Material Science concrete 1

Material Science (concrete) 1
Name
Professor
Course number
Dec 9 2017
Introduction
The durability of reinforced concrete (RC) structures is primarily determined by the
quality of the outer part or the concrete cover of the reinforcement. There are scientific standards
that give guidelines to produce durable concrete based on the provisions for the concrete
composition. Therefore, a procedure is needed to examine the quality of finished concrete
structures. Therefore, this report is for an experiment that examines the permeability of concrete
at the surface for pure Portland cement (control) and compares it with concrete elements
containing different cement replacement materials. In this case, the samples to be tested contain
pulverished fuel ash (pfa), ground granulated blast furnace slag (ggbs) and micro silica
(condensed silica fume-csf).
Apparatus
The apparatus used in the first experiment are,
Permeability tester/vacuum cell
Pressure regulator/pump
The apparatus used in the first experiment are,
Material Science (concrete) 2
Control compressive testing machine
Pundit
Schmidt Rebound Hammer
Procedure
Once the test concrete element is placed in the vacuum cell, the stopcock is opened and a
vacuum is produced by the pump in both chambers. The evolution of pressure is recorded
continuously from the start until the desired level of vacuum is achieved. Then the stopcock is
stopped hence the pump can only act chamber to balance the pressure in both chambers at any
moment. All the values are recorded for the analysis of permeability of coefficient.
In the second experiment (testing of concrete containing cement replacements material),
the procedure is as follows. The control concrete sample is placed in Schmidt rebound hammer
testing machine to measure the ultrasonic pulse velocity and the rebound number. The same test
is done on the other samples containing cement replacement materials. Secondly, using the
compressive testing machine, the ultrasonic pulse velocity for the control sample and all the
other samples is done and the values recorded.
Results
The following are the values recorded from the experiments done in the lab;
Ultrasonic Pulse Velocity (UPV) measurements (km/sec)
Material Science (concrete) 3
100% conctere
(control)
pfa
concrete
ggbs
concrete
microsilica (csf)
concrete
4.767
4.674
4.845
5.042
Schmidt Hammer measurements
100% conctere
(control)
pfa
concrete
ggbs
concrete
microsilica (csf)
concrete
36.9
39.6
41.8
47.9
Compressive Strength measurements (Mpa)
100% conctere
(control)
pfa
concrete
ggbs
concrete
microsilica (csf)
concrete
19.7
21.15
25.2
26.16
Concrete mix
Normal and Cement replacement - w/c 0.5
pfa (Pulverised fuel ash) 30%
ggbs (Ground Granulated Blast furnace Slag) 60%
Microsilica (condensed silica fume) 10%
Cement content
Kg/m3
water
Kg/m3
Fine Agg
Kg/m3
10mm Agg Kg/m3
20mm Agg
Kg/m3
360
180
518
437
874
Cement content
Kg/m3
pfa kg
water
Kg/m3
Fine Agg
Kg/m3
20mm Agg
Kg/m3
252
108
180
518
874
Material Science (concrete) 4
Cement content
Kg/m3
pfa kg
water
Kg/m3
Fine Agg
Kg/m3
20mm Agg
Kg/m3
144
216
180
518
874
Cement content
Kg/m3
pfa kg
water
Kg/m3
Fine Agg
Kg/m3
20mm Agg
Kg/m3
324
36
180
518
874
Control
pfa (30%)
ggbs (60%)
Microsilica
(10%)
Kt-Permiability coefficient
(X10
-16
m
2
)
1.484
1.49
1.308
2.753
L-Depth of air penetration
54.6mm
54.8mm
53.8mm
59.5mm
Quality class of concrete
surface
bad (4)
bad (4)
bad (4)
bad (4)
Material Science (concrete) 5
Material Science (concrete) 6
Data analysis
Outlined above are the results of various tests that were conducted in the lab. There are
various scientific trends that can be observed from the results. On the analysis of Ultrasonic
Pulse Velocity, the recorded values show that the value of the UPV increases with some
elements and decreases with other elements. For instance the value of the UPV in pfa concrete is
lower as compared to the 100% PC concrete (control). However, the UPV values for both ggbs
and microsilica (csf) concrete are higher than the 100% PC concrete (control). However when
you compare the behavior of the UPV and the strength of the concretes, you notice that there is a
difference. As the UPV decreases and increases in some of the concrete elements, their strength
increases gradually from 19.70Mpa for 100% PC concrete (control) to approximately 26.16Mpa
for microsilica csf concrete. The scientific view of this trend is that the strength of concrete
increases when the three additives are added distinctively to the Portland cement. However, the
strength is not the same. As a result, we can scientifically state that the strength of concrete
elements is higher with csf Microsilica and lower with ggbs concrete and pfa concrete
respectively (Torrent, R.J.1992).
