CEMENT GRINDING AIDS
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)
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)
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)
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
