In the realm of construction, architectural concrete stands as a testament to precision and artistry. The selection of materials, meticulous formwork, and precise placement all converge to create stunning architectural concrete finishes. In this blog post, we’ll delve into the nuances of architectural concrete construction, emphasizing its importance in achieving the designated architectural appearance. We’ll also explore additional subtopics, such as cement selection and surface treatments, to provide a comprehensive guide for those in the construction industry.
Formwork for Architectural Concrete
Materials: The foundation of architectural concrete lies in the choice of formwork materials. High-density options like steel, glass fiber-reinforced plastic, and exterior-grade plywood panels are favored. These materials ensure continuous, true, and smooth architectural finishes.
Tolerances: Conforming to the American Concrete Institute (ACI) 117 standards is paramount. High-density, non-vapor transmitting form faces are a must, ensuring that the final concrete surface aligns perfectly with the design reference standard.
Design Criteria: Face sheet deflection should not exceed 1/400 of its span, and concrete ties and bolts must be sized to withstand form design pressures.
Cement for Construction of Architectural Concrete
Source: It is advisable to source cement from a single, reliable source. This helps maintain consistency and quality throughout the construction process.
Conformance: Cement should conform to ASTM standards such as C150, C595, C845, or C1157, ensuring it meets the specific requirements of architectural concrete.
Admixtures: While certain admixtures can enhance architectural concrete properties, it’s crucial to avoid those containing calcium chloride to prevent adverse effects.
Mixing and Transporting Architectural Concrete
Equipment: Dedicate clean equipment exclusively for architectural concrete transport to prevent contamination.
Colored Concrete: When working with colored concrete, ensure it is transported in full loads to maintain uniformity in color and appearance.
Uniform Proportion: Deliver concrete with uniform proportions and slump to achieve the desired architectural outcome.
Conveying and Placement of Architectural Concrete
Support: Provide adequate support for concrete transporters, pump lines, wheelbarrows, and foot traffic to avoid disturbing reinforcements and concrete placement operations.
Quality Assurance: Engineer or architect approval of formwork and reinforcement placement before concrete placement is crucial to maintaining precision.
Efficiency: Prevent delays in concrete placement through effective scheduling and minimize splatter on formwork faces.
Consolidation: Ensure concrete is placed without segregation, in horizontal layers, and vibrate it for maximum consolidation.
Formwork Stripping
Timing: Strip formwork from vertical architectural concrete surfaces after achieving a compressive strength of 7 MPa or 24 hours post-placement, whichever is later.
Surface Maintenance: Maintain the surface appearance to match the accepted field mockup by breaking off fiberglass ties flush with the concrete surface and texturing it to match adjacent areas.
Curing Architectural Concrete
Moisture: Mist the concrete surface with water before applying curing compounds.
Manufacturer Guidelines: Apply curing compounds according to the manufacturer’s instructions and ensure complete contact when using cotton mat curing.
Repairs and Cleanup
Defects: Address surface defects promptly to maintain the designated architectural concrete appearance.
Curing: Cure repaired areas with a curing seal or waterproof cover, following commonly accepted techniques determined during field mockup.
Treatment Types for Architectural Concrete
Now, let’s explore various treatment types to achieve diverse architectural concrete finishes:
- Aggregate Exposed by Abrasive Blast: Suitable when concrete reaches a minimum compressive strength of 14 MPa.
- Aggregate Exposed by Removing Retarded Surface Paste: Commonly involves the use of surface retarders. Timing and weather conditions are critical to achieving uniform aggregate exposure.
- Acid Etch: Reserved for horizontal surfaces, applied after concrete matures for at least 14 days and exceeds 30 MPa in compressive strength. Wet the concrete before acid application.
- Mechanical Tooling (Bush-Hammering): Employed after concrete matures for at least 14 days and surpasses 30 MPa in compressive strength.
- Water Blast: Utilized to expose aggregate while adhering to the design reference standard, typically deferred until compressive strength exceeds 30 MPa.
In conclusion, architectural concrete construction demands meticulous attention to detail, precision in formwork, and adherence to standards. With the right materials, techniques, and treatments, achieving stunning architectural concrete finishes is not only possible but a testament to craftsmanship in the construction industry.