37

CHAPTER-III

EXPERIMENTAL PROGRAM

3.0 INTRODUCTION

Reactive powder concrete (RPC) has initiated an interest and

possibility of expecting ultra high performances from commercially

available materials. They possess ultra high strength and high ductility

with advanced mechanical properties and consist of a specific

microstructure, which was optimized by precise gradation of all

particles in the mix to yield maximum density. It uses extensively the

pozzolanic properties of highly refined silica fume and optimization of

the Portland cement chemistry to produce the high strength hydrates.

The properties of hardened Ultra High Performance Concrete (UHPC)

were determined by the very dense structure of this material. The

microstructure of UHPC differs significantly from normal- and high-

strength concrete. With respect to the mechanical behavior, UHPC with

fibres shows, depending on the type and quantity of fibres contained in

the mix, ductile behavior under compression as well as in tension. In

contrast to this, UHPC without fibres behaves brittle, if no additional

measure such as confinement is chosen. Since the pre-peak behavior

does not show significant differences, the elastic properties of UHPC

with and without fibres can be described, in common whereas the

influence of fibres has to be described separately. By introducing fine

steel fibres, they can exhibit remarkable strengths and energy

absorptions. However, lot of research works were carried out for the

38

production of RPC, which is an UHPC, very few studies, precisely

compares in detail their mechanical properties with UHPC. In addition,

the role of fibre addition on the compressive and flexural strengths of

RPC is required to understand and set optimum limits on the fibre

content.

This chapter presents the details of development of Reactive Powder

Concrete and the various test programs conducted. The study is aimed

at identifying and optimizing the salient parameters that influenced the

mixture proportions of the Reactive Powder Concrete and its curing

methods. Also, study of various mechanical properties of RPC is carried

out to find the feasibility of using RPC as structural components such

as angle sections. The various test programs are as follows.

3.1 EXPERIMENTAL SCHEDULE

Production of RPC with a target compressive strength of

approximately 200 MPa using conventionally available materials (viz.,

cement, fine aggregate, silica fume, quartz powder, and micro fibre) and

following appropriate heat curing cycles.

1. Study of mechanical properties of RPC

2. The effect of fibre addition on the compressive and flexural strengths

was also studied to establish optimum limits on fibre content.

3. Investigation on use of RPC for specific application.

4. Design of RPC mixes for target compressive strength of 150-200 MPa

5. Material characterization by conducting studies on following

Mechanical properties

39

i. Study of compressive strength of RPC

ii. Stress-strain characteristic of RPC under compression

iii. Study of Tensile Properties of RPC by conducting

a)Direct tension test using Dog-bone shaped specimen

b) Evaluating the cracking behavior of RPC under tension using

the micro-mechanical modeling technique.

iv. Three point bending test

v. Shear strength

6. Investigation on use of RPC for specific Applications

i. Performance Evaluation of RPC angle section with various

heights under compression.

ii. Performance Evaluation of RPC angle sections under flexure.

iii. Performance Evaluation of RPC infilled tubes under

Compression.

7. Investigation on Connection Details.

i. Study of Bolted RPC plates under direct tension.

3.2 MATERIALS USED AND THEIR PROPERTIES

Ordinary Portland cement confirming to IS: 12269 was used for the

study. The silica fume used in this study had a Blain’s fineness of

20m2/g. The silica fume contained 94% silicon dioxide while the quartz

powder contained mostly silicon dioxide. The chemical composition and

the particle size distribution of the cementitious powders are shown in

Table 3.1 and 3.2. Standard sand confirming to IS: 650 were used for

producing Reactive powder concrete (RPC). The maximum and nominal

40

size of aggregates used for RPC is 2.36mm respectively. Based on size

of aggregates, two lengths of micro steel fibres were used 6mm, and

13mm micro-steel fibres (for RPC). Eventually the workability was

controlled using adequate quantities of third generation poly-carboxylic

based superplasticizers. The properties of these fibres are shown in

Table 3.4. The mix proportions used for the production of RPC are

tabulated in Table 3.5.

3.3 FORMULATION AND PROPERTIES OF RPC

A Reactive Powder Concrete formulation developed at the Structural

Engineering Research Center, Chennai, based on extensive

investigations [Harish et. al., 200719, Dattatreya.J.K., et. al., 200835]

was used for production of RPC and the behavior of cylinders with

various combinations of fibre content are investigated. The various

experimental activities involved in this study were presented in the

following paragraphs.

