The most important components of a building construction are the columns-beams-slabs which are made of Concrete and the walls which are made of bricks and plaster. The main ingredients in concrete are cement, sand, stone chips, water and steel reinforcement. As an Architect, I have described all these building materials along with the features of good quality.
Usage of Cement in Buildings:
Cement is the binder that holds concrete and mortars together and hence it plays the most critical role in giving strength and durability to your home. It is used to make concrete for slabs, foundations, beams, columns, lintels, chhajja (sunshades), and mortar for brickwork, plastering, flooring and other such work.
Types of Cement used in house construction:
Cements used for domestic building such as your home are basically of three types:
- Ordinary Portland Cement (OPC): A combination of clinker and gypsum.
- Portland Slag Cement (PSC): A combination of good quality blast furnace slag (from the iron and steel industry) with clinker (which makes OPC) and gypsum.
- Portland Pozzolana Cement (PPC): A combination of fly-ash (from thermal power plants) with clinker and gypsum.
Ideal cement for house construction:
The best cement for house construction is blended cement like PSC and PPC. But please note that good quality blended cements like PSC and PPC will take more time to set. However the final strength after 28 days will be much more.
Features of good quality cement:
- Reduced water requirement.
- Improved workability .
- Less permeable to moisture.
- Improved resistance to acids and chlorides.
- Reduced heat of hydration.
- Easier to finish.
- Reduced shrinkage.
- Reduced leaching problems because it is low on free lime.
The colour of cement has no relation to the strength characteristics. There is a wrong impression that darker color cement gives better strength. In fact, darker color cement causes the workers to add more sand than allowed in cement-sand mortar for plastering, which can then cause problems.
Selecting the right cement for your house:
It is very important that you use only a reputed brand of cement. Good brands of cement may cost 2 to 5% more but offer quality, consistency and reliability as well as 10 to 20% greater strength characteristics. Cement accounts for a mere 12 to 18% of the total expenditure on your home. So, using cheaper cement gives you little overall savings but a greater risk to the strength of your building!
The right way of using cement in construction:
Cement must be added to the concrete and mortar in a precise, consistent manner. Too little or too much cement in concrete and improper water-cement ratios cause lower strengths, shorter design life and lower durability. Never try to save on cement use by diluting the concrete mix. Remember, that by using 30 to 40 bags less of cement, you would save no more than Rs 3000 to Rs 4000.
Usage of sand in house construction:
Along with cement, sand is a very important ingredient in mortars and concrete. Therefore the proper selection of sand is critical in the durability and performance of the concrete/mortar mixture.
Ideal Sand for house construction:
River sand is the best for construction. However due to its scarcity and exorbitant price, filter sand and manufactured sand are also used nowadays. The price of sand includes three or four components - base cost, transportation, handling and number of intermediaries. Therefore procuring sand in bulk directly from the source will be cheaper than the neighbourhood dealer, except when you need smaller quantities.
Features of good quality sand:
- Must be clear, angular and hard.
- Must be free from clay, mica and soft, flaky material
- Should be graded, which means it should be a mix of fine, medium and coarse sand
- Must be free from contaminants like sea salt.
- Moisture (water) content must be consistent and should not exceed 7%. When mixing concrete the moisture content must be taken into consideration.
- Proper selection of sand is critical in the durability and performance of your concrete mixture. It should be:
Selecting the right sand for house construction:
Even though good sand is very difficult to procure and the price is very high, it is better to use good sand rather than filter sand. But if the cost is a big factor, filter sand is available at a cheaper rate. It is sand mixed with dust/soil. Filter sand can be made better by washing off all the dust particles with water. You could also vary the type of sand that you use based on the type of work. For example, for rcc slabs, rough sand can be used whereas fine sand can be used for plastering. A simple way of checking the quality of the sand - It should not be sticky when you take it in your hand.
Manufactured sand: also called M-sand is being promoted by the government as a cheaper alternative to natural sand because of the scarcity of good quality natural sand. Experts vouch that manufactured sand is not only a viable alternative to natural sand, but superior in many ways. Mortars and concrete using M-sand as fine aggregate are superior when compared to those using natural sand. The ready-mix concrete manufacturers are already using manufactured sand.
