I.Introduction

There has always been, and will always be, a need to test products and

materials to prevent disasters. Critical physical parameters must be

measured to quantify performance and strength, ensuring our safety and

the safety of our environment.

Most commonly, the compressive strength of concrete is measured to

ensure that concrete delivered to a project meets the requirements of

the job specification and for quality control. It is important that

the concrete cylinder be cured in standard and tested for the

acceptance testing for specified strengths, verifying mixture

proportions for strength, and quality control by the concrete

producer.

The strength results of cured concrete cylinders are used for

determining the time at which a structure is permitted to put into

service and evaluating the adequacy of curing and protecting concrete

in the structure.

Concrete mixtures can be designed to provide a wide range of

mechanical and durability properties to meet the design requirements

of a structure. The compressive strength of concrete is the most

common performance measured used by engineers in designing buildings

and other structures. Compressive strength of concrete is the basis if

the mixture and water-cement ratio yields the maximum strength or if

the sample can sustain large loads.

Specifically the activity aims to:

1. Determine the slump of freshly made concrete with different

water-cement ratio for consistency.

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2. Prepare cylindrical concrete specimen for testing compressive

strength.

3. Store and cure the specimen with varying number of days of

curing.

4. Determine the compressive strength of concrete with different

water-cement ratio and varying days of curing.

II. Materials and Methods

A. Materials

a. Cylindrical mold – A 6 x 12 inch (150 x 300mm) metal mold, use

where the concrete paste is placed and stored until it

hardens. Shown in figure 1 were the materials and equipment

used in the preparation of concrete specimen.

b. Slump cone – use where it is filled with concrete paste for

the determination of slump of concrete for consistency.

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Fig. 1a Cylindrical Mold

c. Tamping rod – An iron made rod use to strike of the concrete

paste in the cylidrical mold to reduce an amount of voids in

the freshly made concrete as shown in fig. 3.

d. Ruler – A calibrated instrument for getting the value of slump

before forming cylindrical concrete specimen for test.

e. Cement – A substance for making concrete paste that mixed with

water and hardens in a considerable time.

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Fig. 1c Tamping Rod

Fig. 1b Slump Cone

f. Aggregates – A broad term that serve as a reinforcement in

creating concrete cylindrical specimen. Aggregates can be

classified as coarse and fine aggregates.

g. Water – A substance that enables cement when mix with

aggregates hardens with time to sustain some load.

h. Trowel – make the concrete paste level at the top of the

cylindrical mold and use also for mixing concrete components

properly.

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Fig. 1d Portland cement

Fig. 1e Fine Aggregates

Fig. 1f Coarse Aggregates

i. Plain sheet – a steel made sheet use where the preparation of

the concrete specimen is possible to prevent the concrete

paste from wasting.

j. Shovel – made possible the mixing of the concrete components

for making cylindrical concrete specimen.

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Fig. 1g Trowel

Fig. 1h Steel Plain Sheet

Fig. 1i Shovel

k. Universal Testing Machine (UTM) – a machine where the cured

concrete specimen is place for testing the compressive

strength of particular specimen.

l. Curing tank – filled with water where the concrete specimen is

immerse after the initial curing period.

B. Methods

a. Preparation of materials

From the laboratory room, materials for making concrete

specimen where carried and placed in the field. The plain

sheet was laid on the ground. Using the aluminum can, a

desirable amount of cement and aggregates were possible. An

aluminum can was exactly equal to 2 kilograms.

To have sufficient concrete paste to be place in mold for the

three groups, an equivalent amount of 6 kilograms for cement

(3 scoops of a can), 12 kilograms for fine aggregates (6

scoops of a can), and 18 kilograms for coarse aggregates (9

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Fig. 1j UTM with specimen and its large dial

scoops of a can) were properly mixed. Figure 2 shows the

preparation and mixing of materials for making concrete paste.

