CEMENT “Cement is a crystalline compound of calcium silicates and other calcium compounds having hydraulic properties” properties” (Macfadyen, 2006). Cements are considered hydraulic because of their ability to set and harden under or with excess water through the hydration of the cement’s chemical compounds or minerals. There are two types which those that activate with the addition of water and pozzolanic that develop hydraulic properties when interact with hydrated lime Ca(OH)2.
Type of cements Types of cement
Composition
Purpose
Rapid Hardening Cement
Increased lime content
Attains high strength in early days it is used in concrete where form work are removed at an early stage.
Quick setting cement
Small
percentage
aluminium accelerator
sulphate and
of Used as
in
works
is
to
be
an completed in very short period
reducing and concreting in static and
percentage of gypsum with running water. fine grinding Low heat cement
Manufactured by reducing tri- It is used in massive concrete calcium aluminate
Sulphates resisting cement
construction like gravity dams
It is prepared by maintaining It is used in construction the percentage of tricalcium exposed to severe sulphate aluminate below 6% which action by water and soil in increases sulphates
power
against places
like
culverts,
canals
linings,
retaining
walls,
siphons etc. Blast furnace slag cement
It is obtained by grinding the It
can
clinkers with about 60% slag economic
used
for
works
consideration
is
and resembles more or less in predominant. properties of Portland cement High alumina cement
It is obtained by melting It is used in works where mixture of bauxite and lime concrete is subjected to high and grinding with the clinker temperature, frost, and acidic it is rapid hardening cement action. with initial and final setting time of about 3.5 and 5 hours respectively.
White cement
It
is
prepared
from
raw It is more costly and is used
materials free from iron oxide.
for architectural purposes such as pre-cast curtain wall and facing panels, terrazzo surface etc.
Coloured cement
It is produced by mixing They are widely used for mineral
pigments
with decorative works in floors.
ordinary cements. Pozzolanic cement
It is prepared by grinding It is used in marine structures, pozzolanic
clinker
with sewage works, and for laying
Portland cement
concrete under water such as bridges, piers dams etc.
Air entraining cement
It is produced indigenous
by
air
adding This type of cement is special
entraining suited
agents such as resins, glues,
to
improve
the
workability with smaller water
sodium salts of sulphates etc cement ratio and to improve during the grinding of clinker. Hydographic cement
frost resistance of concrete.
It is prepared by mixing water This repelling chemicals
cement
has
workability and strength.
high
http://theconstructor.org/building/building-material/cement/types-of-cement-compositionuses/5974/ Copyright 2015 The Constructor Civil Engineering Home
Raw Material of Cement
The raw materials needed to produce cement (calcium carbonate, silica, alumina and iron ore) are generally extracted from limestone rock, chalk, clayey schist or clay. Suitable reserves can be found in most countries. The raw materials are extracted from the quarry by blasting. They are then crushed and transported to the plant where they are stored and homogenized. They’re been heated at high temperature form a rock-like substance that is ground into the fine po wder. http://www.lafarge.com.ng/wps/portal/ng/2_2_1-Manufacturing_process 2016 Lafarge
Manufacture Process of Cement
Cement is the basic ingredient of construction and the most widely used construction material. It is a very critical ingredient because only cement has the ability of enhancing viscosity of concrete which in returns provides the better locking of sand and gravels together in a concrete mix. A) Manufacture Phase Production of cement completes after passing of raw materials form the following six phases. 1. Raw material extraction / Quarry 2. Grinding, proportioning and blending 3. Pre-heater phase 4. Kiln phase 5. Cooling and final grinding 6. Packing and shipping
Phase 1: B) Phase 1: Raw Material Extraction Generally cement plants are fixed where the quarry of limestone (raw material) nearby. This saves the extra fuel cost and makes cement somehow economical. Raw materials are extracted from the quarry and by mean of conveyor belt material is transported to the cement plant. There are also various other raw materials used for cement manufacturing. For example shale, fly ash, mill scale and bauxite. These raw materials are directly brought from other sources because of small requirements. Before transportation of raw materials to the cement plant, large size rocks are crushed into smaller size rocks with the help of crusher at quarry. Crusher reduces the size large rocks to the size of gravels.
