chapter 4 durability studies on...

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CHAPTER 4

DURABILITY STUDIES ON PMMFRHPC

4.1 GENERAL

This chapter presents the durability aspects of Polyolefin

Macro-Monofilament Fibre Reinforced High Performance Concrete. The

experimental studies on durability properties of PMMFRHPC, such as void

permeability, water absorption, permeability, acid resistance, impact

resistance, drying shrinkage, Rapid Chloride Penetration Test (RCPT), and

corrosion resistance -impressed current voltage test were carried out. The

results of durability studies of properties of PMMFRHPC have been

discussed. Mathematical models for the durability studies of concrete are also

developed and validated.

4.2 EXPERIMENTAL PROGRAMME

4.2.1 Materials Used

The various materials (Cement, Fly ash, Metakaolin, Fine

aggregate, Coarse aggregate, Water, Superplasticizer and Polyolefin

macro-monofilament fibre) used for the experimental investigation were

given under 3.2.1

4.2.2 Mix Proportioning

Mix proportioning was done based on ACI 211.4R-08 “Guide for

selecting proportions for high strength concrete with Portland cement and

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other cementitious materials”. The summary of mix proportions used for

experimental investigation was discussed under 3.2.2 and presented in

Table 3.5.

4.2.3 Details of Test Specimens

The experimental investigation of PMMFRHPC was done under

three Phases as shown in Figure 1.1. The summary of the cast specimens for

durability studies are given in Table 4.1.

Table 4.1 Details of the Specimen Cast for Durability Studies

Sl.No.

Shape Dimensions in mm

Number of Specimens

Cast

Age in Days

Type of Test Carried Out

1. Cube 100 x 100 x 100 15 28,56 and 90 VoidsPermeability

2. Cube 100 x 100 x 100 15 28,56 and 90 WaterAbsorption

3. Cube 100 x 100 x 100 45 28,56 and 90 PermeabilityH2SO44. Cube 100 x 100 x 100 30 28,56 and 90

HCl

5. Disc152 diameter

63.5 height 63 28, 56 and 90 Impact

Resistance

6. Prism 285 x 75 x 75 63 28, 56 and 90 DryingShrinkage

7. Cylinder100 diameter

200 height 45 28, 56 and 90 Chloride Ions

8. Cylinder100 diameter

200 height 45 28, 56 and 90 Corrosion

Resistance Total specimens 321

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4.2.4 Voids Permeability

In the present investigation, percentage of water absorption and

percentage of permeable voids were determined as per the procedure given in

ASTMC 642-97. The absorption and permeable voids were determined using

100 mm cubes. Saturated surface dry cubes were kept in a hot air oven at

105 oC till a constant weight was attained. The ratio of the difference between

the mass of saturated surface dry specimen and the mass of the oven dried

specimen at 105 oC to the volume of the specimen (1000 ml.) gives the

permeable voids in percentage as given in the Equation (4.1):

Permeable voids = [(A – B)/V] x 100 (4.1)

where,

A = weight of surface dried saturated specimen after 28 days.

B = weight of oven dried specimen in air.

V = volume of sample (considered as 1000 ml).

The oven dried cubes after attaining constant weight were then

immersed in water and the weight gain was measured at regular intervals until

a constant weight was reached. The absorption at 30 min. (initial surface

absorption) and final absorption (at a point when the difference between two

consecutive weights at 12 hours interval, almost negligible) were determined.

The final absorption in all cases was determined at 96 hours. The absorption

characteristics indirectly represented the volume of pores and their connectivity.

4.2.5 Water Absorption

Saturated Water Absorption (SWA) Test was carried out on

100 mm cube specimens at the age of 28, 56 and 90 days of curing as per

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ASTM C 642-97 .The specimens were weighed before drying. The drying

was carried out in a hot air oven at a temperature of 105o C. The drying

process was continued, until the difference in mass between two successive

measurements at 24 hours interval agreed closely. The dried specimens were

cooled at room temperature and then immersed in water. The specimens were

taken out at regular intervals of time, surface dried using a clean cloth and

weighed. This process was continued till the weights became constant (fully

saturated). The difference between the saturated mass and oven dried mass

expressed as a percentage of oven dry mass gives the saturated water

absorption.

4.2.6 Permeability

The test was conducted as per IS 3085-1965. The permeability test

setup is shown in Figure 4.1. The equipment comprises of three cells, each

square in cross section mounted on stands. These cells were connected with

connecting pipe through valve. A pressure regulator was mounted on a

pressure chamber with two pressure gauges one 0-20 kg/cm2 gauge and the

other 0 - 15 kg/cm2. First one showed the input pressure and the second

showed the test pressure. The pressure was regulated by turning the handle of

pressure regulator in the clockwise direction to the desired pressure.

A pressure chamber fitted with a Schrader valve water inlet for

pouring water and valve provided as a water source. Standard cubes of

150 mm size were cast and cured for 28, 56 and 90 days. After the curing

period, it was taken out and allowed to dry for two days and the four faces of

the cube were painted to prevent penetration of water from sides. Then the top

surface was effectively sealed to achieve water tightness. Glass bottles were

kept in bottom position to collect the water percolating through the specimen.

Compressor was started and the pressure equal to 0.5 MPa/second was

applied to the water column. The quantity of water passing through the cube

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was collected at the bottom, in the glass bottle through the funnel being

maintained in humid atmosphere to prevent losses due to evaporation. The

operating pressure, quantity of water collected, time of observation etc., at

intervals were recorded. The test was conducted till the uniform rate of flow

was obtained. The co-efficient of permeability was then calculated.

Figure 4.1 Permeability Test setup

4.2.7 Acid Resistance

The chemical resistance of the concrete was studied through

chemical attack by immersing the specimens in an acid solution. After

28 days period of curing, the specimens were removed from the curing tank

and their surfaces were cleaned with a soft nylon brush to remove weak

reaction products and loose materials from the specimen. The initial weights

were measured and the specimens were identified with numbered tokens that

were tied around them. The specimens were then immersed in 3% H2SO4

solution and 3% HCl solution, for the pre-determined period maintaining a

constant pH value of 4 throughout the test period. The solution was replaced

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at regular intervals to maintain the required concentration throughout the test

period. The mass of specimens were measured at regular intervals upto

90 days, and the loss of mass of specimens was determined. Some of the

cubes were immersed in HCl and H2SO4 as shown in Figure 4.2.

