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Incorporation of physical and chemical properties of fly ash in modeling hydration of ternary cementitious binders. Graduate Assistant: Prasanth Tanikella Faculty Advisor: Jan Olek. Introduction. Proposed approach to estimate synergic action (1). Modeling of hydration of cement.

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Incorporation of physical and chemical properties of fly ash in modeling hydration of ternary cementitious binders

Graduate Assistant: Prasanth Tanikella

Faculty Advisor: Jan Olek

Introduction

Proposed approach to estimate synergic action (1)

Modeling of hydration of cement

  • Traditional products of hydration of cement include calcium silicate hydrate, calcium hydroxide, AFm and Aft phases and hydrogarnet
  • Depending on the type of fly ash used, addition of these pozzolanic materials alters the kinetics of hydration as well as the amounts and composition of the hydrated products
  • Efficiency factors
  • Efficiency factor for compressive strength
  • Efficiency factor to determine the pozzolanic effect of the admixtures
  • k = (ГSWS,P/WS,C)(1-aW/C)
  • Quantification of Synergic action
  • Synergic Action (SA)
  • SA = P(Tf+Tm) – (WfPTf + Wm PTm)
  • Strength Gain (SG)
  • SGi = Ri – (Rc.Ccem)
  • Cpoz
  • where,
  • fc’ – compressive strength
  • K – constant which depends on cement type
  • W,C,P – Water ,Cement and Fly ash contents respectively
  • k – efficiency factors
  • ГS – Weight fraction of SiO2 in secondary cementitious materials (SCM)
  • WS,P & WS,C- Weight fraction of silica in SCM and cement respectively
  • PTi – measured compressive strengths of the system
  • Wi – weight proportion of ash in the blend
  • Ri – compressive strength of the specimen at a given age
  • Rc – compressive strength of the reference at the same age
  • Ccem & Cpoz – proportions by weight of cement and sum of cement and pozzolan in each mixture respectively
  • Fig 2: SG versus SA values for ternary cements
  • Synergic action is known to be affected by curing time and temperature in the form of the constant ‘a’
  • (1) S.K. Antiohos et al. / Cement and Concrete Research 37 (2007) 877-885
  • Hydration properties of ternary binder systems modeled using CEMHYD3D
  • Steps in hydration modeling
  • -Creation of a 3D microstructure
  • -Simulation of hydration and microstructure development (this includes hydration kinetics and chemistry, temperature and curing conditions
  • Virtual testing of the resulting microstructure
  • Modeling of fly ash in ternary binders
  • CEMHYD3D is equipped with modeling the effects of incorporation of fly ash in the binder
  • The hydration reactions in the presence of fly ash in cement are identified and the volumetric stoichiometries on a pixel basis are used
  • Pozzolanic properties, the activation energies of the reactions and pH of the solution are accounted for
  • Present model is limited in the availability of data to model the synergistic effects of fly ash in ternary binders

Research Objectives

  • The focus of the present research is on studying and modeling the influence of variations in chemical composition of fly ashes on potential synergistic effects in ternary (cement + slag/silica fume + fly ash or cement + 2 different fly ashes) cementitious systems
  • To explore the feasibility of modifying the CEMHYD3D program (Fig 1) to account for the use of fly ashes with particular chemical compositions in ternary cementitious systems
  • Fig 1 : 3D rendition of hydrated
  • particles using
  • CEMHYD3D

Characterization of selected fly ashes

  • Fly ashes (both class C and class F) selected from 20 sources commercially available in Indiana
  • Properties evaluated
  • -Total Chemical Analysis
  • -Particle Size Distribution
  • -Magnetic particle content
  • -X-Ray diffraction analysis
  • -Scanning electron microscopy
  • -Strength activity index

Summary

  • The influence of chemical and physical characteristics of fly ashes on the synergistic effects in ternary binders will be evaluated
  • Modification of CEMHYD3D model will be attempted using fly ash characterization information obtained from this project