Page 314 - New Trends in Eco efficient and Recycled Concrete

274 New Trends in Eco-efficient and Recycled Concrete

where x c, RAC and x c, NAC are carbonation depths of RAC and NAC, respectively.
The relationship [Eq. (10.10)] is valid only for concrete mixes with CEM I cement,
which was the case in this work. This relationship was used to correlate the required
cover depth of RAC to that of the NAC mix in order to provide equal durability,
Table 10.5.
As for the fire resistance, previous research showed that concrete with aggregate
both fully and partially replaced with coarse RCA exhibited good performance
under elevated temperatures and post-fire mechanical and durability properties,
which was comparable or even better than conventional concrete performance
(Vieira et al., 2011; Sarhat and Sherwood, 2013; Xiao et al., 2013; Kou et al.,
2014). Therefore, there should be no differences in the structural fire design
between RAC and NAC mixes, and same requirements of Eurocode 2 Part 2
were applied to both concrete mixes, Table 10.5.
In determining the depth of the concrete cover it was assumed that the carbon-
ation rate coefficient (k-factor) is equal to 0 on the top surface of the slab, accord-
ing to recommendations in CEN/TC229/WG5-N012 (2016) for elements inside
buildings in dry climate and covered with tiles, parquet and laminate. So, the mini-
mum top cover was determined to satisfy bond (c min,b ) and fire-resistance require-
ments, which were assumed to be same for both NAC and RAC. The bottom
surface of the slab was assumed to have no extra cover, so the minimum bottom
cover was determined to satisfy bond (c min,b ), durability (c min,dur ) and
fire-resistance requirements, see Table 10.5. The value of c min,dur for RAC was cal-
culated on the basis of c min,dur for NAC according to Eurocode 2 Part 1 require-
ments and equation [Eq. (10.10)]. In all cases, minimum cover was increased to
allow for the deviation with a value Δc dev 5 10 mm.
According to Eurocode 2 Part 1, minimum 28-day characteristic compressive
strength for XC1 and XC3 class is 25 and 30 MPa, respectively. The requirement
for XC3 was not satisfied in the NAC1 and RAC2 cases. The slightly lower charac-
teristic strength (less than 10%) in these cases was considered to have a minor
effect.
Results of the design values are presented in Table 10.6 where designation of a
particular slab (S) includes the type of concrete mix and aggregate quality (NAC or
RAC; 1 for high RCA quality and 2 for low RCA quality) and the XC (XC1 or
XC3). All slabs, whether made with NA, high- or low-quality RCA and whether
exposed to XC1 or XC3, fulfil Eurocodes’ requirements for strength, serviceability,
durability and fire resistance. So, full functional equivalence was achieved. The
component material amounts in Table 10.6 present reference flows and input data
for comparative LCA.

10.4.2 LCA model
Case studies were performed with the goal of comparing the environmental impact
of the life cycle of RC floor slabs in residential buildings. Varied parameters were:
type of concrete mix (NAC and RAC), quality of RCA (RAC1 and RAC2), XC