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. What nominal maximum sizes of aggregate are recommended? A. According to 26.4.2.1 (a)(5) of ACI 318-19, nominal maximum size of coarse aggregate shall not exceed the least of (i), (ii), and (iii): (i) one-fifth the narrowest dimension between sides of forms (ii) one-third the depth of slabs (iii) three-fourths the minimum specified clear spacing between individual reinforcing bars or wires, bundles of bars, prestressed reinforcement, individual tendons, bundled tendons, or ducts These limitations shall not apply if, in the judgment of the licensed design professional, workability and methods of consolidation are such that concrete can be placed without honeycombs or voids. Similar information can be found in ACI 211.1. In concrete slabs, the nominal maximum size should not exceed three-fourths of the minimum clear spacing of reinforcing bars or one-third of the section depth (ACI 302.1R). The commentary R26.4.2.1(a)(5) of ACI 318-19 states that the size limitations on aggregates are provided to facilitate placement of concrete around the reinforcement without honeycombing due to blockage by closely-spaced reinforcement. Because maximum aggregate size can impact concrete properties such as shrinkage, and also the cost of concrete, the largest aggregate size consistent with the requirements of 26.4.2.1 should be permitted. With the w/cm fixed, the larger the nominal maximum size of aggregates, the lower the cement content for a given consistency. Or, stated differently, for a given cement content, the larger the nominal maximum size of aggregate, the lower the water requirement. When strength requirements are high, however, smaller nominal maximum size aggregate will produce the highest strength for a given w/cm (ACI 363R, ACI 211.4R). References: SP-1(02); ACI PRC-211.1-22; ACI 318-19; ACI 302.1R-15; ACI 363R-10; ACI 211.4R-08 Topics in Concrete: 318 Building Code; Aggregate; Codes; Slab; Specifications
Q. What nominal maximum sizes of aggregate are recommended?
A. According to 26.4.2.1 (a)(5) of ACI 318-19, nominal maximum size of coarse aggregate shall not exceed the least of (i), (ii), and (iii): (i) one-fifth the narrowest dimension between sides of forms (ii) one-third the depth of slabs (iii) three-fourths the minimum specified clear spacing between individual reinforcing bars or wires, bundles of bars, prestressed reinforcement, individual tendons, bundled tendons, or ducts These limitations shall not apply if, in the judgment of the licensed design professional, workability and methods of consolidation are such that concrete can be placed without honeycombs or voids. Similar information can be found in ACI 211.1. In concrete slabs, the nominal maximum size should not exceed three-fourths of the minimum clear spacing of reinforcing bars or one-third of the section depth (ACI 302.1R). The commentary R26.4.2.1(a)(5) of ACI 318-19 states that the size limitations on aggregates are provided to facilitate placement of concrete around the reinforcement without honeycombing due to blockage by closely-spaced reinforcement. Because maximum aggregate size can impact concrete properties such as shrinkage, and also the cost of concrete, the largest aggregate size consistent with the requirements of 26.4.2.1 should be permitted. With the w/cm fixed, the larger the nominal maximum size of aggregates, the lower the cement content for a given consistency. Or, stated differently, for a given cement content, the larger the nominal maximum size of aggregate, the lower the water requirement. When strength requirements are high, however, smaller nominal maximum size aggregate will produce the highest strength for a given w/cm (ACI 363R, ACI 211.4R).
References: SP-1(02); ACI PRC-211.1-22; ACI 318-19; ACI 302.1R-15; ACI 363R-10; ACI 211.4R-08
Topics in Concrete: 318 Building Code; Aggregate; Codes; Slab; Specifications
Search other resources on the ACI website for answers to technical questions