Architectural Concrete; Top 9 Best Practices
Architectural concrete is more than just looks.
It's got to be pretty on the outside and strong on the inside - and that makes it expensive. If you want the best quality, you have to pay for it.
Architectural concrete is on the rise and has become a staple of construction today.
So, chances are that your business will come across a project that needs it. And when you do, you'll want the highest quality architectural concrete. So, here's how you get it.
First, PAY for architectural concrete. If you’re going to hold a project to the highest standards, you need to pay for it. You don’t go to the doctor for a check-up and expect him to throw in heart surgery for free.
Paying for the architectural concrete is paying for the science behind it.
The creation of architectural concrete as a design element is influenced by:
1. Formlining & formwork system
2. Concrete mix, including the type of cement and aggregates. 3. Added pigments 4. Selection of a suitable release agent. 5. Subsequent surface treatment, such as washing, sanding, polishing, and sand-blasting. 6. Hydrophobising impregnation, color varnishing, and coatings.
It's not cheap or easy!
Getting the right materials and the right person for the job is essential.
GFS has done thousands of jobs and we want to work with you to make your project work. And to that end, we want to give you these best practices for free:
Number 1 To solve the color variation between trucks and get an accurate slump, have the trucks mix at the site for 1 minute per yard then sit with the barrel not turning for 30 to 45 seconds to allow the trapped air to escape. The driver will argue and tell you that it has been spinning in route, but it has not been spinning at full speed and has sloshed around more than mixed.
Number 2 When pumping you should make sure the driver keeps the concrete above the hopper so the paddles can’t bring in more air.
Number 3 My preferred mix design is a slump of 9 inches plus or minus 1 inch with a water/cement ratio of 0.40 maximum. The rest of the slump is produced with superplasticizer, not water. Water will just flow straight to the bottom and leave the rock behind.
Number 4 For 8-foot or higher walls, it is sometimes necessary to add a VMA (viscosity-modifying admixture). This prevents segregation by keeping the paste thicker which keeps the rock suspended.
Number 5 Concrete will also start to segregate after 20 feet of travel in the pump lines, so limit the length of the pump lines as much as possible.
Number 6 Keep the pump hose buried in the concrete about 12 inches using a long tremie pipe. This is the single most important thing if you can’t do anything else. Do not ever let the concrete fall more than 1 foot. This will cause immediate segregation of the rock and create air pockets.
Think of pouring a Dr. Pepper in a glass. If you just dump it in, it will fizz up because the carbonation is trying to get to the top and trapping itself. Sometimes it is worth making the wall thicker just to have room to get a 4 to 6 inch hose to the bottom. You should not have to relocate the pump either. With this mix design, the concrete will flow and the pump truck should let it flow by itself instead of constantly relocating the pump hose. The concrete will push the hose up letting the operator know to move it.
Number 7 Vibrating should mainly be done with the vibrator being pulled up not going down. The vibrator should be in the off position on the way down and then pulled out a rate of 1 foot per 2 seconds. Avoid a constant up and down motion. This is how the vibrator gets stuck between the rebar and form. Plus it will push the rock to the bottom and the paste out to the sides.
Number 8 To help seal the plywood edges, I recommend double-facing forms and using a 3 mm weather strip between the plywood joints. This keeps the paste from leaking out and leaving the sand behind which is what causes the dark spots at your form joints. I like to use ¾-inch BB plywood then stagger my joints with ½” HDO plywood.
Number 9 Lastly, I prefer Olympic multi pour HDO plywood. It has more of a matte finish which is more forgiving and allows the air to dissipate. I have had problems with other form panels causing tiger stripping and dye coming off the film and staining the concrete.
Get the Right Materials for Architectural Concrete
GFS gang form is specifically engineered for architectural concrete. It provides the highest quality finish while maintaining a high production rate and it can be custom made to any job site condition. See some of our architectural concrete projectsusing gang forms.
Getting the right materials and the right person for the job is essential. GFS has done thousands of jobs and we want to work with you to make your project work.