Hydraulic Cement PDF

HYDRAULIC CEMENT Concrete is the world’s most widely used construction material, and the Portland Cement Association estimates its annual production in excess of 5 billion cu yd. Concrete has many characteristics that make it such a widely used construction material. Among them are raw material ava...

HYDRAULIC CEMENT Concrete is the world’s most widely used construction material, and the Portland Cement Association estimates its annual production in excess of 5 billion cu yd. Concrete has many characteristics that make it such a widely used construction material. Among them are raw material availability, the ability of concrete to take the shape of the form it is placed in, and the ease with which its properties can be modified. The ability of concrete to modify such properties as its strength, durability, economy, watertightness, and abrasion resistance is most important. As illustrated in Table 4–1, there are a great many variables that affect the properties of concrete. The ease with which concrete can be modified by its variables can often work to the disadvantage of the user if quality control is not maintained from the first to the last operations in concrete work. Basically, concrete is 60 to 80 percent aggregates (i.e., sand and stone), which are considered “inert” ingredients, and 20 to 40 percent “paste” (i.e., water and Portland cement), considered the active ingredient. These materials are combined, or mixed, and cured to develop the hardened properties of concrete. HISTORY The development of cementing materials can be traced back to the Egyptians and Romans and their use of masonry construction. The Egyptians used a cement produced by a heating process, and this may have been the start of the technology. Roman engineering upgraded simple lime mortars with the addition of volcanic ash which increased their durability, as evidenced by the sound structures that still stand. A good example of the durability and longevity of Roman concrete is the Aqua Virgo built around 19 B.C. Today it still carries spring water over 11 miles to the Trevi Fountain in Rome. The development of concrete or cement technology as we know it today probably can be traced back to England, where in 1824 Joseph Aspdin produced a portland cement from a heated mixture of limestone and clay. He was awarded a British patent, and the name “portland cement” was used because when the material hardened, it resembled a stone from the quarries of Portland, England. Several of Joseph Aspdin’s contemporaries were involved in the same research, but evidence shows that he fired his product at approximately the clinkering temperature, thus producing a superior product. The production of portland cement in the United States dates back to 1872, when the first portland cement plant was opened at Coplay, Pennsylvania. Today, the production of portland cement is considered a basic industry, and it occurs in almost all regions of the world. MANUFACTURE OF PORTLAND CEMENT The manufacture of portland cement requires raw materials which contain lime, silica, alumina, and iron. The sources of these elements vary from one manufacturing location to another, but once these materials are obtained, the process is rather uniform (Table 4–2).  Common Sources of Raw Materials used in the manufacture of Portland cement Calcium Iron Silica Alumina Sulfate Aragonite Clay Clay Aluminum ore refuse* Gypsum Calcite Iron Ore Marl Clay Limestone Mill scale* sand Fly ash* Marl shale Shale Shale CaO Fe2O3 SiO2 Al2O3 * Industrial by-product Source: Portland Cement Association Fly ash is a byproduct from burning pulverized coal in electric power generating plants. During combustion, mineral impurities in the coal (clay, feldspar, quartz, and shale) fuse in suspension and float out of the combustion chamber with the exhaust gases. As the fused material rises, it cools and solidifies into spherical glassy particles called fly ash. Fly ash is collected from the exhaust gases by electrostatic precipitators or bag filters. As illustrated in Figure 4–1, the process begins with the acquisition of raw materials such as limestone, clay, and sand. The limestone is reduced to an approximately 5-in.size in the primary crusher and further reduced to 3/4 in. the secondary crusher. All of the raw materials are stored in the bins and proportioned prior to delivery to the grinding mill. The wet process results in a slurry, which is mixed and pumped to storage basins. The dry process produces a fine ground powder which is stored in bins. Both processes feed rotary kilns where the actual chemical changes will take place. The material is fed into the upper end of the kiln, and as the kiln rotates, the