Applied Clay Science 13 Ž1998. 245–253
Making building products by extrusion and cement stabilization: limits of the process with montmorillonite clay M. Temimi ) , K. Ben Amor, J.P. Camps I.N.S.A. Laboratoire G.T.Ma. 20, aÕenue des Buttes de Coesmes, 35000 Rennes, France ¨ Received 12 June 1997; accepted 27 May 1998
Abstract The addition of cement to a montmorillonite clay does not result in an adequate stabilization of end products which are extruded. This can be explained as follows: firstly, Ca2q ions of the binder are adsorbed by montmorillonite preventing the hydration of the binder and secondly, montmorillonite is very susceptible in contact with water because of its expansive property. Other mixtures have been tested by substituting progressively montmorillonite by kaolinite which has been successfully used in some previous research works. A ‘stabilization threshold’—corresponding to the minimum amount of montmorillonite and defined by a water resistance criterion—allows to determine under which conditions extrusion is possible. It appears that clay masses containing more than 5% montmorillonite cannot be stabilized with economically justified amounts of cement. Silico–aluminous fly ash has been used in such cases in order to benefit from the filler and possibly pozzolanic effects of this additive. The use of fly ash allows also to contribute to the problems of waste elimination. The results show that the products containing fly ash have a good dimensional stability, water resistance and mechanical properties. A small quantity of montmorillonite Ž5%. acts in such a case as a plasticizer. q 1998 Elsevier Science B.V. All rights reserved. Keywords: montmorillonite; stabilization; extrusion; cement; kaolinite; fly ash
1. Introduction Previous works carried out by Molard et al. Ž 1987. and Temimi Ž 1993. related to the cold stabilization by cement of extruded clay products, have )
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[email protected] 0169-1317r98r$19.00 q 1998 Elsevier Science B.V. All rights reserved. PII: S 0 1 6 9 - 1 3 1 7 Ž 9 8 . 0 0 0 2 5 - 8
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shown that it is possible, under some conditions, to make building materials with qualities that can be compared to those of more traditional products like fired earth bricks and concrete blocks and with a cost which can be kept lower, because of the lower energy they need for their processing. As an example, the so-called S.B.F. process ŽStabilisation des Briques a` Froid. , was tested successfully in an experimental house built in the area of the I.N.S.A. in 1980. Another more recent example is the brick factory in Burkina Faso where building elements according to the S.B.F. process are produced. The price of these products is about three times cheaper than fired earth bricks. Recent experiments by Ben Amor et al. Ž1997. were not so successful because the used earth contained a certain amount of montmorillonite. Its expansive behaviour and its capacity to adsorb Ca2q ions from the cement have induced a negative effect. Therefore, different compositions have been tested by substituting progressively montmorillonite by other components, such as kaolinite and fly ash, in order to determine the optimum conditions for cold stabilization of extruded clay products.
2. Materials and methods Clay is necessary to give cohesion and plasticity to a mass to be extruded. Two clays were used: – Montmorillonite from C.E.C.A. Ž Honfleur, France. . It is commercialized as a powder under the name of ‘Bentonite Clarsol FTP 3’. The chemical composition of this clay is given in Table 1. – China clay Ž kaolinite. from the Ploemeur deposit ŽBretagne, France.. Table 2 gives the chemical composition of this clay. This clay was chosen because a number of tests had already been carried out in the I.N.S.A. laboratory highlighting its stabilization ability by several kinds of cements and allowing reliable comparisons between different stabilization methods. The fly ash used is a waste material from the electric plant of Cordemais ŽLoire Atlantique, France.. Its main components are silica and alumina. This material is chosen because of its filler and pozzolanic properties. As a binder, an ordinary portland cement ŽC.P.A. 55. was used. The main function of the binder Table 1 Chemical composition of montmorillonite SiO 2
Al 2 O 3
Fe 2 O 3
TiO 2
CaO
MgO
K 2O
Na 2 O
Li 2 O
60.2%
14.0%
3.8%
0.4%
1.1%
2.4%
1.1%
3.8%
Traces
Weight loss at 10008C s13.2%.
