Concrete is a composite material made up of water, aggregate, and cement, which is a fine powder made of limestone and other minerals. Cement is heated to form clinker, which is ground into a powder and mixed with gypsum to create cement. The most commonly used type of cement is Portland cement. The ratio of aggregate-cement-water is important for the properties of concrete, and good aggregate is necessary for a strong final product. Concrete is used in various construction projects and can be recycled, but cement production contributes to carbon dioxide emissions.
The main difference between concrete and cement is that concrete is a composite material made up of water, aggregate and cement. Cement is a very fine powder composed of limestone and other minerals, which absorbs water and acts as a binder to hold concrete together. While cement is a building material in its own right, concrete cannot be made without cement. The two terms are often misused interchangeably, but concrete and cement are distinctly separate products.
Cement
Cement is made from limestone, calcium, silicon, iron, and aluminum, among other ingredients. This mixture is heated in large kilns to approximately 2,700°F (1,482°C) to form a product known as clinker, which roughly resembles marbles. These are ground into a powder and gypsum is added, creating the gray flour-like substance known as cement. When water is added to concrete, it triggers a chemical process that allows it to harden.
Portland Cement
There are many different types of concrete, but the most commonly used type in construction is Portland cement. Joseph Aspdin of Great Britain developed the building material in the 1700s when he discovered that adding clay to limestone and heating the mix allowed the resulting mix to set anywhere. Portland cement is a type of hydraulic cement, which means that when water is added, it starts a chemical reaction that doesn’t depend on how much water there is. This allows the concrete to harden underwater and remain strong even in wet conditions. The different types of hydraulic cements are mainly used in concrete and mortars.
concrete
Concrete, by contrast, is a masonry material that uses cement to bind crushed stone, rock, and sand together, also called aggregate. Cement makes up 10% to 15% of the total mass of concrete; the exact proportions vary depending on the type of concrete to be made. The aggregate and cement are mixed thoroughly with water, which initiates the chemical reaction causing the cement to harden and set. Before this happens, the concrete mix can be poured into a mold so that it hardens into a specific shape, be it a block or slab.
The time required for the concrete to set depends in part on the amount of gypsum added to the mix. This time can be sped up by adding calcium chloride or slowed down by adding sugar. These compounds work by affecting the development of the hardening crystals which form as the cement sets. Concrete exposed to freezing and thawing conditions may have additional chemicals added to help prevent cracking.
Relationships concrete and cement
The properties of concrete greatly depend on the ratio of aggregate-cement-water in the mix. The water/cement ratio is the most important, as too little water will make the concrete difficult to work with, while too much will weaken the final product. This ratio is calculated with the following equation:
r = 8.33 qH2O / Wc
In this calculation, r is the ratio, qH2O is the amount of water in US gallons, and Wc is the weight of the cement in pounds. A ratio of at least 0.25 is required for curing concrete, with values of 0.35 to 0.4 being typical for most applications.
Aggregate is also important, as it makes up over 60% of a concrete mix and in some cases up to 80%. Larger rocks require less cement, which means less water is needed and a stronger final product can be made. Aggregate is also less expensive than concrete, so a higher percentage can lower the cost. In general, good aggregate has a combination of rocks of many different sizes, with a specific average and maximum size; these stones must be clean and strong and must not contain clay or other minerals that can absorb water.
The high rock content of concrete makes it extremely strong and is often used in pavers for swimming pools, high-rise buildings, subways and lamp posts as well as sidewalks, driveways and streets. The ingredients in both concrete and cement are some of the most abundant on Earth, and both can be recycled. However, cement production requires a large amount of energy, due to the high temperatures required, and the industry has been criticized for its contributions to carbon dioxide emissions.
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