Advantages of manufactured sand:
- The appropriate quality of rock suitable for construction can be used for manufactured sand;
- There is no clay content in M-sand;
- M-sand is scientifically graded to comply BIS specifications;
- Customizing the different grades depending upon the need of construction ensures consistent quality throughout the construction cycle.
- M-sand is half the price of natural sand.
AGGREGATES (STONE CHIPS)
Usage of aggregates in concrete:
Technically, known as coarse aggregates, stone chips are a major ingredient of concrete, giving it strength and solidity. The quality of concrete depends very much on the characteristics of aggregates used.
Features of good quality aggregates:
- Stone chips should be angular or round, not flat or flaky.
- They should not contain marks or layers of any other colour.
- They should be free from mud and other impurities, which are harmful for concreting. It is advisable to wash the stone chips before mixing to make it free from dust, dirt and mud.
- They should be well-graded, which means these should contain sizes from 5mm to 20mm in proper proportion, so that voids are minimal.
Selecting the right aggregates for house construction:
Aggregates should be well-graded and should contain sizes from 5mm to 20mm in proper proportion, so that voids are minimal. This will make a strong and durable concrete. At the same time, this will save on cement. So, always insist on graded aggregates and not 'pure' aggregates which result in larger voids within the concrete and more cement consumption
One should get aggregates from the source to get the best price.
Usage of reinforcing steel in concrete:
Reinforcing steel contributes to the tensile strength of concrete. Concrete has low tensile, but high compressive strength. The tensile deficiency is compensated by reinforcing the concrete mass through insertion of plain or twisted mild steel bars.
Features of good quality steel:
- Steel bars/rods should be reasonably clean and free of rust.
- Bars that cannot be easily bent manually or mechanically should be rejected.
- Optimum length bars must be chosen to reduce wastage in cutting.
- To avoid laps, shorter bars must not be accepted.
- Welded lengths of bars should not be accepted.
Selecting the right steel for your house construction:
Both branded and unbranded bars are available. It is wise to buy good brands like SAIL. During construction, ensure that size and the type of steel reinforcement used is exactly as per the engineering design specifications.
Tips in using water:
- You must use only potable water in quality concrete production.
- Brackish or salty water must never be used.
- Contaminated water will produce concrete and mortars with lower durability, erratic set characteristics and inconsistent colour.
Usage of Bricks in house construction:
For most of the buildings two types of Bricks are used:
- Red soil bricks - the size is 9"x4.5"x3". They may be wire-cut or table moulded
- Cement blocks - the sizes vary. They are of two types: Hollow blocks or solid blocks (Hollow blocks are preferable but nowadays they are not easily available)
- Fly ash bricks - are used as an alternative to the regular bricks or cement blocks as they are lighter in weight.
- With Hollow and solid cement bricks, you can complete wall construction faster than normal red bricks.
Features of good bricks for construction:
- They should be show uniform texture and colour.
- When broken, they must not leave lumps and grit.
- Ensure that bricks are not made from saline clay.
- Look for proper and uniform burning.
Categories of bricks used in house construction:
Features of 1st Class Bricks:
- Perfect in size/shape.
- Red to cherry-red in colour
- Do not break when dropped from waist height
- Do not absorb more than 15 to 17% of their own weight if kept submerged for 1 hour under water
- Suitable for precision work such as exposed
Features of 2nd Class Bricks:
- Not so uniform as 1st class bricks in shape/size/quality of burning.
- Do not absorb more than 25% water of own weight if kept submerged under water for 1 hour.
- Good for brickwork wherever subsequent plastering is to be done.
Features of 3rd Class Bricks:
- Much inferior to 2nd class bricks in terms of shape/size and burning.
- Absolutely out of size and shape, overburnt, fused with more bricks, with a honeycomb texture.
Features of Jhama/Overburnt Bricks:
- Dark red to black in colour.
- These bricks are unsuitable for any kind of brickwork, and are only used in broken pieces for consolidation of foundation soil and sub base of floors brickwork.
Selecting bricks for house construction:
Bricks may be purchased directly from the brick fields located close to your area to get it at a lower cost. Keep samples for conformity to ordered quality.