Valorization of fly ash in the cold stabilization of clay materials

ELSEVIER Resources, Conservation and Recycling 15 (1995) 219-234

resouzces, conservation and recycling

Valorization of fly ash in the cold stabilization of clay materials

M. Temimi a,., j.p. Camps b, M. Laquerbe c a lnstitut National des Sciences Appliqu~es (INSA), Laboratoire GTMa, 20, Avenue des Buttes de Co~smes,

35043 Rennes, France b lnstitut Universitaire de Technologie, Rennes, France

c lnstitut National des Sciences Appliqu~es, Rennes, France

Received 13 February 1995; revised 1 June 1995; accepted 18 June 1995

Abstract

It is possible to valorize fly ash by using it in clay materials cold stablized by means of a binder (cement or lime) and extrusion shaped. Fly ash is an industrial waste. Its utilisation in manufacturing processes as described here allows, on the one hand, to obtain low cost building materials, like bricks or blocks and, on the other hand, to solve some serious pollution problems of waste elimination. The mechanical properties, water resistance, dimensional stability and accelerated ageing of products containing ash are significantly improved when compared to those of clay-binder mixes. This may be explained as follows:

• a better hydration of the binder of mixes containing ash, • the filler effect of passive ash grains, • the pozzolanic effect, a property of silico-aluminous fly ash which is able to fix lime, with water,

thus producing hydrated compounds.

Keywords." Clay; Fly ash; Cold stabilized; Building material; Extrusion; Hydration; Filler effect; Pozzolanic effect

1. Introduction

A number of studies concerning clay-based building materials which are cold stabilized and which are shaped by extrusion, have shown that it is possible, under some conditions, to make products whose properties can be compared to those of more traditional materials like baked earth bricks or concrete blocks. These products are cheaper than their traditional equivalents due to the lower quantity of energy they need for their processing.

* Corresponding author.

0921-3449/95/$09.50 © 1995 Elsevier Science B.V. All rights reserved S S D 1 0 9 2 1 - 3 4 4 9 ( 9 5 ) 0 0 0 3 8 - 0

220 M. Temimi et al. / Resources, Conservation and Recycling 15 (1995) 219-234

AI:~ 03

B VERRE$ LAITIERS

BASALTES ~ CLINKER PORTLANO

( ~ CV de CORDEMAIS 1 CV de GARDANN[:

POU770L,A.NES ~ CIMENTS ALUMINEUX

Fig. 1. Chemical composition of fly ash in CaO-A1203-SiO2 system.

Several tests have been carried out to determine what parameters influences the production process. It appears that the differences observed have several origins [ 1-5 ] :

• the mineralogical nature of the clay, • the nature and the amount of binder, • the addition of different elements (admixtures, fibres, sand).

Fly ash is a waste material that could be valorized in the building industry. It is used mainly in concretes and cements where it improves the quality of these materials [6,7]. Using it in clay products may offer some advantages:

• in comparison with the fly ash effects in concrete, this addition could allow either to improve the properties and the performances of the end products or to lower the amount of binder used for a new extrusion-made material,

• it also contributes to the elimination of the pollution caused by this waste. The first point has been experimentally investigated by testing different compositions of

clay-fly ash-binder mixtures.

2. Materials and testing

2.1. Materials

Fly ash It is a waste due to the mineral part of coal which remains after burning. The fly ash used

in this work was supplied by the electric plant of CORDEMAIS (Loire Atlantique, France). Its main components are silica and alumina as shown by Fig. 1 and Table 1.

M. Temimi et al. / Resources, Conservation and Recycling 15 (1995) 219-234

Table 1 Range of chemical composition (%) of fly ash from CORDEMAIS

221

SiO2 A1203 Fe203 CaO MgO K20 Na20 SO2 LOI

42-54 22-32 4-15 2-7 1-3 1-5 0.5-5 0.2-2 2.5-7

Specific area 'Blaine' = 0.34).5 m2/g.

