Carbon-friendly Pneumatic Flow Mixing (PFM) to Rapidly Recycle Waste Mud for Land Reclamation in Hong Kong

Professor Choi, Clarence Edward   (Project Coordinator (PC))

Professor Ye Hailong   (Co-Investigator)

Lee Siew Wei   (Co-Investigator)

Duan Huanfeng   (Co-Investigator)

Tang Alan K.Y.   (Co-Investigator)

36

2023-02-01

2026-01-31

4901300

Carbon-friendly Pneumatic Flow Mixing (PFM) to Rapidly Recycle Waste Mud for Land Reclamation in Hong Kong

""Waste management"", ""reduction""

Environmental Sciences

Biology and Medicine (M)

GTF202110116

Green Tech Fund (Second Round)

2021

On-going

Please refer to Annex A for mud volume estimation and B for references.a)To provide experimental data for the application of low-carbon Pneumatic FlowMixing (PFM) as a new method of land reclamation in HK. The new method will recyclethe millions of cubic meters of annual dredged mud (EPD 2022; Appendix A) producedfrom routine harbour maintenance and coastal construction spoils as a new fill materialfor land reclamation. It is expected that additional waste mud will be produced fromconstruction spoils and dredging for the construction of link roads and infrastructuredevelopment for the Lantau Tomorrow Vision (LTV) initiative. As such, PFM will providea means to manage and recycle this newly generated waste mud instead of disposing itin sediment pits located in the open sea.b)To investigate the use of low-carbon binders based on geopolymers that have beenproven to mechanically perform well in marine environments (i.e., quick lime, binarylime- metakaolin binder, and slag-based geopolymer binders) for use in PFM insteadof traditional Portland cement, which contributes to about 7% of the globalanthropogenic carbon emissions annually (Maddalena et al. 2018). In fact, the cementinjected into the ground using another reclamation technique (i.e., Deep CementMixing) for the Third Runway of the Hong Kong International Airport (HKIA) wasestimated to be about 1% of the global cement consumption at the peak of itsconstruction. The embodied carbon emission is estimated to be equivalent to 12% ofthe HK’s annual footprint. It is expected that low-carbon binders will play a pivotalrole in the decarbonisation efforts of the construction industry. Based on similarstudies, it is expected that alternative binders have the potential to reduce theembodied carbon emissions by up to 70% compared to the use of traditionalPortland cement (Juenger et al. 2011; Jiang et al. 2014).c)To provide an optimised low-carbon PFM design and its corresponding geotechnicaldesign parameters specifically for HK mud. Existing overseas experience is insufficientfor HK because the properties of the mud in HK is fundamentally different comparedwith the mud overseas. The resulting mechanical properties of the stabilised mud arehighly dependent on the organic and water contents of the parent mud (Kitazume2016). An optimised low-carbon PFM design will minimise the overuse of constructionmaterials (i.e., expensive binders) and the generation of excess spoils.d)To reveal the geotechnical risks of using low-carbon PFM for different geotechnicalapplications, including land reclamation, backfill to support seawalls, shallowstabilisation, and post-reclamation excavation for temporary works. By identifying theprevailing failure mechanisms for different geotechnical applications, the factor ofsafety used in subsequent design can be optimised for safe and cost-effectiveconstruction.e)To develop a high fidelity numerical tool to model the multi-phase mixing andtransport of the stabilised mud in pipelines to enable field scale operations of low- carbon PFM (i.e., position of barges for mixing in the field; length and diameters ofpipelines required; intervals between pulses of compressed air and its pressure;predicted ejection pressure from the pipelines for land reclamation and backfill).f)To provide the world’s first set of design guidelines for low-carbon PFM withconsideration of post-reclamation construction risks. The guidelines are timely and willbe used by the Sustainable Lantau Office (SLO) and Civil Engineering and DevelopmentDepartment (CEDD) to apply low-carbon PFM to the LTV initiative, which is expected tocommence construction in 2027.