ch 6 results and discussions of slightly acidic substance

7/31/2019 Ch 6 Results and Discussions of Slightly Acidic Substance

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6.1 Effect of Slightly Acidic substance

6.1.1 Effect of Calcium Chloride (CaCl2)

The effect of presence of calcium chloride (CaCl2) in mixing water on setting times of

cements (Blended Cement (BC) and Silica Fume Blended Cement (SFBC)), compressive

strength of Blended Cement Concrete (BCC), Silica Fume Blended Cement Concrete

(SFBCC) and Steel Fibre Reinforced Blended Cement Concrete (SFRBCC) is presented in

the following sub sections:

6.1.1.1 Effect on setting times of Blended Cement (BC)

The effect of CaCl2 on initial and final setting times of BC is shown in Table 5.33 and

Fig. 5.73. From the table and figure, it is observed that both the initial and final setting times

accelerate significantly with an increase in calcium chloride concentration in the deionised

water. Significant change in initial setting time is observed at 1.0 g/l. The initial setting time

is 37 minutes less than that of the control mix at the maximum concentration of 2.0 g/l. Also

the change in the final setting time becomes significant at a concentration, i.e., 1.0 g/l; it is

329 minutes, which is 32 minutes less than that of the control mix.

Table-5.33. Setting times of Blended Cement corresponding to CaCl2 concentrations

Sl.No Water sample

Setting time in minutes & Percentage change

Initial % change Final % change

1Deionised water

(Control)133 -- 361 --

2 0.2 g/l 125 -6.15 348 -3.613 0.5 g/l 117 -12.14 342 -5.32

4 1 g/l 103* -22.42 329 * -8.98

5 1.5 g/l 101 -24.08 321 -11.19

6 2.0 g/l 96 -27.94 310 -14.12

*- Significant

For comparison purposes, the effect of CaCl2 on the setting times of OPC is also

presented in Fig. 5.73. The results of OPC were taken from the study of Reddy, 2004. It can

be observed from the figure 5.73 that the setting times of BC and OPC differed marginally

and the effect of CaCl2 is very much similar on both OPC and BC. The setting times of


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blended cement (BC) are slightly higher when compared to OPC at all CaCl2 concentrations.

This is expected due to the presence of fly ash in the BC.

Singh N.B et al (2002) studied the effect of calcium chloride on hydration of rice

husk-blended Portland cement. From their study it was observed that, at 2% of CaCl 2, the

setting times have come down when compared with control specimen. This type of

observation also noticed in the present investigation.

0.0 0.2 0.4 0.6 0.8 1.0 1.2 1.4 1.6 1.8 2.0 2.2

100

150

200

250

300

350

400

Settingtime(mins)

Concentration of CaCl2

(g/l)

BC-Initial Setting time

BC-Final Setting time

Line of significance

OPC-Initial Setting time (Reddy, 2004)

OPC-Final Setting time (Reddy, 2004)

.

Fig.5.73.Setting times of Blended Cement vs CaCl2 concentrations

6.1.1.2 Effect on setting times of SFBC

The effect of CaCl2 on initial and final setting times of SFBC is shown in Table 5.34

and Fig. 5.74. From the table and figure, it is observed that both the initial and final setting

times accelerate significantly with an increase in calcium chloride concentration in the

deionised water. Significant change in initial setting time is observed at 1.0 g/l. The initial

setting time is 40 minutes less than that of the control mix at the maximum concentration of

2.0 g/l. As observed in case of initial setting times, same trend has occurred w r t final setting

time at concentration, i.e., 1.0 g/l; it is 316 minutes, which is 52 minutes less than that of the

control mix compared to the level at maximum CaCl2 tested concentration i.e. 2 g/l.


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For comparison purposes, the effect of CaCl2 on the setting times of OPC is also

presented in Fig. 5.74. The results of OPC were taken from the experimental studies of

Reddy, 2004. It can be observed from the figure 5.74 that the setting times of SFBC and OPC

differed marginally and the effect of CaCl2 is very much similar on both OPC and SFBC. The

setting times of blended cement (SFBC) are slightly higher when compared to OPC at all

CaCl2 concentrations. This is expected due to the presence of silica fume in the said cement

(SFBC). Setting times of both BC and SFBC are presented in one graph namely Fig. 5.75,

which exhibit similar trend with an increase in the concentration of CaCl2.

Table-5.34. Setting times of SFBC corresponding to CaCl2 concentrations

Sl.No Water sample



1Deionised water

(Control)142 -- 368 --

2 0.2 g/l 133 -6.08 354 -3.68

3 0.5 g/l 125 -12.15 348 -5.41

4 1 g/l 112* -20.78 335 * -9.02

5 1.5 g/l 108 -24.23 326 -11.34

6 2.0 g/l 102 -28.27 316 -14.07

*- Significant

0.0 0.2 0.4 0.6 0.8 1.0 1.2 1.4 1.6 1.8 2.0 2.2

100

150

200

250

300

350

400

Settin

gtime(mins)


(g/l)

SFBC-Initial Setting time

SFBC-Final Setting time


OPC-Initial Setting time (Reddy, 2004)

OPC-Final Setting time (Reddy, 2004)

Fig.5.74.Setting times of SFBC vs CaCl2 concentrations


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0.0 0.2 0.4 0.6 0.8 1.0 1.2 1.4 1.6 1.8 2.0 2.2

100

150

200

250

300

350

Settingtime(mins)

Concentration of CaCl2 (g/l)





Fig.5.75. Setting times of BC, SFBC vs CaCl2 concentrations

5.3.1.3 Effect on Compressive Strength of Blended Cement Concrete (BCC)

The effect of CaCl2 concentration on the compressive strength of BCC is presented

in Table 5.35 and Fig. 5.76.The results indicate that the increase in compressive strength for

all the samples of BCC irrespective of their age is nominal and below significant level. When

CaCl2 concentration is maximum, i.e., 2.0 g/l, the increase in compressive strength is 3.87%

and 4.12% at the age of 28 days and 90 days respectively, after comparing with that of cubes

prepared with the deionised water (control test sample).

For comparison purposes, the effect of CaCl2 on the compressive strengths of OPCC

is also presented in Fig. 5.76. The results of OPCC were taken from the research work of

Reddy, 2004. It can be observed from the figure 5.76 that the compressive strengths of BCC

and OPCC differed marginally and the effect of CaCl2 is very much similar on both OPCC

and BCC. The compressive strengths of BCC are slightly higher when compared to OPCC at

all CaCl2 concentrations.

Table-5.35. Compressive strength of BCC corresponding to CaCl2 concentrations


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Sl.

No

Water

Sample

Blended Cement Concrete

Compressive Strength % variation

28 days 90 days 28 days 90 days

IDeionised

Water

(Control)

23.89 27.47-- --

II

i0.2 g/l 23.97 27.55 0.33 0.28

ii 0.5 g/l 24.04 27.64 0.64 0.63

iii 1 g/l 24.29 27.99 1.68 1.9

iv 1.5 g/l 24.48 28.26 2.49 2.87

v 2.0 g/l 24.81 28.60 3.87 4.12

This type of observation was also noticed by Singh N.B et al (2002) and Nattapong

Makaratat et al (2011). During hydration process the chemical interaction between CaCl2 and

C3A takes place resulting in formation of Friedel salts, leading to dissolution, leaching and

expansive salt formation. The blended cement is more resistant to aggressive atmosphere,

than ordinary Portland cements, in the presence of CaCl2. Due to presence of pozzolana

material in the concrete in hand (BCC), increase in the compressive strength has occurred.

0.0 0.2 0.4 0.6 0.8 1.0 1.2 1.4 1.6 1.8 2.0 2.2

23

24

25

26

27

28

29

Compressivestr

ength(N/mm

2)


(g/l)

BCC-28 days

BCC-90 days

OPCC-28 days (Reddy, 2004)


Fig.5.76. Compressive strength of BCC vs CaCl2concentrations


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0.0 0.2 0.4 0.6 0.8 1.0 1.2 1.4 1.6 1.8 2.0 2.2

0.0

0.5

1.0

1.5

2.0

2.5

3.0

3.5

4.0

4.5

%v

ariationincomp.strength


(g/l)

BCC-28 days

BCC-90 days



Fig.5.77. % variation in compressive strength of BCC vs CaCl2 concentrations

5.3.1.4 Effect on Compressive Strength of SFBCC

The effect of CaCl2 concentration on the compressive strength SFBCC is presented

in Table 5.36 and Fig. 5.78. The results indicate that the increase in compressive strength for

SFBCC samples of both 28 and 90 day age is nominal and below significant level. When

CaCl2 concentration is maximum, i.e., 2.0 g/l, the increase in compressive strength is 3.91%

for 28 day concrete and 4.05% for 90 day concrete respectively, when compared with that of

cubes prepared with the deionised water (control test sample).

