72

CHAPTER 5

EXPERIMENTAL INVESTIGATION

5.1 GENERAL

In this chapter, the tests carried out on all the specimens cast to the

details described in chapter 4 are discussed. The casting and testing of

Geopolymer concrete specimens were done according to the specifications

followed for ordinary Portland cement mortar and concrete. Initially, mortar

cubes of size 70.6mm x 70.6mm x 70.6mm conforming to IS: 10080-1982

were tested for compressive strength. Test procedures for the compressive

strength of mortar cubes as per IS: 4031-1982 (Part 6) were followed.

Similarly, the compressive strength of 150mm x 150mm x 150mm concrete

cubes was ascertained by testing as per the procedures stipulated in IS:

516:1959. Split tensile strength test was conducted on 150mm x 300mm size

cylinders cast and tested in accordance to IS: 5816-1999. Durability tests on

both OPC concrete cubes and Geopolymer concrete cubes were conducted

according to ASTM C642 and the results were compared. Tests were carried

out on 100mm x 100mm cross section and 500mm long beams without

reinforcement to obtain flexural strength of both ordinary Portland cement

concrete and Geopolymer concrete specimens.

Reinforced cement concrete and reinforced Geopolymer concrete

beams of series-A and Series-B were manufactured and subjected to two point

loading test to investigate and compare the results of reinforced cement

concrete and reinforced Geopolymer concrete on the flexural behavior,

73

cracking moment, ultimate moment and maximum deflection. Series-C beams

of size 100mm x 100mm in cross section and 500mm long were cast using

Geopolymer concrete and were subjected to aggressive environment for 180

days. These tests were done to study and determine the durability and residual

flexural strength of reinforced Geopolymer concrete beams.

5.2 COMPRESSIVE STRENGTH TESTS

5.2.1 Mortar Cubes

Geopolymer mortar cubes were cast in three layers, in accordance

to IS 10080-1982. Each layer was well compacted by a tamping rod of 12mm

diameter. After compaction, the top surface was leveled using a trowel and

left for 24 hours to dry in room temperature of 280C with 60% humidity. On

the next day, at room temperature of 290C and 54% humidity, they were kept

inside the dry-heat chamber for curing. The Heat cured Geopolymer mortar

cubes, prepared using low calcium class F Indian fly ash, fine aggregate and

alkaline solution made of different combinations of sodium silicate, sodium

Figure 5.1 Testing of Geopolymer mortar cube

74

hydroxide, potassium silicate and potassium hydroxide were tested in a 2000

kN capacity hydraulic compression testing machine, as per IS: 4031-1982

(Part 6). Totally, twelve numbers of mortar cubes, three each for the various

combinations, were cast and tested. The testing of Geopolymer mortar cubes

in the compression testing machine is shown in Figure 5.1. The compressive

strength at failure is calculated using the formula (5.1)

Ultimate compressive load (N) Compressive strength (N/mm

2) = (5.1)

Area of cross section of specimen (mm2)

5.2.2 Concrete Cubes

5.2.2.1 Destructive test

Geopolymer concrete cubes of size 150mm x 150mm x 150mm

cast using low calcium class F Indian fly ash, fine aggregate, coarse aggregate

and alkaline solution made of sodium silicate and sodium hydroxide were

tested in accordance with IS: 516-1959. Geopolymer concrete cubes were

manufactured and tested to various trial mixes to achieve compressive

strength of 30 N/mm2 and 50 N/mm

2. For each grade of concrete, three

numbers of specimens were cast and tested in a hydraulic compression testing

machine of capacity 2000 kN. Six numbers of companion concrete cubes of

the same size, three each for normal and high strengths, made of ordinary

Portland cement were cast and cured in a water pond for 28 days. At the end

of 28 days, the OPC concrete cubes were also tested and the failure load was

noted. The load divided by the cross sectional area of cube gave the required

compressive strength and calculated as per formula (5.1).

5.2.2.2 Non-destructive Test

5.2.2.2.1 Ultra sonic pulse velocity test

Ultrasonic pulse velocity method involved measuring the time of

travel of an ultrasonic pulse passing through the concrete to be tested. The

75

time travel between initial onset and the reception pulse was measured

electronically.

