I n d . Eng. Chem. Res. 1994,33,2795-2800
2796
Lithium Salts in Rapid Setting High-Alumina Cement Materials Tomislav Matusinovic,’ Nevenka Vrbos, and Danijel Curlin Department of Chemical Engineering and Technology, University of Zagreb, Marulikev trg 19, 41000 Zagreb, Croatia
The influence of lithium salts on rapid setting and hardening of high-alumina cement (HAC) has been investigated. The integral analyses of the results have been made in order to test the process of hardening. The chemistry of hydration of HAC in the presence of lithium salts has been studied using solution analyses, X-ray diffraction techniques, setting time measurements, and compressive strength measurements.
Introduction Although the rapid setting and hardening of highalumina cement (HAC) represents a process of commercial and industrial importance, the chemical processes involved during the hydration are not yet well understood. The research presented here is an attempt to contribute in this direction. Lithium salts have been reported as accelerating setting agents for high-alumina cement materials in patent literature (Salmoni, 1937; Aldera, 1969; Hovase et al., 1972). The setting times of HAC pastes could be influenced by the addition of small amounts of several materials (Parker, 1952). It has been proposed that the lithium salts caused accelerated setting of HAC by rapid hydration of cement components (Rodger and Double, 1983). It is shown that both cations and anions of alkali metal salts have a profound effect on chemical reactions which cause the hardening of HAC (Currell et al., 1987). Systematic studies of the effect of the variety of lithium salts lead to the proposal that the pH of the mixing salt solution could have a major influence upon the setting kinetics (Novinson and Crahan, 1988). The alkali metal salts caused the strength development of HAC materials at early ages (MatusinoviC and Vrbos, 1993). Solid state NMR data indicate that aluminum in monocalcium aluminate is entirely 4-coordinated,but all the principal hydration products contain 6-coordinated aluminum. The 27AlNMR work shows that the hydration of HAC proceeds via conversion of 4- to 6-fold-coordinated aluminum (Muller et al., 1984). In situ 27Alwide-line NMR measurements during the hydration process have provided good estimates of the induction period and the rate of the phase conversion. Lithium carbonate eliminates the induction period but leaves the rate of the phase conversion essentially unchanged (Luong et al., 1989). Experimental Section The high-alumina cement used was taken from a regular production of “ISTRA CEMENT INTERNATIONAL”, Pula, Croatia. The cement has the following oxide mass fraction composition: CaO, 40.2%; Al2O3, 39.0%; Fez03, 11.7%; FeO, 4.3%; Si02, 1.9%. The principal compound is monocalcium aluminate, CaA1204 (CAI, with 12Ca0-7Al203(C1A7) and ,!?-Ca2SiOa(P-CzS) as minor compounds. Li2CO3 used was a commercial Analar grade reagent. Lithium hydrometaaluminate, LiH(Al02)2*5H20(LiA) was prepared in our laboratory (Dobins and Sanders, 1932). Setting Time Measurement. The setting time was determined using a modification of the American Society
* To whom correspondence
should be addressed.
