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Building with Tilt-Up | Frequent Questions

FAQ: Panel Forming

The TCA Technical Committee provides answers to common questions about Tilt-Up construction as well as some tips and techniques.

 

Where is the best place to cast the Tilt-Up panels?

On the floor slab as close as possible to their final position.

Is there a particular sequence or pattern in which the panels should be cast?

They should be cask with the lifting sequence in mind, so that the top panel on a stack is the first to be placed and so that it is not necessary to lift and reset panels. Consideration should also be given so that a panel still on the floor will not block the setting or bracing of another. Crane reach and travel should be considered as well. The panels should be cast so that the crane can lift them with a minimum of handling, and so that the concrete ready-mix truck can reach them. If possible, it is desirable to cast them with the inside face up so that the connections are visible, lifting inserts are patched to the inside, and so the wind braces can be connected before the panels are lifted.

What is the best method to form panels?

The edge forms are usually of wood with a bracket or wooden block periodically connected to the floor. These brackets are spaced to reduce deflection in the edge forms during placement. These brackets are glued, nailed, or bolted to the floor, depending upon the acceptability of the required patching to the owner.

How do I hold reinforcing steel and embedment items in placed?

All items should be adequately chaired for elevation and wired in place. If possible, the critical connection inserts should be spaced off the edge form to maintain accuracy. Do not try to wet-set items as the concrete is placed.

What are the recommended tolerances for the panels?

The tolerances for Tilt-Up construction supported by the TCA can be obtained from the THE TILT-UP CONCRETE ASSOCIATION’S GUIDELINE SPECIFICATIONS in Standard 3-part CSI Format as found in section 1.6. Tolerances in this section address the following:

  • Height & Width of Basic Panel
  • Thickness
  • Skew of Panel or Opening
  • Openings Cast Into Panel
  • Location/Placement of Embedded Items
  • Deviation of Concrete Reinforcing Steel Cover
  • Joint Width Variation
  • Joint Taper and Panel Alignment.
What can be done with bolts or dowels that stick up and get in the way of screeding or sacked casting?

Use threaded inserts that are flush with the panels to replace protruding bolts. Use threaded inserts or bent dowels to replace projecting dowels.

How high can you stack panels?

Panels can be stacked as high as desired, since it is unlikely that the floor will be overloaded. However, it will not be possible to place concrete directly from ready-mix trucks if over about three feet high. Another consideration is the lifting techniques off of a stack of panels. It is generally necessary to slide the panels a distance equal to its thickness before attempting to rotate, or it will fall off the stack.

How do you form stack-cast panels?

There are several ways currently in use that have variations of jump forms. Basically, the lower panel is cast with a form that is two panels thick. The first panel is cast and cured for a day, and then the reinforcing and hardware are installed in the next panel above it. The second panel is poured and cured for a day, and then the double thickness form is moved up one thickness to form the next panel. The form is held to the panel for this purpose with various items, including bolt, J-hooks and J-snap-ties.

How do you stack-cast when the lower panel has a large opening?

The hole can be blocked out in wood or filled with wet sand. A thin layer of concrete, grout or plaster is cast over it and trowelled to match the panel surface. Bond-breaker is then applied to the surface to seal it and prevent bonding of the concrete above it.

How do you form small block-outs and feature strips in panels?

Wooden, plastic, polystyrene, or metal blocks or strips are used. They should be non-corrosive and non-staining, firmly fixed in place so they will not move during placement. Those that have to be removed should be tapered for easy stripping.

What slump and strength should the concrete be for panels?

This will be specified in the design material, but the comments in Section B. Question 4, are generally used.

Should exposed aggregate be cast up or down?

With proper care, either can be done effectively. Exposed aggregate up has the advantage of you being able to see what the aggregate job will look like, but requires patching the lifting holes in the aggregate, and if it is large aggregate, there can be problems with the lift inserts.

If greater than 1½" rock exposure is used, the quick disconnect lifting system cannot be used, and the coil bolt system will require grout pads for bearing to be pieced at each lift insert. Exposed aggregate up will also require that the bracing be attached after panels are lifted, which slows down the lifting procedure. The exposed aggregate down leaves the finish a mystery until after the erection is complete. With aggregate down, the rock can be carefully pressed into a sand bed, and the concrete cast over it.

Care must be taken that workmen finishing the panel, vibrators, or concrete coming out of the ready-mix chute do not disturb the rock pattern. Retarder can be used for smaller exposures.

About the TCA

Founded in 1986, the Tilt-Up Concrete Association (TCA) strives to improve the quality and acceptance of site-cast Tilt-Up construction, a method in which concrete wall panels are cast on-site and tilted into place. Tilt-Up construction is one of the fastest growing industries in the United States, combining the advantages of reasonable cost with low maintenance, durability, speed of construction and minimal capital investment. At least 10,000 buildings, enclosing more than 650 million square feet, are constructed each year using this construction method.

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