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Meso-structural modelling in recycled aggregate concrete 459

2.50 9.00
8.33
8.00
2.00 1.70 2.11 7.00
Ultimate tensile stress (MPa) 1.50 4.00 Ultimate tensile stresses (Hayder et al. 2017) 5.00 Property of crack (mm)
6.00

4.00
Maximum crack (Hayder et al. 2017)
1.00
Average crack width (Grassl et al. 2010)
2.00
0.50 Crack length (Grassl et al. 2010) 3.00
1.16
0.39 1.00
0.01
0.02
0.00 0.00
0 2 4 6 8 10 12 14 16 18
Aggregate diameter (mm)
Figure 15.4 Effect of aggregate diameter on ultimate tensile stress and crack properties.

assume its modulus of elasticity to be 0.2 0.8 times that of the mortar and constant
across its width (Abu Taqa et al., 2015; Zhang et al., 2016); a third group deems
the modulus of elasticity to be constant and its thickness ($0.01 mm) to be greater
than the actual value (Rodrigues et al., 2016; Kim and Abu Al-Rub, 2011); and a
fourth defines the properties based on nanoindentation findings (Xiao et al., 2013b;
Sa ´ez del Bosque et al., 2017). The common denominator in all is the assumption
that interface thickness is constant in all directions.

15.3.2 Prior meso-structural modelling

Meso-structural models that attempt to simulate conventional concrete are built
around three phases (Keinde et al., 2014): natural aggregate (gravel), aggregate/
cement matrix (mortar) ITZ and matrix or mortar (cement 1 sand). Recycled con-
crete containing recycled coarse aggregate exhibit greater ITZ heterogeneity than
the conventional material: if the aggregate is recycled from concrete, it consists in
unbound aggregate and aggregate with attached mortar and, if mixed, in varying
percentages of bitumen, ceramic materials, gypsum or wood as well as unbound
aggregate or aggregate with attached mortar (Fig. 15.5). Concrete with 100%
recycled concrete aggregate exhibits not the three phases found in conventional
concrete (Fig. 15.6), but five (aggregate, new mortar, new ITZ, old mortar and
old ITZ).