Info for Precast/Prestress plants

[asixth]

Hi guys,

I have recently designed some prestressed concrete beams and was looking for some information on how prestressed concrete units are actually made. I have organised a trip to a local facility but was wondering if anyone has some information on the process of making prestressed concrete beams.

 

[JStructsteel]

Its really simple, the tendons are streched between two end anchors, and then the concrete poured. Forming is usually done on beds, so the only forms are the sides. usually after a overnite cure they are stripped out and set in the yard to cure.

 

[cooperDBM]

The Prestressed/Precast Concrete Institute (PCI) will have what you need at

http://www.pci.org.

Their design handbook is a good reference. If you're in Canada you can contact CPCI at

http://www.cpci.ca.

They also produce a good design manual.

Your site visit will be a great value to you.

 

[asixth]

jrisebo,

Don't they need to wait for the concrete to achieve a design strength before they strands can be cut.

 

[JStructsteel]

Yes, usually its around 3500 if I remember correct. Precasters ususally use high cemement ratios, so that still is obtainable overnite. without prestress, 2500 is what they shoot for. Different plants have different mixes, times, etc.

 

[hokie66]

Steam curing is also often used to accelerate strength gain in precast elements.

 

[concretemasonry]

Very often you are not aware of the heat used for accelerated curing since it could be steam, hot water, hot oil or electric that is often built into the curing area floor or the molds.

The concrete mixes are highly proprietary for the local materials, products and curing. Normally, a precaster will only use its own mixes since using something different could be in contflict with the PCI certification program. The program is well established through the years and is used by the upper 85% of the industry. The certification is not just the mix design but is a very advanced and monitored quality program that puts the quality variations for poured concrete to shame by a large factor.

Dick