Driven by an almost limitless color palette and realistic pattern options, as well as long-lasting beauty, colored and stamped concrete is often the material of first choice for residential paving. Now those same qualities of decorative concrete that drive its residential use have contributed to its use in public spaces. Municipalities are using colored and textured concrete for their streetscape projects: sidewalks, crosswalks, streets and intersection, parks, parking areas, parkways, and medians.
Creative opportunities abound
Small and large communities are concerned with the attractiveness of their downtown shopping or business districts. Creating an environment that encourages people to stroll and shop is often the catalyst for dressing up streets and sidewalks. Designers want to create a physically and visually connecting theme between shops, parks, and parking areas. Decorative paving is the answer. Whether it is creating an “old town” look complementing a town's historic past or an “upscale and urban vibe” that celebrates an areas gentrification, concrete paving presents many opportunities for creativity.
When compared to concrete pavers, decorative concrete offers more color and pattern combinations. Craig Schripsema, senior project manager with Rowe Inc., a multidisciplined civil engineering firm in Flint, Mich., likes the versatility of concrete both in design as well as in installation. The colors and patterns available and the relative ease of installing an eye-catching design often sells the job, particularly to merchants who want a sidewalk with a wow factor, but with minimal interruption to business. Decorative concrete is the answer.
New concrete can be colored by using an integral coloring admixture, which typically is mixed into the ready-mixed concrete at the batch plant. It is available in powder or liquid formulations, which are generally used with a normal gray portland cement mix design. The colors produced are best described as muted earth tones. Shake-on color hardeners also are used to color new concrete. A prepackaged blend of silica quartz sand, cement, and color, this material is applied topically and finished into the plastic, uncured concrete. The product creates earth tone colors as well as light or vibrant hues. The cured colored hardener surface is very dense and wear resistant. Both coloring systems utilize fade resistant synthetic iron oxides as the coloring agent.
Once the concrete is colored, it can be finished simply with a float or broom finish, as you would finish plain gray concrete. A more creative option would be imprinting a pattern or texture with stamping tools. Numerous natural stone, brick, and cobble patterns are available. A colored powder release agent is applied over the colored, uncured surface. This acts as a bond breaker when the stamping tool is tamped into the surface. A few days after the stamping has been completed, the cured concrete surface is power washed, leaving a residue of release powder as an accent or secondary color over the imprinted colored concrete.
Landscape architects often are involved with the design of streetscape projects. Their eye for design, balanced with the need for long-term functionality and durability, makes their expertise important for a successful installation. Once the design is approved, writing a thorough specification is critical. The specification not only addresses materials, but also of equal if not greater importance, are the methods and procedures of installation. Doug Schultz, a landscape architect with Rowe Inc., is an advocate of thorough specifications for decorative concrete installations. Some of the details that he addresses in specifications include reference to ASTM C979 “Standard Specification for Pigments for Integrally Colored Concrete,” color combinations and finishing methods, contractors' qualifications, and very importantly, mock-up requirements. Considering the size and highly visible nature of streetscaping projects, the experience and talent of the installer is critical. Schultz believes that having a qualified contractor base not only minimizes problems during installation, but it also helps to create a level of assurance for city leaders that they are going to get what they want.
A city manager's perspective
When questioned about choosing decorative concrete over other paving materials, the consistent answer from public works officials revolved around versatility and durability issues. Considering the many products available for coloring concrete—integral color, shake-on color, stains—when combined with stamping or even simple brooming and banding, imagination may be the only limit. Again, compared to concrete pavers, it was thought that there were more creative and unique options available with concrete. Additional comments about concrete pavers included concerns about freeze/thaw heaving, sand mess, and damage from snowplow blades. Decorative concrete was viewed as a very durable system, even in crosswalk, parking, and similar high-use surfaces, and in northern climates when the surface frequently is exposed to snow, ice, and salt.
Maintaining decorative concrete
Stamped concrete is durable, but it does require periodic maintenance, particularly cleaning and resealing. Concrete is a rigid sponge. Unsealed, it can be prone to dirt build up from spilled food and drink, foot traffic, or automobile fluids. One way to control the effects of dirt is to select colors and/or patterns that visually minimize or hide its presence. The other of course is with the application of a film forming sealer. Typically, city maintenance personnel handle cleaning and resealing. It is important that the slip resistance of the finished surface is evaluated prior to the installation. This is best done with a mock-up. Also important are repairs to the decorative concrete after trenching, for example. Generally, the installing contractor handles this by providing a small supply of materials and tools to the municipality, as well as training for city personnel.
Howard Jancy is business development manager for Butterfield Color Inc., Aurora, Ill.