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di silicate anion ratio during the hydration of CSF-containing cement paste
CEMENT and CONCRETERESEARCH. Vol. 17, pp. 108-114, 1987. Printed in the USA 0008-8846/87 $3.00+00. Copyright (c) 1987 Pergamon Journals, Ltd.
THE INFLUENCE OF SILICA FUME ON THE MONO/DI SILICATE ANION RATIO DURING THE HYDRATION OF CSF-CONTAINING CEMENT PASTE A.Durekovi6 and K.Popovi6 Civil Engineering Institute,Faculty of Civil Engineering Science,University of Zagreb,41 Zagreb,J.Raku~e l, Yugoslavia
(Communicated by D.M. Roy) (Received Oct. 7, 1986) ABSTRACT The influence of silica fume addition on silicate polymerization during hydration of portland cement pastes was studied. Trimethylsilyl derivatives were identified by gas-liquid chromatography. DTA/TGA method was applied for determination of the free lime content in hydrated paste samples.The obtained results point to the conclusion that pozzolanic reaction causes the shift towards Si-anion dimerization during hydration of csf-blended cement pastes. INTRODUCTION Applying the TMS-method for the first time,Lentz's researches /1,2/ have shown that Si anion monomer turns to dimer and polymer form when anhydrous cement is subjected to hydration.After series of modifications /3,4,5,6/ Tamas et al. /7/ improved the method by means of suppressing the side reactions.This improved method has provided the most exact results for easily soluble silicates /8,9,10/. Lentz's original method,however,is still suggested for the determination of higher Si-anions /ll/. It has been found that the content of Si-monomers registered in TMS studies on calcium-silicate and cement paste equals the amount of unreacted starting silicate minerals measured by the QXRD-method on the same samples /I1,12,13, 14/.The dispersty of the Si-anions cement xerogel is influenced,beside the hydration time,also by curing temperature /10,13,15,16/ and the admixtures present in the mix /10,15,17,18/. This paper reports the results of the research on the influence of pozzolanic reaction,caused by the condensed silica fume admixture,on Si-anion condensation followed by the change in Si2/Si I anion relationship during the hydration in csf-containing cement pastes. EXPERIMENTAL The materials used in this work were an ordinary portland cement and the silica fume from ferrosilicon alloys production. Chemical composition of star-
108
Vol. 17, No. 1
109 SILICA FUME, CEMENT, TMS, DISILICATE
ting materials,determined according to JUS B.C8.020 (and BS 4550:Part 2:1970) are given in Table I. TABLE l: Chemical composition of starting materials (percent by weight)
Compound
SiO 2
Ordinary portland cement
Silica fume from ferrosilicon alloys production
19.65
86.92
AI203
5.50
2.26
Fe203
3.10
1.42
61.88
i. 15
MgO
1.70
O. 60
SO 3
3.40
O. 61
K20
O. 98
i. 50
Na20
O. 38
O. 48
L.o.i.
1.57
4.80
CaOfree Ins. residue
i. 12 i. 15
-
CaOTot .
Three mixes were prepared from those materials using water/(cement+silica fume) ratio of 0.68: One pure portland cement paste (marked PC) and two pastes in which the cement was replaced by 5 weight percent of silica fume (marked 5P) and lO weight percent of silica fume (marked lOP). Cement,silica fume and destilled water were weighed and hand mixed in the open beakers.To minimize the bleeding the pastes were periodically mixed until the seting has just begun.Then they were cast into plastic molds and kept for the time up to 20 hrs in a humid box.After demolding the samples were placed under lime water for the remaining hydration time.Casting and curing were done at 20°±3°C. After definite time of 1,3,7 and 28 days the specimens of each hardened cement paste were crushedinto small pieces.The hydration was stopped by milling and washing with aceton /19/ and finally by drying for 48 hrs in vacuum generated by using a rotary pump.In such way prepared samples were stored until measuring in a desicator over silica-gel and KOH. Differential thermal and thermogravimetric analysis has been employed to detect the variations in the free lime content of hydrated cement pastes.The amount of calcium hydroxide was determined by measuring abrupt weight loss in the temperature rang~ from 510 ° to 6OO°C. The weight loss curves were recorded between 20 ~ and 1OOO~C using a MOM-derivathograph (Hungary) which utilizes A120~ as a control material at heating rate of iO degrees Celsius per minute. Port~on of 500 mg "aceton stopped" samples were analysed. The structure of silicate anions and their changes during hydration in the cement pastes were investigated by use of trimethylsilylation method.The silylation technique as described by Tamas et al. /7/ has been applied.The samples in the range O.130-O.4OOgram were added into previously homogenized mix of
llO
Vol. 17, No. l A. Durekovic and K. Popovic
d±methylformamide (DMF,20 ml),hexamethyl-disiloxane (HMD,IO ml) and trimethylsilyl chloride (TCI,IO ml). The SiO2-concentration of O.158 mg/ml of silylating mix was constant in all samples. A "Varion 3700" gas chromatograph equipped with flame ionization detector was~made for analysis of silylated derivatives whichwere tested without prior stripping of organic solvent.The column was 3 ~m O x 3.66 m L stainless steel pipe packed with methylsilicon oil 3% SE 30
O
•
I
Q
D
B
O
O
O
O
°
°
•
are shown in Figures 1,2 and 3 °
°
°
•
•
°
•
•
•
•
•
O
° •
•
°
•
°
°
°
°
°
°
°
°
°
°
°
°
°
°
I
ii
i il :
......
