4
1 Static Mechanical Properties of UHPCC
fume is more expensive than fly ash and ultra-fine slag for its limited production, the
present UHPCC is relative low-costs and energy saving.
1.2.2 Specimen Preparation and Curing
For the preparation of the UHPCC, a forced single-axis mixer with a capacity of
60L and a constant mixing speed (47 rpm) was used. To achieve good workability,
particle distribution and packing density, mixing procedure for the present UHPCC
was controlled rigorously. Firstly, since the small particles tended to agglomerate
and it was easier to break these chunks when the particles were dry, the cementitious materials (cement, silica fume, ultra-fine mineral admixture) and sand were
put together simultaneously and dry-mixed uniformly for 3 min. Secondly, the water
pre-mixed with super-plasticizer was then added gradually and mixed for 3 ~ 5 min.
Finally, steel fibers were dispersed carefully by hand into the mixture and mixed for
another 3 ~ 5 min in order to guarantee the fibers well distributed throughout the
matrix. The shear action of steel fibers helped to destroy any remaining agglomerates
in the fresh mixture, thus improving the workability of the composites.
After the prepared matrix was poured into moulds, the freshly cast specimens were
covered with plastic sheets to prevent moisture losing and kept at room temperature
for 24 h. Then, they were demoulded and cured in a standard curing room with the
temperature of 17.7 ~ 21.7 °C and relative humidity of 98.4% for another 28 days.
After that, the specimens were taken out of the standard curing room and stored at
room temperature until the time of tests. All the specimens were cast from the side
face to ensure that the pressure-bearing surfaces are parallel to each other and the
flatness tolerance is less than 0.0005d (d s is the length of specimens) according to
the Chinese standard GB-T50081-2002 (2003). Table 1.3 lists the arrangement of
the present tests, in which three specimens were tested in each batch and total 165
Table 1.3 Test arrangement
Test
Steel fiber volume
fraction (%)
Steel fiber type
Specimen size
(mm × mm ×
mm)
Specimen number
Cubic
compression
0 ~ 2.5
S, H
100 × 100 ×
100
33
Axial
compression
0 ~ 2.5
S, H
100 × 100 ×
300
33
Direct tension 0 ~ 2.5
S, H
unnotched
dog-bone
33
Four-point
flexure
0 ~ 2.5
S, H
100 × 100 ×
400
33
Three-point
flexure
0 ~ 2.5
S, H
100 × 100 ×
400
33
1 Static Mechanical Properties of UHPCC
fume is more expensive than fly ash and ultra-fine slag for its limited production, the
present UHPCC is relative low-costs and energy saving.
1.2.2 Specimen Preparation and Curing
For the preparation of the UHPCC, a forced single-axis mixer with a capacity of
60L and a constant mixing speed (47 rpm) was used. To achieve good workability,
particle distribution and packing density, mixing procedure for the present UHPCC
was controlled rigorously. Firstly, since the small particles tended to agglomerate
and it was easier to break these chunks when the particles were dry, the cementitious materials (cement, silica fume, ultra-fine mineral admixture) and sand were
put together simultaneously and dry-mixed uniformly for 3 min. Secondly, the water
pre-mixed with super-plasticizer was then added gradually and mixed for 3 ~ 5 min.
Finally, steel fibers were dispersed carefully by hand into the mixture and mixed for
another 3 ~ 5 min in order to guarantee the fibers well distributed throughout the
matrix. The shear action of steel fibers helped to destroy any remaining agglomerates
in the fresh mixture, thus improving the workability of the composites.
After the prepared matrix was poured into moulds, the freshly cast specimens were
covered with plastic sheets to prevent moisture losing and kept at room temperature
for 24 h. Then, they were demoulded and cured in a standard curing room with the
temperature of 17.7 ~ 21.7 °C and relative humidity of 98.4% for another 28 days.
After that, the specimens were taken out of the standard curing room and stored at
room temperature until the time of tests. All the specimens were cast from the side
face to ensure that the pressure-bearing surfaces are parallel to each other and the
flatness tolerance is less than 0.0005d (d s is the length of specimens) according to
the Chinese standard GB-T50081-2002 (2003). Table 1.3 lists the arrangement of
the present tests, in which three specimens were tested in each batch and total 165
Table 1.3 Test arrangement
Test
Steel fiber volume
fraction (%)
Steel fiber type
Specimen size
(mm × mm ×
mm)
Specimen number
Cubic
compression
0 ~ 2.5
S, H
100 × 100 ×
100
33
Axial
compression
0 ~ 2.5
S, H
100 × 100 ×
300
33
Direct tension 0 ~ 2.5
S, H
unnotched
dog-bone
33
Four-point
flexure
0 ~ 2.5
S, H
100 × 100 ×
400
33
Three-point
flexure
0 ~ 2.5
S, H
100 × 100 ×
400
33