Civil Engineering Reference
In-Depth Information
ceramics or concrete, such as mortars, aerated concrete or lightweight concrete.
The requirements in terms of density concern the oven-dry density.
If, for type 1, the relationship between the density and minimum water
absorption is very close to what is expected for concrete aggregates, for type 2 the
maximum allowed water absorption is quite high. It is common to have exclu-
sively ceramic aggregates with water absorption values of this magnitude, but with
aggregates mainly of concrete, where the brick portion is lower than 30 %, this
criterion does not seem conditioning. The same line of reasoning can be assumed
for type 3 aggregates, which, despite the low permissible minimum density, is
associated with very high water absorption. No limit is set in terms of water
absorption for type 4 aggregates, because, despite having more materials such as
mortars, plasters or aerated concrete, they should not be used for demanding
purposes, where this property can be quite important.
De Brito (
2005
) and Hansen (
1992
) reported a series of experimental studies
where densities of around 2,300 kg/m
3
for concrete aggregates and 2,000 kg/m
3
for masonry aggregates were obtained. Thus, it is expected that for the minimum
values of allowable densities and based on the compositions imposed, there are
great difficulties in complying with the code, also because there is still a tolerance
of 150 kg/m
3
, and one can thus obtain densities of 1,850 kg/m
3
(type 1 and 2
aggregates) and 1,650 kg/m
3
(type 3 aggregate). Even for type 4 aggregates, in
which quite lighter materials than concrete can be found, the density of 1,500 kg/
m
3
is not very restrictive, since in the most unfavourable case 80 % of the con-
stituents is masonry.
Chlorides and Sulphates
The maximum allowed levels of chlorides and sulphates in RA are shown in
Table
7.4
. Regarding chlorides content in RA, the German standard is quite
demanding. By considering the use of RA in structural concrete, the German
standard specification of chloride content is quite reasonable because chloride
attack is a major problem in concrete, since chloride-induced corrosion causes
severe damage of the reinforced steel and therefore reduces the strength capacity
of the element. However, for less demanding uses of reinforced concrete, chlorides
are not a threat. In the case of type 3 and 4 aggregates, which cannot be used in
structural concrete, the specified limit is quite strict in comparison to the Brazilian
specification.
Table 7.4
Maximum chloride and sulphate contents in RA (DIN 4226-100)
Properties
Type of aggregate
1
2
3
4
Maximum amount of acid soluble chlorides (w/w) (%)
0.04
0.15
Maximum amount of acid soluble sulphates (w/w) (%)
0.8
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