Civil Engineering Reference
In-Depth Information
ash formed during volcanic eruptions (Siddique, 2011) exhibit a low LOI
(1%), along with an 80% acid, and around a 5% alkali content.
Silica, alumina and iron oxide account for around 80% of natural zeolitic
tuffs (Ahmadi and Shekarchi, 2010; Uzal and Turanli, 2012), which also
have a low alkali content (3-5%) and medium LOI values (6-9%).
Chemical analyses of trasses reveal that the Rhine variety has LOI values
of 4.6-11.8%, the Bavarian variety 6.1-8.8% and the Austrian variety 15%.
The sum of their acid components comes to around 75%, although differences
exist in the alkali content: 9% in the first, 4% in the second and 3% in the
third (Schwiete et al., 1968). Spanish opaline has high silica contents, from
87 to 90%, barely more than traces of alkalis (0.5%) and 3% LOI (Sánchez
de Rojas et al., 1993).
The Greek pozzolans, such as Santorin earth, have silica, alumina and iron
oxide contents of 65.1, 14.5 and 5.5%, respectively, and 6.5% alkalis with
a LOI of 3.5% (Mehta, 1981). These values do not differ substantially from
the pozzolanic material studied by Moropoulou et al. (2004), who reported
silica, alumina and iron oxide values of 69.7, 12.3 and 2.3%, along with
4% alkalis and 7.4% LOI, although the literature also contains data on other
Greek materials with higher LOI (Turanli et al., 2004).
Of the organic pozzolans, möler has a LOI of 5.6% and a combined
silica, alumina and iron oxide content of 86%, whereas the LOI values for
diatomaceous earth range from 7 to 15%, even though both materials have
80-90% acid components and an alkalic content of under 1% (Calleja, 1969;
Soria, 1983; Sánchez de Rojas, 1986; Sánchez de Rojas et al., 1993).
The amorphous silica rock in the Isparta Keciborlu region have silica and
alumina contents of 92.48% and 2.60%, respectively, and 1.12% alkalis with
a LOI of 1.85% and sulphur (SO
3
) contents are low (davraz and Gündüz,
2005, 2008). Also, the bentonite clay of Pakistan meets the requirements of
chemical composition of natural pozzolans (silica and alumina contents of
54% and 20% and iron oxide content of 8.6%), with a LOI of 5.4% and an
alkalic content of under 5% (Memon et al., 2012).
Mineralogical composition, which is a determinant for material activity, also
varies widely from one pozzolan to another. The main crystalline component
of pumice is augite, a pyroxene and a major constituent of eruptive rocks.
Magnetite and hematite may also be present in this stone (Sánchez de Rojas,
1986; Sánchez de Rojas et al., 1993).
The chief constituents of volcanic tuff are feldspars and zeolites. Ordinary
trachytic, pyroxenic or augitic tuff consists of alkaline feldspars and may
therefore contain high percentages of alkalis and iron- and magnesium-bearing
minerals (Calleja, 1969).
diatomaceous earth comprises calcite, quartz and traces of opal-cT
(cristobalite-tridymite) and usually has high loss on ignition values (up to
15%) (Sánchez de Rojas, 1986; Sánchez de Rojas et al., 1993).
