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Allowable formwork fins, other surface projections, surface voids and tolerances are defined in the new ACI specifications. Form-facing material requirements. ACI no longer specifies form-facing material requirements. The older version, ACI , specified no form-facing material requirements for Rough-Form Finish but had specific requirements for a Smooth-Form Finish that required the form-facing material to produce a smooth, uniform texture on the concrete.
For a Smooth-Form Finish, ACI did not allow form-facing materials with raised grain, torn surfaces, worn edges, dents or other defects that would impair the texture of the concrete surface.
ACI also required facing materials to be set in an orderly and symmetrical arrangement and required the contractor to keep the number of seams to a practical minimum. The revised specification only requires the form-facing materials to produce the specified appearance and texture as specified for SF Surface voids. ACI required tie holes and surface defects to be repaired but failed to define surface defects.
This was a major shortcoming of the old specification and typically resulted in costly disputes or repairs for concrete contractors, especially when surface defects were not defined in the project documents. Because ACI specifies the size of acceptable surface voids or more specifically specifies what size voids must be repaired, concrete contractors should be able to avoid costly disputes and unexpected repairs.
ACI did not address bugholes or surface air voids that commonly occur on formed surfaces - nether does the revised ACI specification. However, bugholes have been indirectly addressed by specifying the size of surface voids that must be repaired.
Therefore, bugholes and other surface voids are acceptable for as-cast formed finishes unless voids exceed the specified allowable widths and depths. Specifiers should select a rubbed finish i. If projections exceed these heights, ACI requires removal. Surface tolerances. ACI specifies the upper limits for abrupt or gradual surface irregularities for as-cast formed surfaces.
Classes A-D correspond with exposure conditions or aesthetic requirements of formed surfaces. Abrupt irregularities such as form offsets are measured within 1 inch of the irregularity and perpendicular to the surface.
For gradual irregularities, the gap between the concrete surface and a 5-foot straight-edge is measured between the contact points.
Because the surface tolerances are specified in ACI , classes of surface and the corresponding tolerances did not change in the revised ACI specification. ACI requires a mockup panel for SF In addition to showing the finish of the formed surface, mockups typically establish the minimum acceptance criteria for the as-built surface finishes.
Therefore, mockups should represent the quality of the finish that will likely be achieved during the actual construction. Concrete contractors should not cast mockups using new formwork but use seasoned formwork that represents the quality of the formwork that will be used on the project.
Anticipate formwork wear and tear as the project progresses. Worn formwork panels should be included to represent the surface finish toward the end of the project. Contractors should use the same formwork release agent and application method, concrete placing and consolidation techniques, formwork removal times and curing method as planned for the project. These factors will affect the appearance and texture of the surface finish.
Consider using two different loads of freshly mixed concrete for casting the mockup. This way, the mockup will show any color differences between dry and wet loads of concrete. Also, use several formwork panels so the mockup will have seams. Make tie hole and surface repairs so the mockup truly represents the finish that will be produced during construction. This requirement is similar to the old ACI specification that required a Rough-Form Finish for surfaces not exposed to public view and a Smooth-Form Finish for surfaces exposed to public view.
Changing to "exposed to view" may simplify the criterion, but disputes as to what surfaces are exposed to view and not exposed may still occur. For this reason, concrete contractors should address unspecified as-cast finishes in the bid documents to avoid post-construction disputes. Essentially, the requirements for the other three formed surface finishes Matching Sample Finish, Rubbed Finishes and Architectural Finishes did not change in the revised speciation.
Here is a review of those specifications. Matching sample finish. Surface finish required to match sample panel furnished to contractor. Contractor must reproduce a mockup of the sample finish on an area at least square feet. Architectural finishes. Produce specified architectural finish including special textured and exposed aggregate finishes. January 10, Rubbed finishes free of bugholes consist of either smooth-rubbed, grout-cleaned rubbed or cork-floated finishes.
Here a worker is producing a grout-cleaned finish free of bugholes by rubbing a grout into the surface voids. Surface Finish Rubbed finishes Smooth-Rubbed - No later than the day following formwork removal, wet surface and rub it with an abrasive such as a carborundum brick until a uniform color and texture are produced. When insufficient paste can be drawn from the concrete itself, use a cementitious materials grout made from the same source as the concrete.
Mix to the consistency of thick paint and scrub grout into voids and remove excessive grout. Cork-Floated - Remove ties, burrs and fins, wet surface and apply stiff grout consisting of equal parts of portland cement and sand.
Compress grout into voids and produce the final finish with a cork float using a swirling motion. Shear Wall Success. How to Estimate In-place Strength of Concrete.
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DRM is included at the request of the publisher, as it helps them protect their copyright by restricting file sharing. Visit FileOpen to see the full list. ACI May Specifications for Structural Concrete.
New Surface Finishes for As-Cast Formed Concrete
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