Selection Of Constituent Materials

Published Date: 02 Nov 2017

CHAPTER 3

METHODOLOGY

3.1 Introduction

This chapter presents the methods and procedures adopted to achieve the predetermined aims and objectives of the study. Since it was a lab-based experimental research, a proper planning of work was necessary to respect the time frame and make proper usage of the resources available for the research. The project was devised as follows:

Establishing an overall program of work.

Selection of constituent materials.

Conducting preliminary investigations on:

Aggregates, and

Macro synthetic fibres; according to relevent standards.

Carrying out a specific mix design using the preliminary investigations data.

Carrying out the laboratory procedures:

Addition and mixing,

Casting, finishing and curing, and

Concrete testing; according to relevent standards.

Analysis of test results and report writing.

3.2 Overall Program of Work

The overall program of work consisted of three distinctive parts:

Selection of dosage rate of macro synthetic fibres.

Planning of concrete mixes.

Planning of tests:

Preliminary lab tests to be done on aggregates and macro synthetic fibres according to relevent standards.

Tests to be performed on fresh and hardened properties of concrete.

Selection of Dosage Rate of Macro Synthetic Fibres

The dosage rates of macro synthetic fibres that would be used for each mix was selected based on the literature review; and were 2.0 kg/m3, 2.5 kg/m3 and 3.0 kg/m3 respectively. These dosage rates of macro synthetic fibres were chosen so as to avoid the need of a superplastizer which would influence the effects of macro synthetic fibres on concrete properties.

Planning of Concrete Mixes

Macro Synthetic Fibre Reinforced Concretes (MSFRCs) produced in this study were each assigned a mix code as shown in Table 3.1 along with their descriptions.

Table 3.1: Mix Codes of MSFRCs

Description

Mix code

MRFRC including Strux 90/40

MS1

MRFRC including BarChip Macro

MS2

Two pairs of concrete mixes (A and B) were designed and batched in the laboratory. Each pair of concrete mixes consisted of a control (plain concrete) and macro synthetic fibre based concrete mixes with increasing fibre content (2.0 kg/m3, 2.5 kg/m3 and 3.0 kg/m3). Each MSFRC mixes (MS1 and MS2) were compared with the given control mix. The same control mix was used for both pair of concrete mixes. The classification of concrete mixes is given in Table 3.2.

Table 3.2: Classification of Concrete Mixes

Pairs of mixes

Mix code

Fibre content (kg/m3)

Mix 1

Mix 2

Mix 3

Mix 4

A

MS1

0 (control)

2.0

2.5

3.0

B

MS2

0 (control)

2.0

2.5

3.2.3 Planning of Tests

3.2.3.1 Preliminary Investigations on Aggregates and Macro Synthetic Fibres

The physical properties of aggregates and macro synthetic fibres to be investigated are given in Table 3.3 and Table 3.4 respectively along with their relevent standards used.

Table 3.3: Properties of Aggregates to be Investigated

Test Property

Standards

Relative Density

BS 812: Part 2: 1975

Water Absorption

BS 812: Part 2: 1975

Grading

BS 812: Part 1: 1975

Table 3.4: Properties of Macro synthetic fibres to be Investigated

Test Property

Standards

Water Absorption

BS 812: Part 2: 1975

Tensile strength

BS EN 14889: Part 2

3.2.3.2 Investigations on Fresh and Hardened Properties of Concrete

The fresh and hardened concrete properties studied in this research are presented in Table 3.5 and Table 3.6 respectively together with the specifications of the specimen, quantity per batch, volume, timing and their relevent standards used.

Fresh Concrete Properties

Table 3.5: Fresh Concrete Properties Investigated and their Relevent Standards

Test Property

Quantity per batch

Volume (m3)

Timing (days)

Standards

Slump

1

0.010

0

BS 1881: Part 102: 1983

Plastic Density

1

0

BS 1881: Part 107: 1983

Hardened Concrete Properties

Table 3.6: Hardened Concrete Properties Investigated and their Relevent Standards

Test Property

Test Specimen

Quantity per batch

Volume (m3)

Timing (days)

Standards

Compressive strength

100×100×100 mm cubes

6

0.006

7, 28

BS 1881: Part 116: 1983

Hardened density

100×100×100 mm cubes

6

0.006

7, 28

BS 1881: Part 114: 1983

Flexural strength

75×75×300 mm prisms

3

0.006

28

BS 1881: Part 118: 1983

Tensile splitting strength

150 mm Φ × 300 mm long cylinders

3

0.015

28

BS 1881: Part 117: 1983

Modulus of elasticity

150 mm Φ × 300 mm long cylinders

2

0.010

28

BS 1881: Part 5: 1970

Drying shrinkage

75×75×300 mm prisms

3

0.006

28,42,43,44

BS 1881: Part 5: 1970

Note: The same 100×100×100 mm cubes for compressive strength test were used for the hardened density test prior to crushing.

