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

10mm Agg

Kg/m3

20mm Agg

Kg/m3

252

108

180

518

437

874

Material Science (concrete) 4

Cement content

Kg/m3

pfa kg

water

Kg/m3

Fine Agg

Kg/m3

10mm Agg

Kg/m3

20mm Agg

Kg/m3

144

216

180

518

437

874

Cement content

Kg/m3

pfa kg

water

Kg/m3

Fine Agg

Kg/m3

10mm Agg

Kg/m3

20mm Agg

Kg/m3

324

180

518

437

874

Control

pfa (30%)

ggbs (60%)

Microsilica

(10%)

Kt-Permiability coefficient

(X10

-16

)

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)

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

). This coefficient rises to 1.496(X10

-16

) 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.

358–365.

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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