Triisopropanolamine (TIPA) is a tertiary amine. The cement industry uses TIPA as a grinding aid, and it is also used in concrete admixtures. The addition of small amounts of TIPA can result in a significant increase in the strength of cement pastes at different ages (Gartner, E. and Myers, D., 1993). It was proposed that tri isopropanolamine (TIPA) does not improve the mechanical properties of hydrated Portland cement paste, but rather improves mortar and concrete strength by acting on the interfacial transition zone (ITZ) between the Portland cement paste and sand or aggregate(Perez, J. et al, 2003). However, the compressive strength data for 10 Portland cement (with TIPA) tested as cement paste, as well as two different kinds of mortar after 28 days hydration was recently presented (Sandberg, PJ. and Doncaster, F., 2004). The average strength improvement with TIPA was 10% in the hydrated Portland cement paste and 9% in the mortar, clearly showing that the strength enhancement is not dependent on an ITZ mechanism. It is noted that GAs blended with TIPA molecules are known by their capability to promote cement hydration reactions, thereby leading to increased compressive strengths(Perez; J. P. et al,2003)(Sandberg; P.J. and Doncaster; F., 2004) (Assaad; J.J. and Issa; C.A., 2014).
Unlike industrial mills, laboratory grinding mills operated over given time interval do not account for CL, therefore leading to different cement particle size distribution (PSD) curves (Bhatty; J. et al, 2004) (Fidan; B., 2011). This consequently alters cement properties such as water demand, rheology, and hydration processes such as heat release, setting time, volume change, and strength development (Zhang;Y.M.&Napier-Munn;T.J.,1995)(Bentz; D.P.1999).
It is noted that the Blaine measurement can’t effectively represent the entire PSD, given the fact that two cement with different ratios of fine-to-coarse particles and described by different PSD can possess the same Blaine value (Ferraris; C.,2002)(Delagrammatikas; G. and Tsimas; S.,2004). The differences in PSD curves determined under laboratory and industrial mill conditions were noticed by several researchers in the cement and mineral grinding industries(Assaad; J.J. and Issa; C.A., 2014) (Mejeoumov; G.G., 2007) (Fidan; B., 2011); the laboratory tests yielded significantly wider PSD curves than those experienced in practice. ASTM C465 Standard Specification for GAs related such changes to cement flowability and mill retention time (MRT) during grinding (ASTM C465, 2010).
The MRT can be defined as the average time necessary for the bulk material to pass through the tube mill (Sottili; L. and Padovani; D., 2002). Hence, to properly evaluate GA effect on cement properties, the standard recommends the realization of full-scale tests over enough time to ensure reaching equilibrium conditions and stable circulating load (CL) (ASTM C 465, 2010). The CL is defined as the average number of times that the material circulates through the grinding system before becoming the product.
In the literature, limited attempts have been made to quantify the scale effect (i.e. industrial versus laboratory mill) that could result from GA additions on cement fineness and properties.
Grinding is one of the most inefficient unit operations in the cement industries where fine particles are produced by grinding, viz. mineral, cement, pigment, metal powder, etc. The effect of diethanolamine modified lignin on grind ability and cement performance including standard consistency, setting times and compressive strengths was studied. To the best of our knowledge, this is the first report about the usage of diethanolamine modified lignin as cement grinding aids. As known, lignin is one kind of natural macromolecular material; because of the active epoxy group, the diethanolamine modified lignin system has many side reactions such as epoxy ring opening reaction with hydroxyl and methoxy group.
In particular, in the cement industry, huge amounts of clinker, coal and other raw materials are needed for grinding. It has already been proved that grinding aids sometimes referred to as grinding additives are one of the most effective measures to maximize energy saving and improve grinding efficiency in the cement grinding process(Choi, H. et al, 2010)( Hasegawa, M. et al,2001).
Small percentages of grinding aids can effectively improve the performance of the mill, reduce the particle size and increase the specific surface area of the cement under the same grinding condition. Grinding aids are certain to surface active chemicals, a variety of materials have already been used as grinding aids, such as triethanolamine (TEA), tri isopropanolamine (TIPA), glycol, glycerol, organic acetates, and calcium sulfate (Katsioti, M. et al,1954)( Gao, XJ. et al, 2011). Two important mechanisms (Rebounder’s strength reduction theory and Mardulier’s particle dispersion theory) have been suggested in order to explain the action of various grinding aids (Moothedath, SK., and Ahluwalia, SC., 1992). However, the action mechanisms of grinding aids which remarkably improve the grinding efficiency with small adding amount have not been understood perfectly.
Therefore, if actually using some new compounds and chemicals as grinding aids at the present technical level, empirically determining the variety and quantity of the compounds and chemicals based on experimental data is very important. As a renewable material, lignin is a constituent of all plants, including annual plants and wood, and is second in the natural abundance in the organic world after cellulose (Nadif, A. et al, 2002).
Meanwhile, lignin is unusual because of its heterogeneity and lack of a defined primary structure. Lignin is a cross-linked racemic macromolecule with molecular masses in excess of 10,000. It is relatively hydrophobic and aromatic in nature (Del Rio, JC et al, 2001). However, through chemical modification of the active groups (phenolic hydroxyl, carboxyl and hydroxyl) in lignin molecular, a variety of lignin-based high value-added fine chemicals and polymer materials have been produced and widely used in oil well additives, cement and concrete additives, dyestuff dispersants, agricultural chemicals and other industrial binders(Matsushita, Y. and Yasuda, S., 2005)(Singh, NB., 2002).
