CHAPTER 5: SUMMARY OF FINDINGS AND OBSERVATIONS, CONCLUSIONS AND RECOMMENDATIONS 2009-2010

CHAPTER 5

SUMMARY OF FINDINGS AND OBSERVATIONS, CONCLUSIONS AND

RECOMMENDATIONS

This chapter presents the summary of findings, conclusions and recommendations of the

researchers. These are based on the results gathered by the researchers.

SUMMARY OF FINDINGS AND OBSERVATIONS

The following observations present some of the characteristics of concrete cylinder

samples containing natural fibers and plain concrete cylinder samples during mixing and when

subjected to ultimate compressive test:

1. During the mixing process, we observed that as the fiber content increases, the faster the fresh

concrete mixture became stiffen. Its consistency lowers because the fiber absorbed the water

from the mixture.

a. When coconut coir fibers were added in the fresh concrete mixture, from 0.10% to

0.75% fiber-cement ratio, the presence of the fiber does not greatly affect the consistency

of the fresh concrete mixture although it decreases its slump values from 60mm to 36mm

which is 17% to 64% decrease in slump values.

b. Pineapple fibers have slump values of 20mm and 18mm at 0.25% and 0.75% fiber-

cement ratio respectively. Although it has lower slump values compared to the normal

concrete which has 50mm slump height, the time it takes to absorb the water present in

the mixture is longer compared to the concrete containing abaca and sugarcane bagasse.

c. Sugarcane bagasse has the lowest slump height, ranging from 6mm to 21mm when

0.25% and 0.75% fiber-cement ratio were used. Sugarcane bagasse absorbed the water

present in the mixture in a very short period of time. Because of the water absorption

done by the sugarcane bagasse, the concrete mixture stiffens.

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CHAPTER 5: SUMMARY OF FINDINGS AND OBSERVATIONS, CONCLUSIONS AND RECOMMENDATIONS 2009-2010

d. Abaca fibers have lower slump values which is 21mm and 19mm at 0.25% and 0.75%

fiber-cement ratio compared to coconut coir and pineapple fibers. Although it has lower

slump, its consistency is still within the desired range when 0.10% and 0.15% fiber-

cement ratio were used.

2. Test cylinders with higher content of fiber reduce the compressive strength of the concrete due

to the congestion of fibers. The congestion of the fiber may lead to reduce bonding and

disintegration since packing is more difficult. Eventually void is introduced into the system:

a. Specimens with coconut coir fibers decrease its compressive strength by 7.4% to 7.8%

but then it increases by 4% to 11% at fiber-cement ratio of 0.25%, 0.75%, 0.10% and

0.15% respectively.

b. From 4% to 25% increase in compressive strength at 0.10% and 0.15% fiber-cement

ratio of sugarcane bagasse, it decreases from 15.6% to 53.9% when the fiber cement ratio

of 0.25% and 0.75% were used.

c. 8.9% up to 30% was the decrease in compressive strength of concrete cylinders with

0.25% and 0.75% fiber-cement ratio of pineapple fibers.

d. Concrete cylinders with abaca fibers also lower its compressive strength by 8.9% up to

33.7% when 0.25% and 0.75% fiber-cement ratio were used.

3. When plain concrete test cylinder was subjected to compression test, small initial cracks

formed on the surface of the test cylinder. Cracks progress abruptly and magnified at the center

of the test cylinder, followed by the shattering and bursting to failure. Failure condition is sudden

as the ultimate compressive load was attained. And when the concrete cylinders which contain

natural fibers were subjected to compression test at failure loads, the test cylinders were still

intact even when failure load was attained. Smaller cracks progressed especially with higher

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CHAPTER 5: SUMMARY OF FINDINGS AND OBSERVATIONS, CONCLUSIONS AND RECOMMENDATIONS 2009-2010

amount of natural fibers, from top of cylinders towards the center. This manifest the fiber

contribution in stopping or delaying the propagation of cracks. Figure 4.5 to 4.8 shows the test

cylinders after compression test. The cylinders which contain natural fibers were still intact at

maximum compressive load; unlike with the normal concrete, it split into two after the maximum

compressive load was attained. This shows that the brittle failure of plain concrete was

transformed to semi-ductile failure with the presence of natural fibers.

4. During the compressive test, all the concrete cylinders which contain 0.15% for each natural

fiber, the average load ranges from 380 KN to 480 KN which is obviously higher than the design

load. The concrete cylinders increase its compressive strength by 4% up to 25% compared to the

normal concrete.

5. By comparison, sugarcane has the highest compressive strength among the other concrete

cylinder which contains coconut coir, abaca fiber and pineapple fiber.

CONCLUSIONSFrom the previous chapter, it can be shown that the compressive strength of concrete mixture

containing natural fibers is significantly affected by the following factors: physical and chemical

composition of natural fibers, percentage of fiber and length of fiber. Based on the results of the

experiment, the following conclusions are drawn:

1. We concluded that the concrete mixture which contains 0.10% fiber-cement ratio has the

highest consistency compared to higher fiber-cement ratio. It only means that workability

decreases with the increase of fiber content. This is due to the water absorption

characteristics of the natural fibers which absorbed water during mixing and gave low

values of slump during slump test. Also, the increase in fiber content will increase the

volume of water being absorbed by the fibers. Thus, the increase in fiber content and the

increase of water being absorbed will delay the setting time period of the concrete

compared to the concrete with lesser amount of fiber.

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CHAPTER 5: SUMMARY OF FINDINGS AND OBSERVATIONS, CONCLUSIONS AND RECOMMENDATIONS 2009-2010

2. We concluded that adding natural fibers to the concrete mixture increases the

compressive strength. Even though adding natural fiber contributes to the increase in

strength, the strength does not increase linearly as the fiber content increases. In other

words, the increase in strength is only up to certain fiber content of 0.15%.

3. We concluded that the presence of natural fibers in concrete prevents or delays cracking

and transforms the brittle failure of plain concrete into gradual and ductile failure. But,

the increase in fiber content increases the volume of voids present in the composite. The

presence of voids can reduce the compacted fiber matrix mass of the composite. Thus,

0.15% fiber-cement ratio should be applied in order prevent crack formation and to

minimize the formation of voids

4. We concluded that at 0.15% fiber-cement ratio, all the specimens increase their

compressive strength which is higher by 4% to 26% compared to the normal concrete

5. We concluded that among the natural fibers that was added in the concrete mixture in

different percentage, sugarcane has the highest compressive strength. From the design

compressive strength of 20.7Mpa, the concrete which contains 0.15% sugarcane bagasse

has the compressive strength of 26.423Mpa which is 26% higher than the desired

compressive strength.

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CHAPTER 5: SUMMARY OF FINDINGS AND OBSERVATIONS, CONCLUSIONS AND RECOMMENDATIONS 2009-2010

RecommendationsThe study has its own limitation and therefore, the following recommendations are made

for future studies to improve the current work:

1. To use 0.15% fiber-cement ratio to maintain the consistency and workability of the fresh

concrete mixture.

2. To use sugarcane bagasse at 0.15% fiber-cement ratio to increase the compressive

strength by 26%

3. To utilize natural fibers in concrete mix in order to prevent and delay the spread of cracks

in future construction projects.

4. To experiment more in order to validate the adequacy of 0.15% fiber-cement as an

admixture for concrete mix. Try to evaluate the fiber-cement ratio of 0.11% to 0.20%

5. To utilize sugarcane bagasse in concrete mix since it has the higher compressive strength

6. To study how to treat the natural fibers before adding in the concrete mix. It might lessen

the volume of water being absorbed by the natural fibers.

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