Why use Prestressed Concrete vs. Cast-in-Place Concrete? What is Precast/Prestressed Concrete?

The short, salesperson’s answer is “it’s a superior building material.” Now I’m sure long before you reach the end of this you will have figured out that I’m not a salesperson. Whether it be because of the fascination I have with the manipulation of material properties, because of the lack of wordsmithing prowess that engineers are generally known for, or because I just told you, either way, when you read “Design Engineer” at the bottom it should make sense.

So what makes it a superior building material? Because it’s precast? Because it’s prestressed? Is there a difference between the two? I mean, even the trade organization for these building products felt the need to differentiate them in their name, Precast/Prestressed Concrete Institute (PCI). It can be a little confusing sometimes.

Precast refers to any piece of concrete that is cast at a different location from the final building site and the cured (hardened) piece is transported to site when the site is ready for delivery, whether it is prestressed or reinforced with conventional reinforcement bar. This is compared to the alternate method of cast-in-place where forms are assembled at the building site and ready mix concrete trucks deliver the wet concrete to be placed and once the concrete is cured the forms are removed. Since both are working with the same material, there are bound to be some similarities in the processes. Both require formwork to hold the wet concrete in the desired shape until it is cured and both have some type of steel reinforcement to help concrete meet the design requirements, but that’s about where it ends. Beyond that the different aspects of the processes start to really determine what kind of product you’re going to end up with. The largest of these aspects would have to be the controlled environment throughout production that precast concrete can offer. Because of the ability to strictly control the environment in which the concrete cures, the tolerances, and therefore quality, you are able to achieve with precast outpaces cast-in-place by leaps and bounds.

Now on to the really fun stuff, prestressed. Prestressed concrete is primarily a form of precast concrete. I have to say primarily because there is technology available to prestress on site, but the feasibility of the application is rare. Generally, if you have the ability and infrastructure to produce precast concrete, you are set up pretty well to produce prestressed concrete. The basic idea of prestress plays on the desirable attributes of concrete and steel. Anyone that works with concrete will know compression is good, bending (which results in tension forces) is bad. And anyone that works with steel will know that compression isn’t necessarily bad, but it is mostly used in situations where tension will be present.

To prestress a piece of concrete:

  1. Steel strand made up of individual cables woven together are stretched and held in that position (imagine when you pull on a rubber band) inside of the form.
  2. Concrete is then cast around these steel cables and left to cure and bond to the steel cables.
  3. Once the concrete reaches sufficient strength (is hard enough), the steel cables are cut away from the supports holding them in their stretched position (letting go of the rubber band).

Since the steel cables are determined to return to their original position just like the imaginary rubber band did, this allows the tension force that was required to stretch the steel cables to squish the concrete together, also known as compression. Not only that, but when you concentrate the steel cables towards the bottom of the member you can create an upward force from the prestressing, resulting in compression on the bottom and tension on the top, or better known as camber. Now when this member is loaded up and wants to bend and deflect, it wants to put the top into compression and the bottom into tension. So the applied load must overcome the counteracting forces already in the member from the prestressing. Pretty slick, huh? I think so. That right there is the ultimate difference between cast-in-place and prestressed, because for a cast-in-place beam it is immediately put into tension on the bottom face because it is only reinforced with conventional reinforcement bar. This method uses the tension properties of steel, but not to take advantage of the compressive properties of the concrete, only to resist the load. This leads to earlier cracking and lower design strength. That’s why I’m all about prestressing, because inch-for-inch and pound-for-pound it is simply not possible for cast-in-place to compete. You would either have to shorten the span or deepen the beam, and we all know how well that typically goes over.

Now when you hear the buzz terms of “better crack control”, “better durability”, “higher span-to-depth ratio”, or any of the many others when compared to cast-in-place, you’ll know that it is first and foremost because it is precast. We control our enviroment so we can better control our product. On top of that, all of those advantages are made possible by prestressing the precast concrete. Using the natural advantage of steel to make concrete even more advantageous. This is why prestressed is so often referred to specifically instead of under the umbrella term of precast, because in the words of one of my past professors, Dr. Reza, “it’s a game changer.”

