Is Precast Concrete Right for Your Next Construction Project?
- By Ellen Kollie
- April 1st, 2007
Let’s get right to the point: precast concrete is not the same as cast-in-place concrete or tilt-up concrete. Instead, precast is plant-manufactured concrete products. Sometimes it is referred to as prestressed, because the concrete contains a stretched prestressing strand, thus creating a greater strength and load-carrying capacity.
Because precast and prestressed products are manufactured in plants certified by Chicago-based Precast/Prestressed Concrete Institute (PCI) and audited by independent engineers, they meet minimum standards.You have trained personnel performing the same functions every day, said Peter I. Finsen, executive director of Atlanta-based Georgia/Carolinas chapter of PCI.There’s a greater opportunity for quality, unlike a job site, where you have different people all the time.
Precast is a product that campus administrators should know about and consider for their construction projects, simply because it offers numerous benefits, some of which include durability, energy efficiency, and sustainability.
Aesthetic and Exterior Versatility
PCI likes to says that one of precast’s benefits is versatile aesthetics. It doesn’t need to be gray concrete, and often it does have a much higher finish. We have the ability to vary the color, form, and texture to create a variety of architectural finishes integrated into one component, explained Finsen. For example, we can use forms to mold the concrete to take on different patterns, and we can embed thin brick or stone. We can pigment it with colors. And, we can finish it using sand blasting or chemical retarders to expose the aggregates for different textures.
A second advantage of precast is design flexibility. Precast offers a lot of flexibility because of what you can do with the forms, said Jay Cariveau, director of Business Development and Marketing for Greenville, SC-based Metromont, one of the largest precast producers in the country.
We have the capability to do both structural elements and the architectural façade or enclosure, explained Finsen. With the façade, we can build insulated wall panels (concrete/insulation/concrete) with any of our architectural finishes on the exterior surface. This allows an efficient edge-to-edge insulation for a better thermal envelope.
In addition, this manufacturing process involves only one trade, the precaster. Building a traditional load-bearing wall would include a number of trades, such as steel framing, metal stud installation, exterior sheeting, masonry brick, and interior drywall.
Another precast advantage is durability. In fact precast concrete has tensile strengths of 5,000 PSI and up, because manufacturers want it to reach a high early strength so they can pull it out of the mold in about eight hours. The economy of the manufacturing process is to make a repetitive product, quickly, noted Finsen. The benefit is that the concrete is denser and less permeable so, typically, precast panels do not need to be waterproofed. You don’t get moisture through them, and there is no food source to foster the growth of mold and mildew.
The durability means that precast, which has a 50- to 100-year life, also has less maintenance throughout its life. There’s no repointing of brick and no waterproofing the joints. You basically don’t have to do anything, says Finsen. If you’re in an area of high acid rain, you may have to wash it.
A fourth benefit of precast is the speed of construction. Finsen cites that a precast wall system with thin brick cast in can be erected 10 times as fast as typical brick-and-block construction.
For example, administrators at Bryan College in Dayton, TN, had a quick need for a residence hall. It would have 120 beds and be three/four stories tall. We spoke with the contractor, owner, and architect about building a total precast structure, said Cariveau. We provided insulated, load-bearing exterior walls with cast-in-place brick and a sandblasted finish. Plus, the corridor walls, floor system, roof system, elevator shaft and stair towers are all precast. We erected the precast building system in February, and the students moved in on August 9.
Safety and Security
Another benefit of precast is safety and security, chief of which is fire resistance. This is an excellent benefit in any building, but especially in residence halls.
Concrete doesn’t burn. If a building’s interior walls are precast and you experience a fire in one room, the interior materials like drapes and furniture will burn, but the fire won’t spread to another room. In addition, precast doesn’t need to be coated with other materials to meet fire codes, as does steel or wood.
Precast’s sixth benefit is its thermal mass and energy efficiency. Because of its density, concrete has the ability to absorb and store large quantities of heat. This thermal mass allows concrete to react slowly to changes in outside temperature — and reduce peak heating and cooling loads. This delay improves the performance of heating and cooling equipment, thus saving energy.
