A Concrete Block or Concrete Masonry Unit (CMU) is a standard-size rectangular block used in building construction. Concrete blocks are some of the most versatile building products available because of the wide variety of appearances that can be achieved using them.
What are the Concrete blocks?
These are usually made in huge sizes to make blockwork quicker and consume less cement in joints than brickwork. If the level of the voids is over 25%, then they are hollow blocks, and blocks with voids under 25% are only perforated blocks. The cellular concrete blocks are for the most part alluded to as lightweight aerated concrete blocks. All these blocks are extensively used for partition walls and non-loadbearing walls. Hollow blocks are specially designed for load bearing walls, which help in reducing dead loads of masonry in buildings. Blocks can also be manufactured with cement and sand and are called cement-sand blocks or with cement and soil called soil-cement blocks which have low strength and are used for budget construction.
Concrete blocks entered the building scene in the late 19th century with a whirlwind of various patents for block designs and production. After Harmon Palmer invented the first commercially successful concrete block machine in 1900, the industry expanded quickly with different makers delivering the blocks with their stone-like surface created through either a mould or the use of special aggregates in the concrete mix. Although stonelike concrete blocks were popular for the first quarter of the 20th century, they fell out of fashion following World War II.
What are different types of Concrete Blocks?
- Autoclave Aerated Concrete (AAC) Blocks - AAC blocks are precast, foam concrete, sustainable construction material made from aggregates of quartz sand, calcined gypsum, lime, Portland cement, water and aluminium powder. In the wake of blending and moulding, the concrete is autoclaved under heat and strain and it consequently gains its particular properties. AAC blocks are sought after, inferable from their high strength, load-bearing and warm protection properties. AAC block is utilized as a construction material for interior and exterior structures. The blocks might be covered with a plaster finish or with siding materials like facade bricks or vinyl siding. AAC blocks are generally utilized in the development of residential chains and different sorts of private properties, industrial and business structures, like hotels, workplaces, emergency clinics and schools. As a result of their phenomenal heat insulation capacity, AAC bricks find their use in interior and exterior construction projects. They are ideal for high-rise structures.
2. Hollow Concrete Blocks - Hollow blocks, which have holes taking up more than one-quarter, (and usually more than half) of their cross-sectional area, are used in building boundary fences and other large structures. The holes make them lighter in weight and can be used to run wiring or piping through them. One can also run rebar through the holes for greater stability. Hollow concrete blocks are available in three grades:
- Grade A has a minimum density of 1,500 kg/m3.
- Grade B has a density of less than 1,500 kg/m3.
- Grade C has a density greater than 1,000 kg/m3.
Grades A and B are used for load-bearing concrete block walls whereas grade C finds its use for non-load-bearing walls.
3. Solid Concrete Blocks - Fully solid concrete blocks look like grey bricks but are typically larger. They provide excellent protection from strong winds. They can also be used for projects such as garden walls, retaining walls, foundations, steps, and fireplaces. Solid concrete blocks are usually heavier than hollow blocks and at the same time be cost-effective as well.
4. Fly Ash Blocks - Fly ash Block (FAB) is a building material, specifically masonry units, containing class C or class F fly ash and water. Compressed at 28 MPa and cured for 24 hours in a 66 °C steam shower, then hardened with an air-entrainment agent, the bricks are profoundly durable as compared to traditional clay bricks. Attributing to the high concentration of calcium oxide in class C fly ash, the brick is portrayed as "self-cementing". The manufacturing method saves energy, reduces mercury pollution in the environment, and often costs 20% less than traditional clay brick manufacturing.
Differences Between AAC Blocks & Fly Ash Blocks
Differences Between Solid Blocks & Hollow Blocks
Laboratory Testing of Concrete Blocks
Similar to bricks, concrete blocks also need to be tested for their quality and performance. The IS Code IS 2185: 2008 has all the different types of tests that can be conducted on different types of concrete blocks. Below are the most common tests conducted on concrete blocks
- Dimension Test - All blocks should be checked in this step. The length, width and height are measured with a steel scale. If it is a hollow block, then the web thickness and face shell are measured with a calliper ruler. A report of average length, width and height of the block and average minimum face shell and minimum web thickness using recorded dimensions should be prepared and confirmed with the claimed dimensions.
2. Density Test – In this test, 3 blocks shall be taken to conduct this test. To determine the density of the block, first, heat the block in the oven to 100 degrees Celsius and then cooled it to room temperature. Now take the dimensions of the block and from that find out the volume and weigh the block. The density of the block is determined from the below relation and the average density of 3 blocks will be the final block density. Density of block = mass/volume (kg/m3)
3. Compressive Strength Test - Eight blocks are taken to determine the average compressive strength of concrete masonry blocks. The blocks should be tested within 3days after being collected in the lab. The age of each block shall be 28 days. The blocks are then placed in a compressive strength testing machine. After the blocks are placed in the testing machine, one-half of the expected maximum load is applied at a constant rate, and the remaining load is applied in not less than 2 minutes. The load at which the masonry unit fails and the maximum load divided by the gross sectional area of the unit will give the compressive strength of the block. Similarly, testing the remaining 7 blocks is conducted and the average of 8 blocks strength is the final compressive strength of the concrete block.
What are different Field Tests of concrete blocks?