for Testing Materials (ASTM)method C 804-75. In our modification, the penetration of the needle into the hardening paste was measured every 10 s, rather than every 10 min, due to the rapid setting time for the lithium salt modified paste. The experiments used a waterlcement (wlc)ratio of 0.24 and were repeated three times to obtain reliable standard deviations and statistical means. Compressive Strength Measurement. Compressive tests were run on specimens at different ages according to ASTM C 349-77. The specimens (40 x 40 x 160 mm) were prepared according to ASTM C 109 (w/c = 0.44). Three specimens were tested for each age. Solution Analysis. Cement slurries made with a mass fraction of 0.05% Li2CO3 (w/c = 1.5) were mixed by means of a magnetic stirrer for prescribed time intervals and then rapidly filtered to extract the aqueous solution. The ambient temperature was 23 “C. Details of the mixing and filtering system and the procedures for analysis were described by Thomas (Thomas et al., 1981a,b). After filtration, aliquots of the solution were immediately analyzed for the following ions: 1. Calcium. Volumetric EDTA titration after complexing Fe and Al with ethanolamine (Welcher, 1958). 2. Aluminum. Gravimetric analysis, by precipitation with NH40H and addition of NH4C1 (Furman, 1968). 3. Lithium. Atomic absorption spectrometry (Patassy, 1965). X-ray Diffraction. Samples of hardened cement were cured for 24 h a t room temperature and finely ground. X-ray diffraction traces were obtained with a Philips PW 1010 goniometer system using CuKa radiation. The quantitative determination of LiA precipitated in HAC material with Li~C03(initial concentration was 4.0 mM) was performed by X-ray examination using corundum as an internal standard. The intensity ratio of the 0.75 nm LiA line and the 0.2085 nm corundum (a-AlnO3)line was determined spectrometrically. The slope of the calibration line was 0.3344 (Klug and Alexander, 1962). Results and Discusion
While the hardening of HAC pastes, mortars, and concretes are the results of the hydration processes, they can be studied indirectly through compressive strength and setting time measurements. The influence of the different mass fraction of Li2CO3 on the compressive strength of HAC mortars has been studied. The results of the compressive strength measurements, given in MPa, have been transformed and expressed as a percent
0 1994 American Chemical Society
2796 Ind. Eng. Chem. Res., Vol. 33, No. 11, 1994
Table 1. Compressive Strengths at Early Ages of HAC Mortars and HAC Mortars Made with Different Mass Fractions of Lid303 (w/c = 0.44) fraction of the final compressive strength/%
compressive strengthlMPa HAC w(LizC03)
+
HAC
timeh
HAC
0.05%
0.03%
0.01%
0.5 1.0 1.5 2.0 2.5 3.0 3.5 4.0 4.5 5.0 5.5 6.0 6.5 7.0 8.0 9.0 10.0 15.0 20.0 2160
a a
0.69 3.37 4.96 10.31 14.84 18.25 24.39 27.15 28.17 31.60 34.21 36.89 37.17 38.33 38.47 39.89 41.08 42.46 43.07 68.70
a
a
a b 8.14 b 16.12 b 27.75 b 33.95 b
a b 4.25 b 11.77 b 28.33 b 37.25 b b b 48.50 b b 54.69 57.71 60.00 91.00
a
a a a a
0.91 3.70 12.95 18.59 30.06 33.20 36.08 40.52 44.52 48.19 50.97 58.14 58.46 92.50
b b 45.00
b b 46.21 48.44 53.75 85.00
HAC
0.05%
1.0 4.0 14.0 20.9 32.5 35.9 39.0 43.8 48.0 52.1 55.1 62.9 63.2 100.0
1.0 4.9 7.2 15.0 21.6 26.6 35.5 39.5 43.0 46.0 49.8 53.7 54.1 55.8 56.0 58.6 59.8 61.8 62.7 100.0
+ w(LizC0~) 0.03%
0.01%
9.6
4.7
19.0
12.9
32.7
31.1
39.9
40.9
52.9
53.3
54.4 57.0 63.2 100.0
60.1 63.4 65.9 100.0
Test could not be performed because specimens were too soft to be removed from the mold. Test was not performed. 3.6
3.2
' I2 . 8 \o
I L
W
rz1
2.4
c I
2.0
1.6
1.2
0.8
0.4
1
I
I
1
2
4
6
8
Figure 1. First-order rate law analyses: (a) HAC, Y = 0.325t - 0.703; (b) HAC L i ~ C 0 3Y , = 0.334t - 0.129; (d) HAC 0.05% Li2CO3, Y = 0.340t + 0.127.
