Cement

What is Cement?

Cement is the basic building material required for any kind of construction. Cement is made of using limestone, clay, silica sand, calcium, aluminium and other ingredients. Utmost care should be taken while choosing cement for your construction, it is available in three major grades (OPC, PPC & PSC Grade) and also of many brands to buy online at NirmaanKart Ranchi.

How is Portland cement made?

Cement manufacturers mine materials such as limestone, shale, iron ore, and clay, crushed and screened the rock, and place it in a cement kiln. After being heated to extremely high temperatures, these materials form a small ball called “clinker” that is very finely grounded to produce portland cement.

Lime and silica make up about 85 percent of the ingredients of cement. Other elements include alumina and iron oxide. The rotating kiln that cooks the materials resembles a large horizontal pipe with a diameter of 10 to 15 feet and a length of 300 feet or more. One end is raised slightly. The raw mix is placed in the high end and as the kiln rotates the materials move slowly toward the lower end. Flame jets at the lower end heat all the materials in the kiln to high temperatures that range between 2,700 and 3,000 degrees Fahrenheit.

This high heat drives off, or calcines, the chemically combined water and carbon dioxide from the raw materials and forms new compounds (tricalcium silicate, dicalcium silicate, tricalcium aluminate and tetracalcium aluminoferrite). For each ton of material that goes into the feed end of the kiln, two thirds of a ton comes out the discharge end, called clinker. This clinker is in the form of marble sized pellets. The clinker is very finely ground to produce portland cement. Manufacturers often add gypsum and/or limestone during the grinding process.

What is difference between cement and concrete?

Although the terms cement and concrete often are used interchangeably, cement is actually an ingredient of concrete. Concrete is a mixture of aggregates and paste. The aggregates are sand and gravel or crushed stone; the paste is water and portland cement.

Cement comprises from 10 to 15 percent of the concrete mix, by volume. Through a process called hydration, the cement and water harden and bind the aggregates into a rocklike mass. This hardening process continues for years meaning that concrete gets stronger as it gets older.

Portland cement is not a brand name, but the generic term for the type of cement used in virtually all concrete, just as stainless is a type of steel and sterling a type of silver. Therefore, there is no such thing as a cement sidewalk, or a cement mixer; the proper terms are concrete sidewalk and concrete mixer.

How do you control the strength of cement concrete?

Cement is the simplest approach to increase strength. The proportion of water to cement in the cement paste holding the particles together is the factor that most significantly affects concrete strength. The concrete will be weaker and vice versa the higher this percentage is. More water will have a negative impact on every measurable good physical characteristic.

What does 28-day strength of cement concrete mean?

Concrete hydrates, becoming stronger and hardening. The process of hydration goes on for a very long time. It begins quickly and then slows down over time. It would take several years before concrete’s ultimate strength could be determined. This would not be feasible, thus the specification drafting authorities decided that all concrete should be tested after 28 days. At this age, a large portion of the hydration has already occurred.

Why does cement concrete crack?

Concrete, like all other materials, will slightly change in volume when it dries out. In typical concrete this change amounts to about 500 millionths. Translated into dimensions-this is about 1/16 of an inch in 10 feet. The reason that contractors put joints in concrete pavements and floors is to allow the concrete to crack in a neat, straight line at the joint when the volume of the concrete changes due to shrinkage.

What are the recommended mixing ratio of good cement concrete?