The purpose of this study is to find a substitute for clinker known as mineral component, to make new or different kinds of composite cement. This chapter presents the review of related research of the study for potential materials as mineral component for the production of Portland cement.
What is Portland Cement?
The ASTM C 150 cited by Federal Highway Administration of the United States Department of Transportation defines Portland cement as "hydraulic cement (cement that not only hardens by reacting with water but also forms a water-resistant product) produced by pulverizing clinkers consisting essentially of hydraulic silicates, usually containing one or more of the forms of calcium sulphate as an inter ground addition".
The Pavement Interactive Core series of articles defines Portland cement as "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."
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ASTM Standard C 219-94 defines Portland cement as a hydraulic cement produced by pulverizing Portland-cement clinker, and usually containing calcium sulphate and blended hydraulic cement as a hydraulic cement consisting of two or more inorganic constituents (at least one which is not Portland cement or Portland cement) which separately or in combination contribute to the strength-gaining properties of the cement, (made with or without other constituents, processing additions and functional additions, by intergrinding or other blending) (Hewlett, 1998).
What is Portland Cement Clinker?
Portland cement clinker is a dark grey nodular material made by heating ground limestone and clay at a temperature of about 1400 C-1500 C. The nodules are ground up to a fine powder to produce cement, with a small amount of gypsum added to control the setting properties which range in size from 1mm to 25mm or more and are composed mainly of calcium silicates, typically 70 percent - 80 percent (Winter, 2005).
Portland cement clinker contains four main minerals (Winter, 2005):
Alite: approximately tricalcium silicate (typically about 65 percent of the total)
Belite: approximately dicalcium silicate (typically about 15 percent of the total)
Aluminate: very approximately tricalcium aluminate (typically about 7 percent of the total)
Ferrite: very approximately tetracalcium aluminoferrite (typically about 8 percent of the total)
CEMEX Materials Safety Datasheet defined Portland cement clinker as odourless grey nodules to dust insoluble in water. The principal constituents are calcium silicates and aluminates. Small amounts of alkalis, lime and chlorides are also presents together with trace amounts of heavy metals including chromium.
Material Safety Data Sheet for Portland Cement Clinker of Ash Grove Cement Company defines Portland cement clinker as a sintered material produced by heating to high temperature (greater than 1200 degrees Celsius) a mixture of substances such a limestone and shale from the earth's crust. The substances manufactured are essentially hydraulic calcium silicates contained in a crystalline mass, not separable into the individual components.
Importance of Mineral Component (MIC)
The Cement Industry Federation defines (MIC) mineral components as natural or artificial mineral materials with hydraulic properties, used as a clinker or cement substitutes (e.g. blast furnace slag, fly ash, pozzolana and gypsum).
The process in producing cement is very costly both in energy and resources. Using suitable mineral components may lower the clinker factor and it may help in reducing the fuel/electrical and raw materials needed to produce cement. Another important reason in replacing clinker is its significant driver of lowering the CO2 emissions. A potential material that can be used as mineral component should have the ability to mix with lime and contains high pozzolan activity index. The pozzolan is defined by ACI 116R as "a siliceous and aluminous material, which in itself possesses little or no cementitious value but will, in finely divided form and in the presence of moisture, chemically react with calcium hydroxide at ordinary temperatures to form compounds possessing cementitious properties. It is either a raw or calcined natural material that has pozzolanic properties (for example, volcanic ash or pumicite, opaline chert and shales, tuffs, and some diatomaceous earths)."
Chemical and physical properties of Natural Pozzolan
When a mixture of Portland cement and a pozzolan reacts, the pozzolanic reaction progresses like an acid-base reaction of lime and alkalies with oxides (SiO2 + A12 O3 + Fe2O3) of the pozzolan. Two things happen. First, there is a gradual decrease in the amount of free calcium hydroxide with time, and second, during this reaction there is an increase in formation of CSH and calcium alumino silicates that are similar to the products of hydration of Portland cement. According to Lea (1971) cited by KrajÄ‰i, et. al. (2007), the partial replacement of Portland cement by pozzolan of high SiO2/R2O3 (R2O3 = Al2O3 + Fe2O3) ratio has been found to increase the resistance of concrete to sulfate and seawater attack (R2O3 is approximately the summation of the Al2O3 and Fe2O3 contents). This is, in part, attributable to the removal of free hydroxide formed in the hydration of Portland cements.
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According to Mehta (1987) cited by KrajÄ‰i, et. al. (2007), the result is that the hardened cement paste contains less calcium hydroxide, more CSH, and other products of low porosity. Research on the hydration of blended cements made with natural pozzolans of volcanic origin (Santorin earth, pozzolana) indicated that pore refinement resulting from pozzolanic reaction is important for enhancing chemical durability and mechanical.
