Mechanical Properties of Palygorskite Clay Stabilized with Polyelectrolytes

Two polyelectrolytes of opposite charges, sodium polystyrene sulfonate (PSS) and polydiallyldimethylammonium chloride (PDADMAC), were investigated to stabilize palygorskite clay at varying dosages of 0.2, 0.8, 1.6, and 3.2 % by the dry weight of the soil. Both PSS and PDADMAC improved the unconfined compressive strength of the palygorskite clay. PSS was effective at all the polymer contents studied after 7 days of dry curing and the strength increased with the dosages of PSS added, ranging from 2 MPa (0.2 % PSS) to 3.1 MPa (3.2 % PSS), compared with 1.5 MPa of the untreated soil. PDADMAC, on the other hand, showed comparable strength improvements as PSS did at the high polymer contents of 1.6 and 3.2 % but did not work at 0.2 and 0.8 % dosages. Under wet curing at 100 % relative humidity, PSS improved the strength of the clay by 40 % (620 kPa at 0.2 % PSS) to 77 % (764 kPa at 1.6 % PSS) compared to the untreated clay (440 kPa). PDADMAC exhibited less improvement than PSS under wet conditions but still worked at dosages of 0.8 and 1.6 %. Besides strength, the resilient modulus and fracture toughness of the treated specimens increased by approximately 10 % and 66 %, respectively, when treated with 1.6 % PSS, which was the optimum content based on the strength results. PDADMAC-treated palygorskite, however, exhibited cracking during curing for both tests, showing potential drying crack issues. The adsorption of PSS and PDADMAC on palygorskite clay were also measured using ultraviolet–visible spectroscopy, and binding between these polymers and palygorskite has been confirmed. The measured adsorption capacities of PSS and PDADMAC were comparable (2.9 and 2.7 mg/g, respectively), while the PSS was somewhat more efficient in improving soil mechanical properties.