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Improvement of clayey / lateritic materials for road pavement application

Laterite is a highly weathered material, rich in iron oxides, alumina or both. It is almost devoid of bases and primary silicates, but may contain large quantities of quartz and kaolinite. Nodules are concretions originally composed of kaolinite-associated hematite and are characterized by a deep red color and a high hardness. They are usually the product of sandstone rocks alteration often strongly weathered and oxidized (iron oxides and / or aluminum oxides). They can be found just below lateritic hills as scree.
In this work, a mineralogical and mechanical study of clayey / lateritic soils used in road construction are presented. These lateritic soils can be improved through a treatment based on the use of lateritic nodules taken in situ or other hydraulic road binders.
Improvement of geotechnical parameters of lateritic materials when combined with nodules is discussed in the light of chemical and mineralogical observations by Environmental Scanning Electron Microscopy (ESEM) coupled to an X-ray Energy Dispersive Spectrometer (EDS).
More precisely, this paper shows that lateritic soils treatment with 10% nodules allows making them usable in road construction. Parameters as CBR indices are highly increased. In order to confirm and further characterize the laterites behavior before and after treatment, comparative mechanical tests (shear tests and oedometer tests) were performed. Enhanced values are found for cohesion and internal friction angle. Treatment made soils passing from weak mechanical properties close to a sandy clay material predominantly sandy to a soil with strong and sufficient properties.
Oedometer tests showed a decrease in void ratio and a calculated hydraulic conductivity. Moreover, treated soil is less compressible than the soil without treatment: compressibility coefficient is reduced, and oedometer modulus is greater. The nodules thus increase laterite rigidity, due to the relatively high amount of iron. The system improving is also confirmed by the increase of the bulk density.
We can conclude that nodules, with their high iron oxide content (hematite) and kaolinite play a stabilizing role on the fine fraction of the existing matrix (presumably illite). Crushed nodules densify the mixture and increase soil bearing lateritic by a contribution of kaolinite from the heart of the nodules. Linear swelling of the untreated material is much higher than that of the treated one. Therefore the swelling potential of the untreated material is also reduced.

Author(s):

Nadia Saiyouri    
Bordeaux University, Institute of Mechanics and Engineering, I2M GCE, UMR CNRS-5295, Bordeaux
France

Mahamadou Souley Issiakou    
Bordeaux University, Institute of Mechanics and Engineering, I2M GCE, UMR CNRS-5295 / A. Moumouni University Niamey – Geology and Geomorphology Laboratory, Niamey, Niger
France

Richard Fabre    
Bordeaux University, Institute of Mechanics and Engineering, I2M GCE, UMR CNRS-5295, Bordeaux
France

Yannick Anguy    
Bordeaux University, Institute of Mechanics and Engineering, I2M SPI, Treffle ParisTech, UMR CNRS-5295 Bordeaux
France