78
4 Triaxial Compressive Behavior of UHPCC …
in diameter. Also the partial silica fume was replaced by the ultra-fine industrial
waste powder, e.g. fly ash and ultra-fine slag. Table 4.1 indicates that the ultra-fine
industrial waste powder (silica fume, ultra-fine fly ash and slag) accounts for 40% of
the binder, the ratio of expensive silica fume is only 10%, and the water-binder ratio
is 0.3. Since the production of cement and fine quartz sands consumes much more
energy and resources, and silica fume is more expensive than fly ash and ultra-fine
slag for its limited production, the present UHPCC is low-costs and energy saving.
The volumetric ratio of the mixing fibers were designed as 2% and the straight
brass-coated steel fiber was chosen since it provides a good trade-off between workability and mechanical properties of concrete. The equivalent diameter, length and
tensile strength of steel fibers were 0.175 mm, 13 mm and 3000 MPa, respectively.
Provided by the manufacture, Jiangsu SOBUTE new material Co., Ltd, the compressive strength and density of the basalt aggregates are 210 MPa and 2800 kg/m
3 ,
respectively. The water-reducing ratio of the PCA®-I polycarboxylic type HRWR
(high-range-water-reducer) was no less than 35%, which is also developed by Jiangsu
SOBUTE new material Co., Ltd.
4.3.2 Mixing Procedure
To achieve good workability, particle distribution and packing density, mixing procedure for the present UHPCC was controlled rigorously. All the fine particles and
coarse aggregates were blended before adding water and HRWR because small particles tend to agglomerate and it is easier to break these chunks when the particles are
dry. At first, the dry cementitious materials (cement, fly ash, silica fume, slag) and
sands were put together simultaneously and mixed uniformly for 3 min, then the
coarse basalt aggregates were added and mixed uniformly for 1 min. Secondly, the
water and super-plasticizer were added together and mixed for 3 ~ 5 min. Finally,
steel fibers were incorporated 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 the fibers helps to destroy any remaining agglomerates in the mixture, and thus
improvs the workability of the composites. A vertical pan mixer with a capacity of
60L and a constant mixing speed (47 rpm) was used. UHPCC is a self-consolidating
concrete which does not require heat and high pressure preparation. The slump and
spread of the present UHPCC were about 230 mm and 610 mm, respectively, which
satisfies the workability requirements of on-site constructions.
The prepared matrix was poured into 50 × 100 mm cylindrical plastic moulds, the
freshly cast specimens were kept in the moulds for 24 h. Then, they were demoulded
and cured in a standard climate with temperature of 17.7 ~ 21.7ºC and relative
humidity of 98.4% for 28 days. Afterwards, the specimens were taken out of the
curing room and cured in air. To minimize the influences of the aging on the behavior,
the triaxial compressive test was conducted at 120 days after the specimens were
cast. Two batches of UHPCC specimens (CF90 and CF130) listed in Table 4.1 were
4 Triaxial Compressive Behavior of UHPCC …
in diameter. Also the partial silica fume was replaced by the ultra-fine industrial
waste powder, e.g. fly ash and ultra-fine slag. Table 4.1 indicates that the ultra-fine
industrial waste powder (silica fume, ultra-fine fly ash and slag) accounts for 40% of
the binder, the ratio of expensive silica fume is only 10%, and the water-binder ratio
is 0.3. Since the production of cement and fine quartz sands consumes much more
energy and resources, and silica fume is more expensive than fly ash and ultra-fine
slag for its limited production, the present UHPCC is low-costs and energy saving.
The volumetric ratio of the mixing fibers were designed as 2% and the straight
brass-coated steel fiber was chosen since it provides a good trade-off between workability and mechanical properties of concrete. The equivalent diameter, length and
tensile strength of steel fibers were 0.175 mm, 13 mm and 3000 MPa, respectively.
Provided by the manufacture, Jiangsu SOBUTE new material Co., Ltd, the compressive strength and density of the basalt aggregates are 210 MPa and 2800 kg/m
3 ,
respectively. The water-reducing ratio of the PCA®-I polycarboxylic type HRWR
(high-range-water-reducer) was no less than 35%, which is also developed by Jiangsu
SOBUTE new material Co., Ltd.
4.3.2 Mixing Procedure
To achieve good workability, particle distribution and packing density, mixing procedure for the present UHPCC was controlled rigorously. All the fine particles and
coarse aggregates were blended before adding water and HRWR because small particles tend to agglomerate and it is easier to break these chunks when the particles are
dry. At first, the dry cementitious materials (cement, fly ash, silica fume, slag) and
sands were put together simultaneously and mixed uniformly for 3 min, then the
coarse basalt aggregates were added and mixed uniformly for 1 min. Secondly, the
water and super-plasticizer were added together and mixed for 3 ~ 5 min. Finally,
steel fibers were incorporated 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 the fibers helps to destroy any remaining agglomerates in the mixture, and thus
improvs the workability of the composites. A vertical pan mixer with a capacity of
60L and a constant mixing speed (47 rpm) was used. UHPCC is a self-consolidating
concrete which does not require heat and high pressure preparation. The slump and
spread of the present UHPCC were about 230 mm and 610 mm, respectively, which
satisfies the workability requirements of on-site constructions.
The prepared matrix was poured into 50 × 100 mm cylindrical plastic moulds, the
freshly cast specimens were kept in the moulds for 24 h. Then, they were demoulded
and cured in a standard climate with temperature of 17.7 ~ 21.7ºC and relative
humidity of 98.4% for 28 days. Afterwards, the specimens were taken out of the
curing room and cured in air. To minimize the influences of the aging on the behavior,
the triaxial compressive test was conducted at 120 days after the specimens were
cast. Two batches of UHPCC specimens (CF90 and CF130) listed in Table 4.1 were