Tests & quality control
Given the type of mineral (andesite) and its compressive strength, water absorption, Los Angeles value and other properties, this stone is well suited for use as ballast. The tests below were carried out on the mine's stone and ballast by the Markazi Province Technical & Soil Mechanics Laboratory. At present the material is approved by the national railway and is the best ballast in the west of the country.
| Test | Standard | Result | Limit |
|---|---|---|---|
| Los Angeles abrasion loss (grading F, 1,000 revolutions) | AASHTO T96 | 11% (both samples) | ≤ 30% |
| Sodium sulfate soundness loss (coarse fraction) | AASHTO T104 | 0.3% | < 5% (max 8%) |
| Freeze–thaw loss (coarse fraction) | AASHTO T103 | 0.7% | — |
| Micro-Deval abrasion loss | INSO 14874-1 | 7.0% | — |
| Apparent specific gravity | AASHTO T85 / T84 | 2.829 – 2.837 | ≥ 2.6 |
| Bulk (true) specific gravity | AASHTO T85 / T84 | 2.725 – 2.755 | ≥ 2.6 |
| Water absorption | AASHTO T85 / T84 | 0.9 – 1.2% | 1% (2% worst case) |
| Clay lumps | ISIRI 4978 / ASTM C142 | 0.0% | — |
| Material finer than 75 µm | ISIRI 446 / ASTM C117 | 0.1% | — |
| Elongated (needle) / flaky particles | BS 812 | Elongation 19 – 20%, flakiness 9 – 10% | — |
| Flat & elongated particles (ratio 1:3) | ISIRI 4791 / ASTM D4791 | 4.6 – 7.4% | — |
| Loose unit weight | ASTM C29 | 1,683 kg/m³ | — |
| Gradation | AASHTO T27 | The grading curve lies within the specified envelope | — |
Ten cylindrical cores (H/D ≈ 2.0) were tested: five saturated (Ø 6.5 cm, H ≈ 13 cm) and five dry (Ø 7.3 cm, H ≈ 14.6–14.8 cm). Each test took 4 to 5.5 minutes to failure. (ASTM D2938)
| Core | Saturated (kg/cm²) | Dry (kg/cm²) |
|---|---|---|
| 1 | 1,082 | 1,130 |
| 2 | 660 | 1,299 |
| 3 | 916 | 1,517 |
| 4 | 896 | 896 |
| 5 | 729 | 1,192 |
| Average | 857 | 1,207 |
Dry — average
1,207 kg/cm²
Requirement in section 3-8: more than 1,200
Saturated — average
857 kg/cm²
Requirement in section 3-8: more than 800
AASHTO T 275
| Sample | Specific gravity | By dimensions |
|---|---|---|
| 1 | 2.676 | 2.650 |
| 2 | 2.790 | — |
| 3 | 2.729 | — |
ASTM C294
The laboratory notes that the name is based on observation and field experience; exact naming requires a thin section and chemical analysis.
The wear and breakage of ballast is measured by the Los Angeles test over 1,000 revolutions. The procedure is given in ASTM C535 for particles larger than 2.54 cm and ASTM C131 for particles smaller than 2.54 cm.
Soundness reflects the stone's durability through dry and wet, cold and heat and other chemical agents that erode aggregate over time. It is checked by the sulfate-corrosion test: the loss in weight over 5 continuous dry–wet cycles in sodium (or magnesium) sulfate solution, per ASTM C88, should be below 5% and at most 8%.
Specific gravity and porosity are among the most important properties of ballast: the material must have a suitable density and be affected as little as possible by moisture. Per ASTM C127 the specific gravity of ballast is at least 2.6 T/m³ and its maximum water absorption is 1%, or 2% in the worst case.
The stone must be strong enough to carry all concentrated stresses, so the uniaxial strength of a cylindrical core is examined. For a core 5 cm in diameter and 10 cm high, tested alternately dry and saturated, the minimum strength exceeds 1,200 and 800 kg/cm². The core is loaded at about 0.2–1 MPa per second and takes at least 30 seconds to reach failure.
Use of the line does not stop in any season or rainfall, so ballast must keep its quality and durability as the seasons change.
The amount of deleterious material in ballast must not exceed the permitted limit.
Results are taken from the laboratory reports reproduced in the Nangerd operating-licence extension plan (Winter 1403). A consignment certificate is issued on request once the test has been carried out on that consignment.
Ballast in the technical dossier →
