Blended Cement with Blast Furnace Slag

          The blast furnace slag (BFS) needs to be processed before it added as cement replacement. The processing of BFS, starting from slag granulation, moisture reduction  and finally grinding (comminution), leads to the production of ground granulated blast furnace slag (GGBS). GGBS can be added to cement or concrete mix as a partial replacement for cement, as stipulated by the national standards. The BFS obtained from steel plants contains moisture. The moisture reduction is generally integrated with the processing of BFS.

          The size reduction of BFS granules can be carried out in the ball mill, roller press, or vertical roller mill (VRM) or by a suitable combination of these equipment. In comparison to the cement clinker, the BFS is moist, fine grained, more abrasive, and harder to grind. The moisture content should be less than 4%, if grinding is done in a ball mill. In the roller press, moisture content up to 1%–2% is desirable for satisfactory performance. The VRM can dry and grind BFS up to 10% moisture content. It is desirable to dry BFS in a separate unit, for higher moisture contents.

          The activity of BFS is proportional to the glass content. The activity of inferior quality BFS (lower glass) can be improved by increasing its fineness but at a higher expense of the grinding energy, which increases exponentially with fineness, at higher fineness. On the other hand, BFS with higher glass can be ground relatively coarser (to save energy); that will give the advantage of lower water demand with good activity.

           The fineness expressed in terms of unit surface area (cm2/g, Blaine) is not a unique property, as the cements that have identical unit surface areas can have different particle size distributions, represented by RRSB (Rosin-Ramler-Sperling-Bennett) parameters. The fineness of cement can be unambiguously characterized by defining the surface area (cm2/g, Blaine) and one of the two parameters related to size distribution, namely, the slope (n) or the position parameter (x′), in the RRSB diagram. German Standard, DIN 66145: “Graphical representation of particle size distributions, RRSB-grid,” contains the mathematical equation of the distribution function and its application.

           Thus to bring out full potential, all aspects of GGBS production, namely granulation, storage, drying and grinding need attention.

Ref: “Mineral Admixtures in Cement and Concrete”, CRC Press (http://www.crcpress.com/product/isbn/9781439817926). Author: Dr J D Bapat (http://www.drjdbapat.com)

Written for engineers, book focuses on making more workable and durable concrete using mineral admixtures. For each mineral admixture, book looks at manufacturing and processing, physical characteristics, chemical and mineralogical composition, quality control, and reported experiences. It also examines the provisions of national standards.It encourages engineers to more effectively use these and other wastes in cement and concrete to support more sustainable growth of industry. Buy this book online to obtain 20 % discount and free shipping. Download details: http://bit.ly/online_purchase

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Case for Greater Utilisation of Fly Ash in Cement and Concrete

The “pulverized fuel ash” (PFA) or the so-called fly ash (FA), used as a mineral admixture in cement and concrete, is a product of the pulverized coal firing system, through conventional boilers, mostly used in the thermal power plants. While carbon burns in oxidizing surroundings, the inorganic mineral matter gets sintered and liquefied at high temperature. The melt flows down the walls of the furnace and about 25% gets collected as “bottom ash” (BA). It is crushed before disposal. The rest, PFA or FA, gets entrained in the up-flowing hot gas in the form of fine particles, which get trapped in the economizer, air-preheater, mechanical separator, and, finally, battery of electrostatic precipitators (ESP).

As a general practice in many countries, PFA and BA are mixed with water and transported to ash ponds/lagoons. The ash thus deposited in lagoons is called “lagoon ash” (LA) or “pond ash.” It causes problems besides occupying huge stretches of agricultural land. Notwithstanding the greater utilization of PFA (and BA) in recent times in cement and concrete, in bricks, and for land filling, a large quantity of ash still lies unutilized.

As per several estimates, the cement industry contributes about 5% of the global generation of carbon dioxide. The cement industry’s sustainable program developed by the World Business Council for Sustainable Development (WBCSD) prepared an “Agenda for Action” for a 5 year period from 2002 to 2007, endorsed by the leading cement manufacturers of the world. The agenda addressed the issues of (a) climate protection, (b) fuels and raw materials use, and (c) emission reduction besides other issues.

Ref: “Mineral Admixtures in Cement and Concrete”, CRC Press (http://www.crcpress.com/product/isbn/9781439817926). Author: Dr J D Bapat (http://www.drjdbapat.com)

Written for engineers, book focuses on making more workable and durable concrete using mineral admixtures. For each mineral admixture, book looks at manufacturing and processing, physical characteristics, chemical and mineralogical composition, quality control, and reported experiences. It also examines the provisions of national standards.It encourages engineers to more effectively use these and other wastes in cement and concrete to support more sustainable growth of industry. Buy this book online to obtain 20 % discount and free shipping. Download details: http://bit.ly/online_purchase

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Italcementi plans to combine bio and fossil fuels effectively

Recently, the Italcementi group unveiled a new plan to supplement their fossil fuel consumption with renewable fuels. These new fuels are coming from algae grown on site at their Gargenville, France plant.

