The acceleration and retardation of set high alumina cement by additives

CEMENT and CONCRETE RESEARCH. Vol. 7, pp. 420-432, 1987. Printed in the USA. 0008-8846/87 S3.00+O0. Copyright (c) 1987 Pergamon Journals, Ltd.

THE ACCELERATION AND RETAFE)ATION OF SET HIGH ALLNINA CEMENT BY ADOITIVES

B.R.Currell

(]),

R.Grzeskowlak ( 1 ) ,

H.G.MLdgley (2) and J . R . Pa r s onage (1)

(]) School o f C h e m i s t r y , Thames P o l y t e c h n i c , Woolwtch, London SE]8 6PF (2) I l m l n s t e r Cement Research, 24, Summerlands Park D r l v e , l t m l n s t e r , Somerset, TA]9 9BN

(Communicated by A.M. Majumdar) (Received Feb. 2, 1987)

ABSTRACT The s e t o f h l g h a l u m l n a cement (HAC) p a s t e s may be c o n s i d e r a b l y I n f l u e n c e d by t h e a d d l t t o n o f v e r y s m a l l q u a n t i t i e s o f c h e m l c a l compounds, From t h e measurement o f s e t t l n g t l m e and t e m p e r a t u r e flee. wlth a conduction calorimeter. I t l s shown t h a t b o t h c a t l o n s and a n l o n s have a p r o f o u n d e f f e c t on t h e c h e m l c a l r e a c t i o n s whlch cause t h e h a r d e n i n g o f HAC, The e f f e c t s on t h e t l m e o f s e t t l n g may be summarlsed as f o l l o w s : f o r c a t l o n s L I ~ Na < none < K, ~ Ca < Mg < Sr < NH4 f o r a n l o n s OH ~ none < CI < NO3 < Br < a c e t a t e The e f f e c t o f a n l o n s , e x c e p t f o r t h e h y d r o x y l l o n , causes a r e t a r d a t i o n In t h e s e t t l n g as a r e s u l t o f r e p l a c e m e n t o f OH groups l l n k e d t o A I , r e f e r r e d t o as l o n p e n e t r a t i o n , p r e v e n t i n g t h e f o r m a t i o n o f o x o b r l d g e s . The r e t a r d a t i o n o t s o t w l l l be governed by t h e r a t e o f r e p l a c e m e n t o f OH by o t h e r a n l o n s and t h e s t a b i l i t y o f t h e new s p e c l e s formed. The d r a m a t l c e f f e c t o f OH l s due t o t h e r e p l a c e m e n t o f H20 by OH In t h e AI e n v i r o n m e n t l e a d l n g t o a f u r t h e r centre for oxobrldge formation.

Introductlon In 1952 Parker (l) reported that the setting times of High Alumlna Cement (HAC) pastes could be Influenced by the addltlon of small amounts, approx 0.5% by weight on the weight of cement, of many materlats. He consldered that the major influence was the pH of the solutlon, the hlgher the pH the faster the set took place. Robson (2) d i sc us s ed t h e e f f e c t s o f a d d i t i v e s and c o n c l u d e d t h a t d l l u t e s o l u t i o n s o f sodium, p o t a s s i u m and c a l c l u m h y d r o x i d e and o r g a n i c bases such as t r i e t h a n o l a m l n e were a c t l v e a c c e l e r a t o r s o f s e t b u t magnesium and b a r l u m h y d r o x i d e c o u l d cause r e t a r d a t i o n p o s s l b l ~ due t o b u f f e r a c t i o n . Sodium and p o t a s s i u m c a r b o n a t e s and s i l i c a t e s reduce t h e s e t t l n g t i m e o f HAC, H i g h l y d l l u t e d s u l p h u r i c a c l d i s s a i ~ t o produce q u i c k s e t t l n g b u t s l m l l a r c o n c e n t r a t i o n s o f h y d r o c h l o r i c and a c e t i c a c l d s r e t a r d . L i t h i u m s a l t s have been

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421 SET, ACCELERATION, RETARDATION, HIGH ALUMINA CEMENT

suggested as a c c e l e r a t o r s . Robson a l s o dLscusses t h e a c t L o n o f m a j o r q u a n t L t L e s o f addLtLons such as 10% o r more o f P o r t l a n d cement, 20 t o 25% o f caLcLum s u l p h a t e o r gypsum p l u s t e t r a caLcLum aLumLnate t h L r t e e n hydrate. ALL o f t h e s e addLtLons LnvoLve m a j o r changes Ln t h e h y d r a t e mLneraLs produced, e . g .

e t t r L n g L t e from t h e HAC-ceLcLum s u l p h a t e mLxes.

