Proceedings of National Conference”GEPSID” held on October 11-12, 2014, Ludhiana 422 EFFECT OF PHOSPHOGYPSUM AND COIR FIBRES ON STRENGTH AND SWELLING CHARACTERISTICS OF LIME STABILIZED BENTONITE Sujeet Kumar 1 , Vidya Tilak B 2 and Rakesh Kumar Dutta 3 1 Research Scholar, Indian Institute of Technology (BHU), Varanasi, Uttar Pradesh, India-221005, Sujeetkumar.ce@gmail.com, Tel.: +91-9696651536 2 PG Student, National Institute of Technology, Hamirpur, Himachal Pradesh, India-177005 3 Professor, Civil Engineering Department, National Institute of Technology, Hamirpur, Himachal Pradesh, India, 177005 Abstract: The paper presents the effect of addition of phosphogypsum and coir fibre on the compaction, unconfined compressive strength and swelling characteristics of bentonite-lime mix. The content of lime, phosphogypsum and coir fibre was varied from 0 to 10 %, 0 to 10 % and 0 to 2 % respectively. The curing period was varied from 3 to 28 days. The results of this study reveal that the dry unit weight and optimum moisture content of bentonite + 8 % lime increased with the addition of 8 % phosphogypsum whereas the dry unit weight decrease and optimum moisture content increases with the addition of 1.0 % coir fibres. The strength ratio of bentonite increases with the addition of lime-phosphogypsum-coir fibres. The swelling characteristics of bentonite were markedly reduced with the addition of 8 % lime, 8 % phosphogypsum and 1.0 % coir fibres. The end-time of primary swelling of bentonite + 8 % lime + 8 % phosphogypsum + 1.0 % coir fibres in duration of 40 days was 80 % less than that reached by bentonite. This accelerated reduction in swelling of bentonite brings new hope for the construction activities on such problematic areas. The microstructural development of bentonite modified with 8 % lime and 8 % phosphogypsum were studied through techniques like the scanning electron microscope and the electron dispersive absorption x-ray diffraction to account for the changes in the structure of bentonite with the addition of lime and phosphogypsum. Scanning electron micrographs of the bentonite specimens modified with lime showed the formation of cementing compounds in forms of compact matrix which increases with the increase in curing period. Further, this development led to the improvement in strength ratio which was also observed in strength test results. Scanning Electron Micrograph (SEM) and Electron dispersive absorption x-ray diffraction (EDAX) study shows the emissions of Ca, Si and hydrates and Ca, Al and S with the addition of lime and phosphogypsum in bentonite respectively. The improved strength characteristics and reduction in swelling of bentonite with the addition of lime-phosphogypsum-coir fibre can be used for the construction activities on such problematic areas. Keywords - Bentonite; Lime; Phosphogypsum; Coir fibre; Compaction, Unconfined Compressive Strength; Swell potential; SEM-EDAX.