Stabilization of calcareous subgrade soils with polyelectrolytes: mechanisms and mechanical properties

ABSTRACT

Organic polyelectrolytes, i.e. anionic poly(sodium 4-styrenesulphonate) (PSS), cationic poly(diallyldimethylammonium chloride) (PDADMAC) and their polyelectrolyte complexes (PECs) were evaluated for stabilisation of calcareous sandy subgrade soil. This paper investigated the effects of polymer type, surface charge type of PEC, concentrations of PEC solutions and dosages of polymer solutions added to the soil on improvement of soil mechanical properties. We found that anionic polymers, for both PECs and individual polyelectrolytes, were superior to their cationic counterparts in improving soil strength. Besides, the constituent polyelectrolytes, PSS and PDADMAC, worked better than their PECs for the specific soil investigated. The strength of polymer-treated soils was also found to increase with the increase in dosages of the polymer solutions as well as curing periods. Furthermore, polymer-treated soil specimens exhibited significant toughness improvement, which was higher than cement-treated samples. Scanning electron microscopy images revealed the abundance of long palygorskite fibres covering the surfaces of larger calcite and dolomite particles and linking surrounding aggregates after adding polymers. This observation suggests the interconnection of palygorskite fibres and their linking networks between and among coarse aggregates as the likely mechanism of polymer stabilisation of the soil studied.

KEYWORDS:

• Subgrade
• Soil stabilisation
• Polyelectrolytes
• Unconfined compressive strength
• Toughness
• Stabilisation mechanism

Acknowledgements

Open Access funding provided by the Qatar National Library. The findings herein reflect the work, and are solely the responsibility, of the authors. The authors would like to thank Dr. Wubulikasimu Yiming of Texas A&M University at Qatar for help with the SEM and particle size analyses. The assistance of Dr. Akshath Shetty and Dr. Said Mansour of Qatar Environment & Energy Research Institute, Hamad Bin Khalifa University with the XRD and XRF analyses is also gratefully acknowledged.

Disclosure statement

No potential conflict of interest was reported by the author(s).

Additional information

Funding

This publication was made possible by the QNRF grant (NPRP13S-0124-200160: Innovative techniques for stabilisation of Qatari soils and petroleum drill cuttings using organic polymers) from the Qatar National Research Fund National Priorities Research Programme (QNRF – a member of the Qatar Foundation).