ACI 332-20 Code Requirements for Residential Concrete (ACI 332-20) and Commentary.
R5.1—Exposure categories and classes
R.l.1 For Exposure Category RF. Exposure Class RFO should be assigned to interiors and to liiotings. fjundations, and basement walls that are constructed below grade. Concrete deteriorates when exposed to freezing-and- thawing cycles when any portion of the member is in a critically saturated condition during freezing weather. Basement and foundation walls that extend above wade less than 12 in. are unlikely to be saturated and could generally be assigned Exposure Class RFO. Exposure Class RFI or RF2 should be assigned to vertical concrete members where excessive accumulation of ice and snow is not anticipated. Examples include above-grade walls, and columns. Exposure Class RF2 should be assigned to elevated or on-grade horizontal structurally reinforced concrete members that have a likelihood for prolonged contact with water to achieve a saturation state. Exposure class RF3 shall apply to nonstructurally reinforced soil-supported exterior slabs that are subject to l’reezeing-and-thawing cycling and deicing chemicals. Exposure Class RF4 should be assied to the same type of structurally reinforced members as in Exposure Class RF2 but also when exposure to deicing chemicals is anticipated. Examples include above-grade columns and structural slabs exposed to salts in a marine environment. Depending on exposure conditions, garage floors can be classified as RFO to RF3. but not RF4.
Exposure Category RS should be based on a measurement or knowledge of the concentration of soluble sulfates in soil or water that will be in contact with the relevant concrete member. The referenced test methods should be used to measure the sulfite concentrations. Other test methods can provide different results compared with the test methods referenced. Where the predominant soil sulftes are in the form of gypsum. the measured sulfate content will be higher, and these criteria will be conservative. In these cases, it is preferable that a test method that has a history of’ successilil use in the geographic area of the project be permitted and approved by the local building official. Even though concentration of soluble sulfates in seawater will be high, members exposed to seawater should be assigned to Exposure Class
Exposure Category RC is only applicable to concrete members with structural reinforcement and not to plain concrete. The corrosion of’ the small amount of reinl’orcement used as temperature and shrinkage steel in plain or lightly reinforced (temperature and shrinkage steel) concrete members does not represent a problem whereby the structural safety of the member will be compromised.
The user of this document is encouraged to develop a table to assign exposure classes for each concrete member on a project as shown in Table R5. 1.1.ACI 332 pdf download.