material passes slowly from the upper to the lower end at a rate controlled by the slope and speed of rotation of the kiln. As the material passes through the kiln, its temperature is raised to the point of incipient fusion, or clinkering temperature, where the chemical reactions take place. Depending on the raw materials, this temperature is usually between 2400°F (1316°C) and 2700°F (1482°C). Chemical recombinations of the raw ingredients take place in this temperature range to produce the basic chemical components of portland cement. The clinker produced is black or greenish black in color and rough in texture. Its size makes it relatively inert in the presence of moisture. From clinker storage, the material is transported to final grinding where approximately 2 to 3 percent gypsum is added to control the setting time of the portland cement when it is mixed with water. The resulting concrete will have improved shrinkage and strength properties. The portland cement produced is either distributed in bulk by rail, barge, or truck or packaged in bags. Bulk cement is sold by the barrel, which is the equivalent of four bags or 376 lb, or by the ton. Bag cement weighs 94 lb and is considered to be 1 bulk cubic foot of cement. CHEMICAL COMPOSITION OF PORTLAND CEMENT Portland cements are composed of four basic chemical compounds, shown with their names, chemical formulas,and abbreviations. The relative percentages of these compounds can be determined by chemical analysis. Each of the components exhibits a particular behavior, and it can be shown that by modifying the relative percentages of these compounds, the behavior of the cement can be altered. 1. Tricalcium silicate: 3𝐶𝑎𝑂 ∙ 𝑆𝑖𝑂2 = 𝐶3 𝑆 Tricalcium silicate hardens rapidly and is largely responsible for initial set and early strength. In general, the early strength of portland cement concretes will be higher with increased percentages of C3S. 2. Dicalcium silicate: 2𝐶𝑎𝑂 ∙ 𝑆𝑖𝑂2 = 𝐶2 𝑆  If moist curing is continued, the later strength after about 6 months will, be greater for cements with a higher percentage of C2S. Dicalcium silicate hardens slowly, and its effect on strength increases occurs at ages beyond one week. 3. Tricalcium aluminate: 3𝐶𝑎𝑂 ∙ 𝐴𝑙2 𝑂3 = 𝐶3 𝐴 Tricalcium aluminate contributes to strength development in the first few days because it is the first compound to hydrate. It is, however, the least desirable component because of its high heat generation and its reactiveness wit soils and water containing moderate-to-high sulfate concentrations. Cements made with low C3A contents usually generate less heat, develop higher strengths, and show greater resistance to sulfate attacks. 4. Tetracalcium aluminoferrite: 4𝐶𝑎𝑂 ∙ 𝐴𝑙2 𝑂3 𝐹𝑒𝑂3 = 𝐶4 𝐴𝐹𝑒 Tetracalcium aluminoferrite assists in the manufacture of portland cement by allowing lower clinkering temperature.C4AFe contributes very little to the strength of concrete even though it hydrates very rapidly. Most specifications for portland cements place limits on certain physical properties and chemical composition of the cements. Therefore, the study of this material requires an understanding of some of these basic properties. Type of Potential Compound Composition % Blaine Portland C3S C2S C3A C4AF Fineness Cement m2/kg I 54 18 10 8 369 II 55 19 6 11 377 III 55 17 9 8 548 IV 42 32 4 15 340 V 54 22 4 13 373 White 63 18 10 1 482 Water-Cement Reaction Hydration is the chemical reaction that takes place when portland cement and water are mixed together. The hydration reaction is considered complete at 28 days. The reaction depends on available moisture. Figure below indicates strength gains for different curing conditions. When cement is mixed with water to form a fluid paste, the mixture will eventually become stiff and then hard. This process is called setting. A cement used in concrete must not set too fast, for then it would be unworkable, that is, it would stiffen and become hard before it could be placed or finished. When it sets too slowly, valuable construction time is lost. Most portland cements exhibit initial set in about 3 hours and final set in about 7 hours. If gypsum were not added during final grinding of normal portland cement, the set would be very rapid and the material unworkable. False set of portland cement is a stiffening of a concrete mixture with little evidence of significant heat generation. To restore plasticity, all that is required is further mixing without additional water. There are cases where a flash set is exhibited by a cement, and in this case the cement has hydrated and further remixing will do no good. The actual setting time of the concrete will vary from job to job depending on the temperature of the concrete and wind velocity, humidity, placing conditions, and other variables. The ability of a cement to develop compressive strength in a concrete is an important property (Table 4–4).The compressive strengths of cements are usually determined on standard 2-in.