Page 554 - New Trends in Eco efficient and Recycled Concrete

502 New Trends in Eco-efficient and Recycled Concrete

Figure 17.2 Detail of the ettringite inside a pore of a recycled aggregate.

17.3 Influence of sulphur on recycled concrete
production

17.3.1 Flexural and compressive strength
Flexural tests performed on specimens in which the S 8 has been incorporated show
that the fracture due to mechanical testing is transmitted through the sulphur and no
separation is observed. The observed interfacial transition zone (ITZ) shows a good
bond between the sulphur coarse aggregate and the cement paste (Thomas et al.,
2013). Also, in the (Thomas et al., 2013) research, a loss of compressive strength is
observed when the sulphur S 8 is incorporated as coarse aggregate.
Fig. 17.3 shows a specimen of mortar to which S 8 sulphur has been incorporated
as aggregate. This figure corresponds to the fracture surface of a bending test of a
4 3 4 3 16 cm mortar specimen performed to check the mechanical and chemical
compatibility of phases. Sulphur aggregates of 5 mm in maximum size can be
observed, through which the fracture of the bending test has propagated.
Pure sulphur presents a compressive strength of around 20 MPa and can increase
to 60 MPa depending on the mix with sand (Grassi, et al., 1987). The coarse aggre-
gate of sulphur S 8 reduces the flexural and compressive strength in proportion to
the percentage of incorporation. The compressive damage zone (CDZ) or a combi-
nation of distributed axial splitting and localised deformation zone (Markeset and
Hillerborg, 1995) are the cause of the loss of mechanical properties. The results and
the observed fracture surfaces indicate that the sulphur addition works as an inclu-
sion that affects the flexural and compressive strength in proportion to the size of
the sulphur aggregate (Miled et al., 2004).
The results of the mechanical characterisation of RC mixes of different authors
show that the incorporation of RA leads to a loss of compressive strength of the