X-ray diffraction analysis on the effect of silica fume and water in blended cement paste.
X-Ray diffractometer is a handy tool in cement chemistry for characterization and elucidation of constituent mineral phases obtained during cement hydration. The possibility of absolute measurement, identification of mineral's structure and studying variation in phases are the strength of the XRD analysis. The identification of calcium silicate hydrate, ettringite and its conversion is most complicated in earlier stages of hydration. This can be dealt easily with their XRD pattern, by determining the amount of unreacted [C.sub.3]A, [C.sub.4]AF and [C.sub.3]S as a function of hydration time directly [1,2]. This can also be correlated with the setting time and strength measurements. The amount of hydration products, setting time and strength also alter with the influence of elements present in the water as ions. The importance of water in cement paste has been ascertained by Ghorab et al . Hence in the present study, the obtained admixtured paste using two different waters were analysed with the help of XRD patterns, compared with its setting time and strength and studied the hydration processes.
Metarils and Experimental1
In the present article commercial OPC having the composition (using chemical analysis) CaO-63.14%; Si[O.sub.2]-21.41%; [Al.sub.2][O.sub.3]-5.11%; [Fe.sub.2][O.sub.3]-3.06%; S[O.sub.3]-2.50%; MgO2.44%[Na.sub.2]O-0.51%; [K.sub.2]O-0.32% and LOI; 1.51% and D-20 Elkem Microsilica Silica Fume (SF), with a chemical composition of CaO-0.34%; Si[O.sub.2]-91.00%; [Al.sub.2][O.sub.3]-1.21%; [Fe.sub.2][O.sub.3]-3.37; S[O.sub.3]-0.31%; MgO-1.18%; [Na.sub.2]O-0.46; [K.sub.2]O-1.24 and LOI-0.89% were used. Sugar factory effluent water (EW) and distilled water (DW) were used to prepare pastes.
The carried out water analysis are given in Table 1. The setting time and strength of the pastes (OPC + 5% SF, OPC + 10% SF, OPC + 15% SF, OPC + 20% SF, OPC + 25% SF) were measured. Since OPC + 20% SF (Blends) is found to possess optimum value it has alone been utilized for this study  with OPC (control).
The dry samples of OPC:SF in 80:20 is prepared by addition method and hydrated to different ages in a water/solid ratio 0.4 . The hydration was stopped at appropriate time intervals by adding drop of acetone and were dried at 110[degrees]C for few hours ground the powder.
Also the measured initial, final setting time using Vicat's apparatus and strength using Unico compressive strength testing machine available at Civil and Structural Engineering Department, Annamalai University, are presented in fig 1&2 respectively.
Samples were recorded for its pattern using X-ray diffractometer PANalytical (Philip-Netherlands-Pert), available at National Institute for interdisciplinary Science and Technology, Trivandrum. Cu-[K.sub.[alpha]] radiation ([lambda]=1.5405A) at 40 kV and 30 mA is made use of. "X" Pert software is used to deconvolate the pattern. All the XRD patterns were recorded from 2[theta]=10[degrees] to 70[degrees] in the range 2[degrees]/min at 298K.
[FIGURE 1 OMITTED]
[FIGURE 2 OMITTED]
Results and Discussion
The XRD pattern of anhydrous cement (control), silicafume and OPC+20% SF (Blend) admixtured cement samples are shown in Fig.3. The peaks were identified with "d" spacing and confirmed using JCPDS file also coincides well with other researchers [1,5].
In the anhydrous control (Fig 3a) C3S phase has more intense peak at 32.20[degrees] (d=2.77[Angstrom]). The other phases [C.sub.2]S-32.50[degrees](d=2.74[Angstrom]), [C.sub.3]A-26.51[degrees] (d=3.34[Angstrom]) and [C.sub.4]AF at 44.10[degrees] (d=2.05[Angstrom]) are less intense than the [C.sub.3]S phase. Both [C.sub.3]S and [C.sub.2]S are having a satellite peak at 41.30[degrees] (d=2.18[Angstrom]) and 51.81[degrees] (d=1.76[Angstrom]) respectively. A more intense pattern due to calcium sulphate at 30.51[degrees] (d=2.79[Angstrom]) is also observed. Fig 3(b) shows anhydrous SF. It contains amorphous material with small quantities of crystallized and possibly silicon or silicon carbide. A medium peak centered at 21.70[degrees] (d=4.10[Angstrom]) is predominant and is very close to one of the peak of tridymite . The other peaks at 26.71[degrees] (d=3.32[Angstrom]) are having a medium intense may be due to quartz or silicon carbide present in SF . The XRD pattern (Fig. 3c) of anhydrous SF blend, is almost same of that of control, but the intensity of peak is altered by addition of SF.
XRD pattern of DW hydrated control at different periods are shown in fig 4. From fig 4(a), the peak at 23.12[degrees], is due to ettringite formation. As time proceeds the intensity of the peak at 23.12[degrees] increases whereas 30.51[degrees] and 26.51[degrees] decreases. This is an evidence for the interaction between gypsum and [C.sub.3]A phase resulting in ettringite . In fig 4(b) new peaks at 31.34[degrees] and 56.64[degrees] starts visualizing where as the intensity of the peak at 23.12[degrees] decreases. This may be attributed to conversion of ettirngite to monosulphate  according to the following equations.