Chase Radue, EIT
Design Engineer

Why Prestress the Exterior Layer of Insulated Wall Panels?


Did you know that many precast concrete wall panel manufacturers do NOT prestress their exterior layer in an insulated sandwich wall panel?  In fact, some precasters don’t even use mild reinforcement (steel).  They do this because it either cuts costs and/or they don’t have the capabilities to do so.  Either way, it’s a loss for the customer.  There’s probably a good majority of people who don’t even understand the benefits of having a prestressed architectural layer.  I’ll try and explain…

Although reinforced concrete is generally a better construction material than the ordinary stuff, it’s still brittle and liable to crack in tension.  Reinforced concrete can fail in spite of its steel, letting water in, which then causes the concrete to deteriorate and the rebar to rust.  The solution is to put concrete permanently into compression by prestresssing (also called pretensioning). Compression is the cunning trick that helps to stop cracking (and stops cracks from spreading if they do form).

Other Benefits of a Prestressed Exterior Wythe:

  • Aesthetically more pleasing panels due to the absence of cracks
  • Improves structural capacity and handling capabilities
  • Allows for composite design without the use of solid concrete (which is a big deal in colder climates)
  • Can reduce the required structural layer thickness
  • Helps resist thermal bowing along with camber & deflection issues
  • Higher strength concrete is provided to ensure the bonding of the strand

Dave Eilertson
Sales – Southern Minnesota/Southern Wisconsin

The question is…

So the question is, knowing no two days are identical, what makes a great day in your life? Is your great day a chronological list day? Does it include sore, achy muscles from a job well done? Is it something simple, like a smile from a coworker you helped? Or perhaps seeing the final product of a day’s worth of concentrated effort from you and your team? We each have our own motivations, job duties, burdens, and visions along with our knowledge, experiences, and past baggage. So the challenge is, list out what makes a great day in your world and leave that baggage behind.

Some thoughts for your list?

  • I know it’s going to be a great day when I wake up.
  • I wake up my children for the day and get a sleepy “Good morning dad”.
  • I get up early, have breakfast and play with my dogs for a few minutes.
  • I have a morning workout at the gym.
  • I spend time with the scriptures.
  • I have an easy commute to work.
  • Someone will genuinely tell me they appreciate what I do and are thankful for the service I provide. This can apply at home, at work, or in the community.
  • Helping co-workers find traction and great meaning in their work.
  • Learning new skills at work
  • Connecting with my children and learning what they are doing.
  • A chance to do some yard work.
  • Time in the man-cave watching sports or cranking up the 70’s tunes.
  • Staying in touch with friends on social media.
  • Spending time with your extended family
  • An hour or two of evening downtime.

You have the power to turn a bad day into a great one by making conscious decisions to do so. Focus on the good instead of the bad, and simple pleasures can turn your day around. My great day is a mystery of what is to come in the hours and days ahead.

“I am convinced that life is ten per cent what happens to me and ninety per cent how I react to it.”

-Charles Swindoll

Rick Ostgard
Sales – Twin Cities

Got a second?

Actually, it usually takes longer than a second.  This is commonly a large part of our day-to-day activities…talking to people.  You’ve heard the stats – women speak an average of 20,000 words per day while men speak an average of 7,000 words.  While this statistic might be alarming to some, the fact that we are verbally communicating is a major baseline for how we interact with each other.  Whether it’s at work or at home, we have internal, external, and follow-up conversations to help guide us through our daily routines.

Internal Communication

  • Example at work: “Hello Peter, what’s happening…uh, we sort of have a problem here. You apparently didn’t put one of the new cover sheets on your TPS reports. You see, we’re putting the new cover sheets on all TPS reports now before they go out.  Did you see the memo about this?”
  • Example at home: “Hey honey, did you pick the tomatoes in the garden today so the crazy chipmunks don’t ambush the plants and stuff their faces full of them again? I wanted to make some salsa tonight but cannot if we don’t have another batch of tomatoes.”

