Portland Cement. Portland цемент
Portland Cement Discount | Portland Cement 42.5 Prices
Normally the buyers will look at the 'best' prices and that is usually the company that is willing to come in on a low commission basis!
If you feel you need to "waste our time" by requesting from us a) "Soft Offers" without giving us any official documentation from your client or b) request FCO's in which you want us to include $4 to $6 per MT in commissions for you, we will NOT work with you! If you need a "Price Quotation" without supplying us an ICPO and/or LOI plus a BCL, please refer to the price tables on this web site.
Lessons to be learned: Please...
|Don't ask...||...for photos! We are not a photo agency and they aren't worth the sending as they proof nothing!|
|Don't ask...||...for "past performance" as it says nothing about the seller's ability to supply tomorrow!|
|Don't ask...||...for pricing without a buyer's LOI or ICPO and BCL attached!|
|Don't ask...||...for a FCO without having a positive response to your buyer's LOI.|
|Don't believe...||...that the sending of a LOI automatically causes the sending of a FCO or draft contract.|
|Don't think...||...we have no other person besides you to talk to... (your inquiry is important to us, but it is NOT the only one we are busy with!)|
|Don't think...||...that cement deals about several hundred millions of Dollars are closed within minutes, hours or a day!|
|Don't start...||...an inquiry by telling us "how much commissions" you have to get... (no contract closed - no commission - no discussion!)|
|Don't tell...||...us that you have to share your (future) commissions with 8 brokers in the background... and that you require us a) to increase our prices or b) want to share with us the commissions "equally" between "10 people"...! We don't care if you have 20 brokers or just one broker you deal with! How would you feel if we tell you that the $2 commission has to be shared "suddenly" with 25 others "equally"...? Meaning we bring in Grandpa, Grandma, Uncle Tom and his sister in law and so on... you get the picture? Brokers with this kind of requests are being deleted in our database within 5 seconds!|
|Don't think...||...that we can afford to "chat with you" on Skype for 30 minutes everyday... We work with more than 60 agents around the world and that would cost us 1,800 minutes or 30 hours PER DAY!!!|
|Don't submit...||..."blank" letters or copy and paste LOI's into emails without correct company information.... They are useless and we will not work with them!|
|Don't submit...||...LOI's which are older than 3 to 5 days. If you send us LOI's or ICPO's which are 2 or 3 weeks old... They are "outdated" and we will not work with them!|
|Don't submit...||...your LOI's on Saturday's and then call us 12 hours later on Sunday morning to ask if the FCO is ready... Our Cement Suppliers, our Cement Buyers and we have a private life too... how about you?|
|DO SEND...||...us your LOI's or ICPO's from your client's on proper company letter heads with BCL attached via e-mail and you will have a Full Corporate Offer and/or a DRAFT contract in your e-mail Inbox within maximum 48 hours! We offer fast, efficient and "no-nonsense" superior service combined with excellent prices! It's that simple! Are you ready...?|
Respecting Buyers as Intelligent and Careful People
Cement buyers are careful people and it pays to respect them. You must realize that the more cement they purchase, the more careful they must be, because $1 per MT more can waste tens of millions. You have to give them credit for being intelligent, because intelligent buyers will shop around. If your prices are not competitive, you are not going to sell as much cement and you won't earn many commissions. Your buyers will meet someone who is connected to us and those buyers will enjoy the best prices. They won't buy from those who overcharge them!
Do you want to close deals or hunt for Ghosts?
If you are trying to "overcharge" a client and the next broker makes an offer $1 lower than you, you are OUT of the game, trust us! We have clients signing our FCO's sometimes within 1 day and they want the contracts immediately signed because our prices are LOW. Give the buyer an incentive to buy FROM YOU and not walk away! Can you do that?
What is the difference between ordinary people and billionaires?
When it comes to making a "great deal" and saving money they are both the same! Remember that ordinary people and billionaires still look around which gasoline station is the cheapest when they fill up their car tank with fuel... and that's only peanuts in comparison to the figures in Cement Commodity Trading! So do you really think you can get away with it and add $2, $3, or even $4 in commissions on a 20,000,000 MT deal? When was the last time that you closed a cement deal and made $20,000,000 up to $80,000,000 in commissions...???
