Deep Foundations: Study on Effect of Drilling Fluids on Concrete Integrity-Paper

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The study examines how bentonite and synthetic polymer (PolyMud) drilling slurries affect concrete compressive strength during bored-pile and diaphragm-wall construction. Concrete cubes were tested after 7 and 28 days, using two mixing protocols and slurry quantities equivalent to 5%, 20% or 30% of the design-mix water volume.<br /><br />In Protocol 1, slurry replaced an equal volume of mix water, keeping the water-to-cement ratio broadly unchanged. At 28 days, all mixes exceeded the 48 MPa target mean strength. Strength generally remained consistent, although bentonite showed some decline as its proportion increased. PolyMud had no substantial adverse effect in these tests.<br /><br />In Protocol 2, slurry was added to the concrete, increasing the water-to-cement ratio. Strength decreased as the added slurry increased. At 30% addition, 28-day strengths fell to about 40–41 MPa, below the target mean; at 5% and 20%, results were around or above the target, with one PolyMud mix slightly below it.<br /><br />The results indicate that the effect depends on how slurry enters the concrete: replacing mix water had little impact under the tested conditions, while adding slurry—and thereby increasing the water-to-cement ratio—reduced strength, particularly at 30%. The authors stress preventing localized concrete–slurry intermixing during tremie placement and recommend using a separator at the tremie outlet. They also identify reinforcement bond and pile–soil skin friction as areas requiring further research.

Keywords

bentonite

PolyMud

drilling slurry

concrete compressive strength

bored-pile construction

diaphragm wall

water-cement ratio

tremie placement

concrete-slurry intermixing

reinforcement bond