K=Kaolinite Q---Quartz M = M u $cov i te

M K*0 k ~

,

20 1S 10 S

Fig. 2. X-Ray diffraction diagram of china clay.

Table 2 Chemical composition (%) of china clay

degr~s 8

SiO 2 A1203 Fe203 TiO2 CaO MgO K20 Na20 Li20

48.5 37.0 0.8 0.1 0.1 0.2 1.1 0.1 traces

Weight loss at 1000°C = 12.1%; specific area 'B.E,T.' = 11.5 m2/g.

Clay Clay is necessary to give the cohesion and plasticity which allow the mixture to be

extrusion shaped. A monomineral China clay (kaolinite) as shown by X-ray diffraction diagram (Fig. 2), was used. It is extracted from the PLOEMEUR deposit (Southern Brit- tany). Table 2 gives the chemical composition of this clay. The main interest of this choice was to use a clay on which a number of works had been already carried out in the lab, highlighting its stabilization ability by several kinds of cements and allowing reliable comparisons between different stabilization methods.

Binders As they make bonds between the matter particles, the binders can stabilize the material

to be produced. Two binders were checked, an ordinary portland cement, C.P.A. 55 according to French

standards, and an artificial hydraulic lime 'Lafarge 100' also defined by French standards [8].


Fig. 3. Diagram of the extruder.

1- Mixing room 2- Mixer paddle 3- Grate 4- Manometer 5- Vacuum pump 6- Endless screw 7- Extrusion room 8- Die 9- Extruded product 10- Motor block

4

Table 3 Composition of mixtures studied

Mixtures Clay (%) Fly ash (%) Cement (%) Lime (%) Water (%)

M.1.T 80 0 20 0 28 M.I.1 60 20 20 0 28 M.1.2 40 40 20 0 28 M.1.3 30 50 20 0 28 M.2.T 80 0 0 20 28 M.2.1 60 20 0 20 28 M.2.2 40 40 0 20 28 M.2.3 30 50 0 20 28

Table 4 Scale of quality

Mark Quality

no cracks - very good cohesion superficial light cracks - very good cohesion superficial sharp cracks - good cohesion deep cracks - weak cohesion important deep cracks - condition on the verge of failure general cracking or breaking up - no cohesion

2.2. Tes t ing

M a k i n g p r o c e s s

The samples are ext rus ion shaped by means o f a laboratory mach ine s imilar to that used

in industr ial br ick factor ies (Fig. 3) . Af te r mixing , the mix is in t roduced into the mach ine

and is d rawn out, thanks to the push under v acu u m o f a screw, through a die w h o s e

M. Temimi et al. / Resources, Conservation and Recycling 15 (1995) 219-234

1,5 M1.T • I, MI.1

1,4 - M1.2

1,3 8 MI.3 12

(a)

1 1 0 1 0 0 1 0 0 0

Log Time, days

223

1,6 1,5 M2.T (b)

8 M 2 . l ~ i L t

1,4 .t M2.2

1,3 ~ M2.3 J

~" 1.1

~ 1,0

.... 0,9

0.8

0,7 I

0,6

0,5 . . . . . . . . ~ . . . . . . . . ' . . . . . . . . 10 100 1000

Log Time, days

Fig. 4. Diagram showing the variations of shrinkage ( A L / L ) n vs. t ime for: (a) cement, (b) lime.

dimensions and shape have been chosen in order to cut 16 cm long and square cross sectioned (4 × 4 cm 2) prismatic samples.

Immediately after their extrusion, the samples are stacked in an air-controlled room (temperature 20°C, relative humidity 50%).

Mixture elaboration

All the mixtures contain fly ash, cement or lime, clay and water. Different compositions are tested in order to check their ability to be extruded and to define the threshold of the clay amount below which the extrusion is impossible.

A reference sample does not contain any fly ash and its water quantity, the lowest which allows efficient extrusion, is kept for all the other samples using the same binder. Many previous experiments have shown that this water amount corresponds to the plasticity limit of the clay.

