Cement is used for variety of applications in construction and manufacture of building materials. It is always used with other materials like sand, aggregate, water etc., Therefore its performance in a particular application depends not only on its own quality but also on its correct usage and quality of other materials used along with it.
Therefore we hope the following guidelines or tips on its usage will greatly help you build long lasting homes.
To begin with, let us see how to check whether the cement is genuine or not.
- Purchase only genuine recognized brand.
- Ensure that the bag has ISI mark with license no.
- Ensure that the bags are stitched properly and no lumps are present.
- You may check the Week No and Month and Year of manufacture.
Commonly available types of cement in the market are:
- OPC 43 Grade
- OPC 53 Grade
- Portland Pozzolana Cement
- Portland Slag Cement
Good cement alone will not ensure strong and durable structure. Other materials used in the concrete play equally important role. The other materials used in concrete are sand, coarse aggregates, water and sometimes chemical admixtures. Now let us see how to select good raw materials for concrete
Sand is used in concrete to fill the space between coarse aggregate or Kankara to make concrete dense. River sand is preferable but manufactured sand can also be used if it is of good quality with less fines. Following precautions should be taken while selecting sand.
- Sand used should be free from impurities like clay lumps, mud, silt etc. Simple field test to identify good sand is: if you take handful of sand, rub between your palms and release, then mud should not stick to your palm.
- It should be free from organic matters and chemicals
- Fine sand is better for plastering. Coarse and medium sand should be used for concrete.
- Sea sand is not good for RCC work.
There are three types of coarse aggregates with maximum sizes as 40 mm, 20mm and 10 mm respectively. 40 mm size coarse aggregatesare generally used in PCC or Road. Well graded coarse aggregates for general purpose concrete should contain both 20 mm and 10 mm sizes in the ratio of 60:40.
- Coarse aggregates should be chemically inert.
- Coarse aggregates used should be round or cubical in shape. Avoid angular aggregates.
- Coarse aggregates should be free from organic matters.
- Generally we should avoid flaky and elongated aggregates
Water is a necessary evil for cement. Without water, cement is of no use. To get the strength from cement, we need to add water. But if you add water more than required, it will reduce the strength of the concrete. The optimum quantity of water varies from work to work. Following guidelines may be used.
- For concrete, use about 25 to 30 liters per bag
- Generally potable water is better for concreting
- Generally avoid sea water for RCC works