From t h i s b r l e f summary I t can be seen t h a t t h e r e Ls some c o n f u s i o n a b o u t t h e mechanism o f a c c e l e r a t i o n o r r e t a r d a t i o n o f s e t ; P a r k e r suggests pH b u t Robson r e p o r t s t h a t b o t h h l g h OH s o l u t i o n s , and t h o s e o f Low pH, e . g . s u l p h u r l c acld, are a c c e l e r a t o r s . T h l s p a p e r Ls an a t t e m p t t o e x p l a l n t h e c h e m l c a l mechanisms l n v o l v e d in t h e s e t t l n g o f HAC when s m a l l addLtLons a r e made, ExperLmentaL TechnLques

The hLgh aLumLna cement used was a normal p r o d u c t L o n o f CLment Fondu from t h e Grays, Essex p l a n t o f t h e L a f a r g e AtumLnous Cement Co., The g e n e r a l anaLysLs o f such a cement was CaO, 36~; AL203, 41%; FeO, 10%: Fe203,6N; whLch Ls equLvaLent t o a compound c o n t e n t o f CaO.AL203 55%, p L e o c h r o L t e 6%, f e r r L t e 17N, o t h e r s 22%. To p r e p a r e t h e samples o f p a s t e s t h e addLtLves were weLghed Lnto dLstLLLed w a t e r t o gLve t h e requLred c o n c e n t r a t L o n , ( a L L experLments used a w a t e r / c e m e n t r a t l o o f 0 . 2 7 ) t h l s was t h e n hand mlxed w l t h t h e a p p r o p r i a t e weLght o f cement. The mLxes were s t o r e d as f a r as possLbLe a t 18 * 3 °C under moLst condLtLons. The s e t t L n g tLme was measured by t h e method proposed by MauLtzsch and MeLnhoLd (3) whLch LnvoLved t h e measurement o f t h e depth o f p e n e t r a t L o n Lnto a hardenLng p a s t e o f a brass cone lO mm hLgh x 3 mm dLam, under a Load o f lOOg. I t was found t h a t some o f t h e p a s t e s c o u l d s u s t a l n t h e cone w l t h o u t marklng even though t h e y were c l e a r l y n o t hardened. The depth o f p e n e t r a t L o n a t t h e e a r l L e r t l m e s varLed c o n s L d e r a b l y . Some a d d L t l v e s made t h e mLx e x t r e m e l y fLuLd whLLe o t h e r s produced even wLth t h e same w a t e r / c e m e n t r a t L o , d r y , c r u m b l y , unworkable mLxes; t o r e c o r d t h L s e f f e c t t h e d e p t h o f p e n e t r a t L o n a t 30 mLns a f t e r mLxLng has been r e c o r d e d as w e l l as t h e tLme f o r z e r o p e n e t r a t L o n . The conductton caLorLmetrLc apparatus consLsted of a pLastLc cyLLnder about 20 mm dLam x 80 mm., whLoh contaLned the paste Lnto whLch was Lnserted a chromeL aLumeL thermocoupLe; thLs was opposed by a sLmLLar cyLLnder o f set hLgh aLumLna cement paste. The dLfterence Ln temperature was recorded, so t h a t one dLvLsLon of the recorder was equLvaLent t o 0.63 °C. The caLorLmeter head was placed Ln a vacuum flask and matntaLned a t room temperature whLoh was 18 ± 3 oC. I t was notLoed t h a t there was always an knLtLaL temperature rLse of about l oC durLng the f L r s t 2 mkns a f t e r mLxLng, the temperature then decreased slowly over the next 60 mLns. The LnLtLaL temperature rLse was consLdered t o be due t o the heat of wettLng of the powder. There followed two temperature maxLma sometLmes c l e a r l y dLfferentLated,, sometLmes merged Lnto one broad peak. In the L a t t e r case Lt was u s u a l l y possLbLe t o dLscrLmLnate between t h e two peaks by c u r v e f L t t L n g . The p a r a m e t e r s r e c o r d e d were t h o s e recommended by

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Vol. 17, No. 3 B.R. Curre11, e t a l .

MathLeu ( 4 ) : T O , t h e tLme f o r t h e f L r s t d e v L a t L o n f r o m t h e s t e a d y s t a t e ; TLmax, t h e tLme f o r t h e t e m p e r a t u r e r L s e t o reach a maxLmum: Ln t h e s e L n v e s t L g a t L o n s t h e r e w e r e two such maxLma Tmax 1, Tmax 2; H Ls t h e maxLmum t e m p e r a t u r e o f t h e Tmax; and, L, t h e wLdth a t h a L f peak h e L g h t . T o was t h e Least c L e a r L y defLned p a r a m e t e r and most reLLance was p l a c e d on t h e Tmax . measurements, D L f f e r e n t L a L thermaL a n a L y s l s was c a r r l e d o u t on an a p p a r a t u s as d e s c r L b e d by MLdgLey ( 5 ) , 700 mg samples were used wLth a heatLng r a t e o f 12 oC/mLn. The c o n d u c t L v L t y was measured a t 9 v o l t s , 50 Hz (NevLLLe ( 6 ) ) wLth s t a L n L e s s s t e e l p r o b e s 0 . 0 5 mm dLam. LmpLanted Lnto t h e p a s t e 10 mm a p a r t t o a d e p t h o f 10 mm. Th~ ¢ondugtenGe ws~ ChQGked agaLn~t varLou~ 8oLutLon8 o f KCL and c a L L b r a t e d f r e q u e n t L y a g a L n s t known r e s L s t a n c e s . Changes Ln c o n d u c t L v L t y w e r e t a k e n t o be when t h e r e was a d e v L a t L o n f r o m t h e s t e a d y s t a t e o f g r e a t e r t h a n two dLvLsLons Ln t h e r e c o r d e r . WLth hLgh aLumLna cement p a s t e s t h r e e d e v L a t L o n s were d e t e c t a b l e , aLthough wLth t h e a d d L t L v e t h e s e c o u l d merge Lnto one. ResuLts

P a r k e r ( I ) c a r r L e d o u t t h e most d e t a L L e d s t u d y o f t h e e f f e c t s o f a d d L t L v e s on t h e s e t t L n g o f hLgh aLumLna cement p a s t e s . F o r hLs L n v e s t L g a t L o n s he TABLE 1 Effects

o f AddLtLves on t h e S e t t L n 9 tLmes o f HLgh AtumLna Cement

(Data from P a r k e r (I)) AddLtLve a t 0.5% w.w.

