Design considerations must balance a variety of needs, including aesthetics, function and financing. Each plays a role in achieving success with the finished project. Architectural precast concrete not only can ensure these general goals are met, but it provides a myriad of life-cycle and ancillary benefits that are difficult to match with other materials.
Architectural precast concrete offers the building owner peace of mind that results from the certain knowledge that the building’s walls have long-term durability and require little or no maintenance to preserve their original look. This requires high cement contents and low water-cement ratios. Combined with good compaction and curing in a controlled factory environment, these factors ensure a dense, highly durable concrete. A low water-cement ratio has been proven to increase resistance to weathering and corrosion. Entrained air may be used to improve freeze-thaw resistance in particularly severe environments.
Architectural precast concrete panels provide the designer with an unlimited architectural vocabulary of expression. Whether the project’s aesthetic intent is traditional or contemporary, precast concrete can be shaped in a cost-effective manner. The material is incredibly responsive to the designer’s needs. The only limits are imagination and creativity.
Visual interest in the building’s façade can be enhanced with architectural devices such as ribs, bullnoses, reveals, chamfers or casting against various types of formliners. Precast may be designed with a combination of concave, convex and flat sectional shapes.
Taking advantage of precast’s initial plasticity can economically create these shapes, adding considerable aesthetic appeal to a project. Design flexibility is possible in both color and texture by varying aggregate and matrix colors, size of aggregates, finishing processes and depth of exposure.
Combining different finishes using the same or different concrete mixes within a single precast concrete unit can provide additional flexibility. A highly articulated pattern of color and texture develops a richness of architectural expression.
Commitment to Quality
Architectural precast concrete units produced by PCI-certified plants are produced under strict, factory-controlled conditions to ensure a high quality façade in the desired shapes, colors and textures along with close tolerances. Every PCI member must undergo two stringent unannounced inspections each year by independent auditors to maintain PCI certification. The inspections focus on the process by which the unit is produced, as well as the plant’s general operation.
Certification pays off for owners and designers because it produces fewer worries about onsite discovery of units out of tolerance, connection details that aren’t cast precisely or finishes that aren’t matched from panel to panel. It also minimizes the need for continuous inspections.
Life Cycle Cost
When comparing the cost of alternative façade systems, the cost throughout the design life of the building needs to be evaluated. A precast façade can be designed to match the intended life of a building with minimal maintenance, providing substantial long-term savings. Precast concrete panels present a durable aesthetically pleasing exterior surface that is virtually air and watertight and does not require painting. This helps the building remain in first class condition long after the mortgage is repaid, ensuring its desirability to future tenants or owners. It also means attractive refinancing can be accomplished more advantageously, too.
Precast’s speed of erection and its ability to be cast and erected in all kinds of weather aid the entire construction team. Since the casting process does not rely on other critical-path activities to begin, units can be produced as soon as drawings are approved, ensuring units are ready for erection as soon as foundation work and other site preparation is completed. These advantages allow the building’s shell, whether load-bearing or cladding, to be enclosed quickly. This, in turn, lets interior trades begin work earlier and reduces overall construction time.
Faster completion reduces interim financing costs, results in earlier cash flows, and produces other economic benefits. This ultimately lowers the building’s long-term overall cost and can make the use of precast concrete more economical than other façade materials.
Load-bearing panels can reduce framing costs by providing a column-free perimeter. Depending on the floor plan, there also is potential for reducing the number and/or size of interior columns, adding layout flexibility. This results in a more efficient and less costly construction. Cost savings are greatest for low -to mid-rise structures of three to 1 0 stories with a large ratio of wall-to-floor area.
Precast concrete panels can be designed to provide a high degree of energy efficiency for the buildings they enclose. Recessed window walls, vertical fins and various other sculptured shapes facilitate the design of many types of shading devices for window areas to reduce glare and solar gain. This provides economies in the cost of the air-conditioning system by reducing thermal load. Specific wall thermal characteristics can be designed for each face of the structure to suit its sun orientation.
To obtain a range of R-values, precast concrete walls may have insulation applied to the back, or the insulation may be incorporated into a sandwich wall panel to reduce heating and cooling costs. The thermal mass inertia of concrete, which is recognized in ASHRAE standards, also reduces peak heating and cooling loads, thus saving energy year-round by reducing large daily temperature swings.
Other Inherent Benefits
Architectural precast concrete is non-combustible with inherent fire-resistant capability, creating a safe envelope that helps protect personnel, equipment and the building itself. That in turn reduces insurance rates. It also eliminates the need and cost of additional fireproofing measures, except on structural-steel frames.
In addition, the inherent sound attenuation properties due to precast concrete’s mass provide an economical acoustical barrier to exterior or interior noise penetration. These attributes enhance the cost effectiveness of precast panels. The life-safety and tenant benefits provide a potent marketing asset when attracting long-term occupants. Precast concrete is an environmentally sound material. It is produced from natural materials. No toxic substances are produced in its production or use. Also, the production energy consumption of the concrete is quite small. The thermal mass of concrete saves energy year-round by reducing temperature swings.
Concrete’s high albedo (or ratio of light reflected) has the added quality of reflecting heat as well as light, thus reducing the “heat island” effect and higher temperatures endemic to urban areas. The resulting lower overall temperatures can make a difference in the amount of electricity consumed in air conditioning and can reduce smog formation, potentially improving air quality in urban areas. Precast wall panels can be reused when buildings are expanded. Non-loadbearing panels on the end simply are disconnected from the framing and additional panels and framing are added on each side. With the new addition in place, the end panels can be replaced. Concrete measures up well in regard to sustainability. It strikes a perfect balance between meeting today’s needs and natural resources for tomorrow.
As a single unit, precast panels provide one source for supplying the entire exterior wall system. When load-bearing precast structural floors along with panels are specified, it concentrates the complete shell with one certified and reliable producer. This approach ensures complete responsibility and accuracy for meeting design specifications rests with only one supplier. The precaster is responsible for all manufacturing and constructability issues. This reduces the number of subcontractors and minimizes trade coordination. Also, the producer’s competent staff of plant engineers is available to assist the design team.
PCI member precasters can offer detailed expertise that allows the development of design techniques, engineering innovations and scheduling improvements that save time and money from conceptual design to project completion. To maximize these benefits, the design team should interact with the precaster early in the project’s development stage. This ensures each element is as cost effective as possible and will take full advantage of precast’s inherent performance characteristics. The result will be a functionally efficient, aesthetically pleasing structure produced on time and on budget that meets all programmatic needs.
~ Information provided courtesy of PCI.