From the given value of water-cement ratio, the amount of

water needed to make concrete paste was calculated to achieve

consistency.

b. Determination of Slump in Concrete

The slump cone was placed on an area with level, rigid surface

and free of vibration from the surrounding. It was held firmly

by stepping on its two feet. After mixing properly the cement,

aggregates and water, the obtained concrete paste was placed

in the slump cone with a circular motion of the scoop to

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Fig. 2a Mixing of cement and aggregates

Fig. 2b Adding of water in the mixtureof cement and aggregates

distribute the concrete evenly in the cone. The slump cone was

divided into equal three layers. The first layer was filled

evenly and was rod 25 times over its entire length as shown in

Figure 3.

The second layer was filled next with an obtained concrete

mixture. Again it was rod 25 times but just penetrating the

first layer.

Then the third layer was filled and rod 25 times. The top

surface of the slump cone was stroke off with trowel to remove

excess concrete paste and to level with the top of the slump

cone.

Then the slump cone was removed carefully from the concrete

that was put on the slump cone by pulling it vertically but

continuous. The amount of the slump cause by concrete paste

was then immediately measured by the use of a ruler. The slump

was measured between the original center of the concrete paste

and the top surface of the slump cone. The amount of slump was

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Fig. 3a Tamping of the first layerby tamping rod

then recorded. Shown below were the value of slump was

obtained.

c. Preparation of cylindrical concrete specimen

Before concrete paste was placed in the mold, the cylindrical

mold was coated lightly with a mineral oil for easy removing

of the concrete specimen after the initial curing period.

After getting the slump of concrete, the cylinder mold was

placed on a level surface free of vibration. The obtained

concrete paste was placed on the cylinder mold by distributing

it evenly around the perimeter of the cylinder mold. The

number of layers was determined by the mold size. The mold was

filled first one-third of its height.

The mold with concrete paste was rod penetrating through the

bottom layer and distributing the strokes uniformly over the

cross section of the mold. The number of strokes is determined

by the diameter of the cylinder. The layer was rod 25 times

with the specified tamping rod. Shown in Figure 4a and 4b, the

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Fig. 3b Getting the slump of 0.55 w/c ratio

filling and rodding of freshly made concrete in the

cylindrical mold in the first layer.

Then another layer was filled with an obtained concrete paste

distributing the concrete evenly in the mold. The second layer

was rod penetrating just into the first layer and after

rodding the second layer 25 times; the third layer or the top

layer was filled with concrete paste. The tamping rod

penetrate just into the second layer when rodding the third

layer.

After tamping the top layer, the sides of the cylindrical mold

was tap lightly by hand and by tamping rod to release any

entrapped air along the sides of the mold or what we call as

voids. The surface of the mold was leveled with a trowel to

remove excess concrete. See Fig. 4c

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Fig. 4a Filling of freshly madeconcrete in the mold

Fig. 4b Rodding of freshly made concrete in the mold

Then the specimen was moved to the storage area and leave

undisturbed for the initial curing period or for 24 hours. The

top of the specimen was labeled for easy distinction of the

specimen for each group.

d. Curing and storing of cylinder specimen

After forming or molding the concrete cylinder by putting it

in a cylindrical mold, the specimen was moved to the storage

area for initial curing period, not disturbing the concrete in

its plastic state and permits to harden as shown in Figure 5a.

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Fig. 4c Removing of excessconcrete by a trowel

Fig. 5a Specimen in the storagearea for the initial curing period

The test specimen is again transported after the initial

curing period and removed the concrete specimen from its mold.

The obtained cylindrical concrete test specimen was

immediately immersed in a curing tank maintained in a desired

temperature. The water in a tank is not flowing water. Refer

to Figure 5b.

e. Determination of compressive strength of concrete specimen

The concrete specimen was now ready for testing after

specified number of days of curing concrete specimen. These

specimens were different in their water-cement ratio for

comparison of each group.