InLtLaL S e t (MLns)

FLnaL Set (MLns)

None NaOH C.,a(OH)2 +

34 10 9

212 50 160

NaCL KCL CaCL2 MgCL2

76 275 195 160

450 410 -

MgSO4.6H20

225

311

+ s a t u r a t e d soLutLon

used a f L x e d c o n c e n t r a t L o n o f 0 . 5 ~ by weLght on t h e weLght o f cement and r e c o r d e d t h e LnLtLaL and fLnaL s e t usLng t h e B r L t L s h S t a n d a r d ( 7 ) VLcat needle test. A s e L e c t L o n o f hLs r e p o r t e d d a t a a r e gLven Ln TabLe 1, P a r k e r c o n c l u d e d t h a t t h e f a c t o r governLng t h e s e t t L n g tLme was pH, t h e g r e a t e r t h e pH t h e e a r L L e r t h e s e t t L n g tLme. To see Lf any f u r t h e r LnformatLon on t h e c h e m L s t r y LnvoLved c o u l d be e L u c L d a t e d c o n d u c t L o n c a L o r L m e t r y was c a r r L e d o u t . For the fLrst serLes c o n c e n t r a t L o n s o f 0 . 5 ~ w/w, as used by P a r k e r , w e r e used. The r e s u l t s a r e

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423 SET, ACCELERATION, RETARDATION,

HIGH ALUMINA CEMENT

TABLE 2 Conduction

Calorimetry R e s u l t s

wlth

Varlous

Additives

a t 0.5% w / w o f

Cement g mol none LLCL 1.19 NaCL 0,85 KCL 0.68 MgCL 2 0.53 CaCL 2 0.45 NaBr 0.49 NaOH 1.3 K0H 0.89 Ca(OH)2 x KNO3 0.49 FeSO4 7H20 0.18 CuSO4 5H20 0.20 AL2(SO4) 3 14H20 0.08 Na2CO 3 0.47 -

Tn (mlns) 130 0 240 55 158 770 1200 55 95 15 150

Tmmy1 (mlns) 265 30 330 270 217 897 1350 90 160 175 330

H L (oC) (mlns) 5.0 120 38.4 25 5.6 50 16.1 90 13.0 40 11.8 60 9.0 1400 19,0 40 9.9 50 10.5 60 5.6 120

T~2 (mlns) 345

H (°C) 16.3

L (mlns) 100

380 305 246 925

27.8 18.0 28.0 19.8

80 140 60 130

125 200 240 395

8,6 24,8 15.5 24,2

70 90 80 80

210

300

6.3

80

380

38.3

45

650

800

6.3

200

900

6,3

200

285 130

420 340

8.6 8,7

160 100

510 390

16.5 16.1

90 200

acetic acLd

no t e m p e r a t u r e

rlse

at

2880 mLns ( 2 d a y s )

x saturated sotutlon

g L v e n i n T a b l e 2. From t h L s d a t a f o r e x a m p l o , o f Tmax 1 f o r c a t l o n l c chlorides was:-

it was s e e n t h a t

the order

LL << Mg < none < K < Na < Ca and f o r

sodium tons, OH ( CI ( CO3 ( Br.

From T a b l e . 2 i t can be s e e n t h a t t h e m o l a r c o n c e n t r a t i o n s varied considerably, from 0.]8 to 1,30 and I t was c o n s i d e r e d t h a t t o f o l l o w c h e m l c a L r e a c t L o n s I t w o u l d be more s u l t a b l e t o use a c o n s t a n t m o l a r

the

concentratlon,

InLtLatLy. to fLnd suLtabte concentratLons fLve series were LnvestLgated: NaCL. KOH. NaOH. LLCL and LL2CO 3. The r e s u l t s a r e g L v e n Ln T a b l e s 3 a - e , From t h e d a t a Ln T a b l e 3a L t was s e e n t h a t . u s l n g Tmax 1 . NaCL r e t a r d s a t all concentratLons examined, the hLgher the concentratLon the greater the

retardation. From t h e d a t a I n T a b l e s 3b and c I t was s e e n t h a t h y d r o x i d e s a c c e l e r a t e the reactLons, the hLgher the concentratLon the greater the acceteratLon. I t s h o u l d be n o t e d h e r e t h a t w L t h t h e a d d l t L o n o f b o t h sodLum and p o t a s s L u m h y d r o x i d e t h e mLx. a t a w / c r a t i o o f 0 . 2 7 . became a l m o s t unworkable.

424

Vol. 17, No. 3 B.R. Currell, et a l .

