EFFECTS OF ALKALINITY PRESENT IN WATER ON STRENGTH AND SETTING PROPERTIES OF FLY ASH CONCRETE

V Venkateswara Reddy JNT University India

H Sudarsana Rao JNT University India KN Jayaveera JNT University India

29th Conference on OUR WORLD IN CONCRETE amp STRUCTURES 25 - 26 August 2004

Singapore

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29th

Conference on OUR WORLD IN CONCRETE amp STRUCTURES 25 - 26 August 2004 Singapore

EFFECTS OF ALKALINITY PRESENT IN WATER ON STRENGTH AND SETTING PROPERTIES OF FLY ASH CONCRETE

V Venkateswara Reddy JNT University India H Sudarsana Raomiddot JNT University India

KN Jayaveera JNT University India

Abstract

The effect of alkalinity on setting time and strength development fly ash concrete is assessed under the laboratory conditions The results indicate that the initial and final setting times either retarded or accelerated depending upon the type of alkalinity imparted by Na2C03 or NaHC03 Sodium carbonate when present in water acc~lerated both the initial and final setting time when its content is equal to 6 gIl and 4gl respectively Sodium bi- carbonate when present in water retarded both the initial and final setting time when its content is equal to 4 gl and 6gl respectively The rate of development of compressive strength and tensile strength decreased with increase in concentration of both Na2C03 and NaHC03 when its content was exceeded by 6 gIL and 10 gIL respectively

Keywords cement concrete setting time compressive strength tensile strength alkalinity

1 Introduction Concrete is one of the most durable construction materials available Cement one of the ingredients in concrete is one of the most energy-intensive structural materials to produce however it is the atmospheric pollution released during the production of cement that is cause for great environmental concern The best opportunity to reduce the CO2 attributed to manufacturing cement is to reduce the amount of cement required for concrete mix designs Mineral admixtures such as replacement pozzolonas can be substituted easily for portions of the required cement Fly ash which consists of small glassy spheres that form while the burned coal residue cools rapidly is the most common cement replacement pozzolonas used in concrete Fly ash is the waste by-product resulting from the combustion of coal for electricity generation and it has many benefits beyond CO2 reduction When fly ash is used in concrete it acts like a cement and actually replaces a percentage of the Portland cement Cement and fly ash using in fly ash concrete are mixture of complex compounds The reaction of these with water leads to setting and hardening when it is gauged with water The CA (Tricalcium aluminate) C3S (Tri calcium silicate) and CAF (Tetra calcium alumina ferrite) phases of cement react very rapidly and the gauging water become saturated with Ca(OHh formed in the hydrates rather slowly The initial setting is attributed to hydration reactions The C2S (Dicalcium Silicate) phase the reactions of C3 A C3S and CAF (lea 1956) The aqueous phase is essentially a solution of the hydroxide and sulphates of Ca Na amp K and it is likely that equilibrium sets in among then (Price 1951)

The quality of the water plays an important role in the preparation of concrete Impurities in water may interfere with the setting of the cement and may adversely affect the strength of the concrete (Neville 1970) The chemical constituents present in water may participate in the chemical reactions and thus affect the setting hardening and strength development of concrete A popular yard stick to the suitability of water for making concrete is that if it is fit for drinking it is fit for making concrete The IS

537

456 (2000) code stipulates the water quality standards for mixing and curing of concrete works In some arid areas local drinking water is impure and may contain an excessive amount of acids due to contamination by industrial wastes The effects of acids on setting hardening and strength development of fly ash concrete are not known much Hence an investigation is carried out in order to evaluate the effect of alkalis (sodium carbonate amp sodium bi-carbonate) in setting time and strength of fly ash concrete under laboratory conditions The results of the same are presented in this paper

2 Materials and Methods

Cement The cement used in the present investigation is of 53 grade ordinary Portland cement The percent composition of the major compounds present in cement are presented in Table-1

TABLE 1 Percentage compositions of the major compounds present in the test cement

SLNo Name of the compound Conversion formula

Of

Present 1

Tricalcium silicate (3CaO Si02)

407(CaO)-76(Si02)shy6 72(AI20 J)-1 43(Fez~-285(S03)

5149

2 Dicalcium silicate (2CaO Si02l

287(Si02-0754(3Cao Si02) 2337

3 Tricalcium aluminate (3CaO~02)

265(Ab~)-169(FezOJ) 931

4 Tetracalcium alumino ferrite (4CaO A~02 F~03)

304(Fe20 J) 1170

Fly ash The fly ash used in the present investigation is of low -lime fly ash (CaOlt10) The percent composition of the major compounds present in fly ash is presented in Table-2

