Frequently Asked Questions

Below are a variety of questions that we are asked on a regular basis. If you don’t find the answer to your question here, please feel free to fill out the form and submit a question or pick up the phone and give us a call! We’d be happy to help you with whatever questions you have!

GENERAL

  1. Why use precast concrete?

    Precast concrete is the ideal solution for your next residential or commercial project. Precast concrete provides durability, flexibility, and versatility both in the design and construction stages of the project. Precast concrete homes and building have great fire ratings and often eliminate the costly process of fireproofing.

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  2. Why build a precast concrete home?

    Concrete homes are extremely sound and durable. A total precast home is extremely mold and mildew resistant compared to a traditional wood or brick home. Total precast homes have no beams and columns in the basement which provides long clear spans for a very flexible design. Precast concrete homes have a very high fire rating and provide a great storm shelter because of their strength. Precast floors are great when combined with radiant heat.

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  3. Why use concrete construction for a prefabricated building?

    Concrete construction is extremely fast, and very durable. Buildings can be erected in any weather condition including harsh winters. Concrete, prefabricated buildings have great fire ratings, are very sound, and versatile.

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  4. What is the difference between Precast concrete construction vs. traditional construction?

    Concrete construction is durable and long lasting, and retains its value throughout time. Precast concrete construction lessens the construction process which saves money on financing costs.

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  5. How flexible is precast concrete design?

    Whether you use our wall panel system, or our hollow core floor system, or if you build a total precast home, the design possibilities of concrete construction are endless. Call us today to learn more. You’ll be surprised at how versatile precast concrete is!

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  6. Why use Prestressed Concrete vs Poured Concrete?

    Prestressed concrete has very good crack control and strength to weight ratio. Precast concrete is able to create longer, thinner spans than poured concrete.

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  7. Why is concrete so heavy?

    In fact, concrete is actually 31% of the weight of structural steel. Concrete weighs 150lbs/ft3, steel is 490lbs/ft3. In office structures, a completed concrete structure (floors, walls, roof, beams, columns etc.) could be as much as 19% lighter than a composite steel frame and concrete slab building.

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  8. What kind of Quality Control/Quality Assurance is in place in the precast industry?

    PCI has three different certification programs:

    Plant Certification – First introduced in 1967, covers the overall management of the quality system within precast/prestressed plants.

    Personnel Training and Certification – First introduced in 1985, covers the qualification and certifications of the people doing the product inspections and managing the Quality Assurance departments within precast/prestressed plants.

    Erectors Qualification/Certification – First introduced in 1999, covers the training and qualification of field services personnel.

    For more information on the PCI Certification program, refer to PCI Manuals for Quality Control – MNL116 or 117 that can be found on the PCI website at www.pci.org.

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STRUCTURAL/ENGINEERING

  1. What happens when a prestressed strand is cut in a finished piece of concrete?

    Visually or safety wise, nothing immediate would happen. The structural capacity of the member could be affected if any type of reinforcing is cut (prestressed or mild reinforcing). A structural engineer should be consulted before cutting any type of reinforcement.

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  2. How are fire ratings calculated in concrete?

    The most common practice is to follow the PCI Manual MNL 124, “Design for Fire Resistance of Prestressed Concrete.”

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  3. What is the relationship between the Engineer of Record and the Precast Specialty Engineer?

    The Engineer of Record is responsible for the structure in its entirety and delegates the design of the components to the specialty engineers involved in the project. This is the case in precast/prestressed concrete as well as many other products (wood, steel etc.). This relationship is well defined by the National Council of Structural Engineers Association (NCSEA).

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  4. What are the benefits of precast in terms of fire?

    Precast/prestressed concrete is non-combustible and provides endurance against fire as in any type of concrete. The use of precast/prestressed concrete floors and walls provides excellent compartmentalization in multi-family or office structures.

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  5. What are some key things to look for when inspecting precast?

    Good bearing conditions i.e. bearing pad is in correct location, surface is uniform

    Structure is plum, well aligned

    Welding of connections is appropriate and complete to stage of construction

    Loads being applied at time of inspection are appropriate to intended design

    For further detail, refer to PCI’s Erection Manual MNL 127 and Tolerance Manual MNL 135. Any specific questions should be answered by a structural engineer.

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  6. What kind of testing has been done in cracking of precast?

    Refer to PCI Committee on Quality Control Performance Criteria “Fabrication and shipping cracks in prestressed…” PCI Journal Volume 28 and 30. For a more complete list see PCI’s Design Handbook MNL 120.

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  7. What are the minimum requirements for joints between precast products?

