Mechanical and Durability Properties of Clay Bricks and Autoclaved Aerated Blocks

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Bricks and Concrete are the highly used materials in the field of civil engineering field. Usually every material depends upon on its mechanical charactertics and durability properties. In earlier times stones were bonded by natural bonds to form an irregular structure and later on stone were transformed into various shapes for the need of construction. Within the time bricks were formed by heating clay bonded with various materials before concrete, as there were mud bricks molded by hand and dried in sun and as the time passed kiln was there to make them stronger and last long. In contrast to bricks, concrete was formed earlier with the help of lime and gypsum which helped to create the word pozzolanic, which was invented by village name Pozzuoli. Both materials have a vast history behind the production and improvements of them according the time.

In this study, clay bricks and autoclaved aerated blocks are studied on basis of mechanical and durability properties, production and various techniques which help to use them in fields.

               Figure 1 Clay Bricks                                       Figure 2 Autoclaved Aerated Bricks

Figure 1 Source“

Figure 2 Source “




       Bricks are the essential material for every construction to make walls, pavements, roads and every other which is related to masonry construction. Bricks are the mixture of the clay which is bonded with lime and cementitious materials which are further burned and formed in a shape. There are main two methods or type of bricks which are fired and non-fired bricks as both methods are different, but materials used information are quite similar. According to countries bricks are classified according to the durability of it and on basis of grades of quality.


  • Fired Clay Bricks
  • Calcium Silica Bricks
  • Engineering Bricks
  • Custom Fly Ash Bricks

Figure 3 Clay Brick-Source””)



Aerated concrete is one type of the light weight concrete which is also termed as cellular concrete, further it can also be divided into method of production and types of admixtures. Aerated autoclaved concrete is made of foaming agent which is made by injecting the foaming agent material into concrete or in the mortar. Foaming agent is made according to the aluminium powder and other slurry elements into concrete and makes hydrogen bubbles.

In earlier time yeast and egg material used to be there in concrete to make it foamed during construction stage. Autoclaved aerated concrete is having better flowability, less self weight and large molecular packing which makes less aggregates usage with medium strength and good insulation properties.

Figure 4 Autoclaved Aerated Block-Source “




Clay is one of the materials which is available in ample quantity on earth and from a long-time process of brick manufacturing has not been changed. There are numerous properties which are in keep in view while production of bricks, properties like plasticity, compressive strength and rigidity.

Manufacturing Process of Bricks are shown below in schematic diagram-


Figure 5 Manufacture Process of Clay Bricks

Mining of Raw Material-

Fine clay particles are mined with large power equipments then clay is transported to the areas where further process will be carried out. Material which has been excavated is stored properly which should not get moisture due to weather conditions.

Figure 6 Mining Equipment-Source “

Sieving of Raw Materials-

Materials which are excavated are carried out under screening process where desired particle size is maintained. According to the desired strength and type of bricks clay and sand is been sieved under controlled environments.

Mixing of Raw Materials-

After the sand and clay is been sieved, further materials is been mixed with lime and sometimes bonding agents to form bricks in a perfect manner. Various types of bricks are been made according to strength type, materials which are mixed are decided according to strength achieved.


Materials which are mixed and prepared according to the desired strength are put into mould. Mould are made according to the standard sizes and are being filled with materials.

Figure 7 Brick Moulds-Source”


Moulds having materials are taken in large kiln where drying process is been carried out. Under high heats materials bonds and becomes rigid and therefore bricks are formed.


Figure 8 Kiln-Source“


AAC blocks are made of natural raw materials which consists fly ash, foaming agents, water and clay. AAC blocks has a great thermal property and can be widely used in those places where insulation and thermal properties are in need during construction. AAC blocks also has low density which can be better in reducing loads on foundation sections. AAC blocks are made of non-toxic materials therefore it is eco friendly product.

Production method of AAC blocks is shown below-

Figure 9 Manufacture Process of AAC Blocks


According to type of strength needs cement grade is selected in terms of compressive strength after curing stages. AAC depends on grade of cement as well as curing stage.


Portable water is used in addition to that water should be free from any kind of impurities.


According to the calcium content fly ash grade is selected and mixed with other materials. Each fly-ash has different calcium and lime content which are selected according to mix design of concrete on strength basis.


Superplasticizer is a type of additive mixture which makes bonding of materials faster under less time and decreases setting time of concrete.

