A COMPARITIVE ANALYSYS OF AAC BLOCKS VS BURNT BRICKS.

Bricks are the building blocks of the wall. The strength and durability of the wall, eventually of the whole building depends upon the bricks. Red bricks are the oldest and the most common type of brick used. The popularity of red bricks can be attributed to its easy availability, durability, low cost, convenience and feasibility.

However, due to growing population, the demand for red bricks too increased. To match the swelling demand for red bricks, fertile land needs to be sacrificed which India, being a developing country cannot afford. Plus, the scarcity of skilled labour and the increasing cost of kiln fuel makes the red bricks costlier. That’s why to balance the demand and supply of bricks, alternative solution for bricks were researched. This has led to the use of concrete blocks as an alternative material.

As my senior colleague once told, “The red colour of brick was so popular in olden days, that when the Autoclaved Aerated Concrete (AAC) blocks and?fly ash?bricks entered the market, there was a?lot of resistance by the people to use it, as it was grey in colour and was made from ‘ash’, which was some how not acceptable.

There are various types of cement blocks available in the market. However, the most used are AAC blocks. AAC blocks are one of the major achievements of the 20th century in the field of construction. Fly ash, a by-product of industries is used in the manufacturing of AAC blocks making it?eco-friendly materials. In fact, fly ash disposal was a headache and such option have made its use more beneficial to the environment. It is a revolutionary material offering a unique combination of high durability and strength, low weight and superior ecological ‘green’ features.

Hence, here in, we give you a brief comparison between AAC blocks Vs Red bricks to help you make the right and informed choice.

01. General

AAC Block

• AAC Blocks are lightweight building materials cut into masonry blocks or formed as larger planks and panels.
• AAC Block is relatively uniform in size and does not contain coarse aggregate phase.

Red Bricks/Clay Bricks

• Red brick is a small block, made up of clay ceramic?material used in masonry construction.
• Bricks are less uniform in size and texture as compared to AAC blocks.

02. Raw Material

AAC Block

• AAC blocks are manufactured from the mixture of fly ash,?cement, lime, gypsum and an aeration agent.

Red Bricks/Clay Bricks

• Conventional red bricks are made from a mixture of clay (alumina), sand, Lime, iron oxide and Magnesia.
• Natural soil is used for production of Bricks. Hence, ultimately it will vary depending upon the quality of local soil, i.e. Top soil of Earth’s Crust.

03. Uses

AAC Block

• AAC Block can be used to build both internal and external walls.
• According to ‘IS 2185(Part3)-1984’ (Specification for Concrete Masonry Units), Autoclaved Aerated Concrete blocks can be used for

– Load bearing and non-load bearing internal walls,

–?Partition?and panel walls,

– Inner leaf of?cavity walls?or as backing to?brick masonry

– For external load-bearing walls

– Panel walls in steel or?reinforced concrete frame structure, if protected from weather by rendering or by some other adequate treatment.

Red Bricks/Clay Bricks

As a Structural Unit

• Red bricks are strong, hard and durable; therefore, they are used as a construction material in creating different structures such as
• Buildings
• Bridges
• Foundations
• Arches?and cornices
• Pavements

As an Aesthetic and finish surface

• Bricks are used as per its different colours, sizes and orientations to get different surface designs. As an aesthetic material bricks can be used
• As Facing Bricks
• Architectural Purposes
• Exposed practice work

