Page 379 - New Trends in Eco efficient and Recycled Concrete

334 New Trends in Eco-efficient and Recycled Concrete

Figure 12.2 Physical and chemical factors influencing leaching. (https://www.vanderbilt.
edu/leaching/leaching-process/).

include the following processes: desorption, complexation, mineral dissolution and
mass transport processes that affect major and minor matrix components.
Thus, the chemical and physical factors that affect the release of chemical spe-
cies on leachates of recycled aggregates (Fig. 12.2) are the following:

Physical and chemical reactions (internal).
External stresses (due to the surrounding environment).
Loss of matrix constituents.
Physical degradation of the solid matrix (motivated by cracking or erosion).
Thus, the release of constituents from monolithic materials is controlled by diffusion
mechanisms, whereas in granular aggregates the release is controlled by the percolation
effect of water though the material. Under that situation, two processes cause the
release of constituents from materials to the water phase: Chemical processes (dissolu-
tion of minerals, adsorption and availability) and the physical transport processes
(advection, surface wash-off and diffusion). In practice, the combination of both pro-
cesses cause element release on leachates (Van der Sloot and Dijkstra, 2004).

12.2 Leaching characteristics of unbound recycled
materials

Leaching is the process by which soluble components are transferred from a solid
matrix material to an aqueous medium (Fig. 12.3). Because the exact reproduction