Page 224 - New Trends in Eco efficient and Recycled Concrete

194 New Trends in Eco-efficient and Recycled Concrete

The detailed scanning electron microscope (SEM) microphotography of this forma-
tion known as a brick and mortar structure is shown in Fig. 8.2.

8.3 Mollusc shell as aggregate for concrete

The published results in literature demonstrate that the difference between mollusc
species, to be used as aggregates, is small and the changes are mainly in colour,
texture and form. All shells are composed of calcium carbonate up to 95%, but they
present differences in the mineralogy of the carbonate.
Periwinkle shells are one of the most common molluscs used in concrete and are
used as a substitute for natural coarse (Falade, 1995; Adewuyi and Adegoke, 2008;
Osarenmwinda and Awaro, 2009) and fine aggregates (Nguyen et al., 2013). Oyster
shells have also been studied as a substitute for fine aggregate in concrete (Yang
et al., 2005, 2010; Kelley, 2009) and for both fine and coarse aggregate (Elliott
Richardson and Fuller, 2013). Finally, cockle, scallop and mussel shells have been
studied as coarse aggregates (Mijan et al., 2011; Muthusamy and Sabri, 2012;
Sugiyama, 2004; Barnaby, 2004) and also as sand (Yoon et al., 2003; Kelley, 2009)
in concrete. All of these studies concluded that the workability, density and com-
pressive strength of concrete decreases as the percentage of seashells increases. It
was also determined, that the use of seashells affects the tensile splitting strength,
modulus of elasticity, drying shrinkage and water permeability of concrete.

8.3.1 Recycling treatment of mollusc shells
Most of the authors in the literature (Table 1.1) do not mention having carried out
any cleaning or deworming treatment on the seashells (Cuadrado-Rica et al., 2016;
Muthusamy and Sabri, 2012; Barnaby, 2004) and a few have used waste shells after
some form of complex cleaning. Some of them have cleaned shells for 4 or 24 h
(Agbede and Manasseh, 2009; Othman et al., 2013; Yang et al., 2010) in a labora-

tory oven (110 or 105 C), others have heat-treated them at 250 300 C(Mijan
et al., 2011) and other authors have washed and air-dried the seashells at room tem-
perature (Falade, 1995; Adewuyi and Adegoke, 2008). In one case the shells were
cleaned with bleach, white vinegar solution or baking soda and using different abra-
sives (Kelley, 2009).
Martı ´nez-Garcı ´a et al. (2017) indicated that the most appropriate treatment
would be a simple treatment, involving low energy consumption and resulting in a
commercially safe by-product. This author recommends heat treatment at 135 C for

32 min.

8.3.2 Experiences in the use of mollusc shells as aggregates

Numerous works cover the use of aggregates from different seashells to replace
conventional aggregates for the manufacture of concrete. Table 8.1 includes the