“STUDY OF NATURAL FIBERS AS AN ADMIXTURE FOR CONCRETE MIX DESIGN” (CHAPTER 4)

CHAPTER 4: PRESENTATION, ANALYSIS AND INTERPRETATION OF DATA 2009-2010

CHAPTER 4

PRESENTATION, ANALYSIS AND INTERPRETATION OF DATA

In this various tests conducted on the specimens will be looked into. This study aims to

investigate the workability and the compressive strength of the concrete mixture which contains

natural fibers as an admixture. All the specimens were cured in a water tank before testing.

Natural fibers were added with the fiber-cement ratio of 0.10%, 0.15%, 0.25%, and 0.75%

respectively.

Table 4.1: Results of quality test for fine and coarse aggregates

TEST

COARSE

AGGREGATES

FINE

AGGREGATES

SPECIFIC GRAVITY 2622 2344

MOISTURE CONTENT 0.37 %

1.46 %

ABSORPTION 0.79 2.5

UNIT WEIGHT ------------------------- -------------------------

•LOOSE 1475 1412

•RODDED 1663 1610

FINENESS MODULUS - 2.82

Table 4.1 shows the result taken from the physical and mechanical test for fine and

coarse aggregates.

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DESIGN PARAMETERS

These parameters were computed as stated in the ACI mix design method, the parameters

are the following:

Choice of slump…..………..25mm (minimum)

100mm (maximum)

Maximum aggregate size…..19mm

Mixing water……………….205 kg/m3 (non air entrained)

Water cement ration………..0.68 (non air entrained)

Cement content…………….301.5 KG

Coarse aggregate content…..1028kg

Fine aggregate content……..732kg

Mixing water…………........193.1 kg (adjustment for aggregate moisture)

Table 4.2: Summary of design mix

Quantities/(m3) Cement (kg) Water (kg) F.A (kg) C.A. (kg)Fiber

content

per m3 301 192 823 1032 -

Control 6.5 4.1 17.7 22 -

*0.10% 6.5 4.1 17.7 22 6.5

0.15% 6.5 4.1 17.7 22 9.75

*0.25% 6 3.8 16 20.5 15

0.75% 6 3.8 16 20.5 44.9

Table 4.2 shows the summary of the design mix as computed based on the ACI mix

design method.

* The 0.25% and 0.75% are the first trial mix; the factor of safety is 25%

* The 0.10% and 0.15% are the second trial mix; the factor of safety was adjusted to 35%

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SLUMP TEST

The slump height was measured in terms of millimeters unit. The results of the test are as

follows:

Table 4.3: Results of Slump Test for first trial

SPECIMENS

*WEIGHT

OF FIBER

(g)

WEIGHT

OF

CEMENT

(kg)

WEIGHT

OF

SAND

(kg)

WEIGHT

OF

GRAVEL

(kg)

SLUMP

HEIGHT

(mm)

REMARKS

PASSED/FAILED

Control 0 6 16 20.5 50 passed

0.25% fiber content

Coconut coir 15 6 16 20.5 60 passed

Pineapple 15 6 16 20.5 18 failed

Sugarcane 15 6 16 20.5 20 failed

Abaca 15 6 16 20.5 21 failed

0.75% fiber content

Coconut coir 44.9 6 16 20.5 36 passed

Pineapple 44.9 6 16 20.5 20 failed

Sugarcane 44.9 6 16 20.5 6 failed

Abaca 44.9 6 16 20.5 19 failed

The design slump height for this research is from the range of 25mm to 100 mm, table

4.3 shows that only the normal concrete and the concrete which contains coconut coir has the

passing slump height.

*the weight of the fiber is based from the fiber-cement ratio stated in the previous chapter

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Figure 4.1: slump test result for first trial

Figure 4.1 shows the result of the slump test done in the first trial of mixing. The design

range is from 25mm to 100mm, but the result shows that for nine batch mixes, majority of the

results are below the minimum slump height of 25mm. Compared to the control (normal

concrete), its slump height is 50mm which is within the design range. It only means that the

control has higher workability and consistency compared to the concrete mixture which contains

0.25% and 0.75% fiber content (pineapple, sugarcane bagasse and abaca)

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Table 4.4: Results of Slump Test for second trial mix

SPECIMEN

*WEIGHT

OF FIBER

(g)

WEIGHT

OF

CEMENT

(kg)

WEIGHT

OF SAND

(kg)

WEIGHT

OF

GRAVEL

(kg)

SLUMP

HEIGHT

(mm)

REMARKS

PASSED/FAILED

Control 0 6.5 17.7 22 98 passed

0.10% fiber content

Coconut coir 6.5 6.5 17.7 22 83 passed

Pineapple 6.5 6.5 17.7 22 47 passed

Sugarcane 6.5 6.5 17.7 22 65 passed

Abaca 6.5 6.5 17.7 22 56 passed

0.15% fiber content

Coconut coir 9.75 8.2 16 22 62 passed

Pineapple 9.75 8.2 16 22 38 passed

Sugarcane 9.75 8.2 16 22 29 passed

Abaca 9.75 8.2 16 22 34 passed

Table 4.4 shows the result of the slump test for the second trial. The fiber-cement ratio in

this trial is 0.10% and 0.15% respectively. It shows that all the slump height is within the design

range of 25mm to 100mm

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*the weight of the fiber is based from the fiber-cement ratio stated in the previous chapter

Figure 4.2: slump test result for second trial

Figure 4.2 shows the result of the slump test done in the second trial of mixing. The result

shows good results since all the slump height are within the design range of 25mm to 100mm,

but the concrete mixture which contains natural fibers (coconut coir, pineapple, sugarcane

bagasse, and abaca) are still lower than the plain concrete.

