modeling engineered cementitious composites (ecc)
TRANSCRIPT
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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