For comparison purposes, the effect of CaCl2 on the compressive strengths of OPCC


Reddy, 2004. It can be observed from the figure 5.78 that the compressive strengths of

SFBCC and OPCC differed slightly and the effect of CaCl2 is very much similar on both

OPCC and SFBCC. The compressive strengths of SFBCC are slightly higher when compared

to OPCC at all CaCl2 concentrations. Similar type of observation was also noticed by Singh

N.B et al (2002) and Nattapong Makaratat et al (2011). Due to presence of silica fume as

pozzolana material in the concrete there is an increase in the compressive strength.


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Table-5.36. Compressive strength of SFBCC corresponding to CaCl2 concentrations

Sl.

No

Water

Sample

SFBCC



I

Deionised

Water

(Control)

26.09 29.8-- --

II

i0.2 g/l 26.17 29.90 0.32 0.34

ii 0.5 g/l 26.25 29.97 0.61 0.58

iii 1 g/l 26.52 30.36 1.64 1.87

iv 1.5 g/l 26.81 30.70 2.75 3.02

v 2.0 g/l 27.11 31.01 3.91 4.05

0.2 0.4 0.6 0.8 1.0 1.2 1.4 1.6 1.8 2.0 2.2

23

24

25

26

27

28

29

30

31

Compressivestrength(N/mm

2)


(g/l)

SFBCC-28 days

SFBCC-90 days



Fig.5.78. Compressive strength of SFBCC vs CaCl2 concentrations


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0.0 0.2 0.4 0.6 0.8 1.0 1.2 1.4 1.6 1.8 2.0 2.2

0.0

0.5

1.0

1.5

2.0

2.5

3.0

3.5

4.0

4.5

%v



(g/l)

SFBCC-28 days

SFBCC-90 days



Fig.5.79. % variation in compressive strength of SFBCC Vs CaCl2 concentrations

5.3.1.5 Effect on Compressive Strength of SFRBCC

The effect of CaCl2 concentration on the compressive strength Steel Reinforced

Blended Cement Concrete is presented in Table 5.37 and Fig. 5.80 and 5.81. The results

indicate that the increase in compressive strength for samples of 28 day and 90 day age is

nominal and below significant level. When CaCl2 concentration is maximum, i.e., 2.0 g/l, the

increase in compressive strength is 3.91% and 4.1% for 28 and 90 day concrete respectively,

when compared with that of cubes prepared with the deionised water (control test sample).

The combination of compressive strength results of BCC, SFBCC and SFRBCC are

depicted in Fig.5.82 and from which it is observed that SFRBCC exhibits higher compressive

strengths compared to BCC and SFBCC. This may be due to incorporation of steel fibres in

the concrete.

Table-5.37. Compressive strength of SFRBCC corresponding to CaCl2 concentrations

Sl.

No

Water

Sample

SFRBCC



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I

Deionised

Water

(Control)

29.04 33.1-- --

IIi 0.2 g/l 29.12 33.21 0.28 0.32

ii 0.5 g/l 29.23 33.30 0.66 0.59

iii 1 g/l 29.55 33.74 1.77 1.92

iv 1.5 g/l 29.78 34.02 2.55 2.79

v 2.0 g/l 30.18 34.46 3.91 4.1

0.0 0.2 0.4 0.6 0.8 1.0 1.2 1.4 1.6 1.8 2.0 2.2

23

24

25

26

27

28

29

30

31

32

33

34

35

Compressivestrengt

h(N/mm

2)


(g/l)

SFRBCC-28 days

SFRBCC-90 days



Fig.5.80. Compressive strength of SFRBCC vs CaCl2 concentrations


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0.0 0.2 0.4 0.6 0.8 1.0 1.2 1.4 1.6 1.8 2.0 2.2

0.0

0.5

1.0

1.5

2.0

2.5

3.0

3.5

4.0

4.5

%v



(g/l)

SFRBCC-28 days

SFRBCC-90 days



Fig.5.81 % variation in compressive strength of SFRBCC vs CaCl2 concentrations

0.0 0.2 0.4 0.6 0.8 1.0 1.2 1.4 1.6 1.8 2.0 2.2

24

25

26

27

28

29

30

31

32

33

34

35

36

37

38

39

40


2)


(g/l)

BCC-28 days

BCC-90 days

SFBCC-28 days

SFBCC-90 days

SFRBCC-28 days

SFRBCC-90 days

Fig.5.82. Compressive strength of BCC, SFBCC, SFRBCC vs CaCl2 concentrations

5.4.1.6 Powder X-ray Diffraction Analysis and SEM Imaging

Powder X-ray Diffraction patterns are presented in Fig. 5.83 and 5.84 is for the BCC

and SFBCC specimens prepared with CaCl2 (1.0 g/l) in deionised water. Upper portion of the


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said graph indicates the XRD pattern of the control sample prepared with deionised water.

Perusal of the said graphs establishes that the compounds such as 3CaO.Al2O3.CaCl2.10H2O

(Friedels salt), C2S, C3S, Calcium Hydroxie (CH), CaCl2 and C-H-S are found at 11.90, 16

0,

170, 21

0, 28.2

0and 37

0respectively. Comparing with control sample, the sample of CaCl2

additionally consists of Friedels salt and Calcium Chloride.

Setting times of the BC were observed to get accelerated with the increase in CaCl2

concentration in the mixing water. From the literature, addition of calcium chloride

accelerates the setting times. The same is observed when the CaCl 2 is added in mixing water

in the present investigation. Possible reason for CaCl2 accelerating the hydration of C3A as a

result setting process is accelerated.

Compressive strength also has increased with an increase in the concentration of

CaCl2. Chemical equation when CaCl2 is added in mixing water with cement is given below.

The XRD patterns indicates that the peak of C-S-H at in CaCl2 is higher than the peaks of C-

S-H of control sample, which indicates that the strength of the NaCl added samples has

increased when compared with the control sample.

CaCl2 + 3 CaO.Al2O3 + 10H2O 3CaO.Al2O3.CaCl2.10H2O


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13/81

Fig.5.84. XRD pattern of SFBCC sample prepared with CaCl2 (1 g/l) in deionised water


14/81

Fig.5.83a. SEM image of of BCC specimen with 1.0 g/l of CaCl2 in deionised water


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Fig.5.84a. SEM image of SFBCC specimen spiked with 1.0 g/l of CaCl2 in deionised water

5.2.5.7 Effect of CaCl2 on Chloride ion Permeability

The rapid chloride permeability levels in terms of coulombs passed through

OPCC, BCC and SFBCC observed are tabulated and listed in the Tab.5.38 to 5.40. By

comparing the coulombs passed, which gives chloride ion permeability, it is observed that the

chloride ion permeability of OPCC is high at both 28 and 90 days age against BCC and then

SFBCC. Quantum of coulombs passed and percentage of variation in the charge passed are

depicted in Fig. 5.85 and 5.86 below. A glance at the said results and the graphs establishes


16/81

that the chloride ion permeability of all the three concretes studied has decreased with the

increase in the concentration of CaCl2 up to 0.3 g/l which is the maximum experimented

concentration. At maximum CaCl2 concentration i.e. 0.3 g/l, percentage of variation in

coulombs passed through BCC concrete sample has changed 5.21% at 28 days age compared

to 2036 coulombs for the control sample of BCC at the same age.

Table- 5.38. Chloride ion permeability in terms of coulombs passed in OPCC corresponding

to CaCl2concentrations

Sl.No Water sampleCoulombs passed

28 days % change 90 days % change

1Deionised water

(Control)2265 1418

2 0.2 g/l 2249 -0.71 1407 -0.81

3 0.5 g/l 2236 -1.26 1397 -1.49

4 1 g/l 2200 -2.87 1382 -2.57

5 1.5 g/l 2188 -3.42 1372 -3.24

6 2.0 g/l 2160 -4.65 1351 -4.75

Table- 5.39. Chloride ion permeability in terms of coulombs passed in BCC corresponding to

CaCl2concentrations


28 days % change 90 days % change1

Deionised water

(Control)2036 1187

2 0.2 g/l 2027 -0.45 1175 -0.97

3 0.5 g/l 2000 -1.78 1166 -1.73

4 1 g/l 1982 -2.64 1157 -2.5

5 1.5 g/l 1944 -4.51 1142 -3.76

6 2.0 g/l 1930 -5.21 1128 -4.99

Table- 5.40. Chloride ion permeability in terms of coulombs passed in SFBCC corresponding

to CaCl2concentrations

Sl.No Water sample Coulombs passed28 days % change 90 days % change

1Deionised water

(Control)1959 1026

2 0.2 g/l 1949 -0.5 1021 -0.51

3 0.5 g/l 1935 -1.24 1014 -1.19

4 1 g/l 1911 -2.47 1001 -2.45

5 1.5 g/l 1891 -3.46 989 -3.58

6 2.0 g/l 1875 -4.28 976 -4.87


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Parande A.K et al (2011) reported same behavior with respect to chloride

permeability on cement mortars. Based on their studies, it was noticed that the chloride

permeability (electric charge (coulombs)) was more in OPC than PPC. The permeability

results reflect the interconnected pores network of concrete in which ions migrate. The use of

porous concrete would not lead to lower permeability of concrete. If the interfacial between

aggregate and cement is intact then the lesser pores are formed which will lead minimal

migration of ions, ultimately resulting in lower permeability. This mechanism may be one of

the reasons to get lower chloride permeability in BCC.