UPV meter concreteTransducer

Figure 5.2 Ultra sonic pulse velocity instrument

The path length between transducer divided by the time of travel

gave the average velocity of wave propagation. Based on the velocity, the

quality of concrete was judged from Table Schematic diagram of ultrasonic

pulse velocity and experimental set up of ultrasonic pulse velocity test are

shown in figure 5.2. The procedure of ultrasonic pulse velocity test is as

follows. Firstly, the surface of the concrete specimens was rubbed with the

carborandum stone in order to get the uniform surface and care was taken to

keep the surface of the concrete free from dust and water. Grease was applied

on both the opposite ends of the specimens. Transducers were also applied

76

with grease in order to avoid the air gap between the transducers and the

concrete surface. The transducers were placed and pressed on opposite sides

of the cube and the pulse transmission in terms of micro seconds was

measured. After traversing a known path length (L) in the concrete the

vibration pulse was converted into an electrical signal by a second electro-

acoustical transducer held in contact with the other surface of the concrete

member and an electronic timing circuiting enabled the transit time (T) of the

pulse to be measured.

The UPV (V) can be calculated using equation (5.2).

Ultra sonic pulse velocity, V = L/T. (5.2)

The quality of the concrete was related with this pulse velocity

given in Table 5.1.

Table 5.1 Relation between pulse velocity values and quality grindings

for concrete

Velocity Classification (Quality)

4.0 and above Very good

3.5 to 4.0 Good

3.0 to 3.5 Medium

3.0 and below Poor

5.2.2.2.2 Rebound hammer test

To fix the concrete mixture proportions, not only destructive test

but also non-destructive test was done. The description of rebound hammer

and the procedure done are presented here. The spring controlled hammer

77

mass slides on a plunger with in a tubular housing. The plunger rotates against

a spring when pressed against a concrete surface and this spring is

automatically released, when tensioned, causing the hammer mass to impact

against the concrete through the plunger. When the spring controlled mass

rebounds it takes with it a rider which slides along a scale and is visible

through a small window in the side of casting. The rider can be held in

position on the scale by depressing the locking button. The scale reading is

known as the rebound hammer and is an arbitrary measure as it depends on

the energy and the mass used.

With this number, the compressive strength of concrete was

obtained from graph attached with the instrument. The readings very sensitive

to local variations of the concrete, especially aggregate particles close to

surface. Therefore it necessitated to take several readings at each test location

and to find their average between 9 and 25 readings taken over an area not

exceeding 300mm2 with the impact points not less than 20mm from each

other or from the edge. The compressive strength was noted referring to the

graph and noted.

5.3 SPLIT TENSILE TEST

For the mixtures of M30, M50, G30 and G50 concretes, three

specimens of 150mm x 300mm size cylinders for each mixture were cast and

split tensile strength test was carried out in accordance with IS: 5816-1999.

The diametrical compressive load along the height of the cylinder

was applied and the ultimate load at failure or rupture was noted for

calculation. The maximum load when divided by the appropriate geometrical

factors gave the split tensile strength of the specimen of concrete.

78

Split tensile strength,dl

P2fst

! (5.3)

where

fst = split tensile strength

P = Ultimate load at failure in N

l = Length of cylindrical specimen in mm

d = Diameter of cylindrical specimen in mm.

5.4 RAPID CHLORIDE PENETRATION TEST (RCPT)

The Rapid Chloride Penetration Test (RCPT) has been developed

as a quick test which is able to measure the rate of transport of chloride ions

into concrete. This test was conducted as per ASTM C 1202-94. Concrete

discs of size 90mm diameter and 35mm thickness were cast. Moulds were

made by cutting annular steel pipes of desired length. Crude oil was applied

around the inner surfaces of the mould, prior to filling it with concrete, for the

easy removal of specimens from the mould. After 24 hours, the disc

specimens were removed from the mould and subjected to heat curing for 8

hours at 700C. After curing, the specimens were tested for chloride

permeability. All the specimens were dried free of moisture before testing.

After curing, the concrete specimens were subjected to RCPT by impressing

60V.