Figure 1: Extraction of raw material and crushing material
C) Phase 2: Proportioning, Blending and Grinding
The raw materials from quarry are now routed in plant laboratory where, they are analyzed and proper proportioning of limestone and clay are making possible before the beginning of grinding. Generally, limestone is 80% and remaining 20% is the clay.
Then, the cement plant grind the raw mix with help of heavy wheel type rollers and rotating table. Rotating table rotates continuously under the roller and brought the raw mix in contact
with the roller. Roller crushes the material to a fine powder and finishes the job. Raw mix is stored in a pre-homogenization pile after grinding raw mix to fine powder.
Figure 2: Proportioning of raw material at plant ce ment laboratory
D) Phase 3: Pre-heating Raw Material
After final grinding, the material is ready to face the pre-heating chamber. Pre-heater chamber consists of series of vertical cyclone from where the raw material passes before facing the kiln. Pre-heating chamber utilize the emitting hot gases from kiln. Pre-heating of the material saves the energy and make plant environmental friendly.
Figure 3: Preheating of raw material
E) Phase 4: Kiln Phase
Kiln is a huge rotating furnace also called as the heart of cement making process. The raw material is heated up to 1450oC. This temperature begins a chemical reaction so called decarbonation. In this reaction material (limestone) releases the carbon dioxide. High temperature of kiln makes slurry of the material. Kiln is heating up from the exit side by the use of natural gas and coal. When material reaches the lower part of the kiln, it forms the shape of clinker.
Figure 4: Rotary kiln
F) Phase 5: Cooling and Final Grinding
After passing out from the kiln, clinkers are cooled by mean of forced air. Clinker release the absorb heat and cool down to lower temperature. Released heat by clinker is reused by recirculating it back to the kiln. This too saves energy.
Figure 5: Clinker cooler
Then, final grinding. There is a horizontal filled with steel balls. Clinker reach in this rotating drum after cooling. The steel balls tumble and crush the clinker into a very fine powder. This fine powder considered as the cement. During grinding gypsum is also added to the mix in small percentage that controls the setting of cement.
Figure 6: Rotating ball mill
G) Phase 6: Packing and Shipping Material is directly conveyed to the large storage tanks of cement from grinding mills. Further, it is packed to about 20-40kg bags. Only a small percent if cement is packed in the bags only for those customers whom need is very small. The remaining cement is shipped in bulk quantities by mean of trucks, rails or ships.
Figure 7: Transportation of cement from storage tanks
H) Manufacture Process Cement Flow Chart
http://www.engineeringintro.com/uncategorized/cement-manufacturing-process/ 30 August 2012 Jalal Asfar
GYPSUM PRODUCT
Gypsum is an evaporite mineral most commonly found in layered sedimentary deposits in association with halite, anhydrite, sulfur, calcite, and dolomite. Gypsum (CaSO4 2H2O) is very
similar to Anhydrite (CaSO4). The chemical difference is that gypsum contains two waters and anhydrite is without water. Gypsum is the most common sulfate mineral. Varieties of gypsum known as satin spar and alabaster are used for a variety of ornamental purposes. However, their hardness limits their durability.
Gypsum rock is slightly soluble in water it not usually found above ground in wet or damp areas, but may be found underground, where it is not affected by the water table. The presence of gypsum on or just below the surface of the ground is often indicated by changes in vegetation; some plants thrive on gypsum-rich (alkaline) soil where as others are not at all tolerant those conditions.
Gypsum rock is usually white or colorless, although it may sometimes have grey, yellow, pink or brown hues. Gypsum is much softer than minerals of similar colour, such as calcite or quartz and is the only one that can be scratched with a fingernail. If a piece of gypsum rock is held over a flame it will turn cloudy and op aque and give off water.
Gypsum is also produced as a by-product of the phosphate fertilizer industry, but in some cases this is slightly radioactive and little use is made of it at present, except as an additive in the manufacture Portland cement. Most recently by-product gypsum is also available from flue gas desulphurization which a process for cleaning up emissions from chimneys to reduce the quantity of sulphurous gases flowing into atmosphere.
ftp://ftp.shef.ac.uk/pub/uni/academic/A-C/ar1mb/PA_GypsumProcessingAndUse.pdf
Uses of Gypsum
1. Manufacture of wallboard 2. Cement 3. Plaster 4. Soil conditioning 5. Hardening retarder Portland cement
http://geology.com/minerals/gypsum.shtml 2005-2016 Geology.com
Manufacture Process of Gypsum Products (Board)
1. Raw material High quality gypsum rock is extracted at quarries or mines near plants or transported by cargo ship, rail or truck.
