One profitable segment of the precast concrete market is devoted to producing ornamental and architectural pieces that are wet-cast one at a time in special forms or molds. Many ornamental concrete producers manage quite successful businesses by marketing each product as a distinct work of art.
The choice of materials, mix design, and release agents is particularly important for ornamental producers.
Because concrete quality depends on water/cement ratio-weight of water divided by weight of cement per batch or cubic yard-too much free water added to a mix for workability can cause problems rather than solve them. Thus, an admixture should provide measurable water reduction in addition to increased workability of the plastic concrete.
Rarely do concrete materials with a 0.40 or lower water/cement ratio (the maximum acceptable level) provide all the workability needed in a mix. Also, about 6% entrained air (microscopic air bubbles) by volume helps homogenize a mix by reducing entrapped air (visible air bubbles) and keeping larger particles suspended and well distributed. Entrained air also imparts freeze-thaw capability to pieces kept outside.
Several admixtures provide water reduction, mix lubrication, and smooth finishes. Some admixture companies have formulated products specifically for ornamental producers, while others offer products that are easily adaptable to this market niche. Thus, the brand used may not be as important as using what works; not all aggregates and cements exhibit the same results with the same admixtures. Here's what some ornamental concrete producers have said about these products.
- Morris Hubbart of Roadrunner Lawn Ornaments Inc., Pana, Ill., likes to use a new Type F superplasticizer from Grace Construction Products that has a recommended dosage rate significantly lower than that of other Type F products. The product provides the necessary plastic-concrete workability without too much free water, and it "just vibrates better," says Hubbart.
- Owner David Reyckert says when Double D Statuary, just north of Corpus Christi, Texas, uses an admixture, it uses Specco Industries' Auger Aid because it keeps the concrete workable longer in hot weather. This admixture exhibits the properties of a midrange water reducer and appears to hold water within the matrix of the concrete, promoting complete hydration of the cement.
- Reyckert's brother, Chet, owns Skiatook Statuary in northern Oklahoma, which has gained notoriety with 10,000-pound concrete gorillas, hippos, and rhinos durable enough to have been placed in a park near Moscow. According to Chet Reyckert, Skiatook Statuary has used both the Specco product and an admixture formulation made locally by a friend. Both admixtures are highly effective, even in a harsh summer environment, says Reyckert.
- Yard Ornaments Inc., near Ada, Okla., is a large producer of ornamental concrete. Owner Curtis Hogue strives to make high-quality concrete. By using a different Specco product in all mixes, the company reaps the benefits of water reduction and workability as well as 5% to 6% entrained air. Not only does this help increase the quality of the product surface, Hogue maintains, but the items themselves require less hand finishing and are durable and less likely to be damaged by shipping or winter weather.
- Much farther north, near Cedar Rapids, Iowa, Ron Zimmerman of Zimmerman Lawn Ornaments uses a low-range water-reducing Specco admixture religiously. Zimmerman says this product provides time to work with the fresh concrete and facilitates uniform distribution of fibers throughout the mix. This admixture also eliminates unsightly watermarks and stains from form stripping.