Table 3 shows the composition of the different mixtures, all the percentages are computed with regard to the weight of the dry part (fly ash, clay and binder) of each mix.

2 2 4 M. Temimi et al. / Resources, Conservation and Recycling 15 (1995) 219-234

2 0

15

10

J- M1 .T

& MI.1

~- M1 .2

(a)

| | .... m| i | ...... m . . . . . . . .

1 0 100 1 0 0 0 Log Time, days

20 (b)

; M2.T

M2.1

15 - M2.2

~ to

5

0 . . . . . . . . ! . . . . . . . . i . . . . . . . .

1 10 1 0 0 101)0 Log Time, days

Fig. 5. Diagram showing the variations of weight loss (Ap/p)n vs. time for: (a) cement, (b) lime.

Testing The different tests set up to define the quality of stabilization are:

• Shrinkage measurement Two marks are plotted near the extremities of the fresh extruded samples. The length

separating these marks is measured at different dates with a cathetometer having a 0.01 mm accuracy.

• Weight loss Samples are weighed at different dates.

• Mechanical resistance according to French testing standards [ 9]. • Water resistance

This test is designed to check the ability of the material to resist the ingress of water and to keep its initial cohesion.

After a 28-day period of storage in the air-controlled room, the samples are immersed in water for 72 h. A scale of quality (Table 4) describing the different grades of alteration is used [ 10].

M. Temimi et al. / Resources, Conservation and Recycling 15 (1995) 219-234 225

• M.I.T ~ (a) ] $ M . I . I ~ ~ [

!

10 100 1000 Log Time, days

41

3

~ 2

M.2.T 4 M.2.1

* M.2.2 4 M.2.3

(b)

a a i ~ • , . I , i . . . . . . . i . . . . 1 1 1 1


Fig. 6. Diagram showing the percentages variations of water of binder hydration (% W.Hyd.) vs. time for: (a) cement, (b) lime.

• Accelerated ageing All the samples, stacked for 1 year in the air-controlled room, were put through accelerated

ageing tests consisting of several immersion/drying cycles. The samples are immersed in water at 20°C for a 24-h period and subsequently dried in an oven at 100°C for the same length of time. The aim of this test is to rapidly check the stability of the material over a long period of use.

After 12 immersion/drying cycles, the dimensional variations of the samples and their mechanical resistance were determined.

Other tests concerning the determination of the water amount of binder hydration and the X-ray diffraction analysis are carried out in order to better explain the difference of results between the mixtures containing fly ash and their respective reference samples. The water amount is determined at different stages thanks to the weighing of the samples, before and after their drying in an oven at 100°C. The X-ray diffraction is executed on the powdery mixtures (powder method).

2 2 6 M. Temimi et al. / Resources, Conservation and Recycling 15 (1995) 219-234

12

lO

8

4 q

2 ~ i

* MI.T

$ MI.1 / ~

(a)

. . . . . . . ! . . . . . . . . i . . . . . . . .


12 • ~ . T (b)

10 8 M2.1

M2.2

8 ~ M2.3

2

0 1 10 100 1000

Log Time, days

Fig. 7. Diagram showing the variations of tensile strength (Rt) vs. time for: (a) cement, (b) lime.

3. Results and discussion

3.1. Shrinkage and weight loss

All the samples shrink when they are stored in the air-controlled room (temperature 20°C, relative humidity 50%). This is mainly due to the evaporation of water present in the structure of the mixtures. As shown in Fig. 4 and Fig. 5, the greater part of the shrinkage and weight loss of all the mixtures occurs at an early stage, during the first few days and becomes practically stable after about 28 days. The value of the shrinkage decreases by fly ash addition. The main cause of shrinkage is the amount of clay, the more fly ash there is instead of clay, the less shrinkage there is. Furthermore, as we will see below, the binder hydration is more efficient.