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Table 2 Chemical composition of china clay SiO 2
Al 2 O 3
Fe 2 O 3
TiO 2
CaO
MgO
K 2O
Na 2 O
Li 2 O
48.5%
37.0%
0.8%
0.1%
0.1%
0.2%
1.1%
0.1%
Traces
Weight loss at 10008C s12.1%.
is that it can stabilize the material because it creates bonds between elementary particles. The samples Ž16 = 4 = 4 cm. are extruded under vacuum by means of a laboratory extruder. After their extrusion, the samples are stored in an air-controlled room at 208C and 50% relative humidity. Different compositions are tested in order to define the threshold of the montmorillonite amount below which extrusion is possible. All the mixtures contain cement, clay Žmontmorillonite andror kaolinite. and water which is added to obtain a homogeneous and plastic paste. Table 3 shows the composition of the different mixtures Žon a dry weight basis. . In order to define the stabilization conditions of soil containing an expansive clay Ž e.g., montmorillonite., a water resistance test had been developed. After a
Table 3 Composition of mixtures studied Mixtures
Montmorillonite Ž%.
Kaolinite Ž%.
Cement Ž%.
M.1 M.2 M.3 M.4 M.5 M.6 M.7 M.8 M.9 M.10 M.11 M.12 M.13 M.14 M.15 M.16 M.17 M.18 M.19 M.20
0 36 0 4 7 8 32 0 7 14 20 28 30 40 50 60 14 28 10 15
90 54 80 76 73 72 48 70 63 56 50 42 40 30 20 10 46 36 15 5
10 10 20 20 20 20 20 30 30 30 30 30 30 30 30 30 40 40 75 80
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Table 4 Scale of quality Mark
Quality
5 4 3 2 1 0
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
28-day period of storage in the air-controlled room, the samples were immersed in distilled water for 1 week. The ability of the material to resist a water attack and to keep its initial cohesion is determined based on the different grades of alteration given in Table 4, according to Bierre Ž1983. . However, this test has the disadvantage that large quantities of material have to be used and a long preparation time is required. Therefore, in parallel to the extrusion tests, a ‘methylene blue’ test is also carried out on the studied
Table 5 Marks of water resistance, values of methylene blue and specific areas of all the mixtures Mixtures
Marks of water resistance
Value of methylene Žgr100 g.
Specific area Žm2 rg.
M.1 M.2 M.3 M.4 M.5 M.6 M.7 M.8 M.9 M.10 M.11 M.12 M.13 M.14 M.15 M.16 M.17 M.18 M.19 M.20
5 0 5 5 4 4 0 5 5 3 3 2 0 0 0 0 4 3 5 5
1.20 8.20 1.00 1.40 1.60 1.80 6.80 0.80 1.40 2.20 3.00 4.60 5.00 7.20 8.00 9.30 1.80 3.00 0.60 0.80
25 172 21 29 33 37 143 17 29 46 63 97 105 151 167 195 37 63 12 17
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Fig. 1. Diagram showing the variations of water resistance marks vs. the values of methylene blue ŽV.B...
mixtures. This test gives an indication of the specific surface area of particles ŽNorme NFP 18 592, 1980. . A relation exists between the behaviour of clay material in water and the specific surface area of this material ŽLautrin, 1989.. If
Fig. 2. Diagram of the stabilization areas of clay–cement mixtures vs. the values of methylene blue ŽV.B...
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Fig. 3. Diagram showing the variations of shrinkage Ž D Lr L. n vs. time for: Ža. 20% cement, Žb. 30% cement.
this method can be applied, it might have many advantages: a rapid and simple method which only requires a small quantity of material. Additional tests are carried out in order to determine the quality of the stabilization of extruded products, i.e., shrinkage and mechanical resistance Ž i.e., tensile and compressive strength. as a function of time.
