IMPROVEMENT OF PHYSICAL-CHEMICAL AND RHEOLOGICAL PROPERTIES OF GHARDAÏA LOESS (SOUTHERN ALGERIA) USING BENTONITE CLAY AND LIME ASMAA RAHMANI 1 *, ABDELKRIM HAZZAB 1 ,HADJ AIMER 1 ,ABDELLAH GHENAIM 2 , AND ABDELALI TERFOUS 2 1 Modeling and Computational Methods Laboratory, University of Saida Dr. Tahar Moulay , Saida, Algeria 2 Laboratory of Mechanics and Environment ICUBE/ INSA, National Institute of the Applied Sciences, Strasbourg, France Abstract—Loess is a collapsible soil; when it collapses, it can cause significant damage to structures built on it. Improvement in the stability and strength performance of loess is necessary to meet engineering needs. In the present study, the effects on the physical-chemical and rheological characteristics of Ghardaïa loess of adding bentonite and lime (southern Algeria) were examined. Rheological characterization of suspensions was implemented to assess the mechanical sensitivity of the bonds and the structural inter-particle resistance to both the chemical effect and mechanical impact. By analyzing the viscosity results and the evolution of the rheological parameters, the improvements needed in terms of the resistance characteristics of the loess-bentonite and loess-lime mixtures were evaluated and confirmed. The loess physical sensitivity was examined through grain-size distribution and plasticity properties. The pH and electrical conductivity of the mixtures were also used to explore structural modifications. Physical test results showed that introduction of the additives changed the loess texture and improved the plasticity of mixtures. Chemical examination (via change in pH and electrical conductivity) revealed the structural changes in the mixtures studied. Rheological test results showed that increasing concentrations of bentonite and lime improves the mechanical strength and increased the yield stress, consistency, and viscosity of the suspensions. The creation of cement interactions between mixture particles explained the increase in those parameters. Hydration, agglomeration, and inter-particle flocculation induced by the additives promoted these interactions. The experimental results led to the conclusion that bentonite and lime may represent an effective means to improve the performance in terms of preventing loess collapse and to increase its resistance to mechanical impact. The results presented in the present study may provide a geotechnical and rheological working database for the control and treatment of loess collapse and landslides in the region under study. Technical data related to loess may, therefore, be beneficial in terms of civil engineering, public works, hydraulics, and the manufacture of construction materials. Keywords—Bentonite . Lime . Loess . Physical-chemical properties . Rheology . Stabilization INTRODUCTION Loess is defined as a wind-blown deposit, composed of silt, fine sand, calcite, and clay (Muhs 2018). This type of soil is located in arid and semi-arid regions (Li et al. 2016). It has aroused considerable interest from members of the scientific community particularly in geotechnical characterization, microstructure, deformation sensitivity, collapsibility, etc. (Yuan and Wang 2009; Marschalko et al. 2013; Chen et al. 2019). Results from previous studies showed that loess can be characterized by an open structure. It may collapse and deform due to disturbances such as loading and wetting. This frequent- ly causes geotechnical disasters such as landslides and settling (Delvoie 2017). The fragility of loess inter-particle forces remains the principal cause of these disasters. In order to cope with these problems, resistance-improvement techniques have been proposed. They consist of strengthening and stabilizing the inter-particle bonds (Jefferson et al. 2005). Most techniques rely on adding cementing agents, such as clay and lime (Pei et al. 2015; Tabarsa et al. 2018). Recent studies explored possible improvement in loess stability and revealed that adding cement, nano clay, fly ash, and polymers can: (1) produce a change in plasticity; (2) improve compressibility; and (3) increase optimal moisture content, California Bearing Ratio (CBR) (Zhang et al. 2017), and cohesion; and (4) im- prove the shear strength. In contrast, the maximum dry density, friction angle, deformation, and loess collapsibility were re- duced (Zhang et al. 2017; Tabarsa et al. 2018; Kong et al. 2018; Phoak et al. 2019; Ma and Ma 2019). Due to their hydration and dehydration capacities, clay minerals possess many useful properties for stabilizing lique- fied soils. They are, therefore, utilized as binders, plasticizers, and lubricants (Evstatiev 1988; Firoozi et al., 2017). Among the clay materials, montmorillonite in bentonite is character- ized by a large water-retention capacity, and by absorption and adsorption properties. Injecting clay into the loess can, there- fore, reduce porosity, decrease or eliminate collapsibility, and increase the deformation modulus (Evstatiev 1988; Jefferson et al. 2005). Other techniques have shown that the addition of lime significantly improves the properties of clayey soils by reducing sensitivity to water and increasing the mechanical strength (Bell 1996; Calik and Sadoglu 2014; Babu and Poulose 2018). Soil resistance is, thereby, reinforced (Ghobadi et al. 2014; Gao et al. 2018). Rheology has many advantages for exploring and evaluating the performance of additives. Its ability to help in examining the modification of soil mechanical properties has been proven (Moreno 2001). Indeed, rheological research has focused on the risks of liquefaction, landslide, and loess collapse as shown in Table 1 where the results note the existence of a relationship Clays and Clay Minerals * E-mail address of corresponding author: ra.hydrau@outlook.com DOI: 10.1007/s42860-020-00092-8 # The Clay Minerals Society 2020