CEMENT MANUFACTURECHE 432 INDUSTRIAL PROCESS

Definition for cement:Finely ground material formed by addition of water, binding paste capable of hardening under water or air and binding together particulate materials

Cement and concrete not synonymous termsConcrete artificial stone made from a carefully controlled mixture of cement, water, and fine and coarse aggregate (usu. Sand and coarse rock)

HistoryCement used by Egyptians to construct Pyramids.Greek and Romans used volcanic tuff mixed with lime for cement 1824, Joseph Aspdin patented artificial cement made by calcinations of an argillaceous limestone.

Advantages:ConvenienceLow costAdaptabilityStrengthDurability

FunctionsBuildingsTunnelsDamsRoadsDecoration purposes

Portland cementsDefinition: product obtained by pulverising clinker consisting essentially of hydraulic calcium silicates.Insuitable for corrosive conditions esp. sea water conditions5 types of portland cement: Type I : regularType II : Moderate-heat-of hardening and sulfate-resistingType III : High-early-strengthType IV : Low-heat Type V : Sulfate-resisting

Production of Portland cementCement clinker produced by wet and dry processesWet process displaced by dry process because saving in heat, accurate control and mixing of raw mixtures

Production of Portland cementRaw materials preparationTwo types of materials: a) calcium (75%) eg. Limestone, chalkb) Silica eg. ClayOther compounds added eg. Sand, waste bauxite and iron ore to adjust composition, gypsum (4-5%) added to regulate setting time of cement.

blastedLimestone + clay quarries (25mm 1.2m)

storage yard crusher (30 mm)Bauxite, iron ore, coal and gypsum unloaded from ships/ barges storage yards

2. Raw material grinding weighed, mixedRaw material grinding mills drying & coarse grinding particles

homogenizing dynamic silo separators usg. air

3. Clinker burningFormation of clinker important process in cement manufactureDry powdered material fed to rotary kilns During burning various rxns take place: evaporation of water, evolution of CO2, reaction between lime and clayFinal product: Hard regular masses of 3 to 20 mm in sizeClinker discharged from kilns (800oC) into coolers (100oC 200oC)

4. Cement grindingFinal stage of grinding clinker and adding setting retarders eg. gypsum, plaster etc.Resulting in cement packed into bags or bulk cement lorries

Pollution Control:Main pollutant dust particlesEquipment used: electrostatic precipitators, gravel bag filters, dust collectors and water spray

Other CementsPozzolans : grinding 2 to 4 parts of pozzolan with 1 part of hydrated limeInhibit cementitious behaviour but becomes so on mixing with limeAdvantage: resists corrosive action of saline solutions and seawater

High alumina cementsFusing mixture of limestone and bauxiteAdvantage: rapid rate of development of strength and superior resistance to seawater and sulfate bearing water

Silicate cementsResist all inorganic acids except HFNot suitable for pH > 7 or crystal forming systems2 parts of silica powder to 1 part sodium silicate

Sulfur cementsResistant to nonoxidizing acids and salts Not applicable for alkalies, oils, greases or solventsCrystalline change in sulfur structure at 93oC limits usage

Polymer concreteConsists of aggregate resins eg. Epoxy or polyesterResins imparts properties eg. Rapid curing, corrosion resistance or high compressive strength

Pictorial flow diagram establishes key processing steps: Cement manufacture