Indian Journal or Chemical Technology Vol. 7, November 2000, pp. 287-291

Effect of cement kiln by-pass dust waste on the physicomechanical properties of alumina cement

H H M Darweesh & N M Khalil

Refractories. Ceramics and Building Mate ri als Department, National Research Centre, Cairo , Egypt

Received 23 February 2000: accep!ed 22 Augus/ 2000

The inlluence of the add ition or cement kiln by-pass dust on the physicomechanical properties of alumina cement on cooling as well as after firing at 1200°C and 1300°C was st udi ed. Results show that the water or consistency as well as set­ting time in crease with the addition of cement dust both on coo ling and tiring. Where as mixing alumina cement with ce­ment dust affects adversely on the specific properties or the cement. the properties are improved on firin g at 1300°C. The free CaO content of· cement dust is partially lllili zed by alumina cement on cooling, but further utili zation occurs on II ring. The XRD ana lysis revealed that by firin g of alumina cement together with cement du st . new calcium sili cate and aluminate phases arc formed, which are responsible for the relati vely hi gher rate of hydration . Accordingly, the physicomcchanical characteristics of the cement are improved.

During last fifty years, growing industrialization has resulted in a major problem of utilization of industrial wastes or by-products generated from various sectors of industries . These wastes often cause many envi­ronmental and health problems. Therefore, all agen­cies and organizations of environmenta l affairs are interested in this problem intensi vely. Utilization of the various by-products, particularly the solid wastes, is a ch ief concern involving energy consumption and sometimes even ecology. The cement kiln by-pass dust is a very dangerous waste material comi ng from the manufacture of P.C. clinker, and it is considered as one of the main direct reasons for air pollution es­pecially in the dwelling zone near or close to the ce­ment factories1

-4. In U.S.A and A.R.E about 10 and

2.5 million tons of thi s waste material are annually produced, respective ly resulting in a very serious waste disposal problem, in addition to the health haz­ards to people. The finely divided cement dust is emitted from cement kilns to prevent the build up of excessive salts in the cement product. Hence, about 18 wt. % of the feed materials may be purged as ce­ment dust waste. This waste material was found to be composed of finely ground raw material s containing CaCO, and Si02, alkali oxides (Na20 & K20) with a layer of alkali sulphate (K2S04 & Na2S04). In thi s form, it is difficult to be directly recyc led to the ce­ment kiln . Therefore, the alkali content must be kept low in order to prevent and avoid concrete decrepita­tion4-6.

On the other hand, th e manufacture of high alu­mina cement is very expensive due to the hi gh prime cost of raw material s, high energy consump­tion and the higher hardness of it s c linker . So, low grade alumina cement containing only 40% Al 20 , was se lected. On this basi s, the main objective of this paper is to study the effect of cement dust ad­dition on the hydration process of the low alumina cement. The physicomechanical properties as well as kinetics of hydration of alumina cement con­taining different forms of cement dust are invest i­gated.

Experimental Procedure The raw materials used in the present study are

low alumina cement (40% Al 20 3) and cement kiln by-pass dust waste. The alumina cement was ob­tained from Egyptian Company for Refractori es, while the cement dust was provided by Hel wan Portland Cement Company, Cairo, Egypt. The raw cement dust was first subjected to a simple leach­ing process usin g hot water, in order to e liminate most of the soluble sa lt s. The chemical analysis of alum ina cement as we ll as raw and leached cemenr dust is shown in Table I . Fig. I shows the X-ray diffraction pattern s (XRD) of th e anhydrous low alumina cement and cement by-pass dust. It is clear that the alumina cement is composed mainl y of C 12A7 and C2AS, while th e cement dust is com­posed of calcite and quartz . A cement mix was

288 IND IAN J. CI-IEM. TECH NOL. . NOVEMBER 2000

Tab le !-Chemical anal ysis of raw materia ls, wt. o/~ .

