Boiling water stripping test method

It is designated as an objective test with high precision. However, it requires a greater amount of operative skills from the laboratory staff and the use of chemicals. As a consequence, hygiene and safety measures are required. 

The boiling water stripping test can be used for any bitumen-aggregate combination, which might be calcareous, silico-calcareous or siliceous aggregates. 

Two samples of coated aggregates (approximately 200 g each) are boiled in 600 ml demineralised water for 10 min and then removed to dry and cool off. The coated aggregate samples are weighed again and each was put in 5 min contact with approximately 200 g of 0.1 N hydrochloric acid in an 800 ml glass beaker, if calcareous aggregates are tested. In case silico-calcareous or siliceous aggregates are tested, use 1 h 1 min contact period and 0.1 N hydrofluoric acid. 

After the contact time has elapsed, separate the hydrochloric acid from the aggregate by pouring the solution gently into a 250 ml graduated cylinder. Titrate a 25 ml aliquot portion with 0.1 N sodium hydroxide or N potassium hydroxide, depending on the type of aggregate used, in the presence of phenolphthalein. Repeat the titration on a second aliquot of 25 ml. Determine the average volume in millilitres of 0.1 N NaOH or KOH required for the titration to the nearest 0.05 ml. 

Then the volume of acid consumed is calculated using a formula, and from that, the percentage (%) of stripped aggregates is determined using a prepared calibration curve. The degree of bitumen coverage (%) is calculated as follows 100-% of stripping. 

---

The copper strip test methods are used to determine the corrosiveness to copper of diesel fuel and are a measure of the relative degree of corrosivity of diesel fuel. Most sulfur compounds in petroleum are removed during refining. However, some residual sulfur compounds can have a corroding action on various metals, and the effect is dependent on the types of sulfur compounds present. One method (ASTM D-130, IP 154) uses a polished copper strip immersed in a given quantity of sample and heated at a temperature for a time period characteristic of the material being tested. At the end of this period the copper strip is removed, washed, and compared with the copper strip corrosion standards (ASTM, 2000). This is a pass/fail test. In another method (ASTM D-849) a polished copper strip is immersed in 200 ml of specimen in a flask with a condenser and placed in boiling water for 30 min. At the end of this period, the copper strip is removed and compared with the ASTM copper strip corrosion standards. This is also a pass/fail test. 

The tests that belong to the first category are (a) the rolling bottle method, (b) the static method and (c) the boiling water stripping method. These tests are described in EN 12697-11 (2012). 

The corrosiveness of perchloroethylene to copper is determined using Soxhlet apparatus. Three pre-weighed strips of copper are used, one placed in the bottom flask, the second in the bottom of the Soxhlet attachment, and the third below the condenser. The specimens are exposed to refluxing solvent for 72 h after which the entire apparatus is flushed with distilled water to wash all acidic substances back to the flask. The water layer is titrated with 0.01 N NaOH to determine its acidity and the strips are weighed to determine weight loss. The results indicate quality of solvent. A different method is used to test copper corrosion by aromatic hydrocarbons. Here, a copper strip is immersed in a flask containing solvent and the flask is placed in boiling water for 30 min. Next, the copper strip is compared wifli ASTM standard corroded copper strips. 

Preparation of the Test Papers. One part of starch is boiled with loo parts of water and the solution filtered. To the filtrate 5 parts of potassium iodide are added and the strips of filter paper are immersed in this. They are then allowed to dry in the air and kept in a closed vessel. The period during which they may be stored depends upon the method by which they have been prepared and the care with which they have been stored. When the papers are prepared according to the instructions of Storm (J. Ind, Eng. Chem., 1909, 1, 802, or Chem. Zentr., 1910,1, 1806) and stored in a glass-stoppered bottle they may be kept for 8 years. 

---