Design Mix Specifications of Plastic Concrete for Dam Cut off Diaphragm Walls-Paper

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The paper examines the design and quality specifications of plastic concrete used in dam cut-off diaphragm walls, which control seepage while accommodating deformation in surrounding ground. It emphasizes that plastic concrete is not structural-grade concrete: it is a low-strength, highly deformable, low-permeability material, closer in behavior to cement-stabilized soil.<br /><br />Its mix typically contains cement, bentonite slurry, aggregates, sand, water and admixtures. Mix design must balance impermeability and sufficient strength to retain shape with workability, cohesion and the capacity for large strains. Excess water can cause segregation, while higher cement content or larger aggregates may reduce the desired deformability. Aggregates below 12.5 mm are recommended.<br /><br />Trial mixes and project data show that confined compressive strength is generally higher than unconfined strength, and that measured performance depends on test conditions. The paper identifies unclear or unsuitable project requirements, including a 30 mm maximum aggregate size, missing tolerances and an unconfined failure-strain requirement of 5%. It recommends clearer, practicable ranges for strength and strain, with test conditions tied to the site’s ground and loading conditions. Suggested ranges include unconfined strength of 1.5–2.5 MPa, confined strength of 2.5–6.0 MPa, and permeability around 10⁻⁸ m/s.<br /><br />The authors conclude that specifications should not apply conventional concrete assumptions. Adequate material trials, consistent monitoring of workability and mix uniformity, and access to specialist testing are essential. Where specifications prove impractical, clients and contractors should promptly agree on feasible quality-control criteria and formally amend requirements.

Keywords

plastic concrete

dam cut-off diaphragm wall

seepage control

low permeability

deformability

mix design

bentonite slurry

unconfined compressive strength

confined compressive strength

quality specifications