2. Crusher Large rocks are crushed into small pieces. At some plants, the crushed rock undergoes a surface drying process before going to the grinding mill.
3. Grinding mill The mill reduces small rocks to a very fine, chalk-like powder called land plaster.
4. Calcine system The land plaster is heated in large kettles to remove most the water from the plaster.
5. Stucco Holding Tank Calcined land plaster called stucco is fed from a holding bin to the mixer by a screw conveyor.
6. Mixer In the mixer, water is added back to the stucco to form a slurry and foam is added to the slurry to make the wallboard more lightweight.
7. Forming station The board forming line starts with two large rolls of recycled paper or fiberglass mats. The slurry is poured onto the bottom sheet and is immediately covered by facing sheet from the other roll. This “sandwich” passes through a pair of forming plates or rolls which determine the thickness of the board. The face paper or mat wraps around the sides of the sandwich to enclose the edges of the board.
8. Board line The board line travels down a long conveyor line in a single continuous piece. During this trip, water rehydrates the stucco, causing it to harden.
9. Cut-off knife At the end of the line, a blade cuts the hardened board into various lengths.
10. Transfer table Here the cut lengths are turned face-side up to protect the face or mat, then fed into the kiln.
11. Kiln The board kiln completes the drying process, leaving the gypsum board virtually moisture-free.
12. Bundler and stacker The bundler “books” the gypsum board by putting two pieces together with the face on the inside. It is trimmed to exact lengths and the pairs of boards are taped together to further protect the board face. The bundles are stacked for transfer to the warehouse for shipping to customers.
Manufacture Process of Gypsum Board Flow Chart
http://www.buildgp.com/DocumentViewer.aspx?repository=BP&elementid=10257
2010
Georgia Pacific Gypsum LLC
QUARTZ SAND
Quartz is a chemical compound consisting of one part silicon and two parts oxygen. It is silicon dioxide (SiO2). It is the most abundant mineral found at Earth’s surface and its unique properties make it one of the most useful natural substances. Quartz is the most abundant and widely distributed mineral found at Earth’s surface. It is present and plentiful in all parts of the world. It forms at all temperatures. It is abundant in igneous, metamorphic and sedimentary rocks. It is highly resistant to both mechanical and chemical weathering. This durability makes it the dominant mineral mountaintops and the primary constituent of beach, river and desert sand. Quartz is ubiquitous, plentiful and durable.
Uses of Quartz
1. The most useful natural materials.
2. Has a hardness of seven on the Mohs Scale which makes it very durable. 3. Chemically inert in contact with most substance. 4. Has electrical properties and heat resistance. 5. Its luster, colour and diaphaneity make it useful as a gemstone and making glass.
Uses Quartz in Glass making
Geological processes have occasionally deposited sands that are composed of almost 100% quartz grains. These deposits have been identified and produced as sources of high purity silica sand. These sands are used in the glassmaking industry. Quartz sand is used in the production of container glass, flat plate glass, specialty glass and fiberglass. Quartz sand particles are colorless or slightly pink, while feldspar sand has a pink or amber color. When quartz sands are crushed they produce particles with sharp, angular edges that are sometimes used to make sandpaper for smoothing wood. Some quartz sand is found in the form of sandstone.
http://geology.com/minerals/quartz.shtml 2005-2016 Geology.com
Manufacture of Glass (Quartz Sand)
1. The raw material include the used glass, are weighed and mixed to the right proportions and transported by conveyor belt to the furnace. Precise adjustments and corrections to the mix are necessary owing the ration of used glass with its ever-fluctuating composition.
2. Forming glass Glass container manufacture is a high temperature process which the raw materials are melted into glass at 1590oC which flows via a series of channels to the glass forming machine. The glass forming machine portions off single drops from the constant flow of glass. There are then fed into various processing stations.
3. Quality assurance and Packaging Every single one of the 10 million glass containers produced daily is tested for compliance with prescribed quality characteristic by a series of linked d evices.
http://de.verallia.com/en/about-glass/glass-production 2010-2016 Verallia
