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344 New Trends in Eco-efficient and Recycled Concrete

12.3.4 Standards and methods of leaching tests of concrete and
cement-based materials
Concrete leaching tests are performed by simulating the processes that occur in real
situations where water circulates around small concrete monoliths and are usually
made in tanks where pure or deionised water circulates around the monoliths by,
making extractions of the water after having circulated in the deposit around the
monoliths.
Specific tests applied to determine the leaching of concrete affect mainly three
variables: aggregates, pH, shape and size of hardened concrete specimen or mono-
lith. There are two important tests to apply in the study the potential leaching of
RAC:

Tests related to the aggregates: Applied mainly to fine and coarse aggregates. It is impor-
tant to know the potential leaching of aggregates, and usually CEN EN 12457 1-5 stan-
dards are used, which are carried out with a certain content of aggregates in deionised
water, applying different liquid/solid (l/s) ratio. The standard CEN EN 12457-4 is the
most commonly used, applying a ratio l/s 5 10. With this test, the aggregates that will
form the concrete can be characterised. These tests are not usually done for the other com-
ponents, that is, cements, additives, etc. They are only applied on the aggregates that will
be part of the concrete, both sand and coarse aggregates.
pH dependence test: CEN/TS 14429:2005 This test is also important because concrete

matrices use to present high pH values, between 12.5 and 14, should be studied for the
behaviour of leachates in this pH range. This test should be applied to aggregates with pH
values higher than 9 or 10.
Tank or monolithic tests: This is the most important test to determine the potential con-
tamination by leaching that concrete could cause in a water medium. There are several
important standards to apply this test, with different specifications:
EA NEN 7375:2004: leaching characteristics of moulded or monolithic buildings and
waste materials:
The purpose of this diffusion test is to simulate the leaching of inorganic components
from monolithic specimens and materials under aerobic conditions as a function of
time over a period of 64 days (Fig. 12.6).
The diffusion test requires at least one piece with the smallest dimension of 40 mm on
all sides, and the volume of the specimen (Vp) in litres must be known.
The unreactive plastic tank or bucket must have a volume two to five times the volume
Vp and the dimensions that the test piece is surrounded by is at least 2 cm of water on
all sides.
Place the sample in demineralised water and with neutral pH and replenish the eluate
at specified times. The pH value at which the leaching takes place is determined by
the material itself.
The preparation of the test piece is carried out by means of manufacturing, curing and
drying in an oven. A subsequent drain is applied to the tank, and immediately after-
wards the tank is refilled with the required amount of water. This step is repeated eight
times, replacing the deionised water each time and applying the times specified in
Table 12.2.
All leachates are extracted, and the weight loss of the tested material is calculated.
Both liquid:solid and liquid:area ratios must be taken into account.