The quality of building lime plays a crucial role in determining the strength and durability of mortar mixes used in construction. Lime is a vital component, particularly in applications like plastering, masonry, and road-making. To ensure its quality, tests can be conducted as either field tests or laboratory tests. While detailed laboratory tests follow the standards outlined in IS 6932-1973, simple field tests provide a quick and efficient way to assess lime quality directly from the kiln, particularly in the form of quicklime (calcium oxide, CaO).
This article discusses the procedures and significance of field tests for building lime, ensuring its suitability for construction work.
Sampling for Physical Tests on Building Lime
Before performing any tests, it is crucial to collect samples correctly to prevent deterioration. Sampling procedures vary depending on the type of lime being tested (quicklime or hydraulic lime). For each lot of lime, three samples are collected. The recommended sample size for quicklime is detailed in the following table:
| Lot Size (Tonne) | Gross Sample Size for Lump Quicklime (Kg) | Gross Sample Size for Powdered Quicklime (Kg) |
|---|---|---|
| Up to 100 | 500 | 250 |
| 101 to 300 | 1000 | 500 |
| 301 to 500 | 1500 | 750 |
| 501 to 1000 | 2000 | 1000 |
For hydraulic lime, a minimum of 5 kg is required for testing. Samples must be collected promptly to preserve their properties for accurate testing.
Field Tests on Building Lime
Field tests, as prescribed by IS 1624-1974, offer a quick and practical approach to determine the quality of lime. These tests include visual inspection, chemical reactivity, and physical evaluation.
1. Visual Examination
Visual examination is a preliminary test to determine the lime’s class:
- Class C lime can be identified by its characteristic white color.
2. Hydrochloric Acid Test
This test evaluates the chemical properties of lime and its classification:
- Procedure:
- Place a leveled teaspoon (approximately 10 cc) of powdered lime in a test tube.
- Add hydrochloric acid until the bubbling ceases.
- Let the mixture stand for 24 hours.
- Observations:
- Bubbling indicates the presence of lime, while insoluble residues signify inert materials or adulteration.
- After 24 hours, a gel forms:
- Thick, non-flowing gel → Class A lime.
- Flowing gel → Class B lime.
- No gel → Class C lime.
3. Ball Test
The ball test determines lime’s quality based on its behavior when mixed with water:
- Procedure:
- Form a ball of lime paste by mixing lime with water.
- Store the ball for six hours and then place it in a basin of water.
- Observations:
- Immediate disintegration → Class C lime.
- Expansion and cracks → Class B lime.
- No adverse effects → Class A lime.
4. Impurity Test
This test assesses the purity of lime by determining the percentage of residue:
- Procedure:
- Mix a known quantity of lime with water in a beaker and allow residue to settle.
- Dry the residue under the sun for eight hours.
- Results:
- Less than 10% residue → Good lime.
- 10–20% residue → Fair lime.
- More than 20% residue → Poor or impure lime.
5. Plasticity Test
Plasticity indicates the ability of lime to be shaped or molded:
- Procedure:
- Prepare a thick paste of lime with sufficient water and let it rest overnight.
- Spread the paste on blotting paper using a knife.
- Observation:
- Lime that displays good plasticity when spread is considered high-quality.
6. Workability Test
The workability of lime is tested by evaluating its ability to adhere to surfaces:
- Procedure:
- Prepare a 1:3 lime-sand mortar mix.
- Use a trowel to throw the mortar mix onto a brick wall.
- Observation:
- If the mix sticks well to the wall, the lime is considered workable and suitable for construction purposes.
Conclusion
Field tests for building lime provide a practical method to assess lime quality on-site, saving time and resources. From visual examinations to chemical and physical tests, these methods ensure the lime meets the required standards for construction work. Understanding and performing these tests can help builders select appropriate lime, ensuring the durability and strength of their structures.