4.2 Influence of alumina particles used as mortars reinforcement

The benefits of alumina particles as reinforcement in two mortars were investigated in [6, 31, 32] by means of quasi-oedometric compression tests performed considering seven microstructures containing or lacking angular or spherical alumina particles. The tests showed a highly beneficial effect of the presence of particles with respect to both the deviatoric strength and the compaction law in both mortars (with and without silica fume) as illustrated in Figure 10, while more conventional tests (3-point bending and simple compression) did not show a such beneficial effect [40] (especially for the matrix without silica fume), proof that the strength of concretes not under confinement is not indicative of the behavior of the same materials under confined loadings. It was also found that the deviatoric strength was more favored by angular particles than by spherical ones and by the addition of silica fume in the

#### Figure 11.

Quasi-oedometric compression tests applied to MB50 microconcrete [16]. (a) Deviatoric behavior and (b) hydrostatic behavior in four dynamic tests performed on dried or wet specimens. (c) Deviatoric behavior and (d) hydrostatic behavior in quasi-static and dynamic tests performed on wet specimens (V8.5 and V11 corresponding to the striking velocities equal to 8.5 m/s and 11 m/s respectively).

Compositions M1 M1M M1Sph M2 M2S M2M M2Sph

) 1366 965.9 1332 941.5

) — — 55.5 39.2

) 569 402.5 555 392.3

) 260 183.5 253 178.9

Shape of particles — Angular Spherical — Angular Spherical Size of particles (mm) — 3–6 4 — 1–3 3–6 4

Composition of mortars and particle-reinforced mortars with and without silica fume used in [6, 31, 32, 40].

Compositions MB50 R30A7 LC HSC

Water/(cement + SF) 0.5 0.64 0.64 0.30 Max grain size (mm) 5 8 10 8

Composition of microconcrete (MB50), siliceous aggregate ordinary concrete (R30A7) and limestone aggregate ordinary concrete (LC), siliceous aggregate high strength concrete (HSC) used in [16, 30, 34, 35].

Quasi-oedometric compression tests applied to a mortar M2 reinforced or not with aggregates (M2M) [6].

Water/(cement + SF) 0.46 0.41

) 4.7 3.4 4.6 3.3

) 0 1084.4 0 1084.4

) — 1008 891 1008

) 1783 838 838 795.4

) 400 263 263 420

) 200 169 169 140

) — —— 46.7

) 12 — — 4.7

Sand (quartz) (kg/m<sup>3</sup>

Compressive Strength of Concrete

Silica fume SF (kg/m3

Cement (kg/m<sup>3</sup>

Water (kg/m<sup>3</sup>

Table 4.

Table 5.

Figure 10.

80

(a) Deviatoric behavior. (b) Hydrostatic behavior.

Admixture (kg/m3

Aggregates (kg/m<sup>3</sup>

Sand (kg/m<sup>3</sup>

Cement (kg/m<sup>3</sup>

Water (kg/m<sup>3</sup>

Silica fume SF (kg/m<sup>3</sup>

Admixture (kg/m<sup>3</sup>

Alumina particles (kg/m<sup>3</sup>

cement paste. In addition, a correlation was noted between the large porosities of millimeter class and the compaction of the concretes under high level of pressure. Finally, it was demonstrated that the experimental data provided by QOC experiments could be used to simulate numerically impact tests involving high levels of confining pressure in front of the projectile head [41].
