Thursday, March 31, 2011

Specifications of TMT Bars for RCC Work in Alumina Refinery

Hi Friends,

Investment towards civil construction work for buildings  and foundations for equipment as well as structural buildings accounts for about 10 to 15% of total capital investment in setting up new Alumina refinery. Hence, I thought of discussing today about the types of thermo-mechanical treated (TMT) bars used as reinforcement in civil construction work, their specifications and other related issues in the present post. 

In general, TMT bars  with matching specifications of Fe415 or equivalent is used for reinforcement strengthening in civil construction. As a rule of thumb, about 1 tonne of Fe415 TMT bars are used in every 10 m3 of RCC work for columns, beams, equipment foundation and roof casting without carrying out any design calculations.  However, to economize the consumption of this component, calculated quantity of TMT bars with higher yield strength are preferred. Specifications with relevant techno-economic details of TMT bars are outlined below-

Specifications of Fe415 as per IS 1786:
yield stress  = 415 N / mm2,
Chemical composition-
% Carbon = 0.30% max.,
% Sulphur = 0.060% max.,
% Phosphorus = 0.060% max.,
% Sulphur + Phosphorus = 0.110% max.

Specifications of Fe500 as per IS 1786:
Yield stress  = 500 N / mm2 min.,
Tensile strength = 545 N/mm2 min.,
Stress ratio, Tensile stress / Yield stress = 1.10 min. 
Chemical composition-
% Carbon = 0.30% max.,
% Sulphur = 0.055% max.,
% Phosphorus = 0.055% max.,
% Sulphur + Phosphorus = 0.105% max.

The above specifications covered under IS1786 are exactly same as those stated in ASTM 615 grade 60, BST 500 of DIN 488 and BS 444 grade 60.

Cost wise Fe500 is about 3 to 5 % more expensive than Fe415 but the requirement of Fe500 will be about 17% less than Fe415 for the same strength of reinforcement. Thus, a net savings of about 12 to 15% have been estimated in carrying out civil construction with Fe500. Many experts in the field have also the same opinions.

Estimated Savings:
Let us estimate the saving just by use of Fe500 in place of Fe415 as calculated (taking certain assumptions on conservative side) below-
Alumina refinery capacity = 1000,000 tpa,
Specific capital investment required = US$550 per tonne of alumina per year,
Civil works = 10% of total capex,
TMT bars = 5% of gross civil quantity,
Savings = 15% of total expenses on TMT bars.
Thus total savings = 1000,000 tpa x US$550/t x 10% x 5% x 15% = US$412500.
Therefore, the total savings works out to 0.40 million US$ just by our right decision on one count.

It is evident from above comparative analysis that Fe500 is the preferred choice over Fe415.

Request to kindly put your views / remarks / comments, if any.


Kunwar Rajendra

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