3.2. Percentages of water of binder hydration

The binder hydration takes place so as to be significant at the early stages ( < 28 days) and continues after 28 days, but more slowly (Fig. 6).

M. Temimi et al. / Resources, Conservation and Recycling 15 (1995) 219-234 227

G

40

35

3O

25

2O

15

10

5 I

0

MI.T

8 MI.I

10

• , | . . . . . !

100 1000 Log Time, days

40

35

30

25

20

15

10

5

0 - -

* M2.T o M2.1

M2.2 o M2.3

(b)

. . . . . . . I . . . . . . . . | . . . . . . . .


Fig. 8. Diagram showing the variations of compressive strength (Rc) vs. time for: (a) cement, (b) lime.

In the clay, the water is to be found in a free or bound condition, as either reoriented or double-layer water [ 11 ]. The substitution of fly ash for a certain amount of clay increases the quantity of free water present in the mixture. Indeed, on the one hand, fly ash has a lower specific area (0.3 to 0.5 m2/g) than clay ( 11.5 m2/g) and, on the other hand, the fly ash grains, spherical or shell-shaped, do not retain more water than the leaf structure of the clay. Thus, the binder hydration is all the more complete as the free water amount is higher.

Furthermore, since the fineness of the clay is more important than that of the fly ash or binder, the clay can prevent the setting of the binder, forming round its grains a kind of protecting envelope [ 12]. The curves illustrated by Fig. 6a and b show well an increase of the percentages of water of binder hydration with that of fly ash contents; in other words with a decrease of clay proportion.

3.3. Mechanical strength

Large differences between the reference mixtures (without fly ash) and the samples containing fly ash are observed in Fig. 7 and Fig. 8. Whatever the date, the resistances of

228 M. Temimi et al. /Resources, Conservation and Recycling 15 (1995) 219-234

x : 2 theta y : 2315. linear Cenm de DiffrsctomCaic Hera-i Longchamb~n

(W ss : o.om Ull: GK,l+Z

x : 2 lhela y : 621. linear Cenae de Difkactonkme Hem-i Longchambon

fly ash added products are always the greatest. Besides, the gradient of strengths (AR/At) ’

where: i, j are dates (i > j) and R,, R, are resistances, respectively, at i and j dates.

M. Temimi et a l . / Resources, Conservation and Recycling 15 (1995) 219-234 229

v I

1 l I

/

(c) ss : 0.0200 tm : Cu Kot 1 +2

l . I[ ...._ < 5.,)00 x : 2 theta y : 1171. linear

Centre de Diffractom6mc Henri Loagchamtxm 6(I.000 >

z

IL,

(d) ss : 0.0200 tm : Cu Ka 1 +2

~. ÷ ~, ~x -" ~ I~ I~ <

< 5.000 x : 2 thcla y : 572. linear 60.000 > Cenltc de Difftactom(~lxie Hcm"z Longchambon

Fig. 9. X-Ray diffraction diagram of: (a) M. 1 .T at l day, (b) M. 1.2 at 1 day, (c) M. l .T at 90 days, (d) M. 1.2 at 90 days. Notations: C=calcite; Q=quartz; M=muscovite; K=kaolinite; C3S=alite; E=ettringite; G=gismondine; C2AH8=2 CaO, A1203, 8 H20; C2SH=2 CaO, SiO2, H:O; CAHIo=CaO, A1203, 10 HeO; C3AHtl =3 CaO, A1203, CaCO3, 11 H20; C4AHI3 =4 CaO, A1203, 13 H20.

is always greater for mixes containing fly ash, especially after 28 days. The resistance improvement may be explained:

• at early ages (up to 28 days), by a better hydration of the binder as shown above in the 2.2 part,

• after a longer while ( > 28 days), by the pozzolanic effect of silico-aluminous fly ash which allows the resistance to increase instead of being stabilized [ 13 ].