Two halves of the specimens were sealed with a PVC container of

diameter 80mm. One side of the container was filled with 3% sodium chloride

solution (that side of the cell was connected to the cathode terminal of the

power supply) and on the other side, 0.3N sodium hydroxide solution was

poured and connected to the anode terminal. The current passed was noted at

every 30 minutes over a period of 6 hours. From the results using current and

79

time, the chloride permeability was calculated in terms of the total charge

passed in coulombs at the end of 6 hours using the formula,

Q= 900 (I0 + 2I30 + 2I60 + 2I90 + …………. + 2I300 + 2I330 + 2I360) (5.4)

where

Q = Charge passed in Coulombs

I0 = Current immediately after voltage was applied in Amperes

It = Current at t minute after voltage was applied in Amperes

The current recorded over a period of 6 hours at an interval of 30

minutes as per the procedure given in ASTM C1202 is presented in Table 5.2.

Table 5.2 Charge passed through RCPT test as per ASTM C1202

Sl. No. Charge passed

in coulombs

Chloride ion

penetrability

1 > 4000 High

2 2000 - 4000 Moderate

3 1000 - 2000 Low

4 100 - 1000 Very low

5 < 100 Negligible

5.5 DURABILITY TESTS ON CUBES

Both ordinary Portland cement concrete and Geopolymer concrete

cubes of size 150mm x 150mm x 150mm were cast to test durability against

sulphate, acid, chloride and water absorption. Observations were recorded on

the second, fourth and eighth weeks after immersion into the solutions.

Twenty seven numbers of OPC concrete cubes for M30 grade and twenty

80

seven numbers for M50 grade were cast. Similarly, a total of fifty four

numbers were cast for G30 and G50 grade 14M concentration of Geopolymer

concrete and fifty four numbers for 12M concentration. Two grades of

concrete (30 N/mm2 and 50 N/mm

2) and 14 M and 12 M concentration of

NaOH were considered as test variables.

5.5.1 Test on Sulphate Resistance

Nine numbers of concrete cubes each of M30, M50, G30 and G50

concretes were immersed in sodium sulphate solution of 5% concentration in

accordance to the procedure given in ASTM C 642. The Geopolymer concrete

cubes were immersed in sodium sulphate solution on the third day after

casting. The cubes were fully immersed in the solution kept in plastic

containers. The cubes were kept at a distance of 50 mm away from the walls

of the container. The containers were covered in order to minimize the

evaporation and to avoid falling of dust. The solutions were replaced every

month with fresh solution and the pH value was maintained neutral

throughout the study period. Also the solution was stirred every week to avoid

deposits on the base of the containers. The visual appearance, residual

Figure 5.3 Cube specimens immersed in 5% sodium sulphate solution

81

compressive strength and change in mass were observed on the second, fourth

and eighth weeks after immersion, and readings were noted. The surface of

the cubes were cleaned, weighed and tested in the compression testing

machine. The cubes inside the container are shown in Figure 5.3.

5.5.2 Test on Acid Resistance

As per the procedure stipulated in ASTM C 642 for ordinary

Portland cement concrete, nine numbers each for M30, M50, G30, and G50

OPC and Geopolymer concrete cubes were immersed in 5% concentration of

sulfuric acid solution kept in plastic containers which is shown in figure 5.4.

The concentrated sulfuric acid of 98% purity and density 1.85g/cc was used to

prepare the sulfuric acid solution of 5% concentrations. 27.5 ml of

concentrated H2SO4 was mixed with 972.5 ml of distilled water to get one

litre of acid solution. The specimens were weighed, recorded as W1 and

submerged so that there was a minimum of 30mm depth of acid above the top

Figure 5.4 Specimens immersed in 5% H2SO4 solution

82

surface of the specimens. The pH value of the solution was monitored

periodically using a pH meter and also by titration with standard alkaline

solution. The initial weights of the specimens were noted and recorded as W1.

Three specimens were taken out from the containers after 2 weeks, 4 weeks

and 8 weeks for testing. Observations were made on visual appearance,

change in compressive strength and change in mass on the second, fourth and

eighth weeks after immersion, and the readings were noted. The specimens

taken out were washed with tap water before being weighed in a digital

balance of 0.1 mg accuracy. The average weight of the three specimens was

noted as W2 and the change in mass was calculated by,

% weight loss = 1

21

W

WW "x 100 (5.5)

5.5.3 Test on Water Absorption

Figure 5.5 Specimens immersed in water

83

The water absorption values for various mixtures of concrete were

determined on 150mm cubes as per the procedure given in ASTM C 642. The

specimens were taken out of the curing tank after the second week, fourth and

eighth week to record the water saturated weight (Ws). The drying was carried

out in an oven at a temperature of 105°C. The drying process was continued

until the difference between two successive measurements were close enough.