Table 3.1 gives the properties of the materials used in this

investigation

The materials used in the present investigation are listed below:

1. Ordinary Portland cement of Grade 53 conforming to IS: 12269 :

1987

2. Silica Fume

3. Quartz powder

4. Standard Ennore Sand conforming to IS: 383 : 1970

41

5. Quartz sand

6. Poly-acrylic ester type Super plasticizer

7. Steel fibre of diameter 0.16mm and length 13mm & 6mm having

tensile strength of 2000MPa.

3.4 PREPARATION OF RPC MIX

The standard mix proportion and quantity of materials per m3 of

reactive powder concrete mix formulation developed at CSIR-SERC,

Chennai is shown in Table 3.5.

1. A Hobart Planetary mixer (Fig.3.1) machine (10 kg capacity) was

used to mix the RPC

2. Well-mixed dry binder powder was then slowly poured in to the

bowl while the mixer was rotating at a slow speed.

3. The water and admixture were slowly added to the mixing bowl

and mixing was continued at slow speed

4. The speed of the mixer was increased and the mixing process was

continued for two to three minutes.

5. Additional mixing was performed at this speed until a uniform

mixture was achieved and the mixture was transformed to a

flowable self-compacting consistency by dosing with additional

SP, if necessary. The total mixing time for the various mixtures

ranged from 5 to 10 minutes.

6. In case of RPC mixtures with fibres, after all the powder

42

ingredients were mixed thoroughly with water and Super

plasticizer (SP) and when flowable consistency was achieved, the

fibres were added to the mixing bowl slowly with the mixer

operating in low gear. Care was taken to ensure random

distribution of fibres. The speed was increased and further

mixing was carried out by incorporating additional SP, if

necessary, to account for the possible stiffening of mixture due to

fibre addition.

Fig. 3.1 Hobart Planetary Type Mixer Machine

These mixing sequences did not result from an optimization process;

rather, they were selected to allow for RPC samples to be taken with

different lengths fibres, to observe the influence of fibres on the

rheology of RPCs.

While in usual fibre reinforced concretes, the addition of steel fibres

results in a drastic decrease of the workability of the mix the opposite

occurs in RPCs. This behaviour can easily be explained by the

43

differences in the relative size of steel fibres with respect to the

maximum size of the coarse aggregate. In usual fibre reinforced

concrete, steel fibre length is of the same order at the maximum size of

coarse aggregate, creating a strong interference with the aggregates.

That is why it was always recommended to slightly decrease the

maximum size of the coarse aggregate in steel fibre reinforced concrete

and to increase the sand content. On the contrary, there is no such

interference in RPC because the steel fibres are 20 times longer (13mm)

than the coarser aggregate (600µm). As a comparison, keeping the

same aspect ratio, adding steel fibres to RPC like adding 400mm long

rebar to a normal concrete made with a 20mm coarse aggregate.

The physical properties such as density, water absorption and air

voids were determined as per ASTM C 642 already tested and

confirmed at CSIR-SERC while formulating the mix proportion. In

addition, the ultrasonic pulse velocity (UPV) measurements were taken

using the PUNDIT apparatus as per ASTM C 597 procedure. The fresh

and physical properties of the RPC mixtures were tabulated in Table

3.6.

44

Table 3.1 Chemical composition of powders

Table 3.2 Physical Properties of the Materials

Sl.No Materials Used Sym Properties

1. Cement C

OPC: 53 Grade; SG = 3.15; SC = 28%; IST = 110 min; FST = 260 min; CS = 58

MPa at 28 days

2. Silica Fume SF

SG = 2.25; % Passing through 45μm sieve in WSA=92 %.

3. Quartz Powder Q

SG = 2.59; % Passing through 45μm sieve in WSA=75 %

4. Ennore Sand SG = 2.63

5. Super Plasticizer SP Poly-Acrylic Ester

Based

6 Micro-steel fibres STF L=6, and 13 mm &

D=0.16mm Note: OPC – Ordinary Portland cement, SG – Specific Gravity, CS – Cube Strength, PSR – Particle

size range, SC – Standard Consistency, WSA – Wet sieve analysis of aggregates, L – Length, D –

Diameter.