( a ) ss : 0.0200 tm : C. ~ 1+2

I 1 Z ~ . ,..~ v

< 5.000 x : 2 them y : 2244. linear Centre de Diffi'acmmeai¢ Hem Lo.gchambon

60.000 )

v (b)

.,,, j' J

~e

÷

n I1

ss : 0.0200 tm : Cu Ktl 1+2

~g ta=l V , ~ g , ~ ~ ,

t , a t ~ L*J

< 5.000 x : 2 theta y : 672. linear 60.000 Centre de Diffractomdlrie Henri Longchambon

The ash grain which is not involved in the pozzolanic reactions also contribute to the increase in resistance by its filler effect [ 13 ].

By another way, X-ray diffraction analysis carried out on the mixtures containing fly ash (M.1.2 et M.2.2) 2 and on their respective reference samples (M.1.T et M.2.T) 2 at 1 day

2 For this notation see Table 3.

M. Temimi et al. /Resources, Conservation and Recycling 15 (1995) 219-234 231

v

(c) ss : 0.0200 t in: Cu K a l + 2

t |

< 5.000 X : 2 t l~m y : 1741. linear Ceatte de Difftaetam~ttie Henri l~tgclmmbtm

60.000 )

Z

L~

÷

N

÷

÷

! J

(d) ss : 0.0200 tm: C u K~ i +2

,r kn nn x ,~ ,- -

< 5.000 x : 2 them y : 590. linear 60.000 ) Centre de Ditrfractometrie Henri Longcham~n

Fig . 10. X-Ray diffraction diagram of: (a) M.2.T at 1 day, (b) M.2.2 at 1 day, (c) M.2.T at 90 days, (d) M.2.2

at 90 days.

and 90 days highlight significant distinctions, especially in hydrated phases; according to the X-ray diffraction diagrams (Fig. 9 and Fig. 10), it appears that:


Table 5 The results of water resistance

Samples M.1.T M.I.1 M.I.2 M.1.3 M.2.T M.2.1 M.2.2 M.2.3

Mark 5 5 5 5 4 5 5 5

• Whatever the date, it is observed for all the mixtures the calcite (CaCO3), Kaolinite (AI2Si2Os(OH)4), quartz (SiO2) and muscovite (KA12(Si3A1)Olo(OH,F)2).

• At l day old, M.1.T et M.2.T do not contain any hydrates when the hydrates such as ettringite (6 CaO, A1203, 3 SO 3, 32 H20), gismondine (CaO, A1203, 2 SiO2, 4 H20) and hydrated calcium aluminate (2 CaO, A1203, 8 HzO) are found in M. 1.2 and M.2.2, M.2.2 containing in addition hydrated calcium silicate (2 CaO, SiO2, H20).

• At 90 days old, only one hydrate is observed in M.2.T, hydrated calcium aluminate (CaO, A1203, 10 H20 ). No hydrate is detected in M.1.T. Added to the precedent hydrates present at 1 day, M.1.2 and M.2.2 contain an hydro-carbonated calcium aluminate (3 CaO, A1203 , CaCO3, 11 H20), M.2.2 also containing another hydrated calcium aluminate (4 CaO, A1203, 13 H20).

3.4. Water resistance

No alteration is observed for samples containing fly ash even though superficial cracks arise on the lime stabilized reference samples. The result of this test is shown in Table 5.

3.5. Accelerated ageing

All the samples are unaffected by accelerated ageing test. Their surfaces are free of cracks (mark 5) excepted for the reference samples which is lightly cracked (mark 4). The dimensional variations of samples containing fly ash are lower (Fig. 11 ) and their loss of mechanical resistance is lower (Fig. 12) than that of the reference samples.

0,8 0,7 ~ Cement Lime

0.6

0,5

0,4

0,3

0,2

0,!

0,0 0 10 20 30 40 50 60

Fly Ash Content, % Fig. 11. Diagram showing the effect of fly ash content on dimensional variations (AL/L).

