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D5335-24 – Standard Test Method Technical Guide
📐 Scope and Specimen Selection
Designation D5335‑24 establishes a standardized laboratory test method for determining the linear (one‑dimensional) coefficient of thermal expansion of intact rock cores using bonded electric resistance strain gauges. This method is intended for evaluation under unconfined stress states across a controlled temperature range of 20 °C to 260 °C, subject to the restrictions detailed in Section 6.1 of the standard. Selection of the test specimen requires careful engineering judgment, as natural discontinuities within the rock mass—such as joints, inclusions, voids, veins, and bedding planes—can significantly influence the thermal expansion behavior.
Test specimens may be evaluated in a saturated, dry, or unsaturated condition. When testing saturated or unsaturated specimens, the standard strictly requires the test temperature to be maintained at least 10 °C below the boiling point of the saturating fluid. This precaution is essential to minimize the effects of fluid evaporation on the strain gauge readings and overall test accuracy, as referred to in Sections 6.3 and 8.4.
| 🟦 Parameter | 📏 Specification |
|---|---|
| Test Temperature Range | 20 °C to 260 °C (with restrictions per Sec 6.1) |
| Specimen Condition | Saturated, Dry, or Unsaturated |
| Stress State | Unconfined |
| Data Units | SI Units (mandated as standard) |
⚙️ Instrumentation, Procedure, and Accuracy
The core of this test method involves bonding electric resistance strain gauges directly to the rock specimen to measure dimensional changes precisely as the specimen undergoes controlled thermal cycling. To ensure measurement reliability, the standard mandates compliance with Practice E83 for the verification and classification of extensometer systems. Furthermore, all data collection, recording, and calculation must adhere to the significant digits and rounding conventions established in Practice D6026. The standard emphasizes that the reported significant digits represent the industry standard for the procedure and may be adjusted by the user to suit specific project objectives.
⚠️ Critical Procedure Note: Section 1.3 specifies that when testing saturated or unsaturated specimens, the test temperature shall be at least 10 °C less than the boiling point of the saturating fluid. Failure to observe this limit can lead to fluid evaporation, compromising the accuracy of the thermal expansion measurement and invalidating the test results.
📊 Key Measured Properties and Referenced Documents
The linear coefficient of thermal expansion is the primary property derived from the strain gauge data. The test method is closely integrated with a suite of other ASTM standards to ensure comprehensive test quality and terminology. For instance, D653 provides the standard terminology for soil, rock, and contained fluids, while D3740 outlines the minimum requirements for agencies engaged in testing. This standard also recognizes alternative methodologies for measuring thermal expansion, such as Test Method E228 (Push‑Rod Dilatometer) and Test Method E289 (Interferometry), providing a robust framework for material characterization.
| 📐 Standard | 🎯 Role in D5335 |
|---|---|
| D6026 | Governs significant digits and data records in geotechnical data |
| E83 | Verification and classification of extensometer systems |
| E228 / E289 | Alternative test methods (Push‑Rod Dilatometry / Interferometry) |
| D3740 | Minimum requirements for testing agencies |
| D653 | Terminology Relating to Soil, Rock, and Contained Fluids |
💡 Best Practice for Specimen Selection: Per Section 1.1, careful judgment should be used when selecting the specimen. Discontinuities in the rock mass (joints, inclusions, voids, veins, bedding) can strongly influence the coefficient of thermal expansion. This method is tailored specifically for intact rock cores, and the presence of such features must be carefully considered during test planning and execution.
❓ Frequently Asked Questions
🔍 What is the specific temperature range