EFFECT OF MIXING AND CURING WATERS ON THE BEHAVIOUR OF CEMENT PASTES AND CONCRETE PART I : MICROSTRUCTURE OF CEMENT PASTES

CEMENT and CONCRETE RESEARCH. Vol. 19, pp. 868-878, 1989. Printed in the USA. 0008-8846/89. $3.00+00. Copyright (c) 1989 Pergamon Press plc.

EFFECT OF MIXING AND CURING WATERS ON THE BEHAVIOUR OF CEMENT PASTES AND CONCRETE

PART I : MICROSTRUCTURE OF CEMENT PASTES

H.Y.Ghorab~, M .S .H i l a I~S and E .A .K ishar~ Cement Chemistry L a b o r a t o r y , U n i v e r s i t y C o l l e g e f o r G i r l s ,

Ain Shams U n i v e r s i t y , H e l i o p o l i s , C a i r o , Egypt ~ S t r u c t u r a l Eng inee r i ng Department, F a c u l t y o f Eng inee r ing

Ca i ro U n i v e r s i t y , Egypt

(Communicated by F.W. Locher) (Received Dec. 31, 1988)

ABSTRACT The i n f l u e n c e o f Sea, ground, N i l e and d r i n k i n g waters on the m i c r o s t r u c t u r e o f some h y d r a u l i c cements i s i n v e s t i g a t e d by means o f X-ray d i f f r a c t i o n a n a l y s i s . The ca lc ium s u l f o - and c a r b o a l u m i - na te hydra tes form w e l l w i t h a water cement r a t i o o f 2. Seawater leads to the p r e c i p i t a t i o n o f gypsum. The h y d r a t i o n products of o r d i n a r y p o r t l a n d cement (OPC) pastes hydra ted f o r a year w i t h the f o u r water types are s i m i l a r . A survey on the a n a l y s i s of waters used i s g i v e n .

I n t r o d u c t i o n

The s u i t a b i l i t y o f use o f n a t u r a l waters f o r m ix ing and c u r i n g cement mor ta rs and conc re te has been e s p e c i a l l y ques t ioned in our coun t r y because o f the i n c r e a s i n g c o n s t r u c t i o n p r o j e c t s in remote areas where d i f f i c u l t i e s are encountered f o r the supply of s o f t wa te r .

The e f f e c t o f seawater , when used f o r m i x i n g , on the cement pastes and conc re te was found to be compa t i b l e w i t h most ac- c e l e r a t o r s ( i ) . I t reduces the t h i c k e n i n g t ime , enhances the h y d r a t i o n process and the c o n s e c u t i v e s t r e n g t h development but r e t a r d s the l a t e s t r e n g t h ( 1 , 2 ) . Well waters w i t h up to I000 ppm S03 and 500 ppm c h l o r i d e can be used f o r m ix ing mor ta r and con- c r e t e (3) and ground water i s recommended f o r conc re te c o n s t r u c - t i o n w i t h a maximum l i m i t o f 300 ppm c h l o r i d e and 300 ppm S04(4). M ix ing o f OPC w i t h s l a g , f l y ash or o t h e r blended a d d i t i v e s im- proves the performance o f cement towards the s u l f a t e a t t a c k (5 ,b)

The e f f e c t o f seawater on the cement and conc re te i s seen to be g e n e r a l l y more worked ou t in the l i t e r a t u r e as compared to o t h e r types o f n a t u r a l wa te r . The n a t u r e of these waters v a r i e s from one coun t r y to the o t h e r depending on the n a t u r e of the

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s o i l , the degree o f p o l l u t i o n and i n d u s t r i a l wastes. I t i s t h e r e - f o r e w o r t h w h i l e c a r r y i n g out d e t a i l e d study on the e f f e c t of our n a t i o n a l waters on the p r o p e r t i e s o f b u i l d i n g m a t e r i a l s . Par t i o f t h i s work w i l l i n c l u d e a d e s c r i p t i o n o f the m i c r o s t r u c t u r e development of the cement pastes mixed w i t h the d i f f e r e n t waters and Par t 2 w i l l deal w i t h the v a r i a t i o n of the phys i ca l and mechanical p r o p e r t i e s of cement pastes and conc re te .

M a t e r i a l s I . Sea Water

The s a l i n e water was procured from the Red Sea at the Suez Canal r eg ion where s a l i n i t y i s known to be h ighe r than the Med i te r ranean . Samples from beaches a t Suez, Fayed, and I s m a i l i a were s u p p l i e d a t d i f f e r e n t t imes and ana lysed . The s u l f a t e , c h l o r i d e , hardness and pH of the waters were measured accord ing to the s tandard methods o f a n a l y s i s of waters and waste w a t e r ( 7 ) . The data presented in Table I show an a lmost cons tan t s u l f a t e ion c o n c e n t r a t i o n o f about 2500 ppm, a remarkab le i nc rease in the hardness o f water in a 2 -year p e r i o d ( f rom 3850 ppm in 1985 to 7640 in 1987) and a less s i g n i f i c a n t f l u c t u a t i o n in the c h l o r i d e ion c o n c e n t r a t i o n du r ing the same pe r i od w i t h an average va lue of about 27600 ppm. Sample No.1 was used f o r m ix ing cement pastes.