i .....
:::
i
i
HEMIM( HM D
iii
:~ t ~ i i:::~ i:i .J"
i
"'~' :::Fi S::}
iili.~i
:-i:it :t
i L ......
-. z:-:
FIG.l: Cl-ealibration chromatogram of ~nhydrous OPC ( S i 0 d - a n i o n )
FIG.2:
Gl-calibration chromatogr{m of hemimorphite ( S i 2 0 ~ - a n i on)
FIG.3: Cl-calibration blank test chromatogram of HMD organic solvent
4- anion are eluaZed at 159 O C (e_uatzon l " " The TMS-derivatives with SiO,, tlme 6.0 mlq . . o. l nutes,FIG.l) ; the TMS-derivatives wlth SlpO 7 anzon are re eased at 229 o C and after 10.6 minutes of injection (FIG.2). T~e HMD ehromatogram of the blank test
Vol. 17, No. 1
III
SILICA FUME, CEMENT, TMS, DISILICATE (FIG.3) shows only small peaks originated from trace compound. The gl chromatograms of TMS-esters derived from the pure portland cement paste (marked PC),hydrated from i to 28 days,as well as from the portland cement paste blended with 5 % (marked 5P) and 10 % (marked lOP) of silica fume respectively,are shown in Figures 4,5 and 6. The chromatograms of OPC paste hydrated from 1 to 28 days (Fig.4) showan increa~e of the intensity of eluation peak at 229°C (h~ with TMS-derivatives of SipOv-anion) and a decrease of the intensity of elua~ion peak at 159°C (hi) which belongs to TMS-derivatives with SiO~-anion. On the basis of the works of Wu et al./3/'and Tamas et al. /7/ the small peak appearing at 284°C could be speculated to belong to TMS-derivatives with linear Si-trimer anion.
FIG. 4:
G1 chromatograms of the soluble TMS-products derived from PC-paste samples after hydration of 1,3,7 and 28 days
FIG. 5:
GL chromatograms of the soluble TMS-products derived from 5% csf blended cement paste samples after hydration of 1,3, 7 and 28 days
112
Vol. 17, No. 1 A. Durekovi~ and K. Popovi6
FIG.6:
G1 chromatograms of the soluble TMS-products derived from l ~ csf blended cement paste samples after hydration of l, 3 and 7 days
The change in the intensity of h 2 and hl,as pointed above,with the promotion of hydration time also lead to an zncrease of their ratio hp/hl,which proves the dimerization of Si-anions during hydration process in t~e OPC paste.Such similar silicate anion dispersity change has been already reported /2,10,16/° Parallel to dimerization of Si-anions in the same hydrated OPC-samples the content level of free lime became higher as the results in Table 2 show.The dimerization of Si-anions and an increase of the free lime content can be said to be characteristics of the normal OPC hydration process.
Hydration time (days)
1 3 7 28
Free lime content as CaO (%) PC
5P
ll.91 14.50 15.80 16.55
ll.OO 13.80 14.O5 15.27
lOP
lO.O0 12.25 12.69 13.42
TABLE 2:
Changes of the free lime content with the time of hydration in the paste of portland cement (PC) and the pastes with 5% (5P) and l ~ (lOP) of silica fume
Like the OPC-paste chromatograms described above,the gl-chromatograms of silica fume containing paste samples also show the intensity increase of peaks at 229°C and a decrease of the intensity of monomer derivative peak (hi) with the progress of hydration tzme.Their ratios hp/h I , however,are higher ~hen compared to OPC samples after equal hydration ~ime The comparison of determined h^/h~ • . ~ 1 ratios in dependence of hydration time for pure PC and csf-blended pastes is presented in Figure 7. The increase of h^/h~ ratio with the ageing of the csf-contai~in~ cement paste samples is accompanied by lowering of their free lime content.
