Microwave-assisted concrete recycling - Microwave-Assisted Concrete Technology: Production, Demolition and Recycling - page 141

4.4 AVAILABLE STANDARDS FOR RCA

With the increasing interest toward the use of recycled aggregates, most
major standards bodies have published documentation on the general
requirements for the use of RCA and RAC. Among the standards available,
the Japanese standard (Japanese Industrial Standards, JIS) is most compre-
hensive. Japan was among the first countries to initiate research on RCA.
Japan introduced recycling laws as early as 1991. Under the “recycled 21”
programme launched by the Japanese Ministry of Construction (MOC) in
1992, targets were set to increase the percentage of recycled demolished
concrete in the ensuing years. By 2000, demolished concrete was 96%
recycled, exceeding the MOC's target of 90%. However, practically all the
RCA were used as subbase material for road carriageways.
Previously, the Japanese standard JIS A 5308 for ready-mix concrete
did not permit the use of recycled aggregates. In response to the recom-
mendations of the JIS Civil Engineering Committee in 1998, the Japanese
Concrete Institute formed a committee to draft a JIS technical report as
a preliminary document to be developed into a JIS standard. This report,
known as TR A 0006, released in 2000, permits recycled concrete to be
used independent of JIS A 5308. However, according to this report, the
strength of structural recycled concrete was capped at 18 MPa. Presoaking
of the recycled aggregates for the control of workability and the use of blast
furnace slag cement or fly ash to counteract alkali aggregate reaction are
also included in the requirements of this standard.
Subsequently, in 2005, this report was published as JIS standard JIS
A 5021 (Japanese Standard Association, 2005) for high-quality recycled
aggregate type “H” for concrete, which is produced through advanced pro-
cessing, including crushing, grinding, and classifying of concrete masses
generated in the demolition of structures. Recycled type H aggregates must
have physical properties satisfying the requirements listed in Table 4.1.

Table 4.1 Physical properties requirement for type H recycled aggregates,
JIS standard

Items Coarse aggregate Fine aggregate

Oven- dry density (g/ cm 3 ) Not less than 2.5 Not less than 2.5

Water absorption (%) Not less than 3 Not less than 3

Abrasion (%) Not more than 35 NA

Solid volume percentage for shape
determination

Not less than 55 Not less than 53

Amount of material passing 75- μ m test
sieve (%)

Not more than 1 Not more than 7

Chloride ion content Not more than 0.04