Blocks
Blocks is usually larger than bricks. Bricks usually portable and can use one hand to lift it. However, the block usually requires both hand to lift it and can be laid more quickly than bricks. But, the bigger size also means less versatility in laying especially when building up ends or corners also laying to curves. Generally blocks are intended to be plastered.
Types of blocks:
Clay blocks
Concrete blocks(more widely used)
Clay blocks
Clay blocks
Pouring the cement into the blocks
Various colour of the block
Various size of the blocks
Clay Blocks:
Clay blocks are generally extruded hollow units. The material used in their manufacture is the same as clay bricks. After firing, clay blocks are dense, hard and brittle (easy to crack) which make them difficult to cut and fix.
Strength:
The minimum average compressive strength for clay blocks are:
Non-loadbearing walls/partition 1.4 N/mm2
Facing and common blocks 2.8 N/mm2
Blocks for loadbearing internal walls 2.8 N/mm2
Concrete Blocks:
Concrete blocks are also known as concrete masonry units Concrete masonry walls correctly designed and constructed will satisfy a variety of building requirements including fire resistance, durability, aesthetics and acoustics. The advantage of lightweight blocks are
· Easier to handle and quicker to lay
· The air in lightweight block provide better sound and thermal insulation
· The lighter weight cause in lighter foundations and structural members
· Can be cut and chased with hand tools and hold nails and screws without plugs
Typical shapes of concrete blocks
Lightweight blocks
Concrete blocks can be manufactured from either natural aggregates or lightweightaggregates. Standard blocks have a more open texture intended for finishing with plaster or plasterboard while paint quality or close textured blocks have a superior finish so that they can be directly decorated. Concrete blocks are generally very stable and durable and can be used for a wide range of applications including situations below ground where they may come into contact with aggressive soils.
Type of concrete blocks:
Solid blocks – no formed holes or slots
Cellular blocks – with cavities (holes) which do not pass through
Hollow blocks – with cavities which pass through.
Autoclaved Aerated Masonry Units
Aerated concrete is unlike traditional concrete as it does not contain coarse aggregates. The normal method of manufacture is to incorporate an aerating agent in the mix. The most common aerating agent is aluminium powder. This reacts with the alkali (derived from the cement and/or the lime) present in the mix to form complex hydrates and hydrogen gas. It is this gas which is responsible for the formation of voids and thus the cellular structure. Powdered zinc (rarely used) may be used instead of aluminium powder. Autoclaved masonry units have good thermal insulation properties, but lower sound insulation than concrete masonry units. They also have a lower range of compressive strengths and need to be handled more carefully. However, they are easy to cut and shape.
Strength
The minimum crushing strength of concrete blocks are given below:
Concrete density1 kg/mm3 | Strength N/mm2 | |
Dense aggregate | 1500-2000 | 2.8-3.5 |
Lightweight aggregate | 700-1500 | 2.8-10.5 |
Autoclaved aerated | 400-900 | 2.8-7.0 |
Weight of block divided by overall volume.
Drying shrinkage:
Using of block with low drying shrinkage can avoid from shrinkage cracks.
Thermal and sound insulation:
Thermal conductivity of block varies with density. However, the lightweight concrete blocks have better thermal insulation compared to those denser block.
Fire resistance:
Block having a good fire resistance.
Durability:
Facoy-made block have a good durable properties.
Appearance:
The appearance of the concrete block work is depend on the quality of block and mortal used beside
also the bonding pattern of the block work.