TabLe 3 d and e gLves t h e d a t a f o r t h e addLtLon o f LLCL and LL2(X)3. The e f f e c t o f LLthLum s a l t s was t o a c c e l e r a t e : f o r t h e chLorLde a t c o n c e n t r a t L o n s between 0 . 0 2 4 and 0.048 g moL. t h e tLmes f o r Tmaxl changed from 228 t o 22 mLns. F o r t h e LLthLum c a r b o n a t e t h e g r e a t e s t change Ln Tmax1 was between 0.0002 and 0.003 g moL., from 140 t o 14 mLns. Both LLthLum s e r L e s showed a pessLma Ln t h e tLme o f maxLmum h e a t e v o t u t L o n LndLcatLng t h a t t h e r e was an optLmum amount o f addLtLve t o produce t h e most e f f e c t L v e a c c e l e r a t o r , f o r LLthLum chLorLde 0.202 g moL and f o r LLthLum c a r b o n a t e 0.054 g moL. However, aLLowance must be made f o r t h e hydroLysLs o f t h e c a r b o n a t e formLng OH-. TABLE 3 E f f e c t o f VarLatLons Ln AddLtLve C o n c e n t r a t L o n s on Peak TLmes Ln ConductLon CaLorLmeter Traces. 3a SodLum ChLorLde wt %

,g m o l / g cement

0 0.25 0.5 1.0 2.0

0 0.425 0.85 1.60 3.20

Tm~l(mlns) 265 275 320 495 1780

Tm~2(mlns) 345 315 350 535

3b PotassLum HydroxLde wt % 0 0.5 1.O

g moL/g cement

Tm~vl(mLns)

T~v2(mLns)

0 0.89 1.78

265 160 115

345 200 150

30 SodLum HydroxLde

wt %

9 mot/9 cement

0 0.5 1.0

0 1.3 2.6

Tmm~l(mlns) Tmmy2(mLns) 265 90 5

345 125 45

3d LtthLum ChtorLde wt%

g m o l / g cement

5.0 2.31 0.85 0.50 0.30 0.21 0.20 0.10 0

1.19 0.55 0.202 0.119 0.071 0.050 0.048 0.024 0

T~v(mlns)

H(°C)

28 30 13 18 16 15 22 228 345

23 49.5 78.0 79.3 78 74.2 76 43.9 16.3

L (mLns) 55 41 17 20 18 2l 20 37 100

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17, No. 3

425 SET, ACCELERATION, RETARDATION, HIGH ALUMINA CEMENT

3e L l t h l u m C a r b o n a t e Tm~w(mlns)

g moL/g cement 0.5 0.071 0.054 0.036 0.018 0,01 0.003 0.0002 0

H(oC)

12 25 10 12 21 23 14 140 345

L (mlns)

35 70 104 101 119 112 121 74 16.3

57 43 15 20 22 25 17 40 lO0

From t h e s e p r e l i m i n a r y e x p e r i m e n t s I t was d e c l d e d t o use a c o n s t a n t concentratLon of 0.05 g mol. for the full examination. Table 4 glves d a t a f o r t h e s e t t L n g t l m e s ( 3 ) and t h L s gave an o r d e r f o r c a t L o n l c chlorides of

the

L l ~ Na < none < S r
<<

additives

at

0 . 0 5 g mol

Na
TABLE 4

Setting

Tln~s wlth

Additives none NaOH KOH LLCL NaCI KCL CaCI 2 K~JCI2 a n h y d . SrCl 2 KNO3

all

AddltLve

Concentrations

FLnaL Set (mlns) 220 240 120 15 210 330 330 330 270 180

a t 0 . 0 5 g mol

Penetration

at 30 mlns ( m )

5.5 0.5 0.6 1.0 3.5 6.0 4.5 >23 * 2.0 0.8

= There was no cohesLvlty a t 60 mLns. the cone penetrated completely.

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B.R. Curre11, e t a l .

TABLE 5 C o n d u c t i o n C~Lorlmetry R e s u l t s w l t h all A d d l t l v e C o n c e n t r a t l o n ~ at 0.05 g mot, Addltlve

To (mlns)

Tm~yl (mlns)

H (°C)

L (mlns)

None LLCL NaCL KCL MgCL 2 CaCL2 SrCL 2 NH4CL NaOH KOH LLOH.H20 LLNO3

130 0 95 115 140 150 150 130 90 130 0 0

265 22 255 280 290 280 325 330 220 350 16 10

5.0 79.0 10.6 8.6 9.3 5.6 8.0 9.9 8.0 8.0 65,0 68.0

120 20 70 60 140 60 120 lO0 60 170 35 15

KNO3

250

455

lO.O

I00

MgSO4 FeSO4 7H20 CuSO4 5H20 AL2(SO4) 14H20

150 180 200 230

240 275 435 355

14.0 8.6 7.0 10.0

70 70

Tm~v2 (mlns)

H (oC)

L (mLns)

