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The Right Concrete for the Right Job

Brent Johnson

When masons traded hammer and chisel for a bucket and trowel, the liberation from granite and limestone quarries advanced architectural building materials to a level that would not be duplicated until the mass production of iron, which flowed like rivers during the guilded age to transform skylines, span rivers, and bridge continents. The enthusiasm for iron and steel, however, eclipsed the greater functionality of concrete, which has only recently re-emerged as a high-perfomance building material.

Today, the processes that result in the highly stable concrete solid phase are well understood. Yet, the formula has changed very little. The basic ingredients of cement, aggregate, and water mixed in roughly equivalent parts remains the incantation that delivered the secret of stone into human hands.

Using precise knowledge of the compositional chemistry of concrete, contractors can make subtle adjustments to the formula to enhance certain desired characteristics. For example, bubbles can be introduced into “air-entrained” concrete to permit water expansion in freezing temperatures. Fly ash, a product of burning coal, can be added to concrete mix to improve workability. Also, accelerants such as calcium chloride can reduce the amount of setting time for well-traveled areas. To increase the strength of cement and prolong the window of workability, a water reducer can be applied to the mix. And these are only a few of the techniques that are commonly used prior to pouring the concrete. There are a whole variety of processes that can be applied to the concrete as it sets and begins to cure.

Chris Stewart, technical services advisor for Bomanite Inc., recommends a few basic rules when using concrete for landscapes.

The first rule is to make sure the subgrade is properly compacted. Stewart suggests compaction of 90-95%.

Wetness is the next critical factor. The ratio of water to concrete determines the strength. This can be measured by a “slump” test. The mix is placed into a cyclinder and then is dumped out, similar to making a sand castle. If the concrete slumps to a height of 4 inches then it should have the appropriate wetness. If higher than 4 inches it may be too dry; lower than 4 inches and it’s probably too wet.

Another component of good concrete that has taken hold in the last 5 years is the use of a polypropylene monofilament mesh that considerably strengthens concrete by shoring-up the inevitable cracking that occurs. This mesh can be mixed into the concrete at the plant and delivered on-site.

Finally, Stewart strenuously argued for the use of large (3/4” or 5/8”) aggregate. Anything less, he insisted, compromises the strength and durability of the concrete, which he maintains should have a minimum strength of 3,000 psi for warm climates, and 4,000 psi for freeze/thaw conditions.

In addition to the structural integrity of the concrete, an increasing attention to color has forced Landscape Contractors to try different types of concrete from the traditional grey portland formulation. White concrete is popular with Landscape Architects because of its uniformity as well as its ability to show contrasts in color. However, the concrete has suffered from the misconception that it is somehow weaker than grey concrete. In fact, the only difference between grey and white concrete is the iron content, which is approximately ten times greater in grey concrete. Another issue that keeps contractors from using white concrete is the added expense. Producers of this product, such as Lehigh Cement, have to be more selective in the kind of aggregate and cement they use. This may contribute to higher costs up front, but when considering the lower expense for pigment and the long-term maintenance of the surface, the cost balances out. Lehigh Cement has looked at the numbers and estimates that the difference in cost is only one percent

Surebond’s Ecology Seal was used to protect the stamped concrete surface at Mission Viejo’s new Kaleidoscope Center

Another technique that is gaining in popularity is concrete coloring. According to traditional methods an iron oxide powder is poured into the mixing truck by hand, taking up to half an hour. Solomon Colors has developed a computerized system that makes this an automated process. The color and percentage of dye are specified on a computer control and a liquid iron oxide dye is metered into a weigh chamber at the ready mix plant. The mixing truck simply backs up to the weigh chamber and the dye is blown directly into the truck. “It’s much better than I ever expected,” said Richard Solomon, who developed the process a year ago. The automated system is saving them money and the color matching is more accurate.

Once the concrete hardens though, that’s only just the beginning. There are a series of additives and treatments that can be applied to concrete that affect the texture, color, and permeability after the surface is cured

Solomon Colors can deliver ready-mix concrete in a variety of colors directly to the jobsite using a proprietary automation process

Surebond’s Ecology Seal (SB-1370) is an epoxy-based sealant that has proven successful in protecting both pavers and concrete from fading, dirt, abrasion, and airborne salts and acids. The fast-curing epoxy can be sprayed or rolled on to a clean, dry surface. It goes on white and dries to a clear, transparent shield. Four hours after application, cars can drive on it. This rapid curing is one of the major benefits compared to relatively slow drying solvent (urethane). And the Surebond sealant doesn’t form a skin while drying. Instead, it dries from the inside out forming a very durable bond with the pavement. During tests conducted by Boeing Aircraft, SB-1370 protected a piece of metal from exposure to boiling acid. LCM.

For more information about specifying concrete contact the Portland Cement Association at 847-966-6200 or log on

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June 27, 2019, 2:02 am PDT

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