Ali Reza Bagheri et al (2012) conducted experimentation on chloride ion permeability

in ternary concrete containing silica fume and blast furnace slag. Herein the authors had

reported that the permeability has decreased considerably. The same trend has been observed

in the present investigation for concrete containing silica fume and BCC (Fly ash based). This

is probably due to the fact that the total pore volume of concrete is not reduced by the

pozzolanic reaction, but the pore structure becomes more discrete. The use of PPC and silica

fume dilutes the pore solution and increases the binding of different ions, leading to lower

permeability for concrete.


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0.0 0.2 0.4 0.6 0.8 1.0 1.2 1.4 1.6 1.8 2.0 2.2

1000

1200

1400

1600

1800

2000

2200

Chargedpassed(coulomb

s)

Concentration (g/l)

28 days BCC

90 days BCC

28 days SFBCC

90 days SFBCC

28 days OPCC

90 days OPCC

Fig.5.85 Charge passed vs CaCl2 concentrations

0.0 0.2 0.4 0.6 0.8 1.0 1.2 1.4 1.6 1.8 2.0 2.2-6

-5

-4

-3

-2

-1

0

Chargedpassed(coulombs)

Concentration (g/l)

28 days BCC

90 days BCC

28 days SFBCC

90 days SFBCC28 days OPCC

90 days OPCC

Fig.5.86 %variation in Charge passed vs CaCl2 concentrations


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5.3.2 Effect of Magnesium Chloride (MgCl2)

The effect of presence of magnesium chloride (MgCl2) in mixing water on setting

times of cements (Blended Cement (BC) and Silica Fume Blended Cement (SFBC)),

compressive strength of Blended Cement Concrete (BCC), Silica Fume Blended Cement

Concrete (SFBCC) and Steel Fibre Reinforced Blended Cement Concrete (SFRBCC) is

presented in the following sub sections:


The effect of MgCl2 on initial and final setting times is shown in Table 5.41 and Fig.

5.87. From the table and figure, it is observed that both the initial and final setting times got

retarded with an increase in magnesium chloride concentration in deionised water. The

retardation for initial and final setting times is significant when the magnesium chloride

content is 1.5 g/l. At the maximum concentration (2 g/l) the initial and final setting times are

39 and 52 minutes more than those of control mix.

For comparison purposes, the effect of MgCl2 on the setting times of OPC is also

presented in Fig. 5.87. The results of OPC were taken from the experimentation of Reddy,

2004. It can be observed from the figure 5.87 that the setting times of BC and OPC differed

marginally and the effect of MgCl2 is very much similar on both OPC and BC. The setting

times of blended cement (BC) are slightly higher when compared to OPC at all MgCl2

concentrations. This is expected due to the presence of fly ash in the BC.

Table-5.41.Variation of setting times of BC corresponding to MgCl2 concentrations

Sl.No Water sample



1Deionised water

(Control)133 -- 361 --

2 0.2 g/l 136 2.54 376 4.24

3 0.5 g/l 145 8.78 380 5.26

4 1.0 g/l 157 18.2 388 7.55

5 1.5 g/l 164* 23.64 393* 8.81

6 2.0 g/l 172 29.02 413 14.37

*- Significant


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0.0 0.2 0.4 0.6 0.8 1.0 1.2 1.4 1.6 1.8 2.0 2.250

100

150

200

250

300

350

400

450

Settingtime(mins)

Concentration of MgCl2(g/l)

BC-Initial Setting Time

BC-Final setting time


OPC-Initial setting time (Reddy , 2004)

OPC-Final setting time (Reddy , 2004)

Fig.5.87.Setting times of Blended Cement vs MgCl2 concentrations


The effect of MgCl2 on initial and final setting times is shown in Table 5.42 and Fig.

5.88. From the table and figure, it is observed that both the initial and final setting times got

retarded with an increase in magnesium chloride concentration in deionised water. The

retardation for initial and final setting times is significant when the magnesium chloride

content is 1.5 g/l. At the maximum concentration (2 g/l) the initial and final setting times are

42 and 58 minutes more than those of control mix.

For comparison purposes, the effect of MgCl2 on the setting times of OPC is also


Reddy, 2004. It can be observed from the figure 5.88, that the setting times of SFBC and

OPC differed marginally and the effect of MgCl2 is very much similar on both OPC and

SFBC. The setting times of blended cement (SFBC) are slightly higher when compared to

OPC at all MgCl2 concentrations. This is expected due to the presence of silica fume in the


21/81

said cement (SFBC). The behavior of setting times of BC and SFBC is depicted in Fig. 5.89.

From this figure it is observed that the initial and final setting times are slightly higher for

SFBC when compared with BC.

Table-5.42.Variation of setting times of SFBC corresponding to MgCl2 concentrations

Sl.No Water sample



1Deionised water

(Control)142 -- 368

2 0.2 g/l 146 2.83 385 4.52

3 0.5 g/l 155 8.98 389 5.64

4 1.0 g/l 168 18.6 393 6.79

5 1.5 g/l 176* 24.21 400* 8.75

6 2.0 g/l 184 29.64 426 15.67

*- Significant

0.0 0.2 0.4 0.6 0.8 1.0 1.2 1.4 1.6 1.8 2.0 2.2

100

150

200

250

300

350

400

450

Settingtime(mins)

Concentration of MgCl2 (g/l)

SFBC-Initial Setting Time

SFBC-Final setting time




Fig.5.88.Setting times of SFBC vs MgCl2 concentrations


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0.0 0.2 0.4 0.6 0.8 1.0 1.2 1.4 1.6 1.8 2.0 2.2

150

200

250

300

350

400

450

Settingtime(mins)

Concentration of MgCl2

(g/l)

BC- Initial setting Time

BC- Final setting Time

SFBC- Initial setting Time

SFBC- Final setting Time

Fig.5.89. Setting times of BC, SFBC vs MgCl2 concentrations


The effect of MgCl2

concentration on the compressive strength of Blended Cement

Concrete (BCC) is presented in Table 5.43 and Figs. 5.90, 5.91. Decrease in compressive

strength Blended Cement Concrete (BCC) specimens prepared with MgCl 2 solution is

observed as the magnesium chloride concentration increases, the maximum concentration

being 2 g/l. There is significant decrease in the compressive strength of concrete cubes of

both 28 and 90 day aged samples at concentration of 2.0 g/l, which is the maximum tested

level of MgCl2, when compared with that of cubes prepared with the deionised water (control

test sample).


23/81

Table-5.43. Compressive strength of BCC corresponding to MgCl2 concentrations

Sl.

No

Water

Sample




I

Deionised

Water

(Control)

23.89 27.47-- --

II

i0.2 g/l 23.76 27.26 -0.56 -0.78

ii 0.5 g/l 22.54 26.11 -5.64 -4.96

iii 1 g/l 22.19 25.71 -7.13 -6.4

iv 1.5 g/l 21.58 25.07 -9.68 -8.74

v 2.0 g/l 20.58 24.20 -13.84 -11.91

For comparison purposes, the effect of MgCl2 on the compressive strengths of OPCC


Reddy, 2004. It can be observed from the figure 5.90 that the compressive strengths of BCC

and OPCC differed marginally and the effect of MgCl2 is very much similar on both OPCC

and BCC. The compressive strengths of BCC are slightly higher when compared to OPCC at

all MgCl2concentrations.


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0.0 0.2 0.4 0.6 0.8 1.0 1.2 1.4 1.6 1.8 2.0 2.218

19

20

21

22

23

24

25

26

27

28


2)


(g/l)

BCC-28 days

BCC-90 days

OPCC-28 days (Reddy , 2004)


Fig.5.90. Compressive strength of BCC vs MgCl2 concentrations

0.0 0.2 0.4 0.6 0.8 1.0 1.2 1.4 1.6 1.8 2.0 2.2

-20

-18

-16

-14

-12

-10

-8

-6

-4

-2

0

%

variationincomp.strength

Concentration of MgCl2(g/l)

BCC-28 days

BCC-90 days



Fig.5.91. % variation in compressive strength of BCC vs MgCl2 concentrations


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5.3.2.4 Effect on Compressive Strength of SFBCC

The effect of MgCl2 concentration on the compressive strength ofSFBCC is presented

in Table 5.44 and Fig. 5.92 apart from indicating percentage of variations in the level of

compressive strength in Fig. 5.93. The significant decrease in the compressive strength of

SFBCC cubes at 28 day, 90 day age is observed at a concentration i.e. 1.5 g/l. When MgCl2

concentration is 2.0 g/l, the decrease in compressive strength is 15.42% and 13.92 for

concrete samples with age of 28 and 90 days respectively, when compared with that of cubes


Table-5.44. Compressive strength of SFBCC corresponding to MgCl2 concentrations

Sl.

