Page 328 - New Trends in Eco efficient and Recycled Concrete

Comparative studies of the life cycle analysis between conventional and recycled aggregate concrete 285

fifteen RCA samples from a stationary recycling plant in Madrid, Spain, where the
recycling process consists of double impact crushing. For a wide range of RCA,
they obtained that 4/8 mm fraction had mortar content from 33% to 55% (m/m),
while it ranged from 23% to 44% for 8/16 mm fraction.
For CO 2 uptake, it is not the content of adhered cement mortar that is important,
but the content of hydrated cement paste. Florea and Brouwers (2013) have tested
the RCA produced in several ways. For RCA obtained by one-stage crushing of lab-
oratory concrete with a water-to-cement ratio of 0.5, the authors reported that
hydrated cement paste content ranged from 10% to 25% (m/m), depending on the
RCA fraction size (from 32 to 4 mm).
It seems, then, like a fair assumption that RAC mixes contain 10% more of the
reactive CaO available in hydrated cement than NAC mixes (at the lowest).
Following the reasoning behind Eq. (10.11) the maximum theoretical CO 2 -uptake tcc
in RAC can be calculated as:

65 44
CO 2 2 uptake tcc 5 1:1 0:95 5 0:53 kg CO 2 =kg cement
100 56
(10.11)
So in the landfilling case, for CEM I RAC the total CO 2 uptake is Eq. (10.6):

CO 2 2 uptake total 5 0:75 0:53 5 0:40 kg CO 2 =kg cement (10.12)

Taking into account the reabsorbed CO 2 over the whole life cycle, calculated
according to [Eq. (10.6)] for NAC mixes and Eq. (10.12) for RAC mixes, two case
studies (2_XC3_A_CO 2 and 2_XC3_C_CO 2 ) were performed. Results are jointly
presented in Figs. 10.9 and 10.10.

Figure 10.9 Influence of CO 2 uptake on GWP of NAC and RAC mixes (consequential
modelling). NAC, natural aggregate concrete; RAC, recycled aggregate concrete; GWP,
global warming potential.