What is Curing of Concrete ?

Curing  

    As you know, the concrete is a mixture of Cement : Sand : Aggregates, apart from these, the water plays major to mix above said materials.

    Not only that, the water regulates the reaction process of concrete, and the chemical reaction process continuous for the period of 28 days (the time where we access the strength of concrete). And in the process of chemical reaction, the water present in the concrete may evaporate in the presence of heat (sunlight). 

    To avoid, the evaporation of water in concrete (which helps in chemical reaction of cement) water sprinkling, gunny bags or ponding will be done. In the process of curing, no water will mix or percolate in the concrete.

Rapid Hardening Cement (IS 8041–1990)

This cement is similar to ordinary Portland cement. As the name indicates it develops

strength rapidly and as such it may be more appropriate to call it as high early strength cement. It is pointed out that rapid hardening cement which develops higher rate of development of strength should not be confused with quick-setting cement which only sets quickly. Rapid hardening cement develops at the age of three days, the same strength as that is expected of ordinary Portland cement at seven days.

The rapid rate of development of strength is attributed to the higher fineness of grinding (specific surface not less than 3250 sq. cm per gram) and higher C3S and lower C2S content.

A higher fineness of cement particles expose greater surface area for action of water and also higher proportion of C3S results in quicker hydration. Consequently, capid hardening cement gives out much greater heat of hydration during the early period. Therefore, rapid hardening cement should not be used in mass concrete construction.

The use of rapid heading cement is recommended in the following situations:

(a) In pre-fabricated concrete construction.

(b) Where formwork is required to be removed early for re-use elsewhere,

(c) Road repair works,

(d) In cold weather concrete where the rapid rate of development of strength reduces the vulnerability of concrete to the frost damage.

Ordinary Portland Cement

Ordinary Portland cement (OPC) is by far the most important type of cement. All the

discussions that we have done in the previous chapter and most of the discussions that are going to be done in the coming chapters relate to OPC. Prior to 1987, there was only one grade of OPC which was governed by IS 269-1976. After 1987 higher grade cements were introduced in India. The OPC was classified into three grades, namely 33 grade, 43 grade and 53 grade depending upon the strength of the cement at 28 days when tested as per IS 4031-1988. If the 28 days strength is not less than 33N/mm2, it is called 33 grade cement, if the strength is not less than 43N/mm2, it is called 43 grade cement, and if the strength is not less then 53 N/mm2, it is called 53 grade cement. But the actual strength obtained by these cements at the factory are much higher than the BIS specifications.

Teating of Cement

Testing of cement can be brought under two categories:

(a) Field testing

(b) Laboratory testing.

Field Testing

It is sufficient to subject the cement to field tests when it is used for minor works. The following are the field tests:

(a) Open the bag and take a good look at the cement. There should not be any visible lumps. The colour of the cement should normally be greenish grey.

(b) Thrust your hand into the cement bag. It must give you a cool feeling. There shouldnot be any lump inside.

(c) Take a pinch of cement and feel-between the fingers. It should give a smooth and not a gritty feeling.

(d) Take a handful of cement and throw it on a bucket full of water, the particles should float for some time before they sink.

(e) Take about 100 grams of cement and a small quantity of water and make a stiff paste.

From the stiff paste, pat a cake with sharp edges. Put it on a glass plate and slowly

take it under water in a bucket. See that the shape of the cake is not disturbed while taking it down to the bottom of the bucket. After 24 hours the cake should retain its original shape and at the same time it should also set and attain some strength.

If a sample of cement satisfies the above field tests it may be concluded that the cement is not bad. The above tests do not really indicate that the cement is really good for important works. For using cement in important and major works it is incumbent on the part of the user to test the cement in the laboratory to confirm the requirements of the Indian Standard specifications with respect to its physical and chemical properties. No doubt, such

confirmations will have been done at the factory laboratory before the production comes out from the factory. But the cement may go bad during transportation and storage prior to its use in works. The following tests are usually conducted in the laboratory.

(a) Fineness test. (b) Setting time test.

(c) Strength test. (d) Soundness test.

(e) Heat of hydration test. (f ) Chemical composition test.

Types of Cement

(a) Ordinary Portland Cement

(i) Ordinary Portland Cement 33 Grade– IS 269: 1989

(ii) Ordinary Portland Cement 43 Grade– IS 8112: 1989

(iii) Ordinary Portland Cement 53 Grade– IS 12269: 1987

(b) Rapid Hardening Cement – IS 8041: 1990

(c) Extra Rapid Hardening Cement – –

(d) Sulphate Resisting Cement – IS 12330: 1988

(e) Portland Slag Cement – IS 455: 1989

(f) Quick Setting Cement – –

(g) Super Sulphated Cement – IS 6909: 1990

(h) Low Heat Cement – IS 12600: 1989

(j) Portland Pozzolana Cement – IS 1489 (Part I) 1991 (fly ash based) – IS 1489 (Part II) 1991 (calcined clay based)

(k) Air Entraining Cement – –

(l) Coloured Cement: White Cement – IS 8042: 1989

(m) Hydrophobic Cement – IS 8043: 1991

(n) Masonry Cement – IS 3466: 1988

(o) Expansive Cement – –

(p) Oil Well Cement – IS 8229: 1986

(q) Rediset Cement – –

(r) Concrete Sleeper grade Cement – IRS-T40: 1985

(s) High Alumina Cement – IS 6452: 1989

(t) Very High Strength Cement – –

HOW TO CALCULATE DEPTH OF NEUTRAL AXIS AND MOMENT OF RESISTANCE

 

HOW TO PREPARE VALUATION REPORT OF N.A. PLOT & EXISTING BUILDING

                       VALUATION REPORT OF N.A PLOT & EXISTING BUILDING

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A) Name of the Property Holder:  Owner Name

 

B) Location of Land: Address of Site / Building 

 

C) Type of Land: N.A Site with Existing Building

 

D) Land/Site Area : :  0 Acres & 1 Guntas 14.75 Anna =  1665 Sq.ft

 

E) Market Value: 2700 Rs/ Sq.ft

 

F) Total Cost of Site = Total Site Area X Market Value

= 1665 Sq.ft X 2700 Rs / Sq.ft = 44,95,500 /-

G) Builtup Area of Existing Building :  803.3 Sq.ft

 

H) Present Construction Cost = 2200 Rs / Sq.ft

 

I) As Building is built in the year 1996, it’s been 24 Years,

Construction Cost after depreciation of 20 % = 1830 Rs / Sq.ft

J) Total Valuation of Building = Total Builtup Area X  Construction Cost

      = 803.3 Sq.ft X  1830 Rs / Sq.ft = 14,70,039 /-

 

Total Cost of Site & Existing Building ( F + J) = 59, 65,539/-

                                                                                                                                   

                                               SAY RS: 59, 66,000/-

 

 

(RUPEES FIFTY NINE LAKHS AND SIXTY SIX THOUSANDS ONLY)