Page 387 - New Trends in Eco efficient and Recycled Concrete

342 New Trends in Eco-efficient and Recycled Concrete

Attack by sea water or water with chlorides.
Acid attack.
It must be taken into account that conventional leaching tests are generally
applied with pure water, and the limits established are determined by tests where
leachates produced by circulating pure water around concrete monoliths are tested.
The fact that concrete degrades in adverse conditions will imply the increasing
of release leves of chemical species to the leachant.
There are several factors (Fig. 12.5) that influence the degradation of concrete,
such as its mechanical resistance, since at lower strength faster degradation pro-
cesses occur and, therefore, the concrete will be less durable. It should be consid-
ered that recycled concretes usually have lower mechanical strengths than
conventional ones, so the degradation and leaching processes will be more pro-
nounced in recycled concretes than in conventional ones with equal cement content
and other components.

12.3.2 Leaching of concrete and cement-based materials
The leaching of the material components of concrete, mainly form the interphase
zone between aggregates and cement paste, produces the emission of non-metallic
components and metals, chlorides and fluorides, etc., into the external environment
due to the porosity of the concrete, both higher and lower mechanical strength and
density.

Figure 12.5 Physical and chemical aspects that affect the leaching process of monolithic
materials (Engelsen et al., 2009).