ASTM D4791
Full Name
ASTM D4791 – Standard Test Method for Flat Particles, Elongated Particles, or Flat and Elongated Particles in Coarse Aggregate
Scope
ASTM D4791 is a standard test method used to determine the percentage of flat, elongated, or flat and elongated particles in coarse aggregate. The shape of aggregate particles significantly influences the properties of construction materials, impacting their placement, workability, and overall performance. This test helps ensure compliance with specifications that limit the presence of these unfavorable particle shapes. It also allows for the assessment of the relative shape characteristics of coarse aggregates, contributing to better material selection and quality control.
The standard outlines two distinct procedures:
- Method A: this method, developed before the Superpave system, is the traditional approach and applies to non-Superpave applications. It involves measuring individual aggregate particles of specific sieve sizes to determine the ratios of width to thickness and length to width. Based on these ratios and pre-defined limits, particles are classified as flat, elongated, or neither.
- Method B: designed specifically for Superpave applications, Method B simplifies the process by comparing the maximum particle dimension to the minimum particle dimension. This method provides a more direct assessment of particle shape for Superpave mix designs.
Test procedure:
- Sample preparation: a representative sample of coarse aggregate is obtained and sieved into specific size fractions according to ASTM C136.
- Particle measurement: individual particles within each size fraction are analyzed. Method A involves measuring the length, width, and thickness of each particle using a caliper or other suitable measuring device. Method B involves measuring the maximum and minimum dimensions of each particle.
- Shape classification: particles are categorized as flat, elongated, or neither based on the calculated ratios (Method A) or the ratio of maximum to minimum dimension (Method B). Specific criteria for these classifications are detailed in the standard, often varying depending on the intended application or specification.
- Calculation: the percentage of flat, elongated, or flat and elongated particles in each size fraction, and for the combined aggregate sample, is calculated.
The shape of coarse aggregate particles plays a crucial role in various construction applications. Excessive flat or elongated particles can negatively affect:
- Compaction: these particles hinder efficient packing and compaction, leading to voids and reduced density in asphalt and concrete mixes.
- Stability: flat and elongated particles can create planes of weakness, reducing the overall stability and strength of the constructed material.
- Workability: high percentages of these particles can make concrete mixes difficult to place and finish, and can affect the ride quality of asphalt pavements.
- Durability: increased voids due to poor compaction can enhance permeability, making the material more susceptible to freeze-thaw damage and other forms of deterioration.
By determining the proportion of flat and elongated particles, ASTM D4791 allows for informed decisions regarding material selection and mix design, ultimately contributing to improved construction quality and longevity.
ASTM D4791 Accredited Laboratory
Applied Testing & Geosciences, LLC is accredited for performing tests using the ASTM D4791 standard. Whether you need to verify compliance with project specifications, optimize mix designs, or assess the overall quality of your aggregates, our testing services can provide the critical data you need.
Contact us today to discuss your testing requirements and ensure the optimal performance of your construction materials.
Resources
Keywords
particle shape; flat particles; elongated particles; coarse aggregate; sieve; dimensions; length; width; thickness; proportions; method A; method B; Superpave; specifications; compliance