As one kind of the most important polymeric surfactants, lignin and its derivatives especially the lignosulfonates have been widely used as concrete additives owing to its advantages including easily available, low cost and environmental friendliness (Singh, NB., 2002) (Miyake, N. et al 1995). Lignosulfonates are also used as auxiliary components for cement grinding aids. However, the poor grinding and strength enhancing performance have limited their further application in the cement and concrete field.
In order to make more efficient use of lignin and its derivatives, researchers have done lots of works and mainly concentrated on the physical or chemical modification to improve its water solubility and surface activity (Ai, Q. et al,2009)( Pang, YX. et al, 2008). During the study on lignin modification and cement additives, we found incidentally that by proper chemical modification lignin had excellent grinding performance and strong retarding effect.
Glycol is a dihydric alcohol where two hydroxyl groups are bonded to different carbon atoms; the general formula for glycol is (CH2)n(OH). The most important glycol is the simplest, ethylene glycol (EG). Glycols used as grinding aids and are also used as raw material for the production of plasticizers and polyester resins, humectants, textile lubricants, and coupling agents. Large volumes of ethylene glycol are consumed as automobile engine antifreeze/coolant. Diethylene glycol (DEG) is used as a dehydrating agent for natural gas for its hygroscopicity. In addition, glycols are used for the production of alkyl-type resins.
The effect of glycol-based GAs from the dihydroxy compound class (including EG, PG and polypropylene glycol (PPG)) on the grind ability of clinker was studied by (Teoreanu and Guslicov, 1999) at dosage rates of 0.03, 0.05 and 0.1% of cement weight. For the same grinding duration, they concluded that the cement specific surface area increased by 29% when using PPG and by 20% with the use of EG and PG. For longer grinding durations when cement Blaine fineness exceeds 3500 cm2/g, the growth of the specific surface area becomes negligible with PPG whereas it varies from 14–24% with EG and PG.
Water solutions of surfactants significantly change the granulometric composition of cement with increased levels of small particle size and simultaneous agglomeration neutralize surface charges as a result dissociation of the surfactant and appearance of ions but have a negative effect on strength characteristics of cement stone. A surfactant solution in glycol merely modifies particle size of powder, but actively prevents agglomeration of fine particles. The modification due to presence surfactants of various reactive radicals, their position in molecule chain length and shape of molecular weight polymeric surfactant (Shakhova; L.D., 2014).
The aggregation process is essentially dependent on clinker nature, the dispersion state of the cement, working conditions of the grinding plant, the kinetic energy of the grinding media and their distribution, and the atmosphere within the mill. Elimination or diminution of ground solid mass aggregation and adhesion effects is carried out in three main ways (Meric, J.P., 1980)( Béke, B., 1973)( Dombrowe, H. et al, 1982) 1) decrease of grinding media size; 2) running of the grinding plant in a closed circuit; and 3) use of surfactants. The use of surface active additives in the grinding leads to a decrease in material hardness, by screening attractive surface forces and promoting fracture by the easier propagation of cracks.
The effect of the surfactants is emphasized at low concentration, ranging between 0.01% and 0.5%. Considerations based on surface science suggest the effect of surfactants is dependent on their nature and molecular structure (Teoreanu, I., Guslicov, G., 1995). The effect of this additive with higher molecular weight is demonstrated to be better than the effect of corresponding inferior dihydroxy compounds, but only for the early stage of the process, which corresponds to larger cement grains or larger pores, respectively. In the considered case, for high specific surfaces, the Traube-Duclaux rule, applicable to the homogenous adsorption, is inverted. Such a finding does not appear when comparing the effect of ethylene glycol and propylene glycol. For such a comparison, even if the difference between the observed effect when using ethylene glycol and propylene glycol is not high, the effect of the latter certainly is better. When using all three additives, it was found that, for the same grinding duration, it yielded an obviously higher specific surface of cement in comparison with the specific surface of the reference (non-additive) cement.
Hasegawa, M. and Kanda, Y., 1993 reported that alcohols were considerably effective as grinding aids for feldspar although the degree of effectiveness varied somewhat with the species and additional quantities of alcohol. Seven kinds of alcohols with different alkyl groups and three kinds of glycols, which have the same hydroxyl groups as alcohols, were used as liquid additives. Benzene and water were also used as additives to compare with the effect of alcohol additives. These additives, except for water, were special grade reagents and used without further Purification. Compared with alcohol and glycol additives, benzene and water were found non-effective as grinding aids for the ultrafine grinding of quartz. A relationship between the specific surface area of product and the grinding time with alcohol additives in the different amounts of addition was investigated. Although the specific surface area with additives increased with grinding time to a maximum value, further grinding caused a decrease in the specific surface area of products, especially with the use of small amounts of additives.
Biodiesel production results in glycerol production as the main by-product in the biodiesel industry. One of the utilization of glycerol obtained from biodiesel production is as a cement grinding aid (CGA). Results showed that crude glycerol content was 40.19% whereas pure glycerol content was 82.15%. BSS value of the cement with CGA supplementation was higher than that of non-supplemented cement (blank) indicating that CGA-supplemented cement had higher fineness than the non-supplemented one. It was also found that pure glycerol 95% and TEA 5% at 80ºC was the optimum CGA used to result in finest cement with BSS value of 4836 cm2/g (Farobie; O. et al, 2012).