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

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The paper describes development of a cost-effective, lower-carbon geopolymer grout for filling the annular space around tunnel-boring-machine (TBM) tunnels. Conventional grouts typically rely on Portland cement, whose production has a substantial carbon footprint and whose material properties have limitations. To offer a practical alternative, the researchers formulated a two-component grout using calcium-rich fluidized-bed coal ash as the aluminosilicate source and standard 3.2-ratio sodium silicate as the activator. Bentonite and admixtures were evaluated to control suspension, bleed, viscosity, and setting.<br /><br />Laboratory testing, including methods adapted from standard cement-grout tests, assessed slurry flow, bleed, gel time, and compressive strength. The resulting slurry had low initial viscosity and could be pumped using existing equipment. Gel times were controllable, and the set grout achieved compressive strengths comparable to those of cement-based grouts. Increasing sodium silicate generally lengthened gel times and increased strength, while bentonite reduced bleed but could cause viscosity to build over time and lower compressive strength. Formulation and admixture choices therefore require balancing stability, pumpability, and strength.<br /><br />Cost modeling indicated that the grout could achieve equivalent material cost per cubic metre to conventional Portland-cement grout when designed to meet comparable performance needs. Its use of fluidized-bed ash and reduced cement content also offers a lower environmental footprint. An expandable version was technically feasible but proved too costly for standard TBM applications.<br /><br />The authors conclude that fluidized-bed-ash geopolymer grout is a promising alternative, but further independent testing is needed, particularly for permeability, durability, tensile strength, and bond performance.

Keywords

geopolymer grout

tunnel-boring-machine

fluidized-bed coal ash

sodium silicate activator

Portland cement alternative

annular space filling

low-carbon material

bentonite admixture

compressive strength

cost-effective grout