Effect o f sea water

from tropical areas

on setting times o f cements

K. THOMAS and W. E. A. LISK (1)

afs0M~

Ce rapport d~crit les premiers r~sultats d'un programme de recherche des influences de I'eau de met et de I'atmosph~re marine sur le ciment et le b~ton darts la r~gion des Tropiques. Ces r~sultats montrent une r~duction de 75 ~o du temps init ial de prise normal pour le ciment g~ch~ avec de I'eau de mer; par contre, on ne d~c~le pas d'influence sur le temps de prise local. On souligne qu'fl est indispensable d'avoir la connaissance pr~alable des propri~t~s du ciment qu'on se procure sur les march~s Iocaux de certaines r~gions d'Afrique, surtout en Sierra Leone, du fait des grandes differences de qualit~ que pr~sentent des ciments de m~me cat~gorie et de m~me classe. Si I'on doit employer de I'eau de mer, cela ne peut s'admettre sans pr~- caution pr~alable qu'avec des ciments dont le temps de prise init ial n'exc~de pas de 30 mn le minimum recommand~ par B.S. 12, 1958.

SUMMARY

This paper reports the first results of a programme of research into the influences of sea water and sea atmosphere on cement and concrete in the tropics. The results discussed here show that up to 7 5 % reduction in the normal initial setting time takes place when cement is mixed with sea water, although no influence on the final setting time is perceptible. It is pointed out that prior knowledge of the properties of cement in the local markets in some areas of Africa, notably Sierra Leone, is necessary, in view of the vast difference in properties of available cements of the same brand and production code number. Where sea water is to be used, only cements with initial setting times not less than 30 minutes in excess of the minimum recommended by B.S. 12, 1958, may be permitted without special percautions being taken.

I. INTRODUCTION

This p a p e r repor ts the effect of sea water from tropical areas on sett ing times of cements, from expe r i ence in the pen insu la r a rea of Sierra Leone.

Until the construct ion of the Guma Valley dam in 1967, F ree town had suffered from a shor tage of water throughout the twelve months of the yea r and particularly, du r ing the dry seasons of the year, namely, October-May, when supply had to be res- t r icted to a few hours a day. Today, while the water supp ly in the munic ipa l a rea of F ree town is quite adequate for d r ink ing pu rposes as well as for indu- strial uses, the supp ly to areas outside the muni- cipality howeve r remains limited. In many areas, especial ly in the seas ide villages, dwel lers have to d e p e n d for their supply of fresh water on streams,

(z) Fourah Bay Col lege, Un ivers i ty of Sierra .Leone, Depar tmen t of Engineering, Freetown, Sierra Leone.

some of which are difficult to reach. The use of these s t reams is cont ro l led and, often, only water for d r ink ing is a l lowed to be drawn. A d d e d to this p r ob l e m has b e e n the inc reas ing t e n d e n c y of city dwel lers to live by the seaside. Building activity has therefore i nc r e a se d in seas ide areas, with the resul t ing inc rease in the d e m a n d for and use of Sandcrete blocks and concrete. It is now common practice to p r oduc e sandcre te and other cement b o u n d materials on the site in areas away from the city. This pract ice cuts down t ranspor t costs and losses due to damage . In seas ide areas therefore, the p rob lems of availabil i ty of satisfactory fresh water for mixing concre te have led to the active considera t ion of the use of, and in a few k n o w n instances, the utilization of sea water for this purpose . It is important therefore, that sett ing times of cement when used u n d e r these new conditions, be carefully s tudied and r ecommenda t ions made for the hand l ing of the material. It is well known that the mix ing and placing techn iques of local bu i lde rs are ra ther s t e reo typed . It has b e e n d i scove red that e v e n

I01

V O L . 3 - - N ~ 14 - - J970 - - M A T I 6 R I A U X ET C O N S T R U C T I O N S

variat ions of the set t ing i imes of locally avai lable cemen t b rands upse t bu i lde r s ' rout ine and have led to was tage of e x p e n s i v e material .

