design intent with Division 09 coating substitutions also able to meet these benchmarks. While gloss measurements are useful in understanding esthetic benchmarks, measuring the surface refinement of the concrete itself requires taking measurements of the surface with Averages Roughness (Ra) measurements. With the help of standards like ASME B46.1-2009 (R2002), Surface Texture (Surface Roughness, Waviness, and Lay)3 easy to measure physical benchmarks helps create a common language and direction for specifiers, contractors, and the entire project team. As an example, a project could require a minimum Ra of 0.6 to 0.4µm (24 to 16µin) on flat polished surfaces, 0.9 to 0.7µm (36 to 28µin) for inclined polished surfaces and then select a sheen and image clarity level from ASTM D5767-18, Standard Test Method for Instrumental Measurement of Distinctness-of-Image (DOI) Gloss of Coated Surfaces, to satisfy certain esthetic requirements (matte finish 10 to 45 per cent, semigloss 46 to 75 per cent, glossy 76 per cent and higher). Now, the design decision-maker and contractor have a familiar, quantifiable language to not only express design intent, but also ensure it has been met.
A floor material needs to be able to withstand wear, pressure, and damage—concrete can do all this, but only if done correctly. All floor materials will eventually show signs of wear given an extensive amount of traffic, but a hard and dense surface is essential to keeping this minimal. When the top surface of concrete is densified by way of microscopic crystallization, the upper portion of the slab becomes extremely hard and abrasion resistant. Sealers or other temporary topical finishes are very soft and will scratch and wear away quite easily.
Densification of the surface also contributes to concrete’s ability to reject dirt and liquids. Produced correctly, concrete is inherently resistant to contaminants. What stays on the surface gets easily removed from the surface. Spills that do not have a chance to get into the pores beneath the surface do not get the chance to become permanent stains.
Therefore, routine maintenance becomes much easier and more likely to occur regularly. Rather than create slabs needing constant reapplication of coatings or sealers that mitigate moisture and vapour transmission, one should design a slab that performs so the requirements for the material and labour are reduced.
Coefficient of Friction
There are still a few specifications that may require static coefficient of friction benchmarks, but the trend has increasingly become to use dynamic coefficient of friction (DCOF) benchmarks. Measuring DCOF with standards like ANSI B101.3, Test Method for Measuring Wet DCOF of Common Hard-Surface Floor Materials, or ASTM E303, Standard Test Method for Measuring Surface Frictional Properties Using the British Pendulum Tester, are great places to start in gaining understanding in what is required to create high traction COF surfaces. Using average roughness to consistently maintain a concrete floor’s surface texture may also be helpful in reducing the need of coatings and sealers while better understanding the performance of the floor over its lifetime.
As a result of the combined characteristics mentioned in the preceding sections, a concrete slab designed to keep out moisture will provide a long-lasting flooring solution which requires minimal maintenance to keep its natural beauty throughout the entire life cycle of the facility. If in case the floor ever does become covered with some other surface-applied finish, it has a much better chance of recovery when the applied flooring has worn out and needs to be removed.
An added benefit of concrete that naturally maintains its volume is its natural moisture mitigation attributes. This is a huge cost saving advantage where there will be installation of moisture-sensitive floorcoverings such as tile, carpet, or epoxy.
By controlling volume loss, both structural and esthetic concrete problems diminish over the lifetime of the facility. In Bill Gate’s Fortune review of Robert Gordon’s “The Rise and Fall of American Growth,” he talked about new “super cements” that would offer the capability to “build infrastructure that lasts 10 times as long as the cement rebar approach.” This journey is already well under way with composite reinforcement, nano infused silica cements, Portland limestone cement (PLC), and metakaolin.
How can someone be assured their design intentions are being met? The preference would be not having to depend on subjective opinions which tend to differ among the perspectives of the owner, architect, and contractor. Instead, the goal is to clearly define quantifiably what is to be achieved as a contract requirement in the specifications. Not until the work has been tested and verified to have met specific requirements can the work be determined to be acceptable.
A performance specification can avoid the visual inspection of what looks good at the time of substantial completion—only to wear off in a relatively short period, requiring costly reapplication of sealers.
Up until now, some of the concrete attributes mentioned in this article have been extremely difficult to achieve. An excellent concrete slab or polished concrete floor is the result of proper materials being applied by a skilled trade. Unless both are carefully identified in the contract documents, one will most likely come upon unsatisfactory results that do not meet expectations (Figure 4). Unfortunately, in the past, it has been all too often that at the very end of construction, with extreme pressure for impending occupancy, the owner is forced into accepting results neither expected nor desired—a tough pill to swallow when money is being exchanged for dissatisfaction just to get occupancy of the facility on time. Even less palatable is the ongoing additional expense that will be incurred to maintain a non-sustainable floor over the life of the building.
To avoid this dismal picture, it is extremely important to take the following steps throughout the construction process:
Polished concrete has recently become a popular design choice among interior designers due to its sustainable qualities and long-lasting esthetic. While it is a false belief that polished concrete is always less expensive than applied coverings, it is often less expensive in logistics and warehouse construction. True polished concrete is also one of the most economical and sustainable choices over the life of a building. It is important the entire project team has a clear understanding of what is meant by “polished concrete,” and then take the necessary steps to ensure the design intent is being met.
Construction professionals are the parents and guardians of their offspring (that is, the facilities they create). Some of the ancient concrete structures built by the Roman Empire and have survived millennia are cherished to this day. It is time again to make outstanding achievements in construction that will endure as economically viable, sustainable structures with durable, long-lasting, useful lives.
Bill DuBois, AIA, CSI, CCS, is an architect with a passion for working with the entire construction project team, which includes owners, designers, constructors, and suppliers. DuBois assists in the decision-making processes necessary for efficient implementation of powerful design solutions and the creation of construction specifications. He can be reached at email@example.com.
Chris Bennett, iSCS, CDT, is president of a North American concrete consultancy that provides owner and designer representation in the development of sustainable concrete solutions and risk reduction. He can be reached at www.BennettBuild.us.
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