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Concrete Casting News from the Hill and Griffith Company

Review of AWWA Standard for Concrete Potable Water Prestressed Concrete Pressure Pipe & Concrete Steel Pressure Pipe

Posted by Hill and Griffith Company on Sep 6, 2018 11:04:40 PM

"The forms shall be cleaned thoroughly and coated with a form-release agent before each use."

Concrete Pressure Pipr 101

(Image from PUBLIC WORKS Magazine.)

I. Introduction

I.A. Background

There are two types of prestressed concrete steel-cylinder pipe:

(1) the lined-cylinder type, with a core composed of a steel cylinder lined with concrete and subsequently wire-wrapped directly on the steel cylinder and coated with mortar; and

(2) the embedded-cylinder type, with a core composed of a steel cylinder encased in concrete and subsequently wire-wrapped on the exterior concrete surface and coated with cement mortar.

The lined-cylinder type, which was first used in the United States in 1942, is furnished in sizes from 16 in. (410 mm) to 60 in. (1,520 mm). The embedded-cylinder type, which was developed later and first installed in 1953, is most commonly manufactured in sizes 48 in. (1,220 mm) and larger. Both types are designed for the specific combination of internal pressure and external load required for the project in accordance with the procedures outlined in ANSI/AWWA C304, Standard for Design of Prestressed Concrete Cylinder Pipe. Prestressed concrete steel-cylinder pipe is used for transmission mains, distribution feeder mains, pressure siphons (including river crossings), penstocks, industrial pressure lines, water intake lines, and other applications. In the manufacture of lined-cylinder pipe, the first step is to fabricate and hydrostatically test the steel cylinder with joint rings attached. The cylinder is then lined with concrete to form the core. The concrete is placed either centrifugally, by vertical casting, or by a radial compaction method. The concrete lining is cured and high-tensile wire is wrapped around the core directly on the steel cylinder. For a selected wire size, the tension and spacing of the wire are controlled to produce a predetermined residual compression in the core to meet design requirements. The wrapped core is then covered with a dense premixed mortar coating applied by a mechanical impact method. In the manufacture of embedded-cylinder pipe, the cylinder and joint rings are constructed and tested in the same manner as lined-cylinder pipe. The cylinder is encased in concrete by vertical casting and mechanical vibration to constitute the core. After curing, the wire reinforcement is wound under tension in one or more layers around the outside of the concrete core containing the cylinder, instead of directly on the cylinder. The exterior coating of premixed mortar is placed by impaction. 

Concrete Pressure Pipe Basics

(Image from PUBLIC WORKS Magazine.)

4.6.5 Concrete for pipe core.

4.6.5.1 General. The concrete in the cores may be placed by the centrifugal method, by the vertical casting method, or by other approved methods.

4.6.5.10 Placing concrete by vertical casting method. The concrete lining or core shall be cast on-end on a cast-iron or steel base ring with rigid steel collapsible forms for the concrete surfaces. The forms shall be designed to ensure that they will have smooth contact surfaces, tight joints, and that they will be firmly and accurately held in proper position without distortion during the placing of the concrete. The forms shall be designed to allow the pipe core to be removed without damaging the surfaces of the concrete. The forms shall be cleaned thoroughly and coated with a form-release agent before each use.

(Remember that any concrete form release used for potable water needs to be NSF approved, like Grifcote LV-50 Plus.)

The transporting and placing of concrete shall be carried out by methods that will not cause the separation of concrete materials or the displacement of the steel cylinder or forms from their proper positions. Adequate methods of mechanical vibration shall be used to compact the concrete in the forms and to ensure satisfactory surfaces. 


Precast Concrete In The Google and NPCA News:

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Precast Concrete Pavement Slabs: Design and Construction Considerations

Annual NPCA Convention - Oct. 4 – Oct. 6, 2018 – Providence, R.I.


 

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Tags: Concrete Forms, Concrete Form Release Agents, Concrete Release Agents, Concrete Casting Supplies, NSF Potable Water Concrete Release Agents, Prestressed Concrete Pressure Pipe, Concrete Steel Pressure Pipe, Grifcote LV-50 Plus, Concrete Form Release

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