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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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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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.