LCA Case: recycling of concrete

Recycling is a special, complex, subject in LCA. This related with the fact that the LCA is to be made "from cradle to grave".
The issue is that recycling has to do with "from grave to cradle" (recycling closes the circle) , so a special set of rules has to be applied to resolve this problem in a practical way (Chapter 4 of the Thesis) . These rules are explained under tab LCA.

This approach of the EVR model is to calculate the 'net eco-benefit of recycling' (negative eco-costs).
The case which is described here, is a rigorous LCA on the recycling of concrete. It is how to calculate the 'net eco-benefit of recycling' in practice, where:

'net eco-benefit of recycling' = {(a + b + c)+ f - (d + e) } x A

where:
a = eco-costs of materials depletion (including eco-costs of land), for 100% virgin material
b = eco-costs of energy ' from cradle to basic material', for 100 % virgin material
c = pol. prev. costs' from cradle to basic material', for100% virgin material
d = eco-costs of energy, including the stages of demolishing, separation, transport, storage and upgrading (to the basic material), at 100% recycled material
e = pol. prev. costs, including the stages of demolishing, separation, transport, storage and upgrading (to the basic material), at 100% recycled material
f = eco-costs of incineration and/or Land Fill.
A = percentage of recycled material
Reference is made to Fig. 6.2a which depicts the general recycling system. See also tab LCA, EoL and recycling.

The case of recycling of concrete is important because of two reasons:
1. Demolished building materials are in many Western countries the biggest flow to Land Fill
2. The mining of gravel for concrete often results in serious degradation of land

The crushed concrete that can be re-used in concrete (to replace gravel) is called aggregate.
The first step in the LCA is to determine the eco-costs of the gravel (100% virgin) and the eco-costs of concrete aggregate (100% recycling). A rigorous LCA is given in Chapter 8 of the Book (tab data, references, 1.1), and is summarized in Fig. 6.2b (eco-costs '07). Note that this is (a+b+c) respectively (d+e) of the abovementioned equation.
The conclusion is that:
- the eco-costs of gravel and aggregate are rather low (0,0035 €/kg resp. 0,0039 €/kg) in comparison to concrete ( 0,0497€/kg), since the highest contribution of eco-costs of concrete stems from cement (0,034€/kg) and use of equipment (0,015€/kg).
- the difference in eco-costs of gravel and aggregate is not significant (the difference is less than the accuracy of these kind of calculations).

However, the big advantage of concrete aggregate is that it doesn't end up in Land Fill ( f in the abovementioned equation).
The eco-costs of Land Fill is 0,118 €/kg, so:

net eco-benefit of recycling = {(a + b + c)+ f - (d + e) } x A = {(0,0032)-(0,0036) + 0,118)} x 1
................................................. = approx. 0,118 €/kg aggregate.

Note: Since the quality of concrete aggregate is less than the quality of gravel, it is good engineering practice to limit the amount of aggregate in concrete to 20%. So there needs to be a destination of the other 80% of the crushed concrete. This is concrete aggregate in roads, see the next tab.

Literature: see under tab data, reference 1.1

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