Oxides Portland

cement

Silica

fume

Sio2 20.49 94.73

Al2O3 5.91 -

Fe2O3 4.07 _

CaO 62.90 _

MgO 1.13 _

Na2O 0.20 0.51

K2O 0.47 _

TiO2 0.20 _

Mn2O3 0.08 _

SO3 1.87 0.2

Free Lime 0.45 _

Chlorides 0.012 0.07

LOI 2.29 1.5

45

Table 3.3 Particle Size Distribution of Powders

* Higher average particle size of silica fume is due to use of fused silica fume

Table3.4 Properties of steel fibres

Type of fibres Dimension of fibre Strength

L(mm) D(mm) MPa

Beakaert carbon straight micro-steel fibres

6 0.16 2000

13

Table 3.5 Standard Mix Proportions for Reactive Powder Concrete

Mix Proportions

SF C Q FA w/c SP STF

0.25 1 0.4 1.1 0.22 3 0.2 (2% by vol.)

Quantity of Materials / m3 of concrete

SF C Q Sand w/c SP STF

kg kg Kg kg l L kg

194 777 311 855 171 29 160 SF – Silica Fume, C – Cement Q – Quartz, FA – Fine Aggregate, W – Water,

SP – Super Plasticizers

Powders Specific gravity

Particle size(µm)

D10 D30 D50 D60

Cement 3.15 49 33 21 14

Quartz 2.59 47.5 31.75 19.5 13.8

Silica fume

2.2 0.55* 3* 7* 9*

46

Table 3.6 Fresh and Physical Properties of the Mixtures

Types of Concrete Flow Density(kg/m3) Porosity(%)

RPC 135 2297 4.25

RPC-1% 6mm 110 2341 2.95

RPC-2% 6mm 105 2378 3.1

RPC-3% 6mm 100 2549 0.65

RPC-1% 13mm 110 2385 2.85

RPC-2 % 13mm 90 2415 3.82

3.5 CURING REGIME

The curing protocol adopted is indicated in Fig. 3.2 and is the

outcome of a study of different combinations of normal water curing,

hot water curing and high temperature curing. [Harish et al., 2008]36

Fig. 3.3 shows the equipments used for the different curing regimes.

After 7 days of different regimes of curing, the specimens were cured in

water until the testing.

47

Fig. 3.2 Curing Regime for RPC

ATC-Ambient temperature, NWC-Normal water curing, ROH- Rate of heating, HWC-Hot Water

Curing, HAC-Hot Air Curing, ROC-Rate of curing, DOT-Date of Testing

i) Normal water curing ii) Hot water curing @ 900C iii) Hot air curing @2000C

Fig.3.3 Equipments Used For Different Curing Regimes

3.6 TESTS FOR MECHANICAL PROPERTIES

The tests conducted for studying mechanical properties of RPC

include compression, direct tension, and flexure. Table 3.7 illustrates

the test program of this investigation. The standard procedure followed

and the dimensions of specimen used for the mechanical tests are

0

50

100

150

200

250

300

0 1 2 3 4 5 6 7 8 9 10

Curing Period (days)

Temperature

(C°)

ATC NWC

ROH: 4.8 hrs

ROH: 1 hr

HWC

HAC ROC: 1 hr

NWC till DOT

48

shown in Table 3.8. The static modulus of elasticity was determined

from compression test as per ASTM C 469 procedure using 100 x 200

mm cylinders for RPC. All the tests were conducted after 28 days of

respective curing cycles. The toughness characteristics of these

concretes were calculated by first plotting the flexural strength -

deflection plot and then calculating the area under the plot. The

toughness index was calculated at different deformation levels namely

I5, I10 and I20 as per ASTM C 1108. The energy absorption characteristic

was conducted for RPC concretes by first plotting the stress-strain

curve in compression and then determining the area under the stress-

strain plot. Table 3.9 gives the mixture proportions of RPC mixtures

with different fibre contents and Table 3.6.

