Page 38 - Curriculum Visions Dynamic Book

(Above and below) Mortar is a combination of sand and cement.
The first hydraulic (water-setting) cement was developed by John Smeaton, a famous English 18th-century builder of lighthouses. It was made by burning clayey limestone (a natural mixture of lime and clay minerals).
Portland cement was first made in 1824 in the kitchen of a British stone mason, Joseph Aspdin in Leeds. His was the first cement made from different materials mixed together rather than relying on naturally occurring mixtures. He heated a blend
of finely ground limestone and clay in his kitchen cooker and ground the mixture into a powder. Aspdin named the product Portland cement because
it resembled the pale-grey limestone quarried at Portland in Dorset, England.
Portland cement is a mixture of lime (calcium oxide, CaO), silica (silicon dioxide,
SiO2), and alumina (aluminium oxide, Al2O3). Small quantities of iron oxide, bauxite (aluminium oxide), and other ingredients may also be added.
The raw materials are limestone, shells or chalk, shale, clay, sand, or iron ore. At the quarries the
raw materials are crushed by primary and secondary crushers down to 19mm across.
At the cement plant the raw materials are mixed together in the correct proportions either dry or as a muddy liquid (slurry). The mixture of raw materials is then fed into the upper end of a tilted rotating cylindrical kiln. The mixture goes through the kiln. Powdered coal or natural gas is forced into the lower end of the kiln and ignited.
Inside the kiln raw materials heat up, and a series of chemical reactions occurs. This is
what produces “clinker” – dark-grey pellets that look like marbles. Cooled clinker is
combined with gypsum and ground into a fine grey powder. The fine grey
powder is Portland cement.
(Below) Once mixed with water, the mortar forms a stiff paste.
(Below) Within a day the mortar has hardened into a hard rocklike substance.
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