04. Advantages

AAC Block

• AAC blocks are very easy to handle and ordinary tools can be used for cutting.
• AAC blocks are available in large sizes and hence less no. of joints. This ultimately results in faster construction on site and less consumption of either?cement-mortar?or chemical and also increasing the strength of wall.
• Earthquake forces are proportional to the weight of building. Due to light weight of AAC blocks, there will be reduction in dead load of the building. Hence AAC blocks are preferred in high seismic zones. Furthermore, less steel will be required in case of RCC structure.
• AAC blocks are made from an inorganic material which helps to avoid termites, damages or losses.
• Use of AAC blocks in the multi-storey building can reduce the consumption of steel and concrete. This reduces the dead load on the structure and increase the?carpet area.
• Reduction in dead?load on the structure?can greatly reduce the size of structural elements which means that it will increase the floor/carpet area.
• Easy to transport to upper floors.
• Use of AAC blocks can significantly reduce the construction time of the project. Time-saving is possible due to the large size of blocks and less curing required before?plaster.
• According to ‘Magicrete’ (India’s frontline manufacturer of Lightweight concrete (AAC) blocks), AAC blocks have a very high thermal insulation index which means that the ambient temperature within these structures doesn’t change rapidly with the external temperature. Hence the building will remain relatively cooler in summers and warmer in winters.
• AAC blocks reduce interior temperature variation maintaining pleasant and healthy temperature for habitant.
• AAC blocks reduce the energy cost of air-conditioning to a greater extent due to its thermal property. there will be approximately 25% reduction in air conditioner load and 25 -30% less electricity consumption on HVAC.
• One AAC block of size (600 x 200 x 100 mm) is equivalent to 6 bricks. Hence it reduces 50% of joints resulting in saving of mortar up to 48%. In case of 150 mm or thicker block masonry, the mortar saving is even more due to the avoidance of vertical?joint.
• Minimal wastage of AAC blocks.
• It is environment-friendly and also saves water as less curing is required. Hence it is popularly used as a green product.
• The initial production cost of AAC blocks may be more; however, as discussed above, it can reduce the consumption of Steel, Cement,?Concrete?and labour. Therefore, the whole project cost gets decreased.

Red Bricks/Clay Bricks

• Red bricks are easy to handle and work with.
• Raw material is easily and abundantly available. So, it is economical. Red Bricks are low maintenance, permanent, hard and durable building materials.
• Compressive strength of brick?is good enough for ordinary construction requirements.
• Different orientations and sizes give different surface textures.
• Demolishing of brick structures is very easy and less time consuming.
• It is reusable and recyclable.

05. Disadvantages

AAC Block

• The production cost per unit for AAC Block is higher.
• Plaster sometimes does not stick properly because of its smooth surface.AAC block work needs care during production itself, so that surface does not become very smooth.
• AAC block also requires a protective finish since the material is porous and would deteriorate if left exposed.

Red Bricks/Clay Bricks

• Time consuming construction
• Red Bricks cannot be used in high seismic zones for?load bearing structures.
• A red brick absorbs water easily so?Efflorescence?may occur due to the presence of salt in water.
• Rough surfaces of bricks may cause moulds growth if it is not properly cleaned.
• Continuous use of Red bricks in construction will lead to extensive loss of fertile top soil and hence potential agricultural land.
• Red bricks are heavy in weight. Since the structure needs to withstand greater weight, more steel is required and hence construction cost is more.
• Big damage to environmental and loss of fertile land due to use of clay soil?excavation?for manufacturing of bricks.

06. Appearence

AAC Block

• Colour of AAC Block is?Grey.
• AAC block comes in big size.

Red Bricks/Clay Bricks

• Colour of clay brick is?Red.
• Clay bricks are smaller than AAC blocks.

07. Properties

(a) Size Available in Market

AAC Block

• 400-600×100-200×100-300mm. However, it may vary slightly depending on the manufacturer.

Red Bricks/Clay Bricks

Standard Modular Size of Red Bricks:

• 190x90x90mm
• 190x90x40mm

Standard Non Modular Size:

• 230x110x70
• 230x110x30

These sizes are more popular in India.

(b) Allowable Variation in Size

AAC Block

• According to ‘IS: 2185’ (Specification for Concrete Masonry Units Part 3 Autoclaved Cellular (Aerated) Concrete Blocks), the maximum permitted variation in the length of the AAC block units is ±5 mm and the maximum variation in the height and width of unit is ±3 mm.
• The AAC Blocks are accurate in size because it is produced by wire cut technology and is a factory product.

Red Bricks/Clay Bricks

• The dimensions of bricks when tested accordance with ‘IS 1077: 1992’ shall be within the following limits per 20 bricks:

a)?For Modular Size:

• Length:?38OO±80 mm
• Width:?1800±40 mm
• Height:

01.?1800±40 mm

(For 90 mm high bricks)

02.?800±40 mm

(For 40 mm high bricks)

b) For Non-Modular Size:

• Length:?46OO±80 mm
• Width:?2200±40 mm
• Height:

01.?1400±40 mm

(For 70 mm high bricks)

02.?600±40 mm

(For 30 mm high bricks)

• The size of Red Bricks is not standard and varies from region to region.