This p a p e r is the ou tcome of one phase of a r e s e a r c h p r o g r a m m e which will c o v e r durabi l i ty of plain and r e in fo rced conc re t e w h e r e the mix ing wate r has b e e n sea water, and the inf luence of sea a tmosphe re on r e in fo r ced conc re t e m e m b e r s cast with water satisfying B.S. 3148, 1959.

chromate as indicator. The quanti tat ive de te rmin- ation of the sulphate const i tuent in each sample was ca r r i ed out g rav imet r i ca l ly u s ing ba r ium chlor ide as the prec ip i ta t ing reagent .

Potassium and sod ium in the samples w e r e esti- ma ted by the flame pho tome t r i c method. Standard methods w e r e a d o p t e d for the de te rmina t ion of magnesium, calcium, and b r o m i d e contents.

Set t ing T i m e A n a l y s i s

2. CHOICE AND COLLECTION OF WATER SAMPLES

Since the p e r c e n t a g e of Salt in wa te r is at its mini- mum. dur ing the rainy season, it was n e c e s s a r y to col lect samples dur ing the d ry season to ach ieve the h ighes t poss ib le concentrat ion, with r e spec t to the d e g r e e of salinity. Estuar ies w e r e a v o i d e d when samples w e r e taken s ince the re is a risk of dilution of the sea water f rom the inflowing r ivers . Areas which had b e e n pol lu ted by waste mat ter d e p o s i t e d by v i l lagers w e r e also avo ided . Samples w e r e co l lec ted off the shores of Goder ich , Lakka, Hamihon, Sussex, BawBaw and No. 2 River, in the F r e e t o w n Peninsula (see Map shown in fig. 1), and these w e r e kept in s ea l ed bottles until r e q u i r e d for use. Care was taken to avoid evapora t ion at all t imes as e x p o s u r e to the t ropical heat can easi ly result in an i n c r e a s e d p e r c e n t a g e of salinity.

3. TEST CARRIED OUT

Sea W a t e r A n a l y s i s

The total ch lor ide content of all the samples was es t imated with s i lver nitrate titration us ing potass ium

The test for set t ing t imes was c o n d u c t e d on a cemen t paste hav ing a wate r content equa l to that r e q u i r e d for a s t andard cons i s tence , using the s tandard Vicar apparatus , and c a r r i e d out as c losely as poss ib le to the British S tanda rd test g iven in B.S. 12 [1]. To be able to r e l a t e the results f rom tests to actual prac t ice tests w e r e c a r r i e d out at r o o m t empera tu re and not at the t e m p e r a t u r e spec i f ied by the British standard. T h roughou t each test the apparatus was c o v e r e d up with a t ransparent mater ia l to minimise evapora t ion loss.

4. DISCUSSION

G e n e r a l R e m a r k s

Test results of set t ing t imes a re g i v e n in Table II. It is s een that only slight d i f f e rences exist b e t w e e n the results of wa te r samples f rom the sites Chosen. Thus, there is justification for m a k i n g genera l iza t ions in discussing these results. Results of sea wate r analysis a re g iven in Table III a n d c e m e n t test results for the various b rands of c e m e n t in the Sier ra Leone marke t a re shown in Table I.

TABLE I

Cement Brand

Cotton tree Code No. 292

Cotton tree O.A. & P. Sample No. 12

Foreign

Source

Sierra Leone

Sierra Leone

U.S.S.R.

U.S.S.R.

U.A.R.

U.A.R.

Type

Ordinary Portland

Initial Setting time

1 h 20 mn

1 h 45 mn

1 h 45 mn

3 h 8 ran

1 h 50 mn

12 mn

Final Setting time

5 h Omn

5 h 15 mn

4 h 05 mn

3 h51 mn

3 h 10mn

2 h 35 mn

" U.A.R. " 8 1/4 mn 1 h 17 mn

" U.A.R. " 8 1/2 mn 1 h 35 mn

" German " 1 h 59 mn 4 h 07 mn

2 h 19 mn

l h 2 m n

42 mn

German

Polish

Polish

Norway

Norway

1 h 40 mn

1 h 56 mn

3 h 27 mn

2 h 48 mn

1 h 10mn

3 h 54 mn

4 h 05 mn

Average soundness

mm

1.33

2.50

1.5

2.00

3.0

1.5

1.8

Consi- stence

%

28.7

28,5

28.5

29.1

28.5

28.5

28.0

Date

1968

1968

1968

1968

1969

1969

1969

1.6 27.5 1969

2.00 28.75 1969

1.5 29.3 1968

1.0

1.8

1.0

1.2

30.4

33.6

24,8

29.3

1967

1967

1967

1967

102

K. T H O M A S - - W . E. A . L I S K

13" 15 13 ~ i�9 13" oS

8" 15

8 ~ I(

Aberdeen

;( . i:. r-i /x,.':.~,/.~ "' ' '~ t" KlssY~"~/ "

