PORTLAND CEMENT
Chemical composition.
Portland Cement is made up of four main compounds: tricalcium silicate (3CaOSiO2), dicalcium silicate (2CaOSiO2), tricalcium aluminate (3CaOAl2O3), and a tetra-calcium aluminoferrite (4CaO Al2O3Fe2O3). In an abbreviated notation differing from the normal atomic symbols, these compounds are designated as C3S, C2S, C3A, and C4AF, where C stands for calcium oxide (lime), S for silica, A for alumina, and F for iron oxide. Small amounts of uncombined lime and magnesia also are present, along with alkalies and minor amounts of other elements
Hydration.
The most important hydraulic constituents are the calcium silicates, C2S and C3S. Upon mixing with water, the calcium silicates react with water molecules to form calcium silicate hydrate (3CaO 2SiO23H2O) and calcium hydroxide (Ca [OH] 2). These compounds are given the shorthand notations C-S-H (represented by the average formula C3S2H3) and CH, and the Hydration reaction can be crudely represented by the following reactions:
2C3S + 6H = C3S2H3 + 3CH
2C2S + 4H = C3S2H3 + CH
During the initial stage of hydration, the parent compounds dissolve, and the dissolution of their chemical bonds generates a significant amount of heat. Then, for reasons that are not fully understood, hydration comes to a stop. This quiescent, or dormant, period is extremely important in the placement of concrete. Without a dormant period there would be no cement trucks, pouring would have to be done immediately upon mixing.
Following the dormant period (which can last several hours), the cement begins to harden, as CH and C-S-H are produced. This is the cementitious material that binds cement and concrete together. As hydration proceeds, water and cement are continuously consumed. Fortunately, the C-S-H and CH products occupy almost the same volume as the original cement and water; volume is approximately conserved, and shrinkage is manageable.
Although the formulas above treat C-S-H as a specific stoichiometry, with the formula C3S2H3, it does not at all form an ordered structure of uniform composition. C-S-H is actually an amorphous gel with a highly variable stoichiometry. The ratio of C to S, for example, can range from 1:1 to 2:1, depending on mix design and curing conditions.
Structural properties.
The strength developed by portland cement depends on its composition and the fineness to whi...
... middle of paper ...
...s.
Dust emission from cement kilns can be a serious nuisance. In populated areas it is usual and often compulsory to fit cyclone arrestors, bag-filter systems, or electrostatic dust precipitators between the kiln exit and the chimney stack.
Modern cement plants are equipped with elaborate instrumentation for control of the burning process. Raw materials in some plants are sampled automatically, and a computer calculates and controls the raw mix composition. The largest rotary kilns have outputs exceeding 5,000 tons per day.
Grinding
The clinker and the required amount of gypsum are ground to a fine powder in horizontal mills similar to those used for grinding the raw materials. The material may pass straight through the mill (open-circuit grinding), or coarser material may be separated from the ground product and returned to the mill for further grinding (closed-circuit grinding). Sometimes a small amount of a grinding aid is added to the feed material. For air-entraining cements the addition of an air-entraining agent is similarly made.
Finished cement is pumped pneumatically to storage silos from which it is drawn for packing in paper bags or for dispatch in bulk containers.
The purpose for this lab was to use aluminum from a soda can to form a chemical compound known as hydrated potassium aluminum sulfate. In the lab aluminum waste were dissolved in KOH or potassium sulfide to form a complex alum. The solution was then filtered through gravity filtration to remove any solid material. 25 mLs of sulfuric acid was then added while gently boiling the solution resulting in crystals forming after cooling in an ice bath. The product was then collected and filter through vacuum filtration. Lastly, crystals were collected and weighed on a scale.
In this experiment, solid calcium nitrate, solid diammonium hydrogen phosphate, and aqueous ammonia are used to form calcium hydroxyapatite.
The focus of the experiment will be a hydrate of copper (Ⅱ) sulfate (CuSO4 ᐧ5H2O) The object of this experiment will be to find the experimental formula for the hydrate of CuSO4 by heating the crystal to dryness. The success of the lab will be determined by how accurate the experimental formula is compared to the actual formula.
