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Friday, April 22, 2022

Why to use block masonry for your home construction? | solid or hollow blocks

With the increasing cost of the burning of clay bricks, blocks made out of soil cement, cement mortar, concrete, aerated concrete, and precast stone concrete (large stone chips embedded in concrete) are becoming more and more popular. These blocks can be solid or hollow. However, the proper use of these materials, especially concrete hollow blocks, is still not understood by most users. Strict technical supervision is required in the construction of buildings with blocks, as otherwise, it will lead to heavy cracking of the walls.

 

Concrete block as a material of construction is dealt with in the book on Building Materials. We will now consider its use in masonry. IS 2185 (Parts 1 and 2) gives the construction details and the standard sizes recommended for blocks to be used in India.

 

The standard sizes prescribed for blocks are the length of 400, 500 or 600 mm, the height of 100 or 200 mm and width of 50, 75, 100, 150, 200, 250 or 300 mm.

 

We use the larger widths for the main walls of the building and the smaller widths for compound walls and partition walls. The commonly made sizes are 400 mm x 200 mm x 200 mm and 400 mm x 200 mm x 100 mm for main and partition walls respectively. These are nominal dimensions including 10 mm mortar joints so that the actual sizes can be 10 mm less. A variation of ±5 mm is allowed as tolerance.


The main types of cement blocks available are the following. They may be solid or hollow. 

1. Concrete blocks

2. Soil cement blocks

3. Light-weight aerated (cellular) concrete block

4. Fly ash cement block

 

Notes:

1. In addition to these, we have also hollow blocks made out of ceramics which are generally not used for walls, but for roofs.

2. Blocks made of aerated concrete (which are usually made solid) are called cellular blocks.

 

We will restrict our study to the more commonly used concrete blocks in this article. Similar rules are applied far other blocks also. Concrete blocks are made of concrete, not mortar. They come in many types, namely solid, hollow, or core types. They are called "hollow" when the percentage of the void is more than 25 per cent (clay bricks in which holes are made for less than 25 per cent of its face area to increase the burning efficiency of the fuel are called perforated bricks).

 

Hollow blocks are those with one or more formed holes or cavities which run through the block. Blocks with one end of these holes closed (so that it can be laid uppermost to provide a continuous surface to spread the mortar for the next course) are called core blocks or closed cavity blocks. Stabilized soil blocks and cement mortar blocks are generally used for low-cost housing and non-load-bearing walls. They have very little strength, only of the order of 1.5 N/mm2.

 

Hollow concrete block construction without additional steel reinforcements performed so poorly and led to so many fatalities during the cyclones in Sydney (Australia) that its use without additional steel reinforcements is now prohibited in Australia in regions prone to cyclones. Only reinforced blockwork (for strength) with core filling (for stability) can withstand such high cyclonic winds. This will also be true for regions of high earthquake intensity.

 

Similarly, the cracking performance of soil-cement block walls in the tropics with concrete roofs on top of the walls due to movement of the top slab has been very poor. It is better to roof over these soil cement block walls, usually used for low-cost construction, with AC sheets, tiles, etc., which are isolated from the walls and produce no thermal movements on the walls.

 

Concrete hollow blocks, as well as solid soil-cement and aerated concrete blocks, are frequently used in place of brickwork. Concrete hollow blocks have the advantages that they can be made strong by introducing steel reinforcement or core filling.

 

Reinforced blockwork is quick in construction, and its performance under all conditions such as cyclones and earthquake loads has been good. Aerated blocks are light and perform very well as filler blocks for multistorey framed buildings. They can also be used to carry light loads.

 

To comply with 9-inch brick sizes, hollow blocks of normal size — 450 mm x 225 mm x 225 mm (18" x 9" x 9") — can also be produced. To build a masonry wall of one square metre, only 10 such blocks are required against 115 clay bricks.

 

In addition to the above work, it requires only 13 litres of cement mortar against over 45 litres for brickwork. It can also be built by an average bricklayer four times faster. However, experience shows that the selection of blockwork should be more for its architectural effect than for its lower cost.

 

In actual practice, plastered blockwork tends to be as expensive as brickwork but can be faster in execution. However, the most popular size of block for buildings is the 400 mm x 200 mm x 200 mm (nominal size) block, which can replace 8 standard metric bricks 200 mm x 100 mm x 100 mm (nominal size). For partition walls, we use blocks of the same length and height as used for load-bearing walls but only 90 mm or 100 mm thick.