345

16.3

100

315 345 385 335 405 390 292 400

15.0 24.3 21.3 15.0 14.3 15.6 30.6 8.0

170 70 80 80 190 110 50 200

515

15.0

I00

295 330 485 405

22.0 28.0 7. 0 16.8

80 60

90

65

and f o r Tmax2 L l << Na < none < K < Ca < NH4 < Sr

For potassium anlons the order uslng Tn~ x l ls none < Cl < OH < NO3 Table 5 also Showed that for llthlum salts at 0.05 g mol concentration t h e o r d e r ls NO 3 ~ OH < C1 ~ none, To l n v e s t l g a t e t h e r o l e o f w a t e r : c e m e n t (w/c) r a t t o HAC pastes o f d i f f e r e n t w a t e r c o n t e n t s were p r e p a r e d , lncLudLng some wLth v e r y u n r e a L L s t l c w/c r a t L o s . As w e l l as w/c r a t l o s , t h e m o l a r r a t L o s o f w a t e r t o CaO.AL203 In t h e cement were c a l c u l a t e d , For t h l s s e r l e s t h e cement powder was p l a c e d In t h e c a l o r i m e t e r c o n t a i n e r , t h e w a t e r added and s t i r r e d tn s l t u . The r e s u l t s a r e g i v e n In T a b l e 6. The r e s u l t s show t h a t TmaxI was reduced as t h e w a t e r c o n t e n t l n c r e a s e d u n t i l t h e m o l a r r a t L o water:CaO.ALL~)3.lOH20 reached 1, a f t e r whlch t h e w a t e r i n excess o f t h a t requLred by s t o l c h L o m e t r y slows t h e r e a c t L o n . O l f f e r e n t L a L Thermal A n a l y s i s was used t o monLtor t h e mLneraLoglcaL changes LnvoLved Ln s e t t L n g processes o f hLgh aLumLna cement p a s t e s . SLnce conductLon c a L o r L m e tr y showed two peaks In t e m p e r a t u r e r i s e , HAC w/c 0.27 wLth no a d d L t l v e s was h y d r a t e d and p o r t L o n s t a k e n a t 70,230, 270,360 and 1240 mLns t o s t r a d d l e t h e two peaks. Thermogran~ on t h e s e samples a f t e r s t o p p l n g t h e r e a c t L o n s wLth methyl a l c o h o l , showed t h e f o l l o w i n g

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17, No. 3

427 SET, ACCELERATION, RETARDATION, HIGH ALUMINA CEMENT

TABLE 6 E f f e c t . o f Water Cement R a t l o on HydratLon o f HLgh Alumlna Cement Pastes by C o n d u c t i o n C a l o r i m e t r y . w/c

0.27 0.40 O. 54 0.81 1 . 08

mol r a t l o water/ CaAI904 0.50 0.75 1.00 1.50 2.00

TO (mlns) 130 100 80 105 105

Tmnxl (mlns) 265 220 210 230 230

H L oC (mlns) 5 . 0 120 9.8 80 9.8 80 6 . 3 150 6 . 3 150

TmA~2 (mlns) 345 290 280 360 360

H (oC) 16.3 9.8 10.3 8.6 8.0

L (mln) 100 100 100 170 170

peaks: a f t e r 70 mlns: 70 oC, t h o u g h t t o be due t o adsorbed w a t e r ; a f t e r 230 mlns: a s l n g l e broad peak a t 100 oC, consLdered t o be caused by t h e d e h y d r a t i o n o f a c a l c l u m aLumLnate h y d r a t e g e l ; a f t e r 270 mlns: s l m l l a r t o t h a t found a t 230 mlns w l t h a s l l g h t L y l a r g e r peak. A f t e r 380 mlns t h e thermogram was v e r y d i f f e r e n t ; t h e r e was a s m a l l s h o u l d e r a t 100 oC, two sharp peaks a t 150 oC and 175 oC whlch was l n t e r p r e t e d as b e l n g due t o t h e d e h y d r a t i o n and d e h y d r o x y l a t l o n o f CaO.AL203 10H20. At 1240 mlns, t h e thermogram was t h a t o f a normal 1 day h y d r a t e d h l g h aLumlna cement p a s t e (Mldgley (8)). I t s h o u l d be added t h a t a l l t h e thermograms showed s m a l l peaks a t a b o u t 290 o and 300 oC due t o t h e presence o f a l u m l n a t r l h y d r a t e and t r l c a l c l u m alumLnate h e x a h y d r a t e , however, sLnce t h e s e peaks were a l s o seen In t h e u n h y d r a t e d cement t h e y were l g n o r e d . The c o n c l u s i o n was t h a t t h e f L r s t peak found on t h e c o n d u c t i o n c a l o r i m e t e r was t h e h e a t o f formatLon o f a caLclum a l u m l n a t e h y d r a t e gel and t h e second was caused by t h e h e a t o f formatLon o f a more s t a b l e monocalcLum a t u m l n a t e d e c a h y d r a t e . MLneraLogLcat a n a l y s L s o f an HAC pas t e w/c 0 . 2 7 , wLth added NaCI a t 0.25% w/w gave a f t e r 210 mLns s m a l l response a t a b o u t 70 oC on t h e thermogram, due t o moLsture: a t 310 mLns., t h e r e was a s m a l l broad peak a t 100 oC w l t h a s h o u l d e r a t 150 oC, t h L s t r a c e was s L m L l a r t o t h a t f o r hLgh aLumlna cement p a s t e w l t h no addLtLve a f t e r 270 mLns. The c o n c l u s i o n was t h a t wLth a d d l t L v e s a t t h e c o n c e n t r a t L o n s used In t h l s l n v e s t L g a t l o n t h e mtneraLogLcat p r o d u c t s a r e t h e same as t h o s e found wLth a normal HAC p a s t e . The DTA thermogram f o r pure s y n t h e t L c CaO,AL203. 10H20 (180 mg) shows t h r e e peaks t h a t can be L d e n t l f L e d a r e : a s h o u l d e r a t 100 ° , a Large peak a t 149 ° f o l l o w e d by a s m a l l e r peak a t 174 oC. An L n t e r p r e t a t l o n o f t h e s e peaks f o r CaO.A1203 10H20 Ls t h a t t h e mlneraL c o n t a l n s t h r e e t y p e s o f w a t e r o r h y d r o x y l groups, one p o s s l b l e arrangement f o r t h e compound l s : Ca[AL(OH)4(H20)2]2.2H20 wLth t h e h l g h peaks a t 100 oC r e p r e s e n t L n g t h e 2H20, a t 149 oC t h e (H20) 2 and a t 174 oC t h e (OH)4. I t has been cLaLmed by Roger and Double (9) t h a t LLthLum s a l t s a c c e l e r a t e t h e h y d r a t L o n o f hLgh aLumlna cement p a s t e s by t h e f o r mat Lon o f C2AH8 and AH3. In t h e e x p e r i m e n t s r e p o r t e d h e r e, T a b l e s 3 d and e w l t h a d d i t i o n s as tow as 0 . 0 2 4 g.moL t h e t e m p e r a t u r e rLse may be as g r e a t as 43.9 oC and

428

Vol.