Figure 4.2 Curing of Cubes in HCl and H2SO4 Solutions

4.2.8 Impact Resistance

The Impact Test was performed in accordance with the impact

testing procedures recommended by ACI 544.5R-10, “Report on the Physical

Properties and Durability of Fibre Reinforced Concrete” Reported by ACI

Committee 544. The test equipment was fabricated according to standards for

testing as per ACI 544.5R-10 and presented in Figure 4.3. For this study disc

specimens of size 152 mm (dia.) x 63.5 mm (thickness) were cast using

PMMFRHPC. For each mix proportion 9 disc specimens were cast and the

test results were obtained for 28, 56 and 90 days of immersion. Totally 63

concrete specimens were cast as per procedures recommended by ASTM.

Specimens were tested at 28, 56 and 90 days of age. Curing and handling of

the specimens were similar to those adopted for finding compression.

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The samples were coated on the bottom with a thin layer of

petroleum jelly or heavy grease and placed on the base plate. The base plate

was bolted to a rigid base such as a concrete floor or a concrete block. A steel

hammer of weight 44.145 N was guided through a steel tube and dropped on

the specimen from a height of 457 mm to transfer impact energy of 20.169 Nm on

the concrete disc specimens. The total number of blows required to detect the

first crack, as well as to cause the ultimate failure by splitting were noted.

From the results, first crack energy was calculated by multiplying the number

of blows required to cause the first crack with the impact energy (20.169 Nm)

and the energy spent for ultimate failure was calculated by multiplying the

number of blows required to cause the splitting of disc specimens and the

impact energy. The schematic diagram of impact test setup and disc

specimens are shown in Figures 4.3 and 4.4 respectively.

Calculation of Impact Energy

For the entire disc subjected to impact loading, damage was

localized at the point of contact and no large fragments fallout from the

specimens. Impact energy was calculated for the discs as reported by

Mohammadi et al (2009)

H = gt2/2 457= 9810 x t2/2 t = 0.3052 sec

V = gt V = 9810 x 0.3052 V = 2994.01 mm/sec

U = mv 2/2 U = Wv 2/2g

U = 44.145 x (2994.01)2/ (2 x 9810) U = 20.169 Nm

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Figure 4.3 Schematic Diagram of Impact Test Setup

Figure 4.4 Disc Specimen

4.2.9 Drying Shrinkage

The drying shrinkage of concrete was determined on prism of size

285 x 75 x 75 mm as per ASTM C-157-08. Drying shrinkage experiments

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were carried out to evaluate the unrestrained volumetric shrinkage of concrete

specimens. After removal from the moulds, steel balls were fixed to the centre

of both the square ends of the specimens. An initial measurement of the

length performed on the length comparator setup is shown in Figure 4.5. For

each mix proportion, three prism specimens were cast and length

measurement was performed periodically by the length comparator at 28, 56,

90 and 120 days.

Figure 4.5 Length Comparator Setup

4.2.10 Rapid Chloride Penetration Test (RCPT)

The most hazardous durability problem in the country is corrosion

of reinforcement in RCC structures. One of the principal sources of this

problem is the ingress of chloride ions into porous concrete. Movement of

ions into a porous medium under a constant gradient is known as diffusion. It

is necessary that concrete is impermeable to chloride ions for quality control

measures. Measurement of chloride diffusion co-efficient requires a long time

for establishment of steady state conditions. Therefore, a direct current (DC)

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potential is usually applied to accelerate the migration of chloride ions. The

RCPT Test Setup is shown in Figure 4.6.

Figure 4.6 Rapid Chloride Penetration Test setup

The RCPT apparatus consists of two reservoirs. The test method

consists of monitoring the amount of electrical current passing through a

water-saturated concrete specimen of size 50 mm thick, 100 mm diameter

when subjected to a 60 V applied through DC current supply for 6 hours. The

total charge passed during this period was calculated in terms of coulombs

using the trapezoidal rule as given in the ASTM C 1202-97,

Q = 900 (I0 + 2 I30 + 2 I60 + .................. + 2 I330 + I360) (4.2)

where,

Q = charge passed (coulombs)

I0 = current (amperes) immediately after voltage is applied, and

It = current (amperes) at‘t’ minutes after voltage is applied.

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If the specimen diameter was other than 95 mm, the value for total

charge passed must be adjusted. The adjustment was made by multiplying the

value established by the ratio between the cross – sectional area of the

standard to that of actual specimen. It is given in the Equation (4.3),

Qs = Q x (3.75/x) 2 (4.3)

where

Qs = charge passed (coulombs) through a 95 mm diameter specimen

Qx = charge passed (coulombs) through x inch diameter specimen

x = diameter (inch) of the non – standard specimen.

A higher amount of electric charge passing through the specimen

during the test represents a higher penetrability of chloride ions into the

concrete. The concrete quality can be assessed according to the RCPT rating

as per ASTMC 1202-97 criteria given in Table 4.2.

Table 4.2 RCPT Ratings

Charge Passed ( coulombs)

Chloride Ion Penetrability

> 4,000 High

2,000 - 4,000 Moderate

1,000 - 2,000 Low

100 - 1,000 Very Low

< 100 Negligible

The testing procedure leads to variation of values and hence, to

minimize the variation, three samples are generally tested and the average

value is reported. (However, the average values of the result of three samples

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should not differ by more than 29 % between two separate laboratories). From

the RCPT, the Q value was applied in the Berke’s equation to calculate

diffusion coefficient, DC values are calculated from Equation (4.4) (Andrade

and Whiting 1996).

