Investigation of Pozzolanic Binders Containing Calcined Laterites
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INVESTIGATION OF POZZOLANIC BINDERS CONTAINING CALCINED LATERITES JEAN PERA, JEAN AMBROISE AND ALI SADR MOMTAZI Laboratoire des Mat~riaux Min6raux, Bft. 407, INSA de Lyon, Avenue Albert Einstein, 69621 VILLEURBANNE Cedex, FRANCE.
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ABSTRACT When heated at 750°C for five hours, African laterites show good pozzolanic activity. The kaolin content of the materials affects their pozzolanicity as indicated by lime reactivity. Blended cements containing 20, 30, 40, and 50% calcined laterite admixture were examined. The rate of hydration was studied from compressive strength up to 90 days of curing and the hydrates formed as measured by DTA and XRD. The burnt laterite addition considerably reduced calcium hydroxide content and contributed to the formation of hydrated gehlenite (C 2 ASH ) and gismondine (CASH). The best compressive streng hs were obtained with blended cements containing 30% calcined laterite. In some cases, there was no more portlandite in binders where the replacement level of cement by burnt laterite was 50% by mass. INTRODUCTION The purpose oh this study was to develop a new binder based on lateritic soil for use in developing countries. Red iron-rich laterites, which are found in huge layers covering most tropical and subtropical areas of the earth, are the largest source of cheap raw materials in many developing countries. Lateritic soils contain mainly clay minerals and iron oxides. They are neither suited for production of baked clay bricks nor production of concrete or calcium silicate blocks. They remain largely unexploited. Stabilization of laterites has been successful with both cement and lime [1, 2]. Another way of developing low cost building materials on the basis of lateritic soils was suggested by Ambroise et al. (3, 5]. After calcination at 800C, clay minerals are transformed into transition phases which display pozzolanic activity. The present paper describes tests performed on three African laterites. RAW MATERIALS Laterites Chemical compositions and physical properties of the laterites used are given in Table 1. Particle size distributions of each laterite were obtained using a laser diffraction instrument MALVERN 2200/3300. Small samples were dispersed in distilled water using a deflocculant (alcohol) and ultrasonics.
Mat. Res. Soc. Symp. Proc. Vol. 245. ©1992 Materials Research Society
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Table 1.
Chemical analysis and physical properties of laterites. Laterite LateriteNN°
Composition and physical properties
Li
L2
L3
Oxides (% by mass) SiO 2 A1203 Fe203 MgO CaO
12.3 12.3 54.2 0.2 0.3
45.3 19.9 20.9 0.1 0.3
76.8 9.4 5.7 0.2 0.4
2 Loss on ignition
16.0
10.9
5.3
Specific area (B.E.T.) m2/g
54
33
16
100
100
60
75
100 50 20
5
15
K2 0 TiO
Size - distribution passing 128 pm (%) 64 pm
12pm 4pm
1pm
0.1 0.8
20 2
0.4 0.8
40 5
0.2 1.6
5
2
The structure of laterite Ll, observed by SEM, was very porous; this morphology can explain the high value obtained for the specific area calculated from adsorption of nitrogen on powdered specimens. The mineralogical
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