+
of a final compressive strength after 90 days. Table 1 and Figure 1 show these data. It can be seen from Table 1 that there is a sudden increase of the compressive strength for HAC mortars up to the age of 3.5 h. HAC mortars with 0.05%lithium carbonate show already after 0.5 h a compressive strength of 0.69 MPa and rapidly increase with aging. Table 1 also shows the time dependence of the compressive strength for HAC mortars and HAC mortars made with different mass fractions of lithium carbonate expressed as a percentage of a final compressivestrength. It is evident that without any additive the growth of
1
10 Tlme/h
12
+ 0.01% Li2CO3, Y = 0.334t - 0.264; (c) HAC + 0.03%
the measurable strength starts after 3.5 h and after 20 h has 63.2% of the final compressive strength. In the presence of lithium carbonate the growth of the compressive strengths starts immediately after mixing. After 20 h there are 62.7%,63.2%,and 65.7%of the final compressive strength, depending on the mass fraction of Li2CO3. The results are in very good agreement with in situ 27Al NMR measurements made by Luong (Luong et al., 1989.) The research was carried out on the HAC samples hydrated with demineralized water and with a solution of LiZCO3. Without lithium carbonate the aluminum conversion starts after approximately a 3-4
Ind. Eng. Chem. Res., Vol. 33, No. 11, 1994 2797 h induction period and appears to end after 18-20 h. The fraction of 4-coordinated aluminum in such a product amounts to approximately 30-40% of the entire aluminum content. The data obtained with 0.05% lithium carbonate shows that the conversion of Al(4) t o Al(6) starts immediately after mixing. Due to this coincidence integral analyses of our results have been made in order to test the process of hardening. Figure 1 illustrates that the process obeys a simple first-order reaction rate, just like the conversion of Al(4) t o Al(6).
If [Al(4)1is expressed as [Al(6)1,then substituting [Al(411 = l - [Al(6)1into eq l, one can obtain
where k is a rate constant and [Al(4)lfand [Al(6)lfare the corresponding concentrations at the point when the reaction was practically completed (after 20 h). Based on this fact it can be empirically tested that the rate of compressive strength changes us time following the relation 3 by analogy with eq 2. 0 and of represent the
(3) compressive strength at any point of the reaction and at the point where the reaction was practically completed (after 20 h), respectively. By integration of (3) one obtains
-Idaf
- a) = Kt
(4)
The -ln(af - a) us time plots thus obtained are generally linear in the period of 6 h after first appearance of the strength, because a t longer times the rate of reaction is not of first order and a greater scattering is observed. Figure 1also shows, that in all cases the process follows first-order kinetics. The rate constant is independent of lithium concentration, and the induction period (ti) decreases significantly by addition of lithium carbonate. Also, the slopes of all straight lines are approximately the same as Luong's plot of -ln[Al(4) - Al(4)fl us time. On the basis of our results and results obtained by NMR, it can be concluded that in the period of 6 h after the appearance of the first strength, only the transformation of Al(4) to Al(6) is responsible for the increase of strength and additives cannot change the kinetic processes of this transformation. It can be seen from the results given in Table 1that the precipitation of lithium aluminate is responsible for the rise of compressive strength of HAC mortars at very early ages. Up to age 4 h the compressive strengths of the cement materials increase with an increase of mass fraction of lithium carbonate. The increase of the compressive strength is caused by precipitation of lithium aluminate which acts as a heterogenous nucleation substrate and promotes the nucleation of the calcium aluminate hydrates. At the age of 4 h, when the precipitation of calcium aluminate hydrates has a dominant contribution to the compressive strength, the mass fraction of Li~C03has a less important influence. The compressive strengths with the total mass fraction of LizC03 are almost equal. After 4 h the compressive
strengths increase considerably, but a higher mass fraction of Li2CO3 causes lesser compressive strengths a t all ages. The induction period during the precipitation of calcium aluminate hydrates from a supersaturated solution is a reflection of the nucleation barrier to the formation of these compounds (Barret et al., 1974). The accelerating effect of lithium salts has been attributed to a removal of this barrier, caused by an initially fast precipitation of lithium hydrometaaluminate (Rodger and Double, 1984). To investigate this matter, the chemistry of hydration of HAC in the presence of lithium carbonate has been studied. Comprehensive analyses of the solutions extracted from cement slurries were carried out a t various time intervals after mixing. The results are shown in Figure 2. In the untreated control sample, Ca2+and A13+ levels rise rapidly within the first 5 min, after mixing reach a maximum after 10-15 min, and then gradually decline. Two processes have been taking place. The first one releases Ca2+and A13+ into aqueous solutions.