There are many mechanisms today, which allow a buyer to advertise efficiently. You can't assume that you have a monopoly. If this report tells you anything, it has to say that the world is very competitive. You have to offer prices, which make it difficult for your buyer to go elsewhere. That's our job and expertise to help you with!
When you are comparing an "inflated" price with another "imaginary" price, no price is low enough. When you force the buyer to face reality, by bringing you a real price, you make him aware that our price is relatively cheap. He's happier, with a higher price, because he can only compare it with one price, the best quote he's ever received. The broker who can do this can close real deals and make real money and put an end to the fantasyland existence of no deals and no commissions.
When a buyer has an imaginary price in his head, it's the broker's fault. Did you know about the GOST certificate requirement, before you quoted a price? If not, then you are at fault, for incompetence and you can't make money if you're still making mistakes. Don't ever quote a price. Just ask what the best price quote the buyer has received is and tell him that we will beat it by $1.
This is the price we want permanently in the head of the buyer. When he asks for a price quote, there is only one thing to say: "My price is $1 per MT cheaper than your best quote, if it's real".
Our aim is to give our buyers the best cement prices in the world!
Let's say the order is 12.6 million MT. Instead of saying it is $1.00 cheaper, you say $12,600,000 cheaper! Thats really exciting point for every buyer, would you agree?
After you say that, it will be impossible for any buyer to pay $12,600,000 more for cement. If you quote a price and you're wrong, you will have a difficult time getting that price out of the buyer's head. Return to first base. Ask him what the best price quote he has is. Tell him we will beat it by $1. Then verify it. If it's not real, bring the news to the buyer. So many brokers quote prices, without knowing what they have or who has it for that price and this is reckless, risky and not rewarding. If you can prove a price isn't real, you are justified in dismissing it.
Remove all the escape doors, if you want to close a buyer, at your price. There can be only one, lowest, real; price quote and you can remove it too, by bidding $1 cheaper. Now, what's left? A price the buyer is happy with, because we saved him $12,600,000! Make sure he understands that.
If you have gotten to know him and know that he owns a yacht and you know the price was $6 million, tell him it's the price of 2 yachts. If he owns a $250,000 Rolls Royce, it's more than 50 Rolls Royce's. It's 50 Rolls Royce's with full gas tanks. That's a significant savings! You've closed all the doors; to your competition and you've opened our door very wide.
There is an abundance of profit in the deal... Let's close! When you have removed all competitors, imaginary or real, a real buyer must do the deal with you/us!
A buyer will do anything to save $12.6 million and you would too, if you were the buyer. Remember that!
Proof of Product:
THE BUYER SHOULD BASE THEIR DECISION ON THE IRREFUTABLE PROOF OF PRODUCT THAT IS PROVIDED BY THE SELLER'S PRIME BANK WHERE TWO PRIME BANK OFFICERS STAKE THEIR PERSONAL AND PROFESSIONAL CAREERS AND REPUTATION OF THE BANK ON CONFIRMING IN WRITING AND BY K.T.T. BANK TO BANK THAT THE SELLER IS KNOWN TO THEM, THE SELLER OWNS THE PRODUCT, THE SELLER HAS SHIPPED THE PRODUCT AND CAN ALSO DELIVER THE PRODUCT AS PER THE SPECIFICATIONS IN THE CONTRACT.
NOTHING LESS SHOULD BE ACCEPTABLE TO A BUYER!
EACH AND EVERY SHIPMENT IS CHECKED AND INSPECTED AT THE PORT OF LOADING BY S.G.S. THE SPECIFICATIONS OF THE PRODUCT ITSELF ARE COMPARED WITH THE SPECIFICATIONS MENTIONED IN THE CONTRACT AND IF THE SPECIFICATIONS DO NOT MATCH EXACTLY THE SHIPMENT IS NOT PASSED BY S.G.S. & NOT SHIPPED.
GLOBAL TRADE IS BASED ON PROOF OF PRODUCT BANK TO BANK BY K.T.T. AND CERTIFICATION BY S.G.S. AND NEVER ON A SAMPLE BASIS.
The bank Credit Suisse will issue POP. Please visit them at (www.creditsuisse.com).
