The Influence of Grinding Method on the Particle Size …
141
Results of tests show that the content of pozzolanic additives in concrete increases
the concrete strength at a later curing period. It is an effect of C-S-H phase formation
as a result of the pozzolanic reaction [12]. The use of mineral additives to cement
also causes reduction of porosity of hardened cement pastes. Tests demonstrate that
pastes with mineral additives had lower porosity than those made of the Portland
cement. In addition, porosity is even lower in case of pozzolanic additives, where
reduction of pore diameters is also observed [12].
Concretes, in particular special concretes (e.g. HPC, SCC) require a large quantity
of a binder, which significantly raises costs of their production, and in consequence it
also has a negative impact on the environment. As it is commonly known, concretes
with the high content of the Portland cement are also more sensitive to shrinkage
cracking. A solution for this problem is application of proper mineral additives, such
as blast furnace slags, fly ash or fillers such as limestone powder or stone powder [17].
Mineral additives mentioned above have also a beneficial impact on consistency and
workability of the concrete mix, process of cement hydration, and in consequence
on properties of the hardened concrete [18].
According to classification given in PN-EN 196-1 standard, there are cements
marked as CEM II, containing up to 35% of the mineral additive, CEM III (blastfurnace cement) with addition of ground granulated blast furnace slag in the amount
from 35% up to even 95 wt% of cement. CEM IV cements contain mineral additives
of pozzolanic properties, while CEM V cements may contain up to 60% of various
mineral additives.
Silica fumes are a by-product during production of silicon metal, especially iron
and silicon alloys in electric arc furnaces in very high temperatures (2500–2800 °C).
Silica fumes are amorphous substance (approx. 85% of amorphous phase) consisting
of very fine particles. The average size of particles is ca. 0.2 µm. The specific surface
area of silica fume is larger by one order of magnitude than the specific surface area
of the cement [19].
Due to the content of amorphous silica as the mineral additive to concrete, silica
fumes show very strong pozzolanic properties [20]. The silica in reaction with the
calcium hydroxide causes formation of C-S-H phase (responsible for the strength)
and in consequence the gradual growth of the strength of the concrete made this way
[20].
Unique properties of silica fume also have a significant impact on properties of the
fresh concrete mix. They increase the cohesion which resist segregation of concrete
ingredients. Silica fumes also cause limitation of so-called bleeding, i.e. water and
fine fractions flowing out of the concrete mix [21–23].
A popular mineral additive used in the cement production is the fly ash. It is
obtained as a by-product in coal fired power plants. Over 80% of unburned carbon
particles leave the furnace together with flue gas. They are collected in result of dust
separation by means of electrostatic or mechanical processes. In majority they have
a spherical shape with dimensions not exceeding 200 µm [19, 20].
Addition of fly ashes increases flowability of the concrete mix without raising its
production costs. It also allows to reduce hydration heat in the concrete built in [24].
Fly ash that raises the concrete strength contains significant quantities of silicon and
141
Results of tests show that the content of pozzolanic additives in concrete increases
the concrete strength at a later curing period. It is an effect of C-S-H phase formation
as a result of the pozzolanic reaction [12]. The use of mineral additives to cement
also causes reduction of porosity of hardened cement pastes. Tests demonstrate that
pastes with mineral additives had lower porosity than those made of the Portland
cement. In addition, porosity is even lower in case of pozzolanic additives, where
reduction of pore diameters is also observed [12].
Concretes, in particular special concretes (e.g. HPC, SCC) require a large quantity
of a binder, which significantly raises costs of their production, and in consequence it
also has a negative impact on the environment. As it is commonly known, concretes
with the high content of the Portland cement are also more sensitive to shrinkage
cracking. A solution for this problem is application of proper mineral additives, such
as blast furnace slags, fly ash or fillers such as limestone powder or stone powder [17].
Mineral additives mentioned above have also a beneficial impact on consistency and
workability of the concrete mix, process of cement hydration, and in consequence
on properties of the hardened concrete [18].
According to classification given in PN-EN 196-1 standard, there are cements
marked as CEM II, containing up to 35% of the mineral additive, CEM III (blastfurnace cement) with addition of ground granulated blast furnace slag in the amount
from 35% up to even 95 wt% of cement. CEM IV cements contain mineral additives
of pozzolanic properties, while CEM V cements may contain up to 60% of various
mineral additives.
Silica fumes are a by-product during production of silicon metal, especially iron
and silicon alloys in electric arc furnaces in very high temperatures (2500–2800 °C).
Silica fumes are amorphous substance (approx. 85% of amorphous phase) consisting
of very fine particles. The average size of particles is ca. 0.2 µm. The specific surface
area of silica fume is larger by one order of magnitude than the specific surface area
of the cement [19].
Due to the content of amorphous silica as the mineral additive to concrete, silica
fumes show very strong pozzolanic properties [20]. The silica in reaction with the
calcium hydroxide causes formation of C-S-H phase (responsible for the strength)
and in consequence the gradual growth of the strength of the concrete made this way
[20].
Unique properties of silica fume also have a significant impact on properties of the
fresh concrete mix. They increase the cohesion which resist segregation of concrete
ingredients. Silica fumes also cause limitation of so-called bleeding, i.e. water and
fine fractions flowing out of the concrete mix [21–23].
A popular mineral additive used in the cement production is the fly ash. It is
obtained as a by-product in coal fired power plants. Over 80% of unburned carbon
particles leave the furnace together with flue gas. They are collected in result of dust
separation by means of electrostatic or mechanical processes. In majority they have
a spherical shape with dimensions not exceeding 200 µm [19, 20].
Addition of fly ashes increases flowability of the concrete mix without raising its
production costs. It also allows to reduce hydration heat in the concrete built in [24].
Fly ash that raises the concrete strength contains significant quantities of silicon and