Dc = 0.0103 x 10-8 x Q0.84, cm2/s (4.4)

In the present study , the Rapid Chloride Penetration Test (RCPT)

was performed as per ASTM C1202-97 to determine the electrical

conductance of HPC and PMMFRHPC mixes at the age of 28, 56 and 90 days

curing and to provide a rapid indication of its resistance to the penetration of

chloride ions. The specimen was fixed between two reservoirs using an epoxy

bonding agent to make the setup to be leak proof. In one reservoir was a 2.4 N

NaCl solution which was connected to negative terminal of DC source and in

the other reservoir, a 0.3 M NaOH solution was connected to positive terminal

of DC source, a DC of 60 V was applied across the specimen using two

stainless steel electrodes (meshes) and the current flowing across the

specimen was recorded at an interval of 30 minutes for a duration of 6 hours.

4.2.11 Corrosion Resistance - Impressed Current Voltage Test

The Impressed Current Voltage Test for concretes was carried out

based on FM 5-522 “Florida Method of Test for an Accelerated Laboratory

Method for Corrosion Testing of Reinforced Concrete using Impressed

Current”. The concrete cylinders of 100 mm (dia.) and 200 mm (height) with

16 mm dia. Fe 415 bar embedded concentrically were tested at the ages of 28,

56 and 90 days. The concrete specimens were immersed in 3% sodium

chloride solution. The embedded rebar was treated as anode and an external

stainless steel electrode served as cathode and a constant positive potential of

30 Volts to this system was applied from a DC source. The variation of

current was recorded with time. A sharp rise in current indicates the

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corrosion, and cracking of the concrete is usually visible thereafter, the time

taken for the initiation if the first crack can be considered as a measure of

their resistance against chloride permeability and reinforcement corrosion.

After cracking, the specimens were taken out, visually inspected, and

carefully split open to assess the corroded steel rod. The reinforcement bars

were then cleaned by dipping it in Clark’s solution for 25 minutes. Each bar

was then weighed again to an accuracy of 0.1 mg. and the change in weight

was observed. The Impressed Current Voltage Test setup is shown in

Figure 4.7.

Figure 4.7 Schematic View of Impressed Current Voltage Test setup

4.3 TEST RESULTS AND DISCUSSION ON DURABILITY OF

PMMFRHPC

The results obtained for the various durability studies of PMMFRHPC

have been presented and discussed.

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4.3.1 Voids Permeability

The results of the Voids Permeability Test on concrete cubes are

listed in Table 4.3. The maximum value of permeable voids obtained for mix

FMHPC00 at 28 days was 4.42 %.The mix FMHPC03 showed the lowest

value of permeable voids absorption and its value 1.87% was lower than the

FMHPC00 mix at the age of 28. Adding PMM fibre to the normal concrete,

the porosity of the concrete was reduced and the main reason were due to

decrease in permeable voids. The test indicated that when more pozzolanic

material was added to concrete, the water absorption reduced. Also mix

FMHPC02 showed a moderate value of 2.56% at 28 days. The PMM fibre

added in ascending order in FMHPC00 mix showed variation according to the

increase in percentage (0.1, 0.2, and 0.3).Voids Permeability is mainly

influenced by the paste phase; primarily, it was dependent on the extent of

interconnected capillary porosity in the paste. The relationship between Voids

Permeability (fvp) and fibre content (x) in percentage is obtained as

fvp = -15.2x + 6.18 at age of 28 days, fvp = -14.7x + 5.28 at age of 56 days and

fvp = -13.8x + 4.42 at age of 90 days, as shown in Figure 4.8

Table 4.3 Test Results of Voids Permeability and Water Absorption

Voids Permeability in % Water Absorption in %

Mix

Fibre Dosage in %

28Days

56Days

90Days

28Days

56Days

90Days

CM - 7.5 6.7 5.9 2.61 1.62 0.82

FMHPC00 - 6.5 5.3 4.5 2.60 1.38 0.80

FMHPC01 0.1 4.3 3.9 3.1 2.35 0.98 0.68

FMHPC02 0.2 2.9 2.1 1.3 2.12 0.82 0.59

FMHPC03 0.3 1.9 1 0.5 1.92 0.66 0.46

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y = -15.2x + 6.18R2 = 0.9691

y = -14.7x + 5.28R2 = 0.9924

y = -13.8x + 4.42R2 = 0.9806

0

2

4

6

8

0 0.1 0.2 0.3Fibre (%)

Figure 4.8 Voids Permeability Vs Fibre Content

4.3.2 Water Absorption

The results of the Water Absorption Test of concrete cubes are

listed in Table 4.3. The result shows that the water absorption reduced when

the admixture metakaolin used. The maximum value of water absorption

obtained at 28 days was 3.01 %. Concrete mixes with higher paste contents

were bound to have higher absorption values than concrete with lower paste

content (at consistent w/c). The lower voids permeability thus observed for

normal vibrated concrete was attributed to the relatively lower paste volume

i.e., smaller capillary pore volume. It was noted that high performance

concretes with fly ash and metakaolin had lesser water absorption. The

increase in paste volume due to the lower specific gravity of fly ash

contributed to an increased capillary pore volume and increased water

absorption in the control mix concrete. The test result indicated that when

more pozzolanic material is added to concrete, the water absorption would

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reduce. Water absorption was mainly influenced by the paste primarily; it was

dependent on the extent of interconnected capillary porosity in the paste.

Concrete mixes with higher paste contents were bound to have higher

absorption values than concretes with lower paste content (at consistent w/c).

The lower water absorption thus observed for normal vibrated concretes was

attributed to the relatively lower paste volume i.e., smaller capillary pore

volume. It was noted that high performance concretes with fly ash and

metakaolin have lesser water absorption. The relationship between water

absorption (fwab) and fibre content (x) in percentage is obtained as

fwab = -2.27x + 2.588 at age of 28 days, fwab = -2.32x + 1.308 at age of

56 days and fwab = -1.11x + 0.799 at age of 90 days, as shown in Figure 4.9.

y = -2.27x + 2.588R2 = 0.9976

y = -2.32x + 1.308R2 = 0.9397

y = -1.11x + 0.799R2 = 0.9956

0

1

2

3

0 0.1 0.2 0.3

Fibre (%)

Figure 4.9 Water Absorption Vs Fibre Content

4.3.3 Permeability

The test results of permeability are shown in Table 4.4. The

permeability of concrete reduced for the optimum dosage of mineral

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admixtures such as fly ash 10% and metakaolin 10% with 0.3% of PMM fibre

for the mix FMHPC03.

