Page 343 - New Trends in Eco efficient and Recycled Concrete

300 New Trends in Eco-efficient and Recycled Concrete

affected by the type or replacement ratio, which leads to a reliable formulation of
the tensile strength based upon compressive strength.
In terms of modulus of elasticity, RAC also presents lower performance, com-
pared with NAC. This is mostly associated with the lower stiffness of RA, as well
as the weaker ITZ between RA and the cement paste (Xiao et al, 2005; Etxeberria
et al., 2006; Rahal, 2007; Casuccio et al., 2008; Corinaldesi, 2010; Gupta et al.,
2011; Barbudo et al., 2013; Bravo et al., 2015a,b,c; Pedro et al., 2017). Silva et al.
(2016) have shown that the modulus of elasticity of 100% RAC is about 0.44 0.96
that of NAC.

11.3.4 Influence on the durability and long-term performance of
concrete
The durability of RAC structures is directly related to several mechanisms that may
damage the concrete matrix, or the existing reinforcements within concrete. Among
them, carbonation and chloride penetration represent the most common problems in
concrete structures, directly affecting rebar corrosion (Ahmad, 2003).
These two phenomena are intrinsically related to concretes’ near surface porosity
(Basheer et al., 2001) which is usually higher in RAC than in NAC (Go ´mez-
Sobero ´n et al., 2001; Go ´mez-Sobero ´n, 2002a,b). This is due to the presence of
porous materials such as adhered mortar, brick or other types of contaminants that
allow a faster transport of fluids into the matrix (Tam and Tam, 2007; Evangelista
and de Brito, 2010; Thomas et al., 2013; Bravo et al., 2015a,b,c). Silva et al.
(2015a e) gathered a vast list of references and concluded that the carbonation
coefficient for 100% RAC (K c ) ranges from 0.82 to 2.47 times that of NAC. In a
parallel investigation, Silva et al. (2015a e) concluded that the chloride diffusion
coefficient (D) of RAC range from 090 to 1.72 times that of NAC.
Regarding long-term effects of RA on the RAC performance, there is a consen-
sus that RAC has larger creep than NAC. This is due not only to the lower stiffness
of RA, but also to the creep of the adhered mortar in the RA themselves (Gome ´z-
Sobero ´n, 2002a,b, 2011; Domingo-Cabo et al., 2009; Fathifazl et al., 2011). The lit-
erature review collected by Silva et al. (2015a e) has shown that the deformation
factor due to creep [usually given as (1 1 ϕ), where ϕ is the creep coefficient] for
RAC varies from 1.05 to 1.40 times that of NAC.

11.4 Methodology for the definition of equivalent
functional unit for recycled aggregate concrete

The previous sections showed that RAC performance is normally lower than that of
NAC. Therefore, the comparative LCA of structural elements made from these two
different materials should not be made using the conventional functional unit of
3
1m of concrete, based exclusively in material constituents. In practical terms,
RAC structural elements will have larger cross-sections, thus requiring a bigger