(50.8-mm) cubes.The results of these tests are useful in comparing strengths of various cements in neat paste conditions. Neat paste is water, cement, and a standard laboratory sand used to standardize tests. The tests will not predict concrete strength values due to the variables in concrete mixtures that also influence strength. The heat generated when water and cement chemically react is called the heat of hydration, and it can be a critical factor in concrete use. The total amount of heat generated depends on the chemical composition of the cement, and the rate is affected by the fineness, chemical composition, and curing temperatures (Figure 4–3).  Approximate amounts of heat generation during the first 7 days of curing using Type I cement as the base are as follows: Type I 100% Type II 80–85% Type III 150% Type IV 40–60% Type V 60–75% Concrete has a low tensile strength; it is approximately 11percent of concrete’s compressive strength. To allow the use of concrete in locations where tensile strength is important or increased compressive strength is required, steel is used to reinforce the concrete. Tests to Characterize Portland Cement Fineness Test (IS 4031 (Part 1) – 1996). The fineness of cement is a measure of cement particle size and is denoted as terms of the specific surface area of cement. The Test is done by sieving cement samples through a standard IS sieve. The fineness of cement is determined by the sieving method. It is measured by the ratio between coarse particles (which retained in 90-micron sieve analysis) to the fineness particles (which passed through the sieve analysis). 𝑊𝑒𝑖𝑔ℎ𝑡 𝑜𝑓 𝑐𝑒𝑚𝑒𝑛𝑡 𝑟𝑒𝑡𝑎𝑖𝑛𝑒𝑑 𝐹𝑖𝑛𝑛𝑒𝑛𝑒𝑠𝑠 𝑜𝑓 𝐶𝑒𝑚𝑒𝑛𝑡 = 𝑊𝑒𝑖𝑔ℎ𝑡 𝑜𝑓 𝑐𝑒𝑚𝑒𝑛𝑡 𝑠𝑎𝑚𝑝𝑙𝑒 The fineness ratio will differ based on the types of cement. Ordinary Portland cement – 10% Low heat cement – 5% Rapid hardening cement – 3 to 5% Importance of fineness of cement More cement coarse particles affect and reduce the rate of hydration. If the hydration rate decreases, then it impacts the strength development of concrete or mortar. More fineness induces dry cracks on concrete surfaces. Fineness cement can easily blend with other ingredients. The fine particles are easily mixed with the water to make the cement paste as compared to the coarser cement particle. Bleeding can be reduced. More fineness means high concrete workability and thus increases the setting time. Density and Specific Gravity of Hydraulic Cement Bulk density of ordinary Portland cement is nearly 1140 kg/m3 or 1.14 g/cm3 (solid particles of surrounded by air voids) and its density (solid particles only) is 2.8 g/cm3. The specific gravity of OPC is around 3.15 (ratio of the density or mass of cement to the density of water at a certain water temperature) Portland-blast-furnace-slag and portland-pozzolan cements may have specific gravities near 2.90. Density of cement and is one of the vital parameters, which determines the mix design of concrete. Since concrete mix proportion is done based on the weight batching not on volumetric so density is a most important factor of cement. 2. Standard Consistency Test (IS: 4031 ( Part 4 ) – 1988) The standard consistency of cement is that consistency, which permit the vicat plunger to penetrate to a point 5 to 7mm from the bottom of the vicat mold when tested. Apparatus Vicat apparatus Balance Gauging Trowel Stop Watch, etc. The standard consistency of cement paste generally varies between 25-35%. So the necessity of the cement test’s consistency is to find the required water-cement ratio. 𝑀𝑎𝑠𝑠 𝑜𝑓 𝑤𝑎𝑡𝑒𝑟 𝑤𝑎𝑡𝑒𝑟 − 𝑐𝑒𝑚𝑒𝑛𝑡 𝑟𝑎𝑡𝑖𝑜 = 𝑥 100 𝑀𝑎𝑠𝑠 𝑜𝑓 𝑐𝑒𝑚𝑒𝑛𝑡 𝑀𝑎𝑠𝑠 𝑜𝑓 𝑊𝑎𝑡𝑒𝑟 = 𝐷𝑒𝑛𝑠𝑖𝑡𝑦 𝑜𝑓 𝑊𝑎𝑡𝑒𝑟 𝑥 𝑉𝑜𝑙𝑢𝑚𝑒 It helps in achieving the desired workability and strength of the concrete mix and for its proper hydration and subsequent strength development. 3. Initial and Final Setting Time Of Cement Test (IS: 4031 (Part 5) – 1988) Theoretically, Initial setting time of concrete is the time period between addition of water to cement till the time at 1 mm2 (needle “C”) fails to penetrate the cement paste, placed in the Vicat’s mold 5mm to 7mm from the bottom of the mold. Final setting time is that time period between the time water is added to cement and the time at which needle “C” makes an impression on the paste in the mold but 5 mm (needle “F”) annular attachment does not make any impression. Calculations Where T1 =Time at which water is first added to cement T2 =Time when needle fails to penetrate 5 mm to 7 mm from bottom of the mould  T3 =Time when the needle “C” makes an impression but the needle “F” fails to do so. 