As for small sites or for cases where blocks cannot be sent to a laboratory for testing, some on-site tests on concrete blocks can be done to check the quality and performance of the blocks. The most common tests of these blocks are mentioned below. It should be noted that these tests don’t require skilled labour so they can be done by anyone.
- Drop Test – A block from a batch is chosen randomly and lifted to one’s chest level, about 4 -4.5 feet from the ground and dropped on a hard ground surface. It can be done either vertically or horizontally along the length of the block. If the sample block breaks into pieces or develops cracks, then it should either be considered as low-quality blocks or can be rejected altogether.
- Corner Test – The corner of a block sample should be pressed with one’s thumbnail on all eight sides one by one. If some particles are broken down from the edge, then these blocks can be classified as of low quality.
3. Chisel Test – A groove is cut into the solid concrete blocks, horizontally running on all four sides of equal depth by using chisels. It should be cut at the centre of the block until the block separates into two pieces. actions. If the process of chiselling is hard and takes a significant amount of time, then it can be considered that the blocks are of good quality. If the depth of the groove while the separation of the block is more, then the block is of good quality. While chiselling, if the block breaks into several pieces, then that block should be avoided as it is of poor quality.
4. Nail Test – In this test, one needs to hammer a nail into the block sample on different faces of the block. If the block resists itself by the insertion of the nail and is harder to hammer the nail, then the block exhibits high resistance.
5. Texture - The blocks should have a grainy surface texture. If the concrete block has a smooth texture finish, then it indicates more quarry dust content in its mix proportion. This weakens the concrete strength which results in a block production of low compressive strength.
6. Shape & Size – The block should have a uniform shape with sharp edges. The tolerance of dimensions on either side should be ±3mm.
How is the Storage and Handling of blocks done?
Blocks are accessible as hollow and solid concrete blocks, hollow and solid lightweight concrete blocks, autoclave aerated concrete blocks, concrete stone masonry blocks and soil-based blocks. Blocks should be unloaded one at a time and stacked in regular tiers to limit breakage and defacement. They shall not be dumped at the site. The stature of the stack will not be more than 1.2 m, the length of the stack being not more than 3.0 m, as far as possible and the width shall be of two or three blocks. Blocks cured for 28 days only should be received at the site. If the curing period is less than 28 days, they shall be stacked separately. All blocks ought to be water-cured for 10 to 14 days and air-cured for another 15 days; therefore no blocks with less than 28 days of curing shall be used in building construction. Blocks shall be placed near the site of work so that minimum effort is required for their transportation. The date of manufacture of the blocks shall be suitably marked on the stacks of blocks manufactured at the factory or site.
Some of the brand manufacturers for AAC blocks in India?
- Aerocon Blocks - Aerocon bricks are regarded as a premier building material in India, providing numerous innovative benefits to construction firms. The manufacturer conforms to IS 2185 Part-3 standards while developing good quality blocks in technically advanced facilities across Chennai, Golan, Jhajjar and Hyderabad. The AAC blocks are manufactured using fly ash, cement, lime & an aeration agent, to ensure top-notch quality.
- Siporex Blocks - Siporex AAC blocks are lightweight, pre-cast building materials that are used widely in applications requiring high heat resistance and thermal insulation. They have been broadly utilised across skyscrapers across the country, inferable to their high thermal insulation and heat resistance. A Siporex block is designed to be lightweight while providing superior sound resistance for all structures.
- JK Lakshmi AAC Blocks - JK Lakshmi is one of India’s leading cement brands, having a wide distribution network across the country. The JK Lakshmi AAC blocks have been enormously used across quintessential architectural landmarks globally, owing to their superior compressive strength, durability, and on-site workability. The AAC blocks manufacturer centres around upgrading product quality and durability, through global advances and conventions. The JK Smartblox AAC product is developed using advanced German technology through innovative ‘Green Separation’ and ‘Horizontal Autoclaving’ processes.
Some of the brand manufacturers for Fly Ash Blocks in India?
- ACC Fly Ash Blocks - Manufactured as per IS 16720:2018, ACC India Limited has “ACC Green Cement Bricks” under its “Green Building Centre” initiative that claims to be saving 15-20% of the cost in wall construction. It has an excellent wall finish that is achieved by preventing seepage and efflorescence has up to 20% of better thermal insulation as compared to traditional clay bricks. They are available in all standard brick sizes, i.e. Standard (190 x 90 x 90mm), Nominal (230 x 110 x 75mm) as well as a 250 x 125 x 75mm configuration.
- KJS Fly Ash Bricks - These concrete blocks are sturdy in build and are extremely appreciated in the markets due to their environment-friendly nature and are manufactured from natural raw materials. These are not only resistant to fire but do not emit any toxic gas when exposed to fire. Available in even sizes these help in creating even and polished walls with minimum plastering. The brand claims to have best in class compression strength and water absorption and since the sizes of their bricks are 24 – 40% more than the competitors, it also reduces the amount of Plastering hence, improving overall project efficiency.
Concrete Blocks are broadly used in building construction all through the country. Its properties such as Durability, Strength & Structural Stability, Fire Resistance, Insulation and Sound Absorption make it reasonable for different kinds of uses. Concrete Blocks are appropriate in regions where brick or stone of satisfactory quality for masonry are not accessible at an effective cost. If the proper variety of aggregates is available for manufacturing, they are used for masonry units for Blocks that can be used for load-bearing or even non-load-bearing walls, partitions and panel walls.
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