AAC Blocks

AAC blocks or Autoclaved Aerated Concrete blocks or lightweight blocks made up of sand, calcined gypsum, lime, water, aluminium powder and cement which is heated under pressure in autoclave. These blocks are used for both interior and exterior construction. It is greyish-white in color and has thermal efficiency three times higher than clay bricks. It is 50% lighter than red bricks and also one-third of cost those bricks. Its sound insulation is approximately 42b and water absorption of about 10% of its weight.

Manufacturing of AAC Blocks

In the manufacture of AAC blocks calcium hydroxide and aluminium powder is reacted in presence of water to form hydrogen. The raw materials that are used in production of AAC blocks are natural which are quicklime, cement, sand and water. In the manufacture of AAC blocks, aluminium is the gas generation agent and quartz sand by quantity is the dominant material. Firstly, sand is ground in ball mills to required fineness. Alternatively, fly ash can also be used. Then ground sand in form of slurry is stored in large tanks with agitators to prevent sedimentation of sand. The gas generation agent, aluminium is dispersed in water. The mixture is poured in oiled molds where further chemical reaction takes place. The mixture expands due to reaction of aluminium and stiffens due to hydration of cement and quicklime. After filling, the mold is transported to pre-curing area which is heated to speed up the chemical reactions. As soon as procuring is finished the hardness of cake and temperature is tested. After that, the cake is tilted in upright position for cutting. During cutting and autoclaving, only cakes rest on autoclave pallets without any mold part. The block length is cut in side trimmer and then block thickness is cut. Finally, the blocks height is cut by cross cutter in which possible wires are used to facilitate high cutting accuracy. Then, the cut cake is picked up by loading machine and put in autoclave trolley. A heated waiting area in front of the autoclaves helps to avoid temperature loss of the cakes prior to autoclaving. During the steam curing the unique crystal structure is formed inside of AAC. After autoclaving, the AAC already gained its final strength. The cakes are transported to separating machine after unloading the autoclave trolleys. Here, the horizontal layers are separated which tend to be fused together during autoclaving. Finally, blocks are packed and ready for sale.

Sizes of AAC Blocks

S. No. Length X Height X Thickness Pcs/m3 Wall Area /m3
1. 625X 250 X 100 64.00 pcs 10.00 sq.mt.
2. 625X 250 X 125 51.20 pcs 8.00 sq.mt.
3. 625X 250 X 150 42.26 pcs 6.66 sq.mt.
4. 625X 250 X 200 32.00 pcs 5.00 sq.mt.
5. 625X 250 X 225 28.44 pcs 4.44 sq.mt.
6. 625X 250 X 250 25.60 pcs 4.00 sq.mt.
7. 625X 250 X 300 21.33 pcs 3.33 sq.mt.

Advantages of AAC Blocks

  • AAC blocks are light in weight. It weighs almost 50% less than other bricks. Hence its light weight leads to reduce transportation and labor cost. Not only this, its lighter weight makes the blocks easy to handle and also increase the chances of survival in seismic activity. Hence it is earthquake resistant also.
  • Usually, AAC blocks are larger in size which leads to faster masonry work hence reducing the construction cost of project.
  • While looking upon construction-design, moisture protection is the important factor that is taken into consideration. AAC blocks have porous structure. The macro pores present in AAC, makes it moisture-proof.
  • It allows diffusion of water hence the usage of AAC blocks leads to great ventilation. It absorbs all the moisture and releases humidity.
  • As compare to other concrete, it produces 30% less solid waste along with decrement of 50% of greenhouse gas emission. So, AAC blocks are environment- friendly.
  • Talking about longevity of AAC blocks, they are not affected by harsh climates. Also, it does not get degrade easily by normal climate conditions. Hence, AAC blocks are long-lasting.
  • When fire-safety point of view is taken into consideration, AAC blocks can be looked upon because of their non-combustible property. It can provide fire-resistance for upto six hours.
  • In the manufacture of AAC blocks no toxic substances are utilized which further do not attracts pests. So, AAC blocks are also termite-free.
  • AAC blocks allows temperatures to be warm in winters and cold in summers because of thermal insulation property which is gained by the formation of hydrogen in production process.
  • AAC blocks are much stronger than other building materials as it have average compressive strength of 3.5 N/mm2.

AAC Blocks VS Red Bricks

S. No. Parameters AAC Blocks Red Bricks
1. WEIGHT COMPARISON 1 AAC Block = Approx. 14.20 Kg 8 Red Bricks = Approx. 35.02 Kg
2. IMMERSION IN WATER Not get immersed in water because of light weight Get Immersed in water due to its heavy weight
3. COST OF LABOUR Labor cost of wall of 10ft x 10 ft = Rs.900 (Approx.)
(Because of its larger size less manpower is required)
Labor cost of wall of 10ft x 10 ft = Rs.2000 (Approx.)
(Because of its smaller size more manpower is required)
4. JOINTS AND WORKABILTY For 10ft x 10 ft wall 50 AAC blocks are required. So there are approximately 162 joints in that wall which leads to fast construction. For 10ft x 10 ft wall 585 red bricks are required. So there are approximately 1656 joints in that wall which leads to slow construction.
5. COST OF MORTAR It costs approx. Rs.650 for construction of 10ft x 10 ft wall It costs approx. Rs.1350 for construction of 10ft x 10 ft wall
6. DRY DENSITY Class 1 – 651-750 kg/ m3
Class 2 – 751-850 kg/ m3
Class 3 – 851-1000 kg/ m3
(Less dead load on structure)
Class 1–1600-1720 kg/ m3
Class 2–1721-1820 kg/ m3
Class 3–1821-1920 kg/ m3
(More dead load on structure)
7. COMPRESSIVE STRENGTH 5 N/mm2
(More strong)
3.50 N/mm2
(Less strong)
8. WATER ABSORPTION RATIO It should not be more than 10% of its weight It should not be more than 20% of its weight
9. FIRE RESISTANCE Upto 6 Hours Upto 2 hours