1.4 Test Results and Discussion
19
to assess the flexural behavior of UHPCC according to ASTM C1609/C1609M-12
(2012).
Taking MOR for example, the energy which is equivalent to the area under
the load–deflection curve up to MOR is denoted as the toughness Toughness MOR .
According to ASTM C1609/C1609M-12 (2012), the flexural strength at MOR can
be derived as
f MOR = P MOR
L
bh 2
(1.2)
where f MOR is the flexural strength at MOR. L is the span length; b and h are the width
and height of specimen, respectively.
Based on Fig. 1.17, Table 1.7 lists the corresponding deflection δ, flexural strength f
and Toughness at four points, i.e., LOP, MOR, L/600 and L/150. “FN400-0”, “FS4000” and “FH400-0.5” denote the test No. and the capital “F” represents the four-point
flexural test.
Figures 1.19 and 1.20 show the flexural strengths and toughness of UHPCC at
the points LOP, MOR, L/600 and L/150, respectively. Based on the Table 1.7 and
Figs. 1.19 and 1.20, it indicates that, (i) addition of steel fibers has little influence
on the flexural strength, the corresponding deflection, and the toughness at the point
LOP, which is consistent with the conclusion derived by Kazemi and Lubell (2012).
This is because that the matrix of UHPCC mainly carries the load in the linear elastic
stage before the point LOP, the contribution of steel fibers has not been developed;
(ii) both the flexural strengths and toughness of UHPCC increase with the rising
of steel fiber content at the points MOR, L/600 and L/150, thus adding steel fibers
can effectively improve the load carrying capacity and energy absorption capacity
of UHPCC. Additionally, the micro-straight steel fiber is more influential when the
steel fiber content is larger than 1.5%.
1.4.3.2 Maximum Flexural Strength
Table 1.8 further shows the maximum flexural strengths of all the UHPCC specimens,
in which “—” denotes that the data is not collected or discarded due to the large
deviation. It should be noted that, for the “FH400-2.0” specimens, the deviation
between the maximum value (16.5 MPa) and the intermediate value (14.2 MPa) is
16.2%, which exceeds the accepted range. Thus the intermediate value is regarded as
the maximum flexural strength according to the Chinese standard GB-T50081-2002
(2003).
Figure 1.21 illustrates the effects of steel fiber content and type on the maximum
flexural strength of UHPCC. It indicates that, addition of steel fibers has favourable
effect on improving the maximum flexural strength. In detail, for the UHPCC with
micro-straight steel fiber, when the volume fraction of steel fiber varies from 0.5
to 1.5%, the maximum flexural strengths almost keep unchanged, then the corresponding values gradually increase with the rising of steel fiber content. For the
19
to assess the flexural behavior of UHPCC according to ASTM C1609/C1609M-12
(2012).
Taking MOR for example, the energy which is equivalent to the area under
the load–deflection curve up to MOR is denoted as the toughness Toughness MOR .
According to ASTM C1609/C1609M-12 (2012), the flexural strength at MOR can
be derived as
f MOR = P MOR
L
bh 2
(1.2)
where f MOR is the flexural strength at MOR. L is the span length; b and h are the width
and height of specimen, respectively.
Based on Fig. 1.17, Table 1.7 lists the corresponding deflection δ, flexural strength f
and Toughness at four points, i.e., LOP, MOR, L/600 and L/150. “FN400-0”, “FS4000” and “FH400-0.5” denote the test No. and the capital “F” represents the four-point
flexural test.
Figures 1.19 and 1.20 show the flexural strengths and toughness of UHPCC at
the points LOP, MOR, L/600 and L/150, respectively. Based on the Table 1.7 and
Figs. 1.19 and 1.20, it indicates that, (i) addition of steel fibers has little influence
on the flexural strength, the corresponding deflection, and the toughness at the point
LOP, which is consistent with the conclusion derived by Kazemi and Lubell (2012).
This is because that the matrix of UHPCC mainly carries the load in the linear elastic
stage before the point LOP, the contribution of steel fibers has not been developed;
(ii) both the flexural strengths and toughness of UHPCC increase with the rising
of steel fiber content at the points MOR, L/600 and L/150, thus adding steel fibers
can effectively improve the load carrying capacity and energy absorption capacity
of UHPCC. Additionally, the micro-straight steel fiber is more influential when the
steel fiber content is larger than 1.5%.
1.4.3.2 Maximum Flexural Strength
Table 1.8 further shows the maximum flexural strengths of all the UHPCC specimens,
in which “—” denotes that the data is not collected or discarded due to the large
deviation. It should be noted that, for the “FH400-2.0” specimens, the deviation
between the maximum value (16.5 MPa) and the intermediate value (14.2 MPa) is
16.2%, which exceeds the accepted range. Thus the intermediate value is regarded as
the maximum flexural strength according to the Chinese standard GB-T50081-2002
(2003).
Figure 1.21 illustrates the effects of steel fiber content and type on the maximum
flexural strength of UHPCC. It indicates that, addition of steel fibers has favourable
effect on improving the maximum flexural strength. In detail, for the UHPCC with
micro-straight steel fiber, when the volume fraction of steel fiber varies from 0.5
to 1.5%, the maximum flexural strengths almost keep unchanged, then the corresponding values gradually increase with the rising of steel fiber content. For the