Lightweight Particles in Aggregate

C 123: Standard Test Method for Lightweight Particles in Aggregate

Ensuring the quality and durability of concrete structures begins with the careful selection and testing of constituent materials. For civil engineers and materials professionals, understanding the presence and impact of lightweight particles in aggregates is crucial. AASHTO's Standard Test Method for Lightweight Particles in Aggregate (C 123) provides an essential and authoritative procedure for this critical assessment, safeguarding against potential performance issues in your projects.

What is C 123?

AASHTO C 123 is an industry-leading standard test method for quantifying the proportion of lightweight particles within aggregate samples. Originating from established engineering practices, its primary purpose is to provide a reliable, repeatable, and proven technique for identifying and measuring materials that may adversely affect the performance of concrete, such as coal, lignite, chert, and shale.

Scope & Purpose

This comprehensive standard governs the procedure for determining the percentage of lightweight particles in both fine and coarse aggregates through a sink-float separation process using a heavy liquid of a specified specific gravity. It outlines the required apparatus, heavy liquid preparation, sampling protocols, and detailed procedural steps for conducting the test. The scope specifically covers the identification of particles lighter than a defined density threshold, crucial for conformance with concrete aggregate specifications. It does not, however, address the petrographic identification of all aggregate types or the direct measurement of aggregate strength.

Who Must Comply?

• • Primary audience: Materials Engineers, Civil Engineers, Geotechnical Engineers, Laboratory Technicians, and Quality Control Inspectors.
• • Industries affected: Construction, Civil Engineering, Infrastructure Development, and Materials Testing Laboratories.
• • Compliance nature: Primarily recommended and often mandatory as a contractual requirement in project specifications.
• • Enforcement: Compliance is typically verified by project owners, specifiers, and independent testing agencies during material qualification and project quality assurance.

Key Requirements Overview

The standard requires professionals to:

• • Utilize a heavy liquid with a precisely maintained specific gravity to effectively separate lightweight particles.
• • Prepare aggregate samples by drying and sieving them to appropriate sizes before immersion.
• • Perform the sink-float separation method, ensuring thorough agitation and careful decanting of floating particles.
• • Accurately determine the mass of lightweight particles and calculate their percentage relative to the total sample mass.
• • Adhere to safety precautions when handling specific heavy liquid solutions, as they can be toxic.

Related Standards & References

AASHTO C 123 is frequently used in conjunction with other essential standards. AASHTO M 80 (or ASTM C 33) Specification for Concrete Aggregates establishes the limits for lightweight particles that C 123 helps verify. Furthermore, AASHTO T 104 (or ASTM C 127/C 128) Test Methods for Density, Relative Density (Specific Gravity), and Absorption of Aggregate may be referenced for understanding aggregate properties that influence lightweight particle behavior and for preparing samples. AASHTO T 2 (or ASTM D 75) Practice for Sampling Aggregates ensures representative samples are collected for testing.