𝐼𝑛𝑖𝑡𝑖𝑎𝑙 𝑆𝑒𝑡𝑡𝑖𝑛𝑔 = 𝑇2 − 𝑇1 𝐹𝑖𝑛𝑎𝑙 𝑆𝑒𝑡𝑡𝑖𝑛𝑔 = 𝑇3 − 𝑇1 Initial setting time gives an idea about how fast cement can start losing its plasticity and the final setting time of cement gives an idea about how much Time cement takes to lose its full plasticity and gain some strength to resist pressure. As per standards, the initial setting time of cement should be less than 30 min for OPC cement. Whereas, final setting should not be more than 10 hrs for OPC cement. Soundness Test of Cement IS: 4031-Part 3-1988 The soundness of cement indicates the stability of any cement during the volume change in the process of setting and hardening.In case the volume change in cement is unstable after setting and hardening, the concrete element will crack, which can affect the quality of the structure or even cause serious accidents, known as poor dimensional stability. 1. Placing a cement paste formed by gauging cement with 0.78 times the water required to give a paste of standard consistency on lightly oiled mold on a lightly oiled glass sheet and covered with another lightlty oiled glass sheet with weight on top. 2. Submerge the whole assembly in the water at a temperature of 27 ± 2°C and keep there for 24 hours. Then measure the indicator points to the nearest 0.5 mm. Submerge the mold again in the water at the temperature prescribed above. 3. Bring the water to boiling, with the mould kept submerged, in 25 to 30 minutes, and keep it boiling for three hours. Remove the mould from the water, allow it to cool and measure the distance between the indicator points. 4. The difference between these two measurements indicates the expansion of the cement. This must not exceed 10 mm for ordinary, rapid hardening and low heat Portland cement. If in case the expansion is more than 10 mm as tested above, the cement is said to be unsound. An unsound cement will exhibit cracking, disruption, and eventual disintegration of the material mass. This delayed-destruction expansion is caused by excessive amounts of free lime or magnesium. The free lime is enclosed in cement particles, and eventually the moisture reaches the lime after the cement has set. 5. Heat Of Hydration Test IS 4031-1968 During the Curing of Concrete, Hydro-thermal Reaction takes place, resulting in the production of heat because of chemical reactions. The rise of heat in concrete could be as high as 50oC. Hence in order to reduce such heat, low-heat cement is used. The test is carried out using a calorimeter using the principle of heat gain. Apparatus Calorimeter, insulated wood case, thermometer plus holder, vacuum jar with stopper, glass funnel, stirring paddle, and chuck are the apparatus required for the test. Result It has been Standardized that the low heat cement should not generate heat of 65 Calories per gram of cement in 7 days and 75 Calories per gram for the duration of 28 days. 7. Tensile Strength Test (IS:456 2000) The Tensile Strength of Cement is the maximum load that cement in its hardened state can withstand without fracture when tension is applied. It is necessary to test the tensile strength of cement because concrete structures are highly prone to tensile cracking due to various kinds of load applied. As compared to Compressive Strength Tensile strength is very low. Apparatus Testing Machine Tamping Rod Concrete Mold Trowel Result The Tensile Strength of Cement is between 3-5 MPa i.e 300 – 700 psi. 8. Chemical Composition Test (IS 269-1998) The components present in cement for forming cement as the complete products are lime or limestone, silica (SiO2), alumina (Al2O2), magnesia (MgO), etc. Among which most important raw materials required for making cement are limestone, clay, and marl. Flame Photometer and ELE Flame Photometer are the instruments used to know the constitutes of Cement. Result A good cement should have the constitution of components as listed, Lime or Limestone – 62% (Highest) Silica (SiO2) – 22% Alumina (Al2O2) – 7.5% Magnesia (MgO) – 2.5 % Other Components – remaining 6%  Type I This type is a general concrete construction cement utilized when the special pavements and sidewalks, (Normal) properties of the other types are not required. It is used where the concrete reinforced concrete buildings, will not be subjected to sulfate attack from soil or water or be exposed to bridges, railway structures, tanks, severe weathering conditions. It is generally not used in large masses because reservoirs, culverts, water pipes, of the heat generated due to hydration. and masonry units. Type II Type II cement is used where resistance to moderate sulfate attack is piers, abutments, and retaining (Moderate important, as in areas where sulfate concentration in groundwater is higher walls, highway pavements than normal but not severe. Type II cements produce less heat of hydration or than Type I, hence their use in structures of mass such as. They are used in Modified) warm-weather concreting because of their lower temperature rise than Type I. The use of Type II for highway pavements will give the contractor more time to saw control joints because of the lower heat generation and resulting slower setting and hardening.  