Raw material Oxides

L.O. I Si02

Al20.1 Fe20 3

CaO MgO Na20 K10 so,1 Cl Ti01 Free CaO

i

70

Low alumina cement

S.OH 40. 12 10.65 42 . 13 0.32 0.09 0. 15

1.46

o CJ2A7 • CzAS • Calcite ll 8,uortz

Raw cement

dust

17.63 10.26 1.65 1.28

48.05 2.02 3.82 2.4 1 6.62 6.26

19.36

Alu m ino cement

50 30

28 ( Cu - K~ )

Leac hed cement

du st

20.50 12 .04 1. 86 1.53

53 .61 l .X4 2.24 1.95 4.43

18 .83

10

Fig. 1-XRD patterns of the anhydrous low alumina cement and cement by-pass dust.

then prepared from 90 wt. % alumina ce me nt a nd 10 wt. % leached cement dust, which in turn was mixed in a porcela in ball mill u si ng 2 ba lls fo r 2h

in order to obtain the co mpl e te homogeneity of th e mix. A part of the cement mix was fired at 1200°C. Another part was f ired at 1300°C. T he resultin g

materials were then grou nd well to pass through 200 mesh si eve. Tabl e 2 shows that the re are fo ur

cement mixes: pure al u mina cement (M 0), al umin a cement blended with I 0 % leached cement dust (Mt) , fired alum ina ce me nt mi xes at 1200°C (M 2)

and 1300°C (M.J), respec tivel y . T he wate r of co n­sis te ncy as we ll as setting ti me o f the va ri o us ce­ment pas tes were direc tl y carr ied out usi ng vicat

7 ~ apparatu s ··. T he cement pastes were pre pa red us -

Table 2- Mix compos itions of raw mate rials at differen t ex ­perimental conditions

Low Leached Firing temp.,

No alumina cement dust cemen t % %

oc

Mo 100 Ml 90 10 M1 90 10 1200 MJ 90 10 1300

in g the prede te rmined water of consistency, and

then cas t in one inch s tee l c ubi c moulds , cured for 24 h in a humidity chamber at 100% R .H and co n­

stant room temperature o f 23 ± l °C , demo ulded

and cured in tap water for l, 3, 7 and 28 days . The

broken specime ns from the de te rmination of com­pressi ve s trength ') were imme rsed in I: I methanol­

acetone mixture to s top the hyd rat io n . The mecha­

n ism of hydra ti o n was studied by measurin g the

chem ica ll y-co mbined water conte nt which was per­

formed o n th e bas is of ig nition loss . The free CaO content was determined by the extraction method

of Franke 10. The phase composition of some se­

lected sa mpl es was identi fied by XRD analysis whic h was employed by a Philips X- ray Diffracto­

meter, Mod. 1390 with Ni-filter, Cu-Ka radiation.

Results and Discussion Genera ll y, th e main phase s of a lumina ce ment

are CA, CA 2 a nd C 12 A 7 depe nd ing o n the CIA­ratio . The most predominant hydration product s

are CAH 1o, C 2AH R, CAH 6 a nd AH .,. The on ly sta­ble hydrates a t ord in ary temperature are g ibbs ite

(AH3) and cubic C 3AHr,. Furth ermore, the a lumin a

cement provides h igh st rength development in the

ea rly pe ri od of hydration compared with the ordi­nary Portland ce ment. Howeve r, a part of th e hi gh s tren g th is often lost d urin g the co nvers ion reac­ti o n of calci um aluminate hydrates as the time of

hydration proceeds . Duri ng thi s co n version , the porosity increases causin g a temporary loss of s tre ng th . By time, the poros ity th a t deve lops due to

th is convers ion , may be f ill ed again w ith th e newiy formed hydratio n products resulting in a strength gai n . Hence, the rate and exte nt of this co nversion

d . I h . I 10 II e termllle t 1e c ange t n streng t 1 · . The res u lts of water of consistency and setting

t ime (i n it ial a nd f inal ) of the variou s cemen t pastes

are shown in Tab le 3. The W/C-rat io has a major effect on the specifi c prope rties of the cement so

DARW EES H & KH ALI L: EFFECT OF CEMENT KILN BY-PASS DUST WASTE ON ALUMI NA CEMENT 289

Table 3-Water of consistency as we ll as set ting time or the various cemen t pastes.

