Industrial Waste Aggregates - Recycled Aggregate in Concrete - page 49

cementitious mixes. The density of this slag (3,900 kg/m 3 ) is higher than that of
traditional aggregates, suggesting it may have advantages over these aggregate
materials in certain applications, such as in noise barriers. The X-ray diffraction
(XRD) showed the presence of inclusions of metallic iron, although the principal
crystalline components detected were FeO and ZnS.
Metwally et al. ( 2005 ) reported the use of a slag produced from recycling of
spent lead-batteries as aggregate in concrete production. Recycled-lead slag (RLS)
was used as both fine and coarse aggregate in concrete manufacture after crushing
into the desired gradation by using a roller mill. The physical and mechanical
properties of the used fine aggregate (sand and fine lead-slag) and coarse aggregate
(gravel and coarse lead-slag) are given in Table 2.16 . The coarse lead-slag were
washed carefully and dried before mixing to remove any impurities and organic
matters, which may weaken its bond with the cement paste. Mixing water was
clean tap water free from impurities and organic matters.
Pereira et al. ( 2000 ) reported the use of a salt cake slag, produced from alu-
minium scrap re-melted as partial replacements of either sand or cement in the
preparation of cement mortar production after washing. Non-washed slags cannot
be mixed with cement due to the volumetric expansion observed during setting,
high chloride content and release of high concentrations of noxious gases. As the
concentrations of some toxic elements in the majority of these slags are very high,
before application the environmental suitability as well as the long-term
mechanical and durability performance of concrete containing slag must be
evaluated for the application of these materials as aggregate in concrete.
2.5 Other Waste as Aggregate
The meat and bone mill bottom ash (MBM-BA) used by Cyr and Ludmann ( 2006 )as
a fine aggregate in cement mortar preparation has a grading size between 0 and 2 mm
and a mean diameter of 0.4 mm (Fig. 2.7 ). The physical properties of MBM-BA are
presented in Table 2.17 . The bulk density of MBM-BA is around 900 kg/m 3 and
much lower than that of normal sand (1,500 kg/m 3 ). The average density of the ash is
2,900 kg/m 3 . The external specific surface area, calculated from the density and the
particle size distribution (considering cylindrical particles), is about 3 m 2 /g. The
BET method gives a specific surface area of 3,000 m 2 /kg, which is a thousand times
higher than the value calculated using the particle size distribution. This significant
difference is related to a large open porosity of the grains, leading to water absorption
of 11 %, a very high value compared to normalised siliceous sand (less than 1 %).
The strength of MBM-BA is evaluated using a friability coefficient, defined as
the ratio between the mass of crushed particles (less than 0.1 mm) and the whole
mass of material before crushing. The friability coefficient of MBM-BA, measured
as 37 %, is well within the specified value, which is 40 % for 60 MPa concrete
intended for building construction.