“study of natural fibers as an admixture for concrete mix design” (chapter 3)

CHAPTER 3:RESEARCH METHODOLOGY 2009-2010

CHAPTER 3

RESEARCH METHODOLOGY

This chapter discussed the research methodology, project design, project development,

operation and testing procedures and also the evaluating procedures that will be used for this

research.

Research Method

This research will be using the ACI Mix Design Standard for normal concrete in

computing the design mix: volume of water, the weight of cement, sand and gravel, and the

ASTM standards for the physical and mechanical testing of fine and coarse aggregates.

Experimental method will be used in this study to investigate and evaluate the effect of

natural fibers when added to normal concrete in different percentage. There will be a series of

trials that will be conducted in this research. If the first trial failed to attain the objective of this

research, another trial will be conducted until the objectives were attained. Every trial will have

the same design mix as computed based on the ACI standards, the fiber-cement ratio; which is

the independent variable in this research will be the one that will be evaluated.

This research attributed the change in workability, consistency and compressive strength

to the effect of the fiber- cement ratio in the concrete mixture in different percentage.

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The figure below shows the flowchart done to arrange and explain all the main activities which

will be carried out all throughout the research.

Figure 3.1: Flow chart (Project Design and Development)

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LITERATURE REVIEWLITERATURE REVIEW

COLLECTING OF RAW MATERIALSEXTRACTING OF FIBERS

SELECTING TYPE OF CEMENT, FINE AND COARSE AGGREGATES

COLLECTING OF RAW MATERIALSEXTRACTING OF FIBERS

SELECTING TYPE OF CEMENT, FINE AND COARSE AGGREGATES

MIX PROPORTIONS (ACI Design Standards)

WATER / CEMENT RATIO

PERCENTAGE OF FIBERS

MIX PROPORTIONS (ACI Design Standards)

WATER / CEMENT RATIO

PERCENTAGE OF FIBERS

LABORATORY RESEARCHPREPARING & SELECTING RESEARCH INFORMATION

DATA COLLECTION

LABORATORY RESEARCHPREPARING & SELECTING RESEARCH INFORMATION

DATA COLLECTION

ANALYSIS AND EVALUATIONTESTING OF SPECIMENS

DATA ANALYSIS

SPECIMENS COMPARISON

ANALYSIS AND EVALUATIONTESTING OF SPECIMENS

DATA ANALYSIS

SPECIMENS COMPARISON

PREPARE REPORT ON RESEARCHPREPARE REPORT ON RESEARCH

RESEARCH PRESENTATION

RESEARCH PRESENTATION

DECIDE TOPIC AND RESEARCH OBJECTIVEDECIDE TOPIC AND

RESEARCH OBJECTIVE


Quality Test of Fine and Coarse aggregates

The fine and coarse aggregates will be tested first to determine the physical and

mechanical properties; the specific gravity, moisture content, water absorption, abrasion, unit

weight and the fineness modulus of sand that will be needed for the design mix.

Proportioning the trial mix based on ACI Mix Design Method for normal concrete

Choice of slump

If slump is not specified, a value appropriate for the work can be selected in the table below:

.

Table 3.1: Choice of slump

Type of constructionSlump

(mm) (inches)

Reinforced foundation walls and footings 25-75 1-3

Plain footings, caissons and substructure walls 25-75 1-3

Beams and reinforced walls 25-100 1-4

Building columns 25-100 1-4

Pavements and slabs 25-75 1-3

Mass concrete 25-50 1-2

*Slump may be increased when chemical admixtures are used, provided that the admixture-treated concrete has the

same or lower water-cement or water-cementitious material ratio and does not exhibit segregation potential or

excessive bleeding.

