Alternative building blocks

ALTERNATIVE BUILDING BLOCKS

1. FLY ASH BRICKS

Pulverised ash brick (PAB) technology is a process of converting industrial waste materials into quality building materials. At present, the technology is well established in converting thermal power plant waste into quality bricks.

P AB technology uses fly ash, filler materials (usually coarse sand or stone crusher dust) and additives (lime, gypsum or cement). The strength of the bricks can be engineered by varying the compositions. Equipment used can be manual or mechanised. Mechanised machines deploy hydraulic compaction to produce a variety of bricks and can be operated through electric or diesel power.

Fly Ash

Pulverised coal ash (PCA) is one of the major residues generated during the combustion of coal in thermal power plants. Though PCA is a waste product for the power sector, it is used as a raw material, primarily, in construction. PCA is generally classified into three types depending upon its particle size and zone of collection.

Fly Ash’is the extremely fine ash ‘flying' along with flue gases that is trapped in electro-static precipitators (ESP) and collected. The relatively coarser ash generated at the bottom of the boilers is mixed with water, made into slurry and pumped into fill sites called “ash ponds'. This ash forms the bulk of the ash generated and is termed as 'Pond Ash'. Depending upon the boiler design and efficiency, the ratio of fly ash to pond ash varies between 70:30 and 80:20.

In some older and relatively inefficient thermal power plants, a coarser variety of ash is generated called 'bottom ash'. This has appreciable carbon content but cannot be collected separately. This is also mixed with pond ash and pumped to ash fill sites.

Advantages of Fly Ash Bricks

1. High compressive strength

2. High strength to weight ratio

3. Lower water absorption

4. Uniform in shape and size; require less mortar in brick work.

5. Environment friendly - uses fly ash, less energy intensive compared to clay bricks

2. SAND LIME BRICKS

Sand lime bricks are made by mixing sand, lime and water. It is followed by a chemical process during wet mixing. The mix is then moulded under pressure forming the brick. Sand lime bricks find greater use in the United States and Germany.

Advantages of Sand Lime Bricks

1. Offer excellent strength as a load-bearing member

2. Shape is uniform and presents a smoother finish; wall plastering is not required

3. Good acoustic insulation

4. Good heat and humidity accumulation

5. Excellent fire resistance

6. Have gray color and possess pleasing appearance

7. Better noise absorbing qualities

3. AUTOCLAVED AERATED CONCRETE (AAC)

AAC is produced by mixing quicklime with cement, sand, water, gypsum and aluminium powder. It results in slurry that rises and sets to form lightweight honeycomb structured blocks. Quicklime, also known as calcium oxide (Cao), is a caustic alkaline substance. Quicklime has been used by humans for centuries for many things such as mortar, flux, in mixtures to waterproof boats and for whitewashing houses.

Advantages of AAC

1. It is a lightweight, precast, concrete building material.

2. It provides thermal insulation, fire-resistance and mold-resistance for a masonry structure used for housing and industrial buildings.

3. It is recognized as a sustainable building technique

4. It is very resource efficient, as densities can be achieved in the range of 250 kg/m' for brick materials.

Uses: Quicklime, which offers dedicated reactivity and fineness, is one of the key elements in the process to cast AAC products. These include blocks, wall panels, floor panels, roof panels, cladding (facade) panels and lintels.

4.  CONCRETE BLOCKS

Solid and hollow concrete blocks are manufactured to meet the requirements of building blocks in towns and cities. These blocks may be termed as artificial stones, since they replace stones in masonry construction. They are manufactured with lean mixes of cement, sand and aggregates of size less than 12 mm. Round aggregates are preferred over sharp-edged aggregates. Solid concrete blocks of size 400 mm × 200 mm × 150 mm are commonly manufactured. They also come in a wide variety of shapes and sizes. A comparison of solid and hollow concrete blocks is given in Table 1.

TABLE 1 COMPARISON OF SOLID AND HOLLOW CONCRETE BLOCKS

The advantage of using concrete blocks is that the construction activity is fast. Mortar requirement for finishing the surface is less and plastering is not necessary. Both solid and hollow blocks can be used for the construction of load bearing as well as partition walls. They are ideally suited for the construction of compound walls. Solid blocks are used for paving where holes would be dangerous or inconvenient.