The version presented here may differ from the published version or from the version of the record. Please see the repository URL above for details on accessing the published version and note that access may require a subscription.

Lime and/or Ordinary Portland cement (OPC) are the traditional binders used in soft soil 17 stabilisation. However, their manufacture has a negative impact on the environment. This 18 paper reports the results of experimental work for the optimisation of a binary blended 19 cementitious binder (BBCB) using two types of fly ash as an alternative for use in soft soil 20 stabilisation. The optimum content of the high calcium fly ash (HCFA) was initially 21 determined along with the effect of grinding activation on the performance of HCFA. 22 Subsequently, the effect of palm oil fuel ash (POFA) pozzolanic reactivity on the engineering 23 properties of soft soil, stabilised with HCFA, was investigated by producing different binary 24 mixtures of HCFA and POFA. Based on the Atterberg limits and unconfined compressive 25 strength (UCS) tests, the combination of POFA with HCFA results in a considerably lower 26 plasticity index (PI) and higher compressive strength than those obtained from the soil treated 27 with HCFA alone. Substantial changes in the microstructure and binders of the stabilised soil 28 over curing time were evidenced by SEM imaging and XRD analysis. A solid and coherent 29 *Revised manuscript with no changes marked Click here to view linked References structure was achieved after treatment with BBCB as evidenced by the formation of C-S-H, 30 portlandite and ettringite as well as secondary calcite.

Soil stabilisation using traditional binders such as Ordinary Portland Cement (OPC), has a serious negative environmental impact, specifically carbon dioxide (CO 2) emissions as a result of the manufacture of OPC. Because of this, the use of sustainable binders has become a critical issue to help reduce cement production through the use of by-product materials. This research seeks to develop a new ternary blended cementitious binder (TBCB) to replace cement for soft soil stabilisation. Different ternary mixtures containing wastes i.e., high calcium fly ash (HCFA), palm oil fuel ash (POFA) and rice husk ash (RHA) along with flue gas desulphurisation (FGD) gypsum used as a sulphate activator and grinding agent, were examined. The results illustrate that ternary mixtures improved the engineering and mechanical properties of stabilised soil. The results indicated that the plasticity index (PI) was reduced ACCEPTED MANUSCRIPT from 20.2 to 13.0 and the unconfined compressive strength (UCS) increased after 28 days of curing from 202kPa to 944kPa using the optimum non-FGD activated mixture. FGD contributed significantly by increasing the UCS to 1464kPa at 180 days of curing, which surpassed that for the reference cement (1450kPa), and by improving the soil consistency limits; where the PI decreased to 11.7 using TBCB compared with 14.5 for the soil treated with the reference cement. X-ray diffraction (XRD) and scanning electron microscopy (SEM) analysis revealed substantial changes in the diffraction patterns and microstructure components of the TBCB paste over the curing period, confirming the formation of cementitious products. A solid, coherent and compacted structure was achieved after treatment with TBCB as evidenced by the formation of C-S-H, CH and ettringite.