M. Temimi et al. /Resources, Conservation and Recycling 15 (1995) 219-234 233

20 Cement{{ • , year in air conditioned ~om (a)] • Immersion/drying [] 1 year in air conditioned room

15 Lime [ ] Immersion/drying

5

0 0 20 40 50

Fly Ash content,%

)

~3 e~

5° t 40

30

20

10

Cement { •

Lime { [] []

1 year in air conditioned room Immersion/drying 1 year in air conditioned room Immersion/drying

(b)

0 0 20 40 50

Fly Ash Content, % Fig. 12. Diagram showing the effect of fly ash content on tensile (Rt) and compressive (Rc) strength.

4. Conclusion

The addition of silico-aluminous fly ash to clay-based building materials which are cold stabilized and extrusion shaped, improves the quality of these products thanks to the physical and chemical properties of the fly ash (specific area, filler effect, pozzolanic effect). There- fore, the fly ash valorization by cold stabilized products is a good answer to the elimination problem. It allows good performance and low cost building materials. Indeed, a number of countries produce a lot of fly ash and the manufacturing process is rather sparing with the energy when compared to that of the traditional firing bricks.

References

[ 1 ] Molard, J.P., Camps, J.P. and Laquerbe, M., 1987. Etude de l'extrusion et de la stabilisation par le eiment d'argiles monomin6rale. Materials and Structures, 20: 44-50.

[2] Ayala, E.V., 1982. Cristallisation des argiles ~ froid. Th~se 3e Cycle, I.N.S.A., Rennes, France.

234 M. Temimi et al. / Resources, Conservation and Recycling 15 (1995) 219--234

[3] Albenque, M., et al., 1982. Etude et mise au point de produits en argile stabilis6e par le ciment. C.B.P.C. Rev., 737.4:217-226 and 738.5: 291-296.

[4] Temimi, M., Ait-Mokhtar, A., Camps, J.P. and Laquerbe, M., 1991. The use of fly ash in clay products stabilized with cement and lime, obtained through extrusion. Proceedings of the Intern. Conf. on Environ. Implic. of Constr. with Waste Materials, Maastricht, 10-14 Nov. 1991, Elsevier, Amsterdam, pp. 451--458.

[5] Temimi, M., Ait-Mokhtar, A., Camps, J.P. and Laquerbe, M., 1992. Utilisation des cendres volantes dans des produits argileux stabilis6s ~ froid et mis en forme par extrusion. Materials and Structures, 25: 397--403.

[6] Van den Berg, J.W., 1991. Quality and environmental aspects in relation to the application of pulverised fuel ash. Proceedings of the Intern. Conf. on Environ. Implic. of Constr. with Waste Materials, Maastricht, 10-14 Nov. 1991, Elsevier, Amsterdam, pp. 441-450.

[7] Berthe, M., 1986. Vingt cinq ans d'utilisation des cendres volantes en France. S.A. Surschiste du Groupe C.D.F., Madrid, Spain.

[8] Normes. NF P 15-300 to 15-312. AFNOR Ed., Paris, France. [9] Normes. NF P 15-400, NF P 18-400 et Suivantes. AFNOR Ed., Paris, France.

[ 10] Bierre, C., 1983. Stabilisation des argiles ~ froid. Rapport de D.E.A., I.N.S.A., Rennes, France. [ 11 ] Sergeev, E.M., 1971. Les forces de coh6sion et l'eau li6e dans les argiles. Bull. B.R.G.M., Sect. II, 1: 9-19. [ 12] Venuat, M., 1980. Le traitement des sols h la chaux et au ciment. Autoed., Pads, France. [ 13] Temimi, M.,1993. Utilisation des cendres volantes dans l'61aboration des mat6riaux argileux stabilis6s

froid ~ l'aide de diff6rents liants et mis en forme par extrusion. Th~se de Doctorat, I.N.S.A., Rennes, France.

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Valorization of fly ash in the cold stabilization of clay materials