Concrete Issues

• By Pieter van der Have
• 08/01/15

Once upon a time I was into rebuilding old cars. A friend and I co-owned a 1937 Chevy for which we had great plans — which barely materialized. One quality of that classy car was its tough steel. Once we had a need for a new hole in the firewall. Where drilling a hole anywhere on a 1965 Dodge was a cinch, the steel used on this buggy was openly defiant. It did not want to be penetrated. The steel used to build this car body was meant to last.

Moving on to concrete — today’s concrete. I currently live in a neighborhood that is barely 10 years old. Since one of my favorite pastimes is to go for an early-morning walk, I see several miles of sidewalks and many driveways. When I visit university campuses throughout the U.S., I see miles of pedestrian walks, external steps and other concrete features. I am consistently struck by the poor condition of so much of this in-your-face feature. I can’t help but wonder why, in a very old neighborhood where I lived for a number of years, concrete that was placed in the 1930s was still in great condition — except for the occasional slabs lifted by assertive roots sent out by huge trees. For that matter, go to Rome and see how concrete placed (without Portland cement) 2000 years ago is still surviving!

On First Sight

I have previously written about how important the appearance of a campus is to the casual visitor as well as the tuition-paying student (or parent). It can be argued that hardscape represents a major aspect to the visual impact of the physical campus. On a campus that I visited recently, a pedestrian walk that had reportedly been placed only a year ago showed serious signs of spalling and flaking. Why is that, when that older concrete did not show any signs of such deterioration?

Spalling (not spalding or spalded) is the process of relatively substantial layers of concrete, including aggregates, separating from the main body. Using the wrong size aggregates, which could allow too much moisture to penetrate into the concrete during winter storms, can cause this. Scaling is a slightly different phenomenon, evidenced by a thin layer at the very surface of the concrete flaking away. It is the latter phenomenon that often leads to unsightly, but not yet unsafe conditions. Even with all of the admixtures and various agents that are often added to a concrete mix at the batch plant, it turns out that some of the problems that we see so frequently with concrete are the result of the batching and/or the installation process.

Installation and Care

Potentially responsible are ill-advised activities such as installation at the wrong time of year, leaving out essential air-entraining agents, using too much fly ash with a high carbon content, finishing the project while there is still water evident on the surface, wrong or dirty aggregates and so on. Let’s not forget about how we ourselves might contribute to the problem: spreading salt or ice melter on concrete that has not yet fully hydrated. The recommendation is to wait for at least a year before application of such chemicals — or to resist forever. Another no-no is to apply some sort of sealer or curing compound on a fresh project before winter; we run the risk of trapping moisture inside the concrete, which in turn can create havoc during the freeze-thaw cycles that regularly occur in much of the country. Presumably, those of us who work in areas where freezing is a rare or nonexistent phenomenon don’t have these kinds of problems, though extreme heat might be.

Once concrete is fully cured (after at least a year or more), we can choose to apply an appropriate sealer. That should help minimize future damage. Exercise care, though. A neighbor once applied a concrete sealer to his slightly sloped driveway. Not knowing any better, he created a dangerous slippery slope during the first freeze, and every time thereafter. The moisture had no place to go.

Pervious Pavement

One product that has gained recent popularity is “pervious” concrete, the theory behind which is that its structure allows moisture to drain through to a substrate during thaw cycles. The concept is impressive, but I have seen and heard of installations that have not been entirely successful. The system might deteriorate quickly, possibly because of excessive voids and not enough structural strength, or because of improper snow removal procedures.

Selecting the right concrete mix and installation is an art as much as a science. It may be worth our investment to find a concrete expert to help develop the best specification for your unique needs. This could offer an attractive bottom line.

This article originally appeared in the issue of .