17, No. 3

B.R. C u r r e l l , et a l .

w l t h g r e a t e r amounts t h e r l s e may be as h l g h as l l 9 oC. Wlth t e m p e r a t u r e r l s e s as g r e a t as t h l s t h e f o r m a t i o n o f C2AH8 and AH3 may be due t o t h e t e m p e r a t u r e r l s e and n o t due t o chemlcal changes. TABLE 7 C o n d u c t i v i t y a t 50 Hz u s l n g V a r l o u s A d d i t i v e s Addltive ( 0 . 5 % w:w) none LIC1 ( a t 0.1%) NaC1 CaC12 MgC12 6H20 SrCl 2 NH4CI NaOH MgSO4 CaSO4 2H20

1 s t change Tlme slope* mlns 55 O. 055

25 0

* s l o p e In a r b l t a r y

2nd change Tlme slope mlns 130 O. 0014

0.08 0.067

unlts

250

0.013

65 230 540 0 155

0.006 0.004 0.005 0.015 0.029

( a p p r o x In c o n d u c t i v i t y

3rd change tlme slope mlns 240 O. 142 0

0.193

480 ]05 285 350 740 65 260 180

0.0]9 0.]05 0.090 0,185 0.078 0.141 0.188 0,]22

v tlme),

C o n d u c t i v i t y e x p e r i m e n t s were c a r r l e d o u t on h l g h a l u m l n a cement p a s t e t o h e l p w l t h t h e e l u c i d a t i o n o f t h e chemlcal r e a c t i o n s . In an HAC p a s t e , w/c 0.27 w l t h no addLtLves, t h r e e changes can be d e t e c t e d . T a b l e 7 g l v e s t h e r e s u l t s w l t h some o f t h e a d d i t i v e s used. In a l l cases t h e r e was a decrease in c o n d u c t i v i t y w l t h t i m e . The hLghest c o n d u c t i v i t y was d e t e c t e d a l m o s t Lmmedlately on mlxLng suggestLng t h a t lons were p r e s e n t In t h e c o n t i n u o u s w a t e r phase o f t h e h y d r a t L n g p a s t e . The f l r s t change In 0 0 n d u ~ l v l t y was o n l y found In t h r e e examples t e s t e d , l~ was posslbly h l d d e n Ln t h e o t h e r s and Lts n o n - d e t e c t i o n may o n l y be due t o p o o r experLmentaL t e c h n i q u e s . I t was c o n s i d e r e d t h a t t h e second changes In c o n d u c t i v i t y were a r e s u l t o f t h e p r e c i p i t a t i o n o f s o l l d phases whlch would remove lons from t h e s o l u t l o n w l t h a concomLtant r e d u c t i o n In conductivity. The t h l r d change in c o n d u c t L v l t y was c o n s i d e r e d t o be caused by breakLng o f t h e c o n t i n u o u s w a t e r f l l m as a r e s u l t o f t h e h y d r a t Lon, TABLE 8 Comparison o f t l m e s f o r I n l t L a l Thlrd ChanAe in Conductlvlty, Addltlve (0.5%) none LLCL NaCL CaCL2 MgCL2 NaOH

Set TLme, F l r s t

S e t t l n g Tlme mlns 212 70 450 195 160 50

Peak In C a l o r i m e t e r , a n d

Calorimetry mlns 265 30 330 897 217 90

ConductLvLty mlns 240 0 480 ] 05 235 65

Vol.

17, No. 3

429 SET, ACCELERATION, RETARDATION, HIGH ALUMINA CEMENT

A comparison o f t h e t h r e e methods o f a n a l y s l s used, s e t t l n g t l m e , c o n d u c t i o n c a l o r i m e t r y and c o n d u c t i v i t y changes a r e g t v e n Ln T a b l e 8. From t h e s e comparisons we c o n c l u d e d t h a t t h e r e was a r e a s o n a b l e c o r r e l a t i o n between t h e t h r e e methods o f a n a l y s i s , t h e s e t t l n g t i m e r e l a t e s t o t h e f l r s t major peak on t h e c a l o r i m e t e r , 1.e. wLth t h e maxlmum r a t e o f f o r m a t i o n o f t h e c a l c l u m aLumlnate h y d r a t e g e l and t h e t h l r d change In c o n d u c t i v i t y was r e l a t e d t o t h e maxlmum r a t e o f f o ' r m a t l o n o f t h e m l n e r a l phase w h l c h caused t h e breakLng o f t h e c o n t i n u o u s w a t e r f l l m . The o n l y d e v i a t i o n b e l n g t h e t l m e f o r t h e T max w l t h c a l c l u m c h l o r L d e . DLscusslon

Any e x p l a n a t i o n o f t h e observed chemlcal and p h y s l c a l changes must t a k e Lnto a c c o u n t t h e above e x p e r i m e n t a l r e s u l t s , namely t h a t : (L)

t h e geLatLon Ls a f f e c t e d [n t h e w a t e r phase,

(lL)

In t h e case o f c a t L o n s , t h e e f f e c t o f LL Lons l s n o t o n l y f a r g r e a t e r t h a n o t h e r Lons, b u t t h a t t h e e f f e c t Lncreases up t o a c e r t a l n c o n c e n t r a t L o n a f t e r w h l c h t h e excess has L i t t l e Lnfluence.

