Q. The recently issued ACI 318-08 Building Code contains several important changes. Do any revisions affect the methods or practices we use to design, mix, or deliver concrete?
A. At the ACI Chicago chapter meeting in September, Dr. Anthony Fiorato, who serves on ACI Committee 318, Standard Building Code, thoroughly explained how the new version will affect producers. The past president of ACI also provided some background on the document before outlining the changes.
While the new ACI document is now available, it could be some time before its provisions directly affect producers' activities. Local jurisdictions adopt and enforce the U.S. building codes.
This allows those local jurisdictions to establish the minimum requirements they feel are necessary to provide for the public health, safety, and general welfare of their citizens. In most circumstances, the building code designates the minimum requirements a design professional may choose regarding the structural design criteria, materials, and construction provisions.
Designers, contractors, material suppliers, and testing laboratories must understand the letter of the particular code or specification being used. Fiorato is concerned that many material suppliers and contractors pay little attention to ACI 318's materials, durability, and construction requirements.
“There can be unanticipated costs and problems with buildings when there are misunderstandings about, or violations of, these requirements,” he said.
With the changes to ACI 318 for 2008, there are some significant implications for all parties involved in the design and construction process.
- Distinction for residential concrete: The new document now clarifies that concrete standards for residential construction are now outlined in ACI 332, Requirements for Residential Concrete Construction and Commentary. Licensed design professionals should use ACI 332 for the design and construction of cast-in-place concrete for one- and two-family dwellings and multiple single-family dwellings.
- Water: There has also been a reference that water used in mixing concrete shall conform to ASTM C1602. But with the revision to ASTM documents, producers may also have the option to use recycled water in certain mixes.
- Admixtures: Admixtures for water reduction and setting time modification shall conform to ASTM C494. Admixtures for producing flowing concrete shall conform to ASTM C 1017. Air-entraining admixtures shall conform to ASTM C 260. All other admixtures used in concrete that do not conform to 3.6.1 and 3.6.2 shall be subject to prior approval by the licensed design professional.
- Reinforcing materials: The document contains new requirements for headed shear stud reinforcement, headed deformed bars, stainless steel bars, and high-strength steel bars.
- Limit set on historical mixture proportion data: ACI 318 now sets a limit of one year on the age of strength test records that can be used to establish a sample standard deviation for proportioning a concrete mix based on field experience.
- 4x8 testing cylinders: In addition to the traditional 6-inch-diameter by 12-inch-high concrete cylinder, the code now officially recognizes using 4x8-inch cylinders for trial mixtures and acceptance testing. Where 4x8-inch cylinders are used, a strength test is the average of the strengths of three cylinders, instead of two, as 6x12-inch cylinders require.
- Defining concrete durability: Under 318-08, licensed design professionals must prescribe new exposure categories and classes for concrete durability requirements. The format of Chapter 4 was revised extensively by introducing exposure categories and classes with applicable durability requirements.