Chemistry and Technology of Cement S1 PDF

 Fayoum uiversity Faculty of science Chemistry department Chemistry and technology of cement Prepared By Prof. Dr / Saleh El- awney  ???? What is cement  Material with adhesive and cohesive properties  Any material that binds or unites essentially l...

 Fayoum uiversity Faculty of science Chemistry department Chemistry and technology of cement Prepared By Prof. Dr / Saleh El- awney  ???? What is cement  Material with adhesive and cohesive properties  Any material that binds or unites essentially like glue What is the function of cement ????  to bind the sand and coarse aggregate together  to fill voids in between sand and coarse aggregate particle  to form a compact mass Hydraulic and non-hydraulic cements. Hydraulic cement  Cement sets and hardens by action of water. Such as Portland Cement  In other “ 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.” Most common Hydraulic Cement is Portland Cement Non-hydraulic Cement  Cement can’t harden while in contact with water, as opposed to hydraulic cement.  It is created using materials such as non-hydraulic lime and gypsum plasters, and oxy-chloride, which has liquid properties.  Two common non- hydraulic cements are : (a) Lime which derived from limestone / chalk (b) Gypsum  It must be kept dry after its utilization in construction, in order to gain strength and hold the structure.  History of cement  In 3000 BC, Ancient Egyptians used mud mixed with straws to bind dried bricks. They also used gypsum or lime mortars – obviously applied in building the Pyramids.  The word "cement" traces to the Romans, who used masonry cement which was made from crushed rock with burnt lime as binder”. Romans are commonly given the credit for the development of hydraulic cement, the most significant incorporation of the Roman’s was the use of pozzolana-lime cement by mixing volcanic  Cement as national product Cement prices in Egypt are among the cheapest in the world, ranging selling price per ton for the consumer in Egypt between 55 - $ 60, with a price in Syria up to $ 140 per ton, and in Saudi Arabia to $ 90 per ton, and in Sudan to $ 180 per ton. Short hand notation in cement chemistry Oxide Notation Common Name wt (%) CaO C Lime 63 SiO2 S Silica 22 Al2O3 A Alumina 6 Fe2O3 F Ferric oxide 2.5 MgO M Magnesia 2.6 K2O K 0.6 Na2O N 0.3 SO3 S 2.0 H2O H --  Types of cement There are five principal types of Portland cement Such as : Type I (Ordinary Portland Cement): is a general-purpose cement suitable for all uses. Type II (Modified Portland Cement): is characterized by lower heat of hydration and moderate resistance to sulphate attack than Type I. Type III (Rapid Hardening Portland Cement): is used when high early strength is desired.  Type IV (Low Heat Portland Cement): can be used when the amount of heat of hydration must be minimized; for example in massive structures. Type V (Sulphate Resisting Portland Cement): should be used when high sulphate resistance is required in soils or ground waters having high sulphate content. Composition of OPC Constituents Tricalcium Silicate 3CaO.SiO2 C3S 50 β-Dicalcium Silicate β-2CaO.SiO2 β-C2S 25 Tricalcium 3CaO.Al2O3 C3A 12 aluminate Tetracalcium 4CaO.Al2O3.Fe2O3 C4AF 8 Alumino-ferrite Calcium sulphate CaSO4.2H2O CS H2 4 (gypsum)  OPC C3S C4AF -C2S C3A Silicate Phases Aluminate Phases  Function of tri calcium silicate (C3S)  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 of dicalcium silicate C2S Hardens slowly  It effects on strength increases at ages beyond one week. Responsible for long term strength  Hydration of silicates Tricalcium Silicate 2 C3S + 6 H C3S2H + 3 CH water C-S-H gel Calcium hydroxide ß-Dicalcium Silicate 2 C2S + 4 H C3S2H3 + CH water C-S-H gel Calcium hydroxide  Function of tricalcium aluminate ( C3A)  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 resistance and increases the volumetric shrinkage upon drying.  Cements with low Tri calcium 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 of tetrcacalcium aluminoferrite( C4AF)  Assists in the manufacture of Portland Cement by allowing lower clinkering temperature.  Also acts as a filler.  Contributes very little strength of concrete even though it hydrates very rapidly.  