Lime has long been recognized as one of the most essential building materials in the construction industry. It is known for its versatility, adaptability, and sustainability. According to IS 712-1973, lime is classified into various categories based on its chemical composition, physical properties, and intended applications in construction. This classification helps determine the most suitable lime for different construction tasks, ensuring the material is used effectively and efficiently.
Lime is an essential material in construction, offering both historical and modern-day relevance. From ancient monuments to contemporary infrastructure, lime has been used for centuries in various forms, including lime mortar, plaster, and as a component in building blocks. The classification of lime is crucial for determining its specific applications, ensuring its properties align with the needs of the construction project.
Classification of Lime as per IS 712-1973
The Indian Standard IS 712-1973 categorizes lime into several classes based on its chemical composition, setting properties, and overall quality. This classification helps determine the suitability of lime for specific construction purposes. Additionally, there are special considerations for materials like carbide lime, a by-product of acetylene production, which can also play a role in construction when used appropriately.
A. General Classification of Lime
The classification system categorizes lime into several distinct classes. Among these, carbide lime deserves special mention. Produced during the manufacturing of acetylene gas, carbide lime is typically a by-product. If fresh, it can be used for specialized plaster works; however, if it is in a semi-solid state, it is not recommended for construction due to its tendency to dry out too quickly.
The classification of lime includes the following primary categories:
- Class A: Eminently Hydraulic Lime
- Class B: Semi-Hydraulic Lime
- Class C: Fat Lime (Quick Lime or White Lime)
- Class D: Magnesium or Dolomite Lime
- Class E: Kankar Lime
- Class F: Siliceous Dolomite Lime
B. Detailed Explanation of Each Lime Class
- Class A: Eminently Hydraulic Lime
- Characteristics: This type of lime is classified as hydraulic, meaning it can set and harden even when exposed to water. This is due to the presence of impurities such as clay and silica. It is an excellent choice for constructions that are exposed to water or harsh weather conditions.
- Applications: Class A hydraulic lime is commonly used in the construction of structures like arches, domes, and buildings that require water-resistant properties.
- Class B: Semi-Hydraulic Lime
- Characteristics: Semi-hydraulic lime has properties that allow it to set under the influence of water, but to a lesser extent than Class A hydraulic lime. It is typically produced from limestone with a moderate content of clay.
- Applications: This class is typically used for small-scale masonry projects, such as walls and facades, where the lime’s ability to set in damp conditions is not crucial.
- Class C: Fat Lime (Quick Lime or White Lime)
- Characteristics: Fat lime, also known as quicklime or white lime, is a non-hydraulic lime that undergoes a chemical transformation when it comes into contact with water. This type of lime is known for its high purity and ability to slake to a fine powder.
- Applications: Fat lime is primarily used for non-structural purposes such as whitewashing, plastering, and as a final coat in finishing work. It is also used in masonry mortar when combined with pozzolanic materials to improve its strength.
- Class D: Magnesium or Dolomite Lime
- Characteristics: Magnesium lime is produced from dolomite limestone, which is rich in magnesium carbonate. This type of lime is more stable and has a slower rate of slaking compared to other types.
- Applications: It is mainly used for finishing work, such as plastering and whitewashing, as it helps to produce a smoother and more durable surface.
- Class E: Kankar Lime
- Characteristics: Kankar lime is made by burning lime nodules, which are naturally found in the soil, especially in regions with a significant presence of silica. This type of lime is hydraulic in nature and can set in moist conditions.
- Applications: Kankar lime is primarily used for making masonry mortar and for applications where its hydraulic properties are required.
- Class F: Siliceous Dolomite Lime
- Characteristics: Siliceous dolomite lime is made from a mixture of lime and silica-rich dolomite. This lime is known for its strength and durability, making it ideal for more demanding construction tasks.
- Applications: It is used for both the undercoat and finishing layers of plasterwork, ensuring that surfaces are smooth, durable, and long-lasting.
Compressive Strength of Lime Mortar Mixes
Lime mortars, often mixed with sand or other materials, are key components in masonry and plastering work. The compressive strength of lime mortar varies significantly depending on the type of lime used. For example, mixes made with Class A hydraulic lime tend to have higher compressive strength compared to those made with Class C fat lime, due to their enhanced setting properties. In comparison to cement mortar, lime mortar may have lower initial strength but offers greater flexibility and durability over time.
Preparation of Lime-Based Products
A. Slaked Lime Preparation
Slaked lime, or hydrated lime, is created by adding water to quicklime, initiating a process known as “slaking.” The process involves the following steps:
- Preparation: Quicklime is placed on a platform that is dry and free of moisture. The lime is produced by heating limestone (calcium carbonate) to high temperatures.
- Addition of Water: Water is gradually added to the quicklime while it is continuously mixed to ensure the lime turns into a fine powder.
- Sifting: The mixture is passed through a sieve to remove any remaining large particles, leaving behind fine, hydrated lime.
- Storage: The slaked lime is then stored in airtight containers or other moisture-resistant packaging until it is ready for use.
B. Lime Putty Preparation
Lime putty is a paste-like substance produced from slaked lime, which is ideal for making lime mortar. The preparation involves:
- Tank Setup: Two tanks (Tank 1 and Tank 2) are set up with Tank 1 at a higher level than Tank 2 to facilitate the flow of liquid.
- Mixing: Quicklime is added to water in Tank 1, and the mixture is stirred continuously to ensure proper slaking.
- Flowing to Tank 2: The slaked mixture is allowed to flow to Tank 2, where it is left to settle for at least 72 hours, during which excess water is absorbed by the dry brick masonry of the tank.
- Final Product: The resulting lime putty is smooth and ready for use in mortar mixes.
Storage and Handling of Lime
A. Storing Quick Lime and Slaked Lime
Lime, both in quicklime and slaked form, should be stored carefully to maintain its effectiveness and prevent unwanted chemical reactions with moisture in the air. Quicklime should be stored in airtight containers or large heaps, while slaked lime is best packaged in moisture-proof materials such as polyethylene bags, gunny bags, or craft papers.
B. Storage Conditions
The storage areas for lime should be dry, weatherproof, and watertight. Proper storage ensures that the material retains its properties and can be used efficiently when required for construction projects.
Handling of Lime and Safety Precautions
Working with lime requires caution, as it can pose health risks if not handled properly. Lime is caustic and can cause severe skin irritation, eye damage, and respiratory issues if inhaled. To minimize these risks, workers must use appropriate personal protective equipment (PPE), including goggles, gloves, boots, and respirators. Additionally, since the process of slaking lime generates considerable heat (exothermic reaction), precautions must be taken to avoid burns or fire hazards on the construction site.
Conclusion
Lime continues to play a vital role in the construction industry due to its versatile properties and range of applications. By adhering to proper classification and handling techniques, construction projects can benefit from lime’s durability, sustainability, and strength. Whether for plastering, masonry, or more specialized applications, understanding the characteristics of each type of lime ensures its optimal use, contributing to safe and long-lasting construction.