M0,-
+
Ca2+ 2~10,-
(5)
+ H,O t A13++ 20H-
(6)
Ca(AIO,),
The second involves the removal of these ions from solution by nucleation and growth of the hydration products when the solubility limits are exceeded.
+
Ca2+ 2Al0,2Ca2+
+ 10H,O zCa(AlO,),*lOH,O
(7)
+ 2A10,- + 9H,O zCa&l,0,*8H,O + 2H+
(8)
Comparing untreated samples with samples treated with lithium carbonate shows that there are considerable changes in the solution chemistry. The Ca2+levels reach about the same values as in the control sample during the first 30 min, but thereafter decrease much more rapidly. Notably, A13+ levels in solution are depressed during the investigated period and do not reach the maximum value found in the control system. Li+ levels also drop very rapidly becoming hardly detectible after about 0.5 h. These data show that A13+ released into solution by hydrolysis of the HAC is immediately precipitated as LiA.
Li+
+ 2Al0,- + 6Hz0
LiH(A10,)2*5H,0
+ OH-
(9)
It acts as a heterogenous nucleation substrate, promoting the nucleation of the calcium aluminate hydrates. The existence of lithium hydrometaaluminate in a HAC paste hydrated in a solution of lithium carbonate has been detected by X-ray diffraction (Figure 3). The hydration process of CA is generally believed to occur through initial dissolution, formation of a metastable gel, and subsequent precipitation, principally Ca&04*1OHz0 (CAHIO)but also CaAl~05*8HzO(CZand their conversion to Ca&0s06Hz0 (c3AH6). The composition of the hydration products shows a time-temperature dependence: the low-temperature hydration product CAHlo is thermodynamically unstable especially in warm and humid storage conditions when a more stable compound, c3AH6, is formed (Mehta, 1986). Comparison of Figure 3 parts a and b shows, in addition to the peaks associated with HAC phases,
2798 Ind. Eng. Chem. Res., Vol. 33, No. 11, 1994
34.0
I E
L
l
32.0 30.0
\
+
n
a +a -
28.0
(3
28.0
24.0
0
AI^+
x x a
(0
A b & AI 3 * withLi*
22.0
AAb
U
4.0
LI+
20.0
3.0
18.0 16.0
14.0
12.0
1
1
I
I
I
I
I
I
I
I
1
5
10
15
20
25
30
35
40
45
50
55
60
Time/ min Figure 2. Concentration vs time curves for solutions filtered from HAC suspension (the initial concentration of Li+ was 9.0mM).
F
1
3s
30
25
20 2 8 CuKd.
c-
Figure 3. X-ray diffraction traces obtained from (a) unhydrated HAC, (b) a hydrated HAC paste made with demineralized water after 24 h, and (c) a HAC paste hydrated in solution of mass fraction 1%Li2CO3 after 24 h.
the hexagonal hydrate CAHlo. The peaks for hexagonal CzAHs are not detectable. The samples were hydrated at room temperature and there was no sign of conversion to the cubic hydrate C&.&. In the sample treated with Li2CO3 (Figure 3c) significant differences are evident. The diffraction peaks are identifiable on the ASTM index with lithium hydrometaaluminate, LiH(~02)26HzO (Berry, 1970). The kinetics of precipitation has been followed by X-ray diffraction. The results are given in Table 2.
