Precast concrete or site cast concrete? This is a crucial question for anyone moving forward with a commercial building project. Depending on your particular needs, you may choose to go with one over the other.
Because on site concrete pouring is custom to the build, it is incredibly versatile. However, it is also far more costly, labor intensive and time intensive. While precast concrete does have to be hauled to location, its unparalleled quality, affordability, and longevity make it stand out against its on-site competitors. In fact, precast concrete has established itself as the preferred approach to concrete construction.
Consider these statistics from the Concrete Producer, a trade magazine focused on the concrete industry. The demand for precast concrete here in the United States in on the rise, with a predicted growth of 6.4% to the tune of $12.2 billion in 2018.
Whether you are a looking to embark on a new construction or simply want to stay on top of the latest building and fabrication trends, this guide will put the differences between the two approaches into perspective.
WHAT IS PRECAST CONCRETE?
Precast concrete is poured and molded over rebar or wire and then cured offsite. This involves pouring concrete into pre-made molds and then cured under ideal conditions within the manufacturing plant itself.
Once hardened and ready for use, those preformed concrete products are shipped to the job site where they are assembled into the desired structure.
WHAT IS SITE CAST CONCRETE?
As opposed to precast, site cast, sometimes known as in-situ concrete, is poured, molded and cured on site.
Like precast concrete, on site concrete is formed in a mold and then lifted in place. However, one of its advantages over precast slabs is that it does not need to be moved far to be lifted into place. For a building that requires large, unwieldy and custom concrete molds, onsite is usually the way to go. Some forms are just too large to fit on the back of a flatbed truck. Conversely, the savings from precast concrete are scaled, meaning that for a small structure, in-situ concrete may be cheaper.
Finally, precast concrete requires more joints and therefore less suited for earthquake prone regions. For those building in places where buildings need to be “earthquake proof,” site cast concrete is usually the preferred option.
However, these are very specific instances where site cast is the best approach. There are significant disadvantages that will be explored more fully later.
ADVANTAGE OF PRECAST
Factory controlled equals factory quality: Concrete strength and quality are contingent upon the curing process. Among other things, climate control is a big part of that.
By curing concrete in a factory, you can tightly control the climate to make sure that the curing process takes place under ideal conditions. That means you can be more confident in the precision of the mold and fabrication along with the strength and consistency of the cast.
Factory efficiency: In addition to quality control advantages, factory cast concrete is more efficiently manufactured, driving down costs. Because precast concrete can be fabricated using assembly line techniques, each cast requires a lot less labor and therefore costs less in labor costs.
Versatility: One argument often used against precast concrete is its perceived lack of versatility. While there are limitations to customization, there are other ways in which a perceived lack of versatility is way off base. Because factory-made precast concrete is shipped to such a wide range of customers for an equally varied range of applications, precast is in many ways more versatile than site cast concrete. A large variety of motifs, colors, and finishes are available, along with smaller precast architectural elements.
Economies of scale: Furthermore, because precast concrete uses standard forms, slabs can be mass-produced, improving the economies of scale. Moreover, because precast concrete is factory made and standardized, there is fixed pricing, which enables you to accurately budget construction costs and avoid going over-budget.
No on-site form work: The form work required for on-site concrete pouring is both time and space intensive. Furthermore, onsite curing requires leaving forms in place for extended periods of time. Not only does this take up space on site, but it also requires you to engage in weather prediction, as those forms need to cure under certain conditions.
Furthermore, there are delicate cost concerns associated with scheduling. An unexpected delay of even a day can take a project dangerously over-budget. By eliminating logistical concerns, scheduling becomes easier which in turn helps to ensure that unexpected costs aren’t accrued.
In other words, on-site form work is a logistical headache. By using factory casting, you can avoid all of the stress of coordinating on-site skilled labor and logistics.
Efficient and sustainable material use: Finally, by using precast concrete, you will be maximizing material efficiency. Because of the precision of precast concrete, material waste is minimized. This is much harder to do on-site, as the labor inefficiency of concrete preparation motivates contractors to mix more concrete than needed, just in case.
Furthermore, concrete is a recyclable material, meaning you can build green efficiency into your precast concrete construction materials.
COMPARING PRECAST VS. SITE CAST CONCRETE
Perhaps the best way to see just how great precast concrete is to highlight the differences between precast and site cast concrete directly. Here are some key aspects between the two methods placed side-by-side
Quality control: Because precast concrete is mixed, poured and cured in a factory, ideal conditions and exacting measurements can be maintained throughout the process. Unfortunately, the logistics of site casting make this far more challenging. You are subject to the humidity and temperature of the day you are doing the casting. You have to do the work using far less precise tools. The result is an inferior quality product even under the most ideal conditions!
Labor efficiency: Precast is much more labor efficient. Because work is done in a factory, the effort is maximized through the use of tools and machinery that simply isn’t available on the job site. Therefore, with site casting, work that might be done with machines has to be instead performed by hand. This is much more labor intensive, thus increasing labor costs and making the process more costly.