I Glouccs ' t~ r

" X . . . . . . _ . . . ~ j ' ~ . ~ R , q c n t

Lakka

HE, mil l ,

\ ,/

Sussex

To ke

S ET T L EMENTS . . . . . . . . . . . . . .

FREETOWN CITY BOUNDARY . . . . . . . .

' F O R E S T RESERVE ...............

('-T A RR E b . . . . . . . . . . . . . . . ROADS ~LUNT A RRED . . . . . . . . . . . . . . . . .

RAILWAY . . . . . . . . . . . . . . . . .

RIVERS . . . . . . . . . . . . . . . . . .

C'JAN I

13*i5

Char lot te

\ N

f

~ " / -96,

\ \

f I" \ \ '~.

KendE,~

13"10

FREETOWN p ENIN SULA-I "~

R/VE~

i

\<

'% ~ % \

\ \.

. \/

-~ Macdonald

%

~ K e r r y Town

i ~ R u s s e l I

T'--u mbu

13"O~

/

~ N e w t o n

ampbr Town

--.4.

8 ~ 25

s' :d

8" 15'

~',o"

FIG, 1.

Sea Water Salts

The analysis of the s ea wa te r shows a p r e d o m i n a n c e of sod ium and ch lo r ide contents. The su lpha te and m a g n e s i u m contents a r e not significant, and potassium, ca lc ium and b r o m i d e exist in t races . Table III shows va lues of pH, total ch lo r ide content, su lpha te content, sod ium content, dens i ty and p e r c e n t a g e sod ium ch lo r ide content for the wa te r s of Goder i ch , Lakka, Hamilton, Sussex, Bawbaw and No. 2 River.

Sett ing T i m e s

As is s e e n f rom Table H, t h e r e is a m a r k e d differ- ence b e t w e e n the initial se t t ing t imes of c emen t m i x e d with s ea w a t e r f rom the pen insu la a r e a and that m i x e d with d i s t i l l ed water�9 On the a v e r a g e the initial set t ing t imes us ing dis t i l led wa te r have b e e n r e d u c e d b y 75 % b y the substi tut ion of s ea wa te r m p l a c e of d is t i l led water . It is in t e res t ing to note that whi le the initial se t t ing t ime is affected,

103

V O L . 3 - - N " f 4 - - 1 9 7 0 - - M A T ~ R I A U X E T C O N S T R U C T I O N S

TABLE II

Type of water Test Consistency No. %

Distilled 1 28.75 2 28.75

Goderich (sea water) 1 29.25 2 29.25

Lakka (sea water) 1 28.25 2 28.25

Hamilton (sea water) 1 28.75 2 28.75

Sussex (sea water) 1 28.5 2 28.5

Bawbaw (sea water) 1 29.2 2 29.2.

No. 2 River (sea water) 1 t 29.25 2 I 29.00

Initial Setting time

52 mn 57 mn

18.5 mn 23 mn

15 mn 10 s. 13 mn 20 s

15 m n 3 s 10 mn

.16 mn 17.5 mn

20 mn 18 mn

Final Setting time

3 h 5 mn 3 h 15mn

3 h 37 mn 3 h 30 mn

3 h 2 h 50 mn

3 h 5ran 3 h 15 mn

Average temperature

oC

30 31.6

29 30.5

28.6 28.8

29 28.7

Average relatively

humidity %

88

89

87

92

J Average

barometric pressure (ins. of Mercury)

3 h 21 mn 3 h 25 mn

3 h 30 mn 4 h 0 m n

29 29.5

30.6 30

91

88

29

29

12 mn 10 mn

3 h 20 mn 3 h 15 mn

29.6 30

93

30

29

29

30

29

the final sett ing t ime and the cons is tency remain fairly constant. The analysis of sea wate r f rom the peninsula has conf i rmed the a b u n d a n c e of sodium ch lor ide in the water . The .contr ibut ion of this subs tance to high initial set t ing of the cements is still not easi ly assessable .