No Water consis tency Set ti ng time, min

% I. S.T F.S.T

Mo 28.0 120 !55 Mt 3 1.0 160 190 M2 29.5 !50 180 M, 29.0 140 170

0

~ 28 ~ . ..... Mo c • <lJ - 24 6 MJ c

0 0 M2 -x u '- X M3

~:/: OJ .... 20 0 f-

~ \J Or

16 f-c d·/:-----· :.0 E 0 u 12 I f- : ,/0/ ;:....

0 ___.... 6. u 8- z__-/ E OJ .c u 4 l _l l L

3 7 28

Cu ri ng time, Days

Fig. 2- Chemi call y-combi ned water contents of the vario us alu­mina cement pastes at different condi ti ons.

that most failures acco mpani ed with cement struc­tures are mainl y due to e ither too much or too littl e water being added during mi xing process 11

• So, the optimum W/C-rati o for the aluminous cement al one was found to be 0 .28 . Thi s rati o increases with the addition of cement dust (M 1). The setting time (initi al and fin al) was also e longated. Thi s is mainl y attributed to th e presence of hi gh a lka li content in th e cement dust, even after th e leaching process, which needs more water demand to pro­duce suitable pas tes4

. T hi s seems to ac hi eve an im­portant advantage whi ch is th e e longati on of the narrow range of setting ti mes of the low alu mi na cement related to its fast settin g and hardenin g property, i. e. the rate of hydra tion is very fast.

In M2 and M, mi xes , th e water of consistency as well as settin g ti me s li ghtly decreases th an those of M 1, but st ill hi gher than those of the alu mina ce-

ment (M0 ). Thi s is esse nti a ll y due to the th ermal reacti ons whi ch may have occurred between the constituents of cement dust and alumina cement durin g firin g e ither through decompos ition or re­combination changes res ulting in the formati on of new phases whi ch required hi gher wate r demand to

. 4 6 hydrate and produce a suttable pas te · . The results of chemi ca ll y-combined water con­

tent s of the vari ous cement mi xes are pl otted in Fi g. 2. It is clear th at the combined water content of all cement pas tes inc reases grad ua ll y as the curing time proceeds. Thi s is primaril y due to th at the rate of hydrati on as we ll as th e formati on of hydrati on products increase as the curin g time pro­gresses. The combined wate r contents of M 1 is much lower than th ose of th e pure a lumina cement (M0) . Thi s is mainl y due to th e hi gher sensiti vit y of alumina cement aga inst the hi gh alkalinity of ce­ment du st whi ch contributes to the presence of re lative ly hi gh amounts of alkali ox ides (Na20 & K20 ) and free CaO. Thi s tends to hinder or at least reduce th e rate of hydrati on of alumina cement 10

.

Although the va lues of combined water of M2 are lower than th ose of th e pure alumina cement (M0),

they are hi gher th an th ose of M 1 at all curin g ages . Moreover, the combined water contents of M, are the hi ghest compared with a ll cement mixes, even M0 . Thi s is princ ipall y du e to the fo rmati on of new phases durin g firin g process whi ch promote the

2.0

6----A-6 6 ;!- 1. 5

0 ..... x:----o c OJ ~ ----0 -o -c 0 X u

-------x--:.__ x <l.J Mo E • 0.5 6 Ml

<l.J M2 <l.J 0 ..._

lL. X M3

0.0 -------·-----·----------· 3 7 28

Curi ng l ime, Ooys

Fig. 3-Free lime contents or the various alumina cement pastes at diffcrcm conditions.

290 INDI AN J. CHEM. TECHNOL., NOVEMBER 2000

rate of hydratio n4. Hence, th e firing of alumina

cement with cement dust is an essential factor wh ich pl ays an important part in the hydration pro­cess of the a lumin a cement.