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Choice of maximum size of aggregate

Large nominal maximum sizes of well graded aggregates have less voids than smaller

sizes. Hence, concretes with the larger-sized aggregates require less mortar per unit volume of

concrete. Generally, the nominal maximum size of aggregate should be the largest that is

economically available and consistent with dimensions of the structure. In no event should the

nominal maximum size exceed one-fifth of the narrowest dimension between sides of forms,

one-third the depth of slabs, nor three-fourths of the minimum clear spacing between individual

reinforcing bars, bundles of bars, or pretensioning strands. These limitations are sometimes

waived if workability and methods of consolidation are such that the concrete can be placed

without honeycomb or void. In areas congested with reinforcing steel, post-tension ducts or

conduits, the proportioner should select a nominal maximum size of the aggregate so concrete

can be placed without excessive segregation, pockets, or voids. When high strength concrete is

desired, best results may be obtained with reduced nominal maximum sizes of aggregate since

these produce higher strengths at a given water-cement ratio.

In this research, the maximum size of the aggregates will be ¾”, approximately 19mm in

diameter.

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The quantity of water per unit volume of concrete required to produce a given slump is dependent on: the nominal maximum size, particle shape, and grading of the aggregates.

Table 3.2: Estimation of mixing water and air content

Mixing water Quantity in kg/m3(lb/yd3) for the listed Nominal

Maximum Aggregates Size

Slump

9.5mm

(0.375i

n.)

12.5mm

(0.5in.)

19mm

(0.75in.)

25mm

(1in.)

37.5mm

(1.5in.)

50mm

(2in.)

75mm

(3in.)

100mm

(4in.)

Non-Air-Entrained PCC

25-50

(1-2)

207

(350)

199

(335)

190

(315)

179

(300)

166

(275)

154

(260)

130

(220)

113

(190)

75-100

(3-4)

228

(385)

216

(365)

205

(340)

193

(325)

181

(300)

169

(285)

145

(245)

124

(210)

150-175

(6-7)

243

(410)

288

(385)

216

(360)

202

(340)

190

(315)

178

(300)

160

(270)-

Typical entrapped

air (percent)

32.5 2 1.5 1 0.5 0.3 0.2

Air-Entrained PCC

25-50

(1-2)

181

(305)

175

(295)

168

(280)

160

(270)

148

(250)

142

(240)

122

(205)

107

(180)

75-100

(3-4)

202

(340)

193

(325)

184

(305)

175

(295)

165

(275)

157

(265)

133

(225)

119

(200)

150-175

(6-7)

243

(410)

228

(385)

216

(360)

202

(340)

190

(315)

178

(300)

160

(270)-

Recommended Air Content (percent)

Mild Exposure 4.5 4.0 3.5 3.0 2.5 2.0 1.5 1.0

Moderate

Exposure6.0 5.5 5.0 4.5 4.5 4.0 3.5 3.0

Severe exposure 7.5 7.0 6.0 6.0 5.5 5.0 4.5 4.0

Selection of water-cement ratio

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Table 3.3: Water cement ratio for Normal Concrete

28-Day Compressive Strength

in MPa (psi)

Water-cement ratio by weight

Non-Air-Entrained Air-Entrained

41.4 (6000) 0.41 -

34.5 (5000) 0.48 0.40

27.6 (4000) 0.57 0.48

20.7 (3000) 0.68 0.59

13.8 (2000) 0.82 0.74

Cement content

The cement content will be computed based on the below formula:

Estimation of coarse aggregate content

Aggregates of essentially the same nominal maximum size and grading will produce concrete of satisfactory workability when a given volume of coarse aggregate, on an oven-dryrodded basis, is used per unit volume of concrete.

Table 3.4: Volume of coarse aggregate per unit of volume of concrete

Nominal

Maximum

Aggregate Size

Fine Aggregate Fineness Modulus

2.40 2.60 2.80 3.00

9.5mm(0.375inches) 0.50 0.48 0.46 0.40

12.5mm(0.5inches) 0.59 0.57 0.55 0.53

19mm(0.75inches) 0.66 0.64 0.62 0.60

25mm(1inches) 0.71 0.69 0.67 0.65

37.5mm(1.5inches) 0.75 0.73 0.71 0.69

50mm(2inches) 0.78 0.76 0.74 0.72

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Estimation of coarse aggregate content

With the quantities of water, cement, and coarse aggregate established, the remaining

material comprising the m3 of concrete must consist of fine aggregate and whatever air will be

entrapped. The required fine aggregate may be determined on the basis of either weight or

absolute volume.

