Modeling Engineered Cementitious Composites

(ECC)

June 16-18, 200819th ACBM/NIST Computer Modeling Workshop

Gaithersburg, Maryland

Ravi Ranade

University of MichiganDepartment of Civil & Environmental Engineering

Advanced Civil Engineering – Materials Research Lab (ACE-MRL)

19th ACBM/NIST Computer Modeling Workshop 2

Engineered Cementitious Composites (ECC) An ultra ductile mortar based composite reinforced with

short random polymer fibers. (Marshall & Cox, 1988 & Li, et al, 1992)

Cement + Sand + Water + Fibers (≤ 2% by vol)

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Tensile strain hardening & Crack width PVA-ECC (Source: Yang et. al.,2008)

PVA Fibers (Length = 12 mm, diameter = 39 µm)

Multiple Cracking

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“Bendable” ConcreteACE MRL

4 point bend test on an ECC Specimen

Multiple cracking at the bottom

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Design Philosophy @ ACE-MRLACE MRL

Structural Properties

Cement Aggregate

Water Slag

Microsilica Fly Ash

Chemical Admixtures

Micromechanical Parameters

Micromechanical Models

Composite Engineering

σcσtEεcrGFEn

Composite Properties

Fiber

Matrix

Lf/dfdfVfEf

Gd, τ, f

Em(σm,Gm)

Interface

Performance Driven Design Approach for ECC (Li, 1993)

Scale Linking in ECC

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Single Fiber PulloutACE MRL

Fiber

P, u

Matrix Crack Surface

Perfectly Bonded Zone τ0, Gd

Debonded Interface τ0

P

u

β > 0

β = 0β < 0

δc

P, σ, u = Single Fiber Force, Stress, Rel. Disp.δc = Critical Displacement (Debond –Pullout)τ0 = Interfacial Frictional StressGd = Chemical BondLe = Embedment lengthEf, df = Young’s Mod, dia of fiberβ = Slip hardening coeffiecientη = (VfEf)/(VmEm)

u

ModelExperiment

Unit Cell

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Bridging Stress – One crackACE MRL

RVE

σB

δ

Φ, z = angle & embedment length variationsVf = Fiber Volume Fractionf = snubbing factorAlso Micro spalling, cook-gordon effects can be added

σB – δ curves from model & experiments on notched ECC specimen

19th ACBM/NIST Computer Modeling Workshop

P

u

β > 0

β = 0β < 0

σ

δ

ss

dJ sssstip

0

)(

0

000

' )(

dJb

σ0

σss

δ0δss

Lf/dfdfVfEf

Gd, τ, f

Em(σm,Gm)

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Analysis & ModelingACE MRL

ITZ

Fiber

Matrix

P, u

Matrix Crack Surface

Perfectly Bonded Zone Debonded Interface

σ

δ

RVE

Beam

10-6 - 10-5 m 10-4 - 10-3 m 10-3 - 10-2 m 1 m 102 m

Single Fiber Pullout

Multiple Fibers bridging a crack

Structural Element with multiple cracks

Structure with ECC elements

Microstructure -Composite Phases

σ

ε

FiniteElementModel

Exp/Estimate Exp/Model Exp/Model Exp/Model

Need a model

Roppongi Tower, Japan

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Modeling ECC Microstructure modeling of ECC similar to NIST models

for downscale linking which will provide the control of properties at sub-micro & nano levels (C-S-H growth) –allowing to engineer those properties to our benefit.

Modeling Challenges: Model fiber & its interface with the matrix. Fiber dispersion and simulation of rheology of the mix Growth of C-S-H and other hydration compounds around the fiber. Estimation of autogenous shrinkage and its competition with the

tensile strength development. Estimation of transport properties and predictions of service life and

life cycle cost. Hydration modeling for cement replacements such as slag, silica

fume, fly ash, etc and their effects on strength and durability Change in properties with time due to deterioration/rehealing

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Problem of Cracking Random cracks in concrete due to various unpredictable

reasons (sensitive to construction practice and environmental conditions, as well as reinforcement details and structural size) lead to untimely deterioration and make the correct service life prediction almost impossible.

ECC Advantage: Smaller crack widths with a known upper limit (~60 μm), independent of reinforcement details and structural size – truly a material property.

Models in place for chloride ion diffusion, permeability, and other transport properties for better prediction of service life of ECC structures. (Need transport simulation in micro-cracked ECC in service)

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Summary Capabilities developed at NIST for modeling

microstructure of concrete can be extended to ECC. ECC is emerging from research laboratory to full scale

field applications. A complete set of computational tools linking various

scales from nano-micro level to the structure level will contribute to strong, durable, economic and sustainable infrastructure.

An open invitation to collaborate!

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References Yang, E.H., and V.C. Li, “Fiber-bridging Constitutive Law of Engineered

Cementitious Composites”, J. Advanced Concrete Technology, 6(1) Feb., 2008.

Sahmaran, M., and V.C. Li, "Durability of Mechanically Loaded Engineered Cementitious Composites under Highly Alkaline Environment", In print, J. Cement and Concrete Composites, Sept 2007.

Sahmaran, M., M. Li, and V.C. Li, "Transport Properties of Engineered Cementitious Composites Under Chloride Exposure," In print, ACI Materials J., 2007.

Li, V.C., "From Micromechanics to Structural Engineering--the Design of Cementitous Composites for Civil Engineering Applications", JSCE J. of Struc. mechanics and Earthquake Engineering, Vol. 10, No.2, pp. 37-48, 1993.

Edward J. Garboczi, et. al., “An electronic monograph: Modeling and Measuring the structure and properties of cement-based materials”, National Institute of Standards and Technology, Gaithersburg, MD, USA.

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19th ACBM/NIST Computer Modeling Workshop

THANKYOU

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