When it comes to outdoor site furnishings, and bollards in particular, concrete helps ensure site and pedestrian safety—while enhancing the aesthetic designs of surrounding areas.
Concrete is an excellent building material used for almost all major buildings and urban infrastructure projects. There are few modern buildings that don't use concrete for at least their foundation. On its own, concrete has a high thermal mass and is resistant to weathering, making it ideal for outdoor use. Concrete can also be easily improved with steel reinforcement and additional surface finishing—both of which can be achieved by precasting.
Precast concrete: Controlled manufacturing
Compared to cast-in-place concrete projects, precast concrete manufacturers have exceptional control in managing the quality and appearance of concrete products. Casting facilities have the benefit of a clean manufacturing environment to minimize impurities. Precast products also use molds, which ensure uniformity across individual items and allow for a high degree of planning and predictability in determining concrete mixes and volumes.
For cast-in-place concrete projects, formwork is often the most costly input, as it requires abundant resources for labor and materials. Relying on offsite manufacturers is an effective way to reduce costs while ensuring quality and performance-specific characteristics. Precast concrete products are shipped ready for use and typically require much less time and labor to install. Precast products are used for a range of applications—including architectural site furnishings, structural building materials, surface pavers and housings for utility conduits and waste management. Reliance Foundry offers a selection of precast concrete bollards.
Reinforced concrete: What concrete lacks, steel provides
On its own, concrete has exceptional compressive strength but is weak in tension and shear strength, which means it is highly susceptible to cracking—especially when subject to significant forces over time.
Precast concrete bollards are available with wide diameters
Steel has exceptional strength properties for withstanding high tension and shear forces, making it ideal for reinforcing concrete. Steel behaves similar to concrete when exposed to environmental variations such as temperature and humidity, which means the two materials typically shrink and expand together. It can be bent, cut or bound into different shapes to accommodate any concrete form—and assembled rapidly into formwork and molds. Together, concrete and steel can be used to build structures with incredible strength and durability, and they require minimal maintenance once installed. Concrete and steel are also both economical and readily available across North America.
Rebar, the most common form of concrete reinforcement
Different types of reinforcement can be used for specific concrete applications. The most common reinforcing material is steel rebar, which contains deformations, or ribs, that interlock and bond with concrete as it cures. Rebar is a versatile material that can be easily bent, cut or spliced together, and different types are available, each with specific properties incorporated for strength, weldability and corrosion resistance.
It's worth noting that steel is generally protected from corrosion by the high PH levels of surrounding concrete. However, lowered PH levels or the presence of excessive marine or de-icing salts can permeate concrete, which can cause imbedded steel to corrode. When embedded steel begins to rust, it expands significantly, causing concrete to crack or spall. At the time of installation, minor surface corrosion won't affect the structural integrity of rebar (and may actually be desired to encourage better bonding). Once sealed, the isolation from external environments halts oxidation. To prevent further corrosion, however, manufacturers can 1) ensure enough concrete has been applied to surround and protect integral steel or 2) use corrosion-resistant materials—such as stainless, galvanized or epoxy-coated steel.
To increase the structural integrity of load-bearing concrete, tension can be applied to reinforcing bars prior to pouring concrete. The tension is then held until the concrete cures. Pre-stressing ensures a more resilient final product in carrying heavy loads.
Strategies for steel reinforcement can vary, and formal projects require that qualified design professionals take into consideration a structure's intended use, location, span lengths and expected loads. Designs also require that accurate parameters be specified for material quantities, grades, sizes and placement within a larger project. The methods used to produce precast concrete offer ideal circumstances for predetermining load designs and ensuring consistent application across a range of products.
Surface finishing makes concrete look good
Bollards protect pedestrian areas
Precast concrete can be designed with a range of colors, textures and finishes that would otherwise be difficult to achieve using cast-in-place methods. These finishes are achieved by using different concrete mixes, aggregate selections and processing methods. Typically, concrete finishes can be grouped into two separate categories: smooth and exposed aggregate.
