how can I prevent slippage on hollow core strands

[o4121]

I'm having a slippage problem when I cut my hollow core planks in the form. My stressing machine has been calibrated recently. I do not have contamination on the strands. My brakes on the samples are good, I'm releasing my lines above what I need to. My strengh on the concrete is good. Please help me! Thank you!

 

[JAE]

Oil or other contaminents on the strand itself? Are they cleaned prior to installation? Slippage is most directly affected by the bond between concrete and strand - I'd look there first.

 

[concretemasonry]

Limestone aggregate to reuduce the sawing cost?

Some limestone can break down slightly in mixing and give you more "dirty" fines than you think.

Dick

 

[rapt]

o4121,

I would be looking at strand coatings. Some strand is coated with water soluble oil for transport.

 

[diazmeyer]

Depends on various variables:

1. Coating on strands (original or contaminants from the bed)
2. Local strength (sometimes breaks are not representative i.e temperature gradients in the slab)
3. Compaction around the wire.
4. Type of hollow core machine used (some movement in the wire occurs while casting, preventing wire/Concrete adherence).

You will have to isolate each one of them in turn, but it will probably clear up before you find out what it was.

Best wishes from Tarragona (Spain)

 

[civilperson]

Wash your strands with soapy water prior to use so that a light coating of rust appears, (or store out in the rain for a few weeks). Tap the stretched strand to knock of the extra rust and then place concrete. Try for a 5000 psi break before sawing the strands.

 

[concretemasonry]

If you are making hollow core plank, you must be in a plant that routinely makes that type of product.

If this is true, join or contact the PCI for technical assistance and the manufactured of the extruder (if it is extruded). If it is wet cast, this may not be an option and your best sources would be the strand supplier and the PCI.

It sould not be necessaey to wash and baby strands because of the limitation of the strand supplier to provide a usable product.

When it comes to material specifications, ASTM standards really only guidelines. Even if a material meets the loose ASTM requirements it may not be, it may not be suitable for your situation. Particle size, shape and physical properties are very important and the handling of the aggregate can degrade the properties of some aggregates between the sampling and use locations. Factory operations require far more sophistication, uniformity and quality control than field or ready-mix applications.

Dick