Fig. 3 represents the res ults of free CaO content of the various alumina cement mixes up to 28 days of hydra ti on. It is c lear th at th e free CaO content of the pure alumina cement (M0) is zero at all cur­ing ages of hyd rati on. Thi s is mainly due to th e fact that th e alumina cements do not prod uce CaO on hydration 10' 11 . The free lime co ntent of th e alu­mina cement mix (M 1) dec reases sli ghtly onl y up to 3 days of hydration , and then stays constant on­ward, whilst th ose of mixes (M 2 and M,) dec rease sharply up to 28 days. This may be attributed to the interaction between the constituents of cement du st and a lumina cement during firing. The rate of co n­su mpti on of CaO co ntent of cement dust is the lowest in M 1 and hi ghes t in M 3 . T hi s is essenti a ll y due to better interaction process that occurs at higher firing temperature ( 1300°C). This shows the parti a l utili zati on of free CaO content of cement dust by alumina cement on coo ling, but maximum utili za ti on is after firing.

The results of compress ive strength of the va ri ­ous cement pastes are represented in Fig. 4. As it is clear, the compress ive strength of all cement pastes increases with curing time up to 28 days of hydra-

sor~------------------------~

• Mo C) 70 - 6 M1 0.. 0 M2 2: _-X

X M3 ----.r:.' 60 - -01 c <ll l..

50 - r Vl <ll .e;/ > Vl 40 Vl <ll l..

Q E 301- :~6 0 u 6

20 I I I I

3 7 213

Curing time, Days

Fig. 4-Compressive strength of the various alumin a cement pastes at different condit ions.

tion. Thi s is mainl y du e to the con tinual depos ition of the new ly fo rmed hydrati on products in side the pore structure of th e hardened cement pastes. This tends to decrease the tota l porosity . Accordingly , the bulk density improves and enhances accompa­ni ed by an increase in th e compress ive strength 10

Furthermore, the rate of increase during initi al stages of hydration is faster tha n at a later stage . This is essenti all y attributed to th e fact that during fi rs t week of its initiati on, about 80% of the alumi­nous cement hydra ti on occurs10·1 1.

The compress ive strength of cement pastes of M 1 is mu ch lower than that of the correspond ing alumina cemen t (M0) . This is mainly du e to th e lower fra cti on of a luminous cemen t which is re­sponsible for th e hydrati on mechanism. Moreover, the cement dust has no hydrauli c properties, in ad­diti on to the hi gher amounts of a lka li es and free lime which affec t adverse ly the spec ifi c properties of alumina cement, es pec iall y the compress ive strength . The addition of cement dust to alumina cement often dec reases the fineness o f th e whole

. H . d I f l I . PI ' mtx. ence, tt ecreases t 1e rate o 1yc ratt on -· · . On th e other s ide, the compress ive strengt h of ce­ment mi x (M 2) is hi gher th an th at of M 1 nearly at all curing peri ods, but st ill fully lower th an that of the pure alumina cement (M 0). Alt hough the com­press ive strength of cement mi x (M :~ ) is still lower than that of th e pure alumina cement during earl y stages of hydration up to 3 days, it becomes hi gher at late r stages . Thi s is fundamentl y du e to th e fact that th e crystallization of the new ly formed phases from the liquid phase during firing impro ves th e workability of the cement and increases th e chance to impro ve th e qu a lity of the cement. This is be­cause the ultimate compressive stren gth depends mainly upon the intrinsic strength of eac h compo­nent and its re lative amount among other compo­nents . This seems to contribute strongly to the

I . I I . h . I I t4-16 re atrve y 1r g compresstve strengt 1 va ues . Fig. 5 illustrates the XRD pat te rns of th e anhy­

drou s and hydrated specimens of the pure alumina cement (M0) as well as those of cement dust/alumina cement mixes after firin g at 1200°C (M2) and 1300°C (M:; ), res pecti ve ly. It is clear that CA and C1 2 A7 are th e main components in the an­hydrous alumina cement. These phases are de­creased gradual! y and new peaks representing C,AH6 and AH, are formed due to hydration . However, few pea ks characteri zing th e anhydrous

