Competition in the marketplace is a good thing, and may the best product win – but when research data are used out of context, a reality check is in order.
By Sue McCraven
During really bad snowstorms, when temperatures hover around 32 F and cars spin off the highway, just staying on the road is a nerve-racking challenge. Maneuvering in behind a giant scraper/salt truck that is shooting out deicer salt and sand is not a bad strategy for staying alive when the concrete pavement is iced over. But wait! Isn’t that calcium chloride (CaCl2) that the scraper truck is spewing all over the concrete surface? And doesn’t material research data prove that concrete mortar dissolves when soaked in a pure (liquid brine) CaCl2 solution?
What’s the deal here? Does this mean CaCl2 always deteriorates concrete? Does this prove that precast concrete paving slabs and CIP concrete pavements are a poor choice for our roadways? Here’s where we all need to stay calm and view the facts. A reality check is in order.
For the precast concrete producer, what does our dicey driving example tell us about using out-of-context research data to trash competing products in the marketplace? Common sense tells us that statements about the corrosive effect of CaCl2 on concrete need to be based on reality: the history of concrete pavement’s in-service performance and its proven durability in cold-weather regions where deicing salts are routinely applied to roadways. More importantly, research database claims of concrete deterioration need to be understood in context with the specific mix design used in research studies. Without knowing the water-to-cement (w/c) ratio, compressive strength, air content, presence/absence of permeability-reducing materials, and cement type that led to the test data, we cannot apply these same data willy-nilly to the real world, where it would appear that CaCl2 and concrete are engaged in a weird wintertime harmony.
FACT: Real-world field performance has shown that air-entrained concrete pavement does not need added protection from deicers.
As the dust settles at this point in our discussion, it should become clear 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 that makes everyone look bad. And we look particularly bad to potential customers who are turned off by the defensive posturing of claims and counterclaims.
Research realities: two examples
So let’s get down to a more specific example of taking 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 anyone 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. Do these research results prove, for example, that the precast concrete grease interceptor in service at our local Freddy’s Fried Chicken restaurant/grease outlet will deteriorate rapidly?
Another research report2 may use graphic 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).
Yes, these graphics can be a bit startling to those unfamiliar with the basis of this research protocol. Setting the gory photos aside, this study reports that air entrainment and a low w/c ratio, in particular, “was an overriding factor in sulfate resistance.” Does this mean that all precast concrete used in contact with sulfur-rich soils will disintegrate?
Stay calm & view the facts: three steps
An informed precaster’s response to derogatory database claims from competitors should be based on the following research realities:
1. First, it is important to note that researchers often use “the upper end of the possible range of concentration for each chemical agent” in their testing, because they want to discover what happens at “extreme” conditions. Researchers are curious by nature, and the upper limits of what is possible in the laboratory make for interesting data, graphs and reports – but these individual high-range data points are not intended to describe typical precast performance in actual field conditions.
2. Secondly, research reports should be assessed in their entirety, with reasonable perspective, and not reduced to a belligerent discourse on a few exhumed data points. For example, most concrete material research summaries on the effects of aggressive chemicals on mortar will usually conclude with a statement indicating it might be a pretty good idea to increase curing time and decrease the w/c ratio. This part of the conclusion has perhaps more relevance to reality than isolated data that reflect extreme test conditions. The same industry study3 that talks about “slow disintegration of concrete exposed to vegetable oils” also lists more than a half dozen protective treatments that mitigate chemical attack. The first tried-and-true defense, however, is designing impermeable concrete based on an informed mix design.
3. Finally, the important questions for the precaster to ask about any laboratory study on concrete deterioration are: “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 SCM5 to increase impermeability?”
FACT: In the end, durability (a long service life) is all about concrete mix design for specific exposures.
Always focus on field performance
A measured, positive and consistent precaster response to unfounded claims of product deterioration must refocus these discussions to precast concrete’s actual performance and durability in the field, how precast works in the real world. Are customers happy with the durability and proven service life of precast concrete products? Yes. What do customers like about precast concrete?
Customers prefer precast concrete, because it has a proven history of strength, durability and structural integrity, and it can stand up to adverse conditions for decades of reliable service without replacement or repair. Precast concrete is the proven premium product that arrives on site as a structural element with its strength intact. Precast concrete underground products, for example, will not deflect, warp, crack or break in service like other materials6 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, including proper soil-lift heights and backfill compaction. After all, “proper installation procedures” usually take more time – and time is money.
So bring on the research data and, as they say in the military, “man up.” The precaster’s response is a calm, confident and consistent reality check for the naysayers in this highly competitive marketplace: “Let’s just focus on product performance in the real world. And may the best product win.”
Sue McCraven, NPCA technical consultant and Precast Solutions editor, is a civil and environmental engineer.
Reference 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.
Reference 2. Kerkoff, B., “Effects of Substances on Concrete and Guide to Protective Treatments,” Portland Cement Association, Skokie, Illinois, 2007.
Reference 3. Kleinlogel, A., “Influences on Concrete,” Frederick Ungar Publishing Co., New York, 1950.
Reference 4. Kuenning, W. H., “Resistance of Portland Cement Mortar to Chemical Attack – A Progress Report,” Research Bulletin RX204, Portland Cement Association, Skokie, Illinois, 1966.
Reference 5. Stark, D., “Durability of Concrete in Sulfate-Rich Soils,” RD097, Portland Cement Association, Skokie, Illinois, 1989.
Reference 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.
1, 2, 6 See Reference 6
3 See Reference 3
4 See Reference 1
5 Supplementary Cementitious Materials