Star Cement Construction Know-hows

Quality of cement has nothing to do with its color.

It is good to use potable quality of water. It should be free from impurities and harmful ingredients. Seawater isn’t recommended. The water fit for mixing is fit for curing too. Use of minimum quantity of mixing water, consistent with the degree of workability required to enable easy placing and compaction of concrete, is advisable Ensure that water is measured and added Low water to cement ratio is essential for good performance of the structure in the long run.

1:1.5:3, where 1 part of cement is to be mixed with 1.5 parts of sand and 3 parts of coarse aggregates. Water requirement for the mix would be less than 25 liters per bag of cement.

The ways in which concrete maybe spoilt are many, most common of them being: Use of too much or too little water for mixing, or water carelessly added during mixing. Incomplete mixing of aggregate with cement Improper grading of aggregates resulting in segregation or bleeding of concrete. Inadequate compaction of concrete Using concrete which has already begun to set. Placing of concrete on a dry foundation without properly wetting it with water. Use of dirty aggregate or water containing earthy matter, clay or lime. Too much troweling of the concrete surface. Leaving the finished concrete surface exposed to sun and wind during the first ten days after placing without protecting it and keeping it damp by proper methods of curing.

The compressive strength is governed by the following factors:
(i)w/c ratio
(ii)characteristics of cement
(iii)characteristics of aggregates
(iv)time of mixing
(v)degree of compaction
(vi)temperature
and period of curing
(vii)age of concrete
(viii)air entertainment
(ix)conditions of testing

Concrete is a mixture of cement, sand, stone aggregates and water.

If a concrete mix is placed in and around a cage of steel rods, it is called Reinforced Cement Concrete (RCC).

Mortar is a mix of cement, sand and water, to be used for brick works/block works and plaster.

Normally the amount of water that is required per bag of cement is 25 -28 liters only.

Portland Pozzolana Cement (PPC) is obtained by either intergrinding a pozzolanic material with clinker and gypsum, or by blending ground pozzolana with Portland cement. Nowadays good quality fly ash is available from Thermal Power Plants, which are processed and used in manufacturing of PPC.

Green concrete has all the three phases – solids, water air. In order to make the concrete impervious & attain its maximum strength it is required to remove the entrapped air from the concrete mass when it is still in plastic state. If the air is not removed completely, the concrete loses strength considerably. It has been that 5% voids reduce the strength by about 30% and 10% voids reduce the strength by over 50%. Compaction eliminates air bubbles and brings enough fine material both to the surface and against the forms to produce the desired finish. One can use such hand tools as steel rods, paddling sticks, or tampers, but mechanical vibrators are best. Any compacting device must reach the bottom of the form and be small enough to pass between reinforcing bars. Since the strength of the concrete member depends on proper reinforcement location, be careful not to displace the reinforcing steel.

The mortar / concrete should be consumed as early as possible after addition of water to it. The hydration of cement starts the moment water is added to it. As the hydration progresses the cement paste starts stiffening and loses its plasticity. The concrete should not be disturbed after this. Normally, this is about 45 –50 minutes.

The term ‘curing’ is used to include maintenance of a favorable environment for the continuation of chemical reactions, i.e. retention of moisture within, or supplying moisture to the concrete from an external and protection against extremes of temperature.

If a concrete mix is placed in and around a cage of steel rods, it is called Reinforced Cement Concrete (RCC).

Walls: Water should be sprinkled from the top such that it covers the whole area of the wall and it should be remain wet.

Slab: Ponding should be done on the slab by constructing bunds of mortar of approximately 1mX1m and water should be stored.

Beams and columns: The beams and columns can be maintained wet by tying gunny bags around the periphery and by maintaining it wet always.

Ponding, continuous sprinkling, covering with wet cloth, cotton mats or similar materials, covering with specially prepared paper, polyethylene, sealing coat applied as a liquid commonly known as ‘curing compound’ which hardens to form a thin protective membrane, are some of the methods by which concrete is cured.

Curing should be started just after the surfaces begin to dry. Normally 7 to 14 days curing is considered adequate.

Bar-bending-schedule is the schedule of reinforcement bars prepared in advance before cutting and bending of rebars. This schedule contains all details of size, shape and dimension of rebars to be cut.

Steel reinforcements are used, generally, in the form of bars of circular cross section in concrete structure. They are like a skeleton in human body. Plain concrete steel or any other reinforcement is strong in compression but weak in tension. Steel is one of the best forms of reinforcements, to take care of those stresses and to strengthen concrete to bear all kinds of loads.