The shape, fineness, particle-size distribution, density, and composition of natural pozzolan particles influence the properties of freshly mixed unhardened concrete and the strength development of hardened concrete. Most natural pozzolans tend to increase the water requirement in the normal consistency test as a result of their microporous character and high surface area. Natural pozzolans can improve the performance of both fresh and hardened concrete when used as an ingredient of portland-pozzolan cement or as an admixture to Portland-cement concrete.
Potential Mineral Component (MIC)
Metakaolin. The burning of original kaolin sand (OKS) provides burn kaolin sand (OBS) which contains metakaolin as a pozzolan. Metakaolin (MK) encompasses as main constituents SiO2 and Al2O3, and in smaller quantities Fe2O3, CaO, MgO, SO3, Na2O and K2O. The high content of SiO2 and Al2O3 in metakaolin (MK) makes it efficient as a pozzolan in cement ad concrete. The high pozzolanic activity is also due to the large portion of small particles of metakaolin (KrajÄ‰i, et. al. 2007).
Pozzolana. It is called hydraulic cement discovered by the Romans and still used in some countries, made by grinding pozzolana (a type of slag that may be either natural-i.e., volcanic-or artificial, from a blast furnace) with powdered hydrated lime. Roman engineers used two parts by weight of pozzolana mixed with one part of lime to give strength to mortar and concrete in bridges and other masonry and brickwork. During the 3rd century BC, the Romans used pozzolana instead of sand in concrete and mortared rubblework, giving extraordinary strength. Used with an aggregate of broken tuff, travertine, brick, or marble, the material contributed to the evolution of new architectural forms in such monumental constructions as the Pantheon and the Baths of Caracalla at Rome (Encyclopedia Britannica).
Waste Clay Materials. According to de Rojas (2009) from his paper "Waste Clay Materials as Pozzolanic Additions", the results show that the calcined clay residues have an acceptable pozzolanic activity, since at the age of 1 day; these residues fixed a 46 percent of lime, 50 percent at 3 days and 80 percent at 90 days. These results show that the calcined temperature of these ceramic materials (by 900 degrees Celsius) is enough to activate the clays, obtaining pozzolanic properties. The ceramic waste additions give positive characteristics to blended cements, due to these wastes contribute to the increment of chemical strength against aggressive medium.
Shale rock. Is a type of sedimentary soft, layered rock that was formed when clay-size particles were deposited in relatively calm, muddy waters. Over a long period of time these particles became compacted to form a porcelain type shale rock. The material is naturally calcined as it was heated by an underground heat source. The calcined shale is highly desirable as a natural pozzolan and ceramic base material.
Calcined Moler Clay. It is otherwise known as Bio Sorb, is calcined clay developed expressly for the horticultural industry. It is a hard and durable material with excellent drainage properties, yet the porous grain structure allows exceptional water retention. TheÂ General grade comprising 5mm to 8mm grain size. Johansson and Andersen (2003) performed an experiment about the pozzolanic activity of moler clay and it shows that the chemical and physical properties of finely granulated calcined Moler according to ASTM C 618 are an excellent pozzolan for the use in concrete.
Sugar Cane Bagasse. Cordeiro et. al. (2004), in his study entitled "Influence Of Mechanical Grinding On The Pozzolanic Activity Of Residual Sugarcane Bagasse Ash" concluded that the results obtained in the investigation indicate that, after an adequate mechanical grinding, the residual sugarcane residual ash can be used as a pozzolanic admixture in concrete. The minimum value of pozzolanic activity index, established by Brazilian standard NBR 12653, was reached after 15 minutes of grinding. Grinding the ash for 120 made possible to obtain a pozzolan with an activity index of 100 percent. An increase on the grinding time from 120 minutes to 240 minutes did not benefit significantly activity of the pozzolan because of the difficulty in grinding sub-micron particles. The results also indicate that the PI increases with the increase of the specific surface area of the sugarcane ash.
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Pumice. The Mineral Information Institute describes pumice as a type of volcanic rock that is produce when lava with a vey high content of water and gases is thrown out of a volcano. The gas bubbles that escape from the lava causes the pumice rock to become frothy and giving it a porous characteristics when it cools and harden. The chemical composition of pumice is the same as rhyolite, which contains over 70 percent silica.
Recycled Concrete. This can be generated in demolished building, roads and bridges. The chemical composition of recycled concrete depends on its exposure to the surrounding. The need for recycling the concrete is now increasing because of the destruction of the structures due to natural calamities which results in decrease of dumping sites for this kind of waste.