    Criteria for joint sizes can vary considerably depending on the product type, size and building movements. Typically, joints in structural products are 1” and architectural products are ¾”. However, there are a number of considerations like building expansion joints, building isolation joints etc. that will dictate joint widths. Please see PCI Design Manual MNL 120 and PCI Tolerance Manual MNL 135 for further information.

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PRODUCTS

  1. What are the benefits of a wall panel system?

    Precast wall panels are an energy efficient alternative to steel and masonry, providing a hard wall and eliminating the need for exterior columns. Precast wall panels are not only energy efficient, but also mold and mildew resistant. Precast wall panels provide flexibility in the design phase of your home or building.

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  2. What is hollowcore?

    Hollowcore is a prestressed concrete slab with continuous voids provided to reduce weight and cost. Hollowcore is primarily used as a floor or roof deck system.

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  3. How is hollowcore made?

    Hollowcore slabs are produced worldwide using a variety of manufacturing processes. Kerkstra has chosen to use a production system developed by Elematic. This state-of-the-art system is a dry cast, extrusion process where zero slump concrete is forced through the machine. The cores are formed with augers and tubes with the concrete being compacted around the cores using high frequency vibrators.

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  4. What are the benefits of hollowcore?

    Hollowcore slabs provide economical, efficient floor and roof systems. Structurally, a hollowcore slab provides the efficiency of a prestressed member for unsurpassed load capacity, span range, and deflection control. In addition, the grouted slab assembly provides a basic diaphragm for resisting lateral loads. Excellent fire resistance is another attribute of the hollowcore slab system. Used as floor-ceiling assemblies, hollowcore slabs have the excellent sound transmission characteristics associated with concrete.

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  5. Will the hollowcore provide a perfectly smooth surface?

    Hollowcore slabs will be cambered as with any other prestressed flexural member. The amount of camber is affected by span, prestressing forces, concrete differences and curing variations. Kerkstra recommends that the erector adjust the bearing elevations and level adjacent slabs to minimize the camber differential. Also, as with any structural concrete component, minor imperfections in the surface should be anticipated.

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  6. What is done to finish hollowcore at the project site?

    The top surface can be finished with a structural, composite concrete topping or by simply ‘feathering’ the joints with latex cement. We do not recommend carpet direct. The underside can be used as a finished ceiling as installed, by painting, or applying an acoustical spray.

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  7. What openings can Kerkstra put in the hollowcore?

    The drycast system used in the manufacturer of the hollowcore slabs is not conductive to providing “finished” openings similar to those available in other Kerkstra products. Kerkstra will provide “rough” square or rectangular openings through the hollowcore slabs required by other trades which are 100 square inches or larger. Kerkstra will review required openings in the hollowcore slabs and if necessary, introduce steel header frames to achieve the openings. In some instances, openings may have to be field cut by others to ensure the structural integrity of the hollowcore slabs during manufacture, shipping and installation.

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  8. What needs to be done to finish the openings?

    Plant provided openings are ‘rough openings”. If openings through the hollowcore slabs are to be left in an exposed condition, others may provide concrete patching or trimming of the opening with another building material.

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  9. What needs to be done for openings less than 100 square inches?

    Holes smaller than 100 square inches should be core drilled by the trade requiring them after the slabs have been erected and grouted. The drilling should be done only with the express written approval of Kerkstra‘’ engineering department.

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  10. Are narrow width slabs available?

    Kerkstra can provide hollowcore slabs narrower than the 4’-0” modular width. A longitudinal saw cutting process after the slab is cured and removed from the casting facility achieves this. To ensure the structural adequacy of the slab, there are restrictions on the widths of slabs that are available. Contact your Kerkstra representative for further information on the range of narrow widths available.

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  11. Will the hollowcore cover the entire floor area?

    The hollowcore slabs will be laid out on Kerkstra’s drawings to minimize the requirements for field pour strips. However, in some instances, pour areas adjacent to walls or around openings may be required. These will be clearly indicated on our layout drawings and details and are the responsibility of others.

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  12. How is the hollowcore erected?

    Hollowcore should be erected by personnel skilled in such work utilizing lifting devices and cranes capable of safely handling the slabs. The slabs are to be positioned and connected to the structure in accordance with Kerkstra drawings and details. The slabs are erected one at a time with slings and spreader bars specifically suited for hollowcore. Your Kerkstra representative can provide you with the information sheet ‘Procedure for the Proper Installation of Precast Hollowcore Slabs’.

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  13. How is hollowcore connected to my building?

    There are numerous methods to connect the hollowcore slabs to the building frame. The type of connection is dependent on the building material the hollowcore bears on or connects to. Kerkstra has a library of cost-effective connection details for concrete, masonry, steel and precast concrete construction.

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