Selecting Exposure Classes for Durability and Requirements for Concrete
For durability of concrete, the ACI 318, Building Code Requirements for Structural Concrete defines exposure classes and applicable requirements for concrete mixtures used to construct buildings. ACI 301, Specification for Concrete Construction incorporates these requirements in the ACI reference specification. NRMCA has developed some simple resources that will help designers select the appropriate durability exposure class and corresponding concrete requirements. This includes an Excel spreadsheet with details from the ACI 318 commentary and additional discussions of performance alternatives and criteria. The accompanying guide has the same information and includes some examples that will help with understanding the process.
The spreadsheet tool and the accompanying guide can be downloaded here and here.
Assigning durability exposure classes is part of the design process and is the responsibility of the licensed design professional (or engineer of record, EOR). EORs are encouraged to use these resources and select concrete requirements that comply with the Code and to minimize other prescriptive requirements for concrete. Specification requirements for concrete that are prescriptive, overly conservative, or generally not applicable to the type of application can adversely impact constructability, performance in service, cost, service life, and sustainability of the constructed structure.