No

Water

Sample

SFBCC



I

Deionised

Water

(Control)

26.09 29.8-- --

IIi

0.2 g/l 25.91 29.54 -0.68 -0.86

ii 0.5 g/l 24.47 28.24 -6.21 -5.24

iii 1 g/l 24.04 28.01 -7.85 -5.99

iv 1.5 g/l 22.51 26.76 -13.72 -10.21

v 2.0 g/l 22.07 25.65 -15.42 -13.92

For comparison purposes, the effect of MgCl2 on the compressive strengths of OPCC


Reddy, 2004. It can be observed from the figure 5.92 that the compressive strengths of

SFBCC and OPCC differed slightly and the effect of MgCl 2 is very much similar on both

OPCC and SFBCC. The compressive strengths of SFBCC are slightly higher when compared

to OPCC at all MgCl2 concentrations. Percentage of variation in compressive strength, with

an increase in the chemical concentration, is also presented in Fig.5.93.


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0.0 0.2 0.4 0.6 0.8 1.0 1.2 1.4 1.6 1.8 2.0 2.2

18

20

22

24

26

28

30


2)


(g/l)

SFBCC-28 days

SFBCC-90 days



Fig.5.92. Compressive strength of SFBCC vs MgCl2 concentrations

0.0 0.2 0.4 0.6 0.8 1.0 1.2 1.4 1.6 1.8 2.0 2.2

-20

-18

-16

-14

-12

-10

-8

-6

-4

-2

0

%



(g/l)

SFBCC-28 days

SFBCC-90 days



Fig.5.93. % variation in compressive strength of SFBCC vs MgCl2 concentrations


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5.3.2.5 Effect on Compressive Strength of SFRBCC

The effect of MgCl2 concentration on the compressive strength of SFRBCC) is

presented in Table 5.45 and Fig. 5.94 and 5.95. There is significant decrease in the

compressive strength of concrete cubes of both 28 and 90 day samples at concentration of 1.5

g/l. When MgCl2 concentration is maximum, i.e., 2.0 g/l the decrease in compressive strength

is 16.83% and 13.99% for 28 and 90 day SFRBCC samples respectively, when compared

with that of cubes prepared with the deionised water (control test sample).


depicted in Fig.5.96 and from which it is observed that SFRBCC exhibits higher compressive

strengths compared to BCC and SFBCC. This may be due to incorporation of steel fibres in

the concrete.

Table-5.45. Compressive strength of SFRBCC corresponding to MgCl2 concentrations

Sl.

No

Water

Sample

SFRBCC



I

Deionised

Water

(Control)

29.04 33.1-- --

II

i0.2 g/l 28.79 32.79 -0.86 -0.94

ii 0.5 g/l 27.15 31.22 -6.52 -5.68

iii 1 g/l 26.78 30.97 -7.78 -6.42

iv 1.5 g/l 24.81 29.56 -14.58 -10.68

v 2.0 g/l 24.15 28.47 -16.83 -13.99


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0.0 0.2 0.4 0.6 0.8 1.0 1.2 1.4 1.6 1.8 2.0 2.2

20

22

24

26

28

30

32

34

36


2)


(g/l)

SFRBCC-28 days

SFRBCC-90 days



Fig.5.94. Compressive strength of SFRBCC vs MgCl2concentrations

0.0 0.2 0.4 0.6 0.8 1.0 1.2 1.4 1.6 1.8 2.0 2.2

-20

-18

-16

-14

-12

-10

-8

-6

-4

-2

0

%



(g/l)

SFRBCC-28 days

SFRBCC-90 days



Fig.5.95 % variation in compressive strength of SFRBCC vs MgCl2 concentrations


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0.0 0.2 0.4 0.6 0.8 1.0 1.2 1.4 1.6 1.8 2.0 2.220

22

24

26

28

30

32

34

36

38


2)


(g/l)

BCC- 28 days

BCC- 90 days

SFBCC- 28 days

SFBCC- 90 days

SFRBCC- 28 days

SFRBCC- 90 days

Fig.5.96. Compressive strength of BCC, SFBCC, SFRBCC vs MgCl2 concentrations

5.3.2.6 Powder X-ray diffraction analysis and SEM Imaging

Powder X-Ray Diffraction patterns, for BCC and SFBCC specimen, are shown in

Fig. 5.97 and 5.98 with MgCl2 (1.5 g/l) in deionised water. Upper portion of the said graph

indicates the XRD pattern of the control sample prepared with deionised water. Perusal of the

said graphs establishes that the compounds such as 3CaO.Al2O3.CaCl2.10H2O (Friedels salt),

C2S, C3S, Calcium Hydroxie (CH), CaCl2 and C-H-S, Brucite and M-S-H are found at 11.90,

160

, 170, 21

0, 28.2

0, 37

0, 44.7

0and 55

0respectively. Comparing with control sample, the

sample of MgCl2 additionally consists of Friedels salt, Brucite, M-S-H and Calcium

Chloride.

Setting times of the BC were observed to get retarded with the increase in MgCl2

concentration in the mixing water. From the literature, chlorides are accelerating the setting

times. The same is observed when the MgCl2 is added in mixing water in the present

investigation.


30/81

Fig.5.97. X-Ray diffraction pattern of powdered BCC sample prepared with MgCl2 (1.5 g/l)

in deionised water

Compressive strength also has increased with an increase in the concentration of

MgCl2. Chemical equations when MgCl2 is added in mixing water with cement are given

below. The XRD patterns indicates that the presence of M-S-H which is responsible in

decrease of compressive strength when compared with the control sample.

2MgCl2 + Ca(OH)2 2Mg(OH)2 + CaCl2

CaCl2 + 3 CaO.Al2O3 + 10H2O 3CaO.Al2O3.CaCl2.10H2O

Mg(OH)2 + C-S-H Mg-S-H + H2O

In case of SFBCC also, compressive strength has decreased with an increase in the

concentration of MgCl2. Chemical equations when MgCl2 is added in mixing water with

cement is already given above. The XRD pattern of SFBCC with mixing water containing 1.5

g/l is presented at Fig. 5. 98. Apart from the above it can be seen that the compressive

strength of the SFBCC is more than the SFBCC because of the presence of silica fume.

Scanning Electron Microscope images were taken, which are depicted as Fig. 5.97a and 98a


31/81

respectively for BCC and SFBCC samples spiked with 1.5 g/l MgCl2 in deionised water.

Results obtained from X-Ray diffraction analysis have also been found to be justified through

these SEM images.

Fig.5.98. X-Ray diffraction pattern of powdered SFBCC sample prepared with MgCl2 (1.5

g/l) in deionised water


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Fig.5.97a. SEM image of BCC specimen with 1.5 g/l of MgCl2 in deionised water


33/81

Fig.5.98a. SEM image of SFBCC specimen with 1.5 g/l of MgCl2 in deionised water

5.2.6.7 Effect of MgCl2 on Chloride ion Permeability

The rapid chloride permeability levels in terms of coulombs passed through OPCC,

BCC and SFBCC observed are tabulated and listed in the Tab.5.46 to 5.48. By comparing the

coulombs passed, which gives chloride ion permeability, it is observed that the chloride ion

permeability of OPCC is high at both 28 and 90 days age against BCC and then SFBCC.

Quantum of coulombs passed and percentage of variation in the charge passed are depicted in

Fig. 5.99 and 5.100 below. A glimpse at the said results and the graphs establishes that the


34/81

chloride ion permeability of all the three concretes studied has increased with the increase in

the concentration of MgCl2up to 2.0 g/l which is the maximum experimented concentration.

At maximum MgCl2concentration i.e. 2.0 g/l, percentage of variation in coulombs passed

through BCC concrete sample has changed 13.23% at 28 days age compared to 2036

coulombs for the control sample of BCC at the same age.


to MgCl2concentrations



1Deionised water

(Control)2265 1418

2 0.2 g/l 2287 0.97 1430 0.87

3 0.5 g/l 2398 5.85 1492 5.25

4 1 g/l 2434 7.45 1511 6.54

5 1.5 g/l 2484 9.69 1552 9.47

6 2.0 g/l 2588 14.25 1590 12.14


MgCl2concentrations

Sl.No Water sample Coulombs passed28 days % change 90 days % change

1Deionised water

(Control)2036 1187

2 0.2 g/l 2088 2.57 1202 1.25

3 0.5 g/l 2169 6.52 1249 5.24

4 1 g/l 2213 8.71 1277 7.61

5 1.5 g/l 2232 9.64 1300 9.54

6 2.0 g/l 2306 13.24 1331 12.12

Table-5.48 . Chloride ion permeability in terms of coulombs passed in SFBCC corresponding

to MgCl2concentrations

Sl.No Water sample Coulombs passed


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1Deionised water

(Control)1959 1026

2 0.2 g/l 1972 0.64 1041 1.45

3 0.5 g/l 2085 6.42 1079 5.21

4 1 g/l 2126 8.54 1104 7.585 1.5 g/l 2149 9.71 1123 9.41

6 2.0 g/l 2247 14.68 1157 12.74


















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37/81




The effect of MgSO4 on initial and final setting times is shown in Table 5.49 and Fig.

5.101. From the table and figure, it is observed that both initial and final setting times of

cement got accelerated with an increase in the concentration of magnesium sulphate in

deionised water. The acceleration in the initial and final setting time is significant when the

magnesium sulphate content equal to 1.0 g/l. The decrease in the initial setting time is about

45 minutes at maximum concentration of 2.0 g/l. In the case of final setting time, a drop of

nearly 40 minutes is observed when the concentration is 2.0 g/l.