The first specimens to be tested for compressive strength in

the universal testing machine (UTM) were the specimen that

attained seven number of days in the curing tank. There were

two specimens to be tested in the UTM with different water-

cement ratio; one specimen is 0.55 water-cement ratio and the

other specimen is 0.65 water-cement ratio.

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Fig. 5b Specimens in the curingtank

Then another two specimen with different water-cement ratio

(0.55 and 0.65 w/c ratio) were tested in the UTM. These

specimens were tested after 14 number of days in the curing

tank.

The last two specimens were tested in the UTM. These specimens

reached the maximum number of days of curing. This time the

specimen were tested with 28 number of days cured in the

curing tank.

The concrete specimen should be centered when placed in the

UTM and the top surface of the specimen should be parallel

with the upper block of the machine as shown.

The maximum amount of load in kilonewton in which the specimen

started to crack its surface in each group was recorded. This

is seen through a large dial of Universal Testing Machine.

This load is called the failure load. See Figure 6a and 6b

where high reading accuracy was possible through large design

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Fig. 6a Placing of specimen in theUTM

of dial and where fracture occurred in the surface of the

specimen when the maximum load was reached.

III. Results and Discussion

From the given water-cement ratio of groups 1, 2, and 3 which is 0.55,

the amount of water needed to make concrete paste is 1.1 liters. This

was calculated below.

0.55=wt.of waterwt.ofcement

Since, the resulting weight of water was in terms of kilograms, it was

converted to make into liters, the volume of water. To be adequate in

amount for the three groups, the obtained volume of water was

multiplied with three. The aluminum can used was exactly 2 kg.

0.55=wt.ofwater

2kg

wt.of water=0.55 (2kg )

wt.of water=1.1kg

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Fig. 6b Maximum load is seen inthe dial

Fig. 6c Fracture occur in itsmaximum load

This is also equivalent to 1.1 liters. Multiplied with three for the

three groups we got 3.3 liters of water needed. The other group

(groups 4-6) has water-cement ratio of 0.65 and they got 3.9 liters of

water. Of course, the water use for mixing is of good quality. It was

clean and free from injurious quantities of alkalis, acid, oils and

other substances that may have adverse effect on concrete strength.

Before making the cylindrical concrete specimen for testing in the

UTM, the slump of different water-cement ratio were measured first.

For the 0.55 water-cement ratio, the slump is 0.8 centimeter. This is

much lower compared to 0.65 water-cement ratio which is 8.8

centimeters. The slump measures consistency in concrete and quality

control.

The cylinder mold was coated inside with a mineral oil first before

concrete paste was filled in because mineral oil makes the concrete

when it hardened easy to remove from the mold.

In tamping the concrete paste in the mold, the strokes should be

uniformly distributed over the cross section of the mold. The number

of strokes is determined by the mold diameter. So for 6 inches

diameter, the number of strokes for each layer is 25 strokes. While

the number of layers to be filled with concrete is determined by the

mold size, so for a 12 inches mold size, the number of layers is 3

equal layers.

The side of the mold should be tap to close the voids in it. The voids

are the spaces of air in the concrete. These voids have something to

do with the strength of the concrete.

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The compressive strength is measured by breaking cylindrical concrete

specimens in a compression-testing machine.

Cylinders should be centered in the compression testing machine and

loaded to complete failure. The specimen was placed on the lower

bearing block, the upper block was almost in contact with the specimen

and it was parallel with the specimen top surface. The spherical head

was carefully and slowly brought into contact with the specimen. The

test load was applied continuously and without shock so that an

accurate maximum load is obtained.

The normal norm when testing concrete specimen and according to

research, the lesser the water-cement ratio or the lesser the amount

of water mixed to make concrete cylinder, the stronger the concrete.

However, the reverse happened when the specimen was tested in the UTM.

The 0.55 water-cement ratio when tested has lower failure load which

has 94 kN compared to 0.65 water-cement ratio of the other group which

has 114 kN. This is base on 8 day curing period.

This was repeated when the 15 day curing period specimen was tested.