What if Peter didn’t get a copy of the memo for the new TPS report cover sheets (like that would ever happen!)?  Or what if the chipmunks devoured all the tomatoes (that could definitely happen!)?  The fact is that if we don’t communicate internally with our coworkers and family members, then things might get missed.  When things get missed, then projects, processes, or situations get more complicated than need be.

External Communication

  • Example at work: “Hello Ms. Client, would you have some time tomorrow to sit down face-to-face to review our scope so we’re clear on our proposal for the total precast parking structure?  I’m really excited about this project and want to make sure everything is covered.”
  • Example at home: “Hey neighbor, can you please try to stop your dog from barking at 2am every morning…it’s driving me insane!  Thanks pal!”

Communicating what’s included in the proposal for the total precast parking structure is much easier when all parties are together in one room.  We can open up the drawings, look through the details, and really discuss and learn a lot more than you could from just a dollar amount on a bid form.  I think in-person meetings are best, followed by phone calls, and then email.  However, if you want to shoot your neighbor a text to shut the dog up that’s fine.  Or you could just tweet it – #annoyingdog #neighborhoodlife #muzzle #stoptheinsanity #sleepdeprived.

Follow-Up Communication

  • Example at work: Milton says, “And then Mr. Lumbergh told me to talk to payroll and payroll told me to talk to Mr. Lumbergh and and and I still haven’t received my paycheck and he took my stapler, and he never brought it back and then they moved my desk to storage room B and there was garbage on it, and I really don’t appreciate garbage.”
  • Example at home: “Hey honey.”
    “Hey sweetie welcome home.”
    “Wait a minute, I don’t see the kids, you picked them up from daycare, right?”
    “Ahhh, no I thought you were going to?”
    “Ahhh, no…uh oh!”

It’s good to see Milton following up to make sure everyone is on the same page.  Apparently, Mr. Lumbergh didn’t communicate all the facts to Milton.  During our business day and especially after meetings, it’s important to follow up to make sure everyone heard the same thing.  The “he-said-she-said” assumptions can sometimes be foggy.  This is where taking meeting minutes and/or emailing out decisions and action items to a group to make sure everyone heard the same thing is key.  And at home, obviously there was a lack of communication on whose responsibility it was to pick up the kids from daycare that day.  But following up before it’s too late helped save the $25 late kid pickup fee.

Mat Boie
Sales – Twin Cities

Reference:  Rappaport, D. and Rotenberg, M. (Producers), & Judge, M. (Director). (1999). Office Space [Motion Picture]. United States: Judgmental Films.

What is Continuous Insulation?

I realize continuous insulation may have been briefly discussed in prior blogs, but it is a frustrating topic that needs continuous education and discussion. This topic reminds me of an analogy from Mr. Rick Ostgard explaining the concept by using a winter coat scenario.

One coat has only strips of insulation, compared to another coat with continuous insulation throughout. 

The summer analogy compares applying sunscreen in strips, compared to continuous sunscreen application. 

In the end, it’s your choice. Do you want to wear a partially insulated coat when it is -10 degrees outside? Do you apply strips of sunscreen for protection from the sun? It seems the construction world is more concerned with the price of wall systems versus what high performance wall systems really are and what they can accomplish. It is up to you to learn about the wall system you want on your next project, but we hope this illustration has helped you understand the concept a little better.

Spencer Kubat
Vice President – Sales/Marketing 

*Original analogy courtesy of Rick Ostgard

Precast Parking Ramp Advantages

The creation of a durable, corrosion-resistant parking structure with a superior life cycle starts with the formulation of quality concrete as follows:

