G8 - Describe Architectural Formwork Flashcards
What is architectural concrete?
Finish exposed.
Why is architectural concrete considered to be an economical choice?
Concrete surface is the finished surface, saving costs of cladding, maintenance costs are also reduced as concrete requires very little maintenance.
What is the normal maximum allowable deflection allowed for architectural concrete?
1/400 Canada 1/360 in the USA
What is FRP and why is it used?
Fibreglass reinforced plastic - used for forms who smooth and/or unusual shapes are desired.
What are form liners used for?
Create textures in concrete - smooth to rough or to create decorative designs.
What look does a ground and polished concrete surface give when coated with a sealer?
Mirrored cut-stone look.
A good forming system will produce what type of architectural concrete surface?
Smooth, flat, uniform colour & texture. Pattern in concrete should have straight clean lines, holes spaced evenly with no honey combing.
Who is responsible for designing forms?
Contractor - but approved by P.Eng
The architectural and structural plans will show the locations and details for:
Construction joints, control joints, expansion joints, chamfers, rustication strips, reveals, and other design features.
What are allowable tolerances?
Allowed deviation from plumb, level positioning, dimension.
Concrete mixes for architectural concrete usually have elevated levels of what two ingredients?
Cement & Plasticizer.
Why is tie spacing important?
Proper strength and give a pleasing appearance.
WHat are the purposes of embedded metals?
Provide protection or support. Provides a welding surface as well.
What type of release agent is normally used on architectural concrete forms?
Non-staining type.
What 3 things are rustication strips normally used for?
Formwork seams, control joints, and construction joints.
When should rustication strips be removed from the concrete?
When the concrete has sufficient strength to resist damage and the strip have had sufficient time to shrink.
When can formwork for architectural concrete be stripped?
Once the P.Eng has been approved.
How is a sand-floated finish created?
Within 6 hours of form stripping, surface is wetted and using a wooden hand float in circular motions, sand is worked into the surface to provide a uniform color.
Tooling with a bush hammer will give what kind of finish?
A rough texture, and can be used to hide form seam lines and other minor defects.
Grinding will give what kind of finish?
Smooth the surface and can be followed up with polishing for a cut-stone mirror-like finish
Color can be added to concrete how?
Pigments to the mix, acid etching, using colored aggregate or adding a dry-shake color/hardener during finishing.
Architectural ceilings may be textured:
Using a form liner, or other materials. May be shaped using dome pans.
To achieve a high-quality surface, it is important for the concrete to consolidate well, to achieve this:
Include increased amounts of cement and plasticizer.
For forms:
A high resin-coated paper-faced plywood is used, but it may also be steel, aluminum, hardboard, insulating board, fibreboard, cardboard, fibre-reinforced plastic, or thin pre-cast concrete panels.
Formwork design needs to show sequencing in what order?
Forming, placing concrete, curing, stirpping and re-shoring, and any other surface treatments.
Embedded metals are anchored to the concrete by?
Deformed rods, bolts, studs or bent bars.
Angle iron must be anchored every 300 mm along their entire length.
To prevent leaking concrete formwork must be watertight how?
Joints between sheathing panels will need to be filled with patching material, caulked or covered.
How must control joints be installed?
Perfectly plumb & level, secured to the formwork at intervals small enough to eliminate movement during the placement of the concrete.
When are waste moulds used?
When there are compound curves or intricate details.
Cutting a saw kerf in rustications trip will help:
Removal of wooden strips, soaking the wooden strips in form oil for a few days is a good technique as well.
How do you place concrete for architectural forms?
Rate of placement needs to be moderate, stud spacing close. Vibrating one layer of placement will into the previous layer will keep the placement lines hidden.
Architectural concrete must reach what strength before stripping?
10 MPa
Rough surface treatments:
May just require patching or plugging of the tie holes and defects, unless tie holes are being left open as an architectural feature.
Sandblasting surface:
Fine texture, but will not fix any imperfections left by the formwork.
Tooling surface:
Rougher texture than sandblasting, the bush hammer chips off the surface of the concrete, exposing aggregate beneath. Bush hammer is rarely done because the amount of labour required.
Exposed aggregate surfaces:
Use gap-graded aggregate, 3/8 diameter.
Rubbed finish:
A rubbed finish is done after any patching has been completed and as soon as after form removal.
The entire surface is wetted and rubbed with an abrasive such as a brick
Sand float finish:
Must be done within 6 hours of form stripping. The surface is wetted, and sand is worked into the surface using a wooden hand flat in a circular motion to produce a uniform color and texture.
