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D3628-15 – Standard Test Method Technical Guide
📋 Scope and Reference Documents
ASTM D3628-15 (Reapproved 2021) provides a standard practice for the selection and use of emulsified asphalts in paving and allied applications. The standard primarily guides users in matching emulsified asphalt types to specific construction methods, whether for new pavements, surface treatments, or maintenance operations. Values stated in SI units are regarded as the standard according to Section 1.2.
⚡ Regulatory and Safety Compliance: Per Section 1.3, users of this standard are responsible for determining applicable safety, health, and environmental practices and regulatory limitations before proceeding with selection and use.
The practice relies heavily on several key referenced documents. Mastery of Terminology ASTM D8 (Materials for Roads and Pavements) is required to understand the base definitions. The material specifications for the emulsified asphalts themselves are found in ASTM D977 (Specification for Emulsified Asphalt) for anionic types and ASTM D2397/D2397M (Specification for Cationic Emulsified Asphalt).
🧩 Emulsified Asphalt Application Categories
The standard defines three broad categories of use for emulsified asphalts, forming the backbone of the selection process. Understanding whether an application involves mixing, spraying alone, or a layered surface treatment dictates the appropriate emulsified asphalt grade.
Asphalt-Aggregate Mixtures: These involve the cold-laid mechanical mixing of emulsified asphalt with aggregate. The resulting material is spread and compacted on the job site. This category is typically used for pavement bases and surfaces, utilizing either open or dense aggregate gradations.
Asphalt-Aggregate Applications: In this method, emulsified asphalt is applied to a prepared aggregate base or pavement surface, with the aggregate placed subsequently. This covers surface treatments like chip seals.
Asphalt Applications: This is a direct spray application of the emulsified asphalt without any aggregate. Common examples include tack coats, fog seals, and prime coats designed to bond layers or seal a surface.
| 🟦 Application Category | 📏 Core Procedure | 🎯 Typical Paving Scenario |
|---|---|---|
| Asphalt-Aggregate Mixtures | Mechanical mixing, spreading, and compaction | Cold-laid base or surface courses |
| Asphalt-Aggregate Applications | Asphalt sprayed over base, then aggregate applied | Single-Surface Treatment (Chip Seal) |
| Asphalt Applications | Direct spray, no aggregate used | Tack coats, fog seals |
📐 Aggregate and Surface Treatment Definitions
The standard provides specific definitions for various surface treatments and the aggregates used within them, critical for proper specification writing and field quality control.
Single-Surface Treatment (commonly known as a chip seal) is the most recognized form, involving a layer of emulsified asphalt immediately followed by a uniform layer of aggregate. A Multiple Surface Treatment is a stacked application where the maximum aggregate size of each successive treatment is typically one half that of the previous layer. The total thickness approximates the nominal maximum size aggregate particle of the first course.
A Graded Aggregate Seal is defined as a single treatment using aggregate graded with little or no mineral filler. The nominal maximum size is typically about 19 mm. It relies on the emulsified asphalt penetrating upward into the aggregate cover, making the sand content critical. This method serves as a lower-cost alternative to a chip seal for rural or lower-volume roads.
💡 Distinction in Seal Types: A “Graded Aggregate Seal” (Sect. 3.2.4) relies on upward asphalt penetration into a graded cover, differing from a standard Chip Seal where the aggregate is simply embedded into the binder. Sieve sizes like the 4.75-mm and 75-µm are critical for defining Sand (Sect. 3.2.7) for these seals.
The standard also carefully defines “Sand” (mineral aggregate passing a 4.75-mm sieve with about 5% passing the 75-µm sieve) and “Sandy Soil” (particles smaller than 2.00 mm, typically exhibiting plasticity). A Sand Seal is a specific bituminous-sand application that functions as a light-wearing and sealing course.
| 🟦 Term | 📏 Definition / Sieve Size | ⚡ Application Context |
|---|---|---|
| Graded Aggregate Seal | ~19 mm nominal max aggregate size, graded with little/no filler | Lower-cost road surface treatment |
| Sand | Passes 4.75-mm sieve; ~5% passes 75-µm sieve | Bituminous-sand application (Sand Seal) |
| Sandy Soil | Particles < 2.00 mm, contains fines with plasticity | Stabilization or sealing of existing surfaces |
| Multiple Surface Treatment | Aggregate size halves each successive course | Durable wearing surface for higher traffic |
❓ Frequently Asked Questions
🔍 What is the primary scope of ASTM D3628-15?
This standard practice covers the selection of emulsified asphalts for various paving and allied uses. It does not specify a single material but provides the framework for matching emulsified asphalt types (anionic or cationic) to their intended construction and maintenance applications.
💡 How are cationic emulsified asphalts specified according to this practice?
Cationic emulsified asphalts are specified under ASTM D2397/D2397M. The practice of D3628 guides the user on *which* of these standard material specifications is appropriate based on the application category (e.g., mixture, seal, or spray).
⚡ What is the fundamental difference between a Graded Aggregate Seal and a Chip Seal?
In a Chip Seal (Single-Surface Treatment), the aggregate is placed over the asphalt. In a Graded Aggregate Seal (Sect. 3.2.4), the aggregate is graded such that the emulsified asphalt must penetrate upward into the cover. The nominal max aggregate size for a graded aggregate seal is typically about 19 mm.
📌 Which referenced standards are essential for implementing D3628-15?
Implementing D3628-15 requires understanding ASTM D8 for terminology, ASTM D977 for anionic emulsified asphalt specifications, and ASTM D2397/D2397M for cationic emulsified asphalt specifications. These documents provide the material properties that satisfy the selection rules outlined in this practice.