  • Low Water/Cement Ratio: The lower the water/cement ratio the more impermeable the concrete will be, the more strength it will exhibit and the less shrinkage-related cracking it will suffer. Wells Concrete typically fabricates parking ramp double tees with ratios as low as 0.35, whereas 0.38 is considered a low water/cement ratio for cast-in-place concrete and even then is extremely difficult to achieve under field conditions. The concrete water/cement ratio is the dominant factor in reducing chloride permeability.
  • Greater Compressive Strength: The greater the concrete strength, the more durable the finished parking structure will be. Wells Concrete’s factory precast prestressed concrete parking deck tees attain minimum concrete strengths of 7,500 psi which is more capable of resisting the forces of deterioration facing parking structures in the Midwest. Site-cast concrete is typically only 4,000 psi.
  • Superior Air Entrainment: The addition of microscopic air bubbles to concrete via air entraining agents increases the concrete’s ability to withstand freeze-thaw cycles. While air entrainment can be adversely affected during on-site placing and finishing procedures, our precast prestressed concrete is produced with close control of air entrainment, ensuring a durable driving surface.
  • Controlled Curing: Concrete attains strength, durability, and resistance to chemical attack when external humidities are kept at their highest levels. Controlling temperature and climatic conditions of site-cast concrete is nearly an impossible task. In our plant, temperature and humidities for the entire curing period are carefully controlled. Federal Highway Administration tests have shown that heat-cured precast prestressed concrete members absorb thirty to fifty percent less chloride in the first inch of concrete when compared to moist-cured cast-in-place slabs.
  • Better Clear Cover: The depth of concrete over reinforcing steel is a critical factor in controlling corrosion. Wells Concrete’s precast pre-stressed deck components have their primary reinforcement well down in the tee webs, away from areas of maximum chloride penetration. Consistent clear cover is almost never achieved in cast-in-place structures.
  • Greater Crack Control: Reducing the frequency of cracks is crucial to corrosion control. Weather conditions during on-site concrete placing can have a major impact on the likelihood that shrinkage cracking will occur. Surface cracking of site-cast concrete may also occur due to negative bending of the slab under load near the supports. Wells Concrete’s precast prestressed deck components typically have positive bending moments reducing the likelihood of flexural cracking on the top surface. In addition, our high-strength concrete promotes greater crack resistance.

Advancements made in the last five to ten years to a precast concrete, pre-topped parking structure, in response to the maintenance concerns that the cast-in-place proponents resort to:

  • Caulked Horizontal Joints: In the early years urethane was used as it was the best caulking material available at the time. Recently the sealant industry has developed high performance silicone parking structure joint sealants that are ideal for sealing the most demanding dynamically moving joints and horizontal applications.
  • Precast Flange-to-Flange Connections: In the early years the typical anchored weld plate from the precast flange of one double tee to the next was simply an embedded galvanized plate that welded with an additional loose galvanized plate that was only 1 inch clear from the top of double tee surface. This anchored weld plate was subject to rusting and deterioration should it be exposed to salts. In response to this the precast parking ramp industry developed a stainless steel anchored weld plate called JVI Vector connectors for shear alignment connections from the precast flange of one double to the next. These connections allow for thermal expansion during field welding, eliminating spalling or cracking. These connections were also positioned 1.5 inches clear from the top of the double tee surface to allow proper room for the backer rod and caulking to bridge the connection.

Mike Mortensen
Regional Sales Manager – North Dakota

Top 10 Reasons to Use Precast Walls

Top 10 reasons to use precast walls for your next project:

  • Precast concrete insulated walls provide energy benefits that can exceed the benefits of mass or insulation used alone in the varying climate conditions we see in the upper Midwest regions.
  • Precast concrete walls act as thermal storage to delay and reduce peak thermal loads.
  • Precast concrete insulated wall panels used as an interior surface can save time and money by eliminating the need for separate stud framing and drywall costs.
  • Precast concrete wall panels can be used as load bearing structures and will save costs by eliminating the need for an additional structural framing system.
  • Precast concrete walls can be designed to be reused for future building expansions.
  • Precast concrete’s durability creates a low maintenance structure, which stands up to harsh climate conditions.
  • Precast concrete colors and finishes can be achieved through the use of various aggregates, cements, pigments and finishing techniques.
  • Precast concrete wall panels can utilize a thin brick veneer that can achieve a traditional appearing facade.
  • Precast concrete walls can be produced with textures including formliner shapes, artwork, and lettering to provide distinctive accent treatments.
  • Precast concrete wall panels can have electrical boxes and conduit cast into the panels, to provide flush electrical fixtures on walls that are not to be framed out.


