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for control of the air content in concrete, anti-foaming agent, shrinkage reducers, anti-corrosion agent, waterproofers (Kuei Suan Jen Hsueh Pao;2012). Besides their expected functions, those grinding aids will usually make noticeable impacts on other properties of concrete like rheological properties, setting behavior, strength development, shrinkage and cracking behaviors (Qiu, X., 2011). Inorganic ingredients, mainly including some inorganic salts and a wide range of organic substances like alcohol, carboxylate acid, ammonia, sugars, surfactants, and polymers, are frequently used in production as GAs alone or in the mixture. The conventional cement and concrete chemistry has comprehensively represented the process of cement hydration, kinetics, microstructural development, the relationship between microstructure and macroscopic properties of cement and concrete.

However, conventional chemistry with inorganic ingredients could not analyze the aspects and the processes for the cases of the addition of various organic substances in modern cement and concrete. The organic substances could change the kinetics of cement hydration by adsorption and complexation, participate into the microstructure of cement hydrates of calcium hydroxide and calcium silicate hydrate that consequently affect the rheological properties, setting behavior, strong growth and even shrinkage and cracking behavior (Shatish Chandra and Per Flodin,1987). The admixture of grinding aids in cement grinding process can save mechanical energy and affect the variations of ?neness characteristics; the action of grinding aids is governed by mechanochemical activation that has been discussed. Grinding is an important operation used widely in various industries, but it is also one of the most inefficient unit operations. In the cement industry where huge amounts of clinker are dry-ground, a large number of studies have been carried out on the grinding aids to improve grinding efficiency of the cement clinker; beneficial observations have been obtained for several decades (Iwabuchi, T. and Res. Assoc, J., 1970).

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However, the action mechanism of grinding aids, which improves the efficiency of the grinding remarkably with a small amount of the addition, has not been understood perfectly despite a large number of useful information (El-Shall H. and Somasundaran, 1984)( Fuerstenau, D.W,1995). If we actually use a grinding aid at the present technical level, we must empirically determine the variety and quantity of the grinding aid based on experimental data. In most of the studies (Tanaka, T. and Kawai, S., 1962) (Sureshan, M.K., and Ahluwalia, S.C., 1992) on grinding aids, the effects of grinding aids have been discussed to get the fine powders of micron sizes, but there are only a few reports (Ikekawa, A. et al, 1991). Grinding aids should even more positively be applied to ultrafine grinding operations with higher energy consumption. However, not only in ultrafine grinding operations but also in fine ones in fields other than the cement industry, grinding aids have scarcely been utilized because the undesirable contamination of the product occurs with the use of the aids (Takahashi, J. et al, 1991).

We must select an appropriate one of grinding aids that has no detrimental effect on downstream processing on the final product. Generally, various chemical additives and treating agents are used in several processes after the grinding process for the purposes, such as the prevention of agglomeration between particles, the stabilization of powder surface and the aid of formation of ceramic powder, etc.

I.3.1 Classification of Grinding Aids

Several of materials have been used as grinding aids which can be classi?ed as liquid and solid grinding aids.

a. Liquid grinding aids such as aliphatic amines, amino alcohols and glycol compounds, including triethylenetetramine (TETA), Tetraethylenepentamine (TEPA), triethanolamine (TEA) and tri isopropanol amine (TIPA).

b. Solid grinding aids such as metaphosphoric and sulfonate, including sodium tripolyphosphate (STPP), dodecyl benzene sulfonic acid (DBA) and calcium lignosulfonate (CL), etc. The plurality of functional groups in grinding aids made them has a strong adsorption that can be adsorbed on the surface and micro-crack of cement particle, forming absorption ?lm, reducing the free energy of particle surface and promoting the propagation of cracks.

TEA is one of the most commonly used grinding aids that has an obvious effect on strength enhancement. Worsfold and Yan 1991 reported that there are different grinding aids have been used and their formulas. There are several types of aliphatic amines such as triethylenetetramine (TETA), tetraethylenepentamine (TEPA) and amino alcohols such as diethanolamine (DEA), triethanolamine (TEA), tri-isopropanol amine (TIPA). Glycol compounds are included such as ethylene glycol (EG), diethylene glycol (DEG). In addition, there are more complex compounds such as aminoethyl ethanolamine (AEEA) and hydroxyethyl diethylenetriamine (HEDETA).
Phenol and phenol-derivates are also used as grinding aids. Other compounds, mentioned in the product data sheets, such as amine acetate, higher polyamines, and their hydroxyethyl derivates, are used, but these are undefined in data sheets. Therefore, these compounds are not considered here, only the listed compounds are reviewed and discussed in more detailed

