Building Techoclogy » Portland cement

Portland cement

blogtopia — Wed, 03 Jun 2009 06:27:25 +0000

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 (as allowed by various standards).

As defined by the European Standard EN197.1, "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." (The last two requirements were already set out in the German Standard, issued in 1909).

Portland cement clinker is made by heating, in a kiln, a homogeneous mixture of raw materials to a sintering temperature, which is about 1450 °C for modern cements. The aluminium oxide and iron oxide are present as a flux and contribute little to the strength. For special cements, such as Low Heat (LH) and Sulfate Resistant (SR) types, it is necessary to limit the amount of tricalcium aluminate (3CaO.Al2O3) formed.

The major raw material for the clinker-making is usually limestone (CaCO3) mixed with a second material containing clay as source of alumino-silicate. Normally, an impure limestone which contains clay or SiO2 is used. The CaCO3 content of these limestones can be as low as 80%. Second raw materials (materials in the rawmix other than limestone) depend on the purity of the limestone. Some of the second raw materials used are: clay, shale, sand, iron ore, bauxite, fly ash and slag. When a cement kiln is fired by coal, the ash of the coal acts as a secondary raw material.

Source: Wikipedia

Mortar

blogtopia — Wed, 03 Jun 2009 06:14:09 +0000

Mortar is a workable paste formed by mixture of cement, water and fine aggregate sand to bind construction blocks together and fill the gaps between them. The blocks may be stone, brick, cinder blocks, etc. Mortar is a mixture of sand, a binder such as cement or lime, and water and is applied as a paste which then sets hard. Mortar can also be used to fix, or point masonry when the original mortar has washed away.

The first mortars were made of mud and clay. Because of a lack of stone and an abundance of clay, the Babylonian constructions were of baked brick, using slime or pitch for mortar. According to Roman Ghirshman, the first evidence of humans using a form of mortar was at the ziggurat of Sialk in Iran, built of sun-dried bricks in 2900 BC. The Chogha Zanbil Temple in Iran was built in about 1250 BC with kiln-fired bricks and a strong mortar of bitumen.

Portland cement mortar (often known simply as cement mortar, or OPC) is created by mixing Portland cement with sand and water. It was invented in 1794 by Joseph Aspdin and patented on 18 December 1824, largely as a result of various scientific efforts to develop stronger mortars than existed at the time.

Polymer cement mortars (PCM) are the materials which are made by partially replacing the cement hydrate binders of conventional cement mortar with polymers. The polymeric admixtures include latexes or emulsions, redispersible polymer powders, water-soluble polymers, liquid resins and monomers.

The speed of set can be increased by using impure limestones in the kiln, to form a hydraulic lime that will set on contact with water. Such a lime must be stored as a dry powder. Alternatively, a pozzolanic material such as calcined clay or brick dust may be added to the mortar mix.

Pozzolana is a fine, sandy volcanic ash, originally discovered and dug in Italy at Pozzuoli in the region around Mount Vesuvius, but later at a number of other sites. The ancient Roman architect Vitruvius speaks of four types of pozzolana. It is found in all the volcanic areas of Italy in various colours: black, white, grey and red.

Source: Wikipedia

Papercrete

blogtopia — Mon, 01 Jun 2009 07:38:43 +0000

Papercrete is a recently developed construction material which consists of re-pulped paper fiber with Portland cement or clay and/or other soil added. First patented in 1928, it has been revived since the 1980s. Although perceived as an environmentally friendly material due to the significant recycled content, this is offset by the presence of cement.

The material lacks standardisation, and proper use therefore requires care and experience. Eric Patterson and Mike McCain, who have been ascribed with independently "inventing" papercrete (they called it "padobe" and "fibrous cement"), have both contributed considerably to research into machinery to make it and ways of using it for building.

The paper to be used can come from a variety of sources. Newspaper, junk mail, magazines, books, etc. obtained from the local dump or from waste bins are all useful. Depending on the type of mixer used to pulp the mix, the paper may be soaked in water beforehand.

A typical homemade mixer uses a small electric motor mounted directly on a shaft with two four-inch square blades attached, resembling milk shake maker. This shaft is suspended in a plastic 55 gallon drum to mix the material.

Papercrete is rapidly gaining a groundswell of support among "do it yourself" builders. It is claimed to be a very attractive building material due to its very low cost, light weight, and high performance. Many owner/builders are contributing to furthering the technology and sharing their experiences over the internet through resources such as "Papercreters".

Source: Wikipedia

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