For comparison purposes, the effect of MgSO4 on the setting times of OPC is also

presented in Fig. 5.101. The results of OPC were taken from the experimentation of Reddy,

2004. It can be observed from the figure 5.101 that the setting times of BC and OPC differed

marginally and the effect of MgSO4 is very much similar on both OPC and BC. The setting

times of blended cement (BC) are slightly higher when compared to OPC at all MgSO 4

concentrations. This is expected due to the presence of fly ash in the BC.

Table-5.49.Variation of setting times of BC corresponding to MgSO4 concentrations

Sl.No Water sample



1

Deionised water

(Control) 133 3612 0.1 g/l 131 -1.51 359 -0.49

3 0.2 g/l 129 -3.08 354 -1.98

4 0.5 g/l 122 -7.91 341 -5.49

5 0.75 g/l 110 -17.13 332 -7.91

6 1.0 g/l 101* -24.02 330* -8.71

7 1.5 g/l 93 -30.21 325 -9.91

8 2.0 g/l 88 -33.47 321 -11.13

*- Significant


38/81

0.0 0.5 1.0 1.5 2.0

100

150

200

250

300

350

400

Settingtime(mins)

Concentration of MgSO4

(g/l)

BC-Initial Setting Time

BC-Final setting time




Fig.5.101.Setting times of Blended Cement vs MgSO4 concentrations


The effect of MgSO4 on initial and final setting times is shown in Table 5.50 and Fig.

5.102. From the table and figure, it is observed that both initial and final setting times of

cement got accelerated with an increase in the concentration of magnesium sulphate in

deionised water. The acceleration in the initial and final setting time is significant when the

magnesium sulphate content equal to 1.0 g/l. The decrease in the initial setting time is about

47 minutes at maximum concentration of 2.0 g/l. In the case of final setting time, a drop of

nearly 41 minutes is observed when the concentration is 2.0 g/l.

For comparison purposes, the effect of MgSO4 on the setting times of OPC is also


Reddy, 2004. It can be observed from the figure 5.102 that the setting times of SFBC and

OPC differed marginally and the effect of MgSO4 is very much similar on both OPC and

SFBC. The setting times of blended cement (SFBC) are slightly higher when compared to

OPC at all MgSO4 concentrations. This is expected due to the presence of silica fume in the


39/81

said cement (SFBC). The behavior of setting times of BC and SFBC is depicted in Fig. 5.103.

From this figure it is observed that the initial and final setting times are slightly higher for

SFBC when compared with BC.

Table-5.50.Variation of setting times of SFBC corresponding to MgSO4 concentrations

Sl.No Water sample



1Deionised water

(Control)142 368

2 0.1 g/l 140 -1.5 366 -0.53

3 0.2 g/l 138 -3.02 360 -2.13

4 0.5 g/l 131 -7.76 350 -4.99

5 0.75 g/l 118 -17.02 339 -7.82

6 1.0 g/l 108* -23.87 336* -8.69

7 1.5 g/l 99 -30.31 332 -9.84

8 2.0 g/l 95 -33.33 327 -11.11

*- Significant

0.0 0.5 1.0 1.5 2.0

100

150

200

250

300

350

400

Settingtime(mins)

Concentration of MgSO4 (g/l)

SFBC-Initial Setting Time

SFBC-Final setting timeLine of significance



Fig.5.102.Setting times of SFBC vs MgSO4 concentrations


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0.0 0.5 1.0 1.5 2.0

100

150

200

250

300

350

400

Settingtime(mins)


(g/l)

BC- Initial setting Time

BC- Final setting Time

SFBC- Initial setting Time

SFBC- Final setting Time

Fig.5.103. Setting times of BC, SFBC vs MgSO4 concentrations


The effect of MgSO4 concentration on the compressive strength BCC is presented in

Table 5.51 and Fig. 5.104 and 5.105. The results indicate that there is a decrease in

compressive strength of BCC cubes prepared with MgSO4 solution is observed as the

magnesium carbonate concentration increases where as there is no significant change in

compressive strength for 28 day and 90 day samples at any concentration. The maximum

concentration considered for experimentation is 2.0 g/l. When the concentration is 2.0 g/l, the

decrease in compressive strength is as much as 0.98% for 28 day concrete and 0.50% for 90

day grade concrete respectively, when compared with that of cubes prepared with the

deionised water (control test sample).

Omar S. Baghabra Al-Amoudi (2002) studied the sulphate effect on plain and blended

cements and the results indicated that there is a change in strength and durability properties.


41/81

The concomitant presence of chlorides with the sulfate ions tends to mitigate NaSO 4 attack

due to the enhanced solubility of gypsum and ettringite thereby inhibiting their expansive

characteristics. In MgSO4 exposures, the chlorides alleviate the gypsum attack in a way

similar to that in NaSO4 environments. However, the chloride ions do not significantly affect

the attack of MgSO4 on CSH. As a consequence, MgSO4 attack on blended cements

exposed to sulfatechloride environments progresses unhindered by chlorides, thereby

converting the cementitious CSH to the non-cementitious MSH.

Table-5.51. Compressive strength of BCC corresponding to MgSO4 concentrations

Sl.

No

Water

Sample

BCC



I

Deionised

Water

(Control)

23.89 27.47-- --

II

i0.1 g/l 23.81 27.46 -0.34 -0.02

ii 0.2 g/l 23.78 27.42 -0.45 -0.2

iii 0.5 g/l 23.77 27.41 -0.52 -0.23

iv 0.75 g/l 23.76 27.40 -0.55 -0.27

v 1.0 g/l 23.74 27.38 -0.64 -0.31

vi 1.5 g/l 23.72 27.35 -0.71 -0.42

vii 2.0 g/l 23.66 27.33 -0.98 -0.5


42/81

0.0 0.5 1.0 1.5 2.0

23.5

24.0

24.5

25.0

25.5

26.0

26.5

27.0

27.5


2)


(g/l)

BCC-28 days

BCC-90 days

Fig.5.104. Compressive strength of BCC vs MgSO4 concentrations

0.0 0.5 1.0 1.5 2.0

-1.0

-0.9

-0.8

-0.7

-0.6

-0.5

-0.4

-0.3

-0.2

-0.1

0.0

%v

ariationincompstrength


(g/l)

BCC 28 days

BCC 90 days

Fig.5.105. % variation in compressive strength of BCC vs MgSO4 concentrations

5.3.3.4 Effect on Strength of SFBCC

The effect of MgSO4 concentration on the compressive strength of SFBCC is

presented in Table 5.52 and Fig. 5.106 and 5.107. No significant increase in compressive

strength is observed with increase in concentration of MgSO4. The maximum concentration


43/81

considered for experimentation is 2.0 g/l. When the concentration is 2.0 g/l, the decrease in

compressive strength is as much as 0.96% for 28 day concrete and 0.49% for 90 day concrete

respectively, when compared with that of cubes prepared with the deionised water (control

test sample).

Shannag M.J, Hussein A. Shaia (2003) investigated the behavior of sulphate

resistance for high performance concretes. The investigation recommended the use of silica

fume in combination with natural pozzolana for better performance in sulphate environments.

When MgSO4 reactswith blended cements, particularly those prepared with silica fume and

blast furnace slag, displayed inferior performance in terms of strength reduction and weight

loss of concrete as compared with plain cements. The inferior performance of blended

cements is ascribable to the consumption of portlandite by the pozzolanic reaction thereby

causing a shift in the reaction mechanisms. Such a shift exacerbates the sulfate attack on C

SH leading to softening, loss of surfacial concrete material and excessive reduction in

strength. Ultimately, MgSO4 attack transforms the cementitious CSH into fibrous, non-

crystalline MSH that possesses no cementing properties. Accordingly, the MgSO4 attack

was manifested by weight loss of material and strength reduction. This mechanism may be

applicable for present work of concrete made with SFBCC and BCC.

Table-5.52. Compressive strength of SFBCC corresponding to MgSO4 concentrations

Sl.