(LLL)

the effect a trend.

o f o t h e r c a t L o n s Ls n o t t o o d L f f e r e n t

and shows

(Lv)

the effect whlch fall

o f OH- Lons Ls much g r e a t e r t h a n t h a t Lnto an estabLLshed sequence,

o f o t h e r anLons

by t h e presence o f c a t L o n s and anLons

(v)

t h e DTA o f t h e c r y s t a l l i n e p r o d u c t can be e x p l a i n e d by assuming 3 d i f f e r e n t t y p e s o f ' w a t e r o f c r y s t a l L L s a t L o n ' i n t h e c r y s t a L L L n e CAH10" I t must a l s o be borne i n mlnd t h a t a l t h o u g h t h e c o - o r d l n a t L o n number o f AL and Ca are s i x i n s o t u t L o n i n t h e s o l i d s t a t e AL remaLns Ln i t s octahedraL envLronment b u t Ca t e n d s t o adopt t h e c o - o r d L n a t l o n o f 8 as Ln CaSO4.2H20 o r g a r n e t s t r u c t u r e s . I t Ls suggested t h a t t h e f o l l o w i n g chemlcaL changes t a k e p l a c e durLng t h e t n t t L a L h y d r a t i o n o f hLgh alumLna cement p a s t e .

CaAI.~04 + 10H20

~ C a ( O H ) 2 + 2[AL(OH)3(H20) 3]

[I]

2[AL(OH)4(H20)2]

Ca(H20)22e ÷

[2]

A nucLeatLon Ls L n t t L a t e d H~

H~

H~

[2]

HO H2o

~

/ H~

OH

430

Vol. 17, No. 3 B.R. Currell, et al.

Leadtng t o a p o s s l b t e s t r u c t u r e t h e m e t a s t a b t e gel [ 3 ] In whLch Ca would requLre a c o - o r d t n a t L o n number o f 8 and At rematns Ln an o c t a h e d r a t envLronment,

H20

H20

AL /

~"-Ca-f

H20

H20

HO ~AL

/

OH

HO

~AL

H20

\

I /

H20

/

\

I

/

OH

\

/

H20

/ \

\ /

~

Ca

H20 ~

At " ~

OH

HO H20

H20

H20

H20

The m e t a s t a b t e gel wLtL acquLre s t a b L L L t y by condensatLon o f monocoordLnated OH groups tLnked t o AL t o form oxobrLdges between two At centres.

H~ At

~

AL

[4]

H20 LeadLng t o t h e c r y s t a L L L n e monocaLcLum aLumLnate d e c a h y d r a t e

CaA¢204.10H20. To produce t h e condensatLon r e p r e s e n t e d by [ 4 ] Lt Ls necessary t o brLng t h e OH group Ln a posLtLon so t h a t a Lone paLr on t h e oxygen can o v e r l a p wLth a d orbLtaL o f AL,. resuLtLng Ln t h e formatLon o f an oxobrLdge and a m o l e c u l e o f w a t e r whLch would remaLn hydrogen bonded t o t h e 0 atom, In t h e c r y s t a L L L n e monocaLcLum atumLnate d e c a h y d r a t e t h r e e t y p e s o f w a t e r o f c r y s t a L L L s a t L o n s h o u l d be d L f f e r e n t L a t e d a t t a c h e d t o e L t h e r AL. Ca o r 0 and t h L s Ls observed Ln t h e thermogram. The condensatLon [ 4 ] wLLL be a f f e c t e d by metal oatLons formLng c o - o r d L n a t L o n LLnkage wLth t h e h y d r o x y l groups. Of t h e Lons studLed LL + s h o u l d be d L f f e r e n t Ln behavLour from t h e o t h e r Lons because o f Lts abLLLty t o form t e t r a h e d r a L symmetry wLth OH groups (10) whLLe t h e o t h e r s wLLL form t h e octahedraL t y p e . ThLs Ls borne o u t by t h e experLmsntaL r e s u l t s o f LLthLum havLng a d r a s t L c e f f e c t b u t t h e d L f f e r e n c e s between t h e o t h e r catLons a r e n o t g r e a t and e x h L b t t a d e f L n L t L v e t r e n d , The sequence does n o t f o l l o w t h e t r e n d o f LonLc radLL ( T a b l e 9 ) b u t r a t h e r t h e f a c t o r Y Ln t h e equatLon pK = aX + ~Y + y r e t a t L n g t o c o - o r d L n a t L o n compounds and whLch Ls derLved from t h e concept o f hard and s o f t acLds and bases ( 1 1 ) .

