THE SPUN PRESTRESSED CONCRETE PRODUCT

The spun concrete products (poles and piles) offers an improved technology that combines the benefits of centrifugal casting with those of prestressing and high strength concrete in the manufacturing process. Spinning is the highlight of the manufacturing process. During spinning the fresh concrete is subjected to very high centrifugal forces that compact the material against the interior of the steel mold and expel excess water in the mix. The overall porosity of the material is therefore reduced, and as a result the hardened concrete is exceptionally dense and is high strength. The higher strength is attributed mainly due to the lower w/c and the higher density of the concrete after spinning.

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THE SPUN PRESTRESSED CONCRETE DESIGN AND MATERIALS

The Poles are designed as member subjected primarily to flexure. Axial load effects should be considered since large considered since large secondary moments may occur due to the deflection of the pole. In the case of guyed poles, the axial loads may be large enough that the pole should be treated as a compression member. Shear and torsion may be significant in some cases but seldom control the design.
The piles are designed as member subjected to axial and flexure. Both axial load and flexure should be considered together because this component is used as part of the foundation, and they support the gravity load as well as the lateral loads which cause bending and shear action on it (earthquake). The codes used as the standard design are JIS A 5335, ACI 543, and Indonesian Concrete Codes (PBI).
Currently concrete design strength range from 50 to 65 MPa. In many cases; however, spun cylinders are made to take advantage of the increased compressive strength due to spinning. The reinforcing steel cage is composed of main and secondary steel. High strength, wire prestressing strand or prestressing wire oriented in the longitudinal direction comprise the main steel reinforcement. Closely spaced spiral steel wire wrapped around the strands provides the necessary secondary reinforcement. The spiral reinforcement, which is normally 5-mm diameter, with yield strength up to 400 MPa, is needed to resist temperature stresses, transfer forces at end parts, and contribute to the torsion and shear strength of the member.

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THE SPUN PRESTRESSED CONCRETE DELIVERY

Truck transportation is the most common method used to haul the concrete poles and piles to the jobsite. Rail and barge are also utilized when feasible or necessary. At the jobsite a crane removes them from the truck using a spread yoke or spreader bar. Typically a two-point pickup are provided to handle poles and piles by crane in horizontal position; however, during erection they are usually handled from one-point pickup at or the center of gravity.
Segmental construction is also used and preferred where it is difficult to transport the full length member or when the poles are to be erected in the congested areas. The poles and piles are made of shorter segments and then assembled at the site using one of several splicing methods..

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THE SPUN PRESTRESSED CONCRETE POLE AND PILE

The spun prestressed concrete pole and pile, they are made in the similar procedure and process of production. The difference between pole and pile is only in the physical dimension and their function/ application. The pole usually has different diameter on the top and the bottom part (conical shape), while the pile has the same diameter for the whole part (cylindrical shape). The pole is an upper ground structure, while the pile is an underground structure. The applications of the pole include decorative street lighting, distribution poles, rail electrification, support for high voltage transmission poles, communication towers, and wind turbine support structure. The pile is used as a deep foundation.

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PRECAST CONCRETE WALL PANELS MATERIAL

Precast concrete panels are fabricated and erected using the same basic materials as for all concrete construction: Portland cement, fine and corse aggregates, admixtures, inserts, insulating materials, and specialty coatings to enhance esthetic appearance.
Architectural precast panels are often made of two types of concrete because of the cost of decorative aggregates and white cement. A backup, or structural, concrete is used for most of the panel thickness, and the concrete for the exposed face of the panel thickness, and the concrete for the exposed face of the panel is selected for its architectural appearance.

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PRECAST CONCRETE WALL PANELS FABRICATION AND DELIVERY

Concrete mix proportioning is generally the same as cast-in-place concrete, but greater emphasis is placed on the ability of the mix to produce the desired finish and durability of the concrete surface. Factors to be considered in the concrete mix are:
- Finish, size and shape of the precast units.
- Method of consolidation.
- Maximum size of coarse aggregate.
- Required comprehensive strength.
- Required surface finish.
- Exposure to severe and the other condition.
Handling and storage procedures should not cause structure damage, detrimental cracking, architectural impairment, or permanent distortion when a panel is being lifted or stripped from the mold, moved to various location for finishing or storage, stored, or loaded or unloaded for delivery and erection. Structural calculation should verify that the panel can be handled in the desired manner, otherwise it should be braced during stripping, handling, transportation and delivery operation.

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PRECAST CONCRETE WALL PANELS DESIGN

Non-load-bearing panels, often called cladding, are in general not significantly different from load bearing wall panels. For design purposes, non-load-bearing panels are assumed to transfer negligible load from other elements. Handling, storage, transportation, and erection consideration are identical for all precast panels. Thermal movement and other volume change effects of the panels are likewise identical for both classes. The codes adopted for designing precast concrete panels are ACI 553R-93 and ACI 318-94.

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