Table 3.7 Experimental program

Mix ID

Fibre

Compression

Flexure

Toughness

Energy absorption

Direct tension

Length (mm)

%

RPC - 0 C C - C _

RPC - 1% 6 1 C C C C C

RPC - 2% 6 2 C C C C C

RPC - 3% 6 3 C C C C C

RPC - 1% 13 1 C C C C C

RPC - 2% 13 2 C C C C C

RPC - 3% 13 3 C C C _ _

RPC - 1%+1%

6+13 2 C C _ C C

RPC - 1%+2%

6+13 3 C C _ C C

C – Tests Conducted

49

Table 3.8 Tests conducted to study the Mechanical Properties of

RPC

Table 3.9 Mixture proportions

C.A.&F.A.,coarse and Fine aggregate, W – Water, SP – Superplasticizers (quantity of SP is

represented in percentage by weight of cementiitous material), SF – Steel fibres (quantity of SF is

represented in percentage by volume of the total mixture

Tests Properties studied

Type of concrete

Standards Specimen size

Compression Stress-strain plot

& Energy absorption

RPC with all % fibres

ASTM C 469 100 x200 mm

cylinder

Tension

Direct tension RPC _ Briquette’s shape(dog-bone shape)

Flexure and toughness

RPC ASTM C 348 70x70x350 mm prism

Mix ID Fibre Length

Mix proportions of RPC concrete with

respect to cement

C S Q FA

W SP %

SF %

RPC

_ 1 0.25 0.4 1.1

0.17 1.5 _

RPC -1% 6mm 1 0.25 0.4 1.1

0.17 1.2 1

RPC -2% 6mm 1 0.25 0.4 1.1

0.17 2.25

2

RPC - 3% 6mm 1 0.25 0.4 1.1

0.20 2.5 3

RPC - 1% 13mm 1 0.25 0.4 1.1

0.17 1.2 1

RPC -2% 13mm 1 0.25 0.4 1.1

0.17 2.2

5 2

RPC - 3% 13mm 1 0.25 0.4 1.1

0.20 2.5 3

RPC- 1%+1%

6mm+13mm 1 0.25 0.4 1.1

0.17

2.25

2

RPC-

1%+2% 6mm+13mm 1 0.25 0.4

1.1

0.20 2.5 3

50

3.7 PREPARATION OF TEST SPECIMENS

3.7.1. Preparation of Compression Specimens

The RPC cylinders of 100mm diameter and 200mm height were cast

with various fibre content and combinations as follows.

i. 1% of 6mm fibres

ii. 2% of 6mm fibres

iii. 3% of 6mm fibres

iv. 1% of 13mm fibres

v. 2% of 13mm fibre

vi. 1% of 6mm fibres + 1% 13mm fibres

vii. 1% of 6mm fibres + 2% 13mm fibres

The specimen for compression tests consisted of 100mm diameter

by 200mm long cylinders. All the specimens were subjected to the

curing regimes as specified in Fig. 3.2 and prepared for the test. Both

the end of the specimen were carefully leveled and coated with sulphur

to get plain and parallel surfaces.

3.7.2 Preparation of Tension Specimen

The most commonly used specimen geometrics for testing of UHPC

(Ultra High Performance Concrete) behavior under tension were so-

called dumb-bell prisms. The shape of such prisms avoids failure in the

area of bond introduction in the specimen, which otherwise occurs due

to an unavoidable multiaxial stress state and/or an abrupt change in

stiffness in the transitory region from loading plates to specimen. A

smooth transition from or wider part of the specimen to the narrow,

51

middle portion as used in the experiments appears to be, at least

theoretically, the most appropriate geometric shape needed to avoid

local stress concentration.

To overcome the problems associated with specimen grips, end

tapered specimen were tested in tension. The geometry of typical

specimen was shown in Fig.3.4. The cross section in the constant

width portion is 200mm. The overall height of the specimen was

350mm and both end edge is 150mm. Special steel moulds were

designed and fabricated for the preparation of direct tension test

specimens. The tension tests were carried out on Dog-bone shaped

tensile specimens with notches 10mm deep 2mm wide cut at middle

length. The cross-sectional area of a typical specimen, at the double-

notched points, is 1886mm2.The geometric details of the specimen are

shown in the Fig. 3.4. Typical test specimen with end grips is shown in

Fig.3.5. Overall, about 32 specimens were prepared and tested

(Fig.3.6).

52

Fig. 3.4 Typical Tension Specimen with dimension

(All dimensions are in mm)

Fig. 3.5 Photographic View of Tension Specimen with End Grips

Fig. 3.6 Over All View of Tension Specimen with various fibre dosages

53

3.7.3 Preparation of Flexure and shear Specimen

RPC beams of size 70 x 70 x 350 mm with different lengths of fibres

[l/d (mm), 6/0.16, 13/0.16] single or in combination and different

volume fractions were prepared and tested.

