Portland Cement
History: Portland cement was developed from natural cements made in Britain in the early part of the 19th
century, and its name is derived from its similarity to Portland stone, a type of building stone that was
quarried on the Isle of Portland in Dorset, England. The Portland cement is considered to originate from joseph
aspdin, British bricklayer from Leeds. Though it was one of his employees (Isaac Johnson) who developed the
production technique, which resulted in more fast-hardening cement with a higher compressive strength. This
process was patented in 1824. His cement was artificial cement similar in properties to the material known as
"Roman cement" (patented in 1796 by James Parker) and his process was similar to that patented in 1822
and used since 1811 by James Frost who called his cement "British Cement". The name "Portland cement" is
also recorded in a directory published in 1823. Aspdin's son William, in 1843, made an improved version of this
cement and he initially called it "Patent Portland cement" although he had no patent. In 1848 William Aspdin
further improved his cement and in 1853 he moved to Germany where he was involved in cement making.It is
generally accepted that it was first manufactured by William Aspdin at Northfleet, England in about 1842. The
German Government issued a standard on Portland cement in 1878
Portland cement is the most common type of cement in general use around the world because it is a basic
ingredient of concrete, mortar, stucco and most non-specialty grout. It is a fine powder produced by grinding
Portland cement clinker (more than 90%), a limited amount of calcium sulfate (which controls the set time)
and up to 5% minor constituents. Portland cement clinker is a hydraulic material which shall consist of at least
two-thirds by mass of calcium silicates (3CaO.SiO2 and 2CaO.SiO2), the remainder consisting of aluminium-
and iron-containing clinker phases and other compounds. The ratio of CaO to SiO2 shall not be less than 2.0.
The magnesium content (MgO) shall not exceed 5.0% by mass.ASTM C 150 defines Portland cement as
"hydraulic cement i.e cement that not only hardens by reacting with water but also forms a water-resistant
product Portland cement.A homogeneous mixture of raw materials to a sintering temperature, which is about
1450 °C for modern cements.
The raw materials for Portland cement production are a mixture of minerals containing calcium oxide, silicon
oxide, aluminium oxide, ferric oxide, and magnesium oxide, as fine powder in the 'Dry process' or in the form
of a slurry in the 'Wet process'. The raw materials are usually quarried from local rock, which in some places is
already practically the desired composition and in other places requires the addition of clay and limestone, as
well as iron ore, bauxite or recycled materials. The individual raw materials are first crushed, typically to below
50 mm. In many plants, some or all of the raw materials are then roughly blended in a "prehomogenization
pile." The raw materials are next ground together in a rawmill. Silos of individual raw materials are arranged
over the feed conveyor belt. Accurately controlled proportions of each material are delivered onto the belt by
weigh-feeders. Passing into the rawmill, the mixture is ground to rawmix. The fineness of rawmix is specified in
terms of the size of the largest particles, and is usually controlled so that there are less than 5-15% by mass of
particles exceeding 90 μm in dia. It is important that the rawmix contain no large particles in order to complete
the chemical reactions in the kiln, and to ensure the mix is chemically homogeneous. In the case of a dry
process, the rawmill also dries the raw materials, usually by passing hot exhaust gases from the kiln through
the mill, so that the rawmix emerges as a fine powder.