Additionally, because machines aren’t involved, the labor needed for on-site casting needs to be skilled rather than unskilled. Thus, not only are more labor hours required, but those labor hours are more costly!
Curing conditions: Because curing conditions can be controlled in a factory, they can be accelerated without sacrificing strength or quality. That simply isn’t the case on site. While you can do certain things to accelerate curing on site, they are difficult and generally not worth the logistical hassle and costs. Furthermore, they run the risk of lower quality concrete, as delicate variables are hard to account for. If you need accelerated curing, precast is the only way to move forward confidently.
Full strength: Because concrete gains strength over time, it isn’t fully strong immediately after drying. However, with precast concrete, that hardening process takes place before arriving on the job site. That’s not the case with site cast concrete. Before you can raise the concrete into place, you have to wait for site cast concrete to harden fully. This can delay construction and increase costs. It is much more time and cost efficient to have fully hardened concrete slabs ready to be placed the moment they arrive.
Furthermore, because precast receives a strength test during quality control inspections in the factory, you do not need to conduct strength tests on site. Strength tests are extremely crucial for ensuring that your building is safe, so if you are doing on site casting, then this is a step that cannot be skipped. Again, because this process is outsourced to the factory with precast concrete, your job site will be much more time and cost-efficient.
Cast ahead of time: With precast concrete, you can do the casting of your materials ahead of time, holding them until they are needed. Unfortunately, overlapping tasks and improving efficiency is all but impossible with site cast concrete. Because of the amount of space and labor required for on-site casting, you generally have to stop construction while you wait for your materials to be ready. This is a costly way to stand around and wait.
Weather: An unexpected rain storm can grind construction work to a halt if it occurs when you are doing site casting. Thankfully, this simply isn’t a problem when it comes to precast solutions. If it is raining when your precast slabs arrive on site, you can lift them into place just as you would during a sunny day.
Insulation: Because precast concrete is factory made, certain elements can be incorporated within the concrete that cannot be added to site cast concrete. Added insulation is one of the most common elements. By adding additional insulation materials within the concrete slab, you can save both labor and architectural design space when constructing a building. Rather than hanging and lining the interior of your building with insulation, the slabs that you lift into place with have the insulating power of traditional concrete with additional hung insulation.
As more builders are chasing green ratings for their building, both for the good PR and the energy savings over the life of the building, precast concrete offers a distinct advantage.
Specialized reinforcement: Finally, just as specialized insulation can be added to precast concrete, specialized structural reinforcements can be added as well. For certain projects, this is crucial, as it allows the panel to bear loads at a thickness that simply isn’t possible with traditional poured concrete. By decreasing the amount of material needed to make a building structurally sound, you are saving money while being less taxing on the resources available.
Furthermore, specialized high strength concrete requires exacting conditions for both mixing and curing. These conditions cannot be controlled on site. However, because factory construction allows for heightened environmental control, you can use specialty high strength concrete for your construction. Again, this allows you to create architectural designs that cannot be achieved any other way.
EXAMPLES OF PRECAST BUILDINGS
There were two main concerns when constructing this building using precast concrete: design and safety. As an art school, design was important. The building had to speak to modern aesthetics and create a learning environment conducive to exploring the possibilities of visual art. But as a school, student safety was paramount. That’s why the builders opted for precast hollow core planks. This type of system has a superior fire resistance rating. Furthermore, the construction reflected the organization’s commitment to sustainability.
Because this building was being added to a pre-existing campus, its design had to blend in with other buildings on the campus. While precasting was still used throughout, it did involve a custom concrete blend. Furthermore, because Hershey Medical Center is a rapidly growing invaluable medical resource for the surrounding area yet, building schedules were quick, and the construction was completed in 4 months.
New retail constructions are often completed as part of large scale development in which land is plentiful. However, urban retail constructions, like this new Target Retail Center, require working within constrained areas with limited available land. However, as a representative of a national brand, the building also had to reflect the architectural branding of its parent company.
Thus, parking was placed below the store, which required precast elements with superior strength. Simultaneously, the building had to be done quickly, as construction was disruptive to the surrounding neighborhood. Again, the efficiency of precast was essential for getting this job done on time.
FINDING A QUALITY PRECAST MANUFACTURER
As you can see, the advantages of precast concrete make it the preferred choice of commercial construction all over the world.
However, if you are building in the mid-Atlantic, look no further than Nitterhouse Concrete Products. Since 1923, we have been providing superior concrete products to the region, partnering with architects and construction companies larger and small to help bring their visions to life.
While you may still need to turn to site cast concrete on occasion, as you move forward, precast concrete provides superior versatility, functionality, affordability and labor efficiency. If you aren’t already using precast for your projects, it’s time to make the switch. And even if are already familiar with the value, you may want to consider whether you are getting the attention you need from your manufacturing partner.
If you’re ready to take the next step and get the wheels moving on your next building project, contact one of our experts for additional planning assistance.