The effect of sod ium chlor ide on c e m e n t has b e e n s tud ied by many authors. Lea [2] has r e p o r t e d the erratic t r end of set t ing t imes of cemen t mor ta r in which the salt was present , and a r g u e d that it has an acce le ra t ing p o w e r on s o m e por t land c e m e n t and a r e t a rd ing one on others. Nevi l le [3] on the o ther hand poin ted out that sod ium chlor ide w a s ' a n acce l e ra to r but not a power fu l one as calcium chlor ide was. Calcium h o w e v e r exists in sea wate r in t races only and can h a v e but a marg ina l �9 in acce le ra t - ing the sett ing t ime in this case.

The re is nothing definite r e p o r t e d so far about the effect o ther salts p r e sen t in sea wate r have on por t l and cement, but some information is avai lable about the effect of some of these salts on h igh alumina cement . For example , .potass ium ch lor ide re ta rds the set t ing time of h igh alumina c e m e n t whilst sod ium sulphate acce le ra tes it.

To the conflicting role which sod ium ch lor ide plays in the acce le ra t ion of the set t ing times, must be a d d e d the compl ica t ing effect of t empera tu re . In s o m e cases hot wea the r tends to inc rease the set t ing time with a resul t ing loss in workabi l i ty and quanti ty while in others the set t ing t ime .has b e e n known to inc rease somewha t as the t e m p e r a t u r e is l owered .

In normal Sea wate r the re a re about 10 and 80 par ts p e r million of ca rbona te and b i ca rbona te r e spec t i ve ly and a small amount of f ree ca rbon-d iox ide . On the a v e r a g e the pH value of sea wa te r in equ i l ib r ium with ca rbon-d iox ide in the a t m o s p h e r e should b e in the r eg ion of 8.2. W h e n the pH va lue is a b o v e 7.5 the re is l ikel ihood of leaching by the ca rbon- d ioxide . At a pH va lue of 7, the content of ca rbon- d iox ide may be tolerable . On the o ther hand b e l o w this value the content is almost cer ta in to be exces s -

ive and may cause d a m a g e to e v e n well m a d e port- land cement concre te .

Orcha rd [4], h o w e v e r , s e e m s to be satisfied that water with a pH value of b e t w e e n 6 and 8 is a safe and satisfactory mix ing water . The results in Table IIt show the values in exces s of Orcha rd ' s - recommendat ions. This r e e m p h a s i z e s the n e e d for care in the use of wa te r f rom the sea. It is c lea r that each of the impor tant consti tuents p re sen t in sea water act ing sepa ra t e ly has a different effect on the sett ing t i m e s - - s o m e a c c e l e r a t e others retard. It is also clear that the net effect of all these salts plus the effect of t e m p e r a t u r e is a definite inc rease in the set t ing time.

The p e r c e n t a g e r educ t ion in se t t ing time as r e co r d - ed in these tests is se r ious e n o u g h to g ive rise to g r a v e p rob lems in the hand l ing of cement bound materials, espec ia l ly concre te .

Opera tors on the site a re mos t ly unski l led techni- cians who may not be aware of the quick sett ing effect of sea water. There fore , if too l a rge a quantity of mater ial is m i x e d with sea water , was tage and e x p e n s e may result.

TABLE III

Sea Water

Goderich Lakka Hamilton Sussex Bawbaw No. 2 River

Total pH Chl. ralue in

g/1

8.5 18.5 8.3 13.8 8.2 17.5 8.5 18.1 8.2 17.9 8.3 17.6

Sul- phate in g/l

3.14 1,44 2.74 2.91 1.18 2.83

So- dium

g/1

11.3 11.7 11.6 11.3

Den- ~/o So- sity dium

Chlo- g/cc ride

1.03 3.11 1.02 2.32 1.02 2.92 1.02 3.04 1.025 3.02 1.025 2.98

"It is assumed that chloride is present predominantly as sodium chloride.

