76
4 Triaxial Compressive Behavior of UHPCC …
4.3 Mixing Optimization of UHPCC and Triaxial
Compression Test
4.3.1 Compositions
For the protective structures withstanding high-speed projectile impact, the resistance
of concrete target depends mainly on the compressive strength of the target as well
as the size and strength (hardness) of the coarse aggregates (Zhang et al. 2005a,
b; Langberg and Markeset 1999; Wu et al. 2015a; Dancygier et al. 2007, 2014; Wu
et al. 2015b). Therefore, adding the high-strength coarse aggregates into the concrete
matrix, probably results in the decrease of compressive strength of the concrete to
some extent, but enhancing the impact resistance.
As for the target strength, Zhang et al. (2005a, b), Langberg and Markeset (1999),
Wu et al. (2015a) have experimentally found that the penetration depth of projectiles
are no longer decreasing obviously when the compressive strength of the targets are
larger than a certain value. Moreover, the compressive strengths of 90 ~ 150 MPa
were recommended for protective structures by comprehensive considerations on
the protective efficiency and production costs. Besides, as for the shapes (straight,
hooked, twisted) and volumetric fractions of steel fibers, Wu et al. (2015a), Máca
et al. (2010), Sovják et al. (2015) and Peng et al. (2016) have proposed that volume
fraction of the straight steel fibers with 1.5 ~ 2% is the optimum choice with respect
to the mechanical properties, workability, crack prohibiting ability as well as the cost
of the matrix.
The optimal UHPCC was prepared by State Key Laboratory of High Performance
Civil Engineering Materials, Jiangsu Research Institute of Building Science in China.
The traditional high performance concrete is often costly and low production efficiency for its expensive raw materials (e.g. high content of silica fume, fine quartz
sand and small-sized steel fiber). More importantly, the casting and curing of ultrahigh strength concrete (e.g. RPC) needs high temperature (90 ~ 400 °C) and sufficient
pressure to expel the excess liquids and air from the fresh mixture, which limits its
large-scale on-site construction applications.
Table 4.1 lists the present mixing proportion of UHPCC, in which all the ingredients are commercially available in China. To reduce the porosity of binder and
improve the interface zone between coarse aggregates and cement pastes, four cementitious materials were used in the present study, including the Chinese standard
Graded 52.5 P.II type Portland cement (GB175-2007 2008) from Xiaoyetian corporation (20 ~ 30 µm in particle diameter), silica fume (particle size of 0.10 ~ 0.26 µm,
density of 2.1 g/cm
3 , specific surface area of 20,500 m
2 /kg) from Elkem company,
ultra-fine fly ash (density of 2.7 g/cm
3 ) from Nantong electric power plant and ultrafine slag (particle size of 3 ~ 6 µm, density of 2.8 g/cm
3 ) from Jiangnan cement
plant.
Compared with the traditional high performance concrete, the ground fine quartz
sand (the size was less than 0.6 mm) was substituted by easily obtained natural
river sand with maximal diameter of 2.5 mm and basalt aggregates with 5 ~ 10 mm
4 Triaxial Compressive Behavior of UHPCC …
4.3 Mixing Optimization of UHPCC and Triaxial
Compression Test
4.3.1 Compositions
For the protective structures withstanding high-speed projectile impact, the resistance
of concrete target depends mainly on the compressive strength of the target as well
as the size and strength (hardness) of the coarse aggregates (Zhang et al. 2005a,
b; Langberg and Markeset 1999; Wu et al. 2015a; Dancygier et al. 2007, 2014; Wu
et al. 2015b). Therefore, adding the high-strength coarse aggregates into the concrete
matrix, probably results in the decrease of compressive strength of the concrete to
some extent, but enhancing the impact resistance.
As for the target strength, Zhang et al. (2005a, b), Langberg and Markeset (1999),
Wu et al. (2015a) have experimentally found that the penetration depth of projectiles
are no longer decreasing obviously when the compressive strength of the targets are
larger than a certain value. Moreover, the compressive strengths of 90 ~ 150 MPa
were recommended for protective structures by comprehensive considerations on
the protective efficiency and production costs. Besides, as for the shapes (straight,
hooked, twisted) and volumetric fractions of steel fibers, Wu et al. (2015a), Máca
et al. (2010), Sovják et al. (2015) and Peng et al. (2016) have proposed that volume
fraction of the straight steel fibers with 1.5 ~ 2% is the optimum choice with respect
to the mechanical properties, workability, crack prohibiting ability as well as the cost
of the matrix.
The optimal UHPCC was prepared by State Key Laboratory of High Performance
Civil Engineering Materials, Jiangsu Research Institute of Building Science in China.
The traditional high performance concrete is often costly and low production efficiency for its expensive raw materials (e.g. high content of silica fume, fine quartz
sand and small-sized steel fiber). More importantly, the casting and curing of ultrahigh strength concrete (e.g. RPC) needs high temperature (90 ~ 400 °C) and sufficient
pressure to expel the excess liquids and air from the fresh mixture, which limits its
large-scale on-site construction applications.
Table 4.1 lists the present mixing proportion of UHPCC, in which all the ingredients are commercially available in China. To reduce the porosity of binder and
improve the interface zone between coarse aggregates and cement pastes, four cementitious materials were used in the present study, including the Chinese standard
Graded 52.5 P.II type Portland cement (GB175-2007 2008) from Xiaoyetian corporation (20 ~ 30 µm in particle diameter), silica fume (particle size of 0.10 ~ 0.26 µm,
density of 2.1 g/cm
3 , specific surface area of 20,500 m
2 /kg) from Elkem company,
ultra-fine fly ash (density of 2.7 g/cm
3 ) from Nantong electric power plant and ultrafine slag (particle size of 3 ~ 6 µm, density of 2.8 g/cm
3 ) from Jiangnan cement
plant.
Compared with the traditional high performance concrete, the ground fine quartz
sand (the size was less than 0.6 mm) was substituted by easily obtained natural
river sand with maximal diameter of 2.5 mm and basalt aggregates with 5 ~ 10 mm