Vol.
17, No. 1
I13
SILICA FUME, CEMENT,TMS, DISILICATE h2v
Si2: SLI
2~
FIG..7:
The change of the intensity rati~ hp/h I of glc peaks for Si~O~-/SiOC-TMSderivatives as func~zon o~ hydration tzme for the pure portland cement paste (PC) and the pastes with 5% (5P) and 10% (lOP) of silica fume.
, lOP
/~SP • "1"
PC,
1,0
1
3
7
2.8
hydration t,me Id'~ys)
WT
Since,at all tested ages,the shift towards Si-anion dimerization in the csf-containing cement paste was proportionally dependent on the amount of silica fume,and was related to the lowering of free lime content,the followi~ conclusion should be made: The existence of pozzolanic reaction in the csf-containing cement paste causes the increase of Si-anion dimerization rate.This conclusion also points to the probability that condensation to higher anion polymer in such samples is enhanced. Acknowledgement This material is based on the work supported by the US-Yugoslav Joint Fund For Scientific and Technological Cooperation in cooperation with the National Bureau of Standards,Washington,DC,under Grant 133 NBS PN 486. The work was partly carried out at the Building Materials Division of NBS in Gaithersburg,MD 20899,USA. REFERENCES l)Lentz,CoW.,Inorg.Chem.Soc.,3(4) 5 (1961) 2)Lentz,C.W. ,Highways Res.Board,Washington,DC. ,Sp.Rep.,No 90,269 (1966) 3)Wu,F.F.H. ,Goetz,J., Jamieson,W.D. ,Mason,C.R. ,Jour.of Chromat. ,Vol 48,515(1970) 4)Goetz,J. ,Mason,C.R., J.Chem.Soc., (A) ,2683 (1970) 5)DertG] asset,L. S., Lachowski ,E.E., Cameron, G. G., J. Appl. Chem. Biotechnol. ,2__7,39 (1977) 6)Garz6,G. ,Hoebbel,D. ,Escery,Z.J. ,Ujsz~szi,K. ,Jour.of Chromat. ,16__7,321 (1978) 7 )Tamas, F.D., Sarkar, A. K., Roy, D.M., Proc. Conf. Hydr. Cem. Pastes-Their Strucure and Properties, CemConcr. Assoc., Shefield, 55 (1976)
114
Vol. 17, No. 1
A. Durekovi~ and K. Popovi~
8 )Currell, B. R., Parsonage, J. R., J. Macromol. Sci. -Chem., (A) 16 ,i, 141 (1981 ) 9 )Zhao-Qi Wu, Hirljac, J., Chao-Lung Hwang, Young, J. F., J. Am. Cer. Soc., 66,5, C 86 (1983) iO)Hirljac,J. ,Wu, Z-Q. ,Young, J.F. ,Cem.Concr.Res. ,Vol 13,877 (1983) ll )Currell, B oR., Midgley, H.G., Montencinos, M., Parsonage, J. R., Cem. Concr. Res., Vol 15,889 (1985) 12 )Dent G] ass er, L° S., Lachowski, E. E., Mohan, K., Taylor, H. F.W., Cem. Concr. Res., Vol 8, 733 (1978) 13)Berger,R.L. ,Bentour,A. ,Millestone,N.B. ,Kung,J.H. ,J.Am.Cer.Soc. ,62, 358 (1979) 14)Bentur ,A. ,Berger,R.L. ,Kung, J.Ho ,Millestone,N.B. ,Young,J.F., J.Am.Cer.Soc., 62,362 (1979) 15)Young,JoF.,Berger,R.L.,BenhJr ,A.,ll Cemento,75, (3) 391 (1978) 16)Parrott,L.J. ,CemoConcr.Res.,Vol 11,415 (1981) 17) Uchikawa, H., Furuta, R., CemConcr, Res., Vol ll, 65 (1981) 18)Khan,M.H. ,Mohan,K. ,Taylor,H.F.W. ,Cem.Concr.Res. ,Vol 15,89 (1985) 19 )Kal Ousek, G. L., Kopanda, J. E., Cem. Concr. Res., Vol i, 63 (i 971 )
THE INFLUENCE OF SILICA FUME ON THE MONO/DI SILICATE ANION RATIO DURING THE HYDRATION OF CSF-CONTAINING CEMENT PASTE A.Durekovi6 and K.Popovi6 Civil Engineering Institute,Faculty of Civil Engineering Science,University of Zagreb,41 Zagreb,J.Raku~e l, Yugoslavia
(Communicated by D.M. Roy) (Received Oct. 7, 1986) ABSTRACT The influence of silica fume addition on silicate polymerization during hydration of portland cement pastes was studied. Trimethylsilyl derivatives were identified by gas-liquid chromatography. DTA/TGA method was applied for determination of the free lime content in hydrated paste samples.The obtained results point to the conclusion that pozzolanic reaction causes the shift towards Si-anion dimerization during hydration of csf-blended cement pastes. INTRODUCTION Applying the TMS-method for the first time,Lentz's researches /1,2/ have shown that Si anion monomer turns to dimer and polymer form when anhydrous cement is subjected to hydration.After series of modifications /3,4,5,6/ Tamas et al. /7/ improved the method by means of suppressing the side reactions.This improved method has provided the most exact results for easily soluble silicates /8,9,10/. Lentz's original method,however,is still suggested for the determination of higher Si-anions /ll/. It has been found that the content of Si-monomers registered in TMS studies on calcium-silicate and cement paste equals the amount of unreacted starting silicate minerals measured by the QXRD-method on the same samples /I1,12,13, 14/.The dispersty of the Si-anions cement xerogel is influenced,beside the hydration time,also by curing temperature /10,13,15,16/ and the admixtures present in the mix /10,15,17,18/. This paper reports the results of the research on the influence of pozzolanic reaction,caused by the condensed silica fume admixture,on Si-anion condensation followed by the change in Si2/Si I anion relationship during the hydration in csf-containing cement pastes. EXPERIMENTAL The materials used in this work were an ordinary portland cement and the silica fume from ferrosilicon alloys production. Chemical composition of star-
108
Vol. 17, No. 1
109 SILICA FUME, CEMENT, TMS, DISILICATE
ting materials,determined according to JUS B.C8.020 (and BS 4550:Part 2:1970) are given in Table I. TABLE l: Chemical composition of starting materials (percent by weight)
Compound
SiO 2
Ordinary portland cement
Silica fume from ferrosilicon alloys production
19.65
86.92
AI203
5.50
2.26
Fe203
3.10
1.42
61.88
i. 15
MgO
1.70
O. 60
SO 3
3.40
O. 61
K20
O. 98
i. 50
Na20
O. 38
O. 48
L.o.i.
1.57
4.80
CaOfree Ins. residue
i. 12 i. 15
-
CaOTot .
Three mixes were prepared from those materials using water/(cement+silica fume) ratio of 0.68: One pure portland cement paste (marked PC) and two pastes in which the cement was replaced by 5 weight percent of silica fume (marked 5P) and lO weight percent of silica fume (marked lOP). Cement,silica fume and destilled water were weighed and hand mixed in the open beakers.To minimize the bleeding the pastes were periodically mixed until the seting has just begun.Then they were cast into plastic molds and kept for the time up to 20 hrs in a humid box.After demolding the samples were placed under lime water for the remaining hydration time.Casting and curing were done at 20°±3°C. After definite time of 1,3,7 and 28 days the specimens of each hardened cement paste were crushedinto small pieces.The hydration was stopped by milling and washing with aceton /19/ and finally by drying for 48 hrs in vacuum generated by using a rotary pump.In such way prepared samples were stored until measuring in a desicator over silica-gel and KOH. Differential thermal and thermogravimetric analysis has been employed to detect the variations in the free lime content of hydrated cement pastes.The amount of calcium hydroxide was determined by measuring abrupt weight loss in the temperature rang~ from 510 ° to 6OO°C. The weight loss curves were recorded between 20 ~ and 1OOO~C using a MOM-derivathograph (Hungary) which utilizes A120~ as a control material at heating rate of iO degrees Celsius per minute. Port~on of 500 mg "aceton stopped" samples were analysed. The structure of silicate anions and their changes during hydration in the cement pastes were investigated by use of trimethylsilylation method.The silylation technique as described by Tamas et al. /7/ has been applied.The samples in the range O.130-O.4OOgram were added into previously homogenized mix of
llO
Vol. 17, No. l A. Durekovic and K. Popovic
d±methylformamide (DMF,20 ml),hexamethyl-disiloxane (HMD,IO ml) and trimethylsilyl chloride (TCI,IO ml). The SiO2-concentration of O.158 mg/ml of silylating mix was constant in all samples. A "Varion 3700" gas chromatograph equipped with flame ionization detector was~made for analysis of silylated derivatives whichwere tested without prior stripping of organic solvent.The column was 3 ~m O x 3.66 m L stainless steel pipe packed with methylsilicon oil 3% SE 30
O
•
I
Q
D
B
O
O
O
O
°
°
•
are shown in Figures 1,2 and 3 °
°
°
•
•
°
•
•
•
•
•
O
° •
•
°
•
°
°
°
°
°
°
°
°
°
°
°
°
°
°
I
ii
i il :
......