Table 4.4 Test Results of Permeability Test

The Co-efficient of Permeability (K) K= QL/(ATH) x 10-7 cm/sec Mix

Fibre Dosagein % 28 Days 56 Days 90 Days

CM - 5.29 4.43 3.57

FMHPC00 - 5.09 4.25 3.39

FMHPC01 0.1 4.98 4.18 3.32

FMHPC02 0.2 4.89 3.95 3.09

FMHPC03 0.3 4.76 3.7 2.84

The maximum permeability obtained by the FMHPC00 is 5.09x10-7

at 28 days. The lowest value of permeability obtained by the mix FMHPC03

is 4.76 x10-7 at 28 days. The permeability was reduced, when the metakaolin

and fly ash is equally replaced along with fibres. For FMHPC00 specimen

developed with replacements of fly ash and metakaolin, the corresponding

permeability was also found to be lesser. This may be due to the high paste

volumes (due to replacements of fly ash and metakaolin), water contents and

super plasticizer dosages adopted in producing HPC which result in decreased

porosity. The relationship between permeability (fp) and fibre content (x) in

percentage is obtained as fp = -1.08x + 5.092 at age of 28 days,

fp = -1.88x + 4.302 at age of 56 days and fp = -1.88x + 3.442 at age of

90 days, as shown in Figure 4.10.

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y = -1.08x + 5.092R2 = 0.9952

y = -1.88x + 4.302R2 = 0.9511

y = -1.88x + 3.442R2 = 0.9511

2

4

6

0 0.1 0.2 0.3

Fibre (%)

Figure 4.10 Permeability Vs Fibre Content

4.3.4 Acid Resistance

The Acid Resistance Test was conducted by using sulphuric acid

and hydrochloric acid at a concentration of 3% dilution. From the results it

was found that the resistance of concrete to sulphuric acid in the mix with

mineral admixtures was far greater than that of control mix. Most resistance

was offered by a mix containing 10% metakaolin and 10% fly ash. A similar

result was found in the case of hydrochloric acid also. The results of acid

resistance test of concrete cubes were listed in Table 4.5. The result showed

that the percentage of weight loss reduced when the percentages of

metakaolin increased. The maximum value of weight loss was obtained for

mix FMHPC00 at 28 days and it was 2.12 % in sulphuric acid. The mix

FMHPC02 showed a value of 0.62% of weight loss and mix FMHPC03

showed a value of 0.56 % comparatively low than the control mix at 28 days

in sulphuric acid. In case of hydrochloric acid, the maximum weight loss

obtained for mix FMHPC00 at 28 days is 0.96% at 28 days. The mix

FMHPC03 showed a value of 0.39% at 28 days. Mix FMHPC03 showed a

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moderate weight loss of 0.43%. Every mix showed a difference in weight loss

between control mixes. Adding fibres to the normal concrete, the porosity of

the concrete was reduced this was the main reason for decrease in weight loss.

Figure 4.11 Cubes Cured in H2SO4 Figure 4.12 Cubes Cured in HCL

The Concrete Cube Test specimens attacked by sulphuric acid lead

to leaching of maximum part of outer surface. And it was observed that no

pores or voids were formed but the surface of the specimen was completely

washed out. The acid attack leached away the calcium compounds of cement

paste formed in concrete through the hydration process, as well as the calcium

in calcareous aggregate. The reaction is primarily between the offending acid

and calcium hydroxide. Acid attack weakens the concrete structurally and

reduces its durability and service life. The compressive strength of the cubes

was reduced in all the mixes after curing in sulphuric acid, the reduction of

strength maximum in mix FMHPC00 at a percentage of 2.12% at 28 days

curing in sulphuric acid. The relationship between acid resistance H2SO4

(fcu)and fibre content (x) in percentage is obtained as fars = -350x + 2497 at

age of 28 days, fars = -285x + 2454 at age of 56 days and fars = -285x + 2379

at age of 90 days, as shown in Figure 4.13. The relationship between acid

resistance HCl (fcu) and fibre content (x) in percentage is obtained as

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farh = -351x + 2497 at age of 28 days, farh = -285x + 2473 at age of 56 days

and farh = -285x + 2398 at age of 90 days, as shown in Figure 4.14.

y = -350x + 2497.5R2 = 0.9646

y = -285x + 2454R2 = 0.9982

y = -285x + 2379R2 = 0.9982

2250

2400

2550

0 0.1 0.2 0.3

Fibre (%)

Figure 4.13 Acid Resistance (H2SO4) Vs Fibre Content

y = -351x + 2497.4R2 = 0.9609

y = -285x + 2473R2 = 0.959

y = -285x + 2398R2 = 0.959

2250

2400

2550

0 0.1 0.2 0.3

Fibre (%)

Figure 4.14 Acid Resistance (HCl) Vs Fibre Content

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Table 4.5 Loss of weight due to Chemical Exposure of H2SO4 and HCl

H2SO4

Loss in weight, gms HCL

Loss in weight, gms Mix

Fibre Dosage in % 28

Days56

Days90

Days28

Days56

Days90

DaysCM - 2555 2480 2405 2567 2492 2417

FMHPC00 - 2500 2455 2380 2500 2475 2400

FMHPC01 0.1 2465 2425 2350 2465 2447 2372

FMHPC02 0.2 2415 2395 2320 2414 2405 2330

FMHPC03 0.3 2400 2370 2295 2400 2394 2319

In hydrochloric acid FMHPC00 mix showed a maximum value, but

less when comparing with sulphuric acid. In control mix, the reduction of

compressive strength was more. Mix FMHPC03 was the lowest value in both

the acids. Hence, concrete with metakaolin and fly ash equally replaced

provides a better durable concrete.