TABLE I Chemical A n a l y s i s o f S a l i n e Water Supp l ied from Suez Canal Region

Sample S i t e Supply pH S03 T o t a l Ca C1 s o l . No. Time Hardness s a l t s

ppm ppm ppm ppm ppm

I Cabanon 4.85 7 .6 2533 3683 580 31030 - - - 2 Canal Club 4.85 8 .5 2533 3850 - - - 23700 - - - 3 I s m a i l i a 4.87 8 .0 2500 7640 1200 27090 - - - 4 I s m a i l i a 7.87 7.9 2458 7600 1500 27390 25.7 5 Fayed 7.87 8.0 2500 7300 1300 27860 30.6 6 Cabanon 7.87 8 .0 2458 7800 I000 28320 40.5 7 Canal Club 7.87 8 .0 2491 7500 1400 27860 34.6

2. Ground Water Most o f the ground water samples analysed f o r the purpose o f

the p r o j e c t were found to be below the agg ress i ve l i m i t s p e c i f i e d f o r the conc re te a t t a c k . The f i r s t sample was taken from a con- s t r u c t i o n s i t e near the Pyramids from a depth o f 18 meters. Then

Chemical A n a l y s i s TABLE 2

of Ground Water Supp l ied from D i f f e r e n t S i t e s around Ca i r o

To ta l Sample S i t e Supply pH S03 Hardness Ca Cl

No. Time ppm ppm ppm ppm

I M a r i o u t i a 4.85 7 .8 431 307 - - - 315 2 Maadi 4.85 8 .6 900 452 232 685 3 Margh 4.87 7.9 450 500 340 170

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a second bulk supp ly was ob ta i ned from ano ther c o n s t r u c t i o n s i t e

a long the r i v e r N i l e in southern C a i r o . The water was a t a depth o f around 5 meters which e x p l a i n s i t s r e l a t i v e l y h igh s a l i n i t y , rep resen ted in the s u l f a t e s ~ compared to the o the r water samples (Tab le 2) . A t h i r d bulk supply was taken from a v i l l a g e about 15 km n o r t h e a s t o f Ca i ro a t a depth o f 30 m. For the present s tudy, ground water No.2 was used f o r m ix ing cement pastes.

3. N i l e Water The samples s t u d i e d were procured from the N i l e r i v e r or i t s

branches near C a i r o . Some of the samples were s u p p l i e d tw ice from the same source a t d i f f e r e n t t imes and analysed f o r comparison. The r e s u l t s o b t a i n e d (Tab le 3) show t h a t the c h l o r i d e con ten t l i e s between 18 and 30 ppm and the s u l f a t e c o n c e n t r a t i o n v a r i e s between 21 and 83 ppm S03. Sample No . l was used f o r mix ing cement pastes and conc re te .

TABLE 3 Chemical A n a l y s i s o f the N i l e Water

To ta l Sample S i t e Supply pH S03 Hardness Ca C1

No, Time ppm ppm ppm ppm

1 Gamgara 6.85 8.6 56 75 35 28 2 Qanater 4.87 8.1 21 140 80 30 3 Gamgara 7.87 7.8 50 240 160 21 4 Mansoura 7.87 7.8 58 160 120 19 5 Banha 7.87 7.4 33 160 120 22 6 Shubra 7.87 7.9 41 160 120 18 7 Qanater 7.87 8.6 83 160 i00 26

4. Tap Water Table 4 g i ves a survey on the c o n c e n t r a t i o n o f tap water

w i t h i n two years t ime . TABLE 4

Chemical A n a l y s i s of D r i nk i ng Water

Sample Date pH S03 Cl No. ppm ppm

i 6.85 7.3 35 32 2 9.85 7.i 34 46 3 3.87 8.0 26 50 4 6.87 7.6 37 64 5 6.87 7.4 33 60 6 7.87 7 .5 22 60 7 7.87 8 .2 24 38 8 7.87 7.4 26 38 9 7.87 7 .9 30 35 i0 7.87 8.2 27 60

The r e g u l a r a n a l y s i s of tapwater shows a v a r i a b l e c o n c e n t r a t i o n o f the s u l f a t e and c h l o r i d e ions d u r i n g the pe r i od of study l y i n g f a r below the maximum p e r m i s s i b l e l i m i t f o r the use in concre te mixes.