Rick Hodek
Sales – North Dakota

Work stressing you out?

Every year someone I know inevitably makes the comment about how overworked they are. I like to follow up their statement with one question: “How much PTO (paid time off) do you have?” Most of the time the response is well over two days of vacation. When I press them about why they do not disappear for a Friday or, better yet, take a week off, the response I commonly get back is either they are saving it in case they need it or just the thought of the amount work that stacks up while they are away is more stressful than the unhealthy work life balance they currently possess. When they do not use their paid time off they contribute to the already staggering statistic that U.S. employees typically leave about 429 million paid vacation days on the table every year.

I personally think one of the most beneficial things about taking some time off is allowing for a clarity break. I want to be clear: when I refer to taking PTO, I mean being completely off the grid; no email, no phone, and no clue about what is going on. Now I realize that most of the people that are reading this are either nodding in agreement or am thinking I am crazy, but please bear with me. When you are completely disconnected for a period of time a couple of things should happen.

The first thing you will notice is it feel like a weight is lifted off your shoulders (if you truly are disconnected and not cheating by skimming the emails as they float in). The relief of stress will change the way you think and problem solve. Think about past decisions you have had to make when you felt annoyed, angry, stressed or were in pain. Your mindset is different. Your patience is different. Literally the way you interpret everything is different. A few days being completely disconnected should help to reset your state of mind.

The other major reason to take a much needed clarity break is you will see the day to day items you deal with differently. When we are stressed or rushed we all tend to get into problem solving mode, or the more accurately defined fire-fighting mode, but that doesn’t always solve the real issue. When you remove yourself from the process you get a chance to see exactly what the intangibles are that you bring to the process. By completely disconnecting, it also puts both the team and the processes that you have built to the test. When you come back you will have a refreshed state of mind to easily identify what holes you need to plug or what team members need help.

So if you are an employee, takes some time off. You deserve it. The same applies to managers. I am sure your direct reports will thank you.

Greg Roth
Director of Operations

The hidden benefits of total precast buildings

Total precast concrete structures offer many benefits to both the design and construction process as well as the operation and longevity of the building. A total precast concrete building system combines all structural elements with architectural features and finishes to achieve almost any desired look.

Design and construction benefits:

  • Reduce the number of trades on site, eliminating potential schedule gaps and reducing the cost of crew & equipment mobilizations for each of the different trades.
  • Fewer details with interfacing materials will reduce the risk of fit problems caused by the differing installation tolerances of non-like materials.
  • Temporary bracing can be greatly reduced because the precast floor and roof members are erected simultaneously with the walls.
  • Precast stair systems are installed as the building goes up, eliminating the installation, removal, hassle and cost of temporary stair systems.
  • Because the precast components are installed as they arrive, virtually no storage or lay-down areas are needed, resulting in a cleaner and safer job site.
  • Windows can be pre-installed at the production facility.
  • Electrical items can be cast into the precast pieces eliminating exposed conduit.

Samaritan Bethany (Rochester, MN), Jackson Fire & Ambulance Station (Jackson, MN), Higher Ground (Minneapolis, MN)


Building operational benefits:

  • Speed to market: construction rates of one floor per week can easily be achieved.  Time from start of construction to first day of operation can be greatly reduced.
  • Precast offers some of the lowest sound transmission rates of any building material. Whether the space is residential, hospitality, or shared retail, the neighbor’s complaints about noise become a thing of the past.
  • Precast walls offer continuous insulation sandwiched between two layers of high strength concrete, reducing heat loss in the winter months and cooling loss in the summer.
  • Mold resistant structures.  Precast concrete offers no food source for mold to grow.
  • Precast concrete is noncombustible and is naturally heat and fire resistant. This, along with resistance to mold, can lead to greatly reduced insurance premiums when compared to other combustible building materials. Monthly insurance premiums can quickly exceed the perceived cost savings of lesser building materials.

