Effects of specimen preparation methods on polymer–montmorillonite interactions and hydraulic conductivity of polymer-modified bentonite–sand mixtures

In this study, carboxymethylcellulose (CMC) was used to modify bentonite (PMB) via wet blending (WB) and dry blending (DB) methods and then polymer-modified bentonite–sand mixtures (PMBSM) were produced based on PMB. Free swell index and hydraulic conductivity ( k ) tests were conducted on these specimens. Several experiments, including X-ray diffraction (XRD), cation exchangeable capacity ( CEC ) and Fourier transform infrared spectroscopy (FTIR) were used to elucidate how polymer interacted with montmorillonite for different preparation methods. Scanning electron microscopy (SEM) and energy dispersive spectroscopy (EDS) tests were used to elucidate the PMBSM microfabric characteristics. Swell index results indicated higher swelling potential of WB-PMB than that of DB-PMB. XRD, CEC , and FTIR test results suggested that polymer intercalation between montmorillonite layers props interlayer spacing for WB-PMB. DB-PMB had a phase-separated interaction by which polymer chains did not interact with montmorillonite. Hydraulic conductivity tests indicated that low k , approximately 10 times lower than BSM, was maintained by DB-PMBSM for all bentonite contents (Bc). By contrast, WB-PMBSM and BSM had similar k under low Bc conditions (10 %). However, when the Bc increased to 30 %, WB-PMBSM exhibited lower k than either BSM and DB-PMBSM, suggesting that different mechanisms control k of WB and DB-PMBSM. Conceptual models were proposed, relating the interaction mechanism and hydraulic performance of PMBSM.