The benefits of such a system as this are three-fold. The first benefit is the fact that less carbon dioxide is being released in the air. Secondly, the algae can be dried and used as a partial replacement of the plant’s fossil fuels. Finally, waste heat from the plant can be used during the drying process instead of being discharged to the atmosphere.

View Dr J D Bapat's activity in cement manufacturing & concrete

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Burning agri-waste can save energy in cement manufacturing

Holcim Lanka Ltd has started using agricultural waste to generate power in the cement manufacturing process.

Chairman of Holcim Lanka, Manilal Fernando, "This initiative has helped the company to reduce production cost by almost 30%," he said.

The company is using rice husks, straw, agricultural waste and other waste materials to generate power. 

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A stone for CO2: useful for cement industry

Iceland is experimenting with pumping carbon dioxide underground and converting it into rock

Researchers are now pumping CO2 underground in a process that will convert the greenhouse gas into rock. This technique may be a model for other power plants and cement plants to control their emissions, creating a climate change solution literally set in stone.

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EPA regulation on mercury and other harmful pollutants

The US Environmental Protection Agency (EPA) is issuing final rules that aim to limit emissions of mercury and other harmful pollutants from Portland cement production. This move sets the country’s first limits on mercury air emissions from existing cement kilns as well as strengthening the limits for new kilns.

 

The new measure will be fully implemented in 2013 and reduce annual emissions of mercury by 16,600lb or 92%, according to EPA estimates. In addition, the ruling is expected to lower hydrocarbons by 83% or 10,600 t, particulate matter by 92% or 11,500 t and acid gases (measured as HCl) by 97% or 110,000 t. Sulphur dioxide and nitrogen oxide levels are forecast to be cut by 78% and 5%, respectively.

 

Mercury in the air deposits into the water, where it changes into methylmercury, a bio-accumulating toxin. People are primarily exposed by eating contaminated fish with children and women of childbearing age particularly vulnerable to its neuro-damaging effects. The agency expects that the entire rule package will yield US$ 7-19 in public health benefits for every dollar in costs, which it estimates at around US$ 350 m annually.

 

While the cement industry’s national body, the Portland Cement Association (PCA), welcomes the rules being less stringent than those originally proposed in May 2009, it remains concerned that the regulations may still force several US cement plants to close. According to PCA, the compliance with the rule will cost the industry several billion dollars and require investments in pollution control equipment at a time when available capital is considerably constrained due to the state of the economy. Moreover, the large number of other regulatory requirements anticipated to affect the industry over the coming years complicates acquiring and installing the necessary emission controls for this rule. That could lead to additional cement plant closures, job losses and a reduction in US cement production capacity. It also fears the new legislation will fail to reduce global mercury (and other toxic) emissions as more cement imports are likely to originate in countries with less stringent legislation, which may also become home to new cement plants.

 

Meanwhile, the first casualty of the new rules appears to have emerged in the shape of Ash Grove Cement Co’s Durkee plant in Baker County, Oregon. Federal regulators have declined to create a special category of mercury emission rules that would take into account the higher mercury content of the plant’s limestone deposit. The company voluntarily spent around US$20 m over the past two years in installing equipment that removes around 90% of mercury, but following the new EPA ruling, still falls 5% short of the EPA standard. Ash Grove has said it cannot meet the standard with current technology. However, the EPA may consider giving the company extra time to comply with the new limits.

Ref: Cemnet News Bulletin, 13th August 2010

International journals on cement

Here is a list of some international journals on cement

(1) Cement International

Verlag Bau+Technik GmbH

Postfach 12 01 10
40601 Düsseldorf, Germany

Editor: Dr. Stefan Deckers
Tel. +49 (0) 2 11/9 24 99-51
deckers@verlagbt.de

(2) ZKG International

Bauverlag BV GmbH
Avenwedder Str. 55, 33311, Gütersloh, Germany

Editor-in-Chief
Dr. Petra Strunk

petra.strunk@bauverlag.de

(3) World Cement

Palladian Publications Ltd.

15 South Street, Farnham
GU9 7QU
Surrey, UK

enquiries@worldcement.com

(4) International Cement Review

Tradeship Publications Ltd
Old Kings Head Court
15 High Street
Dorking, Surrey
RH4 1AR, UK

Email: info@CemNet.com

What consumers should know about cement

WHAT CONSUMERS

SHOULD KNOW ABOUT CEMENT

Dr J D Bapat

An individual planning to build a house of his own or a builder goes to the market to buy cement for the construction work. Cement is freely available in the market under different types, grades and brand names. Each type and grade cater to the specific requirement of the construction. Many times consumers do not have the full knowledge of these aspects. Besides the cost, the quality of cement is important from the point of view of strength and durability. Some technical aspects about cement, which every consumer building a house buying from a builder would like to know, are explained in the following paragraphs.