It was observed that the test specimen were least attacked by HCl

acid and hence, the loss of weight leaching effect was also minimum. In most

cases, the reaction between the attacking acid and calcium compounds will

form calcium salts, which could be soluble in water. These salts would then

be leached away, causing a loss of volume and cohesion of the paste.

Both the Figures 4.11 to 4.12 in case of H2S04 and HCl clearly

showed that the coarse aggregate used here was not attacked by the acid. The

maximum size of the aggregate was restricted by passing through a sieve of

12.5 mm In this way, the aggregates actually protect the concrete. Based on

the experimental investigation, it was observed that loss of compressive

strength decreased with ages subjected to hydrochloric acid and sulphuric acid

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exposure. It was observed from the experimental investigations, the

percentage loss of compressive strength was higher with the increase in fly

ash, metakaolin and fibre content. But with the increase of age, percentage

loss of compressive strength was reducing. This property was due to gain in

strength with the increase in ages.

4.3.5 Impact Resistance

The experimental results of the impact resistance of the concrete

mixes with admixtures and without fibers and the remaining five mixes with

admixtures containing 0.1, 0.2, 0.3, 0.5 and 0.7 percentage of fibers were

consider in this investigation and presented in Table 4.6 and shown in Figure

4.15. The impact strength of the mix FMHPC01 was 18.18 - 72.72% higher

than the FMHPC00 with the increase in age. But for the mix FMHPC05 and

FMHPC07 the average increase in impact strength was varying between 51-

103% higher than the FMHPC00 mix with the increase in ages. On attaining

the age of 90 days, the addition of fibre improved the strength characteristics

of the FMHPC mixes with fibres significantly to 100% higher than mix

without fibre. The maximum impact strength achieved by the FMHPC07 mix

was 450.37 kNmm at 90 days 437.06.70 kNmm at 56 and 336.22 kNmm at

28 days respectively. Whereas, the mix FMHPC00 without fibre achieved an

impact strength of 342.87 kNmm at 90 days, 322.70 kNmm at 56 days and

221.86 kNmm at 28 days respectively. Three factors namely fibre, age and the

compressive strength of the mix mainly had contributed to the improvement

of impact strength. On an average FMHPC03, FMHPC05, FMHPC07 attained

impact strength of 47% higher than FMHPC00 at 28 days whereas, the same

mixes achieved impact strength of 100% higher than FMHPC00 at 90 days.

Further with the addition of fibre dosage above 0.3%, the improvement of

impact resistance is meager. Thus the fibre, compressive strength and age

constituted the improvement in impact strength. The relationship between

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impact resistance (fir) and fibre content (x) in percentage is obtained as fir =

154.2x + 246.1 at age of 28 days, fir = 150.3x + 351.5 at age of 56 days and

fir = 142.3x + 369.6 at age of 90 days, as shown in Figure 4.16.

150

300

450

0 0.2 0.4 0.6 0.8

Fibre dosage (%)

28 days 56 days 90 days

Figure 4.15 Variation of Impact Strength at Different Ages

y = 154.29x + 246.16R2 = 0.8306

y = 150.32x + 351.56R2 = 0.7587

y = 142.31x + 369.63R2 = 0.757

200

300

400

500

0 0.2 0.4 0.6 0.8Fibre (%)

Figure 4.16 Impact Resistance Vs Fibre Content

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Table 4.6 Impact Strength of Concretes

Specimen Weight in kg.

Energy Absorbed in Nm

MixFibre in % 28

Days56

Days90

Days28

Days 56

Days90

DaysCM - 4.12 4.19 4.23 201.69 302.53 322.70

FMHPC00 - 4.10 4.18 4.23 221.86 322.70 342.87

FMHPC01 0.1 4.08 4.12 4.15 262.20 363.04 383.21

FMHPC02 0.2 4.20 4.24 4.27 289.02 403.38 410.04

FMHPC03 0.3 4.10 4.13 4.15 316.05 423.55 443.72

FMHPC05 0.5 4.08 4.11 4.13 329.36 430.20 443.72

FMHPC07 0.7 4.16 4.19 4.22 336.22 437.06 450.37

4.3.6 Drying Shrinkage

The experimental observations on the drying shrinkage value

(percentage change in length) of the concrete mixes are presented in Table 4.7

and shown in Figures 4.17. In the case of fibre concretes, the appearance of

the crack was delayed, compared to plain concrete. Free drying shrinkage of

all the fibre concretes was lesser than the plain concrete. The maximum

shrinkage at 120 days was observed to be around 0.12% for plain concrete.

The rate of shrinkage decreased rapidly with time. It was observed that 40 to

80 percent of shrinkage occurred within 90 days. The maximum percentage

of the rate of shrinkage decreased at 56, 90 and 120 days by 70%, 76% and

77% respectively when compared to the 28 days. The relationship between

drying shrinkage (fds) and fibre content (x) in percentage is obtained as

fds = 0.041x - 0.030 at age of 28 days, fds = 0.072x - 0.069 at age of 56 days

and fds = 0.0772x - 0.0803at age of 90 days, as shown in Figure 4.18.

89

Figure 4.17 Drying Shrinkage of Concretes

y = 0.0416x - 0.0307R2 = 0.6754

y = 0.0721x - 0.069R2 = 0.8375

y = 0.0772x - 0.0803R2 = 0.9009

-0.1

-0.08

-0.06

-0.04

-0.02

00 0.2 0.4 0.6 0.8

Fibre (%)

Figure 4.18 Drying Shrinkage Vs Fibre Content

90

Table 4.7 Test Results of Drying Shrinkage Test

Mix 28 days 56days 90 days 120 days

CM 0.06267 0.10000 0.11467 0.12267

FMHPC00 0.04267 0.08133 0.08933 0.09200

FMHPC01 0.02267 0.05867 0.06933 0.07467

FMHPC02 0.01600 0.04933 0.06400 0.06667

FMHPC03 0.01200 0.03867 0.04933 0.05200

FMHPC05 0.00800 0.02933 0.03733 0.04000

FMHPC07 0.00800 0.02667 0.03333 0.03467

4.3.7 Rapid Chloride Penetration Test (RCPT)

The results of the Rapid Chloride Penetration Tests of the mixes are

given in Table 4.8. From the test results, it was observed that the lowest value

charge passed was for the mix having fibre dosage as 0.3%. It was also noted

that the addition of pozzolanic material such as fly ash and metakaolin

increased the penetration resistance of concrete when compared to control

mix. It was also noted that as the curing period increased, the penetration

resistance increases due to the depletion of calcium ions in the gel pore fluids

and subsequent reduction of pH and the development of constricted

discontinuous and tortuous pore structure. As a result of pore structure

becoming relatively more refined due to the pozzolanic reactions, the high

conductivity path or the least resistive paths for the ions would be decreased.