Our Allocation Holder accepts non-transferable Instruments. The prices are as follows:
- Non Transferable will increase the price with US$1.00/MT
- A BG with payment in advance before shipping will reduce the price with US$1.00/MT
Please MARK clearly the payment option required:
A - Non-Transferable, Fully Funded Revolving Stand-by Letter of Credit (FFRSLC). This Irrevocable FFRSLC should be valid for 14 Months and 16 days (Based on a 12 Month contract). Fully Funded = Total Contract Value.
B - Irrevocable, Non-Transferable, Monthly Revolving Documentary Letter of Credit (MRLC) and require a one month Stand-by Letter of Credit (SBLC) or one month Irrevocable, Transferable Bank Guarantee (BG) valid for 14 Months and 16 days (Based on a 12 Month Contract).
C - Two month Irrevocable, Non-Transferable SBLC or Irrevocable, Transferable BG valid for 14 Months and 16 days (Based on 12 Month contract) with monthly payment by Telegraphic Transfer (TT).
D - Irrevocable, Confirmed, Non-Transferable, Revolving Documentary Letter Of Credit (MRDLC) revolving for eleven months with a face value of one months shipping (+/-5%). The above payment terms will be guaranteed with Irrevocable, Assignable Standby Letter of Credit (SBLC) or bank guarantee (BG) for a one month shipping value. Payment for the last shipment will be drawn against the SBLC or BG. All these instruments will be valid for 14 months and 16 days on a 12 month contract and issued or confirmed by a top 50 Western Bank.
Swift message MT 799: (All these instruments will be valid for 14 months and 16 days based on a 12 month contract and issued or confirmed by a top 50 Western Bank.)
(Buyers must use one of these two payment options for their contract)
TT every month guaranteed by a SBLC or BG to the value of 120% of the monthly value. (120% = Monthly value plus 20%)
Monthly Revolving Letter of Credit (MRLC) assured for the full contract term.
Each opportunity is priced separately based on a clear ICPO (addressed to us) and a BCL.
All Contracts have been drawn by International Attorneys conforming to the International Trade and complying with ICC rules of arbitration. Theses contracts are drawn to protect both the Seller and the Buyer and are acceptable to the top fifty banks worldwide. The wording of our Financial Instruments is tested and has been found acceptable by the top one hundred banks worldwide. Our Bank has to protect the Seller and the Buyer and comply with the rules and standards for the International Trade. We facilitate our transactions and financial administration through our Companys Attorneys Trust account which is protected by the Attorneys Fidelity fund against theft and /or the misappropriation of any funds. We are flexible in accepting Variations of Payments Methods, but complete contradictions will not allow us to facilitate a transaction with you.
The reason why we require a BG or SBLC in certain options:
The MRLC will be opened and cannot be canceled by either the buyer or seller. BUT the bank can. If there is, for any reason, not enough money in the buyers account, the bank will not open that months L/C.
Due to shipment every 7-10 days, the next months shipment will already be at sea when payment is to be made! The Supplier has already sent the next shipment and there is no L/C available for payment!
Due to the fact that the cement is already paid for by the Supplier, they will require payment for that from the buyer! Then and only then, will the Supplier use the BG or SBLC to pay for that shipment! The BG or SBLC is to guarantee the monthly payment method. Why shipment every 7-10 days? The mills do not wait for the vessel to return to port to reload for the next months shipment. That will have the effect of the buyer only receiving there allocation of monthly cement every third month! That's why they ship every 7 to 10 days to deliver as per contract their monthly quota!
We will only accept above stated payment options. The buyer may use the BG (SBLC) to pay for the last months shipping as the current draft contract is setup for.
The next Steps:
Portland Cement | Pavement Interactive
Portland cement is the chief ingredient in cement paste – the binding agent in portland cement concrete (PCC). It is a hydraulic cement that, when combined with water, hardens into a solid mass. Interspersed in an aggregate matrix it forms PCC. As a material, portland cement has been used for well over 175 years and, from an empirical perspective, its behavior is well-understood. Chemically, however, portland cement is a complex substance whose mechanisms and interactions have yet to be fully defined. ASTM C 125 and the Portland Cement Association (PCA) provide the following precise definitions:
- Hydraulic cement: An inorganic material or a mixture of inorganic materials that sets and develops strength by chemical reaction with water by formation of hydrates and is capable of doing so under water.
