Methods of Tests for Building Limes, Part 11: Determination of Setting Time of Hydrated Lime
1983 Edition

The apparatus specified for determining hydrated lime setting time includes a penetration needle mounted on a rod, known as the needle (C), and a mould for creating the lime test block. The test involves lowering the needle gently onto the lime surface and allowing it to penetrate. Initially, the needle fully penetrates the block, and the initial setting time is recorded when the needle no longer penetrates more than 5 ± 0.5 mm into the material. This method ensures reliable and repeatable measurements as per the standard.

The initial setting time is defined as the interval from adding water to hydrated lime until the test needle fails to penetrate beyond 5 ± 0.5 mm into the test block. To measure this, prepare the test block, position it beneath the needle rod, gently lower the needle to contact the surface, and release it to penetrate. Repeat this procedure until the penetration depth criterion is met. The elapsed time is then recorded as the initial setting time, ensuring consistent assessment of lime setting characteristics.

Testing must be performed under controlled conditions: the temperature of the lime, water, and testing room should be maintained at 27 ± 2 °C, with relative humidity not less than 90%. Additionally, the environment should be free from drafts to prevent drying or temperature fluctuations, and all equipment must be clean before use. These parameters are critical to obtaining consistent and accurate test results.

For final setting time determination, the standard needle (C) of the Vicat apparatus is replaced with a needle fitted with an annular attachment (F). The needle is carefully applied to the lime test block surface. The lime is considered finally set when the needle alone leaves an impression, but the annular attachment does not. If a surface scum is present, testing is done on the underside of the sample. This approach accurately identifies the transition from plastic to solid state of the hydrated lime.

While the standard does not explicitly specify scum removal procedures, best practices include carefully removing any scum with a clean spatula or brush without disturbing the test block. Ensuring the surface is smooth and uniform before testing is essential. If scum persists, preparing a fresh sample is recommended to avoid inaccurate results. Strict adherence to testing conditions, such as temperature and humidity, is also necessary to minimize scum formation and ensure valid test outcomes.