Influence of Stearic Acid on Portland Cement Performance as Grinding Aids Haoxin Li 1,a, Jiansen Yang 1,b, Hongbo Zhu 1,c

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1 Advanced Materials Research Online: ISSN: , Vols , pp doi: / Trans Tech Publications, Switzerland Influence of Stearic Acid on Portland Cement Performance as Grinding Aids Haoxin Li 1,a, Jiansen Yang 1,b, Hongbo Zhu 1,c 1 Key Laboratory of Advanced Civil Engineering Materials of Ministry of Education, Tongji University, Shanghai , China; a bosomnxin@126.com, b yjs508@163.com, c zhuhongbo501@sohu.com Key words: Cement; Stearic acid; CH; AFT; C-S-H Abstract: Different contents of stearic acid were added to mixtures, and the influences of stearic acid as grinding aids on portland cement performances, including specific surface, compressive strength, hydration heat, Ca(OH) 2 (CH) content, C-S-H gel and ettringite (AFT) content were discussed in this paper. The results show that the addition of small amount of stearic acid is enough, and excessive addition of stearic acid is not a good matter to cement grinding. Adding a small amount of stearic acid, not only don t improve the compressive strength, but also lower the compressive strength significantly. Although the specific surface of samples with 0.1% stearic acid is lower than that of the samples with 0.025% stearic acid and reference, the compressive strength appears of higher than others. Addition of stearic acid affects not only on the rate of heat liberation, but also the hydration heat significantly. The addition of stearic acid has uncommonly impact on the content of CH, C-S-H and AFT in cement paste at 3 days, 7days and 28 days hydration age, the samples with 0.1% stearic acid has higher content of CH, C-S-H and AFT than others, and lower conversion content of AFT from 3days to 7days and 7days to 28 days. This can explain why the cement with 0.1% stearic acid is provided with the higher compressive strength than others, from the perspective of hydration production composition. Introduction Cement world production currently accounts approximately 1.6 billion ton/year and the grinding process consumes nearly 2% of the electricity produced in the whole world. The clinker grinding step consumes about one-third of the power required to produce 1 ton of cement. In order to save the energy, the grinding aids (GA) are commonly added to improve the grinding process of clinker. The most important functions of GA are to accelerate crushing, eliminate agglomeration and decrease specific surface energy of clinker. There are many different materials used as grinding aids, including solids and liquids. The liquids are aliphatic amines, aminealcohols and glycol[1-5]. The solids are graphite, colloidal silica, fatty acids including stearate, myristate, oleic acid and lauric acids. The effects of fatty acids on the compressive strength of cement and the gindability of cement were investigated by Ali Tugrul et al[6]. But there has not been any literature about influence of stearic, myristate, oleic acid and lauric acids on the cement performance, especially the hydration characteristic. In this study, the influence of stearic acid on cement performance was investigated systematically, especially, the effects of stearic acid on the cement hydration was discussed. Experimental Materials Stearic acid, hard, white, waxlike solid of composition CH 3 (CH 2 ) 16 COOH melting at 71.5 C, is chemical reagent, and the content is 99%. The clinker was from Haibao cement Factory of China, the chemical components were given in table 1. All rights reserved. No part of contents of this paper may be reproduced or transmitted in any form or by any means without the written permission of Trans Tech Publications, (ID: , Pennsylvania State University, University Park, USA-04/03/16,21:53:15)

