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198 New Trends in Eco-efficient and Recycled Concrete

20%
Falade A
Falade B
Change of hardened density (%) –10% Adewuyi A
10%
Falade C
0%
Adewuyi B
Olufemi C
–20%
Nguyen VA
Nguyen VB
–30%
Nguyen CA
–40%
Nguyen CB
0 10 20 30 40 50 60 70 80 90 100
% Aggregate substitution Nguyen CC
Periwinkle Scallop Crepidula

Figure 8.3 Variation of hardened density of concrete with marine shells as aggregates.
periwinkle. In the scallop, Nguyen (Nguyen et al, 2017) makes two series with dif-
ferent mix compositions, which even starting from different concrete densities
3
(1875 and 1975 kg/m ), reach very similar drop values (6.1% and 6.6%, respec-
tively) for a percentage of 60% replacement. In the case of the use of crepidula
shells, the variations with respect to the reference are also softer than those shown
with periwinkle. The author of this chapter made three different compositions, A, B
and C, using aggregates of 4 6.3 mm in A, 2 4 mm in B and 2 6.3 mm in C. For
a substitution percentage of 40% in the three series, the reductions of density were
of 4.6%, 1% and 0.8%. It is remarkable that the series that does not include an
aggregate size less than 4 mm is the one that experiences the greatest drop in
density.
From this it can be deduced that for any type of species, the hardened density
of concrete with marine shells is lower the greater the percentage of substitution of
aggregate and the greater the size of the same. It is probable that the lazy form
of the aggregate creates greater cavities in the concrete matrix, and is one of the
causes of this phenomenon.

8.4.2 Fresh state
The slump values of different concrete mixes incorporating shells as aggregates can
be seen in Fig. 8.4.
The general trend is that the greater the percentage of aggregate of mollusc
shells used, the greater the reduction of the consistency. In the case of studies that
used periwinkle, as in density, the Falade (Falade, 1995) series are the ones that