Magnesium hydroxide, seawater and olive mill wastewater to reduce swelling potential and plasticity of bentonite soil

•We prepare samples of clayey soil mixed with olive mill wastewater, mg-hydroxide and seawater.•We study the changes in geotechnical and mineralogical properties of the soil.•The high swelling potential of clayey soil diminishes after treatment.•Some of the treatments could make the soil be suitable for use in construction.

The improvement in physical properties of expansive soils after addition of non-conventional additives is studied. The tested agents were magnesium hydroxide, seawater and olive mill wastewater. The use of these materials, which can be obtained from natural sources or as by-products derived from industrial processes, can lead to greater sustainability of the construction process. In the case of olive mill wastewater, its management is still an issue in many regions where production of olive oil is a main economic activity. The untreated soil used was a sample of pure bentonite. To evaluate the effects of the additives, the physical properties of the soil such as compaction, consistency, bearing capacity and swelling pressure were studied. The mineral compositions of the treated soils were evaluated by XRD tests. Test results showed that the non-conventional additives tested reduced the plasticity and the swelling potential of the soil. Indeed the tested agents proved to be very effective to produce reductions in the swelling pressure of 60–87% in comparison with the original swelling pressure of the untreated bentonite. X-ray diffraction tests proved that magnesium hydroxide, seawater and olive mill wastewater promoted mineral changes within bentonite, especially smectite to illite conversion. This conversion is due to the alterations promoted by the additives on conditions such as pH and concentration of different cations (magnesium, calcium, potassium, etc.) The mineral modifications occurred are behind the sharp reductions in swelling pressure and plasticity of bentonite.