Smooth concrete surfaces
Smooth surfaces can be created by giving precast concrete either an as-cast or light sandblasted finish. An as-cast finish is created by simply pulling concrete from its form and applying little or no additional processing. As-cast finishes offer a very clean profile and are conducive to painting. However, it can be difficult to achieve a consistent color across as-cast finishes for larger projects. There are a number of variables that can affect the final appearance of concrete, including the type of cement used, mixing, weather and conditions for curing.
It's worth noting that small air voids, or bug eyes, will be more noticeable across smooth concrete surfaces, which, depending on the application, can be a disadvantage. Voids can be removed with additional concrete sacking, but this can be an expensive added process. Light sandblasting is often applied to achieve a more uniform and smooth appearance—minimizing variabilities in the color and texture of binding cement—but it will also make voids and other imperfections more noticeable.
Exposed aggregate concrete
Aggregate collected from British Columbia's Fraser Valley
Exposed aggregate requires additional processing to reveal the stones used in a concrete mixture. Aggregate materials typically comprise about 60–70 percent of a concrete mix, and a multitude of different aggregate-types can be used. Once exposed, aggregates can have a significant effect on the color, appearance and texture of concrete. Exposed aggregate finishes tend to be more uniform and consistent than smooth finishes, virtually eliminating the appearance of voids and other imperfections—both up close and from a distance.
Aggregate can be exposed to different degrees to achieve a range of textures and color casts—or to preserve the presence of the concrete mix.
- Light exposure involves sandblasting a concrete surface until aggregates are just visible through the concrete mix, which still maintains a significant presence in the overall surface appearance.
- Medium exposure removes more of the surface concrete, creating a more balanced aesthetic between aggregate and cement.
- Deep exposure exposes as much aggregate as possible—about a third of each stone or half of the smallest stone size—to make it the dominant feature.
Aggregates are typically exposed though sandblasting, but chemicals are sometimes used in forms to limit curing. This makes surfaces easier to remove.
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Additional concrete finishes
In addition to sandblasting, a range of other processes are available to alter concrete surfaces—including acid etching (similar to sandblasting but allows more preservation of color and detail); form liners, which involve lining forms with additional materials to achieve unique textures; and additional tooling, which is often used to achieve a broken-stone texture.
Depending on the final application, controlling surface finishes can be difficult and costly when implemented onsite. Concrete casting facilities offer more controlled environments for planning and implementing desired finishes—many of which would be near impossible to achieve otherwise.
Molds can be modified easily to achieve different results. Adding cut-outs helps ensure products won't interfere with utility lines. Molds can also be formed to aid installation or to reduce overall material and weight. Decorative reveals and other textured effects can be added to enhance appearances while ensuring uniformity.
Concrete bollards and outdoor site furnishings
Using precast concrete for architectural and landscape furnishings is an ideal means for creating consistent and unique aesthetics across outdoor spaces. Site furnishings typically serve dual purposes—providing functional value while also enhancing visual elements of a building or surrounding site. Read more about how to plan site furnishing layouts.
A range of decorative concrete styles are available
Reliance Foundry specializes in outdoor bollard designs. Reinforced concrete is an ideal material for bollards, as it offers protective strength and visual appeal.
Reliance Foundry concrete bollards have been designed with steel reinforcement for high-impact protection. Epoxy-coated rebar is cast directly into bollards and should be embedded deep into solid substrates to ensure they won't be dislodged in the event of a collision.
Bollards are manufactured with an exposed aggregate finish suitable for withstanding wear and pollutants of high-traffic urban environments. Aggregates are collected from British Columbia's Fraser Valley—emblematic of the Pacific Northwest and suitable for any landscape or architectural style.
This content is provided for informational purposes only. A professional engineer or design professional should be consulted for any performance-specific application related to structural performance or aesthetic design.
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- National Precast Concrete Association. The Little Book of Concrete: A Guide to the One Hundred Advantages of Precast Concrete. 2006.
- Portland Cement Association. "Concrete Technology." Portland Cement Association website., accessed June, 2014.
- Precast/Prestressed Concrete Institute. "Reveals." PCI Designer's Notebook.
- Precast/Prestressed Concrete Institute. "Design Factors Affecting Aesthetics of Architectural Precast Concrete." PCI Designer's Notebook.
- Precast/Prestressed Concrete Institute. "Design Resources." PCI website, accessed June 2015.