Tag: some important compounds of magnesium and calcium

The most common raw rock types used in cement production are:

1. Limestone (supplies the bulk of the lime)
2. Clay, marl or shale (supplies the bulk of the silica, alumina and ferric oxide)
3. Other supplementary materials such as sand, fly ash/pulverised fuel ash (PFA), or ironstone to achieve the desired bulk composition

Gypsum is called the retarding agent of cement which is mainly used for regulating the setting time of cement and is an indispensable component. Without gypsum, cement clinker can condense immediately by mixing with water and release heat. The major reason is that C3A in the clinker can dissolve in water quickly to generate a kind of calcium aluminate hydrate, a clotting agent, which will destroy the normal use of cement. The retardation mechanism of gypsum is: when cement is hydrated, gypsum reacts with C3A quickly to generate calcium sulfoaluminate hydrate which deposits and forms a protection film on the cement particles to hinder the hydration of C3A and delay the setting time of cement.

Gypsum is called the retarding agent of cement which is mainly used for regulating the setting time of cement and is an indispensable component. Without gypsum, cement clinker can condense immediately by mixing with water and release heat. The major reason is that C3A in the clinker can dissolve in water quickly to generate a kind of calcium aluminate hydrate, a clotting agent, which will destroy the normal use of cement. The retardation mechanism of gypsum is: when cement is hydrated, gypsum reacts with C3A quickly to generate calcium sulfoaluminate hydrate which deposits and forms a protection film on the cement particles to hinder the hydration of C3A and delay the setting time of cement.

The first stage of hydration is characterized by the rapid dissolution of clinker

${ Ca } _{ 3 }Si{ O } _{ 5 }+3{ H } _{ 2 }O\longrightarrow 3{ Ca }^{ 2+ }+4{ OH }^{ - }+{ H } _{ 2 }Si{ O } _{ 2 }^{ 4- }$

 immediately after the wetting of the clinker powder. In calorimetry measurements,  a large exothermic signal is measured due to wetting and dissolution of clinker. The wet clinker releases ions such as calcium, silicate and hydroxide to the solution. From the evolution of these ion concentrations the dissolution rate of clinker can be evaluated.

Because of their relatively high cost, calcium aluminate cements are used in a number of restricted applications where performance achieved justifies costs:

1. In construction concretes, where rapid strength development is required, even at low temperatures.
2. As a protective liner against microbial corrosion such as in sewer infrastructure.
3. In refractory concretes, where strength is required at high temperatures.
4. As a component in blended cement formulations, for various properties such as ultra-rapid strength development and controlled expansion are required.
5. In sewer networks for their high resistance to biogenic sulfide corrosion.

Its full name is reinforced cement concrete, or RCC. RCC is concrete that contains steel bars, called reinforcement bars, or rebars. This combination works very well, as concrete is very strong in compression, easy to produce at site, and inexpensive, and steel is very very strong in tension.

all given options are correct . Sheets, blocks, pillar and pipes are made from concrete produced from cement.

All of the following statements are correct.
Portland cement is the most commonly used cement for construction work.
Portland cement is made from raw material which consist of 60% lime (calcium oxide), 25% silica (silicon dioxide), 5% alumina. The rest is iron oxide and gypsum (calcium sulphate).
Portland cement gets its name from the stone  quarried from the Isle of Portland in England which has a similar texture.

The options (B) and (D) are correct statements.
Cement is an important material in construction.
Sheets, blocks, pillars and pipes are made from concrete produced from cement.
Cement is a dry greenish grey powder with fine particles.
Cement is made from silica (sand), alumina, lime, iron oxide and magnesia.

Portland cement is used in the manufacture of