Georgia State University, for example, recently built a 2,200-student, multi-building residence complex. The buildings range from eight stories to 15 stories. The exterior wall system was originally designed as brick and steel stud, with an R-19 batt insulation (effective R-value per ASHRAE of R-7.1), said Cariveau. We were able to provide a thermal efficient precast wall system and achieve an effective R-value of 12. This allowed the mechanical equipment requirements to be reduced, saving approximately $700,000 in initial upfront equipment cost. Additionally, lower annual HVAC operating costs will be realized.
Precast contributes positively to sustainable development efforts. For starters, the site is less disturbed because construction materials, like brick, cement, and insulation don’t have to be stored on site. The precast is brought to the site on a flatbed truck and put in place with a crane. As a bonus, site disturbance is a rating element for LEED.
Moreover, precast has re-use and recycle benefits. For example, seating can be pulled from a stadium and re-used elsewhere. In fact, much of the seating for the Olympic Stadium (now Turner Field) was removed and used at local schools.
If you know you’re going to expand a building in the future, a precast end wall can be removed and replaced once the two side walls are lengthened. A traditional load-bearing wall would need to be torn down, with only a portion of the materials being recoverable.
Additionally, during precast manufacturing, there is minimal waste of raw materials because it’s built to size in the plant.
To be blunt, precast is often not going to be the lowest first cost from a raw materials standpoint because of the quality and materials that go into it. However, it can be competitive with other materials, especially buildings that are two or more levels. Know, too, that cost savings are realized in other areas, such as general conditions, because fewer trades are involved in the building construction.
Fortunately, cost is definitely a benefit when you consider life-cycle costs. Precast is more durable than other materials, thus requiring less maintenance and operating costs. As already noted, its energy efficiency reduces HVAC operating costs. And, often the owner achieves lower insurance costs because of precast’s inherent fire resistance.
The Georgia State residence complex came out with an equivalent installed cost, noted Cariveau. Our firm served as the precast engineer, manufacturer and installer. We worked in the evenings using the contractor’s tower crane, thus saving time and money. In addition, the contractor saved money from not having to scaffold the building.
Cariveau noted that precast was also used to construct a mixed-use facility at Clemson University. The end result boasts many of the benefits listed here, including expedited construction; minimized risk in a multiple-contractor project; and allowing the owner, developer, and contractor to have a firm budget and scope of work for the building envelope early in the project.
Check out precast for your next campus construction project.
For more information on precast construction, visit the Precast/Prestressed Concrete Institute Website at www.pci.org, or the Georgia/Carolinas Precast/Prestressed Concrete Institute Website at www.gcpci.org.
What About Modular Construction?
Writer: Stephanie Russell
Modular construction is not the same as precast concrete construction. The biggest difference between the two is mobility. Campuses of all sizes must deal with fluctuating populations. Modular addresses the need to expand, relocate, and even downsize facilities in a short timeframe. Classrooms and other spaces can be added and subtracted much more easily, either to an existing structure or as a standalone building. Precast offers the same advantages as modular in terms of manufacturing in a controlled environment and saving time by doing the site work simultaneous to manufacturing. However, after installation, precast typically cannot be moved or expanded upon with the ease that modular can.
In addition to its mobility, modular construction has other benefits. Colleges and universities have been experiencing something of a construction boom in recent years. Construction spending has more than doubled through the last decade, and with that comes shorter and shorter timelines for completion. That is where college and university administrators can enjoy the true benefits of modular. The buildings are manufactured in a quality-controlled environment at the same time site work is being completed. Compared to traditional construction, this can save months of construction time and, more importantly, allow you to get back to the business of teaching students and serving your communities much more quickly.
When choosing modular, the key is to choose a vendor who is going to be a true partner in solving your space needs. Modular is not like traditional construction; you need a company with the expertise to manage a modular project from concept to completion. The company you choose should have the resources to stand behind their buildings, know local building codes, and offer full-service capabilities.
Stephanie Russell is director of Marketing for Dulles, VA-based Resun Corp. (www.resun.net), a provider of modular space solutions.