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TECHNICAL PAPER

information on embodied energy of individual material used in cementitious material and other low carbon cements are used
the structure [96,97] . Knowing the quantities used in construction in concrete, this factor may be multiplied with national clinker
and that used during repair against serviceability limit failure, factor (NCF), which is of the order of 0.7 - 0.75 in India now. NCF
[95]
life cycle embodied energy can be estimated . The initial varies in temporal dimension. NCF is 1 for OPC quantity used
embodied energy (IEE) of concrete per cubic meter can be directly in construction when no supplementary cementitious
written as, material is added at site.

IEE = E CN + (E C W C + E CA W CA + E FA W FA + E W W W + ...admixtures etc.) (60) The fossil fuel consumption is divided into two components of
life cycle embodied energy i.e., IEE and EER, neglecting the net
where, E in above equation represents embodied energy, that recovered energy at demolition and recycling, would contribute
is the sum of production and transportation energy and, W to carbon emission and hence carbon land required. Unlike
represents mass of ingredients, cement (C), coarse aggregate cement clinker production, none of the other components
(CA), fine aggregate (FA), water (W), and other mineral and of embodied energy are derived exclusively from fossil fuel.
chemical admixtures etc., per cubic meter of concrete. The Hence, it is appropriate to multiply the total embodied energy

by a factor, fossil fuel ratio (FFR), i.e., national level factor
subscripts of E and W indicate the respective ingredient. E CN
represents energy embodied due to casting, erection etc., i.e. representing fraction of energy from fossil fuel in the overall
overall construction, is about 5 % of total embodied energy of energy consumption by the nation, in the context of carbon
construction with a range of 1.2 - 10 % . Life cycle embodied emission. Other justification for using FFR less than unity is;
[98]
energy would depend upon repair cycle or service life. The cement is only about 15 % of the total quantity in concrete and
service life with respect to most of the deteriorations is related with clinker factor of around 0.7, it amounts to only 10-11 %.
loss of protection capacity of the cover concrete to rebar. As Besides, it affects only the production energy component of
a result, often patch repairs are undertaken whereby cover embodied energy. Accounting for CO 2 from fossil fuel would
concrete is replaced completely by fresh material. The material depend upon the carbon content of varying hydrocarbon
for repair may be similar to the original material. The number system or coal, pet-coke etc. used as fuel in the overall fossil fuel
of such repair required would be the ratio of intended design system. A value of 0.02 kg of CO 2 for every mega Joules (MJ)
life to repair cycle or the service life. Assuming that concrete up energy from fossil fuel has been generally accepted based on
to cover depth is replaced on both sides, the ratio of quantity historical emission and consumption data [1,63,93,94,96] . Thus, total
of repair material to original material will be same as the ratio amount of CO 2 emission during intended design life of concrete
of 2 times cover depth to depth of the section. However, cover (LCCE) in the structure can be written as,
concrete in the complete structure may not be replaced, hence
a multiplying factor, e R , is used to account for extent of repair.
The factor e R is assumed to be same for every individual cycle of (62)
repair. Thus, embodied energy of repair (EER) can be expressed
approximately in terms of initial embodied energy (IEE) as [63,95] , The V CS is the volume of concrete in the structure and m C is the
mass of cement in one m of concrete.
3
(61)
2
Reported CO 2 absorption factor (CAF) for forest is 0.095 kg/m
In Equation 61, d c , d s are the cover depth and depth of the with average production factor of 0.125 kg of timber/m of
2
[96]
section respectively. “t il ” and “t sl ” are intended design life and forest . The forest land required with continuous recycling
service life of concrete respectively. IEE and EER both would of forest during intended design life of structure thus can be
contribute to EFP of the structure. calculated on this basis.
Fossil fuel namely, pet coke etc., together with alternative EFP(structurecarbon) = LCCE × EQF F /CAF (63)
fuels from waste are used directly in cement production.
Transportation and production of other components of concrete The Equation can be written as,
may use partly, primary energy from fossil fuel and partly, (64)
secondary electrical energy from both renewable and non-
renewable sources. In addition, calcination of lime during OPC where, A S is the area occupied by the structure while subscript F
clinker production results in direct emission of CO 2 . The 100 and B represent forest land and built-up area for the respective
mass units of limestone produce 56 units of CaO and 44 units equivalent factors. Both A S and LCCE are areas in same unit, may
of CO 2 . Thus, for clinker having 65 % CaO, the CO 2 emission be in square meters. However, since BC and EFP are calculated
is 44 / 56 × 0.65 = 0.51 unit of CO 2 by mass per unit mass of on annual basis, LCCE shall be divided by t il to obtain N es for the
cement. However, in larger national scale, when supplementary concrete in the structure.

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