The oven-dried specimens were weighed after they got cooled to room

temperature (Wd). Using these weights, the saturated water absorption (SWA)

was calculated by the formula (5.6). The specimens immersed in water are

shown in Figure 5.5.

The water absorbed was calculated using equation (5.6).

SWA = [(Ws -Wd) / Wd] ×100 (5.6)

where

Ws - Weight of the specimen at fully saturated condition in kg,

Wd - Weight of oven- dried specimens in kg.

5.5.4 Chloride Attack Test

Sodium chloride (NaCl) solution with 5% concentration was used

as the standard exposure solution for all tests. The specimens were immersed

in the sodium chloride solution in a plastic container and the volume

proportion of sulphate solution to specimens was maintained as four to one.

The change in mass and change in compressive strength were observed at

regular intervals.

84

5.6 FLEXURE TEST ON BEAMS WITHOUT

REINFORCEMENT

Beam specimens of standard size 100mm x 100mm x 500mm were

cast to determine the flexural strength of both plain ordinary Portland cement

concrete and Geopolymer concrete. Beams were cast to the specification of 30

N/mm2 and 50 N/mm

2 and the concentration of sodium hydroxide (NaOH)

was ranged from 8M to 14M. All beams are simply supported over an

effective span of 400 mm and tested in a frame load test machine of capacity

1000 kN. A single, central, concentrated load was placed over the span of the

beam. Prior to placing the specimens in the machine, the beam surfaces at the

location of supports and loads were smoothly ground to eliminate unevenness.

The load was incremented until failure occurred and the ultimate load was

observed to calculate the flexural strength of beams using the equation (5.7).

f = (M/I) x y (5.7)

where

M = PL/4

P = ultimate load in N

L = span of beam in mm

F = flexural strength in N/mm2

I = moment of inertia in mm4

y = D/2 in mm

5.7 REINFORCED CONCRETE BEAMS (SERIES-A AND

SERIES-B BEAMS)

All beams were simply supported over an effective span of

3000mm for Series-A beams and 1850 mm for Series-B beams. They were

tested in a load frame test machine of capacity 500 kN. In Series-B beams,

85

three beams of size 150mm x 200mm in cross section and 2000mm long were

cast for M30 and G30 grades of concrete and sodium hydroxide (NaOH)

concentration was kept as 12M. Another set of beams for series-A beams to

the size of 200mm x 300mm x 3300mm long were cast for M30, G30, M50

and G50 concretes with NaOH concentration being 14M. Two concentrated

loads were placed symmetrically over the span of the beam. The distance

between the loads was 923 mm and 617 mm for Series-A beams and Series-B

beams respectively. Linear Variable Differential Transducers (LVDTs) were

used to measure the deflections at select locations along the span of the beam,

to monitor deflections. All LVDTs were calibrated prior to the tests. The

relationship between the output of the LVDTs in milli-volts (mV) and the real

movement in millimetres (mm) was determined to be linear. Prior to placing

the specimens in the machine, the beam surfaces at the location of supports

and loads were smoothly ground to eliminate unevenness. All the specimens

Figure 5.6 Experimental test set up for flexure test

86

were given a white wash in order to facilitate the marking of cracks. Both the

ascending and descending (softening) parts of the load-deflections curve were

recorded for each test beam. The measurement of the softening part (after the

peak load) was continued until either the limit of the LVDT travel at mid-span

was reached or no further information was recorded by the data logger due to

the complete failure of the specimen. The experimental set up is shown in

Figure 5.6. The load at first crack, the ultimate load and the maximum

deflection at the ultimate load were noted. The test results of the reinforced

cement concrete and the Geopolymer concrete beams were compared and

investigated.

