pozzolans - mert yücel...
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Materials of Construction-Pozzolans 1
Pozzolans
Chapter 07
Wikipedia.org
Materials of Construction-Pozzolans 2
Pozzolan - Historical background
The oldest concrete-like material discovered so
far is in a place on the halfway between Tel-Aviv
(capital of Israel) and Ramallah (a city in Palestine)
and dates from about 7000 BC.
Remains of a wall of a Natufian house
It was used for flooring, and consists of quicklime, made by burning limestone, mixed with water and stone which set into a hardened material.
Construction materials – IIlston & Domone
Materials of Construction-Pozzolans 3
Pozzolan – Historical background
Mortars made from lime, sand and gravels dating from about 5000 BC. have been found in Western Europe, and similar mixtures were used by the ancient Egyptians and Greeks some three to four thousand years later.
Early concrete-like materials produced by
Romans were also of this type, but during the second century BC, it was the Romans who first made hydraulic binders, i.e. one which reacts chemically with the mix water, and is therefore capable of hardening under water and is subsequently insoluble.
Construction materials – IIlston & Domone
Materials of Construction-Pozzolans 4
Pozzolan – Historical background
The binding material (cement at that time) was a mixture of lime and volcanic ash from a source near Pozzuoli, a small town near Vesuvius Volcano, Italy.
This ash contained silica and and alumina in an active form which combined chemically with the lime; the term pozzolana is still used to describe such materials.
Construction materials – IIlston & Domone
Materials of Construction-Pozzolans 5
Pozzolan – Historical background
The dome of the Pantheon seen
from the hill of Janiculum
Mortars produced by combining binding material with aggregates were used in many of the great Roman structures, for example in the foundations and columns in aquaducts, and, in combination with pumice (a lightweight aggregate) in the arches of the Colosseum and in the dome of the Pantheon in Rome.
Construction materials – IIlston & Domone
Materials of Construction-Pozzolans 6
Pozzolan
Pozzolan is a siliceous or siliceous and aluminous material, which in itself possesses little or no cementitious value but will, in finely divided form and in the presence of moisture, react with calcium hydroxide to form compounds having hydraulic cementitious properties.
In addition to high silica and alumina contents, pozzolans contain small amounts of iron oxide, calcium oxide, magnesium oxide, and alkalies.
The artificial pozzolans contain some amount of carbon.
Materials of Construction-Pozzolans 7
Classification of Pozzolans
Natural: Volcanic ash, volcanic tuff,
pumicite, diatomaceous earth...
Artificial: Fly ash, silica fume, blast
furnace slag, burned clay….
Materials of Construction-Pozzolans 8
Volcanic Ash, volcanic tuff
Volcanic ashes are bits of pulverized rock and glass created by volcanic eruptions, less than 2 millimetres in diameter.
After falling to the ground after the eruption, the ash deposited on the ground becomes known as an ashfall. Ashfall may become cemented together to form a solid rock called tuff.
Composed of mainly alumino silicates, quick cooling of magma results in amorphous phases.
Materials of Construction-Pozzolans 9
Pumicite (Pumice)
Pyroclastic, highly
porous, amorphous,
lightweight material
Materials of Construction-Pozzolans 10
Diatomaceous Earth
Diatomaceous earth
consists of fossilized
remains of diatoms,
a type of hard-
shelled algae.
These organic
residuals can lead to
silica contents up to
94%.
Materials of Construction-Pozzolans 11
Artificial Pozzolans
Fly Ash: a by-product from the burning
of pulverized coal in power plants.
Silica fume: (often called microsilica)
extremely fine particles of silica
condensed from the waste gases given off
in the production in silicon metal industry
Materials of Construction-Pozzolans 12
• Granulated blast furnace slag (GBFS)
obtained by rapid cooling of slag that is a
by-product of pig iron production.
• Burned (calsined) clay or shale
A clay or shale heated, and rapidly cooled
and ground.
• Rice husk ash
obtained by burning rice husks
Artificial Pozzolans
Materials of Construction-Pozzolans 13
Pozzolanic Reactions
Silis + Calcium Hydroxide + Water → Calcium-Silicate-Hydrate
(C-S-H)
C-S-H provides the hydraulic binding property of the
material.