Table 3.5: First Estimate of mass of fresh concrete

Nominal Maximum size of

aggregate, mm

First estimate of concrete unit mass, kg/m3

Non-air-entrained concrete Air-entrained concrete

9.5 2280 2200

12.5 2310 2230

19 2345 2275

25 2380 2290

37.5 2410 2350

50 2445 2345

75 2490 2405

150 2530 2435

Adjustments for aggregate moisture

The aggregate quantities actually to be weighed out for the concrete must allow for

moisture in the aggregates. Generally, the aggregates will be moist and their dry weights should

be increased by the percentage of water they contain, both absorbed and surface. The mixing

water added to the batch must be reduced by an amount equal to the free moisture contributed by

the aggregate.

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Collection and Preparation of Raw Materials

Cement

Locally produced Type 1 Portland cement will be used in the investigation of composite

materials. The table below shows the chemical composition of typical Type 1 Portland cement

Table 3.6: Chemical composition of Portland cement

Constituent Percentage by weight

Lime (CaO) 62.561

Silica (SiO2) 19.757

Alumina (Al2O3) 5.591

Iron Oxide (Fe2O3) 3.393

Magnesia (MgO) 1.233

Sulfur Trioxide (SO3) 2.382

(P2O5) 0.078

(N2O) 0.019

Loss of ignition 2.144

Water

In the production of concrete, water plays an important role. The water that will be used

should not contain any substance that might affect the hydration of cement and affect the

durability of concrete. Generally, drinking water from the tap will be used for the concrete mix.

Fine and Coarse aggregates

The aggregate component of a concrete mix occupies 60 to 80 percent of the volume of

concrete, and heir characteristics influence the properties of concrete. The coarse aggregates that

will be used have an approximately 19mm in size. The gravel is then first passed through sieves

to get the desired maximum 19-mm diameter gravel. Fine aggregates commonly known as sand

should comply the requirements of the American Concrete institute (ACI) mix design method.

The sand and gravel are kept in the laboratory to dry before being used.

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Figure3.2: sieving of coarse aggregates

Natural Fibers

Extracted fibers of coconut coir, sugarcane, banana, and pineapple are cut with a scissor

to a length of approximately 1cm. The fibers are then dried at room temperature for couple of

hours so as to remove the absorbed water.

(a) Abaca (b) Coconut coir (c) Pineapple (d) Sugarcane bagasse

Figure 3.1: natural fibers

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Test Specimens

The cement composites for testing will be prepared in the form of cylinders with

dimensions of 150mm in diameter and 300mm high for compression test. 27 specimens will be

made and tested for the first trial mix.

Table 3.2: distribution of specimens for first trial

For the second trial batch mix, the fiber content will be 0.10% and 0.15%, there will be a

total of 27 specimens, these will be distributed as follows:

Table 3.3: distribution of specimens for second trial

Slump Test

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A slump test is performed on all batches to measure the workability of the fresh concrete

in accordance with ASTM C 143-78 (slump test of Portland cement concrete). This test is used

to monitor the consistency of the mixture from batch to batch.

Curing of test specimens

Specimens are cured in accordance with ASTM C 31-84, standard method of making and

curing concrete test specimen in the field. The specimens will be cured in water tank before

testing.

Figure 3.3: curing of cylinders

Compressive Strength Test

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The ASTM C 39-86, standard method for compressive strength of cylindrical concrete

specimens for plain concrete is also applies to concrete containing coir fibers, sugarcane

baggase, pineapple, and abaca fibers. In this method, a concentric compressive force is applied to

the ends of a 150mm diameter concrete cylinder with a height of 300mm at a constant rate of

5kn/sec until failure will occur at the load P. the compressive strength f’c in N/mm2 (MPa) will

be calculated by

Compressive strength

Where:

P = ultimate compressive load of concrete (KN)

A = surface area in contact with the plates ( mm2)

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“study of natural fibers as an admixture for concrete mix design” (chapter 3)

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