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H y d r a t i o n Procedure

The e f f e c t o f water type on the behav iou r of neat cement pastes has been s t u d i e d by means of X- ray d i f f r a c t i o n a n a l y s i s us i ng a P h i l l i p s type 1390 d i f f r a c t o m e t e r w i t h Cu K - r a d i a t i o n and Ni f i l t e r . O r d i n a r y p o r t l a n d cement (OPC), EI -Karnak cement (EKC) manufactured by g r i n d i n g 25% s i l i c e o u s sand w i t h OPC c l i n k e r , and p o r t l a n d b l a s t f u r n a c e s lag cement (PBC) w i t h 35% s lag have been mixed w i t h the abovementioned types of water us ing a water cement r a t i o of 2. The h y d r a t i o n proceeded in w e l l s t op - pered p l a s t i c b o t t l e s f o r 2, I0 and 30 m inu tes , I hour , 1,7 and 28 days. For OPC samples the h y d r a t i o n was f o l l o w e d up to one yea r . The samples were shaken from t ime to t ime and a t the d e f i n i t e t ime i n t e r v a l the r e a c t i o n was stopped by i s o p r o p y l a l - c o h o l . The samples were f i l t e r e d o f f , d r i e d a t 50 degrees C e l s i u s f o r one day then ana lysed by means of X- ray d i f f r a c t i o n .

R e s u l t s and D i scuss i on

The h y d r a t i o n p roduc ts formed by m ix ing OPC w i t h tap wa te r , N i l e water or ground water f o r t ime up to 28 days are q u i t e s i m i l a r . R e p r e s e n t a t i v e samples are shown i n F i gu re I . The e t - t r i n g i t e phase appears a t a d - v a l u e of 9 .7 A and i s seen to e x i s t w i t h o u t a remarkable i n c r e a s e i n a l l samples up to 28 days. Th is o b s e r v a t i o n does no t n e c e s s a r i l y mean the presence of t h i s phase i n a smal l amount but m igh t be a t t r i b u t e d to i t s smal l p a r t i c l e s i z e and scann ing e l e c t r o n microscope s t u d i e s are needed f o r f u r - t h e r e x a m i n a t i o n .

No o t h e r h y d r a t i o n p roduc ts are to be de tec ted in the d i f - f r ac tog rams up to one day where the p o r t l a n d i t e phase s t a r t s to show up and i n c r e a s e s markedly f o r l onge r h y d r a t i o n p e r i o d . The appearance of p o r t l a n d i t e c r y s t a l s i s accompanied by a decrease i n the amount o f the anhydrous c l i n k e r phase ( a l i t e , b e l i t e , C3A and C4AF) which d i f f r a c t i o n l i n e s are c o l l e c t i v e l y found i n the m idd le of the d i f f r a c t o g r a m s , i . e . , between 3.02 and 2.b0 A. The c a r b o n a t i o n process i s observed i n the 3-day hydra ted sample where the monocarboaluminate hyd ra te i s de tec ted bes ide the c a l - c i t e . Both phases are found to i n c r e a s e w i t h t ime .

The h y d r a t i o n of OPC i n sea water causes a r a p i d p r e c i p i t a - t i o n of the gypsum phase wh ich appears a l r e a d y a f t e r two minutes from the r e a c t i o n s t a r t ( F i g u r e 2 ) . The gypsum phase i nc reases d u r i n g the f i r s t hour and the 9.7 A l i n e of e t t r i n g i t e i s w e l l r e c o g n i s e d . Gypsum does no t remain up to 28 days but i n s t ead the c a l c i u m c a r b o - , s u l f o a l u m i n a t e h y d r a t e form.

The amount o f h y d r a t i o n p roduc ts formed d u r i n g the h y d r a t i o n process o f EKC w i t h tap wa te r , ground water and N i l e water exceeds t h a t o f the OPC hydra ted under o t h e r w i s e s i m i l a r c o n d i - t i o n s . Th i s i s seen from the o b v i o u s l y h i g h e r i n t e n s i t i e s of the p o r t l a n d i t e and e t t r i n g i t e phases a f t e r one day, shown i n F i g . 3 w i t h the N i l e water as an example. The gypsum formed d u r i n g the h y d r a t i o n process i n sea water i s r a p i d l y consumed in f avou r of the s u l f a t e - b e a r i n g monophase f o r m a t i o n ( d - v a l u e a t 8 .2 A) . The

872 Vol. 19, No. 6 H.Y. Ghorab, et al.

Id

2 E 10

20 15 10 5 ~--g

Fig . I . X-Ray D i T f r a c t i o n of OPC Paste with Tap Water

Vol. I9, No. 6 873 WATER CHEMISTRY, MICROSTRUCTURE EFFECT

!L 28

20 15 10 5 Q

F i g . 2. X-Ray D i f f r a c t i o n of OPC Paste w i th Sea Water

874 VoI. 19, No. 6 H.Y. Ghorab, el: al.

I !H C- J 28d ~V~ CH Mc E

I Ctinker

F i g . 3. X-Ray D i f f r a c t i o n o f EKC Paste w i t h N i l e Water

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q u a l i t a t i v e behav iour of the phases i s g e n e r a l l y s i m i l a r to t ha t of the OPC h y d r a t i o n .