The relationship between rapid chloride penetration test (RCPT) (frcp) and

fibre content (x) in percentage is obtained as frcp = -6489.x + 3079 at age of

28 days, frcp= -3798x + 1454 at age of 56 days and frcp= -2686.x + 967.9 at

age of 90 days, as shown in Figures 4.19.

91

y = -6489.9x + 3079.3R2 = 0.9938

y = -3798x + 1454.4R2 = 0.9997

y = -2686.5x + 967.95R2 = 0.9448

0

1500

3000

4500

0 0.1 0.2 0.3

Fibre (%)

Figure 4.19 RCPT Vs Fibre Content

Table 4.8 Test Results of Rapid Chloride Penetration Test

Charge Passed as per ASTM Equivalent

(coulombs)

Degree of Chloride ion Penetrability Based on Charge

PassedMix

28 days 56 days 90 days 28 days 56 days 90 days CM 3639.9 2325 1697.1 Moderate Moderate Low

FMHPC00 3141.9 1449 1218.5 Moderate Low Low

FMHPC01 2343.3 1077.9 677.7 Moderate Low Very Low

FMHPC02 1767.3 704.4 322.2 Low Very Low Very Low

FMHPC03 1170.6 307.5 241.5 Low Very Low Very Low

4.3.8 Diffusion Co-efficient for Mixes

The diffusion co-efficient for the mixes containing control mix and

fly ash, metakaolin replaced concrete with fibre dosage 0.1%,0.2% and 0.3%

are given in Table 4.9. From The results indicated that the diffusion

92

co-efficient value decreased as the fibre dosage increased and also the curing

period was extended. The decrease in diffusion co-efficient value indicated

that the concrete exhibited increased penetration resistance. The fibres used

provide excellent resistance to the salts.

Table 4.9 Diffusion Co-efficient of Concretes

Diffusion Co- Efficient (cm2/s)Mix

28 days 56 days 90 days CM 1.00961E-06 6.93E-07 5.32E-07

FMHPC00 8.92234E-07 4.66E-07 3.46E-07

FMHPC01 6.97417E-07 3.63E-07 2.46E-07

FMHPC02 5.50273E-07 2.54E-07 1.32E-07

FMHPC03 3.89314E-07 1.27E-07 1.03E-07

4.3.9 Corrosion Resistance (Impressed Current Voltage Test)

In the accelerated electrolytic corrosion test, constant voltage

studies were carried out on control mix and HPC mixes containing fly ash,

metakaolin with fibre dosage 0.1%, 0.2% and 0.3% for 28, 56 and 90 days of

curing. The loss of weight of rebar for the mixes at 28, 56 and 90 days of

curing are shown in Tables 4.10 to 4.12 respectively.

From the test results it was observed that the loss in weight in rebar

due to corrosion was less for concrete mixes with higher fibre dosage of 0.3%

and high for control mix. The control mix showed greater loss in weight than

replacement mixes with different fibre dosage. The increased resistance to

corrosion was mainly due to the pozzolanic activity and the fibres that

contributed primarily to reduced inter connected porosity. It was the pore

structure which attributed to the ultimate reduction of corrosion. The intensity

93

of current was measured for different fibre dosages at 28, 56 and 90 days of

curing. It showed that the intensity of current measured decreased with

increase in fibre dosage and as the curing period increased, the number of

days for the concrete to develop initial crack also increased. The relationship

between corrosion resistance (fcr) and fibre content (x) in percentage is

obtained as fcr = -8.96x + 5.589 at age of 28 days, fcr = -6.6x + 4.14 at age of

56 days and fcr = -4.66x + 2.614 at age of 90 days, as shown in Figure 4.20.

y = -8.96x + 5.589R2 = 0.9286

y = -6.6x + 4.14R2 = 0.8994

y = -4.66x + 2.614R2 = 0.8428

0

2

4

6

0 0.1 0.2 0.3

Fibre (%)

Figure 4.20 Corrosion Resistance Vs Fibre Content

Table 4.10 Accelerated Electrolytic Corrosion Results for 28 Days Curing

Mix Loss of weight of Rebar %

Visual Observation of Specimen Placed in 3.5% NaCl Solution After 28 Days

CM 8.5 Severe Corrosion

FMHPC00 5.48 Severe Corrosion

FMHPC01 5.05 Mild Corrosion



94


MixLoss of weight

of Rebar % Visual Observation of Specimen Placed

in 3.5% NaCl Solution After 56 Days CM 4.39 Mild Corrosion






Mix Loss of weight of Rebar %

Visual Observation of Specimen Placed in 3.5% NaCl Solution After 90 Days

CM 3.3 Mild Corrosion





4.4 CORRELATIONS AMONG VARIOUS HARDENED

PROPERTIES

4.4.1 Correlation between Impact Energy and Compressive Strength

The impact energy at 28 days is related with compressive strength

concrete mixes, as shown in Figure 4.21. The coefficient of determination

(R2) for the estimated impact energy was 0.9936. Relation between impact

energy (fir) and compressive strength (fcu) is as per Equation (4.5).

fir = 6.354e0.0536 fcu (4.5)

95

y = 6.354e0.0536x

R2 = 0.9936

200

260

320

64 66 68 70 72 74

Compressive strength f cu (MPa)

