المواد الخام المستخدمة في صناعة الأسمنت.

‫المادة‪:‬‬ ‫التصميم كمال الدين‬ ‫محمود جعفر‬ ‫اإلنشائي‬

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‫المحتويات‪-:‬‬ ‫‪ -1‬االسمنت وأنواعه‪.‬‬ ‫‪ -2‬مكونات االسمنت‪.‬‬ ‫‪ 1-2‬المواد الخام‪.‬‬ ‫‪ 2-2‬مرحلة التصنيع‪.‬‬ ‫‪ 3-2‬التفاعل مع الماء‪.‬‬ ‫‪ 4-2‬المنتج النهائي‪.‬‬ ‫‪ -3‬الخواص الميكانيكية لألسمنت‪..‬‬ ‫‪ -4‬الخواص الكيميائية لألسمنت‪.‬‬ ‫‪ -5‬الخواص الفيزيائية لألسمنت‪.‬‬ ‫‪ -6‬الحرارة المتولدة من تفاعل األسمنت مع الماء‪.‬‬ ‫‪ -7‬تكون المنتج النهائي وآلية الربط‪.‬‬ ‫‪ -8‬زمن الشك لألسمنت‪.‬‬ ‫‪ -9‬التغيرات الحجمية ‪.‬‬

‫الفرقة‬ ‫الخامسة ‪-‬‬ ‫تشييذ‬

.‫ االسمنت وأنواعه‬-1 ‫) الناعمة التي تتصلب فتملك بذلك خواصا‬binder( ‫( هو تلك المادة الرابطة‬Cement( ‫األسمنت‬ .‫تالصقية بوجود الماء‬ ،‫ يستخدم في أعمال اإلنشاءات بوجه عام‬:(Portland cement) ‫االسمنت القياس البورتالندي‬ : (Types of Portland Cement)‫أنواع االسمنت البورتالندي‬ . Ordinary Portland cement – Type Ι:‫األسمنت البورتالندي العادي‬ ،‫يستخدم في أعمال اإلنشاءات بوجه عام‬ .Modified cement - Type ΙΙ ‫األسمنت البورتالندي المتصلب في درجة الحرارة العالية‬ ‫ أو في اإلنشاءات الخرسانية المعرضة‬،‫يستخدم في الحاالت التي تتطلب حرارة تميؤ معتدلة‬ ‫لتأثيرات متوسطة من الكبريتات‬ . Rapid-hardening Portland cement – Type ΙΙΙ ‫األسمنت سريع التصلب‬ ‫ و سرعة التصلب وتولد سريع للحرارة‬،‫يتصف هذا النوع بدرجة نعومة أكبر من األسمنت العادي‬ ‫يستخدم األسمنت سريع التصلب في إنشاء الطرق‬ .Low heat Portland cement – Type ΙV ‫أسمنت بورتالندي منخفض الحرارة‬ . Sulfate-resisting Portland cement – Type V ‫األسمنت المقاوم للكبريتات‬ .White Portland cement ‫األسمنت األبيض‬

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Table 1. General features of the main types of Portland cement. Classification

Characteristics

Applications

Type I

General purpose

Fairly high C3S content for good early strength development

General construction (most buildings, bridges, pavements, precast units, etc)

Type II

Moderate sulfate resistance

Low C3A content (<8%)

Structures exposed to soil or water containing sulfate ions

Type III

High early strength

Ground more finely, may have slightly more C3S

Rapid construction, cold weather concreting

Type IV

Low heat of hydration (slow reacting)

Low content of C3S (<50%) and C3A

Massive structures such as dams. Now rare.

Type V

High sulfate resistance

Very low C3A content (<5%)

Structures exposed to high levels of sulfate ions

White

White color

No C4AF, low MgO

Decorative (otherwise has properties similar to Type I)

The differences between these cement types are rather subtle. All five types contain about 75 wt% calcium silicate minerals, and the properties of mature concretes made with all five are quite similar. Thus these five types are often described by the term “ordinary Portland cement”, or OPC.