Note: All Dimensions are in mm

Fig.3.7 Fig. 3.8

Fig. 3.7 Beam Specimen Schematic Diagram Fig. 3.8 Photographic views of Beam Specimens

Table 3.10 Details of Notched RPC Beam Specimens

Serial no. ID Fibre content (%)

6mm 13mm

1 R0 0 0

2 RS2 2 0

3 RD21 2 1

4 RD32 3 2

5 RS2L 0 2

6 RS3L 0 3

3.7.3.1 Specimen Geometry

Specimens prepared were beams of rectangular cross section with a

notch at the mid-length to a depth of 1/6 times the beam depth. The

depth (D) and width (B) of the cross section of the specimen were both

70 mm. The loading span (S) was 300 mm (0.3D). The total length of

the specimen (L) was 350 mm (3.5D). The notch depth width (ao) was

54

5mm. The notch was formed by embedding an acrylic plate of the 5mm

thickness during casting. Adequate measures were taken to prevent

bonding between the plate and concrete. The specimens shall be

subjected to testing in a condition immediately after completion of the

specified curing procedure.

3.7.4 Preparation of test specimen for Bolted Plates

A Reactive Powder Concrete formulation developed at the Structural

Engineering Research Centre, Chennai based on extensive

investigations is used for production of RPC plate elements and the

behaviour of bolted plates was investigated under direct tensile loading

which is the most critical condition for a bolted connection. The various

experimental activities involved in this study are presented in the

following paragraphs.

3.7.4.1 Casting

RPC panels were cast in wooden moulds of clear dimensions of 350

x 350 mm and thickness 15mm. The RPC mix was poured into the

mould and compacted in two layers using a Table vibrator. After 24

hours specimens were demoulded and subjected to the specified curing

regimes optimized by CSIR-SERC (Fig.3.2). Cured specimens were cut

to the required dimensions using concrete cutting machine. Holes were

drilled using concrete drilling machine at 1.5d, 2.5d and 3.5d from the

edge of plates (d- diameter of the bolt hole).

55

3.7.5 Preparation of Angle Specimens

3.7.5.1 RPC-Angle casting device

For casting the RPC angles, a special device was designed and

fabricated as shown in the Fig-3.10. Using the special mould angle

sections of 80mm x 80mm x 10mm angle sections were cast for 1m

length. Then the angle sections were cut to different heights or lengths

to conduct the flexure and compression tests. The mould consists of

two V-shaped plates, one fixed and the other one movable, which is

fitted with a handle. The concrete is placed on the fixed angle and

pressed against, by the movable angle plate. A plate with bolt holes is

fixed at the bottom angle mould to fix the thickness of angle sections.

The thickness of the angle sections can be adjusted, by fixing the

moving angle mould to the corresponding bolt holes fixed at the bottom

angle mould. With this mould one can cast angle sections of thickness

5mm, 6mm, 8mm, 10mm, 12mm, 14mm, 16mm and 20mm.

The following describes the specimens used in this study for

determining the mechanical properties of various RPC angles.

Specimens of 80mm x 80mm x 10mm angles sections with the

following volumes of fibres contents were caste for testing.

1. 1% of 6mm fibres

2. 2% of 6mm fibres

3. 3% of 6mm fibres

4. 1% of 13mm fibres

5. 2% of 13mm fibres

6. 1% of 6mm fibres + 1% 13mm fibres

7. 1% of 6mm fibres + 2% 13mm fibres

56

57

Fig. 3.11(a) Fig. 3.11(b)

Fig.3.11 a &b Angle casting mould for RPC

3.7.5.2 Description of the mould

A rigid four-legged self-straining frame with top sides connected by

angle section is the main frame of the mould. At 17 cm from the bottom

of the mould, a channel section was fixed as crossbeam as shown in

Fig. 3.10. Over the cross beam a 20 x 12 cm angle section of 100 cm

length was connected longitudinally. Another channel section was

placed in inverted position to get flat surface on top and welded over

the movable angle section as shown in Figs.3.11a&b. Over the flat top

surface of 100 cm length 10 cm size angle was placed with both free

edges faced top and free edges in same horizontal line and the angle

joint portion on middle line of the base channel and rigidly welded. End

plates on both sides of the bottom angle were fixed by bolt and nut to

avoid the RPC mix leakage at sides. This angle acts as base of the

mould. A rotatable vertical shaft was fixed at the centre of the movable

angle. The vertical shaft was fully threaded and passed through the

threaded hole which was fixed at the top of the frame. By rotating, the

58

pressure is transferred through the movable angle to the materials in

the base fixed angle mould. Fig.3.10, Figs.3.11 (a) &3.11(b) shows the

details and photographic view of the device.