Figure 4.21 Correlation between Impact Energy and Compressive Strength

4.4.2 Correlation between Water Absorption and Compressive Strength

The water absorption at 28 days is related with compressive strength

concrete mixes, as shown in Figure 4.22. The coefficient of determination (R2) for

the estimated water absorption was 0.9462. Relation between water

absorption (fwab) and compressive strength (fcu) is as per Equation (4.6).

fwab = 52.478e-0.0452 fcu (4.6)

y = 52.478e-0 .04 52x

R2 = 0.9462

1

3

4

64 66 68 70 72 74


Figure 4.22 Correlation between Water Absorption and Compressive Strength

96

4.4.3 Correlation Between Permeability and Compressive Strength

The permeability at 28 days is related with compressive strength

concrete mixes, as shown in Figure 4.23. The coefficient of determination

(R2) for the estimated permeability was 0.9239. Relation between

permeability (fp) and compressive strength (fcu) is as per Equation (4.7).

fp = 9.7057e-0.0097 fcu (4.7)

y = 9.7057e-0.0 09 7x

R2 = 0.9239

4.70

5.08

5.46

64 66 68 70 72 74


Figure 4.23 Correlation between Permeability and Compressive Strength

4.5 MATHEMATICAL MODELLING FOR DURABILITY

PROPERTIES OF PMMFRHPC

4.5.1 Statistical Approach

A mathematical model is a description of system using

mathematical concepts and language. The process of developing a

mathematical equation is termed as mathematical modelling. Identification of

process control parameter, based on statistical approach was given by Ghezal

and Kamal Khayat (2002). Models were developed for the durability studies

at the ages of 28, 56, and 90 days.

97

The response function representing any of the recorded response

can be expressed as in the Equation (4.8)

Y = f (F/M) (4.8)

The relationship selected is a single degree response surface

expressed as follows

Y = a0 + a1[F/M] (4.9)

Variables, F refers fibre, M refers mortar composite (cement,

metakaolin, fly ash, water, super plasticizer and fine aggregate), a0 refers

regression constant and a1 refers Variables co-efficient.

4.5.1.1 Voids Permeability Model

The Voids Permeability Regression Models, (fvp) in percentage

developed in the study were based on the variables given in Equation (4.9).

Models were developed for 28,56 and 90 days as presented in the

Equations (4.10) to (4.12) respectively.

fvp = 4.12 – 2.62 F/M R2 = 0.934 (4.10)

fvp = 3.281 – 2.581 F/M R2 = 0.940 (4.11)

fvp = 2.565 – 2.462 F/M R2 = 0.925 (4.12)

4.5.1.2 Water Absorption Models

The Water Absorption Regression Models, (fwab) in percentage

developed in the study are based on the variables given in Equation (4.9).

Models developed for 28, 56 and 90 days are presented in the Equations (4.13) to

(4.15).

98

fwab= 2.250 – 0.346 F/M R2 = 0.997 (4.13)

fwab= 1.005 – 0.431 F/M R2 = 0.882 (4.14)

fwab= 0.644 – 0.160 F/M R2 = 0.992 (4.15)

4.5.1.3 Permeability Models

The Co-efficient of Permeability Regression Models, (fp) in cm/sec

developed in the study are based on the variables given in Equation (4.9). Models

developed for 28, 56 and 90 days are presented in the Equations (4.16) to (4.18).

fp= 4.959 – 0.214 F/M R2 = 0.856 (4.16)

fp= 4.038 – 0.316 F/M R2 = 0.942 (4.17)

fp= 3.178 – 0.316 F/M R2 = 0.942 (4.18)

4.5.1.4 Acid Resistance Models

The acid resistances, mass losses regression models in grams


developed for 28, 56 and 90 days as presented in the Equations (4.19) to (4.24).

Sulphuric acid (H2SO4)

fars= 2453.381 – 67.721 F/M R2 = 0.864 (4.19)

fars= 2415.02 – 49.64 F/M R2 = 0.948 (4.20)

fars= 2340.017 – 49.641 F/M R2 = 0.948 (4.21)

Hydrochloric acid (HCl)

farh = 2454.907 – 71.071 F/M R2 = 0.831 (4.22)

farh= 2432.99 – 47.784 F/M R2 = 0.947 (4.23)

farh= 2457.99 – 47.784 F/M R2 = 0.947 (4.24)

99

4.5.1.5 Impact Resistance Models

The Impact Energy Absorbed Regression Models, (fir) in Nm


developed for 28, 56 and 90 days are presented in the Equations (4.25) to (4.27).

fir= 296.545 + 63.526 F/M R2 = 0.817 (4.25)

fir= 400.153 + 63.098 F/M R2 = 0.864 (4.26)

fir= 415.589 + 59.847 F/M R2 = 0.876 (4.27)

4.5.1.6 Drying Shrinkage Models Shrinkage Value %

(Change in Length)

The Drying Shrinkage Value (change in length) Regression

Models, (fds) in percentage developed in the study are based on the variables

given in Equation (4.9). Models developed for 28, 56 and 90 days are

presented in the Equations (4.28) to (4.30).

fds= -0.019 + 0.021 F/M R2 = 0.856 (4.28)

fds= -0.046 + 0.032 F/M R2 = 0.877 (4.29)

fds= -0.056 + 0.034 F/M R2 = 0.879 (4.30)

4.5.1.7 RCPT Models

The RCPT Regression Models, (fds) in coulombs developed in the

study are based on the variables given in Equation (4.9). Models developed

for 28, 56 and 90 days are presented in the Equations (4.31) to (4.33).

frcp= 2186.95 – 1122.05 F/M R2 = 0.950 (4.31)

frcp = 1011.83 – 800.222 F/M R2 = 0.812 (4.32)

frcp = 671.560 – 595.89 0 F/M R2 = 0.828 (4.33)

100

4.5.1.8 Corrosion – Loss of Weight of Rebar Models

The Corrosion Loss of Weight of Rebar Regression Models, (fcr) in

percentage developed in the study are based on the variables given in

Equation (4.9). Models developed for 28, 56 and 90 days as presented in the

Equations (4.34) to (4.36).

fcr= 4.67 – 2.11 F/M R2 = 0.822 (4.34)

fcr= 3.19 – 1.06 F/M R2 = 0.922 (4.35)

fcr= 2.015 – 0.880 F/M R2 = 0.829 (4.36)

4.5.2 Validity of the PMMFRHPC Models

The validation of models establishes a precise correspondence

between durability properties of concrete and a complete abstract interpretation

and strong preservation could be formulated by the interpretation as

completeness properties. Nevertheless, the model was used to calculate the

durability properties of various PMMFRHPC mixtures produced in the

present study and the predictions were compared with experimental results

and validated, the general trend of results and the major characteristics were

discussed in terms of the discrepancies.

