Concrete is a highly valued   building material because it lends itself   generously for use in a  variety of ways and conditions. Besides that, concrete products are like wine, becoming better -that is stronger and harder -with age. This marks them out as ideal for constructing public buildings and similar projects that should last for a hundred of years. Concrete blocks can either    be dense or light-weight. Dense blocks are made from a mixture of crushed granite, limestone, gravel and water. On the other side of the coin, lightweight blocks, are manufactured by mixing sand, cement and water. Also, Lightweights blocks can be produced from clay, blast furnace slag, sintered ash and pumice. After mixing the ingredients, the mixture is cast in moulds, vibrated and comes out on the other side as blocks. These blocks  must undergo a curing process before they are ready for use.

Aerated  concrete blocks  are  manufactured  by  the  addition of  aluminium powder  to  fine  mixture  of  sand, lime ,pulverized fuel  ash, and Portland cement. The hydrogen gas generated by reaction of the aluminium powder with the mixture, creates a non-interconnected enclosed small spaces structure in the finished blocks.

Concrete offers a rich menu of various types   of blocks and include but not limited to the following:

  1. Solid blocks
  2. Cellular blocks:-have enclosed spaces within its structure.
  3. Hollow blocks-Have a few holes running from one end of the block to the other end, so that you can see straight through it.
  4. Interlocking blocks-can be joined by virtue of parts that fits into other parts of adjacent blocks.

The standard block sizes are 9 by 9 equivalent in millimeter to (390 by 190 by 190 mm), 6 by 9 which is equivalent to (390 by 140 by 190 mm) and 4 by 9 equivalent to (390 by 90 by 190 mm).  In most cases, blocks   are grey in color or buff (light yellow brown color -similar to the color of sand).

Concrete blocks application  and prices in Kenya 

Concrete blocks  are   faster  to build with,  compared  to  bricks-especially  when using   lightweight blocks .Also  they  are  durable ,  maintenance  free   and as  we have already mentioned become harder as well as   stronger  with age.

Dense blocks and certain aerated blocks are suitable for below damp proof   course foundations. Other types of blocks are suitable for foundation where the ground is not damp or soggy. Lastly blocks are used for constructing security walls, load bearing  walls in buildings , wall capping,column capping  and concrete pavement blocks  in towns and driveways.

The mortar used to join individual blocks in courses should be weaker than blocks to allow for movement. Below damp proof course, the mortar should be stronger in order to give it extra capacity to the weather this damp conditions.

Plaster  should  be  applied  in two  coats  up to  13 mm. Fair-face block work  may be  left plain or  painted. And Block works that is to be clad with tiles should first be   rendered or covered with mixture of cement and sand

Kisumu concrete products ltd( KCP) sells  its in-house manufactured solid concrete blocks beginning at Kshs 75, Kshs 70 and Kshs 55 a piece for 9 by 9, 6 by 9 and 4 by 9 block sizes respectively. Hollow brick are sold at between Kshs 90 and Kshs 110 for each piece. Finally Concrete paving blocks are sold between Kshs 750 and Kshs 1250 per piece. These prices can be used as barometer of the general price levels of concrete products in Kenya.

Copyright© 2017

Sources :Materials  for Architects and Builders by Arthur Lyons PhD.



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