(c) Dry Density

AAC Block

• Dry density of AAC block varies from 451 kg/m3?to 1000 kg/m3.
• The low dry density of AAC blocks reduce the load on the foundation and other?structural components in a structure?leading to 55% reduction in weight of walls. Because of reduction in self-weight, AAC block construction attracts less earthquake load.

Red Bricks/Clay Bricks

• Dry density of red clay bricks varies from 1600 kg/m3?to 1920 kg/m3

(d) Weight

AAC Block

• Generally, the weight of AAC blocks varies from 3 to 4 kg.

Red Bricks/Clay Bricks

• Generally, the weight of red bricks/clay bricks varies from 2.5 to 7.5 kg.

(e) Compressive Strength

Strength is defined as a capacity to resist force or pressure.

AAC Block

• The compressive strength of AAC blocks varies between 3 to 4.5 N/mm2

Red Bricks/Clay Bricks

• The compressive strength of clay bricks varies between 2.5 to 3.5 N/mm2

(f) Water Absorption

AAC Block

• Water Absorption of AAC block should not be more than 10% of its weight.

Red Bricks/Clay Bricks

• Water absorption of brick?should not be more than 20% of its weight.

If the brick or block absorb more water than the above specified limit, it causes adverse effects on the strength of brick or block as well as the durability of the structure.

(g) Fire Resistance

AAC Block

• According to ‘Portland Cement Association’, Fire resistance of AAC block is excellent, with 8 -inch-thick AAC achieving a 4 -hour rating (actual performance exceeds that and resist fire up to up to eight hours).?Also, it is non-combustible material and will not burn or give off toxic fumes.

Red Bricks/Clay Bricks

• 8-inch-thick wall can resist fire for up to 2 hours.

(h) Thermal Conductivity

The amount of heat transfer from a specific material is called its thermal conductivity.

AAC Block

• The thermal conductivity of AAC block varies from 0.21- 0.42 W/mk
• Thermal conductivity of block is lower and hence less heat transfer happens from block.
• AAC blocks are made up of fly ash and fly ash has a lower thermal conductivity compared to natural clay, which results in more thermal resistant blocks.

Red Bricks/Clay Bricks

• 6- 1.0 W/mk
• The thermal conductivity of the brick is high, and hence heat transfer from brick is more than the AAC block.

(i) Moisture Resistance

AAC Block

• Moisture resistance of AAC block is better than the Red Brick.
• AAC block consists of unconnected micro pores which prevent the capillary transport of moisture over a long distance.

Red Bricks/Clay Bricks

• Moisture Resistance of Red Brick is Average.
• Moisture resistance depends up on water absorption of the brick and proportion of?cement mortar
• 100/115mm wall will not have adequate moisture resistance. If poor, it will make walls damp & wet.

(j) Sound Insulation/Noise Transmission

• Sound insulation is defined as the capacity to reduce sound transmission by the building elements.
• Sound abortion of a material depends on its density. Denser the material, higher will be the reflection of sound. However, if the material is porous in nature, the density of the material gets reduced and the air gaps acts as insulation
• Sound transmission also depends upon the thickness of the wall.

AAC Block

• The AAC block has good sound transmission property due to the presence of air voids.
• 40-45 db sound is reduced by 200 mm thick wall.
• That lightweight also gives a high sound reduction for privacy, both from outside noises and from other rooms when used as interior?partition walls.
• As mentioned above, AAC blocks are light in weight and porous in nature they have very good acoustics properties. Thus, AAC blocks always have good sound insulation compared to clay or red bricks.

Red Bricks/Clay Bricks

• The?brick masonry wall?has good sound insulation property due to its dense structure.
• 150 mm wall reduces the sound by 45db and 50 db by 230 mm wall.

(k) Termite Resistance

AAC Block

• AAC blocks are insect resistant, inorganic and solid wall construction material.
• AAC blocks do not allow spreading of termites and pests and hence increase the life of the wall.

Red Bricks/Clay Bricks

• Red bricks are not termite resistant as they are made from clay which is an organic material.

08. Efficiency

(a) Labour Output

AAC Block

• Less labours are required. The speed of work will be double than that of the clay brick work.

Red Bricks/Clay Bricks

• More labours are required. The speed of red brick work will be slow as compared to the block work.