Vol. 17, No. 3

431 SET, ACCELERATION, RETARDATION, HIGH ALUMINA CEMENT

The f a c t o r Y l s e v a l u a t e d from a t o m l c p a r a m e t e r s which lncLude t h e l o n t c r a d l u s and charge d e n s i t y . In t h e case o f ' n o n e ' Ln t h e experLmentat s e c t k o n a l l o w a n c e must be made f o r t h e f a c t t h a t t h e r e a r e always t r a c e s o f a t k a l l me t a l c a t k o n s b e s l d e t h e r e l a t l v e abundance o f Ca++ lons t o a l l o w t h e r e a c t l o n t o proceed a t a r e a s o n a b l e r a t e .

TABLE 9 Ionlc Radll (r)

and Y Parameters o f S e l e c t e d Ion~

Ll

Na

..K

Mg

Ca

Sr

r(nm)

0.06

0.095

0.133

0.065

0.099

0.113

Y

0.36

0,93

0,92

0.87

1.62

2.08

The r e t a r d a t L o n e f f e c t o f t h e a n l o n Ls r e l a t e d t o t h e s u b s t t t u t L o n o f OH Ln t h e c o - o r d L n a t l o n sphere o f AL [ ~ A L ( O H ) 2 ] * X- - -

[~AL(OH)2X ] -

= [~L(OH)X]

+ OH-

(5)

whLch Leads t o t h e removal o f h y d r o x y l group necessary in t h e process o f o x o L a t l o n . The r a t e o f o x o L a t l o n wLLL be l n f L u e n c e d by t h e s t a b i l i t y of AL complex wLth X LLgand and t h e observed o r d e r OH > none ) CL > NO3 > CO3 ) Br > a c e t a t e l s sLmLLar t o t h e o r d e r o f s t a b t L L t y o f AL 3+ complexes w l t h t h e a n l o n s considered (12). The dramatLc e f f e c t observed on a d d l t l o n o f OH- Ls n o t due t o t h e change In pH b u t t h e f a c t t h a t t h e c o - o r d i n a t i o n sphere o f AL changes. ['-~s. AL(OH)2(H20)]+OHT,.~. [ ~ A L ( O H ) 3 ] + H20 LeadLng t o a g r e a t e r OH avaLLabLLLty f o r t h e o x o L a t l o n process. Excess o f w a t e r beyond t h e s t o l c h l o m e t r L c r e q u i r e m e n t f o r h y d r a t i o n o f aLumLnate p a s t e wlLL s l o w down t h e process o f c r y s t a L L L s a t l o n e l t h e r by removal o f OH from t h e AL c o - o r d L n a t L o n sphere (H20 = X Ln e q u a t l o n ( 5 ) ) o r by occupatLon o f t h e e l e c t r o n p a l r , whLch would t a k e p a r t In t h e oxoLatLon p r o c e s s , due t o hydrogen bonded H20 m o l e c u l e .

References 1.

T.W.Parker, "The c o n s t L t u t L o n o f aLumLnous c e m e n t ' . Proc. ThLrd I n t . Symp.Chemlstry o f Cement, London 1952 p512 (5) Cement and C o n c r e t e A s s o c L a t l o n (1954)

2.

T.D.Robson "Hlgh ALumLna Cements and C o n c r e t e s " John WLLey and Sons Inc. New York. 1967.

3.

M. MauLtzsch and U.MeLnhoLd ' T e s t l n g Methods f o r Set o f Pastes and M o r t a r s "

432

Vol. B.R. C u r r e l l ,

Seventh I n t , Symp. C h e m i s t r y o f Cement. P a r l s p158 - 163. (1982) SeptLma.

III,

pVl

4.

A. M a t h L e u ; ' R e a c t L v L t L e s des ALumLnes e t des ALumLnates de CaLcLum Obtenus" Int,SemLnar CaLcLum ALumLnates TurLn pi-13,(1982), PoLLteonLco DL TurLno

5.

H.G.MLdgLey, "Measurement o f HLgh ALumLna Cement - CaLcLum Carbonate ReactLons by DTA'. CLay MLneraLs 19, (1984)

6,

A. N e v l l l e " P r o p e r t L e s o f Concrete" Pltmans P u b L i s h i n g L l m l t e d London p 4 4 7 . ( 1 9 7 3 )

7.

BrLtLsh S t a n d a r d No. BS 915 (1972)

8.

H.G.MLdgLey "The MLneraLogy o f Set HLgh ALumLna Cement" Trans. B r L t . Ceram.Soc., 66 pl61 - 187, (1967)

9.

S.A.Rodger and D.D.DoubLe 'The ChemLstry o f h y d r a t L o n o f HLgh ALumLna Cement Ln t h e presence o f AcceLeratLng and RetardLng AdmLxtures' Cement and C o n c r e t e Research. 14, p73 - 82 (1984)

10. A,F.WeLLs " S t r u c t u r a l p549 (1962) II.

M.MLsono e t aL. J.

17, No. 3

et a l .

InorganLc ChemLstry" O x f o r d Press 3rd Edn

Inorg.NucL, Chem. 29, 2685 (1967)

12, F.R.G GLmbLett " l n o r g a n L c PoLymers" Butterworth London p80,

(1963)

AcknowLedgements

The a u t h o r s wouLd LLke t o t h a n k Dr. C, FentLman o f L a f a r g e ALumLnous Cement Co., f o r many heLpfuL dLscussLons and t h e p r e s e n t o f cement used Ln t h L s LnvestLgatkon. The m a j o r L t y o f t h e experLmentaL work was c a r r L e d o u t a t ILmLnster Cement Research,