Pozzolanic Activity: Capacity of pozzolan to form
alumino-silicates with lime to form cementitious
products.
Materials of Construction-Pozzolans 14
Factors Affecting Pozzolanic
Activity
1) SiO2 + Al2O3 + Fe2O3 content
2) The degree of amorphousness of its
structure
3) Fineness of its particles
Materials of Construction-Pozzolans 15
SiO2 + Al
2O
3 + Fe
2O
3
The greater amount of these, the greater its activity.
ASTM C 618 & TS 25 → SiO2+Al2O3+Fe2O3 for natural pozzolans > 70%
Fly Ash - ASTM
Class C→ from lignitide or subbituminous coals (SiO2+Al2O3+Fe2O3>50%) (CaO>10%)
Class F→ from bituminous coals and SiO2+Al2O3+Fe2O3>70%
Silica fume → SiO2 ≈ 85-98%
Blast Furnace Slag→ SiO2 ~ 30-40%
Al2O3 ~ 7-19%
CaO ~ 30-50%
Materials of Construction-Pozzolans 16
Chemical Analysis of Typical Fly Ash, Slag, Silica Fume, Calcined
Clay, Calcined Shale, and Metakaolin
Class F
fly ash
Class C
fly ash GBFS
Silica
fume
Calcined
clay
Calcined
shale
Volcanic
Tuff
SiO2, % 52 35 35 90 58 50 53
Al2O3, % 23 18 12 0.4 29 20 43
Fe2O3, % 11 6 1 0.4 4 8 0.5
CaO, % 5 21 40 1.6 1 8 0.1
SO3, % 0.8 4.1 9 0.4 0.5 0.4 0.1
Na2O, % 1.0 5.8 0.3 0.5 0.2 — 0.05
K2O, % 2.0 0.7 0.4 2.2 2 — 0.4
Total Na
eq. alk, % 2.2 6.3 0.6 1.9 1.5 — 0.3
Natural Pozzolans Artificial Pozzolans
Materials of Construction-Pozzolans 17
Amorphousness
For chemical reaction → pozzolans must be amorphous
Volcanic ash, volcanic tuff, fly ash, silica fume are all amorphous by nature.
Clays → contain high amounts of silica & alumina but have a crystallic structure! (Do not possess pozzolanic activity) • However, by heat treatment, such as calcining ~700-
900°C crystallic structure is destroyed & a quasi-amorphous structure is obtained
Materials of Construction-Pozzolans 18
Amorphousness
Clay → does not possess pozzolanic property
Burned clay → possess pozzolanic property
Blast furnace slag → contain high amounts of
silica, alumina & lime.
However, if molten slag is allowed to cool in air, it
gains a crystal structure. * do not possess pozzolanic
property.
However, if it is cooled very rapidly by pouring it into
water, it becomes a granular material & gains
amorpousness. * possess pozzolanic property.
Materials of Construction-Pozzolans 19
Fineness
Pozzolanic activity increases as fineness increases.
Volcanic ash, rice husk ash, fly ash, condensed silica fume are obtained in finely divided form.
Volcanic tuff, granulated blast furnace slag & burned clay must be ground.
Materials of Construction-Pozzolans 20
Determination of Pozzolanic
Activity
Pozzolanic activity is determined by “strength
activity indexes”
Six mortar cubes are prepared (ASTM)
→”Control Mixture” 500 g portland cement+1375 g
sand+242 ml water
→”Test Mixture” 400g of portland cement+100g of
pozzolan+1375g of sand+some water for the
same consistency
Materials of Construction-Pozzolans 21
Strength Activity Index
Compressive testing at 7 or 28 days
Strength Activity Index (SAI) =A/B*100
A=f’c of test mixture
B=f’c of control mixture
ASTM C 618 → SAI ≥ 75%
Materials of Construction-Pozzolans 22
Example
Determine the 7 and 28 day SAI of a natural pozzolan (trass) using the following data. Specimens are
50 mm cubes.
The specimens are tested for each type of mixture at each testing age.
