A Novel pH-neutral Silicate Gel for Bottom Seals-Paper

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The paper presents Neutrogel, a new sodium-silicate gel grout for temporary groundwater barriers, particularly deep-seated bottom seals. Conventional sodium-silicate grouts often used sodium aluminate as a hardener, producing highly alkaline leachate and releasing aluminum, which can harm soil and groundwater. Environmental regulations consequently restricted their use.<br /><br />Neutrogel replaces the metal-containing hardener with a biodegradable natural acid. The resulting gel forms under acidic conditions, while its pH remains stable during setting. Its environmental performance is assessed using an inverted-column test, which measures leachate at the grout–groundwater interface. Tests showed a pH well below the regulatory limit of 10, electrical conductivity at only 20–25% of the limit, and total organic carbon below the permitted threshold. Field trials in fine sand also demonstrated effective grout penetration.<br /><br />The grout was used to construct a 3,620 m² bottom seal at a building project in Karlsruhe, Germany. A post-grouting pumping test measured a residual flow of about 2 m³/h across the excavation—approximately one-tenth of the specified limit—indicating that the seal was technically effective. The project’s permeation-grouting solution had an estimated carbon footprint of just 13% of that of a conventional jet-grouted seal, largely because it required much less material.<br /><br />The authors conclude that environmentally compliant chemical grouting can restore a useful sealing technology without necessarily increasing cost. Neutrogel provides an economical, lower-impact alternative for applications requiring hydraulic sealing, while jet grouting remains appropriate where structural strength is also needed.

Keywords

Neutrogel

sodium-silicate grout

groundwater barrier

bottom seal

biodegradable acid hardener

environmental compliance

leachate pH

permeation grouting

carbon footprint

jet grouting