Title: Microstructural Aspects of the Mechanical Response of Plain Concrete

Author(s): S. J. Pantazopoulou and R. H. Mills

Publication: Materials Journal

Volume: 92

Issue: 6

Appears on pages(s): 605-616

Keywords: cracking (fracturing); damage; hydration; mechanical proper-ties; porosity; stress-strain relationships.

DOI: 10.14359/9780

Date: 11/1/1995

Abstract:
It is generally acknowledged that mechanical properties of concrete such as strength and stiffness are influenced directly by the physical properties of material microstructure. However; this relationship is rarely addressed in constitutive models of material response to mechanical loads. Instead, the most frequently sought alternative for development of such models is by curve-fitting of the database of experimental stress-strain results for each range of nominal cylinder strength, this being related to the water-cement ratio. A simplified constitutive model that recognizes and incorporates the properties of microstructure and its influence on mechanical response is developed in this paper: The model evaluates uniaxial compressive stress at any level of axial strain, using a strain-dependent estimate of material stiffness. The initial elastic modulus of uncracked concrete is evaluated, based on water-cement ratio, age, volume fraction of aggregates, paste porosity, degree of hydration, and paste-aggregate interface properties. Reduction of the initial modulus with increasing load is modeled by the application of a factor that depends on the natural porosity of the material and mechanically induced porosity as it is assessed by the area strain that develops in the cross section supporting the load. Using this approach, it is possible to model the change effected on the initial resistance of the material from progressive microcrack growth and internal damage occurring in the concrete. The sensitivity of the proposed model to several variables was evaluated from parametric studies and by comparisons with available experimental data.