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The figures below show the actual photos taken during the slump test made for

each batch mixes:

(a) (b)

Fresh concrete mixture which contains (a) 0.10% and (b) 0.15% sugarcane bagasse fiber

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(c) (d)

Fresh concrete mixture which contains (c) 0.25% sugarcane bagasse and (d) 0.10% pineapple

fiber

(e) (f)

Fresh concrete mixture which contains (e) 0.15% pineapple fiber and (f) 0.25% pineapple fiber

(g) (h)

Fresh concrete mixture which contains (g) 0.10% coconut fiber and (h) 0.15% coconut fiber

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(i) (j)

Fresh concrete mixture which contains (i) 0.25% coconut fiber and (j) 0.75% coconut fiber

(k) (l)

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Fresh concrete mixture which contains (k) 0.10% abaca fiber and (l) 0.15% abaca fiber

(m) (n)

Fresh concrete mixture which contains (m) 0.25% abaca fiber and (n) 0.75% abaca fiber

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COMPRESSIVE STRENGTH

As described in chapter 3, 27 concrete cylinders with the size of 150mm in diameter and

300mm in length were tested for compressive test. The specimens were tested at 6 days after

curing in a water tank. Specimens were tested for compressive strength by applying increasing

compressive load until failure occurs.

Table 4.5: Results of compressive test for first trial

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The design compressive load for this mix design is 20.7 Mpa. Table 4.5 shows that the

entire specimen with natural fibers has lower compressive strength compared to the normal

concrete

* the remarks indicates whether the concrete cylinders failed or passed the desired compressive strength of 20.7Mpa

Figure 4.3: average compressive strength for first trial

Above figure shows the average compressive strength for each specimen for the first trial

where 0.25% and 0.75% fiber-cement ratio was used. In this figure, it can be seen that the result

was not good since at 0.75% fiber-cement ratio, the entire specimen produces low compressive

strength wherein it does not attain the desired compressive strength of 20.7 Mpa

Since the result of the first trial was not good, the researchers conducted another trial to

attain the design compressive strength wherein the fiber-cement ratio this time was limited to

0.10% and 0.15%

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Table 4.6: Results of compressive test for second trial

Table 4.6 shows the result of the compressive strength test for the second trial. Among 27

specimens, only 2 specimens does not attain the design compressive strength of 20.7 Mpa

* the remarks indicates whether the concrete cylinders failed or passed the desired compressive strength of 20.7Mpa

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Figure 4.4: average compressive strength for second trial

Above figure shows the difference in compressive strength of all the specimens in every

type of fiber and fiber-cement ratio of 0.10% and 0.15% respectively. It clearly shows that at

0.15% fiber content, all the specimens increases their compressive strength by 3% up to 26%

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Figure 4.5: average compressive load vs. fiber percentage

Figure 4.5 shows the average compressive strength of the concrete mixture containing

coir fibers, sugarcane bagasse, pineapple fibers and abaca fibers is greater at the 0.15% fiber-

cement ratio and decreases at 0.25% and 0.75% fiber-cement ratio. The figure shows that

sugarcane bagasse at 0.15% fiber-cement ratio has the highest compressive strength of

26.423Mpa which is 26% higher than the normal concrete.

EFFECT OF PERCENT FIBER

The main effect of the percent fiber contribution can be seen also from the figure 4.5. The

figure shows the average compressive strength for each specimen. The plot indicates that as the

fiber content increases from 0.10% and 0.15%, the compressive strength also increases, but

decreases as the fiber content increases from 0.25% and 0.75%.

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The figure below shows the photos taken after the compression test was done. Cracks can

be seen and the facture can be classified by investigating the crack formation.

(a) (b)

Figure 4.6 (a) concrete mixture which contains 0.25% abaca and (b) concrete mixture which

contains 0.75% abaca after compression test was done

(a) (b)

Figure 4.7: (a) concrete mixture which contains 0.25% pineapple and (b) concrete mixture

which contains 0.75% pineapple after compression test was done

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(a) (b)

Figure 4.8: (a) concrete mixture which contains 0.25% sugarcane and (b) concrete mixture

which contains 0.75% sugarcane after compression test was done

(a) (b)

Figure 4.9: (a) concrete mixture which contains 0.25coconut coir and (b) concrete mixture

which contains 0.75% coconut coir after compression test was done

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Figure 4.10: concrete mixture that contains no fiber after the compression test.

By investigation, all the concrete cylinders which contain natural fibers, from 0.25% and

0.75% fiber content, the cracks made by the ultimate load is quite minimal compared to the

concrete cylinder which contains no fiber. In figure 4.10, it can be seen that the control splits into

two after the test was done, unlike the other specimens; they only produce short cracks in some

area of the cylinder. The probable reason is that, fibers which are randomly placed as the fresh

concrete is mixing, the fibers hold the particles, which act as the roots of the mixture, which can

help lessen the formation of cracks even if it attained its ultimate load.

.

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“STUDY OF NATURAL FIBERS AS AN ADMIXTURE FOR CONCRETE MIX DESIGN” (CHAPTER 4)

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