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Modeling the RheologicalProperties of Concrete

Nicos MartysJames Sims

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Input•Cement Paste

–Viscosity–Yield stress

•Aggregates– grading– concentration

Input•Cement Paste

–Viscosity–Yield stress

•Aggregates– grading– concentration

Output Mortar/concrete•Viscosity•Yield stress

Output Mortar/concrete•Viscosity•Yield stress

Prediction

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Viscosity vs. Solid Concentration

050

100150200250300350400

450500

0.85 0.90 0.95 1.00

Φ/ΦΦ/Φ ∗∗

µ' (

Pa.

s)

Mortars w/o HRWRAConcretes w/o HRWRAMortars with HRWRAConcretes with HRWRAIntermediate concretesConcretres w/ SFModel

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What is Concrete?

• Aggregates: 1- 20 mm

• Sand: 0.5 - 1 mm

• Fine fillers: < 5 µm

• Cement: 1-100 µm

• Water

• Chemical admixtures

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Divide and Conquer

• Cement Paste: Water + Cement Particles +Admixtures + …

• Mortar: Cement + Sand• Concrete: Mortar + Aggregate

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Dissipative-Particle-Dynamics

• Mesoscopic particles represent clusters ofmolecules.

• Interactions conserve mass and momentum,isotropic and Galilean invariant producehydrodynamic behavior consistent withNavier-Stokes equations.

• Molecular Dynamics: Brownian motion +velocity dependent dissipation.

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Dissipative Particle Dynamics

ijijii epprrr ∑Ω+=′

ii

ii pm

trr

rrr ′+=′δ

ijjiijjiij epprrWrrrrr

⋅−−Π−=Ω )()( ω

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Suspension of spherical aggregates

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Tracking of particle motion

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Relative viscosity vs.packing fraction

de Kruif, van Lersel, Vrij, Russel

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Tumbling of an aggregate undershear

Jeffrey’s tumble

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Ellipsoidal aggregates under shear

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High solid fraction suspension under shear

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Rebars

Flow under gravity between rebars

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Future Work

• Larger particle size distribution• Add inter-particle interactions

• Model flow in more complex geometries• Flow around rebars• Multiphase flow