‫‪ 1-2‬المواد الخام المستخدمة في صناعة األسمنت‪.‬‬ ‫الخليط األساسي لصناعة االسمنت يتكون غالبا ً من الطفل )‪ (Clay‬والحجر الجيري )‪(Limestone‬‬ ‫والذي يسخن في درجة حرارة كافية إلحداث التفاعل بينهما إلنتاج سليكات الكالسيوم ‪.(Calcium Silicate).‬‬ ‫المواد الخام األولية في صناعة األسمنت‪:‬‬ ‫‪.1‬‬ ‫‪.2‬‬ ‫‪.3‬‬ ‫‪.4‬‬ ‫‪.5‬‬ ‫‪.6‬‬ ‫‪.7‬‬ ‫‪.8‬‬

‫الحجر الجيري ‪ . CaCo3 Lime‬كربونات الكالسيوم ولكن في الطبيعة يوجد به شوائب كثيرة مثل ‪SiO2‬‬ ‫و‪ Al2O3‬و‪ Na2O3‬و‪ Fe2O3‬وغيرها مثل البوتاسيوم والكلور وغيرها‪.‬‬ ‫رمل السيليكات ‪Silica SiO2.‬‬ ‫الطفلة ‪.clay‬‬ ‫األتربة السطحية ‪(Shale).‬‬ ‫طفلة وأتربة البوكسيت ‪. Alumina Al2O3‬‬ ‫أكاسيد الحديد ‪ :Fe2O3‬وتستخدم كعوامل مذيبة أو صهارة )‪(Fluxing Agent‬‬ ‫الجبس‪ :‬ويضاف في المرحلة النهائية بمطاحن األسمنت‪. Gypsum, CaSO4.2H20.‬‬

‫‪ 2-2‬مرحلة التصنيع "الفرن" وتكويه الكلىكز (‪-::)clinker‬‬ ‫بداخل الفزن تتحد االكبسٍد األربعت مكووت ‪ C4AF ،C3S, C2S, C3A‬وهذي المواد األربعت هً مب‬ ‫ٌسمى ببلكٍلىكز ‪ clinker‬جدٌز ببلذكز أن المزكببث األربع السببقت عببرة عه اختصبر لمب ٌلً‪-:‬‬ ‫‪ ، Fe2O3 = F ، SiO2 = S ، Al2O3 = A ،CaO = C‬أي أن ‪ C3S‬عببرة عه ثالثت جزٌئبث مه‬ ‫‪ CaO‬متحدة مع جزيء مه ‪ SiO2‬ويضاف الجبص في المرحلة النهائية‪.‬‬ ‫‪( CaCO3 → CaO + CO2‬معبدلت احتزاق الحجز الجٍزي)‬ ‫وبذلك فإن المكووات األربعة الزئيسة هي‪:‬‬ ‫(‪Belite (2CaO•SiO2) , Alite (3CaO•SiO2) , Celite (3CaO•Al2O3‬‬ ‫‪Brownmillerit (4CaO•Al2O3•Fe2O3).‬‬

Chemical Composition of Cement and Functions of Ingredients: Cement is a mixture of various chemical compounds. All ingredients have their own specific roles to play and impart different properties to cement.. Variation in the proportion of these elements effects the properties of Cement. Ingredient Lime (CaO) Sillica (SiO2)

%age 60-65 20-25

Alumina (Al2 O3) Iron Oxide (Fe2 O3) Magnesium Oxide (MgO) Na2 O Sulphur Trioxide (SO3)

4-8 2-4 1-3 0.1-0.5 1-2

Effect Controls strength and soundness Gives strength, excess quantity causes slow setting Quick setting, excess lowers strength Imparts color, helps in fusion of ingredients Color and hardness, excess causes cracking Controls residues, excess causes cracking Makes cement sound

Functions of Ingredients in Cement 1. Function of Lime in Cement    

It is the major constituent of cement . Its exact proportion is important. The excess makes the cement unsound and causes the cement to expand and disintegrate. In case of deficiency, the strength of cement is decreased and cement sets quickly. The right proportion makes cement sound and strong.