Foaming agent-

Foaming agents are kept under controlled temperatures and material temperature should not exceed 25C. Foaming agent is mixed 40 molar for 1 litre of water and weight of the foam which is created should not exceed 80 grams per litre for 10 litres of water. Foam should be free from any kind of oil or any other impurity which can hard the composition of cement flyash and foam. Usually foam generator is used which creates foam and mixed with concrete and further it is used with aggregates or steel as well.

Mould sizes can be –

Length – 400, 500, 600mm.

Height- 250 or 300mm

Width – 100, 150 200 or 250 mm


Figure 10 Autoclaved Aerated Concrete-Source”




  • Aesthetic Appeal
  • Termite Free
  • Maintenance Free
  • Flexible Usage in Construction
  • Longevity
  • Economical to Use
  • Reusable


  • Reduces dead load and can perform better in external loadings like earthquake.
  • Decreases thickness of walls.
  • Time saving in constructions.
  • Low thermal conductivity which keeps house cool in summer and warmer in winters.
  • Minimal wastages in production.
  • Reusable
  • High fire resistance.
  • Disadvantages of clay bricks.
  • Increases dead loadings which is harmful in terms of earthquake.
  • Poor insulation.
  • Less compressive strengths.
  • Needs high amount of clay in production which leads to shortage of clays.


  • Production cost is higher.
  • Needs care during production in terms of temperatures.




Bricks can be customized while production materials like fly ash, marble powder or steel fibres can be used. Bricks can be made on basis of high compressive strength which can be more advantageous in terms of residential buildings where life span of structure can be more than usual. Now a day’s bricks are made having more proportion of ceramic material which leads less usage of clay and soils.


Concrete Is the basic thing in the aac blocks which can be made by different admixtures. Concrete highly supports mineral and chemical admixtures under controlled pH scales and also gives higher outputs in compare to bricks. Now a days there are ample of chemicals and minerals which are been tested with concrete on basis of strength and durability.



  • Brick construction is widely used therefore its difficult for system to adopt new methods in construction like AAC blocks.
  • Usage of soil and clays are highly extensive which leads to high soil erosion and deploy of top layer of soil, which is also useful for vegetations purposes.
  • Countries which has severe winter temperatures cannot use bricks on construction purposes due to low thermal properties, where AAC blocks can make a difference in maintaining thermal properties for the structure.
  • In compare to wood for the winter regions, durability and life span of blocks is more which leads to termite free as well as life span is longer.
  • By my opinion AAC blocks are better in compare to bricks, not only in terms of strength but also, they can be customized as well as perform well for the residential and commercial too. AAC blocks do have high construction cost but on other hand gives loner span to structures.


  1. Frank Warner Riepe, U.S Patent 8,240,103 B2, 2012.
  2. N. Narayanan, K. Ramamurthy, (2000), “Structure and Properties of aerated concrete: a review”, Cement & Concrete Composites, Volume 22, pp 321-329.
  3. Xu Lingling, Guo Wei, (2005), “Study on fired bricks with replacing clay by fly ash in high volume ratio”, Construction and Building Materials, Volume 19, pp 243-247.
  4. Yavuz Yardim, A.M.T. Waleed,, “AAC-concrete light weight precast composite floor slab”, Construction and Building Materials, Volume 40, pp 405-410.
  5. Ali J. Hamad, (2014),” Materials, Production, Properties and Application of Aerated Lightweight Concrete”, International Journal of Materials Science and Engineering, Volume 2, pp 152-157.
  6. Krishna Bhavani Siram. K, (2012),” Cellular Light-Weight Concrete Block as a Replacement of Burnt Clay Bricks”, International Journal of Engineering and Advanced Technology, Volume 2, pp 149-151.
  7. Jadhao Vikas. P, Pajgade Prakash. S,(2013), “Influence of Masonry Infill Walls on Seismic Performance of RC Framed Structures a Comparison of AAC and Conventional Brick Infill”, International Journal of Engineering and Advanced Technology, Volume 2, pp 148-153.
  8. URL
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  10. Yothin Ungkoon et al., (2007),” Analysis of Microstructure and Properties of Autoclaved Aerated Concrete Wall Construction Material”, Journal of Industrial and Engineering Chemistry, Volume 13, pp 1103-1108.


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