Civil Engineering Reference
In-Depth Information
Table 6.2 Qualitative rating
of the correlation coefficients
Rating
Values range
R
2
Very good
C 0.95
0.80 B R
2
\ 0.95
Good
0.65 B R
2
\ 0.80
Acceptable
R
2
\ 0.65
Non-acceptable
7. Graphical analysis of the variation of the ratio between the properties of con-
crete with RA and the reference concrete and the ratio between the compressive
strength at 7 days of concrete with RA and the reference concrete (similar to
Eq.
6.1
);
8. Compilation of the data in a table, including the slope of linear regression line
and the respective correlation coefficient.
In the case of the methodology applied for analysis of the literature data
(presented above), the following two additional steps were adopted to complete the
methodology:
9. Superposition of the graphical results of each concrete property for the various
campaigns analysed and determination of the linear regression lines with the
respective correlation coefficient;
10. Correction of the linear regression lines obtained, to make them representative
of the physical behaviour under analysis, forcing them to pass through the
point that corresponds to the RC, with the inconvenience of lowering the
corresponding correlation coefficient.
Table
6.2
gives the qualitative criteria defined in terms of the correlation
coefficient R
2
and applied in both sections.
The methodology's feasibility is explained by the fact that, for conventional
concrete as well, it is possible to establish reliable correlations between the various
properties of hardened concrete and the density (of which the water absorption is
an indirect measure) of the aggregates or the compressive strength at early age.
6.3 Analysis of the Literature Data: Estimation of Long-Term
Properties
This study started with a bibliographic Internet-based survey within the RAC topic,
with emphasis on the published results of international experimental campaigns. The
survey also included scientific journals' papers, article compilations in conferences
and seminars, graduate, master's and PhD theses. To better understand the behaviour
of RAC in the fresh and hardened states, this study set out to collect experimental
data from various international campaigns, and use it to correlate some of the
properties of the aggregates (density and water absorption) and the 7-day com-
pressive strength of concrete with the most relevant properties of the RAC.
