Physical Address
304 North Cardinal St.
Dorchester Center, MA 02124
D490-92 – Standard Test Method Technical Guide
🛢️ Scope and Classification of Road Tar
This specification, designated D490-92 (Reapproved 2016), covers 14 grades of road tar: RT-1, RT-2, RT-3, RT-4, RT-5, RT-6, RT-7, RT-8, RT-9, RT-10, RT-11, RT-12, RT.C.B.-5, and RT.C.B.-6. These grades are utilized in road construction and maintenance, and the standard defines their physical requirements to ensure consistent performance. It is under the jurisdiction of ASTM Committee D04 on Road and Paving Materials and is approved for use by agencies of the U.S. Department of Defense.
📊 Physical Requirements and Test Methods
The tar must meet the requirements specified in Table 1 of the standard. The properties include water content, specific gravity, specific viscosity, float test results, distillation fractions, softening point, and total bitumen content. Each property is determined using the following ASTM test methods:
| 🟦 Property | 📏 ASTM Method | 🎯 Purpose |
|---|---|---|
| Water | D95 | Measures water content |
| Specific Gravity | D70 | Determines density using a pycnometer |
| Specific Viscosity | D1665 | Compares viscosity with water at 25°C |
| Float Test | D139 | Measures consistency of semi-solid materials |
| Distillation | D20 | Determines composition by boiling |
| Softening Point | D36 | Measures temperature susceptibility via ring-and-ball apparatus |
| Total Bitumen | D4 | Determines bitumen content |
The grades are categorized as standard road tars (RT-1 to RT-12) and cutback road tars (RT.C.B.-5 and RT.C.B.-6).
| 📐 Grade Designation | 🟦 Category |
|---|---|
| RT-1 through RT-12 | Standard road tars |
| RT.C.B.-5 and RT.C.B.-6 | Cutback road tars |
⚙️ Test Procedures and Sampling
Material sampling must be performed in accordance with Practice D140. All tests are conducted using the respective ASTM standards. Specific viscosity is reported as a ratio compared to water at 25°C. The distillation test requires close adherence to Test Method D20, and the softening point is critical for grading.
Always sample road tar in accordance with Practice D140 to ensure representative test results and specification compliance.
The float test (D139) and distillation (D20) are essential for characterizing consistency and volatility in road tar grades.
❓ Frequently Asked Questions
🔍 What grades of road tar are covered in ASTM D490-92?
The standard covers 14 grades: RT-1 through RT-12, RT.C.B.-5, and RT.C.B.-6.
💡 How is specific viscosity reported?
Specific viscosity is reported as a comparison with water at 25°C, using Test Method D1665.
⚡ What test method is used for water content?
Water content is determined using Test Method D95 for water in petroleum products and bituminous materials.
📌 Why is Practice D140 important?
Practice D140 ensures that samples are collected consistently and representatively, which is crucial for accurate specification compliance.