DARWEES H & KH ALIL: EFFECT OF CEMENT KIL BY-PASS DUST WASTE ON ALUM INA CEMENT 291

Fig. 5-XRD pal!erns of the an hyd rous and hydrated alumina cement mixes. I ,2: pure alumina cement , 3,4: fired mix at 1200 °C, 5,6: fired mix at 1300 oc.

specimen are still present , but with small er inten­sities. In the anhydrous spec imens of cement dust/alumina cement mixes fired at 1200°C and 1300°C, new phases are detected as calcium sili­cates and aluminates which are formed durin g fir­ing indicating that the thermal reactions between the constituents of both alumina cement and ce­ment dust occurred better at higher firing tem­perature. In the hydrated specimens, calcium sili­cate and aluminate hydrates are formed in amor­phous or fine crystalline state besides C3AH 6 and AH, . The free CaO is also identified showing that most of the free CaO content of the cement du st are utilized in the formation of the new ly formed phases during firing. The residual free CaO content in the hydrated specimens is respon sible to some extent for the dec rease of compressive strength.

Conclusion The addition of cement dust to alumina cement

on coo ling or firin g increases the water of consis­tency as well as settin g time. Mixing the alumina cement with cement dust affects adversely the spe­cific properties of the cement. Firing of alumina cement blended with cem~nt du st at hi gher tem­perature ( 1300°C) evidentl y improves th e ph ysi­comechanical properties such as: workability, combined water and compress ive strength . Hence, the quality of the cement is s li ghtl y improved. The XRD analysis shows that th e firing of cement dust together with the aluminous cement, thermal reac­tions could occur resulting in the formation of new phases as calcium silicates or a luminates which are res ponsible for the re latively hi gher physicome­chanical charac teri stics of the fired cement mi x.

References I Bhatt y M S Y, World Ce111 . 16. II ( 1985) 386. 2 PJrker K I, World Ce111 , I g, I 0 ( 1987) 427. 3 Terry MS. World Ce111, 23.4 ( 1992) 30. 4 Shoaib M M, PhD Th esis, FJculty of Science, Zagazig Uni­

vers it y, Zagazig. Egypt. 1995. 5 Singh N B, Bhattacharjee K N & Shukla A K, Ce111 Co11cr

Res, 25 , 4 ( 1995) 883. 6 Mos leh A M. M Sc Thesis. Inst Env Studies and Res. Ai11

Sha111s University, Egvpt, 1996. 7 ASTM- Sta11dards. C 187-86 ( 1993) 148. 8 ASTM-Standards, C/ 9/ -92( 1993)866. 9 ASTM- Standards, C 170-90 ( 1993) 828. I 0 Hewlett P C, Lea's Che111i.l'lly of Cement and Concrete, 4'11

ed iti on , (John Wiley & Sons Inc. , New York), Toronto, 1998.

II Abdei-Kader A A, Ph D Th esis, Mandaleev Institute for Technology & Chemistry, Moscow, 1992.

12 Amer A A, PhD Th esis, Faculty of Science, Zagazig Uni ver­sity, Zagazig, Egypt , 1990.

13 Abo-EI-Enein S A, Proc !'' lnt Swnp Cem Ind, Assuit 8- I 0 Nov. Egypt , 1997, 29 1.

14 Sayed M, Shanawany A R, Apetri D, Toader A & Sardru , C. Proc !"' lnt Sy111p Ce~n Ind, Assui t 8- 10 Nov, Egypt , 1997 , 277.

15 Gerstner B & Li siecki , K H, (Ger), Rallsto.ffindllstrie, 29. 4 (1986) 102.

16 Sorrentino D, Sorren tino F & George C M. Scalnv, V, IV, Am Ceram Soc ( 1995 ) 4 1.