2 Advanced Materials Research Vols Table 1 Main chemical components of cement clinker Oxids CaO SiO 2 Al 2 O 3 Fe 2 O 3 SO 3 LOI others Content (Mass, %) Methods The different contents, 0.025%, 0.05%, 0.1% and 0.15% (in mass) of stearic acid were added to the mixtures contained about 97% clinker (4850g) and 3% (150g) calcium sulphate (CaSO 4 2H 2 O). Mixtures with different contents of stearic acid were grinded in the ball mill. The speed and grinding run time were 48 rpm, and 40 min, respectively. The ratio of mixture to grinding ball is 1:32, and the weight of grinding ball was 160kg. The specific surface was tested according to Blaine air permeability method. One unite of cement, grinded with different content stearic acid, was mixed with three unites of sand and one a half unite of water. The mortar was placed in metal moulds having dimensions of mm. The moulds were cured at 20 C in a room with relative humidity of 90% for 24 h, then the mortar were removed from moulds and cured in water of 20 C for the periods of 3, 7 and 28 days. After these curing periods, the compressive strengths of prismatic specimens were determined. The hydration heat of cements grinded with different content stearic acid was determined with TAM Air 08 Isothermal Calorimeter. The water to cement ratio was 0.5 and the ambient temperature was 20 C. The thermogravimetric analysis was used to estimate the CH content of cement paste for the different hydration age, and the heating rate is 10 C/min. The C-S-H gel content in cement paste with different hydration time was determined by X-ray diffraction background. The scan speed was 2 /min and the scan scope was 5 o ~90 o of 2θ. The radiation was CuKa1 at wavelength of nm (40 kv). In order to determine the content of AFT,the X-ray diffraction external standard method was used. The scan speed was 2 /min and the scan scope was 8.5 o ~9.5 o of 2θ. The radiation was CuKa1 at wavelength of nm (40 kv).. Result and discussion Specific surface The specific surfaces of cements, grinded with different content of stearic acid for 40 min, were determined, and the results are shown in Fig.1. It is observed that the specific surface of reference cement is 421m 2 /kg, when addition contents of stearic acid are 0.025%, 0.05%, 0.1% and 0.15%, the specific surfaces of cements are 450, 440, 399, 388 m 2 /kg respectively. The specific surface of cement increase up to 6.9% when addition of stearic acid is 0.025%, but the specific surfaces of cements don t increase with the addition content increase of stearic acid, and when the addition content of stearic acid is 0.15%, the specific lower up to 7.9%. The results show that the stearic acid as the grinding aid component, excessive addition is not a good thing for cement grinding. Blaine surface(m 2 /kg) Content of stearic acid (Mass,%) Fig.1. The specific surface of cement with different content stearic acid Compressive strength Table 2 presents the compressive strength of cement grinded with different stearic acid content, at 3, 7 and 28 days. 388

3 1246 Sustainable Development of Urban Environment and Building Material Table 2 The compressive strength of cement grinded with different stearic acid content compressive strength (Mpa) stearic acid content (mass,%) 3d 7d 28d It is can be seen from the results that there is not a linear relationship between the compressive and the addition content of stearic acid. Adding a small amount of stearic acid, not only don t improve the compressive strength, and lower the compressive strength significantly. For example, when the addition of stearic acid is 0.025%, the compressive strength at 3 and 7 days, lower up to nearly 10%. But with increasing of stearic acid addition content, the compressive strength of cement shows an increasing trend. In particular, when addition content is 0.1%, the compressive strength at 3, 7 and 28 days increase of nearly 5%. Hydration heat Fig.2 shows the variation rate of mixtures hydration heat with time in three days. The addition of stearic acid changes the rate of heat liberation. At about hydration 12h, the reference and mixtures with 0.025%, 0.05% stearic acid appears of higher hydration rate than the mixtures with 0.1%and 0.15%. The hydration heat was calculated of mixtures with different content stearic acid in three days. The reference is 337 J/g, the mixture with 0.025% stearic acid is 368 J/g, the mixture with 0.05% stearic acid is 351 J/g, the mixture with 0.1% is 330 J/g, and the mixture with 0.15% stearic acid is 298 J/g. Addition of stearic acid exert the influence on the rate of heat liberation and hydration heat significantly. 8 Rate of heat liberation (mw/g) % content stearic acid 0.025% content stearic acid 0.05% content stearic acid 0.1% content stearic acid 0.15% content stearic acid Hydration time (h) Fig.2 Hydration heat rate of mixtures with different content of stearic acid in three days CH content After different hydration age, the CH content in hydration paste was determined by DTA/TG, and the results are shown in table 3. Table 3 CH content of mixtures with different stearic acid content at different hydration age stearic acid content (mass,%) CH content (%) 3d 7d 28d

