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D4989 – Standard Test Method Technical Guide
📐 Specimen Geometry and Requirements
Test specimens are prepared using ring molds with precise dimensions. The molds are constructed from copper or brass tubing with an inside diameter of 25.40 ± 0.01 mm [1.0000 ± 0.0025 in.] and a height of 12.70 ± 0.01 mm [0.5000 ± 0.0025 in.]. Prior to molding, the molds are coated with a pasty mixture of talc in glycerine to act as a release agent.
| 🟦 Property | 📏 SI Unit | 📐 Inch-Pound Unit |
|---|---|---|
| Inside Diameter | 25.40 ± 0.01 mm | 1.0000 ± 0.0025 in. |
| Height | 12.70 ± 0.01 mm | 0.5000 ± 0.0025 in. |
💡 Ensure that the ring molds are cut smoothly from copper or brass tubing to maintain dimensional accuracy and prevent sample leakage during testing.
⚙️ Test Procedure and Apparatus Specifications
The parallel plate plastometer, a modified form of Williams’ plastometer, is used. Platen A has a mass of 5000 ± 50 g [11.02 ± 0.11 lb]. The specimen is molded into a disc of specified dimensions, heated to the selected temperature, placed between the pre-heated plates, and pressed for a measured time. The apparent viscosity is calculated from the final diameter of the disc. A constant-temperature oven capable of maintaining ±0.1°C [±0.2°F] and a scale accurate to ±0.5 mm [±0.02 in.] are essential.
| ⚡ Component | 🎯 SI Unit | 📐 Inch-Pound Unit |
|---|---|---|
| Mass of Platen A | 5000 ± 50 g | 11.02 ± 0.11 lb |
⚠️ Roofing bitumens are non-Newtonian; this method uses predetermined arbitrary shear stress levels. Results may differ from other viscosity tests such as those in D2171/D2171M (vacuum capillary) or D3205 (cone and plate).
📊 Key Measured Properties and Considerations
The apparent viscosity is derived from the flow behavior under standard conditions. This test method applies to materials with viscosity from 10² to 10⁹ Pa·s [10³ to 10¹⁰ poises]. Sampling must follow Practice D140/D140M, and the test is suitable for roofing bitumens conforming to D312/D312M or D450/D450M. The inherent non-Newtonian characteristics mean results are specific to this technique.
❓ Frequently Asked Questions
🔍 What is the principle of the parallel plate plastometer?
The sample is compressed between two plates under a constant load, and the resulting flow is measured by the increase in disc diameter, which directly relates to apparent viscosity.
💡 How are test specimens prepared?
Specimens are molded in ring molds coated with a talc-glycerine paste to prevent sticking. The molds have an inside diameter of 25.40 mm and a height of 12.70 mm.
⚡ What are the critical apparatus specifications?
The parallel plate plastometer requires a platen mass of 5000 ± 50 g. The oven must maintain temperature within ±0.1°C, and the measuring scale must be accurate to ±0.5 mm.
📌 Why do results vary between this test and other viscosity methods?
Roofing bitumens are non-Newtonian; different shear rates in various test methods lead to different apparent viscosity values. This test uses predetermined, arbitrary shear stress levels, so direct comparison with other methods may not be valid.