- Portland cement: A hydraulic cement composed primarily of hydraulic calcium silicates.
Figure 1. Isle of Portland, England
Figure 2. Limestone at the Portland Bill near Weymouth
Although the use of cements (both hydraulic and non-hydraulic) goes back many thousands of years (to ancient Egyptian times at least), the first occurrence of “portland cement” came about in the 19th century. In 1824, Joseph Aspdin, a Leeds mason took out a patent on a hydraulic cement that he coined “Portland” cement (Mindess and Young, 1981). He named the cement because it produced a concrete that resembled the color of the natural limestone quarried on the Isle of Portland, a peninsula in the English Channel (see Figure 1 and 2). Since then, the name “portland cement” has stuck and is written in all lower case because it is now recognized as a trade name for a type of material and not a specific reference to Portland, England.
Today, portland cement is the most widely used building material in the world with about 1.56 billion tonnes (1.72 billion tons) produced each year. Annual global production of portland cement concrete hovers around 3.8 million cubic meters (5 billion cubic yards) per year (Cement Association of Canada, 2002). In the U.S., rigid pavements are the largest single use of portland cement and portland cement concrete (ACPA, 2002).
Although there are several variations of commercially manufactured portland cement, they each share many of the same basic raw materials and chemical components. The chief chemical components of portland cement are calcium, silica, alumina and iron. Calcium is derived from limestone, marl or chalk, while silica, alumina and iron come from the sands, clays and iron ore sources. Other raw materials may include shale, shells and industrial byproducts such as mill scale (Ash Grove Cement Company, 2000).
The basic manufacturing process heats these materials in a kiln to about 1400 to 1600°C (2600 – 3000°F) – the temperature range in which the two materials interact chemically to form calcium silicates (Mindess and Young, 1981). This heated substance, called “clinker” is usually in the form of small gray-black pellets about 12.5 mm (0.5 inches) in diameter. Clinker is then cooled and pulverized into a fine powder that almost completely passes through a 0.075 mm (No. 200) sieve and fortified with a small amount of gypsum. The result is portland cement. The Portland Cement Association (PCA) has an excellent interactive illustration of this process on their website.
Portland cements can be characterized by their chemical composition although they rarely are for pavement applications. However, it is a portland cement’s chemical properties that determine its physical properties and how it cures. Therefore, a basic understanding of portland cement chemistry can help one understand how and why it behaves as it does. This section briefly describes the basic chemical composition of a typical portland cement and how it hydrates.
Table 1 and Figure 3 show the main chemical compound constituents of portland cement.
|Chemical Name||Chemical Formula||Shorthand Notation||Percent by Weight|
Figure 3. Typical oxide composition of a general-purpose portland cement Mindess and Young, 1981).
When portland cement is mixed with water its chemical compound constituents undergo a series of chemical reactions that cause it to harden (or set). These chemical reactions all involve the addition of water to the basic chemical compounds listed in Table 1. This chemical reaction with water is called “hydration”. Each one of these reactions occurs at a different time and rate. Together, the results of these reactions determine how portland cement hardens and gains strength.
- Tricalcium silicate (C3S). Hydrates and hardens rapidly and is largely responsible for initial set and early strength. Portland cements with higher percentages of C3S will exhibit higher early strength.
- Dicalcium silicate (C2S). Hydrates and hardens slowly and is largely responsible for strength increases beyond one week.
- Tricalcium aluminate (C3A). Hydrates and hardens the quickest. Liberates a large amount of heat almost immediately and contributes somewhat to early strength. Gypsum is added to portland cement to retard C3A hydration. Without gypsum, C3A hydration would cause portland cement to set almost immediately after adding water.
- Tetracalcium aluminoferrite (C4AF). Hydrates rapidly but contributes very little to strength. Its use allows lower kiln temperatures in portland cement manufacturing. Most portland cement color effects are due to C4AF.
Figure 4 shows rates of heat evolution, which give an approximate idea of hydration times and when a typical portland cement initially sets.