4.5.2.1 Validation of Durability Studies Models

Adequacy of the durability models are shown in Table 4.13.

101

Table 4.13 Adequacy of the Durability Models Durability Properties Days F t Standard

Estimate Error Significance Percentage

28 42.58 12.7726.525 0.698 1

56 47.264 10.8856.875 0.652 0.6Voids Permeability

90 36.943 7.8886.078 0.704 0.9

28 1114.083 270.0233.378 0.018 0

56 22.380 13.7614.731 0.158 1.8Water Absorption

90 372.039 96.56319.288 .014 0

28 17.806 121.5514.220 0.088 2.4

56 48.583 110.9466.970 0.079 1Permeability

90 48.583 87.3206.970 0.079 1

28 57.12 18.3497.551 258 0

56 12.976 5.6733.602 386.056 3.7RCPT

90 9.60 4.3513.099 334.16 4.8

28 19.060 197.0214.366 26.956 2.2

56 54.73 110.9466.970 0.079 1Acid Resistance

H2SO4

90 48.583 87.3206.970 0.079 1

28 14.703 164.9913.835 32.210 3.1

56 53.10 462.1767.287 11.396 1Acid Resistance

HCl

90 53.099 462.1767.287 11.396 1

28 22.253 29.4834.717 24.832 0.5

56 16.189 34.1634.024 28.918 1Impact Resistance

90 16.20 37.2124.003 27.572 1

28 7.64 7.6052.764 1.330 4

56 35.66 22.4385.972 0.307 1Corrosion

90 14.551 10.8763.815 0.401 3.2

28 7.752 3.2782.784 0.014 3.9

56 16.805 7.9624.099 0.014 0.9Drying Shrinkage

90 18.972 9.5014.356 0.015 0.7

Notes: F (statistic) = mean square (Regression)/mean square (Residual) t (statistic) = p values ranges from 0 to 0.05 Standard estimate error = square root of mean square for the residual Significance Percentage is <0.05 or 5%

102

4.5.3 Application of the Models

The models are applicable for the concretes with mineral

admixtures fly ash and metakaolin, 12.5 mm size of coarse aggregates and

PMM fibre type. The voids permeability of PMMFRHPC can be estimated

with good accuracy based on the derived model, which can be used to

estimate the durability studies of the PMMFRHPC mixtures. The models of

hardened PMMFRHPC properties would be useful to assess the performance

and thus to facilitate the usage of PMMFRHPC. The ability of models and

variation in the range of models were discussed in validity of the

PMMFRHPC models. The predicated and measured voids permeability for

28, 56 and 90 days are shown in Figure 4.24.

Figure 4.24 Measured Vs Predicted Compressive Strength for 28, 56 and 90 Days

103

4.6 CONCLUSIONS

The following conclusions are drawn from the durability studies of

PMMFRHPC:

Water absorption and voids permeability test conducted in the

laboratory gave a good result for PMMFRHPC, when

compared to the concrete without fibres. It was seen that there

is a decrease in the absorption of water after 56 and 90 days in

PMMFRHPC and voids permeability was also lower.

In 3% concentration of sulphuric acid the leaching was more

and in hydrochloric acid the leaching was less in all the

mixes. HPC with 10% fly ash and 10% metakaolin with

addition of 0.3% of PMM fibre showed an enhanced

resistance by providing a weight loss 53.5% on 28 days &

64.5% on 56 days. The weight loss percentages reduced up to

77% in H2SO4 compared to the High Performance Concrete.

In hydrochloric acid attack, HPC with 10% Fly ash and 10%

Metakaolin with addition of 0.3% of PMM fibre showed a

better resistance by providing a weight loss 49% on 28 days

and 52% on 56 days, lesser than High Performance Concrete.

Through the addition of 0.3% fibres the weight loss

percentages reduce up to 62% in HCl compared to the High

Performance Concrete.

The empirical relations obtained could be used to predict the

impact energy absorption of the PMMFHPC based on

compressive strength. Predicted values of impact energy

based on compressive strength lies within + 10 variations in

the present investigation.

104

Age affected the impact energy characteristics. The maximum

percentage of increase in impact energy absorption at 56 and

90 days was 97 and 103% respectively when compared to the

28 days impact energy absorption.

In the case of fibre concretes, the appearance of the crack was

delayed compared to plain concrete. Free drying shrinkage of

all the fibre concretes was lesser than the plain concrete. The

maximum shrinkage at 120 days was observed to be around

0.12% for plain concrete.

The rate of shrinkage decreased rapidly with time. It was

observed that 40 to 80 percent of shrinkage occurs within

90 days. The maximum percentage of the rate of shrinkage

decreased absorption at 56, 90 and 120 days is 70%, 76% and

77% respectively, when compared to the 28 days.

Rapid Chloride Penetration Test conducted in the laboratory

for HPC with 10% fly ash and 10% metakaolin gives a better

result than that of control mix concrete. The permeability of

HPC was lower than control mix concrete.

The increase in fibre dosage showed reduction in the charges

passed in HPC mixes. Also the increase in curing period

reduced the charges passed (low, very low) indicating that

there was higher penetration resistance as the fibre dosage and

curing period increased.

Thus the above conclusions show that the performance of HPC,

using mineral admixtures such as metakaolin and fly ash, over durability

characteristics was good.

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