Page 520 - New Trends in Eco efficient and Recycled Concrete

468 New Trends in Eco-efficient and Recycled Concrete

Table 15.3 Aggregate properties
Type of aggregate

Parameter Gravel Unglazed ceramic Glazed ceramic
Diameter (mm) 12.5 12.5 12.5
Shape Circular Circular Circular
Elastic modulus (GPa) 109.7 99.9 88.40
Poisson’s ratio 0.2 0.2 0.2

80.00
Unglazed ceramic aggregate Glazed ceramic aggregate Gravel
70.00
3
2
= –0.011x + 0.7687x – 16.659x + 136.03
gravel
y
R 2 = 0.9943
60.00 3 2
Elastic modulus (GPa) 40.00 y glazed ceramic aggregate = –0.0063x + 0.4721x – 11.011x + 105.13
50.00
R 2
= 0.9956
30.00

20.00
3
2
= –0.0052x + 0.3511x – 7.4x + 75.4
unglazed ceramic aggregate
y
2
R = 0.9849
10.00
Cementitous
ITZ
matrix
Aggregate
0.00 (paste)
0 5 10 15 20 25 30 35
Distance from the interface (μ μm)
Figure 15.12 Modulus of elasticity versus distance from the interface in the ITZ. ITZ,
Interfacial transition zone.
Fig. 15.12 shows that the values of the elastic modulus across the ITZs declined gradually
from a maximum at the aggregate surface to a nadir, followed by a moderate rise that stead-
ied near the contact with the mortar. The figure also gives the third-degree polynomials
entered in the model to which the [elastic modulus (y) versus distance (x) between the ITZ
2
and the aggregate] curves were fitted with a very high correlation coefficient (R . 0.95).
The ITZ thickness entered in the model was 30 μm, as shown in Fig. 15.12. That value
was within the range (10 50 μm) assumed by other authors in similar simulations
(Zouaoui et al., 2017). The thickness was assumed to be uniform around the entire perim-
eter and the Poisson coefficient to be 0.2, in keeping with prior studies (Grondin and
Matallah, 2014).
3. Cement matrix (mortar): on the microscale this phase is a heterogeneous material com-
prising fines aggregates, cement matrix and pores. In meso-scale numerical simulations,
however, it is assumed to be homogeneous (Yaghoobi et al., 2017).