Development of a Cost-Effective Geopolymer-Based Annular Grout with Expansion Properties-PPT Presentation

PPT Presentation

Pdf Summary

The presentation evaluates fluidized bed coal ash (FBC) as a lower-carbon alternative to conventional cement-based annular grout used with tunnel boring machines (TBMs). Existing two-component cement grouts perform well but have a substantial CO₂ footprint and rising costs.<br /><br />The proposed FBC grout uses coal ash with bentonite, water, admixtures, and sodium silicate. Unlike higher-cost geopolymer formulations based on slag or fly ash and specialty activators, the FBC approach aims for cement-comparable costs using a conventional sodium silicate. Its properties can be adjusted by changing the water-to-solids ratio, bentonite, silicate concentration, additions of cement or lime, admixtures, and ash source.<br /><br />Typical test results showed workable slurry flow, controlled bleeding, gel times of 20–45 seconds, and compressive strength of 1–2 MPa after one day and 2–4 MPa after seven days. Testing in a TBM simulator produced compressive strength about 10% higher than standard testing.<br /><br />The scoping assessment indicates that FBC grout could be compatible with existing equipment, cost similarly to cement grout, and have roughly one-third of its CO₂ footprint. However, current formulations require higher admixture and sodium silicate loadings. The formulation also needs adjustment for local ash sources, and further optimization could reduce costs and improve performance. Geopolymer grouts offer strong material properties but remain more expensive.

Keywords

fluidized bed coal ash

FBC grout

tunnel boring machines

annular grout

cement grout

carbon footprint

sodium silicate

bentonite

compressive strength

geopolymer grout