Page 393 - New Trends in Eco efficient and Recycled Concrete

348 New Trends in Eco-efficient and Recycled Concrete

Table 12.3 Values of maximum limits for each of the mentioned legislations
Maximum contaminant levels (mg/L)

Metals EPA WHO EU
Zn 5.00 3.00
Cr 0.10 0.05 0.05
Pb 0.015 0.01 0.01

As 0.05 0.01 0.01
Cd 0.005 0.003 0.005
Ni 0.02 0.02
Ba 2.00 0.30
Sr 4.00

12.3.6 Previous leaching studies in recycled aggregate concrete
Gwenzi and Mupatsi (2016) studied the leaching in concrete manufactured with
coal fly ash, applying the EPA-1315 method. The tank leaching test was applied to
determine the concentrations of heavy metals obtained by mass transfer from the
concrete monoliths. Three test pieces were tested by each concrete and the relation
2
of liquid:solid ratio of 10 mL/cm of the monolith thickness (Hattaway et al.,
2013). Leachate was sampled, drained and replaced with fresh distilled after 2 h
and 1, 2, 7, 14, 28, 42, 49 and 63 days, thereafter. The leachates were tested for pH,
EC and Zn, Pb, Cu, Mn and Fe, excluding Ni and Cd which were not detected using
the aqua regia method.
Several authors have verified that the tank test on concrete monoliths presents
high pH values as it favours the neutralisation of certain components such as Zn,
Pb, Mn, Cu and Fe. This fact means that these elements usually are stabilised in
concrete matrices and reduced emissions of these elements are produced by con-
crete leaching processes.
Laforest and Duchesne (2007) conducted research in which leaching of heavy
metals (Zn, Pb, Ni, Cr, etc.) from electric arc furnace dust mixed with granulated
slag (GGBFS) and OPC were determined. Test specimens were evaluated for 84
days applying the ANSI 16.1 standard and it was observed that the specimens made
with OPC showed a greater disintegration of particles, producing higher concentra-
tions of metals than in the monoliths manufactured with GGBFS. It was concluded
that the properties of the leaching solution influence the concentration of metals.
Alkaline environments increase the release of metals and produce a decrease in
the accumulated mass of leached metals. In the concrete samples made with OPC
decalcification occurs at the edges after the leaching process, which causes a