how durable are CLC blocks in place of red bricks or flyash bricks???
Kushal, CLC? obviously something concrete made of cement, but what?
I assume by "red bricks" you mean fired-clay bricks and "flyash bricks" are blocks made of the ash and clinker from coal-fired furnaces?
Modern practice here in the UK is the use of fired-clay bricks to face buildings and then concrete blocks are used for interior walls, although there is increasing use of exterior concrete block walls which are then covered with concrete plaster.
There are various types of concrete blocks, from standard concrete blocks made with cement and gravel, to much lighter concrete blocks made either with a lighter aggregate or sandwiches with slabs of polystyrene inside.
Frank John Snelling
Cellular Lightweight Concrete blocks are as durable as redbricks or flyash bricks. They are chosen because of their light weight and better thermal features (insulating property). However, due to their physical structure they may or may not be suitable to arbitarily drive nails into the walls or for improper retofitting. They need to be cut and drilled properly as per necessity. Also, their cost comared to red bricks and flyash bricks is a little higher although it highly depends on the proximity to the manufacturing facility, transport costs etc. Typically the high cost incurred into CLC blocks is seen as a permium with a pay back on running Air conditioning bills in the long run which are low compared to buildings with CLC and flyash bricks.
Kushal, I forgot to answer your original question "how durable are..."
If the red bricks (I assume these are fired clay) you mention are some form of hollow brick, then they are rather brittle like flower pots. On the other hand these hollow bricks probably insulate better.
Whereas, if the red bricks are solid then they should be much more durable than CLC blocks, and depending upon the colour of the fired-clay, bricks which are more purple than red (and known as engineering bricks) are more highly fired and are specifically used for structural purposes.
Frank John Snelling
Kushal, there is another form of smooth fired-clay red brickwork called "Terracotta" which can still be seen on some Victorian buildings in Britain. Note: Terracotta is the generic name for pottery, but I do not know if these Victorian bricks were made only for decorative facing purposes or for structural purposes.