(b) Carpet Area

AAC Block

• Since AAC Blocks are thin, available carpet area will be more. This is very important where cost of houses is very high.

Red Bricks/Clay Bricks

• Due to more thickness of bricks, available carpet area will be less. But not suitable for high rise and load bearing buildings.

(c) Applicability

AAC Block

• AAC Blocks are recommended for high-rise buildings because it substantially reduces total dead load of the building.

Red Bricks/Clay Bricks

• Red bricks are used for both load-bearing and non-load bearing walls.

(d) Mortar Consumption

AAC Block

• Requires less mortar due to flat and even surface & less number of joints.

Red Bricks/Clay Bricks

• Requires more mortar due to irregular surface & more number of joints.

(e) Speed of Construction

AAC Block

• Speedy construction of wall due to the bigger block size, light in weight and less number of joints.

Red Bricks/Clay Bricks

• The speed of construction of the brick masonry wall is slower than the block construction.

(f) Water Usage

AAC Block

• Block is cured by steam and block masonry requires less curing. Hence less water and less electricity are required.

Red Bricks/Clay Bricks

• Requires more water for curing and hence high amount of electricity bill and labour cost.

(g) Breakage & Utilization?

AAC Block

• Negligible breakage almost 100 % utilisation is possible.

Red Bricks/Clay Bricks

• On an average, 10 to 12% breakage happens on construction site, so 100% utilisation is not possible. Even at some places, due to the poor?quality of bricks, wastage goes up to 33%.

(h) Storage

AAC Block

• Readily available at any time & in any season at a short notice, so no storage required.

Red Bricks/Clay Bricks

• In monsoon, Stock at the site is compulsory which blocks large working area on the site. otherwise work will get stopped.

(i) Efflorescence

AAC Block

• Efflorescence may occur through mortar and water.

Red Bricks/Clay Bricks

• Generally present.
• Efflorescence may occur due to presence of salt in water and sand.

09. Cost

(a) Construct a 1 Cum Wall Cost

AAC Block

• 1 cum block work cost is higher (around INR 3500/- in India).

Red Bricks/Clay Bricks

• 1 cum brick work cost is lower. (around INR 2500/- in India).

(b) Structural Cost

AAC Block

• Steel saving up to 15% & Concrete saving up to 7%.
• AAC Blocks reduce the load on?foundation?due to its light self-weight and saves consumption of steel. Hence reduces the Structural Cost.

Red Bricks/Clay Bricks

• No such saving is possible

10. Environment Impact

(a) Green Product

AAC Block

• AAC Blocks are made from a non-toxic material which does not harm the environment. Usage of fly ash helps in dumping of this-industrial waste. During the manufacturing process, Waste of the AAC Block is recycled and used again. This waste is made from the cutting process. Hence AAC Blocks are a Green product.

Red Bricks/Clay Bricks

• Red Bricks are made from the clay which is naturally available material but it reduces the top fertile soil cover. Hence, it is not eco-friendly.

(b) Earthquake Resistance

AAC Block

• Earthquake forces are proportional to the weight of the building. Since AAC Blocks reduce the weight of building, the safety against earthquakes is more.

Red Bricks/Clay Bricks

• Red bricks are not preferred in earthquake prone regions.

11. Tools Used in Manufacturing Process

AAC Block

• Tools used in manufacturing process of AAC blocks are block making machine, hand operated with and without vibrator and electrically operated with vibrator, block pallets, spades, mortar pans, measuring boxes, compacting rod, trowel, curing pipes etc.

Red Bricks/Clay Bricks

• In the manufacturing of red bricks, brick moulds, cutting wire or strike, wooden plates called pallets, stock boards and other tools are used.

Conclusion

Both AAC blocks and Red bricks have advantages and disadvantages as discussed above. Red Bricks, made from the natural soil, may lead to the erosion of top soil over a period of time. Whereas, AAC blocks uses fly ash and helps in utilising a waste product. The large size, light-weight, fire and termite resistance of AAC blocks saves energy, time, construction cost and imparts durability. But the AAC blocks have some limitations. It is not as widely available as most concrete products, though it can be transported anywhere. If it has to be transported, its light weight is advantageous. Keeping in consideration, the pros and cons of both of these building materials, you may opt for the suitable material.