Page 313 - New Trends in Eco efficient and Recycled Concrete

Comparative studies of the life cycle analysis between conventional and recycled aggregate concrete 273

while for creep coefficient (Lye et al., 2016):

ϕ ~; 28Þ RAC1 5 1:37ϕ ~; 28Þ NAC1 (10.8)
ð
ð
ϕ ~; 28Þ RAC2 5 1:39ϕ ~; 28Þ NAC2 (10.9)
ð
ð
where E cm, NAC1, 2 and ϕ(N,28) NAC1, 2 are modulus of elasticity and creep coeffi-
cient of NAC mixes with the same characteristic 28-day cube strength, respectively.
Based on the statistical analysis of a comprehensive database of RAC and com-
panion NAC beams’ flexural and shear strength (Toˇ si´ c et al., 2016), it was con-
cluded that flexural and shear strength (without stirrups) of RAC beams can be
calculated using the existing provisions of Eurocode 2 Part 1 without any altera-
tions. The same assumption was adopted for RAC slabs’ design in this work,
Table 10.5.
For crack width and long-term deflection calculations the Eurocode 2 Part 1
provisions were used for both NAC and RAC mixes, taking into account their dif-
ferent properties, Table 10.5. In other words, it was assumed that same prediction
models can be used, that is, different NAC and RAC slab serviceability behaviour
was caused only by different concrete properties, and not by different structural
behaviour. This assumption was justified by the experimental results on bond
strength and tension stiffening of RAC mixes published in the literature. Most of
the research performed on the RAC bond strength showed that relative bond
strength (ratio of bond and compressive strength) of RAC with 100% course RCA
was larger or, at least, very similar as in NAC (Xiao and Falkner, 2007; Maleˇ sev
et al., 2010; Kim and Yun, 2013; Prince and Singh, 2013). However, there was also
research which reported lower RAC relative bond strength, as for instance in Butler
et al. (2011). Recent experimental research on tension stiffening behaviour of RAC,
although with 50% course RCA, showed that the use of RCA did not affect the
resulting concrete performance, resulting tensile behaviour and steel-to-concrete
interaction (Rangel et al., 2017).
Regarding durability, two XCs for concrete inside buildings were analysed: XC1
and XC3. The slabs of the 1st 4th floor were designed for XC1 class (dwellings,
low-air humidity), while the slab of the ground floor was designed for XC3 class
(moderate or high-air humidity as parking space was located beneath the ground
floor). Both XCs are related to the carbonation-induced reinforcement corrosion.
The carbonation resistance of RAC has been widely investigated. The results of
studies (Silva et al., 2015) showed that it was possible to correlate the carbonation
resistance with the compressive strength and that this relationship was marginally
affected by the replacement level, type and size of recycled aggregates. The rela-
tionship between the carbonation depth of RAC and NAC with similar mix designs
may be calculated using the following equation (Silva et al., 2016):

2:7

x c;RAC f cm;NAC
5 (10.10)
x c;NAC f cm;RAC