In this experiment, we also observed a trend with regards to the strength of concrete when
you consider the pure concrete element as well as when additives are introduced to the cement.
Scientifically and in considerations to the existing literature, if foreign matter is introduced to
pure cement, there are possibilities to affect the resultant concrete by either making it weak or
stronger. In this case, the additives strengthened the resultant concrete as shown in the
compressive strength measurements table. However, it is necessary to note that the compressive
strength increased gradually from 21.15 to 25.20 and 26.18 (all in Mpa) in pfa, ggbs, and csf
Material Science (concrete) 7
concrete’s respectively. Therefore it is absolutely correct to say that in this case the csf
reinforced concrete is the strongest (Kropp, J. & H.K. Hilsdorf (ed). 1995).
The Schmidt hammer test illustrates a scenario where the rebound number is totally
different with respect to each specimen. According to the collected data, the rebound number for
100% PC concrete is a bit lower than the numbers for all the other specimens. The rebound
number is high in csf concrete decreases in ggbs and pfa respectively. Comparing these results
with the compressive strength table shows that there is a similar trend indicating that the surface
hardness of the four samples increases from 100% PC to pfa, ggbs, and gets higher in csf
concrete respectively. The existing literature shows that it is common for surface hardness of
concrete to increase when most elements are added into the concrete cement.
A Permeability test result shows a different trend all together for the four specimens.
According to the test table, the coefficient of permeability for pure concrete PC concrete is
approximately 1.484(X10
-16
m
2
). This coefficient rises to 1.496(X10
-16
m
2
) for pfa concrete.
However, it is important to note that kt for ggbs (60%) is lower than that of the control concrete.
In scientific applications, it is therefore not advisable to use ggbs (60%) when expecting to
increase the permeability of any slab/concrete. In addition, a cfs concrete is highly permeable
than all the other specimens as shown in the table.
The relationship between the coefficient of permeability Kt and the depth of air
penetration is significantly the same. In this case, the depth L is higher in csf concrete. As seen in
the Kt analysis, the depth of air penetration L is higher in the 100% PC as compared to ggbs
concrete. As a result, the depth of air penetration in ggbs concrete is the lowest in this case hence
the poorest with relationship to concrete permeability.
Material Science (concrete) 8
According to the table for quality classes of cover concrete, all the four specimens are of
bad quality since they lie within the “bad” class number 4 (Romer, M. 1995).
Conclusion
In summary, concrete strength, ultrasonic pulse velocity and surface hardness are affected
when you introduce cement replacement materials into concrete. On the other hand, concrete air
penetration is also majorly affected when the replacement materials for cement are added to co
concrete.
Material Science (concrete) 9
Works cited
Torrent, R.J.,(1992). A two-chamber Vacuumm Cell for Measuring the Coefficient of
Permeability to Air of the Concrete Cover on Site, Materials and Structures, 25, pp.
358365.
Kropp, J. & H.K. Hilsdorf (ed). 1995: Performance criteria for concrete durability.- RILEM
report 12, E & FN Spon, 327 pp
Romer, M. 1995. Effect of moisture and concrete composition on the Torrent permeability
measurement.- Materials & Structures, 38, 541 - 547

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