MUST-READ: ALL YOU WANT TO KNOW ABOUT CONCRETE BLOCKS

 

What are the considerations to use hollow concrete blocks?


CONSIDERATIONS FOR THE USE OF HOLLOW CONCRETE BLOCKS

We have already seen that we choose hollow block construction more for architectural appearance and quickness of construction than for low cost.

 

The second factor that needs consideration nowadays is the non-availability of good quality bricks and the large improvement that has taken place in the quality of concrete blocks which are being produced in India.

 

However, we should remember that if blockwork is to be efficient for construction, the dimensions of rooms, walls, etc. should fit the block size modules so that there will be a minimum number of blocks cut and wasted.

 

We should also note that full advantage blockwork will not be realized unless the complete range of block shapes necessary for the construction is available. In addition to regular blocks, blocks for bond beams for lintels, and blocks for pilasters (rectangular columns in walls) should be available.

 

In the construction of buildings for concealed electric wiring or for fixing of washbasins, etc., special arrangements should be made. Otherwise for easiness of construction brickwork must be prescribed in such places.

 

Masonry construction with solid and cellular blocks is very similar to brick masonry.

 

Hollow concrete block walls are constructed in the following three different ways:

1. Simple masonry (similar to brick) with the hollows untreated—the blocks are laid one over the other breaking bonds in stretcher courses.

 

2. Infilled hollow block masonry with plain concrete infilling.

 

3. Reinforced hollow block masonry with steel reinforcement and concrete infilling for higher strength (used for lintels, retaining walls and walls for multi-storeyed buildings).

 

The two important structural features to remember when using concrete blocks are as follows:

(i) There is an inherent weakness in these blocks for shrinkage and moisture movement. (Hence blocks should be well cured and absorption should be less than 100%.)

 

(ii) Blocks being larger in size and more brittle than bricks, the cracks due to settlements in blockwork will be larger in width than in brickwork. Hence allowable differential settlements should be small.

 

Closed cavity blocks, in which the holes are closed at one end, ensure better load distribution, better insulation properties in cold places and minimum wastage of mortar in the blockwork. With open cavities in hot humid regions, the air current set up in open holes can be considered an advantage.

 

BASIC STEPS IN LAYING OF CONCRETE BLOCK | LAYING OF BLOCKS

Blocks are laid as stretchers breaking bonds as shown in Fig below (p. 64). As already stated, the most important thing is that concrete blocks should dry out thoroughly before use. It requires at least 28 days under normal conditions of normal curing. Solid and closed cavity blocks with one end closed are laid in walls with a full mortar bed as in brickwork.

 

If the walls are constructed of hollow blocks with through holes, the economy in mortar can be made by "shell bedding" where the mortar is laid only on a 5 mm (2 in) strip around the outer edge of the hollow block. Blocks should not be wetted before use (as we specify for brickwork in cement mortar) as the concrete can take up water and then shrink. Excess mortar is gently removed to give a good appearance. The bottom layer of blocks on the foundation is always laid on a full bed of mortar.

 

The third important point to remember in hollow block construction is that the mortar used for blockwork should not be too strong. With strong mortars, when the wall shrinks, it tends to crack up with a few large cracks. With moderately strong mortars, the movement results only in a number of small cracks distributed on the whole length of the wall which will not be noticeable. If cement mortar is to be used, a mix 1:5 with a plasticizer is found to be sufficient. 1:1:6 or 1:2:9 cement lime plaster is preferable to pure cement plaster. The ideal mortar should have the same density, strength and drying shrinkage as the block.

 

Pointing is usually done as in exposed brickwork. The longer the pointing tool, the smoother and better the joint results. The fresh joint is left for an hour to set, and then it is worked on for pointing.

 

Should hollow blocks be filled with concrete?


HOLLOW CONCRETE BLOCKS WITH CONCRETE INFILLING

Hollow concrete blocks (especially those with two through holes) form continuous vertical holes when placed with proper bonding one over the other. They are ideal for concrete filling, as these holes can be completely or partly filled with in-situ concrete as the blockwork proceeds. Mixes with large size aggregates can be used for this purpose. This will add greater strength to the walls. Tests show that filling hollow blocks with plain concrete will give basic strength approximately halfway between these unfilled blocks and solid blocks with the same quality of concrete.

 

WHAT IS REINFORCED CONCRETE HOLLOW BLOCK MASONRY?

