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

Video Transcription

Video Summary

PQ developed a lower-carbon alternative to Portland-cement annular grout used in tunnel boring. Conventional two-component grout performs well but has a high carbon footprint and rising costs, with potential durability and permeability limitations.<br /><br />The team explored two approaches. A high-performance geopolymer using slag or fly ash met technical requirements, including rapid setting, but was too expensive. A more cost-competitive formulation uses fluidized-bed coal ash activated with conventional sodium silicate, sometimes with a small amount of Portland cement. It can be adapted to existing equipment and tuned to local ash sources.<br /><br />Testing showed suitable viscosity, bleed, set time and compressive strength. A lab-built tunnel-boring simulator better reproduced mixing and pressure conditions and produced higher measured strengths. The coal-ash grout’s estimated raw-material emissions were about 80 kg CO₂/m³, versus roughly 270 kg for the cement grout. Current costs are similar; carbon pricing could make the alternative less expensive, with further savings possible through formulation improvements.

Keywords

lower-carbon grout

tunnel boring

geopolymer

coal ash

Portland cement alternative