104

Even when quick set t ing is ant ic ipated, it will still not b e easy to j u d g e w h e t h e r a pa r t i cu la r b r a n d of c emen t can resul t in a w o r k a b l e set t ing time. In these cases, when p o u r i n g commences , difficulties can a r i se in p lac ing and v ib ra t ing the conc re t e satisfactorily. The situation can b e c o m p l i c a t e d w h e r e in some Afr ican countr ies , i m p o r t e d b r a n d s with the same t r a d e mark a n d desc r ip t i on ( see Table I) have different p r o p e r t i e s .

Mixing in small quanti t ies m a y b e helpful but some p recau t ions of p l ac ing f reshly m i x e d conc re t e agains t one p l ace minutes e a r l i e r m a y have to b e i n t r o d u c e d when mix ing with s ea water , w h e r e this is not a lways essent ia l with f resh water . Mixing in small quantit ies, howeve r , cart resul t in the var ia t ion of dens i ty and s t rength.

In addi t ion to mix ing in small ba tches , quick plac- ing may also b e an a d v a n t a g e when mix ing with s ea wa te r but this m e t h o d m a y resul t in o rgan isa t ion p r o b l e m s in a small site;

K. T H O M A S - - W . E. A . L ISK

5. C O N C L U S I O N

It has b e e n shown that the use of s ea wa te r from the S ie r ra Leone Peninsu la for mix ing cement , r e d u c e s the se t t ing t ime b y 75 %. This d e g r e e of reduc t ion is not un impor t an t in d e v e l o p i n g count r ies in the t ropics , w h e r e p r o b l e m s of the s u p p l y of sk i l l ed m a n p o w e r and the en fo rcemen t of con t ro l s . on i m p o r t e d mate r i a l s r e m a i n l a rge ly u n r e s o l v e d .

It should b e the r e q u i r e m e n t for the a p p r o v a l for sale in the Afr ican marke t , that manufac tu re r ' s cer t i - ficates b e p r o d u c e d b y supp l i e s of all b r a n d s of cement . Only when b u i l d e r s have a full k n o w l e d g e of the p r o p e r t i e s of the c e m e n t avai lab le can s ens ib l e use b e m a d e of s e a w a t e r for mix ing p u r p o s e s . The sa fegua rds in B.S. 3148, 1959, which r e c o m m e n d s an ind i rec t test for doubt fu l wa te r can b e e x t e n d e d to mee t the si tuation e n c o u n t e r e d with sea water . This would m e a n that cemen t s with a to l e rance of + 30 minutes on the min imum spec i f i ed b y B.S. 12, 1958, could b e m i x e d with s e a wa te r without spec ia l handl ing techniques .

6. A C K N O W L E D G E M E N T S

This work was c a r r i e d out in the Mater ia ls and St ructures L a b o r a t o r y of Fourah Bay Col lege , the Univers i ty of S ie r ra Leone.

The authors wish to e x p r e s s their g ra t i tude to Mr. A. E. Harr is the Chief Technician of the Depa r t - men t of Chemis t ry , and to Mr. W. E. Davies Sen io r L a b o r a t o r y Technic ian of the Depa r tmen t of E n g i n e e r - ing for the i r ass i s tance in c a r r y i n g out the tests; also to Miss Z. E. Macfoy for typ ing the manuscr ip t .

REFERENCES

[I] Bri t ish S t a n d a r d 12, t958. - - Portland cement (ordinary and rapid hardening).

[2] LEA, F. M. - - The chemistry of cement and concrete. London, Edward Arnold Ltd. , 1956.

[3] NEVILLE, A. M. - - Properties of concrete. New York, John Wiley & Co., t963.

[4] OaCHARD, D. F. - - Concrete technology. New York John Wi ley & Co., 1962.

[5] LALONDE Jr, WILLIAM S. and JANES, MILO F. - - Concrete engineering hand book. New York, McGraw-Hil l . , 1961.

[6] Bri t ish S t a n d a r d 3148, 1959. - - Test for water for making concrete.

105