Mild steel bars conforming to IS: 432 (Part I) and Cold-worked steel high strength deformed bars conforming to IS: 1786 (grade Fe 415 and grade Fe 500, where 415 and 500 indicate yield stresses 415 N/mm2 and 500 N/mm2 respectively) are commonly used. Grade Fe 415 is being used most commonly nowadays. This has limited the use of plain mild steel bars because of higher yield stress and bond strength resulting in saving of steel quantity. Some companies have brought thermo mechanically treated (TMT) and corrosion resistant steel (CRS) bars with added features. Bars range in diameter from 6 to 50 mm. Cold-worked steel high strength deformed bars start from 8 mm diameter. For general house constructions, bars of diameter 6 to 20 mm are used.

Cover blocks are placed to prevent the steel rods from getting exposed to the atmosphere, and to place and fix the reinforcements as per the design drawings. Once the steel is exposed to the atmosphere, corrosion starts. Sometimes it is commonly seen that the cover gets misplaced during the concreting activity. To prevent this, tying of cover with steel bars using thin steel wires called binding wires (projected from cover surface and placed during making or casting of cover blocks) is recommended. Covers should be made of cement sand mortar (1:3). Ideally, cover should have strength similar to the surrounding concrete, with the least perimeter so that chances of water to penetrate through periphery will be minimized. Provision of minimum covers as per the Indian standards for durability of the whole structure should be ensured.
Shape of the cover blocks could be cubical or cylindrical. However, cover indicates thickness of the cover block. Normally, cubical cover blocks are used. As a thumb rule, minimum cover of 2” in footings, 1.5” in columns and 1” for other structures may be ensured.

Lap length is the length overlap of bars tied to extend the reinforcement length.. Lap length about 50 times the diameter of the bar is considered safe. Laps of neighboring bar lengths should be staggered and should not be provided at one level/line. At one cross section, a maximum of 50% bars should be lapped. In case, required lap length is not available at junction because of space and other constraints, bars can be joined with couplers or welded (with correct choice of method of welding).

This is the additional length of steel of one structure required to be inserted in other at the junction. For example, main bars of beam in column at beam column junction, column bars in footing etc. The length requirement is similar to the lap length mentioned in previous question or as per the design instructions.

Reinforcement should be free from loose rust, oil paints, mud etc. it should be cut, bent and fixed properly. The reinforcement shall be placed and maintained in position by providing proper cover blocks, spacers, supporting bars, laps etc. Reinforcements shall be placed and tied such that concrete placement is possible without segregation, and compaction possible by an immersion vibrator.

For any steel reinforcement bar, weight per running meter is equal to d2/162 Kg, where d is diameter of the bar in mm. For example, 10 mm diameter bar will weigh 10×10/162 = 0.617 Kg/m.

Portland Pozzolana Cement (PPC) is obtained by either intergrinding a pozzolanic material with clinker and gypsum, or by blending ground pozzolana with Portland cement. Nowadays good quality fly ash is available from Thermal Power Plants, which are processed and used in manufacturing of PPC.

Plaster protects structure from temperature variations; external attacks of sulphates, chlorides, etc. Plaster also provides smooth & aesthetic surface on RCC & Brickwork surface.

Preferably use cement which releases low heat of hydration. A blended Cement is a good choice.

• Use optimum water at the time of mixing.
• Do not use dry cement on the plaster surface.
• At the junction of Brickwork & RCC, chicken mesh or fiber mesh may be used.
• Wet the surface before plastering.
• Cure the surface for at least 10 to 12 days.

Carpet Area: This is the area of the apartment/building, which does not include the area covered by the walls. Built up Area: The carpet area plus the area of the walls. Super Built up Area: This includes the built up area along with the area under common spaces such as the lobby, lifts, stairs, etc.

Some points which one must pay attention to prior to land deal -

• House plot should not be under any acquisition proceedings of any government bodies .
• Verify from the planning authorities whether the land was designated for residential use.
• The survey number of land is critical.
• Certificate obtained from registrar’s office should confirm that there is no encumbrance on the property.
• The title deed of the land should be clear and an advocate should be consulted for this.
• Verify the rates after contacting some property consultants and some people who have purchased their plots recently. You should also refer guidelines and the market rates published in the government manual of your city/town.
• Stamp duty at the time of registration is mandatory.

Whatever the type of contract, one needs to pay close attention to the following aspects –

• Type of materials
• Quality of work
• Advance payment, if any
• Progress & time schedule
• Future measurement & payment conditions

To give an idea, depending on the finishes you choose, the construction cost should be as follows –

Type of finish in the construction Cost (in rupees) per sq.ft of construction

Top Class Finish
750 – 1000

Medium Class Finish
480 – 700

Simple Class Finish
350 – 550

60:30:10

Once you take house loans, you will repay your amount in monthly installments depending upon the loan amount, total duration and interest rate. This means you have to pay certain amount per lakh rupees during the entire period. This is called Equated Monthly Installments (EMI). The longer is the repayment period smaller will be the EMI. Generally, EMI doesn’t exceed the 50% of household income.