Also responsible for grey color of Ordinary Portland Cement.  Hydration of aluminates Tricalcium Aluminate (C3A) C3A + 3 CSH2 +26 H C6ASH32 Ettringite 2 C3A + C6ASH32 + 4 H 3 C4ASH12 Monosulphaluminate C3A + CH +12 H C4AH13 Calcium aluminate hydrate Tetracalcium Aluminoferrite (C4AF) Similar to C3A  Schematic description of the hydration and structure development in cement paste. Cement grain Ca(OH)2 Ettringite needle C-S-H Rates of hydration of OPC constituents 100 C3A 80 C3S 60 % C4AF 40 C2S 20 0 20 40 60 80 100 Time (days) Compressive strength of OPC constituents 70 60 C3S 50 % 40 ß-C2S 30 20 C3A 10 C4AF 0 20 40 60 80 100 Time (days)  Manufacturing of Portland Cement  The three primary constituents of the raw materials used in the manufacture of Portland Cement are :  a) Lime b) Silica c) Alumina  Lime is derived from limestone or chalk  Silica & Alumina from clay, shale or bauxite  There are two chief aspects of the manufacturing process: First To produce a finely divided mixture of raw materials – chalk / limestone and clay / shale Second To heat this mixture to produce chemical composition  There two main process can be used in the manufacturing of Portland Cement : i) wet process ii) dry process  Wet 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 1510 ºC in horizontal revolving kilns (76 - 153 m) length and (3.6 - 4.8 m) in diameter.  Natural gas, petroleum or coal are used for burning. High fuel requirement may make it. uneconomical compared to dry process  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.  Effect of firing on raw materials  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 calciumaluminate. 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 18 mm in diameter.  The cement clinkers are cooled to about 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 cement silos or bagged.  Cement bags should be stored in a dry place.  ‫مراقبة الخامات‬ ‫األولية‬ ‫محجر الحجر الجيرى‬ ‫جهاز تحليل‬ ‫الخليط الخام‬ ‫يتم التحكم فى الجودة بداية‬ ‫من الخامات األساسية فى‬ ‫المحاجر و ذلك عن طريق‬ ‫البرامج اإللكترونية ثم التحكم‬ ‫الطفلة‬ ‫محجر‬ ‫فى الخليط عن طريق أجهزة‬ ‫التحليل اإلشعاعى و ذلك‬ ‫لتسهيل الحصول على خامات‬ ‫‪،‬متجانسة على الدوام‬  The Control Parameters Lime Saturation Factor Lime Saturation Factor is a means of describing the capacity of the other three major elements to totally use up the lime (Calcium).  Ca O x 100 LSF = 2.81 SiO2 + 1.18 Al2O3+ 0.65 Fe2O3  The Control Parameters Silica ratio Silicates (C3S and C2S) versus aluminates (C3A and C4AF) – Solid/liquid ratio – Indication of the raw mix burnability – Kiln process (coating, rings, dusty clinker) sensitive to SR changes – Typical 2.1 to 2.9. (opt. 2.4 - 2.6) SiO SR  2 2 Al O  Fe O 3 2 3  The Control Parameters Alumina ratio Alumina and iron oxide have fluxing effect Liquid phase promotes the C3S formation Viscosity of the melt decreases as iron increases, increasing the speed of reaction between CaO and SiO2 Lower alumina ratio = easier burning Typical 1.3 to 2.5. (opt. 1.4 - 1.8) Al O AR  2 3 Fe O 2 3 Kiln Stages of Clinker Manufacturing Quarry Crusher Pre blending Burning Homogenization Milling Cooling Clinkering ‫خطة مراقبة الجودة‬ ‫النتائج‬ ‫تحليل‬ ‫سحب‬ ‫العينات‬ ‫العينا‬ ‫ت‬ ‫تقييم‬ ‫اتخاذ‬ ‫النتائج‬ ‫اإلجراء‬ ‫المناسب‬ Cement silo The preparation of cements with advanced mechanical properties and high durability to the surrounding media, especially those of aggressive Sulphate and Chloride attack. The preparation of low cost cements to make up for the low production of cement and to cope with the national and international constructional development. Decreasing the environmental pollution in the industrial areas and their surroundings. Utilization of by-products in cement industry The problem of producing blended cements, namely pozzolanic, and filled pozzolanic cements, has been of considerable scientific and technological interest. The industrial by-products used in the preparation of blended cements such as : Cement dust from cement industry. Granulated slag from the production of pig iron. Phospho-gypsum from the production of phosphoric acid based fertilizer industry. Rice husk ash from the agricultural waste product “Rice husk”. Silica fume from ferrosilicon industry. Fly ash from iron steel industry.  