As the number one material used in construction by ton around the world, concrete is the first choice for stability, adaptability, and strength. Used for thousands of years – from Rome’s Colosseum to just about every pro sports arena in the U.S. – concrete repels fire, burrowing animals, and centuries of abuse from the weather.
In larger office buildings and big industrial, manufacturing, and commercial buildings, large footings are poured in place to provide stability. With the advent of steel reinforcements and advanced engineering, these concrete pilings can withstand an amazing amount of stress. The weight of these building blocks makes it more feasible to pour in place.
However, there are plenty of smaller applications where precast concrete pieces are much more desirable than pour in place. With any construction project, the cost is always going to be a consideration. It is important to look at overall costs, however, not just the base cost of the materials or labor.
No two construction jobs are ever exactly the same, of course. There are enough similarities that both cast in place concrete and precast concrete are viable options. This is especially true in buried infrastructure, where manholes, utility vaults, catch basins, and other concrete structures are needed.
Whether you decide to use cast-in-place concrete on-site or precast concrete products, time spent on the excavation at a job site will be similar for the most part. Project managers may need a little more room for precast so there’s space for riggers to help set the piece in place.
In this respect, setting up forms for pour-in-place won’t need as much room, but the difference is negligible. However, once the excavation is complete, the difference in time is staggering. Once the appropriate bedding is in place, precast concrete pieces can be placed immediately, hooked up, and backfilling can begin.
Site-cast concrete needs time to set up and secure the forms, reinforcements (usually rebar) need to be placed at proper intervals, and everything needs to be inspected for quality control. If forms aren’t the correct width or rebar is incorrectly spaced, the integrity of the concrete could be affected.
Weather also plays a part when working with concrete. Too much rain or other precipitation could affect the ready mixed concrete during a pour. The same could happen on windy days as debris is blown into the forms. Although rare in this neck of the woods, extreme temperatures could also affect pouring concrete and hardening phases.
That just isn’t a worry with precast products, which can be delivered to the construction at any time during any amount of weather. Already tested for strength at the facility, catch basins or electrical vaults can be placed 365 days a year regardless of the weather. These pieces continue to gain strength even after being backfilled.
Speaking of backfill, that can’t happen until the cast-in-place concrete has reached acceptable strength levels. Depending on the season, this could affect the construction schedule at the site. It could take multiple days or even weeks for these concrete slabs to reach optimal strength for backfilling.
During this time, excavation at the construction site needs to be secured to prevent accidents from workers as well as “civilians” who happen to be on site. Nothing affects construction costs as much as days lost to injuries or settling insurance claims due to unsafe working conditions.
As the concrete strengthens to required levels, the forms can be removed and taken from the site and, finally, the backfilling begins. On large scale projects, the amount of time it takes to cast concrete in place is obviously added to the schedule. If a construction manager has the ability to shorten construction, why wouldn’t they?
If you’ve ever worked with buried infrastructure, you know how many different-sized structures may be needed for any single project. Some products, such as vaults, have many different uses, including wet or dry applications. For ease of use, precast vaults are created with several knockouts and multiple strut channels.
The same vault could be produced multiple times but used in several different situations. This improves turnaround times by streamlining production. With cast in place, different forms will need to be set for each location. There is just no way to make pour in place concrete more efficient.
In some cases, cast in place and precast have been used in the same product! Consider manholes, which are used as access points for sewage and other wastewater systems. Until recently, once manholes were placed in the system, workers would be lowered into the structure and create channels to improve flow.
With the introduction of the Perfect Base, that extra step is no longer needed. The Perfect Base is built to exact specifications, aligning the channels with the concrete pipelines already in place or about to be placed. This just isn’t possible when trying to build the channels by hand in place.
Is Precast “Greener” Than Cast In Place?
No matter which production method is used, concrete is a very eco-friendly product. Made with naturally occurring raw materials, concrete is chemically inert and Volatile Organic Compound (VOC) free. That makes it the ideal material to use for buried infrastructure purposes.
Concrete is also a very strong product, made to last decades whether it’s precast or poured in place. Because of that longevity, there is less need for replacement units and fewer repairs, actually reducing the need for more concrete. No wonder this material has been so popular for so long!
Although it might be negligible, precast facilities are able to reduce waste during production. With the ability to trap and recycle wastewater and materials, precast plants send very little debris to landfills. Which isn’t to say cast in place concrete is wasteful – it’s just not possible to reuse concrete that overfills a form or dribbles on the ground during a pour.
Precast is also stronger than pour in place because the production process can be controlled every step of the way. Before any piece leaves the facility, it has been tested for maximum strength. The same can be said for cast in place, but conditions must be close to ideal.
In the end, precast concrete structures are just an overall better product. The one advantage cast in place has – initial cost – is easily offset by the consistent quality, installation ease, and installation speed. In the case of large building footings, cast in place just makes more sense. For smaller, more intricate products, precast can’t be matched.
Have a large buried infrastructure project on the horizon? Rogue Valley Precast was built with more than 180 years of engineering and industry experience. As the local precaster in the Rogue Valley, we can cut turnaround times in half compared to Central Oregon or Northern California facilities. Contact us today to see how we can work together.