Materials

Macro Synthetic Fibre

For the purpose of this research, two different types of macro synthetic fibres were used, namely, Strux 90/40 and BarChip Macro. These fibres were obtained from Premixed Concrete Ltd and as mentioned by the company, they were imported from their respective source of production companies. Strux 90/40 is produced and sold commercially by Grace Construction Products and Barchip Macro is available at Elasto Plastic Concrete (EPC). Table 3.7 below shows the characteristics properties of both macro synthetic fibres obtained from their respective source of production companies.

Table 3.7: Characteristic Properties of Macro Synthetic Fibres

Fibre Type

Strux 90/40

Barchip Macro

Material

Polyolefin

Modified olefin

Cross section

Rectangular

Circular

Surface Texture

Flat

Continuously Embossed

Length (mm)

40

42

Thickness (mm)

0.11

N/A

Width (mm)

1.4

N/A

Diameter (mm)

N/A

1.0

Aspect Ratio

90

41

Specific Gravity

0.92

0.90 – 0.92

Absorption

None

None

Tensile Strength (MPa)

620

550

Modulus of Elasticity (GPa)

9.5

8.2

Melting Point (°C)

160

150 - 165

Ignition Point (°C)

590

Greater than 450

Alkali, Acid & Salt Resistance

High

High

D:\My Works- Year 4\Degree Project\fotos dissertation\Pic_1210_051.jpg D:\My Works- Year 4\Degree Project\fotos dissertation\Pic_1210_052.jpg

Figure 3.1: Macro synthetic fibre Strux 90/40 (Left) and BarChip Macro (Right)

Cement

Ordinary Portland cement (Type 1) was used as binder throughout the project, which conformed to BS 12. Therefore no tests was carried out to determine the physical properties such as density, consistency and soundness.

Aggregates

Rocksand of size 0-4 mm of crushed basaltic type was used as fine aggregates. Crushed basalt of size 6-10 mm and 14-20 mm were used as coarse aggregates. Both fine and coarse aggregates were locally available and in saturated surface dry (SSD) condition.

Water

Tap water was used in the experimental work since it is free from deleterious substances and impurities which might affect the concrete.

Preliminary Investigations

Preliminary Tests on Aggregates

Prior to etablishing a proper mix design for concrete batching, preliminary tests such as sieve analysis, relative density and water absorption were carried out on both fine and coarse aggregates according to their relevent standards as shown in Table 3.3. Graphs and data obtained from these preliminary tests were used for the mix design calculation.

Preliminary Tests on Macro Synthetic Fibres

A water absorption test was carried out on both macro synthetic fibre (Strux 90/40 and BarChip Macro) so as to confirm the information about this physical property shown in Table 3.7. The test devised was similar to that of water absorption of aggregates. Since macro synthetic fibres float on water, the macro synthetic fibres were covered with a wet cloth with a wooden board placed on top of the latter, thus ensuring that the fibres were completely immersed in water.

Mix Design

Using the preliminary investigations data, the mix design was prepared according to the ‘DoE mix design method’ which is based on the tables and figures available in BRE. A concrete mix of grade 30MPa with the target mean strength of 35MPa at 28 days was designed since this concrete grade is the most preferred and widely used on site; particularly for the slabs-on-grade construction. It is to be noted that no factor of safety was added to the characteristic strength. The proportions of the constituent materials for the control mix design (0 kg/m3 fibre) is shown in Table 3.7 and a detailed control mix design is shown in Appendix 1.

Table 3.8: Control Mix Design (0 kg/m3 fibre)

Cement

(kg/m3)

Fine Aggregate

(kg/m3)

Coarse

Aggregate

(kg/m3)

Free Water

(kg/m3)

Absorbed Water

(kg/m3)

Total water

(kg/m3)

6-10

14-20

395

865

390

585

225

42

267

Mixture Proportions

A trial mix was done before starting with the batching for control mix and other concrete mixes. The slump targeted was 60-180 mm and since it was a large slump range, the amount of free water added had to be adjusted in order to achieve a satisfactory workable mix. From the trial mix, the total free water added was reduced to 215 kg/m3. This new free w/c ratio= 0.54 was kept constant for all mixes. For the MSFRC mixes, the same adjusted mix composition as that for the control mix was used. Macro synthetic fibres would be dosed at a rate of 2.0 kg/m3, 2.5 kg/m3 and 3.0 kg/m3 in the adjusted control concrete mix. Table 3.8 shows the exact mixture proportions for all the adjusted design mixes.

