Civil Engineering Reference
In-Depth Information
The negative effects of the presence of mortar on a particular property of
RCA are proportional to its content. In addition, the relative severity of the
impact of such effects (the proportionality ratio between mortar content
and changes in the respective property of RCA) is a function of the ratio
between the values of the respective property for the adhering mortar and
NA. It has been shown that for RCA particles comprising similar types of
embedded NAs and mortar, the relationship between the mortar content
and RCA properties is close to linear [15]. The volume of adhering mortar
varies with the grain size, strength of the parent concrete, and the crushing
process used [12,15]. The effects of these factors are discussed in the fol-
lowing sections.
4.3.1.1 Effects of particle size
The mortar content of RCA varies considerably with the size of RCA par-
ticles. In general, the average mortar content of RCA decreases with an
increase in the RCA particle size. Fine RCA particles may contain cementi-
tious mortar up to as much as 65% of their total weight, whereas the adher-
ing mortar content of coarse RCA is between 20% and 40% [16,19].
4.3.1.2 Effects of the parent concrete strength
Identifying the effects of the parent concrete's strength on the adhering
mortar content of RCA and thereby on the properties of RCA and RAC is
still a subject of active research. In 1998, Hasse and Dahms reported that,
for the same particle size, RCAs derived from weaker parent concrete have
greater dry density and thus less-adhering mortar [20]. Hasse and Dahms
explained that this dependency probably stems from the fact that the mor-
tar in weaker parent concrete sheds off more readily during the crushing
process, leaving more rock particles that are clean. Contrary to the findings
of Hasse and Dahms's study, Grubl and Nealen claimed that the strength
of the parent concrete has practically no influence on the strength of the
new concrete [21]. Grubl and Nealen asserted that the adhering mortar
content of RCA is mainly dependent on the concrete-crushing procedure.
They hypothesised that after the first stage of crushing, only the stronger
portions of mortar remain adhering.
In our recent study, a series of experiments was designed to investigate the
underlying reasons for such discrepancies in the available literature on the
effects of the parent concrete's strength on the mortar content of RCA [15].
The results of this study showed that the discrepancies stem mainly from
the overlapping effects of other parameters, including the size of the NAs in
the parent concrete and the crushing procedure used [15]. It was observed
that when the maximum size of NA in the parent concrete was consider-
ably smaller than the maximum size of the RCA particles produced, the
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