Dog-eat-dog competition between construction materials is a good thing – and may the best product win. But when concrete material research data are used out of context in derogatory product claims, experienced specifiers can separate fact from fiction.
By Sue McCraven
During really bad snowstorms, when temperatures hover around 32 F and cars spin off into the ditches, just staying on the road is a nerve-racking challenge. Maneuvering your vehicle behind a giant scraper truck that is shooting out deicer salt and sand is not a bad strategy for staying alive when the concrete pavement is a sheet of ice. But wait a minute! Isn’t that calcium chloride (CaCl2) that the scraper truck is spewing all over the concrete roadway? And didn’t the last sales pitch you heard use material research data to claim that concrete mortar dissolves when soaked in a pure (liquid brine) CaCl2 solution?
What’s the issue here? Does this mean CaCl2 always deteriorates concrete? Obviously not. Does this research data translate into a rationale that precast concrete paving slabs and drainage structures are a poor choice for highway specifications? Not at all. Here’s where a specifying engineer relies on industry standards to assess concrete’s durability in a cost/benefit analysis of available construction materials.
For the specifier, what does our dicey driving example say about using out-of-context research data to trash competing products just to secure a winning bid? Common sense tells us that statements about the corrosive effect of CaCl2 on concrete need to be based on real-world applications: the history of concrete pavement’s in-service performance and its proven durability in cold-weather regions where road deicing salts are commonly used.
More importantly, all research database claims of concrete deterioration need to be understood in context with the specific mix design used in the studies. Without knowing the water-cementitious material (w/c) ratio, compressive strength, air content, presence/absence of permeability-reducing materials, and cement type that led to the test data, engineers understand that product salesmen cannot apply these same data, carte blanche, to the real world, where CaCl2 and concrete pavement are engaged in a salty symbiosis for driver safety.
FACT: Real-world field performance has shown that air-entrained concrete pavement does not need added protection from deicers.
At this point in our discussion, it should be obvious that using out-of-context research data to digress into deceptive claims about the durability of any competing construction material or product – precast concrete or otherwise – is a waste of time and energy when directed at a knowledgeable audience. Exaggerated product sales pitches look particularly bad to specifying architects and engineers who are not taken in by the inflated hoopla of claims and counterclaims.
Remember college research? Two examples
Let’s get down to a more specific example of how marketers use research data out of context. Let’s say material research data indicate that concrete mortar deteriorates in solutions of acids1 or oils at high concentrations and in conditions of continuous exposure. This result should come as no surprise to any civil engineer if, in fact, the 1 in. x 1 in. x 4 in. mortar samples tested had w/c ratios ≥ 4.0 and a mix design with no silica fume or admixture to increase concrete impermeability. Does this research prove that the precast concrete grease interceptor in service at your local Freddy’s Fried Chicken restaurant/grease outlet can be expected to deteriorate rapidly? Hardly.
Another research report2 may use provocative photos of deteriorated 6 in. x 6 in. x 30 in. concrete beam samples exposed to sulfur-rich soils in Sacramento, Calif. These photos are properly used to demonstrate the visual inspection system (used since 1940) to apply a numerical rating system (from 1 to 5) to identify degrees of deterioration (1 = looks pretty good, 5 = sweep it up). Used out of context, this “evidence” can be a bit startling to those unfamiliar with research protocol. Setting the gory photos aside, this study actually reports that air entrainment and a low w/c ratio, in particular, “was an overriding factor in sulfate resistance.” Will precast concrete components specified for use in sulfur-rich settings disintegrate? No way.
How engineers view research –
A smart specifying architect or engineer knows that the best way to assess derogatory claims from competing products based on research data is to recall research realities from his or her university days:
1. First, engineers know that researchers often use “the upper end of the possible range of concentration for each chemical agent” in their testing, because they are eager to discover what happens at extreme conditions. Researchers are curious by nature, and the upper limits of what is possible (remember the fun of blowing things up in the lab?) in the laboratory make for interesting data and eye-catching graphs. But these high-range data points are not intended to describe typical performance in actual field conditions.
