PRECAST CONCRETE WALL PANELS

Precast wall panels, particularly architectural precast panels, enjoy widespread popularity because of their construction efficiency and esthetic possibilities through the use of aggregates, veneer facing materials, varying shapes, size and texture. The comprehensive report prepared by ACI Committee 533, Precast Panels, focuses on precast concrete wall panels that are produced in established precasting plants, although site precasting is an alternative fabrication method. The ACI 533R-93 should be used together wit ACI 318 "building Code Requirements for Reinforced Concrete", which may be legally binding. The guide covers both load-bearing and non-load-bearing panels. These can be fabricated of either normal weight or lightweight concrete, and may be solid, insulated, ribbed, hollow core, or sculptured. Any of panels can be reinforced with deformed bars, or welded wire fabric, or prestressing tendons.

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.

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.

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.