The h y d r a t i o n of the PBC w i t h tap water , ground water and N i l e water d id not d i f f e r much from one another . The p r e c i p i t a t e d

cc I H 28d

N¢

20 15 10 5 ~--@

F ig . 4. X-Ray D i f f r a c t i o n of PBC Paste w i t h N i l e Water

876 Vol. 19, No. 6 H.Y. Ghorab, et al.

CH Cc C H

v ~ 20 15 10 5 -~ g

F i g . 5. X-Ray D i f f r a c t i o n of PBC Paste w i t h Sea Water

Vol. 19, No. 6 877 WATER CHEMISTRY, MICROSTRUCTURE EFFECT

hydra ted l ime appears i n the f i r s t day as i n the o t h e r two ce- ments. The amount o f p o r t l a n d i t e i n c r e a s e s w i t h t ime and the f o r - mat ion of the c r y s t a l l i n e monocarboaluminate hyd ra te i s not predominant ( F i g . 4 ) . However the amount o f p o r t l a n d i t e formed in the presence of sea water decreases w i t h t ime and the s u l f a t e -

• ~ W ~ 4 to

20 15 10

OUJ

O0 A

5~-0

F i g . 6. X-Ray D i f f r a c t i o n o f OPC Paste w i t h D i f f e r e n t Types of Water a t the Age of One Year

878 Vol. 19, No. 6 H.Y. Ghorab, et al.

bear ing monophase ( d - v a l u e 8.2 A) becomes the predominant product a f t e r 28 days (F i gu re 5) .

The X- ray d i f f r a c t i o n p a t t e r n s of r e p r e s e n t a t i v e samples of the OPC pastes hydra ted f o r one year are shown i n F i g u r e 6. The p roduc ts formed in the presence of the f o u r water types are s i m i l a r except f o r an excess amount of the e t t r i n g i t e over the monophase in the presence of sea wa te r . The phases formed are e t - t r i n g i t e ( d - v a l u e 9.7 A) , s u l f a t e - b e a r i n g monophases ( d - v a l u e 8.2 A) and monocarboaluminate hyd ra te ( d - v a l u e 7.6 A) . Some un- a v o i d a b l e c a r b o n a t i o n i s de tec ted a t a d - v a l u e of 3.03 A and the ca l c ium h y d r o x i d e phase i s e a s i l y de tec ted a t 4 .9 and 2.62 A.

Conc lus i on

I . Gypsum p r e c i p i t a t e s o n l y d u r i n g the h y d r a t i o n of the cements w i t h sea water but d i sappears i n f a v o u r of the ca l c i um s u l f a t e - bear ing monophases. 2. The p r e c i p i t a t i o n of the p o r t l a n d i t e takes p lace in the f i r s t h y d r a t i o n day. I t i n c reases w i t h t ime w i t h the appearance of a s u l f a t e - f r e e monophase i n the presence of tap wa te r , N i l e water and ground water but decreases w i t h the f o r m a t i o n of s u l f a t e - bear ing monophase i n the presence of sea wa te r . Th i s i s most ob- v i o u s i n PBC. 3. The q u a l i t y and q u a n t i t y of phases formed a f t e r one year i n the hydra ted OPC pastes are u n a f f e c t e d by the water t ype .

References

i . R.C.Smith and D . J . C a l v e r t , J. Pet . Techn. , 27, 759 (1975) . 2. M.Kawamura and Y.Yamada, Semento G i j u t s u Nempo, 28, 180 (1974) 3. F.M.Lea, the Chemis t ry of Cement and Concre te , Edward A rno ld ,

L t d . , London (1956) . 4. R .E I -She ikh ,H.EL-D idamony and M.Haggag, T IZ , I07 , 73b (1983). 5. M.Regourd, Pub. SP-&5, Amer. Conc. I n s t . , 63 (1980) . b. V .M .MA lho t ra , G.G.Gare t te and T.W.Bremner, CANMET Repor t ,

80-18E, 27 pp . , 1980. 7. Standard Methods f o r the Examina t ion of Water and Waste Water,

American P u b l i c Hea l t h A s s o c i a t i o n , 439 (1980) . 8. H.Ghorab, M . S . H i l a l and S . A b o u l - F e t o u h , Proc. Symp. Q u a l i t y

and Performance of Cement and Concrete i n the Arab World, Baghdad, I r a k , 187, 2-5 Nov.1987.