5.8 DURABILITY OF REINFORCED GEOPOLYMER

CONCRETE BEAMS (SERIES-C)

Durability study on reinforced Geopolymer concrete beams was

carried out to investigate the applicability of Geopolymer concrete in

structural applications and in aggressive environment. Totally, fifty one

numbers of 100mm x 100mm x 500mm long reinforced beams were cast. The

beams were immersed in 10% concentration of sulfuric acid solution, chloride

solution made by mixing together 5% concentration of HCl and 5%

concentration of H2SO4. Also, 10% concentration of sodium sulphate

Figure 5.7 Specimens immersed in 10% aggressive solutions

87

solution and magnesium sulphate solution were taken for studying the effect

of sulphate attack on reinforced Geopolymer concrete beams. 10%

concentration of solution was prepared for very aggressive exposure and also

to accelerate the test to assess durability of beams in short duration, 180 days.

All mixed solutions were kept in plastic containers and twelve

numbers of beams were immersed in each solution for a period of 180 days.

Two specimens were taken out from the solution at the end of 7, 15, 30, 60,

120 and 180 days. Testing of specimens in the Universal Testing Machine

(UTM) is as shown in Figure 5.8.

Figure 5.8 Flexure test set up of Series-C beams

1. The cracking moment was predicted using the formulae

fcr x Ig

Mcr = (5.8) y

88

where

Mcr = Cracking Moment

fcr = 0.6(fck)1/2

Ig = Gross Moment of Inertia and

y = Depth of NA in Tension zone

2. Predicted ultimate moment is given by

Mu = 0.87fy x (p/100)[1- {(p/100) x (fy / fck)}] x bd2 (5.9)

where

Mu = Predicted ultimate moment

fy = Yield stress of steel

p = Percentage of steel and

fck = Characteristic compressive strength of concrete

3. Experimental ultimate moment for series-A and series-B beams is given by

(Mu) = (Pu x l) / 6 (5.10)

where

Pu = Ultimate load and

l = Effective span of beam

4. Experimental ultimate moment for series-C beam is given by

(Mu) = (Pu x l) / 4 (5.11)

where

Pu = Ultimate load and

l = Effective span of beam

89

5.9 MICROSTRUCTURAL ANALYSES

The microstructural analyses were done for the samples taken from

exposed and unexposed series-C beams for their mineralogical composition.

This was done by:

X-Ray Diffractometer

Scanning Electron Microscope and EDAX study

5.9.1 X-Ray Diffraction Analyses

The samples were taken from the reinforced Geopolymer concrete

series-C beams exposed and unexposed to various harsh environments after

180 days of study period, and which were taken near the exposed top surface.

Samples were of fine powder form and investigated in CECRI, Karaikudi,

Tamilnadu, for their mineralogical composition analysis. X-ray diffraction

measurement is a method for measuring the characteristics, diffraction angles

and intensities from randomly oriented powder crystallites irradiated by a

mono chromate X-ray beam. From the patterns given in the plots, the

mineralogical composition was examined based on reflection angle and peak

intensity.

XRD analyses were done by using a diffractometer with the

following details: PANalytical Make, X’per PRO Model, Cu K (2.2 KW

Max.) source, X’celerator (Semiconductor) detector, Ni foil Beta Filter, The

XRD patterns were obtained by scanning at 2# .

5.9.2 Scanning Electron Microscopy and EDAX Study

The deterioration of specimens was studied by Scanning Electron

Microscopy and EDAX reports. Samples for scanning electron microscopy

(SEM) analysis and EDAX report were taken near the surface (0-1mm depth)

90

of specimens exposed to the harsh solutions. Microstructural studies utilized

SEM (HITACHI S-3000H, Japan) equipped with EDAX analyser for

microstructural observations of the fractured surfaces, which were coated with

evaporated copper for examination. SEM analyses were done at a maximum

magnification of 300,000 x with a high resolution of 3.5 nm. For this analysis,

samples of size 10mm cubes were cut with a saw cutter. The intensity of

precipitation of alumino-silicate gel in the microstructure due to migration of

alkalies, chloride and acid into the specimen was studied. Also, the interfacial

transition zone was viewed from the images. These analyses were done to

depict and compare the characteristic morphology of the reacted products

after chemical attack of the exposed specimens to those of the unexposed

specimens.