For control specimen B7-D=81000 N/2500 mm2=32.4 MPa, B28-D=116700 N/2500 mm2=46.7 MPa
For test specimen A7-D=59700 N/2500 mm2=23.9 MPa, A28-D=86700 N/2500 mm2=34.7 MPa
Thus,
7-D SAI=23.9/32.4x100=73.7%<75% Not satisfactory
28-D SAI=86.7/116.7x100=74.3%75% Satisfactory
Mixture 7-day crushing loads (kN) 28-day crushing loads (kN)
Control mixture 78, 81, 84 112, 118, 120
Test mixture 58, 60, 61 86, 86, 88
Mixture Average 7-day crushing load
(kN)
Average 28-day crushing load
(kN)
Control mixture 81 116.7
Test mixture 59.7 86.7
Materials of Construction-Pozzolans 23
Chemical Composition of
Pozzolans
Silica Fume is mostly SiO2
GBFS→ high amounts of CaO (self-
cementitious)
Class C Fly Ash has CaO (self-cementitious)
Materials of Construction-Pozzolans 24
Chemical Analysis of Typical Fly Ash, Slag, Silica Fume, Calcined
Clay, Calcined Shale, and Metakaolin
Class F
fly ash
Class C
fly ash GGBFS
Silica
fume
Calcined
clay
Calcined
shale
Volcanic
Tuff
SiO2, % 52 35 35 90 58 50 53
Al2O3, % 23 18 12 0.4 29 20 43
Fe2O3, % 11 6 1 0.4 4 8 0.5
CaO, % 5 21 40 1.6 1 8 0.1
SO3, % 0.8 4.1 9 0.4 0.5 0.4 0.1
Na2O, % 1.0 5.8 0.3 0.5 0.2 — 0.05
K2O, % 2.0 0.7 0.4 2.2 2 — 0.4
Total Na2Oeq
alk, % 2.2 6.3 0.6 1.9 1.5 — 0.3
Natural Pozzolans Artificial Pozzolans
Materials of Construction-Pozzolans 25
SILICA FUME FLY ASH
GRANULATED BLAST FURNACE SLAG
Materials of Construction-Pozzolans 26
Uses of Pozzolans
1. By mixing the finely divided pozzolan with calcium hydroxide,
2. By intergrinding pozzolan with portland cement clinker and thus producing portland-pozzolan cements (as an addition in cement production).
3. By adding the finely divided pozzolan to the concrete mixture during or before the batching operation (as a concrete admixture).
Materials of Construction-Pozzolans 27
Direct Use by Mixing Ca(OH)2
This procedure was extensively used in ancient times for producing pastes; pozzolanic concrete was obtained by including aggregate or small pieces of crushed rock in the paste.
However, this method of using is not very common at the present time (pozzolan + lime mixtures are still used in pavement subbases for small applications).
Materials of Construction-Pozzolans 28
Use of Pozzolan in Blended
Cement Production
Blended cements are produced by replacing some amount of clinker with a pozzolan, and grinding the "clinker + pozzolan + gypsum" together.
When the blended cement is mixed with water, the PC portion of it immediately starts to hydrate, so the calcium silicate compounds in the portland cement portion of the blended cement begin to produce calcium-silicate hydrate and calcium hydroxide.
The function of pozzolan in blended cement begins with the production of calcium hydroxide due to the hydration of calcium silicate compounds of the portland cement portion. The pozzolan reacts with this calcium hydroxide and thus new calcium-silicate-hydrate gels are produced.
Materials of Construction-Pozzolans 29
Use of Pozzolan as a Mineral
Admixture for Concrete
Fly ash, ground granulated blast-furnace slag and ground natural pozzolans are commonly used mineral admixtures for concrete. In making concrete, usually 30 to 50% by weight of the cement is replaced with mineral admixtures, and a pozzolanic concrete is obtained by mixing the "cement + pozzolan + aggregates + water" together.
In pozzolanic concrete (similar to blended cements) pozzolan reacts with calcium hydroxide produced upon hydration of calcium-silicate compounds of portland cement and provides additional calcium-silicate hydrate.
The use of finely divided mineral admixtures improves many properties of the fresh and hardened concrete; it provides economy.