Civil Engineering Reference
In-Depth Information
Slump (according to the experience gained in these various experimental studies,
keeping the effective w/c ratio constant usually leads to equal slump values,
regardless of the type of aggregates used); (3) Aggregate size distribution.
As expected, the results presented by each experimental study individually
exhibit a far better linearity and bigger correlation values compared with the
juxtaposed campaigns' values presented below. Various hardened and fresh con-
crete properties were analysed in this study. The primary property analysed for
fresh concrete was density. It showed a proportional decrease as the substitution
rate increased, which can be linked to the lower density presented by recycled
aggregates. The hardened concrete mixes were analysed for their mechanical
properties and durability. Most of these properties had a poorer performance with
the use of recycled aggregates, as expected, and in agreement with the interna-
tional references cited above.
Each property is graphically analysed, with the introduction of a regression line,
corrected so as to pass through the point corresponding to the RC.
6.4.2.2 Concrete Density
The ratio between the hardened concrete densities and the ratio between the
densities of the aggregates in the mixes showed a linear trend with a good cor-
relation coefficient.
Figure
6.10
shows the relationship between the ratio between the hardened
concrete densities and the ratio between the densities and the water absorptions of
the aggregates in the mix and the 7-day compressive strengths of concrete,
respectively. The correlation coefficients (see Table
6.2
) are considered, respec-
tively, good, acceptable and not acceptable.
For every parameter used as an indicator, the concrete density decreases with
the substitution rate because of the lower density of the recycled aggregates, due to
their lower intrinsic porosity (in ceramic and mortar aggregates) or the mortar
adhering to the original aggregates (in recycled concrete aggregates).
6.4.2.3 Compressive Strength
Figure
6.11
depicts the relationship between the ratio between the 28-day
compressive strengths of the hardened concrete and the ratio between the densities
and the water absorptions of the aggregates in the mix and the 7-day compressive
strengths of concrete, respectively. The correlation coefficients are considered,
respectively, acceptable, not acceptable and not acceptable. Although the corre-
lation coefficients were disappointingly low (due to the large number and variety
of studies juxtaposed in the same graph), it is still possible to see a clear trend
towards a fall in compressive strength as the substitution rate increases, explained
by the lower mechanical characteristics of the ceramics and of the mortar adhering
to the NA (in recycled concrete).