Table 3.9: Mixture Proportions for Adjusted Design Mixes

Pair of mixes

Fibre Content (kg/m3)

Cement (kg/m3)

Fine Aggregate (kg/m3)

Coarse Aggregate (kg/m3)

Free Water (kg/m3)

Absorbed Water (kg/m3)

Total water (kg/m3)

6-10

14-20

A

0

395

865

390

585

215

42

257

2.0

395

865

390

585

215

42

257

2.5

395

865

390

585

215

42

257

3.0

395

865

390

585

215

42

257

B

0

395

865

390

585

215

42

257

2.0

395

865

390

585

215

42

257

2.5

395

865

390

585

215

42

257

3.0

395

865

390

585

215

42

257

Laboratory Procedures

Addition and Mixing

A tilting drum mixer was used to carry out the concrete batching. Firstly, the coarse aggregates were added to the mixer followed by macro synthetic fibres. The mixture was dry mixed for 2 minutes and the mixer was stopped. This was done to ensure that the macro synthetic fibres were uniformly distributed. It was made sure that no fibre balls were formed which would affect the concrete’s consistency. The mixer was switched on and the absorption water was added to the mix. The fine aggregate was added to the mix followed by one-quarter of the free water. The mixture was allowed to be mixed for another 2 minute. The machine was switched off and a trowel was used to ensure equal distribution of the aggregate-fibre mix. The cement was added followed by the remaining free water and this was mixed for about 5 minutes. The mixer was stopped again and the trowel was used to scratch the fine aggregate which would stick to the mixer’s surface and the mixing was carried out. The machine was stopped when visually an evenly distributed FRC mix was obtained.

3.6.2 Casting, Finishing and Curing

The freshly mixed concrete was casted in the moulds in two layers. The moulds were cleaned and oiled and the concrete specimens were casted as per BS 1881. A vibrating table was used for proper compaction of each layer. After compaction, a trowel was used to level and smooth the top surface ensuring that the surface was free from macro synthetic fibres. The curing method adopted for this research was water curing. The casted specimens were stored for 24 hours, with wet gunnysacks on top of the moulds. After 24 hours, the specimens were demoulded with care and placed in the water-curing basin at a temperature of 27 ± 2°C.

Concrete Testing – Fresh Concrete

Slump

The slump test was carried out just after mixing and according to BS 1881: Part 102: 1983. In this study, no additional water was added to the fibre reinforced mix during the batching process to have a better understanding of how macro synthetic fibres is really affecting the workability of concrete.

Plastic Density

The plastic density test procedure was performed in accordance to BS 1881: Part 107: 1983. The weight of the compacted fresh concrete in a container of known mass was determined. The plastic density was calculated as the total mass of concrete divided by the volume of the container.

Concrete Testing – Hardened Concrete

Compressive Strength

The compressive strength test was carried out as per BS 1881: Part 116: 1983. For each mix, three 100×100×100 mm cubes were tested at 7 and 28 days respectively. The prepared cubes were instrumented in Bracknell machine, type GD 10 grade A of capacity 2000 kN and the maximum crushing load corresponding at ultimate failure was measured. Compressive strength (N/mm2) was calculated using the equation:

Compressive strength, fcu = P/ab

Where P = maximum crushing load (kN)

a = length of cube (mm)

b = width of cube (mm)

Flexural Strength

For each mix, three 75×75×300 mm prisms were tested at 28 days according to BS 1881: Part 118: 1983 whereby a two-point loading method was used to determine the flexural strength. The flexural strength (N/mm2) of the prisms were calculated using the equation:

Flexural strength, fcf = FL / bd2

Where F = breaking load (kN)

L = span (mm)

b = width of prism (mm)

d = depth of prism (mm)

Tensile Splitting Strength

The tensile splitting strength test was carried out in accordance to BS 1881: Part 117: 1983. Three 150 mm Φ × 300 mm long cylinders were tested at 28 days. The tensile splitting strength (N/mm2) was calculated by the formula:

Tensile splitting strength, fct = 2F / Ld

Where F = maximum load (N)

L = length of specimen (mm)

d = cross-sectional diameter of specimen (mm)

Hardened Density

The hardened density test procedure was done as per BS 1881: Part 114: 1983. The same cubes used for the compressive strength test were used for the determination of hardened density. The hardened density was calculated as the mass of the cube divided by its volume.

Modulus of Elasticity

The method prescribed in BS 1881: Part 5: 1970 was used to determine the static modulus of elasticity of 150 mm Φ × 300 mm long cylinders after 28 days of curing in water. A capping was placed on top of the cylinder to provide a smooth and even surface to apply the load. A preliminary loading was done on the cylinder followed by two set of loadings whereby the strain values were taken. An average of the two strain values were taken as final strain. A graph of stress against strain was plotted and the modulus of elasticity was determined from the gradient of the straight line.

Drying Shrinkage

For each mix, three 75×75×300 mm prisms were used to determine the drying shrinkage. The test was carried out according to BS 1881: Part 5: 1970. After 28 days of curing, a wet measurement taken. After oven dried at 55°C-60°C for 14 days consecutively, a dry measurement of the prisms were taken. This step was repeated for the following two days. The drying shrinkage was calculated as the difference between the wet measurement and the dry measurement and this was expressed as a percentage of the length of the prism.