The precipitation starts immediately after addition of Li2CO3, and it is almost completely finished after 60 min. These data are compared with the data obtained by atomic absorption spectrometry presented in Figure 2. Very good agreement has been found regardless of the different methods of analysis. If precipitated, LiA acts as a heterogenous nucleation substrate and promotes the nucleation of the calcium aluminate hydrates; then the addition of LiA would markedly accelerate the setting time of HAC. The
Ind. Eng. Chem. Res., Vol. 33, No. 11, 1994 2799
Acknowledgment
Table 2. Lithium Hydrometaaluminate: Time Dependence of LiA Precipitation atomic absorption spectrometry
X-ray diffraction time/ min
1 5
10 15 20 25 30 45 60 a
ZMAd w(LiA)/ % ICOR
CLd M
An
A'"
mM
mM
Nomenclature
0.5 0.7 2.3 3.0 3.3 3.4 3.5 3.6 3.7
13.5 18.9 62.2 81.1 89.2 91.9 94.6 97.2 100
14.5 18.1 62.7 81.9 90.4 96.4 97.6 98.8 100
1.2 1.5 5.2 6.8 7.5 8.0 8.1 8.2 8.3
7.8 7.5 3.8 2.2 1.5 1.0 0.9 0.8 0.7
HAC = high alumina cement LiA = LiH(AlOz)z6HzO CA = C d 2 0 4 CAHlo = CaA1~04*10HzO C f l 8 = CdzO.&HzO c3AH6 = Cd206.6Hzo ,!?-CzS= ,!?-CazSiOl wlc = waterlcement ratio w = mass fraction Al(4) = 4-coordinated aluminum Al(6) = 6-coordinated aluminum Y = -ln(uf - a) t = time k = rate constant [ ] = concentration in any time period c = analytical (total) concentration ti = induction period ImT = intensity of rapid setting HAC material line I C ~ =R intensity of corundum line
7.5 9.6 33.5 43.7 47.2 48.7 50.8 52.0 53.5
2.5 3.2 11.2 14.6 15.8 16.3 17.0 17.4 17.9
C L ~ CLid
A and A' are percentages of precipitated LA.
Table 3. Lithium Hydrometaaluminate: Comparison of Setting Times at Different Mass Fractions (Particle Size < 0.05 mm) w(LiA)/% 0
setting time/s
w(LiA)l%
setting time/s
15840 14760 13320 8940 2940
0.2 0.3 0.4 0.5 1.0
1710 700 480
0.0001 0.001 0.01 0.1
a b
Setting of a Setting of HAC with LiA during the mixing time. HAC immediately by adding LiA.
Table 4. Lithium Hydrometaaluminate: Comparison of Setting Time at Different Particle Size (Mass Fraction 0.2%)
particle size/mm setting timds particle sizdmm setting time/s 40.05 0.05-1
The authors acknowledge financial support from the Croatian Ministry of Science and Technology.
1710 2520
1-2 >2
5970 7440
measurements of the influence of different mass fractions of dried powdered LiA on the setting time of HAC have been done. The results of the measurement, given in Table 3, support this idea. If LiA eliminates the induction period then the different particle sizes of LiA would accelerate the setting time of HAC differently. Our measurements of the setting time of HAC for different particle sizes of LiA support this idea (Table 4).
Conclusions Along with rapid setting, small quantities of lithium salts cause the strength development of HAC at very early ages. The integral analyses of the results shows that the process obeys simple first-order reaction kinetics in the period of 6 h after first appearance of the strength. The induction period, preceding the precipitation of calcium aluminate hydrates, is influenced by the nucleation barrier. The accelerating effect of lithium salts has been attributed to a removal of this barrier, caused by an initially fast precipitation of lithium aluminate. Comprehensive analyses of the solutions extracted from cement slurries show that alumina, released into solution by hydrolyses of HAC, is immediately precipitated. X-ray diffraction data support the existence of lithium hydrometaaluminate in HAC paste which was hydrated in a solution of Li2CO3. A syntethically prepared compound, LiA, added in HAC paste, acts as a heterogenous nucleation substrate, which shortens or eliminates the induction period and markedly accelerates the setting time. Different particle sizes of lithium hydrometaaluminate accelerate the setting time differently.
