Blocks Masonry

Various types of blocks can also be used to construct masonry. As these blocks can be made under controlled conditions it is possible to achieve the desired quality. As they can be made to sizes larger than bricks and at the same time true to size and shape, the construction is faster and the quantity of mortar required for the masonry work  is less. The faces of blocks being fairly smooth, the walls can be left unplastered, and even if they are plastered the quantity of mortar required would be less than in brick masonry and very much less than in stone work. 

A variety of blocks are available for use, such as concrete blocks, lime based blocks, soil based blocks etc. 

Concrete Blocks 

Blocks can be solid or hollow. They can be hand made or machine made. The materials required for their manufacture are cement, aggregate and water. Fly ash or other admixtures are also, sometimes used. The concrete mix used for the manufacture of blocks is normally 1 cement to 5 or 6 of combined aggregates (by volume). The fineness modulus of the combined aggregate shall be between 3.6 and 4. The blocks can be compacted in the moulds manually or preferably manufactured in block making machines. The blocks shall be cured for 14 days. Steam curing can be adopted to save time. 

The nominal dimensions of concrete blocks are as given below: 

Length : 400,500 or 600 mm 

Width  : 50,75,100,150,200,250 or 300 mm 

Height : 100 or 200 mm 

Hollow concrete blocks are manufactured in three grades, as described below : 

Grade A 

Load bearing units with a minimum density of 1500 k m3. The average compressive strength shall be 3.5,4.5,5.5 or 7 N/mm (35,45,55 or 70 kg/cm2). The thickness of the face shell and web shall not be less than 25 mm. 

Grade B 

Load bearing unit with a block density between 1030 to 1500 kg/cm2. The average compressive strength shall be 2.3 or 5 N/mm (20.30 or 50 kg/cm2). 

Grade C 

Non-load bearing units with block density between 1000 to 1 kg/m3. average compressive strength shall not L less than 1.5 M/mp (15 kglcm ). 

Solid concrete blocks are ma& for load baring units with a block density of not less than 1800 kg/m3. The average compressive strength shall be between 4.0 to 5 .O  N/mm2(40 to 50 kg/cm2). 

The water absorption of  concrete blocks shall not exceed 10% by weight. 

Precast Concrete Masonry Blocks 

These are precast solid concrete blocks embedded with stone spalls i.e. broken stone pieces (20 to 30% by volume). The concrete is usually made of 1 part of cement and 9 parts of combined fine and coarse aggregate. The mix  is placed in the mould in layers along with stone spalls and compacted. 

The blocks are cured for 14 days. The density mi strength characteristics are similar to that of solid concrete blocks. 

Lime Based Blocks 

These are made from a combination of materials consisting of lime, cement, fly ash, burnt clay pozzolana etc. 

The normal nominal sizes  of blocks are 

Length : 400 mm 

Width  : 100,200 or 300 m 

Height : 100 or 200 mm 

The is of the order of 1000 kg/m3 and compressive strength 3.5 N/mm2 (35 kg/cm2).

Lime Flyash Bricks 

They are made from fly ash (80-90%),  sand (2- 12%) and lime (1-10%) with small quantity of chemical accelerator. They have a density of 1500 kg /m3 a compressive strength of 7.5 to 10 N/mm2 (75 to 100 kg/cm2). 

Sand Lime Bricks

It is composed of sand (91.93%) and lime  (7- 9%). The components are mixed with water and com ressed in moulds under pressure and then autoclaved.  The density is 800 kg/m and compressive  10 N/mm (100 kg/cm ). 

Fly Ash Lime Gypsum Bricks 

This is made from a mixture of fly ash, lime, gypsum and sand. After mixing with water, the mixture is compacted in moulds and cures The density is 1400 kg/m3 and compressive strength 8 to 10 N/mm (80 to 90 kg/cm2). 

Autoclaved Aerated Concrete Blocks 

These are made from fine sand or selected quality of fly ash or mixtures of both and a binder of lime and cement. The cellular character of the blocks, which gives good thermal properties and a high strength to density ratio, is formed as a result of aeration caused by adding traces of aluminium powder. These blocks have a density of 650 k  /m3 and compressive strength of 3.5 to 4.0 N/mm2 (35 to 40 kg/cm2). They have high thermal and sound insulation properties and are fire resistant also. 

Soil Based Blocks 

Most of the soils can be satisfactorily stabilised by the addition of lime or cement. It is however necessary to analyse the properties of the soil through a laboratory testing to determine the optimum quantity of stabilisers to be added to impart the desired properties to the block. Soil containing 0-10% gravel, 40-75% sand, 15-25% silt, and 8-2596 clay is suitable for making blocks. It showld not contain more than 0.5% of organic matter and the pH value should be less than 7. Soil based blocks are cheap and can be used with advantage in the construction of low cost houses.