No

Water

Sample

SFBCC



44/81


I

Deionised

Water

(Control)

26.09 29.8-- --

IIi 0.1 g/l 26.00 29.80 -0.36 0

ii 0.2 g/l 25.98 29.74 -0.43 -0.21

iii 0.5 g/l 25.96 29.73 -0.49 -0.23

iv 0.75 g/l 25.95 29.72 -0.52 -0.26

v 1.0 g/l 25.94 29.71 -0.59 -0.3

vi 1.5 g/l 25.90 29.67 -0.72 -0.43

vii 2.0 g/l 25.84 29.65 -0.96 -0.49

0.0 0.5 1.0 1.5 2.0

26.0

26.5

27.0

27.5

28.0

28.5

29.0

29.5

30.0

Compressivestrength

(N/mm

2)

Concentration of MgSO4(g/l)

SFBCC 28 days

SFBCC 90 days

Fig.5.106. Compressive strength of SFBCC vs MgSO4 concentrations


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0.0 0.5 1.0 1.5 2.0

-1.0

-0.9

-0.8

-0.7

-0.6

-0.5

-0.4

-0.3

-0.2

-0.1

0.0

%v

ariationincompstrength

Concentration of MgSO4(g/l)

SFBCC 28 days

SFBCC 90 days

Fig.5.107. % variation in compressive strength of SFBCC vs MgSO4 concentrations

5.3.3.5 Effect on Strength of SFRBCC

The effect of MgSO4 concentration on the compressive strength of SFRBCC is

presented in Table 5.53 and Fig. 5.108 and 5.109. No marked decrease in compressive

strength is observed with increase in concentration of MgSO4 forSFRBCC at 28 days and 90

days. When MgSO4 concentration is maximum, i.e., 2.0 g/l the decrease in compressive

strength is 0.95% at 28 days and 0.51% at 90 days respectively, when compared with that of

cubes prepared with the deionised water (control test sample).


depicted in Fig.5.110 and from which it is observed that SFRBCC exhibits higher

compressive strengths compared to BCC and SFBCC. This may be due to incorporation of

steel fibres in the concrete.

Table-5.53. Compressive strength of SFRBCC corresponding to MgSO4 concentrations

SFRBCC


46/81

Sl.

No

Water

SampleCompressive Strength % variation


I

Deionised

Water

(Control)

29.04 33.1

-- --II

i0.1 g/l 28.94 33.10 -0.35 0

ii 0.2 g/l 28.90 33.02 -0.47 -0.24

iii 0.5 g/l 28.89 33.01 -0.53 -0.27

iv 0.75 g/l 28.87 33.00 -0.57 -0.29

v 1.0 g/l 28.85 32.99 -0.66 -0.32

vi 1.5 g/l 28.84 32.96 -0.7 -0.43

vii 2.0 g/l 28.76 32.93 -0.95 -0.51

0.0 0.5 1.0 1.5 2.0

28.5

29.0

29.5

30.0

30.5

31.0

31.5

32.0

32.5

33.0

Compressivestrength

(N/mm

2)


(g/l)

SFRBCC - 28 days

SFRBCC - 90 days

Fig.5.108. Compressive strength of SFRBCC vs MgSO4 concentrations


47/81

0.0 0.5 1.0 1.5 2.0

-1.0

-0.9

-0.8

-0.7

-0.6

-0.5

-0.4

-0.3

-0.2

-0.1

0.0

%v

ariation

Concentration of MgSO4 (g/l)

SFRBCC - 28 days

SFRBCC - 90 days

Fig.5.109 % variation in compressive strength of SFRBCC vs MgSO4 concentrations

0.0 0.5 1.0 1.5 2.0

23.5

24.0

24.5

25.0

25.5

26.0

26.5

27.0

27.5

28.0

28.5

29.0

29.530.0

30.5

31.0

31.5

32.0

32.5

33.0

Compressivestrength(N/m

m2)


(g/l)

BCC - 28 days

BCC - 90 days

SFBCC - 28 days

SFBCC - 90 days

SFRBCC - 28 days

SFRBCC - 90 days

Fig.5.110. Compressive strength of BCC, SFBCC, SFRBCC vs MgSO4

concentrations

5.3.3.6 Powder X-ray Diffraction Analysis and SEM Imaging


48/81

Powder X-Ray Diffraction patterns are shown in Fig.5.111 and 5.112 for BCC and

SFBCC cubes prepared with MgSO4 (1.0 g/l) in deionised water. A look at the said graphs

establishes that the compounds such as Ettringite, C2S, C3S, Calcium Hydroxie (CH), C-H-

S, Calcium Sulphate and M-S-H are found at 410, 16

0, 17

0, 21

0, 31.8

0, 22.3

0and 55

0

respectively. Comparing with control sample, the sample of MgSO4 additionally consists of

Ettringite, M-S-H and Calcium Sulphate.

Fig.5.111.XRD pattern of BCC sample prepared with MgSO4 (1.0 g/l) in deionised water

Setting times of the BC were observed to get accelerated with the increase in MgSO4

concentration in the mixing water. From the literature, it is clear sulphates are accerating the

setting times. The same is observed when the MgSO4 is added in mixing water in the present

study. Chemical equations when MgSO4 is added in mixing water with cement are given

below.

MgSO4 + Ca(OH)2 CaSO4 + Mg(OH)2

3CaSO4 + Al2O3 + 32 H2O 3CaSO4.Al2O3.32H2O


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MgSO4 + C-S-H CaSO4.2H2O + M-S-H

Compressive strength has decreased with an increase in the concentration of MgSO4.

The XRD patterns indicate that the formation of ettringite and M-S-H takes place which

obviously decreases the compressive strength of the concrete. When MgSO4 is added in the

mixing water, it reacts with Ca(OH)2 resulting in the formation of CaSO4. Further, CaSO4

reacts with C3A resulting in ettringite production. Ettringite has expansive in nature, hence

compressive strength is decreased.

Fig.5.112.XRD pattern of SFBCC sample prepared with MgSO4 (1.0 g/l) in deionised

water

In case of SFBCC also, compressive strength has decreased with an increase in the

concentration of MgSO4. Chemical equations when MgSO4 is added in mixing water with

cement are already given above. The XRD pattern indicates the formation of ettringite and

M-S-H here also resulting in decreased compressive strength of the SFBCC sample. Scanning

Electron Microscope images were taken, which are depicted as Fig. 5.112a and 113a

respectively for BCC and SFBCC samples spiked with 1.5 g/l MgSO4 in deionised water.


50/81

Results obtained from X-Ray diffraction analysis have also been found to be concurring

through these SEM images.


51/81

Fig.5.111a. SEM image of BCC specimen with 1.0 g/l of MgSO4 in deionised water


52/81

Fig.5.112a. SEM image of SFBCC specimen with 1.0 g/l of MgSO4 in deionised water

5.2.7.7 Effect of MgSO4 on Chloride ion Permeability

The rapid chloride permeability levels in terms of coulombs passed through

OPCC, BCC and SFBCC observed are tabulated and listed in the Tab.5.54 to 5.56. By

comparing the coulombs passed, which gives chloride ion permeability, it is observed that the

chloride ion permeability of OPCC is high at both 28 and 90 days age against BCC and then

SFBCC. Quantum of coulombs passed and percentage of variation in the charge passed are


53/81

depicted in Fig. 5.113 and 5.114 below. Looking at the said results and the graphs establishes

that the chloride ion permeability of all the three concretes studies has increased with the

increase in the concentration of MgSO4up to 2.0 g/l which is the maximum experimented

concentration. Quantum of coulombs passed has gone up from 1959 to 2041 at 28 days for

SFBCC which is an increase of 4.21 %.


to MgSO4 concentrations



1Deionised water

(Control)2265 1418

2 0.1 g/l 2273 0.37 1428 0.74

3 0.2 g/l 2275 0.46 1436 1.24

4 0.5 g/l 2283 0.78 1446 1.98

5 0.75 g/l 2287 0.98 1453 2.45

6 1.0 g/l 2294 1.27 1460 2.98

7 1.5 g/l 2308 1.91 1467 3.47

8 2.0 g/l 2320 2.41 1474 3.95

Table- 5.55. Chloride ion permeability in terms of coulombs passed in BCC corresponding toMgSO4 concentrations



1Deionised water

(Control)2036 1187

2 0.1 g/l 2041 0.25 1192 0.45

3 0.2 g/l 2061 1.21 1202 1.25

4 0.5 g/l 2086 2.46 1212 2.14

5 0.75 g/l 2092 2.74 1221 2.86

6 1.0 g/l 2109 3.58 1231 3.74

7 1.5 g/l 2117 3.96 1237 4.218 2.0 g/l 2129 4.57 1241 4.54

Table- 5.56. Chloride ion permeability in terms of coulombs passed in SFBCC corresponding

to MgSO4 concentrations

Sl.No Water sample

Coulombs passed

28 days % change 90 days % change1 Deionised water 1959 1026


54/81

(Control)

2 0.1 g/l 1968 0.45 1033 0.71

3 0.2 g/l 1983 1.21 1039 1.24

4 0.5 g/l 1996 1.87 1048 2.14

5 0.75 g/l 2001 2.14 1055 2.81

6 1.0 g/l 2009 2.57 1065 3.767 1.5 g/l 2030 3.61 1069 4.21

8 2.0 g/l 2041 4.21 1073 4.58


















55/81

0.0 0.5 1.0 1.5 2.0

1000

1200

1400

1600

1800

2000

2200

2400

Coulombspassed


(g/l)

28 days BCC

90 days BCC

28 days SFBCC

90 days SFBCC

28 days OPCC

90 days OPCC

Fig.5.113. Charge passed vs concentration of MgSO4 concentrations

0.0 0.5 1.0 1.5 2.0

0

1

2

3

4

5

%v

ariation

Concentration (g/l)

BCC 28 days

BCC 90 days

SFBCC 28 daysSFBCC 90 days

OPCC 28 days

OPCC 90 days

Fig.5.114. % variation in Charge passed vs concentration of MgSO4 concentrations


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5.3.4 Effect of Magnesium Bicarbonate [Mg (HCO3)2]

The effect of presence of magnesium bicarbonate [Mg(HCO3)2] in mixing water on

setting times of cements (Blended Cement (BC) and Silica Fume Blended Cement (SFBC)),

compressive strength of Blended Cement Concrete (BCC), Silica Fume Blended Cement




The effect of Mg(HCO3)2 on initial and final setting times is shown in Table 5.57 and


got retarded with an increase in magnesium bicarbonate concentration in the deionised water.

