Concrete Hollow Blocks

CONCRETE HOLLOW BLOCKS

Hollow blocks are the universal type of concrete blocks that have one or more holes which are open at both sides. These blocks are called as artificial blocks, since they replace the bricks in the masonry construction. They are manufactured with lean mixes of cement, sand and aggregate of sizes less than 12 mm. Instead of sharp edged aggregates, round aggregates are used in the manufacture of these blocks. As per the recommendations of the IS 2185 (Part-1) 2005, the total void area shall range from 50% to 75% of the gross cross-sectional area. These holes or cavities reduce the total cross-sectional area of the block and hence the weight of block structure as a whole. For high-density blocks, Portland cement and aggregate, usually sand and fine gravel are used as a raw material. For low density blocks, industrial wastes, such as fly ash or bottom ash are used as the primary raw materials and are often called cinder blocks or breeze blocks.

Hollow concrete blocks are more commonly used in masonry construction. It accelerates the construction process, saves cement and steel and reduces the work expenses at the construction site. These blocks lower the natural weight of masonry constructions and improve the physical properties of walls, such as noise and thermal biley, . 9mad at bus on insulation. They also provide facilities for concealing electrical conduit, water and soil pipes. Standard hollow concrete blocks are available in full size as well as half size. Full-sized blocks are rectangular and have two cores while half-sized blocks are bilo? cubical and contain one core. The nominal dimensions of concrete block are as follows:

❖ Length should be: 400, 500 or 600 mm

❖ Height may be: 200 or 100 mm

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

Hollow concrete blocks are available in different types according to their shape, needs and design such as Concrete Stretcher Blocks, Lintel Blocks, Partition Concrete Blocks, Concrete Pillar Blocks, Corner Concrete Blocks, Jamb Concrete Blocks and Bullnose Concrete Block.

Materials used:

❖ Cement: Cement complying with any of the following Indian Standards like 33, 43 or 53 grades may be used. When cement conforming to IS 269 or IS 8112 or IS 12269 is used, replacement of cement by fly ash conforming to IS 3812 (Part 1) may be permitted up to a limit of 25%.

❖Aggregates: The aggregates used in hollow blocks shall conform to IS 383 for part breplacement of fine aggregate up to a limit of 20%.

❖ Fly Ash: Fly ash conforming to IS 3812 (Part 2) may be used for part breplacement of fine aggregate up to a limit of 20%.

❖Water: The water used for manufacturing hollow concrete blocks shall conform to the requirements of IS 456. It should be free from any substance harmful to concrete or reinforcement, or substance likely to cause efflorescence in the hollow block units. for part breplacement of fine aggregate up to a limit of 20%.

❖Additives or Admixtures: Additives may be added to the cement during manufacture and as admixtures to the concrete mix. Additives or admixtures used in the manufacture of concrete masonry units may be ad no accelerating, water reducing, air-entraining and super plasticizer conforming to IS 9103. Waterproofing agents should conform to IS 2645. For colouring pigments, where no Indian Standards apply; the additives or admixtures shall be shown by test or experience, to be not destructive to bollplan the durability of the concrete.

Physical Properties:

❖ Blocks Density: The block density of hollow concrete blocks are of three types as follows: Grade A, has density more than 1500 kg/m3. Grade B, has density less than 1500 kg/m3. Grade C, has density greater than 1000 kg/m3.

❖ Compressive Strength: The minimum compressive strength at 28 days of hollow concrete blocks shall vary between 3.5 N/mm² to 15 N/mm² for Grade A blocks and 3.5 N/mm² to 5 N/mm² for Grade B blocks.

❖ Water Absorption: The water absorption, being the average of three units, shall not be more than 10% by weight.

❖ Drying Shrinkage: The dry shrinkage of the hollow block units should not exceed 0.06%.

Advantages of Hollow Concrete Blocks:

Hollow concrete block masonry is the faster construction practice and has the following advantages:

❖ Hollow concrete block masonry reduces the cost of labour and materials, since larger size blocks reduces the number of joints in masonry work.

❖ It is a faster and easier construction practice, when compared to the conventional masonry systems.

❖ The hollow concrete blocks are light in weight, so they reduce the weight of the structure and hence light structural member or minimum percentage of steel is required for R.C.C building.

❖ Hollow concrete block masonry is highly durable as it is compacted by to asvilib high pressure and vibration, which gives substantial strength to the block. Adequate curing increases the compressive strength of the blocks.

❖ Due to the rough texture on hollow concrete blocks, good bonding can be obtained between cement mortar and concrete blocks.

❖ These blocks have good insulating properties against sound, heat and dampness.

❖ These concrete blocks need low maintenance and semi-skilled or unskilled labour can also work in this type of construction.

❖ Hollow blocks are low in water absorption than conventional bricks and have good fire resistance.

❖ Reinforcing the hollow block masonry is possible as there is no additional formwork or any construction machinery required.

❖ In the hollow blocks, the voids or cores can be filled with steel bars and concrete for achieving high seismic resistance.

❖ Hollow concrete blocks are eco-friendly materials as industrial wastes, such as fly ash or bottom ash are used as raw materials.

Use of Hollow Concrete Blocks:

Hollow concrete blocks are used in all type of masonry construction such as,

❖ Exterior and Interior load-bearing walls

❖ Fire-safe walls around stairwells, elevators

❖ Fire walls and curtain walls

❖ Partition wall and panel walls

❖ alans Piers, column and retaining walls

❖ Backing for brick, stone, and other facing works

❖ Boundary fences