Page 513 - New Trends in Eco efficient and Recycled Concrete

462 New Trends in Eco-efficient and Recycled Concrete

Figure 15.7 Phases in models proposed by: (A) Contrafatto et al. (2016); and (B) Yaghoobi
et al. (2017).

application of XCT imaging can monitor crack initiation and propagation to a preci-
sion impossible to attain with conventional models. The authors also reported that
the intrinsic heterogeneity of meso-structures caused by the random spatial distribu-
tion of multi-phases can significantly affect concrete macroscopic response, that is,
crack patterns and load-carrying capacities.
Contrafatto et al. (2016) designed a model that assumed concrete to comprise
matrix, aggregate and air voids, with no mention of the ITZ (Fig. 15.7A). Assuming
an axial compression-tested concrete member and contrasting the results with
experimental data, they observed that their model correctly reproduced the linear
properties and peak stress of the concrete analysed.
The meso-structural model proposed by Rodrigues et al. (2016) analysed the
effect of aggregate properties such as size, volume and distribution on tensile
strength and dissipated energy in a cubic concrete specimen tested for uniaxial ten-
sile strength. They observed that with increasing maximum aggregate size, both
peak load and dissipated energy declined. When the volume fraction increases the
peak load also decreases and, regarding the load 3 displacement curves. They also
found the ITZ to be the area subject to highest tensile stress (Fig. 15.8) and the for-
mation site of microcracks (linear behaviour zone) that subsequently propagated
across the cementitious matrix (non-linear behaviour).
In their research, Zhang et al. (2016) attempted to model the effect of the cemen-
titious matrix, ITZ and aggregate parameters on mechanical performance under
direct quasi-static and dynamic tensile loads. They reported that concrete mechani-
cal behaviour was more heavily impacted by ITZ properties than the properties of
the other phases, an indication of the importance of correctly simulating that
region.