Cement varieties: Some common types of cement available off-the-shelf in the market are ordinary Portland cement (OPC) in grades 53, 43 and 33; Portland pozzolana cement (PPC); Portland slag cement (PSC) and so on. For the consumers it is necessary to see that cement conforms to the relevant Indian Standard and the cement bag bears the BIS Certification mark. The Grade 33 OPC may be used for plastering or finishing work, Grade 43 for all general construction work and Grade 53 for the high strength requirements such as multi-storeyed buildings. The PPC and PSC can also be used for general construction work. Besides the long term strength, these cements also improve the durability of structures.

Using cement at site: Using cement at site requires conformation to certain requirements as specified by the relevant Standards. At site, cement is used as mortar (cement+sand) or concrete (cement+sand+aggregate). It is necessary that all the ingredients are mixed properly and in right proportion, mortar/concrete is transported and properly placed and compacted at the construction site and adequately cured. Control on the addition of water (water/cement ratio) is of particular importance. It will be difficult to obtain full benefit from the cement quality, if any of these processes are not carried out properly. Consult your structural engineer on that.

Meaning of the Grade of cement in Indian Standard: The Grade refers to the minimum 28-day compressive strength in MPa, measured according to the standard procedure.Thus 43 Grade cement refers to the standard compressive strength of 43 MPa or 430 kg/sq.cm., at 28 days. Remember that the Grade of cement is only one of the criteria deciding the quality of construction. The desired strength and durability of structure can be ensured only by following good construction practices at the site, as mentioned earlier.

Durability of construction: The structure is called durable when it gives satisfactory, economic, service life over the period for which it is designed. The durable structure has sufficient resistance towards internal and external agents causing corrosion of reinforcement, expansion of concrete due to sulphate attack, alkali-silica reaction and carbonation and deterioration due to freeze and thaw cycles. One major factor contributing to the durability is the permeability of concrete. In general, lesser the permeability, better is the durability.

Test certificate: When you buy cement, ask for the lated test certificate supplied by the cement manufacturer. The test report normally contains values of soundness for free lime and magnesia, setting time, compressive strength (3, 7, 28-day), loss on ignition, insoluble residue, chloride and alkali content. Check these values against those specified by the Standard. The standard values are given in the report itself, in most cases. The meaning of some important tests is as follows:

(i) Soundness: Indicates the extent of expansion that the cement may undergo after setting. Cement with lower expansion is preferred.

(ii) Setting time: The 'Initial Setting Time' indicates the duration within which the concrete is workable and should be placed. The 'Final Setting Time' is the upper limit of time beyond which the concrete shall loose its plasticity and shall begin to harden.

(iii) Compressive Strength: The compressive strength at 28 days indicates the capacity of cement to bear compressive load. The strength at 3 and 7 days is important from the point of view of removal of structural supports and scaffoldings. It should be noted that it is the strength of concrete which is important at the site. Hence the design and control of the concrete mix and construction practice are important.

(iv) Loss on Ignition (LOI): The excess LOI indicates some kind of adulteration or partial setting of cement during storage.

(v) Insoluble Residue (IR): The excess IR is an indication of adulteration

(vi) Chloride and Alkalies: A good quality cement should have lower values of chloride and alkalies, than the upper limits specified by the IS Code, from the durability considerations

(vii) Ideal color of cement: There is no ideal color of cement. It depends upon the chemical composition and the additive materials (fly ash, blast furnace slag) blended with cement during the process of manufacturing. A good quality cement may have a greenish, gray, brownish or blackish color. However color of cement does not affect its physical or chemical properties.

Major cement producers in India

MAJOR CEMENT PRODUCERS IN INDIA

Dr J D Bapat

• ACC Ltd.
• Ambuja Cements Ltd.
• Birla Corporation Ltd.
• Binani Cement Ltd.
• Cement Corporation of India Ltd.
• Chettinad Cement Corporation Ltd.
• Dalmia Cement (Bharat) Ltd.
• Grasim Industries Ltd.
• Gujarat Sidhee Cement Ltd.
• The India Cements Ltd.
• Indorama Cement Ltd.
• Lafarge India Pvt. Ltd.
• Madras Cements Ltd.
• Malabar Cements Ltd.
• Mangalam Cement Ltd.
• Mysore Cements Ltd.
• Orient Cement Ltd.
• OCL India Ltd.
• Penna Cement Industries Ltd.
• Prism Cement Ltd.
• Sanghi Industries Ltd.
• Saurashtra Cement Ltd.
• Shree Cement Ltd.
• Shree Digvijay Cement Co. Ltd.
• Shriram Cement Works
• Tamil Nadu Cements Corporation Ltd.
• Ultratech Cement Ltd.
• Zuari Cement Ltd.