Total precast systems deliver a complete and sound building structure and is the perfect fit for today’s Lean Construction methodology.

Gary Pooley
Regional Sales Manager – Twin Cities

Precast and the New OSHA Silica Rule

The Department of Labor has issued a rule reducing permissible exposure limit of respirable crystalline silica from 250 to 50 micrograms per cubic meter averaged over an eight hour work shift.  This rule goes into effect for OSHA enforcement in the construction industry on June 23, 2017.

Complying with this rule will be a big challenge to construction in general.  While precasters face challenges, they also have advantages against comparable building systems.

  • Precast concrete is manufactured in a factory and shipped to a construction site for assembly. That means all manufacturing processes creating dust occur at our factories, not the job-site.  We can apply engineering controls during manufacturing to capture dust in a factory setting under reproducible conditions rather than a job-site.
  • Most openings are formed into our pieces rather than by cutting concrete. This means the additional dust from cutting openings at the job-site is not created.
  • Precast concrete pieces are custom designed. We can adjust piece layout and add reinforcing to minimize the amount of cutting required at the job-site.
  • Precast has a short construction duration. Coordination of subcontractors to prevent silica dust contamination between trades is likely to become a real concern.  Our short construction duration means our crews create dust fewer days and have to be coordinated with the dust producing activities of other trades fewer days.

Tim Edland, P.E.
Research & Development Director

“CarbonCast” High Performance Insulated Panels

What is it and what are the benefits?

  • Wall panels are composed of two concrete wythes separated by continuous insulation (ci) and connected by “C-GRID” shear trusses.
  • “C-GRID” carbon fiber shear trusses are low in thermal conductivity.
  • Panels are energy efficient and light weight. With the exceptional bonding and strength of carbon fiber trusses less concrete for a lighter panels with superior insulating values.
  • R values available in excess of ASHRAE 90.1 requirements.
  • A panel consisting of wythe thickness of 2-1/2” exterior+ 4” insulation+ 2” interior behaves structurally as if it was an 8-1/2” solid wall. Weighing as much as 40% less than conventional wall panels.
  • Panels can be Load bearing 12’ wide as tall as 40’+
  • Aesthetically versatile. Architectural features and finishes are available to meet any designers vision.
  • Wells Concrete is an authorized manufacturer and a member of the Altus group of precast manufacturers.

Jeff Holt
Sales – Iowa/Southern Minnesota

The Election is over…now what?

We don’t really know what to expect. President-elect Trump, more than any other national politician (at least in modern times) is much less predictable regarding what his actual governing policies will be.  This is due in part to having no political track record for us to examine, but also in part because he appears to operate more on instinct than a well-thought-out political philosophy.

There have been numerous agenda items cited by Mr. Trump, in no particular order:

  • Secure the border
  • Repeal and replace Obamacare
  • Strengthen trade agreements
  • Overhaul financial regulation / Dodd-Frank Act
  • Environmental De-regulation
  • Rebuild infrastructure
  • “Drain the swamp”
  • And last but certainly not least, reform US Tax system

Now at this point, all one can really do is speculate as to what the President elect may accomplish in his term. One area that I’d like to spend a little time studying is the proposed US tax reform. The Trump tax plan proposes the following:

Very fitting to Mr. Trump’s personality, his proposed tax changes are extreme and the likelihood of this drastic of a change is to be debated. Very similar to Obamacare, I think a person can be confident in saying there will be some changes but for a complete repeal, in Obamacare’s instance, or complete tax reform is unlikely.

What the tax reform may look like is a hybrid of the proposed President-elects plan, the existing House GOP blueprint, and the Senate Finance committee.

One thing that is certain is with a Republican President, House and Senate some changes to the existing tax law is bound to happen. I for one, will be anxiously awaiting what comes of President-elect Trump’s “extreme” plans.

Ryan Stroschein
Chief Financial Officer