Significant change in the initial and final setting times is observed at concentration of 0.3 g/l.

When the concentration of the Mg(HCO3)2 is 0.6 g/l (maximum), the differences in initial

and final setting times are 44 minutes and 51 minutes respectively when compared with those

of the control mix.

Table-5.57.Variation of setting times of BC corresponding to various Mg(HCO3)2

concentrations

SL.No Water sample



1Deionised water

(Control)133 -- 361

2 0.1 g/l 137 2.91 365 1.15

3 0.2 g/l 153 14.94 379 5.03

4 0.3 g/l 165* 24.23 392* 8.615 0.4 g/l 170 27.97 399 10.59

6 0.5 g/l 174 31.08 405 12.11

7 0.6 g/l 177 32.92 412 13.99

*- Significant


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0.1 0.2 0.3 0.4 0.5 0.6

100

150

200

250

300

350

400

Settingtime(mins)

Concentration of Mg(HCO3)

2(g/l)




Fig.5.115.Setting times of Blended Cement vs Mg(HCO3)2 concentrations


The effect of Mg(HCO3)2 on initial and final setting times is shown in Table 5.58 and


got retarded with an increase in magnesium bicarbonate concentration in the deionised water.

Significant change in the initial and final setting times is observed at concentration of 0.3 g/l.

When the concentration of the Mg(HCO3)2 is 0.6 g/l (maximum), the differences in initial

and final setting times are 47 minutes and 50 minutes respectively when compared with those

of the control mix.

Table-5.58.Variation of setting times of SFBC corresponding to Mg(HCO3)2 concentrations

SL.No Water sample



1Deionised water

(Control)142 368

2 0.1 g/l 146 3.02 372 1.17

3 0.2 g/l 163 14.86 386 4.89

4 0.3 g/l 176* 24.29 400* 8.63

5 0.4 g/l 182 28.15 406 10.33

6 0.5 g/l 186 31.23 412 12.08

7 0.6 g/l 189 33.01 418 13.64

*- Significant


58/81

0.1 0.2 0.3 0.4 0.5 0.6

100

150

200

250

300

350

400

Settingtime(mins)


2(g/l)




Fig.5.116.Setting times of SFBC vs Mg(HCO3)2 concentrations

0.1 0.2 0.3 0.4 0.5 0.6

120

140

160

180

200

220

240

260

280

300

320

340

360

380

400

420

Settingtime(mins)

Concentration of Mg(HCO3)2 (g/l)





Fig.5.117. Setting times of BC, SFBC vs Mg(HCO3)2 concentrations


The effect of Mg(HCO3)2 concentration on the compressive strength of concrete of

ordinary Portland cement concrete is presented in Table 5.59 and Fig. 5.118 and 5.119.

Increase in the compressive strength and of the BCC specimens prepared with


59/81

Mg(HCO3)2 solution is observed as the magnesium bicarbonate concentration increases, the

maximum concentration studied being 0.6 g/l. The increase in compressive strength for

samples of both 28 day, 90 day age is nominal and below significant level. When Mg(HCO3)2

concentration is maximum, i.e., 0.6 g/l the increase in compressive strength is 5.02% for 28

day concrete and 1.40 % for 90 day concrete respectively, when compared with that of cubes


For comparison purposes, the effect of Mg(HCO3)2 on the compressive strengths of

OPCC is also presented in Fig. 5.118. The results of OPCC were taken from the research

work of Reddy, 2004. It can be observed from the figure 5.118 that the compressive strengths

of BCC and OPCC differed marginally and the effect of Mg(HCO3)2 is very much similar on

both OPCC and BCC. The compressive strengths of BCC are slightly higher when compared

to OPCC at all Mg(HCO3)2 concentrations.

Table-5.59. Compressive strength of BCC corresponding to Mg(HCO3)2 concentrations

Sl.

No

Water

Sample




I

Deionised

Water

(Control)

23.89 27.47-- --

II

i0.1 g/l 24.79 27.60 3.77 0.49

ii 0.2 g/l 24.95 27.64 4.43 0.63

iii 0.3 g/l 25.02 27.68 4.71 0.75

iv 0.4 g/l 25.04 27.80 4.82 1.2

v 0.5 g/l 25.07 27.83 4.95 1.31

vi 0.6 g/l 25.09 27.85 5.02 1.4


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0.1 0.2 0.3 0.4 0.5 0.6

24.5

25.0

25.5

26.0

26.5

27.0

27.5

28.0


2)


2(g/l)

BCC-28 days

BCC-90 days



Fig.5.118. Compressive strength of BCC vs Mg(HCO3)2 concentrations

0.1 0.2 0.3 0.4 0.5 0.6

0

1

2

3

4

5

%v



2(g/l)

BCC-28 days

BCC-90 days



Fig.5.119. % variation in compressive strength of BCC vs Mg(HCO3)2 concentrations

5.3.4.4 Effect on Strength of SFBCC


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The effect of Mg(HCO3)2 concentration on the compressive strength of SFBCC is

presented in Table 5.60 and Fig. 5.120 and 5.121. The increase in compressive strength for

SFBCC samples of 28 day, 90 day age is nominal and below significant level. When

Mg(HCO3)2 concentration is maximum, i.e., 0.6 g/l the increase in compressive strength is

4.99% for 28 day concrete and 1.35% for 90 day concrete respectively, when compared

with that of cubes prepared with the deionised water (control test sample).

For comparison purposes, the effect of Mg(HCO3)2 on the compressive strengths of

OPCC is also presented in Fig. 5.120. The results of OPCC were taken from the research

work of Reddy, 2004. It can be observed from the figure 5.120 that the compressive strengths

of SFBCC and OPCC differed slightly and the effect of Mg(HCO3)2 is very much similar on

both OPCC and SFBCC. The compressive strengths of SFBCC are slightly higher when

compared to OPCC at all Mg(HCO3)2 concentrations.

Table-5.60. Compressive strength of SFBCC corresponding to MgCl2 concentrations

Sl.

No

Water

Sample

SFBCC



I

Deionised

Water

(Control)

26.09 29.8-- --

II

i0.1 g/l 27.09 29.95 3.82 0.51

ii 0.2 g/l 27.27 30.01 4.51 0.69

iii 0.3 g/l 27.31 30.03 4.68 0.78

iv 0.4 g/l 27.32 30.17 4.73 1.23

v 0.5 g/l 27.38 30.18 4.93 1.29

vi 0.6 g/l 27.39 30.20 4.99 1.35


62/81

0.1 0.2 0.3 0.4 0.5 0.6

24.0

24.5

25.0

25.5

26.0

26.5

27.0

27.5

28.0

28.5

29.0

29.5

30.0

30.5


2)


2(g/l)

SFBCC-28 days

SFBCC-90 days



Fig.5.120. Compressive strength of SFBCC vs Mg(HCO3)2 concentrations

0.1 0.2 0.3 0.4 0.5 0.6

0

1

2

3

4

5

%v



2(g/l)

SFBCC-28 days

SFBCC-90 days



Fig.5.121. % variation in compressive strength of SFBCC vs Mg(HCO3)2 concentrations

5.3.4.5 Effect on Strength of SFRBCC

The effect of Mg(HCO3)2 concentration on the compressive strength SFRBCC is

presented in Table 5.61 and Fig. 5.122 and 5.123. The increase in compressive strength for


63/81

samples at 28 day, 90 day age is nominal and below significant level. When Mg(HCO3)2

concentration is maximum, i.e., 0.6 g/l the increase in compressive strength is 4.98% 28 day

SFRBCC, 1.49% 90 day SFRBCC, when compared with that of cubes prepared with the

deionised water (control test sample).


depicted in Fig.5.124 and from which it is observed that SFRBCC exhibits higher

compressive strengths compared to BCC and SFBCC. This may be due to incorporation of

steel fibres in the concrete.

Table-5.61. Compressive strength of SFRBCC corresponding to Mg(HCO3)2 concentrations

Sl.

