NTS STUDY

Manufacturing, Dimensions, and Types of Concrete Blocks

1. Manufacturing Process

The quality of a concrete block depends heavily on the mix ratio and the curing process.

• Mix Ratio: The cement-to-aggregate ratio should not exceed 1:6. Lean mixes up to 1:8 are also common.

• Aggregates: A mix of 60% fine and 40% coarse aggregate (6 to 12 mm "Baby Jelly") is recommended. The Fineness Modulus should be between 3.6 and 4.

• Curing & Drying: Blocks must be cured for 14 days (water changed every 4 days) and then dried for 4 weeks before use to allow for complete shrinkage.

• Steam Curing: Modern factories use steam curing to ensure the blocks are fully shrunk before reaching the construction site.

2. Dimensions and Tolerances (BIS Standards)

Blocks are referred to by their Nominal Dimensions (Actual size + 10mm mortar joint).

• Load-bearing walls: Usually 200mm (actual 190mm) width.

• Filler/Parapet walls: Usually 100mm (actual 90mm) width.

• Tolerance: Max variation allowed is ±5 mm in length and ±3 mm in height/width.

3. Autoclaved Aerated Concrete (AAC) Blocks

These are lightweight blocks made using a chemical reaction.

• Process: Aluminum powder (0.12-0.25% of cement weight) reacts with lime to create hydrogen bubbles, making the block porous and light.

• Autoclaving: Blocks are treated at high temperature and pressure (10-15 atm) for 18 hours. This creates a crystalline structure that does not shrink upon drying.

4. Advantages over Clay Bricks

Concrete blocks offer several engineering benefits:

1. Speed & Efficiency: One standard block (390x190x190 mm) replaces 8 bricks, reducing mortar usage and increasing construction speed.

2. Eco-Friendly: No fertile soil excavation or fuel-intensive burning is required.

3. Insulation: Hollow cores provide excellent thermal and acoustic insulation, reducing air conditioning costs.

4. Deadload Reduction: Significant reduction in the weight of the structure, allowing for more economical foundation and beam designs.

5. Finish: Often requires no plastering, saving additional costs.

5. Important Storage & Usage Tips

• Protection: Blocks must be protected from rain during storage and construction to prevent moisture-induced shrinkage.

• Mortar Rule: The strength of the mortar should not exceed the strength of the block.

• Seismic Areas: In earthquake-prone zones, blockwork must be properly reinforced.