Figure 2. Rate of heat evolution during hydration of a typical portland cement.The result of the two silicate hydrations is the formation of a calcium silicate hydrate (often written C-S-H because of is variable stoichiometry). C-S-H makes up about 1/2 – 2/3 the volume of the hydrated paste (water + cement) and therefore dominates its behavior (Mindess and Young, 1981).
Types of Portland Cement
Knowing the basic characteristics of portland cement’s constituent chemical compounds, it is possible to modify its properties by adjusting the amounts of each compound. In the U.S., AASHTO M 85 and ASTM C 150, Standard Specification for Portland Cement, recognize eight basic types of portland cement concrete (Table 2). There are also many other types of blended and proprietary cements that are not mentioned here.
|I||Normal||General-purpose cement suitable for most purposes.|
|IA||Normal-Air Entraining||An air-entraining modification of Type I.|
|II||Moderate Sulfate Resistance||Used as a precaution against moderate sulfate attack. It will usually generate less heat at a slower rate than Type I cement.|
|IIA||Moderate Sulfate Resistance-Air Entraining||An air-entraining modification of Type II.|
|III||High Early Strength||Used when high early strength is needed. It is has more C3S than Type I cement and has been ground finer to provide a higher surface-to-volume ratio, both of which speed hydration. Strength gain is double that of Type I cement in the first 24 hours.|
|IIIA||High Early Strength-Air Entraining||An air-entraining modification of Type III.|
|IV||Low Heat of Hydration||Used when hydration heat must be minimized in large volume applications such as gravity dams. Contains about half the C3S and C3A and double the C2S of Type I cement.|
|V||High Sulfate Resistance||Used as a precaution against severe sulfate action – principally where soils or groundwaters have a high sulfate content. It gains strength at a slower rate than Type I cement. High sulfate resistance is attributable to low C3A content.|
Portland cements are commonly characterized by their physical properties for quality control purposes. Their physical properties can be used to classify and compare portland cements. The challenge in physical property characterization is to develop physical tests that can satisfactorily characterize key parameters. This section, taken largely from the PCA (1988), lists the more common U.S. portland cement physical properties that are tested. Specification values, where given, are taken from ASTM C 150, Standard Specification for Portland Cement.
Keep in mind that these properties , in general, apply to “neat” cement pastes – that is, they only include portland cement and water. Neat cement pastes are typically difficult to handle and test and thus they introduce more variability into the results. Cements may also perform differently when used in a “mortar” (cement + water + sand). Over time, mortar tests have been found to provide a better indication of cement quality and thus, tests on neat cement pastes are typically used only for research purposes (Mindess and Young, 1981). However, if the sand is not carefully specified in a mortar test, the results may not be transferable.
If construction has a signature material, it's concrete -- the familiar stone-like substance that forms some part of nearly everything we build. And the key to concrete is portland cement- the fine gray powder that binds sand and gravel into concrete's rock-like mass. The mining, production and uses of cement, clay and shale are quite similar. Cement is made from gypsum, shale or clay, and limestone. The term "cement" is most often used to refer to Portland cement. Portland cement, when mixed with sand, gravel, and water, makes concrete, which is an essential element of the construction industry. Portland cement accounts for more than 95% of all cement produced. To make Portland cement, clay, shale and limestone is ground to a powder and baked in a kiln. The baked mixture forms clods (clinkers), which are then ground up and mixed with gypsum. Most of the raw materials are mined in open pits. Michigan traditionally ranks in the five states in terms of cement production. One of the largest cement plant in the state is in Alpena. Making Portland cement requires lots of heavy raw materials and a tremendous amount of energy. Although the terms cement and concrete often are used interchangeably, cement is actually an ingredient of concrete. 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. Portland cement owes both its name and origin to Joseph Aspdin, a British stone mason. Aspdin's quest for a manufactured counterpart to natural or Roman cement - a crude formulation of lime and volcanic ash used as early as 27 BC - led to his discovery and patent of portland cement in 1824. Aspdin heated a mixture of finely powdered limestone and clay in a small furnace to produce hydraulic cement - one that would harden with the addition of water. He named his invention "portland cement" not only to distinguish it from Roman cement, but also as a marketing tool: Concrete made from his new cement resembled a highly prized building stone quarried on the Isle of Portland off the British coast. Today's portland cement still relies on Aspdin's raw materials for its basic components of calcium, silica, alumina, and iron. The most common combination is limestone, clay, and sand. In today's cement production, minerals from a quarry near the plant are ground to fine powder, then blended to the exact proportions needed for the final cement product. Raw materials are processed in a rotating, cylindrical furnace called a kiln. At the hottest part of the kiln, a 1870 C flame heats the raw materials to about 1480 C. Under this intense heat, a series of chemical reactions converts the partially molten raw material to pellets called clinker. With the addition of a small amount of gypsum, the clinker is ground to an extremely fine gray powder. It is now considered portland cement - ready for shipment to concrete producers and then to construction sites. One of the largest Portland Cement plants in the US is located in Alpena, and is shown below. The advantages of placing such a plant in Alpena include: nearness to large supplies of high-quality limestone, gypsum and shale, and access to Lake Huron, thereby facilitating easy shipping of the cement by freighter.