Fig. 4. Diagram showing the variations of tensile strength ŽRt. vs. time for: Ža. 20% cement, Žb. 30% cement.
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3. Results and discussion 3.1. Water resistance and stabilization threshold Table 5 summarizes the results of the methylene blue values Ž and the corresponding specific surface area. and the water resistance classes of all the mixtures. In Fig. 1, it can be seen that the methylene blue values are indicative for the behaviour in water of an extruded product. A value of 1.4 gr100 g Žclay–cement. corresponds to a value of 5 and is considered as the ‘stabilization threshold’, indicating the transition from a bad to a good behaviour. The results can be plotted in a triangular diagram ŽFig. 2.. A clay mass containing e.g., 5% of montmorillonite Ž with regard to the weight of clay components. has to be stabilized with 20% cement Ž with regard to the weight of all dry components. in order to avoid problems during construction. The proportion of cement is 30% when the amount of montmorillonite is 10%. For clay masses containing more than 10% of montmorillonite, the stabilization process requires substantial amounts of binder. This consequently results in lower economic benefits. 3.2. Shrinkage Fig. 3Ž a. and Ž b. show that the largest shrinkage of all the mixtures occurs at an early stage, i.e., during the first days, and remains practically constant after about 28 days. Shrinkage becomes more pronounced with higher montmorillonite quantities. This can easily be explained: the larger the montmorillonite
Fig. 5. Diagram showing the variations of compressive strength ŽRc. vs. time for: Ža. 20% cement, Žb. 30% cement.
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Table 6 Composition of mixtures studied Mixtures
Montmorillonite Ž%.
Kaolinite Ž%.
Cement Ž%.
Fly ash Ž%.
M.7 M.21 M.22 M.23
32 24 10 4
48 36 15 6
20 20 20 20
00 20 55 70
Table 7 Synthesis of results obtained on fly ash added samples Mixtures
M.7 M.21 M.22 M.23
Water resistance
2 2 3 5
Shrinkage Žat 28 days. Ž%. 3.25 2.83 1.32 1.10
Mechanical resistance Žat 28 days. Nrmm2 Tensile
Compressive
2.70 3.85 4.90 5.00
5.70 9.17 14.95 16.00
content, the larger the specific surface area and the larger the shrinkage ŽJouenne, 1975.. Furthermore, the binder hydration in these mixtures is less efficient. Indeed, since montmorillonite has a higher specific surface area Ž 80 m2rg. than kaolinite Ž11.5 m2rg. , the substitution of montmorillonite for a certain amount of china clay reduces the quantity of free water present in the mixture ŽBen Amor, 1995. . The lower the free water amount, the less is the binder hydration. 3.3. Mechanical resistance As it is illustrated in Figs. 4 and 5, the samples containing montmorillonite have a smaller resistance, especially tensile strength. This is due to the cement hydration: more montmorillonite causes efficient hydration of cement. Subsequent to this study, a waste material Ž silico–aluminous fly ash. was also used. The composition of the different mixtures are given in Table 6. The obtained results, summarized in Table 7, clearly demonstrate that water resistance and mechanical properties of the samples containing fly ash are improved and that the shrinkage is reduced. 4. Conclusions The clay masses containing important proportions of montmorillonite cannot be used as a basic material in the extrusion process. Indeed, the end products are
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not stabilized efficiently, mainly because of the properties of montmorillonite Žadsorption of Ca2q ions liberated by the binder and expansion.. A stabilization threshold has been determined. It has allowed to define the minimum amount of montmorillonite below which the stabilization is conclusive. This amount is 5% when the clay mass is stabilized with 20% of cement and 10% if cement content is 30%. More than 10% of montmorillonite requires too much cement to justify the process conditions. In this case, the extrusion process is not more economic. The use of silico–aluminous fly ash in clay materials improves the quality of these products. Therefore, it is a good answer to the elimination problem when fly ash cannot be valorized, besides the obvious reduction of the product cost.
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