i .....
:::
i
i
HEMIM( HM D
iii
:~ t ~ i i:::~ i:i .J"
i
"'~' :::Fi S::}
iili.~i
:-i:it :t
i L ......
-. z:-:
FIG.l: Cl-ealibration chromatogram of ~nhydrous OPC ( S i 0 d - a n i o n )
FIG.2:
Gl-calibration chromatogr{m of hemimorphite ( S i 2 0 ~ - a n i on)
FIG.3: Cl-calibration blank test chromatogram of HMD organic solvent
4- anion are eluaZed at 159 O C (e_uatzon l " " The TMS-derivatives with SiO,, tlme 6.0 mlq . . o. l nutes,FIG.l) ; the TMS-derivatives wlth SlpO 7 anzon are re eased at 229 o C and after 10.6 minutes of injection (FIG.2). T~e HMD ehromatogram of the blank test
Vol. 17, No. 1
III
SILICA FUME, CEMENT, TMS, DISILICATE (FIG.3) shows only small peaks originated from trace compound. The gl chromatograms of TMS-esters derived from the pure portland cement paste (marked PC),hydrated from i to 28 days,as well as from the portland cement paste blended with 5 % (marked 5P) and 10 % (marked lOP) of silica fume respectively,are shown in Figures 4,5 and 6. The chromatograms of OPC paste hydrated from 1 to 28 days (Fig.4) showan increa~e of the intensity of eluation peak at 229°C (h~ with TMS-derivatives of SipOv-anion) and a decrease of the intensity of elua~ion peak at 159°C (hi) which belongs to TMS-derivatives with SiO~-anion. On the basis of the works of Wu et al./3/'and Tamas et al. /7/ the small peak appearing at 284°C could be speculated to belong to TMS-derivatives with linear Si-trimer anion.
FIG. 4:
G1 chromatograms of the soluble TMS-products derived from PC-paste samples after hydration of 1,3,7 and 28 days
FIG. 5:
GL chromatograms of the soluble TMS-products derived from 5% csf blended cement paste samples after hydration of 1,3, 7 and 28 days
112
Vol. 17, No. 1 A. Durekovi~ and K. Popovi6
FIG.6:
G1 chromatograms of the soluble TMS-products derived from l ~ csf blended cement paste samples after hydration of l, 3 and 7 days
The change in the intensity of h 2 and hl,as pointed above,with the promotion of hydration time also lead to an zncrease of their ratio hp/hl,which proves the dimerization of Si-anions during hydration process in t~e OPC paste.Such similar silicate anion dispersity change has been already reported /2,10,16/° Parallel to dimerization of Si-anions in the same hydrated OPC-samples the content level of free lime became higher as the results in Table 2 show.The dimerization of Si-anions and an increase of the free lime content can be said to be characteristics of the normal OPC hydration process.
Hydration time (days)
1 3 7 28
Free lime content as CaO (%) PC
5P
ll.91 14.50 15.80 16.55
ll.OO 13.80 14.O5 15.27
lOP
lO.O0 12.25 12.69 13.42
TABLE 2:
Changes of the free lime content with the time of hydration in the paste of portland cement (PC) and the pastes with 5% (5P) and l ~ (lOP) of silica fume
Like the OPC-paste chromatograms described above,the gl-chromatograms of silica fume containing paste samples also show the intensity increase of peaks at 229°C and a decrease of the intensity of monomer derivative peak (hi) with the progress of hydration tzme.Their ratios hp/h I , however,are higher ~hen compared to OPC samples after equal hydration ~ime The comparison of determined h^/h~ • . ~ 1 ratios in dependence of hydration time for pure PC and csf-blended pastes is presented in Figure 7. The increase of h^/h~ ratio with the ageing of the csf-contai~in~ cement paste samples is accompanied by lowering of their free lime content.
