Quantification of the influences of aggregate shape and sampling method on the overestimation of ITZ thickness in cementitious materials

Abstract

The microstructure of the interfacial transition zone (ITZ) surrounding the aggregate in a cementitious composite is quite different from that of the bulk matrix, because of its distinct physical nature including relatively high porosity and low rigidity. The thickness and volume fraction of the ITZ play a major role in determining the transport and mechanical behaviour of cementitious composites. However, the ITZ thickness may be overestimated when undertaking sectional plane analysis of these composites. Analysis of Platonic particles has previously shown that the sphericity of the particle is an important parameter in determining the overestimation of the ITZ thickness, but this raises the question of whether sphericity is sufficient to uniquely characterize the influence of aggregate shape. This paper investigates the influence of particle shape on overestimation of ITZ thickness for aggregate shapes which have the same sphericity values as Platonic particles; specifically, spheroids of differing geometries. A normal line sampling algorithm, which is designed to replicate the practical experimental process used in ITZ determination, is employed to obtain the apparent ITZ thickness. The influences of particle shape, sampling method and particle size distribution are investigated in terms of the overestimation of the ITZ volume fraction, and the effective diffusivity within three-phase composites, using the differential effective medium approximation.

Areal analysis induced bias on interface thickness around ovoidal particles

“…Garboczi et al [12] employed star-shaped particles to model the shape of realistic aggregates; however, these complex shapes preclude any analytical approach. For the sake of simplification, most of the models employ spheres [13,14], ellipsoids [15,16] , superballs [17,18] and Platonic solids [19] as the inclusions (such as the cement grains, aggregates and pores). As shown in Fig.…”

“…4. Thus, the bias on the determination of the ITZ thickness induced by the systematic line sampling (SLS) approach [16,48] and the normalized line sampling (NLS) approach [19,60] have been analyzed. The thickness of ITZ around aggregates is overestimated by either the SLS or the NLS approaches, and the overestimation degree increases with the increasing sphericity of the aggregate.…”

Effect of Ultrafine Slag Powder on the Rheological Behaviour, Compressive Strength, and Microstructure of Ultra-High Performance Concrete

“…With the same USL content, the induction period and the initial setting time of the paste shortened with an increase in the particle fineness. To date, the strengths, interfacial transition zone, permeability, and total pore structure of concrete have been shown to be improved by USL [12][13][14][15].…”

Investigation on Pore Structure and Permeability of Concrete–Rock Interfacial Transition Zones Based on Fractal Theory

“…The concrete-rock ITZ is characterized by high porosity, poor densification, calcium hydroxide (CH) enrichment, high permeability, and low shear strength, which is generally considered the weak layer and adversely impacts hydraulic structures. Thus, research on the properties of the ITZ has been a hot topic in hydropower engineering projects [1][2][3]. The durability of the concrete-rock structure depends on the penetration of water and corrosive ions into the matrix [4].…”