Subscript f = time when reaction was practically completed Greek Symbols a = polymorphic form of a substance ,!? = polymorphic form of a substance u = compressive strength in percent
Literature Cited Aldera, A. Fluidized Molding Material for Manufacturing Cores and Molds and a Method Therefore. US. Patent 3,600.203, September 1969. Barret, P.; Menetrier, D.; Bertrandie, D. Contribution of the Study of the Kinetic Mechanisms of Aluminous Cement Setting. Gem. Concr. Res. 1974,4 , 545. Berry, L. G. Powder Diffraction File; Joint Committee on Powder Diffraction Standards: Philadelphia, 1970. Currell, B. R.; Grzeskowiak, R.; Midgley, H. G.; Parsonage, J. R. The Acceleration and Retardation of Set High Alumina Cement by Additives. Gem. Concr. Res. 1987,17, 420. Dobbins, J. T.; Sanders, J. P. Determination of Aluminum, Formation of Lithium Aluminate. J.Am. Chem. Soc. 1932,54, 178.
Furman, N. H. Standard Methods of Chemical Analyses, Vol. Z. The Elements; Van Nostrand: Toronto, 1968; p 69. Hovasse, C.; Allemand, P. Setting and Hardening of Aluminous Cement. US.Patent 3,826.665, July 1974. Klug, H. P.; Alexander, L. E. X-ray Diffraction Procedures; John Wiley and Sons, Inc.: New York, 1962; p 410. Luong, T.; Mayer, H.; Eckert, H.; Novinson, T. I. In Situ 27AlNMR Studies of Cement Hydration: Effect of Lithium-Containing Setting Accelerators. J. Am. Ceram. SOC.1989,72,2136. Matusinovi6,T.; Vrbos, N. Alkali Metal Salts as Set Accelerators for High Alumina Cement. Gem. Concr. Res. 1993,23,177. Mehta, P. K.; Concrete Structure, Properties and Materials; Prentice-Hall Englewood Cliffs, NJ, 1986. Muller, D.; Rettel, A.; Gessner, W.; Scheler, G. An Application of Solid-state Magic Angle Spinning 2 7 A l NMR to the Study of Cement Hydration. J. Magn. Reson. 1984,57, 152. Novinson, T.; Crahan, J . Lithium Salts as Set Accelerators for Refractory Concretes: Correlation of Chemical Properties with Setting Times. ACZ Mater. J. 1988,January-February, 12. Parker, T. W. The Constitution of Aluminous Cement. Proceedings Third International Symposium on the Chemistry of Cement, London 1952; Cement and Concrete Association: London, 1954; p 512.
2800 Ind. Eng. Chem. Res., Vol. 33, No. 11, 1994 Patassy, F. Z. Lithium Determination in Waters and Plant Materials by Atomic Absorption Spectrophotometry. Plant Soil. 1966,22,395. Rodger, S.A.; Double, D. D. The Chemistry of Hydration of High Alumina Cement in the Presence of Accelerating and Retarding Admixtures. Cem. Concr. Res. 1984,14, 73. Salmoni, R. Verfahren z u r Verkurzung der Abbindezeit von Tonerdezementen. Deutches Patent 648851, August 1937. Thomas, N. L.; Double, D. D. Calcium and Silicon Concetration in Solution During the Early Hydration of Portlad Cement and Tricalcium Silicate. Cem. Concr. Res. 1981b,11, 675.
Thomas, N. L.; Jameson, D. A.; Double, D. D. The Effect of Lead Nitrate on the Early Hydration of Portland Cement. Cem. Concr. Res. 1981a,11, 143. Welcher, F. J. The Analytical Uses of Ethylendiamine Tetraacetic Acid; Van Nostrand: Princeton, 1958; p 79. Received for review January 4, 1994 Accepted J u n e 28, 1994@
* Abstract published in Advance ACS Abstracts, August 1, 1994.
