Civil Engineering Reference
In-Depth Information
The specified maximum allowed limit for sulphate in type 1-3 aggregates is
lower than that specified in the RILEM specification and British Standard BS
8500-2, which usually allow a maximum of 1 % like the Brazilian standard, NBR
15.116.
7.2.2.2 Specification for Concrete with Recycled Aggregates
In August 1998, the German Committee for Structural Concrete (DAfStb) pub-
lished the specification, ''Concrete with recycled aggregate'' as a supplementary
document to DIN 4226-100, which was based on a 4-year national research pro-
ject, ''Baustoffkreislauf im Massivbau (BIM)''. This standard is divided into two
parts: the first part describes the use of RA in structural concrete and the second
part describes the minimum quality of the RA as well as its control.
Part I: Application in Concrete
This part focuses on the production of RAC and its scope. This specification
allowed using RA for concrete production with maximum 28-day cube strength of
37 MPa, which is generally represented by the C30/37 class concrete. To use RAC
in interior elements, where both coarse and fine RA are allowed, the maximum
allowed replacement amount of NA by RA was kept at 35 % for the C20/25
concrete class. However, the RA collected from known origin can only be used for
the preparation of concrete intended for use in external environments and RA
should be classified as insensitive to alkali-silica reaction. Table
7.5
shows the
maximum levels of aggregates present in the mix which depends on the strength of
the concrete class and the type of proposed application.
Analysing the applicability of the aggregates by the German specification, the
standard seems to have a conservative approach. The RA can only be used to
Table 7.5
Maximum allowed ratio of RA in various types of concrete (DafStB 1998)
Application
Coarse and fine
aggregates in concrete,
D [ 2mm
Fine aggregate
in concrete,
D B 2mm
a
b
a
b
(%)
(%)
(%)
(%)
Interior elements
BC20/25
35
50
7
20
C30/37
25
40
7
20
Concrete exposed to the normal environment
20
30
0
0
Impermeable concrete
Concrete with high resistance to
Freeze-thaw
Chemical attack
a
With respect to total volume of aggregates
b
With respect to total volume of coarse or fine aggregates content