The entire loading device was placed on the table vibrator. The well

mixed RPC mixture was poured in the female angle mould to uniform

thickness. The male angle was lowered up to touch the RPC material

placed in the female angle by rotating the vertical shaft. Vibration was

applied on the entire device. Simultaneously vertical pressure was

applied through the male angle to the material in the female mould.

The thickness guides were fixed on both sides of the female mould.

Pressure was applied until the male angle reaches the thickness guide.

The excess material if any was squeezed out through the gap between

the guide and the male angle. The thickness of the RPC angle product

was possible from 5mm to 20mm. After 24 hours, the pressure on the

material was released by raising the male angle. The specimen was

removed from the female mould and cured by the standardised curing

regime (Fig. 3.2).

3.7.6 Preparation of Reactive Powder Concrete Infilled Tubes

The mix proportion for the infill and the quantity of material used

per m3 of reactive powder concrete mix formulation are as per the Table

3.2 and 3.3.

59

3.7.6.1 Details of Reactive Powder Concrete infilled tubes(RFIT)

Specimens Used

To investigate the performance of RPC infilled steel tubes,

compressive test were carried out. The test specimen details are shown

in Table3.11.

Table: 3.11 Details of infilled RPC Specimen

3.7.6.2 Fabrication of Steel Tubes

Locally available hollow steel tubes of the following dimensions are

used for the fabrication.

Steel tube specification:-

Steel tube diameter = 60 mm Steel tube length = 600 mm

Steel tube thickness = 2 mm

Steel plate diameter (Bottom) = 75 mm Steel plate diameter (Top) = 60 mm

Steel plate thickness = 6 mm

The fabricated steel tube specimens are shown in Fig. 3.12

Fig 3.12 Steel Tube Specimens

3.7.6.3 Casting of Infilled Steel Tube And Controlled Specimens

The prepared mix was poured into the hollow steel tube by a small

trowel and the tube was filled with the prepared mix and it was

Specimen Compressive Test Specimen

Hollow tubes 3

In filled Steel tubes 9

60

properly compacted by a table vibrator. A 10 mm aluminium tube was

provided at the centre of the steel tube, for inserting the 7 mm

prestressing wire. The inside portion of the steel tube is shown in Fig

3.13.

Fig. 3.13 Fig. 3.14

Fig 3.13 Inside Portion of the Steel Tube Fig 3.14 Steel Plate

After the casting, the steel tube is closed with a plate with a central

hole (Fig. 3.14). A central hole was made in the plate for the insertion

of the pre-stressing wire. The pre-stressing of steel tube was carried out

after the curing of the specimen. Inside of the steel tube contains 8 mm

rod which act as a shear connector. It also helps to increase the

bonding between steel tube and the concrete.

3.7.6.4. Casting of Infill

The selected RPC mix details are shown in Table 3.2. The casting

was done in an EIRICH Intensive Mixer, which consist of a rotating pan

of speed 30 rpm placed at an angle of 300 to the horizontal. The inclined

rotor consists of three numbers of steel blades, which can rotate at a

speed varying from 0 to 300 rpm. The mixing was carried out in EIRICH

mixer, until a highly fluid consistency was achieved First dry mixing of

61

ingredients consisting of combination of cement, sand, silica fume was

done for 5 minutes. Subsequently 75% of water and 75% of super-

plasticizer (Structuro-100) with the dry mix was added and again mixed

for 3 minutes. Further the rest of water along with the super-plasticizer

was added and mixed for 5 minutes. Finally steel fibre were slowly

added and mixed for few minutes, till the desired mix consistency was

obtained. The fibre was uniformly distributed throughout the mix

volume. The mixing was continued till the required flow was achieved.

Fig 3.15 shows steel tube specimen just after the casting.

Fig 3.15 Steel Tube Specimens Just After the Casting