Table (1) Grinding Aids

Compound Abb. Formula
Diethanolamine DEA NH-(CH2CH2OH)2
Triethanolamine TEA (CH2CH2OH)3N
Triisopropanolamine TIPA CH3CH(OH)CH23N
Aminoethylethanolamine AEEA NH2-(CH2)2-NH-(CH2)-OH
Triethylenetetramine TETA NH2-(CH2)2-NH-(CH2)2-NH-(CH2)2-NH2
Tetraethylenepentamine TEPA NH2-(CH2)2-NH-(CH2)2-NH-(CH2)2-NH-(CH2)2-NH2
Ethylene glycol EG HO-CH2-CH2-OH
Diethylene glycol DEG HO-(CH2)2-O-(CH2)2-OH
Hydroxyethyl
diethylenetriamine
HEDETA NH2-(CH2)2-NH-(CH2)2-NH-(CH2)2-OH
Phenol – C6H5OH

There are some cement grinding aids (CGA) include triethanolamine (TEA), mono- and diethylene glycol (DEG), oleic acid, sodium oleic, dodecylbenzene sulfonic acid, and sodium lignosulfonic acid (from paper industry) (Sottili; L. et al 2002), sugarcane bagasse ash (Cordeiro; G.C. et al,2009), beet molasses( Gao; X. et al, 2011), triethanolamine (TEA) with potassium hydroxide (Heinz; D. et al 2010), dihydroxy compound class (ethylene glycol, propylene glycol, and polypropylene glycerol), phenol, glycol, alkanol amine , alcohols and glycols( Hasegawa;M. et al 2011), fatty acids(Albayrak; A.T. et al 2005). Katsioti et al 2009 also investigated the impact of some various cement grinding aids such as triethanolamine hydrochloride, triethanolamine, 2,4pyrimidinedione,1,1′,1″-Nitrolotri-2-propanol (TIPA), 1,1’Iminobisi-2-propanol (DIPA), 4-hydroxy-1,8-naphthyridine, benzene, and benzene amine on grind ability and cement performance. Glycerol resulted from jatropha biodiesel industry has similar physical and chemical properties as mono-ethylene glycol (EG) and diethylene glycols (DEG) that make it possible to use as grinding aids. A significant reduction of energy consumption can be noticed during the grinding of Portland cement clinker and gypsum by adding a small quantity of a grinding aid (GA) in the range of about 0.02- 0.10 % of the manufactured cement weight inside the cement mill. The chemical basis of the used GAs includes ethanol mines such as triethanolamine (TEA), monoethanolamine (MEA) and tri isopropanol amine (TIPA), as well as glycols such as ethylene glycol (EG) and propylene glycol (PG) can be considered the main factor.

Because of their highly organic polar nature, GAs are adsorbed on surfaces formed by the fracture of electrovalent bonds (i.e. Ca–O and Si–O), leading to reducing the surface energy forces that cause attraction and re-agglomeration of the newly produced cement particles (Assaad et al., 2008). Approximately 95% of the feed to the cement grinding circuit is clinker and the rest of the feed are ”additives” which includes grinding aids (GAs). The quality of cement is measured by the surface area (Blaine index). It should be noticed that the surface area of the cement powder depends on the size distribution of cement particles (smaller particles have a larger surface area) (Jankovic, A. et al, 2004).

The formation of electrostatic surface charges of opposed polarity causes the cement particles to agglomerate as a result of the forces of attraction acting on them. Consequently, the cement particle agglomeration reduces the efficiency of the mill. This phenomenon is characterized by an increase in energy consumption whilst maintaining constant Blaine. The extent of agglomeration depends on:

• The specific characteristics of the materials to be ground
• The operating parameters of the mill
• The efficiency and distribution of the grinding media
• The fineness of the cement particles,
• The internal operating conditions of the mill (humidity, temperature, ventilation, the condition of the armor plating, etc.).

The agglomeration phenomenon remains one of the priorities of cement manufacturers, hence the importance of grinding aids. The latter enables the partial neutralization of surface charges which have developed during milling. Additives, such as water, organic liquids, and some inorganic electrolytes have been used to reduce the surface free energy of the material being ground with a view to improving grinding efficiency (Sohoni, S. et al 1991).

Although the prime use of grinding aids is to reduce agglomeration of cement particles, their use will also assist in:

• The total or partial elimination of the ”coating” effect on the media,
• An improvement in the separator efficiency due to increased fluidity of fine particles,
• A decrease in pack-set problems in storage silos and bulk delivery trucks,

• An increased bulk and bag cement quality,
• Improved materials-handling (blowing into silos, off-loading trucks, etc.) due to an improved fluidity,
• Improved grinding production capacity.

The grinding aids application is more desirable, due to their significant effects on mechanical properties of cement, whose particle size distribution results narrower and shifted towards shorter diameters (Bathia, JS., 1979). The greater the surface of the hydraulically active components, the higher the Blaine fineness, the faster does the cement harden. Nevertheless, the Blaine value only gives an indication and not an absolute value, as it does not adequately reflect the fine fraction which is an important parameter for the grinding process and for the properties of the binder produced.

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