Besides the known inventions and renovations of the Roman Empire, one of the building materials that the Roman Empire produced was concrete. With its strength, inexpensiveness and its easiness to work, the Roman Empire left an everlasting impact. Concrete that is a mixture of aggregate, which is usually gravel, sand or small stones, binding agents, and water is used to construct buildings and infrastructure. The first one, aggregate, gives the product its mass while the second one, binding agents, is used to harden the product. In the early times of the history, limestone powder was usually used as a binding agent in the mixture. The Romans later used “pulvis puteolanus” (pozzolanic ash), which was a fine volcanic ash as a binding agent and it allowed Romans to have strong concrete that is also durable (Yegeul, n.d.). It was easy to use
The ability to analyze a substance and determine properties of the substance is an important skill for AP Chemistry students. Major concepts for the “Analysis of Alum” laboratory are percent composition, water of hydration, and molecular formula. They will be used in three different experiments to determine the melting point of alum, the mole ratio of hydrated water to anhydrous alum, and percent of sulfate ion contained in alum. The values acquired in the lab should be close to the calculated values of 92.5 ˚F, 12 moles of water to 1 mole of alum, and 59%, respectively.
In commercial processing, the burning takes place in large concrete or steel silos with very little oxygen, and stops before it all turns to ash. It is said that the “procedure leaves black lumps and powder which is about 25% of the original weight. When ignited, the carbon in charcoal merges with oxygen and forms carbon dioxide, carbon monoxide, water, other gases, and significant quantities of energy.” It packs more potential energy per ounce than raw wood. Stated by Goldwyn that the char combust steadily, hot and it produces less smoke and lesser unhazardous
Around the 2nd century BCE, they have learned that by mixing the other concrete ingredients with volcanic sand called pulvis puteolanus made the product stronger and in addition to that it would
Concrete and masonry products contain silica sand and rock containing silica. Since these products are primary materials for construction, construction workers may be easily exposed to respirable crystalline silica during activities such as the following:
Concrete is a composite material used widely in the construction industry. Concrete is basically a mixture of cement, water, aggregates and admixture (sometimes). Cement is a fine gray powder that consists of oxidizes calcium, silicon and aluminum. The aggregate used is normally gravel, crushed stone or sand. Admixture is a solid or liquid substance that gives a certain characteristics of the concrete. The cement reacts with water chemically and binds the aggregates together through a process called hydration during hardening or curing of concrete. It means that water helps in the hardening of the concrete while the cement bind the aggregate and also react with water to form a solid mass.
In this method, a hand turned wheel pushes a piston against the suppository mass contained in a cylinder, so as to extrude the mass into molds.
Waste incineration units produce a lot of carbon dioxide gas approximately around one third of the greenhouse gasses. It also impacts people’s health as they get exposed to the toxic emissions by breathing in the air or consuming contaminated food and water. Additionally, when the garbage gets burnt by the incinerators they end up as ashes which are then emitted from the chimneys, including the toxic materials and end up in specialist landfill sites for hazardous waste.
Air and vapour handling equipment needs to be in place to get rid of vapour in case of solvent being a health hazard.
In the case of the mould process, a quantity of the pulp is placed into a form, with a wire-mesh base (or other draining device), so that the fibres are left coated on the mesh and excess water can drain away. At this time, pressure may be applied to remove more water through a squeezing action. The paper may then be removed from the mould, wet or dry, and go on to further processing.
Agglomeration of the materials so that the briquette stay in the compressed state for use in energy production.
Lime-soda ash is used to remove the carbonate hardness by precipitation. It does not completely remove the hardness however it is effective in reducing it. It is effective if used to soften temporary hardness. To remove the calcium bicarbonate from the water slaked lime is used. By reacting with the calcium bicarbonate it forms a soluble calcium carbonate, which is then removed by filtering. However a restriction of using lime-soda ash is that it will not work on a lab scale experiment. “An additional deterrent to home use of the lime-soda ash treatment is the size of the equipment necessary, together with the high cost of this method of treatment.” (Lime-Soda Ash Water Treatment Method)