Source: Photograph by Randy Schaetzl, Professor of Geography - Michigan State University
This material has been compiled for educational use only, and may not be reproduced without permission. One copy may be printed for personal use. Please contact Randall Schaetzl ([email protected]) for more information or permissions.
COMPOSITION OF PORTLAND CEMENT
Composition of Portland Cement
The principal raw materials used in the manufacture of cement are:
a) Argillaceous or silicates of alumina in the form of clays and shales.
b) Calcareous or calcium carbonate, in the form of limestone, chalk and marl which is a mixture of clay and calcium carbonate.
The ingredients are mixed in the proportion of about two parts of calcareous materials to one part of argillaceous materials and then crushed and ground in ball mills in a dry state or mixed in wet state.
The dry powder or the wet slurry is then burnt in a rotary kiln at a temperature between 1400 degree C to 1500 degree C. the clinker obtained from the kiln is first cooled and then passed on to ball mills where gypsum is added and it is ground to the requisite fineness according to the class of product.
The chief chemical constituents of Portland cement are as follows:
|Lime (CaO)||60 to 67%|
|Silica (SiO2)||17 to 25%|
|Alumina (Al2O3)||3 to 8%|
|Iron oxide (Fe2O3)||0.5 to 6%|
|Magnesia (MgO)||0.1 to 4%|
|Sulphur trioxide (SO3)||1 to 3%|
|Soda and/or Potash (Na2O+K2O)||0.5 to 1.3%|
The above constituents forming the raw materials undergo chemical reactions during burning and fusion, and combine to form the following compounds called BOGUE COMPOUNDS.
|Tricalcium silicate (3CaO.SiO2)||C3S|
|Dicalcium silicate (2CaO.SiO2)||C2S|
|Tricalcium aluminate (3CaO.Al2O3)||C3A|
|Tetracalcium aluminoferrite (4CaO.Al2O3.Fe2O3)||C4AF|
The proportions of the above four compounds vary in the various Portland cements. Tricalcium silicate and dicalcium silicates contribute most to the eventual strength. Initial setting of Portland cement is due to tricalcium aluminate. Tricalcium silicate hydrates quickly and contributes more to the early strength.
The contribution of dicalcium silicate takes place after 7 days and may continue for up to 1 year. Tricalcium aluminate hydrates quickly, generates much heat and makes only a small contribution to the strength within the first 24 hours. Tetracalcium alumino-ferrite is comparatively inactive.
All the four compounds generate heat when mixed with water, the aluminate generating the maximum heat and the dicalcium silicate generating the minimum. Due to this, tricalcium aluminate is responsible for the most of the undesirable properties of concrete.
Cement having less C3A will have higher ultimate strength, less generation of heat and less cracking. Table below gives the composition and percentage of found compounds for normal and rapid hardening and low heat Portland cement.
Composition and compound content of Portland Cement:
|Portland Cement||Normal||Rapid hardening||Low heat|
|(a) Composition: Percent|
|(b) Compound: Percent|
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Portland Cement - Types, manufacturing & functions of ingredients
What Is Cement????