The failure load was greater in 0.65 water-cement ratio specimen than

0.55 water-cement ratio specimen. 0.55 w/c ratio has 121 kN and 0.65

w/c ratio has 165 kN.

The compressive strength of each concrete specimen was calculated by

dividing the maximum load at failure by the average cross-sectional

area of the specimen.

CompressiveStrength (MPa )= MaximumLoad(N)

Cross−sectionalAreaofSpecimen(mm2)

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f'c=PA

These can be summarized by the table below.

Group

Numbe

r

Diamet

er

(mm)

Lengt

h

(mm)

Water

-

cemen

t

ratio

Slump

(cm)

Cross-

sectiona

l Area

(mm¿¿2)¿

Age of

Specim

en at

Test

(days)

Maximu

m Load

(N)

Compressive

Strength ¿

1 150 300 0.55 0.817,671.

4598

94,00

05.319

2 150 300 0.55 0.817,671.

45915

121,0

006.847

3 150 300 0.55 0.817,671.

45940

188,0

0010.639

4 150 300 0.65 8.817,671.

4598

114,0

006.451

5 150 300 0.65 8.817,671.

45915

165,0

009.337

6 150 300 0.65 8.817,671.

45940

194,0

0010.978

From the data, the lower w/c ratio, the lower the slump, that is 0.8cm and higher w/c ratio it was followed that the higher the slump (8.8cm).

For comparison, below is the chart showing the relationship betweenwater-cement ratio, number of days of curing, and compressivestrength.

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Table 1. Summary of data obtained from the activity

0 5 10 15 20 25 30 35 40 450

2

4

6

8

10

12

Relationship between number of days of curing and compressive strength

Days of Curing (Days)

Compressive Strength (MPa)

From the graph above, it was concluded that the more number of days

concrete specimen was cured, the greater the compressive strength, the

stronger it was.

Groups 1 & 4

Groups 2 & 5

Groups 3 & 6

0

2

4

6

8

10

12

0.55 w/c ratio0.65 w/c ratio

Water-cement ratio

Compressive Strength (MPa)

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Figure 1. Compressive strength and days of curing for groups 1, 2, and 3.

The reverse happened in the activity due to some factors that affects

the compressive strength of concrete. It was observed from above that

the higher the water-cement ratio, the higher the compressive strength

and lower water-cement ratio, lower compressive strength. The activity

therefore was a failure activity.

IV. Conclusion

It is of prime importance that the specimens are made and cured

following standard procedures. Any deviation from standard procedures

will result in a lower measured strength. Low strength test results

due to procedures not in accordance with the standards cause undue

concern, cost and delay to the project.

Care must be exercised in the interpretation of the significance of

compressive strength determinations since strength is not a

fundamental or intrinsic property of concrete made from given

materials. Values obtained will depend on the size and shape of the

specimen, batching, mixing procedures, the methods of sampling,

molding, and fabrication and the age, temperature, and moisture

conditions during curing.

Concrete properties vary considerably depending upon the temperature

and humidity that they have been subjected to early on in their life.

Proper moisture conditions and proper temperature control is vital in

order to achieved the best concrete strength.

Since the reverse happened when conducting the activity or the result

of the activity deviate from the standard, therefore the activity is

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Figure 2. Comparison between water-cement ratio and compressive strength of each group.

not good activity. In the activity, lower water-cement ratio, the

lower the compressive strength and higher the water-cement ratio, the

higher the compressive strength. This is due to some factors that

affect the compressive strength of concrete mentioned above.

References:

How Producers can Correct Improper Test-Cylinder Curing, Ward R. Malisch, TheConcrete Producer, Nov 1997, pp 782-805.

NRMCA/ASCC Checklist for Checklist for Concrete Pre-Construction Conference, NRMCA,Silver Spring, MD

Concrete in Practice Series, NRCMA, Silver Spring, MD

www.worldofconcrete.com

www.nrmca.org

www.astm.org

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