2. Second, engineers evaluate research reports in their entirety with seasoned perspective, and are not influenced by a well-delivered sales pitch based on some unearthed data. For example, most concrete material research summaries on the effects of aggressive chemicals on cement mortar will usually conclude with a statement indicating that it might be a pretty good idea to increase curing time and decrease the w/c ratio. B.S.C.E.s know a quality concrete mix has more relevance to service life than data that reflect extreme test conditions. If you commonly specify municipal underground wastewater tanks and pipes, for example, you may have heard product pitches about an industry study3 that describes “slow disintegration of concrete exposed to vegetable oils.” In fact, the actual purpose of this report is to list available protective treatments (coverings/coatings) that mitigate chemical attack in specific corrosive environments. When specifying for durability over a long service life, the critical element is always well-designed and impermeable concrete based on an informed mix design for specific site conditions.
3. Finally, the important questions an astute specifying engineer or architect asks about any laboratory study on concrete deterioration include: “Were the research samples, exposure levels and corrosive-element concentrations representative of quality precast concrete products under typical service conditions? “Does the research data represent today’s precast concrete mix designs that meet industry codes4 for corrosive environments – durable concrete produced with low w/c ratios, the recommended type of cement, perhaps 5% silica fume, and other technological advances in admixtures and supplementary cementitious materials (SCMs) to increase impermeability?
FACT: In the end, specifying for product durability (a long, low-maintenance service life for the owner) is all about a concrete mix design for specific exposures.
An informed and experienced response to unfounded claims of product deterioration focuses on precast concrete’s actual performance and its durability in the field – how you have found precast concrete performs in service. Are owners happy with the performance of precast concrete products specified for their projects? Yes.
What do owners like about precast concrete? Discerning owners and clients prefer precast concrete because it has a proven history of production quality, structural integrity and durability. Precast stands up to adverse conditions for decades of reliable service without replacement or repair. Importantly, precast concrete is the proven premium product that arrives on site as a structural element.
Are you always present during installation?
Do you always have the time to be on site when the vaults, pipes or holding tanks are installed? There is one building material you can depend upon. Precast concrete underground products, for example, will not deflect, warp, crack or break in service like other materials5 where actual product performance, structural integrity and service life depend in large part on the whims of the local contractor in complying with specified installation procedures. Field-experienced engineers know that compliance with soil-lift heights and backfill/compaction specifications requires more time than a quick, haphazard installation. And we all know that few contractors enjoy spending extra time on site – and collecting less money for their efforts.
So let’s see the research data and let the product claims fly. Smart specifiers employ a reality filter for hyped-up money-saving and durability promises from competing construction products. On your highly cost-competitive building projects, don’t overlook a product’s history of performance in your material cost/benefit analysis. And may the product with the best durability and service life for the owner end up in your project specifications.
Sue McCraven, NPCA technical consultant and Precast Solutions editor, is a civil and environmental engineer.
1 See Reference 4.
2 See Reference 5.
3 See Reference 2.
4 See Reference 1.
5 See Reference 6.
1. ACI Committee 318 Report, Building Code Requirements for Reinforced Concrete and Commentary, ACI 318/318R, American Concrete Institute, Farmington Hills, Michigan, 2005, 436 pages.
2. Kerkoff, B., “Effects of Substances on Concrete and Guide to Protective Treatments,” Portland Cement Association, Skokie, Illinois, 2007.
3. Kleinlogel, A., Influences on Concrete, Federick Ungar Publishing Co., New York, 1950.
4. Kuenning, W. H., “Resistance of Portland Cement Mortar to Chemical Attack—A Progress Report,” Research Bulletin RX204, Portland Cement Association, Skokie, Illinois, 1966.
5. Stark, D., “Durability of Concrete in Sulfate-Rich Soils,” RD097, Portland Cement Association, Skokie, Illinois, 1989.
6. “Condition Investigations of HDPE Pipe In-Service in the United States (Six States),” by Wiss, Janney, Elstner Associates, Inc., for The American Concrete Pipe Association, 2002.