Pozzolana It possesses little or no cementitious value but will, in finely divided form react with calcium hydroxide at ordinary and in the presence of moisture, chemically temperatures to form compounds possessing cementitious properties.  Pozzolana can be divided into two main groups, natural and artificial. Natural pozzolanas are mostly materials of volcanic origin and certain diatomoceous earths. Artificial pozzolanas are mainly products obtained by the heat treatment of clays, shales, certain siliceous rocks, Homra, Slag, silica fumes, rice husk ash and pulverized fuel ash.  GRANULATEDSLAG CEMENT In the Production of iron, the blast furnace is continuously charged from the top with iron oxide (ore), fluxing stone (limestone or dolomite) and fuel (coke). Two products are obtained from the furnace, molten iron that collected in the bottom of the furnace and liquid blast-furnace slag floating on the pool of iron. Both are periodically tapped from the furnace at a temperature of about 1500 oC. Quenching with water is the most common process for granulated slags to be used as cementitious materials. More efficient modern granulation system use high pressure water jets impinges on the steam of molten slag at a water-slag ratio of about 10-1 by mass. The Blast-furnace slag is quenched almost instantaneously to a temperature blow boiling point of water, producing particles of highly glassy material. Ground Granulated blast-furnace (GGBFslag) containing 35-50% CaO, 30-40% silica, 10-18%a Al2O3 and small amounts of MgO, and of manganese and iron oxide. When GGBF slag is mixed with water, initial hydration is much slower than Portland cement. Hydration of GGBF slag in the presence of Portland cement depends largely upon break down and dissolution of the glassy slag structure by hydroxide ions release during the hydration of Portland cement GGBF slag reacts with alkali and Ca(OH)2 to produce additional C-S-H Silica fume Silica fume is a by-product of the reduction of high-purity quartz with coal in electric furnaces in the production of silicon and ferrosilicon alloys or other silicon alloys such as ferrochromium, ferromanganese, ferromagnesium, and calcium silicon. RICE HUSK ASH-BLENDED CEMENT Rice husk is a major agricultural by-product. The constituents of husks are both organic and inorganic compounds. It contains lignin, cutin, carbohydrates lipids, organic acids and traces of vitamins. The inorganic is about 13-29% of the hush When the husk is heated under controlled of air (400-800 oC) rice husk ash with SiO2 content ≈ 90% is obtained. The SiO2 ash is mostly amorphous but when heated at about 800 oC, it starts to crystalline. Due to growing environmental concern, and the need to conserve energy and resources, efforts have been made to burn the husks under controlled conditions and to utilize the resultant as a building materials. Rice husk ash as artificial pozzolana  FILLED CEMENT Fillers are natural or artificial materials, which improve the physico-chemical and mechanical properties of the cement such as workability or water retention. They can be inert or have slightly hydraulic or pozzolanic properties. They cause no appreciable increase of the water demand of the cement, in addition to improve the resistance of the concrete or mortar to deterioration in any way or reducing the corrosion protection of reinforcement. Fillers are normally either limestone or any inert material such as sand, glass, ect. Cement plants are being built on or close to a limestone quarry, so that the practice of limestone grinding with clinker is obviously cheap. Limestone dust, which is produced in quarrying operations, possesses disposal and environmental problems. There is current interest, however, in the use of limestone as an addition to Portland cements. The addition of a small quantity, up to 5% of limestone filler has been common practice in many European countries such as France, which has permitted such addition since 1979. Limestone fillers improve physically the denseness of cement composites; furthermore, they are reactive. The formation of carboaluminates leads to accelerate the hydration of C3A, C3S or CA in the high-alumina cements which affect strength.