The vertical holes in conventional block construction can accommodate steel reinforcement and thus be made of reinforced concrete construction when infilled. Similarly, special blocks can accommodate horizontal reinforcements so that horizontal beams such as lintels and horizontal strengthened reinforced concrete bands can be built up with these blocks (see bond beams described below). Such construction is known as reinforced concrete hollow block masonry construction. ACI standard 531-581 and its commentary give valuable information for the design and construction of such works.

 

What are the Benefits of using hollow blocks in construction?

SPECIAL FEATURES OF CONCRETE BLOCK MASONRY

In addition to using fully-cured blocks and lean mortar joints, the fourth most important feature to be incorporated in blockwork, for buildings as different from brickwork, is the need to provide the three features, namely control joints, band beams and joint reinforcements. Unless these are provided, block masonry is bound to result in random cracking due to shrinkage and moisture movements. These are briefly described further.

 

Control joints. Concrete has a higher coefficient of expansion than brickwork. Control joints are continuous joints, usually vertical, built into concrete block masonry walls for controlling thermal movements. They should be located at the change of sections in the form of vertical mortar joints to minimize the cutting of units. They can be shrinkage joints and expansion joints. The shrinkage joints are continuous vertical joints of approximately 18 mm (3/4 inch). These joints are later raked and caulked (filled in). Expansion joints are located at a spacing of 45 to 60 m in suitable locations. These are filled with joint fillers which are compressible materials that close the gap but allow movement.

 

Bond beams. Bond beams are beams such as lintels that are to be provided on top of openings or on top of walls without top loads such as compound walls. It is usually a reinforced masonry course, which is constructed out of specially channel-shaped units which are filled with concrete and reinforced Fif below. It usually serves as a structural element and as a means of crack control on top of openings.

 

For lintels, the reinforcement usually consists of at least two 12 mm bars placed at the top and bottom. For crack control, they are made discontinuous at control joints. Where continuity is required for structural reasons, a dummy joint should be given to control the location of the probable crack.

 

Joint reinforcement. Horizontal joint reinforcements in the form of a minimum of two No. 9 gauge wires at intervals can be used as in reinforced brickwork for crack control. They are expensive and are not generally provided. However, when used as load-bearing walls with RCC slabs resting on the walls, the top three courses at least should be provided with joint reinforcement as shown in Fig below.

 

Is blockwork suggested for a compound wall?

Compound Walls In Blockwork

Unplastered concrete blockwork which is cheaper than plastered brickwork is used nowadays extensively for constructing compound walls as shown in Fig. below. There are many variations in the construction of these walls. One of the popular methods of construction is to use under-reamed piles at convenient intervals of 3 to 4 m with grade beams on top of the piles and the blockwork built on top of the grade beams.

why a concrete masonry building is your best investment


Concrete blockwork.



Vertical reinforcements can be embedded in the hollow of the block at regular intervals from the under-reamed piles, thus strengthening the wall along its length giving lateral resistance to wing loads or earth pressure. The top of these walls should be finished with a coping cast in a channel-shaped block laid on tops such as 225 mm thick lightly reinforced precast or cast in place slab over a closed cavity block laid as the top layer or a bond beam.

 

CONCLUSION

Concrete blocks are commonly used in place of clay bricks resulting in a reduction in cement mortar and also increasing the speed of construction. As manufacturing clay bricks require good soil and high energy, it is also more environmentally friendly. However, there are many special points to be taken care of in good blockwork masonry as compared to brick masonry. They have been briefly described in this article.


Can I use concrete blocks instead of engineering bricks?

YES


Which is a better hollow block or solid block?

Hollow blocks are lighter in weight, thus reducing the dead load on the structure, so steel consumption per square foot is lower when solid blocks are applied to masonry walls. The production cost of a hollow block per unit is lower because the raw materials consumed per volume of the same volume are less compared to a solid block.


Are hollow blocks good for building?

It offers high dimensional accuracy and stable finish, making it an excellent building material for creating load-bearing structures and partition walls. e. These hollow concrete blocks are capable of withstanding high pressures and are therefore widely used in building construction practices.


Are blocks stronger than bricks?

Concrete blocks should have a minimum compressive strength of 1,900 pounds per square inch, but the strength of many blocks exceeds this limit. If we measure the strength in psi, the concrete blocks will come out on top of the bricks. The former can withstand 3,500 PSI, while the range of bricks is found at 3,000 PSI.


Is it cheaper to build with bricks or blocks?

Yes



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