Civil Engineering Reference
In-Depth Information
classification of pozzolans is no easy task, however, for the word covers a
wide variety of materials with different origins and different chemical and
mineralogical compositions. Unsurprisingly, several classifications can be
found in the literature, proposed by Calleja (1969), Massazza (1974, 1993),
Sersale (1980), Soria (1983) and Malhotra (1987), to name a few. all, however,
concur in grouping pozzolans as either natural or artificial. The former require
no processing that would prompt major chemical or mineralogical changes,
for they are inherently active. The latter are the outcome of the chemical or
structural transformation of materials initially devoid of pozzolanicity. The
typically pozzolanic components in this group need heat to be activated.
natural calcined pozzolans form part of this group.
The origin of natural pozzolans may be purely mineral or purely organic,
although some mixed materials can also be found. When of a mineral origin,
pozzolans are usually materials deposited in the proximity of the volcano
after an explosive volcanic eruption. Depending on its viscosity, cooling
rate and gas content, the original magma generates (powdery) ash, pumice
(fragments with small, regular alveoli separated by a thin film of lava), scoria
(regular pores and higher density) and bombs (dense material).
When the incoherent fragments of these original pyroclasts are exposed
to diagenetic cementing processes, they convert into compact rocks known
as tuffs. attendant upon such cementation are the chemical-mineralogical
transformations that have a direct effect on the pozzolanicity of these
materials.The incoherent materials include the traditional Italian pozzolans
from Campania and Latium (respectively the regions of Naples and Rome);
Spanish rock such as the pumice found at campo de calatrava in the province
of ciudad Real, olot in the province of Gerona and almería, in the province
of the same name; Greek materials such as Santorin earth, pozzolans from
the French Massif Central and vitreous rhyolites found in the United States
and India. Tuffs include German trass, used in Roman times, and materials
from the Canary Islands, Naples, Romania and Crimea.
Non-volcanic materials come from rocks that have been simply deposited,
such as clay, or have an organic origin such as diatomaceous earth, which
contains the siliceous skeletons of microorganisms that were deposited
in seawater. They may also contain clay or sand, such as in the Danish
möler, which is of mixed origin. In Spain the largest beds are located in the
provinces of Albacete and Jaén. Materials of this type found in Central Asia
are known as Gliezh, originally schists that were calcined during underground
combustion. In Spain, sedimentary materials known as opaline rock, whose
main component is non-crystalline silica, are found in the provinces of
Salamanca and zamora.
Another material, amorphous silica is basically a sedimentary rock formed
in surface. Actually, it forms in volcanic hydrothermal systems in which
fluids, containing colloidal silica particulates having a definite temperature,