2. Function of Silica in Cement  

It imparts strength to the cement due to formation of di-calcium silicate (2CaO SiO2 or C2S) and tricalcium silicate (3CaO SiO2 or C3S). Silica in excess provides greater strength to the cement but at the same time it prolongs its setting time.

3. Functions of Alumina in Cement   

It imparts quick setting quality to the cement. It acts as a flux (rate of flow of energy) and lowers the clinkering temperature. Alumina in excess reduces strength of cement.

4. Functions of Iron Oxide in Cement  

It provides color, hardness and strength. It also helps the fusion of raw materials during manufacture of cement.

5. Harmful Ingredients in Cement  

Alkali oxides (K2O and Na2O): if the amount of alkali oxides exceeds 1%, it leads to the failure of concrete made from that cement. Magnesium oxide (MgO): if the content of MgO exceeds 5%, it causes cracks after mortar or concrete hardness.

Properties of cement compounds These compounds contribute to the properties of cement in different ways :  Tricalcium aluminate, C3A:It liberates a lot of heat during the early stages of hydration, but has little strength contribution. Gypsum slows down the hydration rate of C3A. Cement low in C3A is sulfate resistant.  Tricalcium silicate, C3S:This compound hydrates and hardens rapidly. It is largely responsible for Portland cement’s initial set and early strength gain.  Dicalcium silicate, C2S: C2S hydrates and hardens slowly. It is largely responsible for strength gain after one week.  C4AF: This is a fluxing agent which reduces the melting temperature of the raw materials in the kiln (from 3,000o F to 2,600o F). It hydrates rapidly, but does not contribute much to strength of the cement paste. By mixing these compounds appropriately, manufacturers can produce different types of cement to suit several construction environments.

Cement Chemistry: Conversely, the chemistry ruling the action of the hydraulic cement is the hydration. Hydraulic cements (such as the Portland cement) are made of a mixture of silicates and oxides, the four main components being: Belite (2CaO·SiO2); Alite (3CaO·SiO2); Celite (3CaO·Al2O3); Brownmillerite (4CaO·Al2O3·Fe2O3). The reactions during the setting of the cement are: (3CaO·Al2O3)2 + (x+8) H2O → 4 CaO·Al2O3·xH2O + 2 CaO·Al2O3·8H2O (3CaO·Al2O3) + 12 H2O + Ca(OH)2 → 4 CaO·Al2O3·13 H2O (4CaO·Al2O3·Fe2O3) + 7 H2O → 3 CaO·Al2O3·6H2O + CaO·Fe2O3·H2O And during the hardening (the chemistry of the reaction of hydration is still not completely clear): (3CaO·SiO2)2 + (x+3) H2O → 3 CaO2·SiO2·xH2O + 3 Ca(OH)2 (2CaO·SiO2)2 + (x+1) H2O → 3 CaO2·SiO2·xH2O + Ca(OH)2 The silicates are responsible of the mechanical properties of the cement, the celite and the browmillerite are essential to allow the formation of the liquid phase during the cooking.

. References: Sidney Mindess & J. Francis Young (1981): Concrete, Prentice-Hall, Inc., Englewood Cliffs, NJ, pp. 671. Steve Kosmatka & William Panarese (1988): Design and Control of Concrete Mixes, Portland Cement Association, Skokie, Ill. pp. 205. Michael Mamlouk & John Zaniewski (1999): Materials for Civil and Construction Engineers, Addison Wesley Longman, Inc.,

Chemical properties include 1) fineness, 2) soundness, 3) consistency, 4) setting time, 5) compressive strength, 6) heat of hydration, 7) specific gravity, and 8) loss of ignition. Each one of these properties has an influence on the performance of cement in concrete. Soundness, which is the ability of hardened cement paste to retain its volume after setting, can be characterized by measuring the expansion of mortar bars in an autoclave