Cement grinding aids

CEMENT GRINDING AIDS

Dr J D Bapat

The cement grinding aids are the additional materials (gas, liquid or solid), admixed in small amounts during the cement grinding process (cement manufacture), which can significantly improve the grinding efficiency, reduce energy consumption, without compromising the performance of the cement. Some commonly used cement grinding aids are triethanolamine (TEA), mono- and diethylene glycols (DEG), oleic acid, sodium oleate, sulphite waste liquor and dodecylbenzene sulphonic acid sodium lignosulphonate (from paper industry).

The cement grinding is an energy intensive process. The addition of grinding aids, during the process of cement grinding, results in improvement of the specific surface and grindability index of the material ground. This is attributed to the additive’s ability to reduce resistance to comminution and to prevent agglomeration of the freshly ground particles (due to neutralization of static charges) and powder coating on the grinding media (balls) and mill liners. The overall result is the reduction in the unit energy consumption and increased mill output. In some cases it is also reported that addition of grinding aids resulted in the improvement of compressive strength of cement at all ages.

The technology of grinding aids has been mostly patented. There are two main categories of the grinding aids:

(a) Those affecting reduction in the unit energy consumption and increase in the mill output

(b) Those affecting increase in the compressive strength and other properties of concrete, besides reducing the unit power consumption, as in (a) above.

Some of the patented technologies are summarised below. The readers are advised to refer to the original patent for detailed information.

Patents:

(i) United States Patent 6005057:

A cement clinker grinding aid which comprises a styrene-maleic anhydride copolymer (SMA) superplasticiser. The SMA is preferably a type with polyoxyalkylene-based side chains. Use of the grinding aid renders the grinding process more efficient and improves the performance of concrete, namely improved workability or reduced water-to-cement ratio for the same workability.

(ii) United States Patent 5084103:

Describes trialkanolamines, such as triisopropanolamine (TIPA) or N,N-bis(2-hydroxyethyl)-N-(2-hydroxypropyl)amine and tris(2-hydroxybutyl)amine as grinding aids for clinkers.

(iii) United States Patent 6290772

Disclosed the use of hydroxylamines including N,N-bis(2-hydroxyethyl)-2-propanolamine and N,N-bis(2-hydroxypropyl)-N-(hydroxyethyl)amine, to enhance the compressive strength of the cement compositions after 1, 3, 7, and 28 days. Also disclosed was a mixture involving other hydroxylamines such as triethanolamine. The patent further claims that these amines could be added as grinding aids in the cement manufacture.

(iv) United States Patents 4204877, 3615785, 5125976 and French Patent 2337699

One of the major classes of grinding aids used today is the oligomers of
lower alkylene glycols, such as diethylene glycol (DEG). They are used because
of their availability and low cost. These glycols have had their grinding
effectiveness enhanced by the inclusion of polyglycerols, lower fatty
acids and sulfonated lignin; unsaturated aliphatic acid and amines; a C₃ aliphatic acid salt and an amine; as well as alcohols and amides

Bibliography:

[1] Elwan M. M., Mahmoud G. A., EI-Didamony H., “Effect of some grinding aids on the grindability of portland cement”, J. Silicates industriels, No 11-12, 2002, pp 141-143

[2] Koki I., Chae-Yong L., Kazuo Y. Makihiko I., “Influence of grinding aids on the fluidity of cement mortar and effect of high temperature grinding on the character of cement”, Japan Cement Association Proceedings of Cement & Concrete, Vol. 59, 2006, pp 66-73

[3] Sohoni S., Sridhar R.,Mandal G., “The effect of grinding aids on the fine grinding of limestone, quartz and Portland cement clinker”, J. Powder Technology, Vol. 67, Iss. 3, 1991, pp 277-286

[4] Sottili L., Padovani D., “Effect of grinding aids in the cement industry, Part 2”, ZKG International J., Vol. 54, Part 3, 2001, pp 146-151

[5] Ito M., Sato K., Naoi Y., "Productivity increase of vertical roller mill for cement grinding", IEEE PCA Cement Industry Technical Conference, Conf. 39, 1997, pp 177-194

[6] Difen L., Shiliu W., “Effect of grinding aids on producing ultrafine particles”, J. Advanced Powder Technology, Vol. 3, No. 1, 1992 , pp. 47-53

[7] Cement Chemistry, Taylor H. F. W., Published by Thomas Telford, 1997