Lesson 7 - Cement Flashcards
a binder, a substance that sets and
hardens and can bind other materials together.
cement
is a mixture of calcareous, siliceous,
argillaceous and other substances.
cement
is the principal binding material of
modern time.
cement
COMPONENTS OF CEMENT
SiO2 content (%) (Silica) 17-25%
Al2O3 content (%) (Alumina)
3-8%
Fe2O3 content (%) (Iron oxide) 0.5-6%
CaO content (%) (lime) 60-67%
Gypsum (Calcium Sulphate)
1-4%
Specific gravity 3.15
General use in concrete Primary binder
the most common type of cement in
general use around the world, used as a basic ingredient of
concrete and mortar.
Portland cement
FUNCTIONS OF CEMENT MANUFACTURING CONSTITUENTS
(i) Lime (CaO)
(ii) Silica (SiO2)
(iii) Alumina (Al2O3)
(iv) Iron Oxide (Fe2O3)
(v) Magnesia (MgO)
(vi) Calcium Sulphate (or) Gypsum (CaSO4)
forms nearly two-thirds (2/3) of the cement.
Therefore, a sufficient quantity of it must be in the raw materials for the manufacturing of
cement.
Lime (CaO)
Its proportion has an important effect on the cement. Sufficient quantity of di-calcium silicate (C2SiO2) and tri-calcium silicate in the manufacturing of cement.
Lime (CaO)
in excess, causes the cement to expand and disintegrate.
Lime (CaO)
It gives strength to the
cement. Excess causes the cement to set slowly.
Silica (SiO2)
The quantity of silica should be LOWER to form di-calcium silicate and tri-calcium silicate in the manufacturing of cement.
False (IT should be enough)
supports to set quickly to
the cement. It also lowers the
clinkering temperature. Excess reduces the strength of the cement.
Alumina (Al2O3)
IT gives color to the
cement. It gives hardness and strength to the cement.
Iron Oxide (Fe2O3)
It also helps in giving color to the cement. excess makes the cement unsound.
Magnesia (MgO)
At the final stage of manufacturing, it is added to increase the setting of cement.
Calcium Sulphate (or Gypsum) (Ca SO4)
HYDRATION PRODUCTS FORMED IN IT ARE MORE COMPLICATED, BECAUSE MANY OF THESE PRODUCTS HAVE
NEARLY THE SAME FORMULA AND SOME ARE SOLID-SOLUTIONS WITH
OVERLAPPING FORMULA.
HARDENED CEMENT PASTES (HCP)
is accomplished by using explosives to blast the rocks
from the ground. After blasting, Excavators (or power shovels) are used to load dump
trucks or small railroad cars for transportation to the cement plant, which is usually
nearby.
Quarrying, Dredging, and Digging
After the raw materials have been transported to the plant, the limestone and shale
which have been blasted out of the quarry must be crushed into smaller pieces. Some of the pieces, when blasted out, are quite large. The pieces are then dumped into primary crushers which reduce them to the size of a softball.
Grinding
In this process, the raw materials are changed to powdered form in the presence of water.
WET PROCESS
In this process, raw materials are pulverized by using a Ball mill, which is a rotary steel
cylinder with hardened steel balls.
WET PROCESS
- This process is generally used when raw materials are soft because complete mixing is
not possible unless water is added. Actually the purpose of both processes is to change the raw materials to fine powder.
WET PROCESS
In this process calcareous material such as lime stone (calcium carbonate) and
argillaceous material such as clay are ground separately to fine powder in the absence of water and then are mixed together in the desired proportions.
DRY PROCESS
This process is usually used when raw materials are very strong and hard.
DRY PROCESS
In this process, the raw materials are changed to powdered form in the absence of water.
DRY PROCESS
After the rock is crushed, plant chemists analyze the rock and raw materials to determine their mineral content. The chemists also determine the proportions of each raw material to utilize in order to
obtain a uniform cement product. The various raw materials are then mixed in proper proportions and prepared for fine grinding.
Blending
The wet or dry mix is fed into the kiln, which is one of the
largest pieces of moving machinery in the industry. It revolves on large roller bearings and is gradually slanted with the intake end higher than the output end.
As the kiln revolves, the materials roll and slide downward for approximately four hours.
Burning
used for the pyroprocessing stage of manufacture of Portland and other types
of hydraulic cement , in which calcium carbonate reacts with silica-bearing minerals to form a mixture of calcium silicates.
Cement kilns
is the solid material produced by the cement kiln stage that
has sintered into lumps or nodules, typically of diameter 3-25 mm.
Clinker
Known as common or general-purpose cement. It is generally assumed unless another type is specified. It is commonly used for general construction especially when making precast and precast-prestressed concrete that is not to be in contact with soils or ground water.
Type I
IT gives off less heat during hydration. This type is for general construction exposed to moderate sulfate attack and is meant for use when concrete is in contact with soils and ground water, especially in the western United States due to the high sulfur content of the soils.
Type II
It has relatively high early strength. This cement is similar to type I, but ground finer. Some manufacturers make a separate clinker with higher C3S and/or C3A content, but this is increasingly rare, and the general purpose clinker is usually used, ground to a
specific surface area typically 50–80% higher.
Type III
It is generally known for its low heat of hydration. A limitation on this type is that
the maximum percentage of (C3A) is seven, and the maximum percentage of (C3S) is thirty-five. This causes the heat given off by the hydration reaction to develop at a slower rate. However, as a consequence the strength of the concrete develops slowly.
Type IV
used where sulfate resistance is important. This type is used in concrete to be exposed to alkali soil and ground water
sulfates which react with (C3A) causing disruptive expansion. It is unavailable in many
places, although its use is common in the western United States and Canada.
Type V
defines five classes of common cement that comprise Portland cement as a main constituent.
These classes differ from the ASTM classes.
EN 197
TYPES OF CEMENT:
- Ordinary Portland Cement
- Sulphate Resisting Cement
- Rapid Hardening Cement (or) High
Early Strength cement - Quick Setting Cement
- Low Heat Cement
- High Alumina Cement
- Air Entraining Cement
- White Cement
It is the variety of artificial cement. Hardening (setting) its colour resembles to rocks near Portland in England. It was first of all introduced in 1824 by Joseph Asp din, a bricklayer of Leeds, England.
ORDINARY PORTLAND CEMENT
This cement requires longer period of curing. This cement is used for hydraulic structures in alkaline water and for canal and water courses lining. It develops strength slowly, but ultimately it is as strong as O.P.C.
SULPHATE RESISTING CEMENT