No

Water

Sample

SFRBCC



I

Deionised

Water

(Control)

29.04 33.1-- --

IIi

0.1 g/l 30.11 33.28 3.69 0.53

ii 0.2 g/l 30.31 33.32 4.38 0.65

iii 0.3 g/l 30.39 33.35 4.66 0.76

iv 0.4 g/l 30.43 33.51 4.79 1.24

v 0.5 g/l 30.47 33.55 4.91 1.35

vi 0.6 g/l 30.49 33.59 4.98 1.49


64/81

0.1 0.2 0.3 0.4 0.5 0.6

24

25

26

27

28

29

30

31

32

33

34


2)


2(g/l)

SFRBCC-28 days

SFRBCC-90 days



Fig.5.122. Compressive strength of SFRBCC vs Mg(HCO3)2 concentrations

0.1 0.2 0.3 0.4 0.5 0.6

0

1

2

3

4

5

%v



2(g/l)

SFRBCC-28 days

SFRBCC-90 days



Fig.5.123. % variation in compressive strength of SFRBCC vs Mg(HCO3)2

concentrations


65/81

0.1 0.2 0.3 0.4 0.5 0.6

24

26

28

30

32

34

36

38


2)


2(g/l

BCC-28 days

BCC-90 days

SFBCC-28 days

SFBCCOPCC-90 days)

SFRBCC-28 days

SFRBCC-90 days

Fig.5.124. Compressive strength of BCC, SFBCC, SFRBCC vs Mg(HCO3)2

concentrations

5.3.4.6 Powder X-ray diffraction analysis and SEM Imaging

Powder X-Ray Diffraction patterns are shown in Fig.5.125 and 5.126 is for the BCC

and SFBCC prepared with Mg(HCO3)2 (0.3 g/l) in deionised water. Upper portion of the said

graph indicates the XRD pattern of the control sample prepared with deionised water. Perusal

of the said graphs establishes that the compounds such as C2S, C3S, Calcium Hydroxide

(CH), C3ACcH and C-H-S are found at 160,

170, 21

0,49

0and 37

0respectively. Comparing

with control sample, the sample of Mg(HCO3)2 additionally consists of C3ACcH (Carbo

Aluminate).

Setting times of the BC were observed to get retarded with the increase in Mg(HCO3)2

concentration in the mixing water. From the literature, bicarbonates are retarding the setting

times. The same is observed when the Mg(HCO3)2 is added in mixing water in the present

investigation. Possible reason is reaction between C3A and Mg(HCO3)2which producescarbo

aluminate which retards the hydration process which in turn retards the setting times.


66/81

Fig.5.125.XRD pattern of concrete BCC sample prepared with Mg(HCO3)2 (0.3 g/l) in

deionised water

Compressive strength has increased with an increase in the concentration of

Mg(HCO3)2. Chemical reactions taken place are depicted in the below equations when

Mg(HCO3)2is added in mixing water with cement is given below. When Mg(HCO3)2is added

to mixing water,the same reacts with calcium silicates thereby extra C-S-H gel is generated

which contributes towards extra compressive strength.

Mg(HCO3)2 + 2Ca(OH)2 2CaCO3 + Mg(OH)2 +2H2O

3CaCO3 + 3CaO.Al2O3 +32H2O 3CaO. Al2O3.CaCO3.32H2O

In case of SFBCC also, compressive strength has increased with an increase in the

concentration of CaCO3. The XRD patterns of Mg(HCO3)2added SFBCC powdered sample

is presented in Fig.5.126. Reason elucidated above holds good here also for increase in

strength, apart from addition of silica fume contributing towards an increase in compressive

strength. Scanning Electron Microscope images were taken, which are depicted as Fig.

5.125a and 126a respectively for BCC and SFBCC samples spiked with 0.3 g/l Mg(HCO3)2


67/81

in deionised water. Results obtained from X-Ray diffraction analysis have also been found to

be concurring through these SEM images.

Fig.5.126.XRD pattern of SFBCC sample prepared with Mg(HCO3)2 (0.3 g/l) in

deionised water


68/81

Fig.5.125a. SEM image of BCC specimen spiked with 0.3 g/l of Mg(HCO3)2 in deionised

water


69/81

Fig.5.126a. SEM image of SFBCC specimen with 0.3 g/l of Mg(HCO3)2 in deionised water

5.2.8.7 Effect of Mg(HCO3)2 on Chloride ion Permeability

The rapid chloride permeability levels in terms of coulombs passed through OPCC,

BCC and SFBCC observed are tabulated and listed in the Tab.5.62 to 5.64. By comparing the

coulombs passed, which gives chloride ion permeability, it is observed that the chloride ion

permeability of OPCC is high at both 28 and 90 days age against BCC and then SFBCC.

Quantum of coulombs passed and percentage of variation in the charge passed are depicted in


70/81

Fig. 5.127 and 5.128 below. A peep into the said results and the graphs establishes that the

chloride ion permeability of all the three concretes studies has decreased with the increase in

the concentration of Mg(HCO3)2 up to 0.6 g/l which is the maximum experimented

concentration. Quantum of coulombs passed has come down from 2036 to 1934 at 28 days

for BCC which is a decrease of 5.02 %.


to Mg(HCO3)2 concentrations



1

Deionised water

(Control) 2265 1418

2 0.1 g/l 2232 -1.47 1393 -1.74

3 0.2 g/l 2202 -2.76 1383 -2.48

4 0.3 g/l 2192 -3.21 1372 -3.27

5 0.4 g/l 2161 -4.57 1363 -3.89

6 0.5 g/l 2153 -4.96 1353 -4.56

7 0.6 g/l 2146 -5.26 1344 -5.21


Mg(HCO3)2 concentrations



1Deionised water

(Control)2036 1187

2 0.1 g/l 2010 -1.27 1175 -0.97

3 0.2 g/l 1987 -2.41 1170 -1.46

4 0.3 g/l 1963 -3.58 1154 -2.78

5 0.4 g/l 1949 -4.26 1149 -3.21

6 0.5 g/l 1936 -4.91 1141 -3.867 0.6 g/l 1934 -5.02 1132 -4.64

Table-5.64 . Chloride ion permeability in terms of coulombs passed in SFBCC corresponding

to Mg(HCO3)2 concentrations



1Deionised water

(Control)1959 1026

2 0.1 g/l 1924 -1.79 1009 -1.68

3 0.2 g/l 1906 -2.73 999 -2.61


71/81

4 0.3 g/l 1890 -3.54 989 -3.57

5 0.4 g/l 1877 -4.21 983 -4.21

6 0.5 g/l 1852 -5.47 970 -5.47

7 0.6 g/l 1842 -5.97 966 -5.87


















72/81

0.1 0.2 0.3 0.4 0.5 0.6

1000

1200

1400

1600

1800

2000

2200


Concentration (g/l)

28 days BCC90 days BCC

28 days SFBCC

90 days SFBCC

28 days OPCC

90 days OPCC

Fig.5.127 Charge passed vs concentration of Mg(HCO3)2 concentrations

0.1 0.2 0.3 0.4 0.5 0.6

-6.5

-6.0

-5.5

-5.0

-4.5

-4.0

-3.5

-3.0

-2.5

-2.0

-1.5

-1.0

-0.5


Concentration (g/l)

28 days BCC

90 days BCC

28 days SFBCC

90 days SFBCC

28 days OPCC

90 days OPCC

Fig.5.128. % variation in Charge passed vs concentration of Mg(HCO3)2 concentrations

5.3.5 Summary on effect of Slightly Acidic substances


73/81

The slightly acidic substances generally present in water are CaCl2, MgCl2, MgSO4

and Mg(HCO3)2. The effect of each of these compounds at various concentrations in

deionised water on the initial and final setting times of concrete and the compressive strength

of concrete specimens has been already discussed in the above sub sections. The behaviour of

slightly acidic compounds is elucidated in a comprehensive manner as follows.

MgCl2 and Mg(HCO3)2 in deionised water retard the initial as well as final setting

processes whereas CaCl2 and MgSO4 accelerate the initial and final setting times (Fig.5.129

and Fig.5.132) at all concentrations.

CaCl2 and Mg(HCO3)2 in deionised water increase the compressive strength concrete

specimens, (Fig.5.133 to Fig.5.138) where as MgSO4 and MgCl2 decreases the compressive

strength. In the case of Mg(HCO3)2 compound, an increase in the compressive strength falls

at 90 days compared to strength of 28 days. Meager increase in the compressive strength has

occurred with Mg(HCO3)2 solutions. By comparing the effect of slightly acidic compounds, it

is evident that CaCl2 and Mg(HCO3)2 effect the compressive strength positively, whereas,

MgSO4 and MgCl2 affect the compressive strength negatively. Hence a lot of care should be

taken when MgSO4 and MgCl2 are present in water.

With regard to chloride ion permeability, it was observed that there is a decrease in

coulombs passed with an increase in CaCl2 and Mg(HCO3)2 in deionised water. However, the

opposite has been observed in case of MgSO4 andMgCl2. Graphs showing the variations for

both BCC and SFBCC, for all four chemicals, at 28 and 90 days are presented as Fig. 5.139

to Fig. 5.142. This reveals that, when the concentrations of CaCl2 and Mg(HCO3)2 are

increased one can see a decrease in chloride ion permeability of all types of concretes.


74/81

0.0 0.2 0.4 0.6 0.8 1.0 1.2 1.4 1.6 1.8 2.0 2.2

90

100

110

120

130

140

150

160

170

Settingtime(mins)

Concentration (g/l)

CaCl2

MgCl2

MgSO4

Mg(HCO3)

2

Line of Significance

Fig.5.129 Variation of initial setting time of Blended Cement vs concentrations of slightly

acidic substances

0.0 0.2 0.4 0.6 0.8 1.0 1

ch 6 results and discussions of slightly acidic substance

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