Vol.
17, No. 1
I13
SILICA FUME, CEMENT,TMS, DISILICATE h2v
Si2: SLI
2~
FIG..7:
The change of the intensity rati~ hp/h I of glc peaks for Si~O~-/SiOC-TMSderivatives as func~zon o~ hydration tzme for the pure portland cement paste (PC) and the pastes with 5% (5P) and 10% (lOP) of silica fume.
, lOP
/~SP • "1"
PC,
1,0
1
3
7
2.8
hydration t,me Id'~ys)
WT
Since,at all tested ages,the shift towards Si-anion dimerization in the csf-containing cement paste was proportionally dependent on the amount of silica fume,and was related to the lowering of free lime content,the followi~ conclusion should be made: The existence of pozzolanic reaction in the csf-containing cement paste causes the increase of Si-anion dimerization rate.This conclusion also points to the probability that condensation to higher anion polymer in such samples is enhanced. Acknowledgement This material is based on the work supported by the US-Yugoslav Joint Fund For Scientific and Technological Cooperation in cooperation with the National Bureau of Standards,Washington,DC,under Grant 133 NBS PN 486. The work was partly carried out at the Building Materials Division of NBS in Gaithersburg,MD 20899,USA. REFERENCES l)Lentz,CoW.,Inorg.Chem.Soc.,3(4) 5 (1961) 2)Lentz,C.W. ,Highways Res.Board,Washington,DC. ,Sp.Rep.,No 90,269 (1966) 3)Wu,F.F.H. ,Goetz,J., Jamieson,W.D. ,Mason,C.R. ,Jour.of Chromat. ,Vol 48,515(1970) 4)Goetz,J. ,Mason,C.R., J.Chem.Soc., (A) ,2683 (1970) 5)DertG] asset,L. S., Lachowski ,E.E., Cameron, G. G., J. Appl. Chem. Biotechnol. ,2__7,39 (1977) 6)Garz6,G. ,Hoebbel,D. ,Escery,Z.J. ,Ujsz~szi,K. ,Jour.of Chromat. ,16__7,321 (1978) 7 )Tamas, F.D., Sarkar, A. K., Roy, D.M., Proc. Conf. Hydr. Cem. Pastes-Their Strucure and Properties, CemConcr. Assoc., Shefield, 55 (1976)
114
Vol. 17, No. 1
A. Durekovi~ and K. Popovi~
8 )Currell, B. R., Parsonage, J. R., J. Macromol. Sci. -Chem., (A) 16 ,i, 141 (1981 ) 9 )Zhao-Qi Wu, Hirljac, J., Chao-Lung Hwang, Young, J. F., J. Am. Cer. Soc., 66,5, C 86 (1983) iO)Hirljac,J. ,Wu, Z-Q. ,Young, J.F. ,Cem.Concr.Res. ,Vol 13,877 (1983) ll )Currell, B oR., Midgley, H.G., Montencinos, M., Parsonage, J. R., Cem. Concr. Res., Vol 15,889 (1985) 12 )Dent G] ass er, L° S., Lachowski, E. E., Mohan, K., Taylor, H. F.W., Cem. Concr. Res., Vol 8, 733 (1978) 13)Berger,R.L. ,Bentour,A. ,Millestone,N.B. ,Kung,J.H. ,J.Am.Cer.Soc. ,62, 358 (1979) 14)Bentur ,A. ,Berger,R.L. ,Kung, J.Ho ,Millestone,N.B. ,Young,J.F., J.Am.Cer.Soc., 62,362 (1979) 15)Young,JoF.,Berger,R.L.,BenhJr ,A.,ll Cemento,75, (3) 391 (1978) 16)Parrott,L.J. ,CemoConcr.Res.,Vol 11,415 (1981) 17) Uchikawa, H., Furuta, R., CemConcr, Res., Vol ll, 65 (1981) 18)Khan,M.H. ,Mohan,K. ,Taylor,H.F.W. ,Cem.Concr.Res. ,Vol 15,89 (1985) 19 )Kal Ousek, G. L., Kopanda, J. E., Cem. Concr. Res., Vol i, 63 (i 971 )