AC271 - Concrete Admixtures
ICC-ES Acceptance Criteria for Concrete Admixtures
Last updated: September 21, 2025
Overview
Concrete admixtures are ingredients other than cement, water, and aggregates that are added to a concrete mix to change its properties. They can be chemical additives or mineral additions. For example, plasticizer or superplasticizer admixtures make fresh concrete flow more easily (improving workability) without adding extra water, and accelerators make concrete harden faster (useful in cold weather), while retarders slow down setting (helpful in hot weather or long transports).
Other admixtures include air-entraining agents that add tiny air bubbles for freeze-thaw durability, and fibers that reduce cracking. By using admixtures, concrete can be tailored to have higher strength, better durability, or other special characteristics as needed for a project. These enhancements work alongside requirements for cementitious exterior wall coatings (AC311) in comprehensive building envelope systems.
Purpose
This acceptance criteria provides a basis for evaluating concrete admixture products that may not be directly covered by existing codes. It establishes testing protocols, performance requirements, and quality standards needed for code approval of these concrete modification systems.
Benefits of Compliance
- Nationwide acceptance by building officials for concrete admixtures
- Streamlined approval process for chemical and mineral additives
- Third-party verification of concrete performance enhancement claims
- Enhanced marketability for specialized concrete applications
Resources
Frequently Asked Questions
What types of admixtures does AC271 cover?
AC271 covers chemical admixtures such as plasticizers, superplasticizers, accelerators, retarders, and air-entraining agents, as well as mineral admixtures and fiber reinforcements added to concrete mixes to modify their properties.
Do concrete admixtures need ICC-ES evaluation?
Admixtures that conform to recognized ASTM standards (such as ASTM C494 for chemical admixtures) may not need separate ICC-ES evaluation. AC271 is primarily for admixture products that fall outside existing standards or make performance claims beyond what standards cover.
How does AC271 relate to concrete mix design approval?
AC271 evaluates the admixture product itself, not the complete concrete mix. The admixture must demonstrate it enhances concrete properties as claimed without negatively affecting other performance characteristics like strength or durability.
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