Material with adhesive and cohesive properties or any material that binds or unites – essentially like glue
Function Of Cement are
to bind the sand and coarse aggregate togetherto fill voids in between sand and coarse aggregate particleto form a compact mass
Types of Cement
2 types of cement normally used in building industry are as follows:a) Hydraulic Cementb) Nonhydraulic Cement
Hydraulic Cement sets and hardens by action of water. Such as Portland CementIn other words it means that hydraulic cement are:“ Any cements that turns into a solid product in the presence of water (as well as air) resulting in a material that does not disintegrate in water.”
Any cement that does not require water to transform it into a solid product.2 common Non-hydraulic Cement area) Lime- derived from limestone / chalkb) Gypsum
Chemical composition of Portland Cement:a) Tricalcium Silicate (50%)
b) Dicalcium Silicate (25%)
c) Tricalcium Aluminate (10%)
d) Tetracalcium Aluminoferrite (10%)
e) Gypsum (5%)
Function :Tricalcium Silicate
- Hardens rapidly and largely responsible for initial set & early strength
- The increase in percentage of this compound will cause the early strength of Portland Cement to be higher.
- A bigger percentage of this compound will produces higher heat of hydration and accounts for faster gain in strength.
Function : Dicalcium Silicate
- Hardens slowly
- It effects on strength increases occurs at ages beyond one week .
- Responsible for long term strength
Function :Tricalcium Aluminate
- Contributes to strength development in the first few days because it is the first compound to hydrate .
- It turns out higher heat of hydration and contributes to faster gain in strength.
- But it results in poor sulfate resitance and increases the volumetric shrinkage upon drying.
- Cements with low Tricalcium Aluminate contents usually generate less heat, develop higher strengths and show greater resistance to sulfate attacks.
- It has high heat generation and reactive with soils and water containing moderate to high sulfate concentrations so it’s least desirable.
Function : Tetracalcium Aluminoferrite
- Assist in the manufacture of Portland Cement by allowing lower clinkering temperature.
- Also act as a filler
- Contributes very little strength of concrete eventhough it hydrates very rapidly.
- Also responsible for grey colour of Ordinary Portland Cement
Manufacturing Of Portland Cement
The 3 primary constituents of the raw materials used in the manufacture of Portland Cement are:a) Limeb) Silicac) AluminaLime is derived from limestone or chalkSilica & Alumina from clay, shale or bauxite
There are 2 chief aspects of the manufacturing process:
FirstTo produce a finely divided mixture of raw materials – chalk / limestone and clay / shale
To heat this mixture to produce chemical compositionThere 2 main process that can be used in manufacturing of Portland Cement that isi) wet process ii) dry process
- Raw materials are homogenized by crushing, grinding and blending so that approximately 80% of the raw material pass a No.200 sieve.
- The mix will be turned into form of slurry by adding 30 – 40% of water.
- It is then heated to about 2750ºF (1510ºC) in horizontal revolving kilns (76-153m length and 3.6-4.8m in diameter.
- Natural gas, petroluem or coal are used for burning. High fuel requirement may make it uneconomical compared to dry process.
- Raw materials are homogenized by crushing, grinding and blending so that approximately 80% of the raw material pass a No.200 sieve.
- Mixture is fed into kiln & burned in a dry state
- This process provides considerable savings in fuel consumption and water usage but the process is dustier compared to wet process that is more efficient than grinding.
Dry Proces & Wet Process
- In the kiln, water from the raw material is driven off and limestone is decomposed into lime and Carbon Dioxide.
limestone ——> lime + Carbon Dioxide
- In the burning zone, portion of the kiln, silica and alumina from the clay undergo a solid state chemical reaction with lime to produce calcium aluminate.
silica & alumina + lime ——> calcium aluminate
- The rotation and shape of kiln allow the blend to flow down the kiln, submitting it to gradually increasing temperature.
- As the material moves through hotter regions in the kiln, calcium silicates are formed
- These products, that are black or greenish black in color are in the form of small pellets, called cement clinkers
- Cement clinkers are hard, irregular and ball shaped particles about 18mm in diameter.
- The cement clinkers are cooled to about 150ºF (51ºC) and stored in clinker silos.
- When needed, clinker are mixed with 2-5% gypsum to retard the setting time of cement when it is mixed with water.
- Then, it is grounded to a fine powder and then the cement is stored in storage bins or cement silos or bagged.
- Cement bags should be stored on pallets in a dry place.