Type III Type III cements are used where an early strength gain is important and heat (Early generation is not a critical factor. When forms have to be removed for reuse as soon as possible, Type III supplies the strength required in shorter periods Strength) of time than the other types. In cold-weather concreting, Type III allows a reduction in the heated curing time with no loss in strength. Type IV Type IV cement is used where the rate and amount of heat generated must large mass placements such as (Low Heat) be minimized. The strength development for Type IV is at a slower rate than gravity dams Type I. It is primarily used in large mass placements such as gravity dams where the amount of concrete at any given time is so large that the temperature rise resulting from heat generation during hardening becomes a critical factor. Type V Type V is primarily used where the soil or groundwater contains high sulfate (Sulfate concentrations and the structure would be exposed to severe sulfate attack. Resisting) Other types of cement Air-Entraining Cements (Types IA, IIA and IIIA) The three cements correspond to Types I, II, and III, with the addition of small quantities of air- entraining materials integrated with the clinker during the manufacturing process. These cements provide the concrete with improved resistance to freeze–thaw action and to scaling caused by chemicals and salts used for ice and snow removal. Concrete made with these cements contains microscopic air bubbles, separated, uniformly distributed, and so small that there are many billions in a cubic foot. White Portland Cement White portland cement is a true portland cement, its color being the principal difference between it and normal Portland cement. The cement is manufactured to meet ASTM C150 and C175 specifications. The selected raw materials used in the manufacture of white cement have negligible amounts of iron and manganese oxide, and the process of manufacture is controlled to produce the white color. Its primary use is for architectural concrete products, cement paints, tile grouts, and decorative concrete. Its use is recommended wherever white or colored concrete or mortar is desired. Colored concretes are produced by using a coloring additive, and the white cement allows for more accurate control of colors desired. Portland Blast-Furnace Slag Cements In these cements, granulated blast-furnace slag of selected quality is interground with portland cement. The slag is obtained by rapidly chilling or quenching molten slag in water,steam,or air. Portland blast-furnace slag cements include two types, Type IS and Type IS-A,conforming to ASTM C595.These cements can be used in general concrete construction when the specific properties of the other types are not required. However, moderate heat of hydration (MH), moderate sulfate resistance (MS), or both are optional provisions. Type IS has about the same rate of strength development as Type I cement, and both have the same compressive strength requirements. Slag is a by-product of smelting (pyrometallurgical) ores and recycled metals. Slag is mainly a mixture of metal oxides and silicon dioxide. Broadly, it can be classified as ferrous (by-products of processing iron and steel), ferroalloy (by-product of ferroalloy production) or non-ferrous/base metals (by-products of recovering non-ferrous materials like copper, nickel, zinc and phosphorus) Waterproof Portland Cement Waterproof Portland cement is manufactured by the addition of a small amount of calcium, aluminum, or other stearate to the clinker during final grinding. It is manufactured in either white or gray color and is used to reduce water penetration through the concrete. ` Portland-Pozzolan Cements IP,IP-A,P,and P-A designate the portland-pozzolan cements with the A denoting air-entraining additives as specified in C595.They are used principally for large hydraulic structures such as bridge piers and dams. These cements are manufactured by intergrinding portland cement clinker with a suitable pozzolan such as volcanic ash, fly ash from power plants,or diatomaceous earth, or by blending the portland cement or portland blast-furnace slag cement and a pozzolan.