What is Stripping Value Test?
The stripping value of aggregates is a measure of the amount of uncovered area observed visually in relation to the total area of aggregates, expressed as a percentage. It is determined to assess the adhesion of bitumen and tar binders to normal types of aggregates, as long as they are dry and not excessively dusty. This issue of stripping is typically encountered in bituminous mixtures that are permeable to water. The test described in this procedure is used for determining the stripping value of aggregates through the static immersion method, when bitumen and tar binders are utilized.
Test Specimen after and before the test.
Aim:
The determination of the stripping value of road aggregates by binders is a crucial test in the field of road construction. This test helps to assess the effectiveness of binders, such as asphalt or bitumen, in adhering to the aggregates used in road pavement. Stripping refers to the loss of adhesion between the binder and the aggregate surface, which can lead to the premature failure of road surfaces, reduced durability, and increased maintenance costs. Therefore, it is important to accurately determine the stripping value of road aggregates by binders to ensure the quality and longevity of road pavements. This test involves subjecting the aggregates to various conditions, such as moisture and temperature, to simulate real-world road conditions, and evaluating the extent of binder adhesion to the aggregates. The results of the stripping value test can provide valuable information for engineers and road construction professionals to select appropriate binders and optimize road pavement designs, ensuring safe and reliable road networks for transportation.
Apparatus Requires for Test:
To conduct this experiment, several apparatus are necessary. These include a thermostatically controlled water bath, which will be used to regulate the temperature of the water used in the experiment. Additionally, an oven will be required to heat the aggregate to a specific temperature. Sieves of sizes 20 mm and 12.5 mm will also be needed to separate the aggregate particles based on their size. A beaker with a capacity of 500 ml will be used to hold and measure the liquids used in the experiment. Finally, a mixer will be used to thoroughly mix the aggregate and bitumen, ensuring a homogeneous mixture for testing.
Procedure:
The aggregate used in the experiment is 200 g of clean and dry material that has passed through a 20 mm IS sieve and is retained on a 12.5 mm sieve. The aggregate is heated to 150°C in preparation for mixing with bitumen. The bitumen binder used amounts to five percent of the weight of the aggregate and is heated separately to 160°C.
Once the aggregate and binder are heated, they are thoroughly mixed to ensure complete coating of the aggregate particles. The mixture is then transferred to a beaker and allowed to cool to room temperature for approximately 2 hours. Distilled water is then added to the beaker to fully immerse the coated aggregates.
The beaker containing the coated aggregates and water is covered and placed in a water bath maintained at 40°C for a duration of 24 hours. After the 24-hour period, the beaker is removed from the water bath and allowed to cool to room temperature. The extent of stripping, or separation of the bitumen coating from the aggregate, is visually estimated while the specimen is still submerged in water.
Test Apparatus to mix aggregate and bitumen.
Result:
The percentage of stone surface that remains coated after the specified periods is reported as the result. This result is obtained by taking the mean value of at least three visually estimated values and rounding it off to the nearest 5 percent. The stripping value of road aggregates is determined through visual estimation and is expressed as a percentage.
Specifications:
The Indian Road Congress (IRC) has established a maximum stripping value of 5 percent for aggregates that are intended for use in bituminous construction, such as surface dressing, penetration macadam, bituminous macadam, and carpet. This specification ensures that the aggregates used in these types of road construction meet a certain standard of quality and performance. The maximum stripping value refers to the amount of moisture that can be absorbed by the aggregate, causing the bitumen to separate from the aggregate surface. By setting the maximum stripping value at 5 percent, the IRC aims to ensure that the aggregates used in bituminous construction are resistant to moisture-induced damage, such as stripping, which can compromise the durability and performance of the road surface. This specification is an important guideline for road construction professionals to ensure that the aggregates used in bituminous construction meet the necessary quality standards and contribute to the longevity and performance of the road infrastructure.
Applications of stripping value test:
Certain types of aggregates may have lower affinity towards bitumen compared to water, resulting in a phenomenon known as stripping, where the bituminous binder may not adhere well to the aggregate surface when exposed to water. The theoretical treatment of this problem is challenging, and therefore, practical adhesion tests, such as the simple stripping test, are often used to assess the ability of the binder to adhere to the aggregate when submerged in water. To mitigate stripping, various anti-stripping agents are available, which can be added to the bituminous mix to reduce the occurrence of this issue.