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ACI 302 floor classes[Subject Prev][Subject Next][Thread Prev][Thread Next]
- To: seaint(--nospam--at)seaint.org
- Subject: ACI 302 floor classes
- From: GSKWY(--nospam--at)aol.com
- Date: Thu, 6 Jan 2005 12:05:24 EST
Since nobody else is posting anything, here is an explanation of the ACI 302 floor classifications.
I should note that I think that ACI 302 has a lot of good information, but the way it is written makes the information hard to find. In particular, the latest version has a lot of words that just get in the way of the trees.
Comments on the below are welcome of course.
ACI 302 FLOOR CLASSIFICATIONS
ACI 302 defines various classes of floors according to their anticipated use and lists recommended concrete strengths, special considerations, and finishing techniques for each class. The classification system oversimplifies the design considerations, but it does provide some insight into performance requirements for different uses.
There are fives classes of one-course floors, three classes of two-course floors, and one class (Class 9) that can be either one- or two-course. Although most slabs used for commercial and industrial applications are one course, two-course slabs are used for certain applications.
The single-course floors (Classes 1, 2, 4, 5, and 6) are defined as follows:
Class 1 floors are exposed surfaces with foot traffic; in some cases, decorative finishes may be required. Class 2 floors are covered surfaces with foot traffic; coverings may include carpet, resilient tile flooring, and ceramic tile. Typical applications for Class 1 and 2 floors are offices, churches, commercial, institutional, and multi-unit residential.
Class 4 floors can be exposed or covered surface with foot and light vehicular traffic in institutional and commercial facilities. Finishing recommendations for surfaces to be covered are similar to those for Class 2 floors.
Class 5 floors are exposed surfaces subject to industrial vehicular traffic with pneumatic wheels and moderately soft solid wheels in manufacturing, processing, and warehousing applications. A hard steel-troweled finish, good uniform subgrade, and appropriate joint layout are required.
Class 6 floors are exposed surfaces subject to heavy-duty industrial vehicular traffic with hard wheels, and heavy wheel loads; they may also be subject to impact loads. As with Class 5 floors, a good uniform subgrade and appropriate joint layout are required. Load transfer devices are required and metallic or mineral aggregate surface hardener may be used to increase abrasion resistance.
Class 3, 7, and 8 floors are two course. Two-course floors may have either bonded or unbonded toppings. Bonded toppings may be used when the surface must have special characteristics, and it would be either too difficult or too expensive to construct the slab monolithically. Bonded toppings can be placed immediately after the base slab is placed or can be deferred until the base slab has hardened. Bonded toppings may also be used to resurface worn or damaged floors. Minimum topping thickness should generally be 3/4 in. (19 mm); in new construction, the base slab should be textured to improve the bond. Because of the relatively small amount of concrete required, concrete for the topping is often site-mixed.
Two-course unbonded slabs may be used to allow the top course to be replaced more easily, or when the two courses need to move independently. The base slab should have a troweled finish; plastic sheeting, roofing felt, or a bond-breaking compound should be used to prevent the slabs from bonding. Two-course unbonded slabs can also be used to resurface floors when contamination would prevent complete bond, or when it is preferable to avoid scarifying and chipping the base course. The joint spacing of an unbonded topping does not have to be the same as the joint spacing in the base slab.
The two-course floors are defined as follows:
Class 3 floors, like Class 1 and 2 floors, are expected to have only foot traffic. The surface can be exposed or covered and the topping can be bonded or unbonded. Unbonded toppings should have a minimum thickness of 3 in. (75 mm); reinforcement may be placed in the topping course to reduce the width of shrinkage cracks.
Class 7 floors, like Class 6 floors, have an exposed surface that will be subjected to hard wheels, heavy wheel loads, and possible impact loading. The topping is bonded and often consists of high-strength concrete with select high-strength mineral or metallic aggregate.
Class 8 floors are floors with unbonded toppings designed for heavy industrial traffic. Minimum topping thickness is 4 in. (100 mm); the thickness is greater than for Class 3 floors because of the anticipated heavier loading. The topping slab should contain enough steel reinforcement to limit the width of shrinkage cracks and prevent movement of the concrete at the cracks. Reinforcement is sometimes continued through the construction joints to reduce curling. Although this may increase cracking, if there is sufficient reinforcement, the cracks will be kept tightly closed. Finishing techniques for the topping slab would be the same as required for a Class 4, 5, or 6 floor.
Class 9 (superflat) floors are exposed surfaces that have critical flatness and levelness requirements. These floors may have defined-traffic such as in highbay, narrow-aisle warehouses or random traffic, such as in television studios. Superflat floors can be constructed as a single-course floor, or as a two-course floor with either a bonded or unbonded topping. ACI 302 provides detailed recommendations for finishing techniques on superflat floors.
References to ACI 302 Classes
The ACI 302 classes are often referenced in literature for slab-on-ground related products. It should be emphasized, however, that ACI 302 is a guide publication, it is not a reference specification and thus cannot be referenced in project specifications. In addition, the criteria given in ACI 302 are recommendations, not requirements; the recommendations for a given floor class may be completely inappropriate for a specific project in that class.
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