Email Address is required Invalid Email Address
In today’s market, it is imperative to be knowledgeable and have an edge over the competition. ACI members have it…they are engaged, informed, and stay up to date by taking advantage of benefits that ACI membership provides them.
Read more about membership
Learn More
Become an ACI Member
Founded in 1904 and headquartered in Farmington Hills, Michigan, USA, the American Concrete Institute is a leading authority and resource worldwide for the development, dissemination, and adoption of its consensus-based standards, technical resources, educational programs, and proven expertise for individuals and organizations involved in concrete design, construction, and materials, who share a commitment to pursuing the best use of concrete.
Staff Directory
ACI World Headquarters 38800 Country Club Dr. Farmington Hills, MI 48331-3439 USA Phone: 1.248.848.3800 Fax: 1.248.848.3701
ACI Middle East Regional Office Second Floor, Office #207 The Offices 2 Building, One Central Dubai World Trade Center Complex Dubai, UAE Phone: +971.4.516.3208 & 3209
ACI Resource Center Southern California Midwest Mid Atlantic
Feedback via Email Phone: 1.248.848.3800
ACI Global Home Middle East Region Portal Western Europe Region Portal
Home > Tools > Frequently Asked Questions
Q. How is the required strength selected, measured, and obtained? A. The structural designer selects the specified compressive strength of concrete, f’c, of the concrete. The building code (ACI 318) requires that the average strength be higher than the f’c by an amount that varies with the variability (standard deviation) of the strength of concrete produced at the plant where the concrete will be obtained for the project (ACI 214). Compressive strength is determined by subjecting standard-cured cylindrical specimens to compression in accordance with ASTM C39. In the event test cylinders show unacceptably low strength, the building code (ACI 318) describes the action that needs to be taken. In pavements, the required strength is frequently expressed as flexural strength, which is determined using standard-cured beams following ASTM C78. Because of the difficulty of making, transporting, and testing beams and the high variability in the beam test, compressive strengths are preferred for acceptance after a relationship between the flexural and compressive strengths is established for the mixture to be used or for the one that is being used (ACI PRC 330). References: SP-1(02); ACI 318-19; ACI 214R-11; ACI 301-20; ACI PRC 330-21; ASTM C39; ASTM C78 Topics in Concrete: 318 Building Code; Codes; Design of Concrete; Specifications for Concrete; Testing of Concrete
Q. How is the required strength selected, measured, and obtained?
A. The structural designer selects the specified compressive strength of concrete, f’c, of the concrete. The building code (ACI 318) requires that the average strength be higher than the f’c by an amount that varies with the variability (standard deviation) of the strength of concrete produced at the plant where the concrete will be obtained for the project (ACI 214). Compressive strength is determined by subjecting standard-cured cylindrical specimens to compression in accordance with ASTM C39. In the event test cylinders show unacceptably low strength, the building code (ACI 318) describes the action that needs to be taken. In pavements, the required strength is frequently expressed as flexural strength, which is determined using standard-cured beams following ASTM C78. Because of the difficulty of making, transporting, and testing beams and the high variability in the beam test, compressive strengths are preferred for acceptance after a relationship between the flexural and compressive strengths is established for the mixture to be used or for the one that is being used (ACI PRC 330).
References: SP-1(02); ACI 318-19; ACI 214R-11; ACI 301-20; ACI PRC 330-21; ASTM C39; ASTM C78
Topics in Concrete: 318 Building Code; Codes; Design of Concrete; Specifications for Concrete; Testing of Concrete
Search other resources on the ACI website for answers to technical questions