4 Advanced Materials Research Vols It is obviously that the CH content of hydration paste with 0.025% stearic acid is lower than others in 3, 7 and 28 days, and hydration paste with 0.1% stearic acid is higher than others in 7 and 28 days. In 3 days hydration age, the reference CH content is higher than others, but the situation changes in other age. In addition to mixture with 0.025% stearic acid, the CH contents in other mixtures are higher than reference in 7 and 28 days. At different hydration age, the addition of different content stearic acid has different effect on the CH content in hydration paste. In the early hydration age, addition of stearic acid has a negative affects, and in later age, besides of mixture with 0.025% stearic acid, the addition of stearic acid play a positive role on the formation of CH. C-S-H content Presented in table 4 are the results related to the C-S-H gel content of mixtures with different content stearic acid at different hydration age. Table 4 C-S-H content of mixtures with different stearic acid content at different hydration age stearic acid content (mass,%) C-S-H content (%) 3d 7d 28d The results show that C-S-H content of cement at different hydration age change due to the presence of stearic acid, and the mixtures with 0.1% and 0.025% stearic acid are provided with the highest and the lowest content of C-S-H during all hydration age in this study respectively, and the content of C-S-H gel is more than 60% at 28 days for the mixture with 0.1% stearic acid. Though, the C-S-H gel contents with stearic acid are higher than the mixture without stearic acid, there isn t a liner relationship between stearci acid and C-S-H gel at 3, 7 and 28 days hydration age, even when the stearic acid content is 0.15%, the C-S-H content decreased. AFT content The AFT content and conversion content from 3 days to 7days and 7days to 28days, of sample added different content stearic acid, is listed in table 5. Obviously, in the same hydration age, the AFT contents of all samples are different due to addition contents of stearic acid, the samples with 0.025% stearic acid has the lowest content of AFT than others, and the samples with 0.1% stearic acid has the highest content of AFT than others, even than the samples without stearic acid. In the different hydration age, the AFT content of all samples decrease with hydration time,and the conversion contents of AFT from 3 days to 7day and 7day to 28 days are different because of addition of different stearic acid content. The samples with 0.1% and 0.025% stearic acid have the lowest and highest AFT conversion content respectively. It is seemed that the addition of stearci acid has uncommonly impact on the AFT conversion content from 3 days to 7days and 7 days to 28 days. Table 5 AFT content of mixtures with different stearic acid content at different hydration age stearic acid content (mass,%) AFT content (%) Conversion content (%) 3d 7d 28d 3d to 7d 7d to 28d

5 1248 Sustainable Development of Urban Environment and Building Material Conclusions From the present study, the following conclusion can be drawn, concerning the effect of stearic acid as grinding aids on the performance of cements. In the term of grinding effects, the addition of small amount of stearic acid is enough, and excessive addition of stearic acid is not a good matter to cement grinding. It is well known that the increased fineness of cement results in better compressive strength. However, this phenomenon did not occur in the case of stearic acid added. Adding a small amount of stearic acid, not only don t improve the compressive strength, and lower the compressive strength significantly. Addition of stearic acid doesn t only exert the influence on the rate of heat liberation, but also the hydration heat significantly. The addition of stearic acid has uncommonly impact on the content of CH, C-S-H and AFT in cement paste at 3 days, 7days and 28days hydration age, the samples with 0.1% stearic acid have higher CH, C-S-H and AFT than others, and lower conversion content of AFT from 3day to 7days and 7days to 28 days. It can explain why the sample with 0.1% stearic acid has the higher compressive strength than others, form the hydration component. Acknowledgements Thanks to Shanghai Baotian New Building Materials Co.,Ltd for the material and fund and special thanks to Key Laboratory of Advanced Civil Engineering Materials (Tongji University) Ministry of Education Shanghai for the testing of samples. References [1] Teoreanu I, Guslicov G. Mechanism and effects of additives from the dihydroxy-compound class on Portland cement grinding. Cem. Concr. Res. 1999, 28(9):9~15. [2] M.Katsioti, P. E. Tsakiridis, P.Giannatos. Characterization of various cement grinding aids and their impact on gindability and cement performance. Construction and building materials. 2009, 23(5):1954~1959. [3] P.B. Rajendran Nair, R. Paramasivam. An analysis of the influence of grinding aids on the breakage process of calcite in media mills. Advanced Powder Technology. 1999,10(3):223~ 243. [4] A. A. Jeknavorian, E. F. Barry, F. Serafin. Determination of grinding aids in portland cement by pyrolysis gas chromatography-mass spectrometry. Cem. Concr. Res.1998,28(9):1335~1345. [5] Heekyu Choi, Woong Lee, Seongsoo Kim. Effect of grinding aids on the kinetics of fine grinding energy consumed of calcite powders by a stirred ball mill. Advanced Powder Technology, 2009, 20(4):350~354. [6] Ali Tugrul, Albayrak, Muzaffer Yasar. Investigation of the effects of fatty acids on the compressive strength of the concrete and the grindability of the cement. Cem. Concr. Res. 2005; 35(2): 400~404.

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