[MATHEMATICAL EXPRESSION NOT REPRODUCIBLE IN ASCII.] (1)
[MATHEMATICAL EXPRESSION NOT REPRODUCIBLE IN ASCII.] (2)
Also a peak at 29.38[degrees] and 47.0[degrees] starts emerging due to the hydration products of CSH and CH respectively ]. This is responsible for transforming the paste from stiffen to plastic. This coincide well with observed setting time (Fig.1). The peak at 29.38[degrees] and 47.00[degrees] (Fig 4(c)) are having an increase in intensity, indicating the reaction proceeding faster. From Fig 4(d-e) the main phases are having lesser intensity than their hydration product C-S-H and its essential reaction is 
2[C.sub.3]S + 6H [right arrow] [C.sub.3][S.sub.2][H.sub.3] + 3CH (3)
2[C.sub.2]S + 4H [right arrow] [C.sub.3][S.sub.2][H.sub.3] + CH (4)
XRD patterns of blended paste using DW at different hydration intervals are shown in Fig 5(a-e). From the figures an elongation in setting time for the blend is evidenced by the transformation of peak at 29.38[degrees]. The other transformation are similar but the intensity is higher than control. After 1 day, [C.sub.3]S peaks are reduced in intensity whereas the CH and CSH peaks observed with an increase in intensity as time eludes. From 28 days, the CH peak (18.0[degrees]) and silica fume characteristic peaks (21.70[degrees], 26.71[degrees]) are decreasing in intensity. It is due to the starting of pozzolanic reaction and as a result CSH peak gets an increase in intensity (Eqn. 5) .
3Ca[(OH).sub.2] + 2Si[O.sub.2] [right arrow] 3CaO.2Si[O.sub.2].3[H.sub.2]O (5)
At 12th week major peaks of Ca[(OH).sub.2] and SF have almost being consumed. The CSH peak is stronger than the control. Also the strength observation supports this.
The XRD patterns of control paste with EW at different intervals are shown in Fig. 6(a-f). Formation of ettringite peak and the ettringite to monosulphate are found to occur earlier than DW. Also a peak at 38.00[degrees] is seen in 4th and 12th week, indicating the Mg[(OH).sub.2] (Brucite) formation in the control paste . This may probably due to higher concentration of [Mg.sup.2+] in EW. This Mg[(OH).sub.2] and secondary gypsum (Eqn 6) is responsible for the reduction in strength  of the paste and is evidenced from the strength observation between 4th to 12th. MgS[O.sub.4] + Ca[(OH).sub.2] + 2[H.sub.2]O [right arrow]
Hence, the strength of the EW paste is lower than that of DW paste in the later periods. Fig 7(a-f) shows the 20% SF blend with EW at different ages. The retardation effect is observed upto 1 day than EW control paste. From 4th week starting pozzolanic reaction occurs (Eqn. 5) is observed from the decreasing trend to Ca(OH) and SF characteristics peak. The brucite peak (38.00[degrees]) is not found since CH is fully consumed by pozzolanic reaction. The SF blends have higher CSH than respective control. It indicates that the SF offers it resistance to sulphate attack. The pozzolonic reaction is higher in DW paste than EW paste.
[FIGURE 3 OMITTED]
[FIGURE 4 OMITTED]
[FIGURE 5 OMITTED]
[FIGURE 6 OMITTED]
[FIGURE 7 OMITTED]
On hydration, the XRD patterns are observed with a reduction in intensity of main phases accompanied by an increase in intensity of their hydration products. It is also observed that the intensity of these peaks depend upon the relative concentration of their own constituents and the aggressive ions, present in water.
* EW control has faster setting than DW control.
* The SF blends have higher CSH (strength) than respective control.
* Due to pozzolanic reaction, after 28 days the Ca[(OH).sub.2] and Si[O.sub.2] are consumed producing secondary CSH in the blends, in the order of DW>EW.
* The paste with EW gives rise to brucite formation whereas the composite with EW does not have it. This implies the resistance effect of SF.
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(1) Cement chemistry notation: C=CaO; S=Si[O.sub.2]; A=[Al.sub.2][O.sub.3]; F=[Fe.sub.2][O.sub.3]; S=S[O.sub.3] and H=[H.sub.2]O
(1) P. Veluchamy, (2) S. Barathan*, (3) (G. Sivakumar and (4) N. Anandhan
(1) Department of Physics, Faculty of Engineering Technology, Annamalai University.
(2) Department of Physics Annamalai University, Tamilnadu-608 002. India.
(3) CISL, Department of Physics, Annamalai University.
(4) SRM University, Kattankulattur, Chennai.
Table 1: Contents ([micro]g/g) of the different waters. Content DW EW Colour Colour less Light Brown Odour Nil Nil Total Dissolved Solids 45 1520 Total Hardness 4 170 Chlorine -- 102 Sodium -- 299 Magnesium 1 1080 Calcium -- 320 Potassium -- 17.2 Iron -- 0.91 Sulphur -- 10.7 Flouride -- 0.2
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|Author:||Veluchamy, P.; Barathan, S.; Sivakumar, G.; Anandhan, N.|
|Publication:||International Journal of Applied Engineering Research|
|Date:||Nov 1, 2009|
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