TABLE 2 Chemical composition of Fly Ash

SLNo CONSTITUENTS Of Present

1 Si02 49-67

2 A~~ 16-33

3 F~OJ 4-10

4 CaO 1-4

5 MgO 02-20

6 S~ 01-20

7 Na20 01-02

8 K20 01-10

9 LOI 01-16

Fine Aggregate The fine aggregate used in this investigation is the river sand obtained from Pandameru River near Anantapur in Andhra Pradesh The properties of sand are presented in Table -3

T bl 3 P a e ro pel res sanrt of d SLNO Properly Unit Result

1 Specific Gravity - 275 2 Bulk Density KNlm 1554 3 Fineness Modulus - 280 4 Particle size variation Mm 009-20 5 Loss of weight with 0124

concentrated Hydrochloric acid

538

Coarse aggregate Crushed Granite stone aggregate of maximum size 20 mm confirming to IS 383-1970 was used The specific gravity and fineness modulus were found to be 2622 and 665 respectively Test results are shown in Table 4

TABLE 4 Grading analysis for coarse Aggregate Sample-5000 gms

SLNO IS Sieve size

Weight Retained (gms)

Cumulative weight retained (gms)

Cumulative retained

passing

1 80mm - - - 10000 2 40mm - - - 10000 3 20mm 83000 83000 1660 8340 4 10mm 119000 202000 4040 5960 5 630mm 31000 233000 4660 3860 6 475mm 74000 307000 6140 5340 7 236mm 193000 500000 10000 -8 118 mm - - 10000 -9 600 microns - - 10000 -10 300 microns - - 10000 -11 150 microns - - 10000 -

Total 500000 66500

Fineness Modulus=66500100 = 665

Water Deionised water spiked with sodium carbonate and sodium bi-carbonate at different concentration is used in mixing water

3 Experimental System The following equipment is used for casting and testing of the specimens

i Cube and cylinder moulds ii 40T UTM (Universal Testing Machine) for cube compressive strength detennination iii Vicats apparatus including moulds confirming to IS 4031 (part 5)-1988 iv Cement concrete cubes and cylinders of M20 and M50 grade are casted with

water containing sodium carbonate and sodium bi-carbonate in the concentration of 1 2 4 610 and 15 giL in mixing water

Setting Time Vicats apparatus confirming IS 4031 (pant 5) 1988 consists of a frame to which a movable rod

having an indicator is attached which gives the penetration weighing 100gms and having diameter and length of 10 mm and 50 mm respectively Vicatss apparatus included three attachmentsshysquare needle for initial setting time plunger for determining normal consistency and needle with annular collar for final setting time

Compressive Strength The test specimens for the determination of compressive strength of concrete are prepared using the standard metallic cube moulds adopting IS procedure for the rodding and hard compactions

The cubes are demoulded after 24 hours of casting and cured in water having similar quality as used in the preparation of mix the cubes are tested for a compressive strength after 28 days and 90 days The compressive strength is computed as the average value of the three samples

Split Tensile Strength The test specimens for the determination of split tensile strength of concrete are prepared using the standards metallic cylinder moulds adopting IS procedure for the rodding and hard compaction The cylinders are demoulded after 24 hours of casting and cured in water having similar quality as used in the preparation of mix The cylinders are tested for split tensile strength test after 28 days and 90 days The split tensile strength is computed as the average value of the three samples

4 Results and Discussion The interpretation of results obtained in this investigation is based on the guidelines specified by IS 456 (2000)

The average of both the setting times of three cement samples prepared from water under consideration are compared with those of the cement specimens prepared from deionised water If

539

the difference is less than 30 minutes the change is considered to be negligible and if the difference is more than 30 minutes the change is considered to be significant

Average compressive strength and average split tensile strength of at least three specimens prepared with water under consideration is compared with that of three similar cases prepared with deionised water (Control) If the difference in the strength is less than 10 it is considered to be insignificant

Setting Time Test results of setting times of the test block made from different water samples and deionised water are reported in fig (1) amp (2)

From the fig 1 it is observed that both setting times are decreased with the increase in concentration of sodium carbonate of mixing water and from the fig 2 it is observed that both the setting times increased with the increase in concentration of sodium bi-carbonate in water Considerable decrease in both the initial and final setting times is observed when amount of sodium carbonate was 6 gil and 4 giL and the significant increase observed at 4 gil and 6 giL of sodium bishycarbonate in mixing water for both initial and final setting times respectively

o

-r-----------------~~==~

~ -~ (11111) 1-=-----~iIiii1iiltili1iiiiilI~_______~~=_1 0-0 )---- shy - ----shy

-~--shy

(hIHIII)

0

52fO

1shyf11M~t~Ht-t~r---~~~mI

to

o o 2 4 bull bull ~ tl ~ ~

CorwentTeIiOII Of 1iICO In gil

Fig 1Variation of Setting times of cement corresponding to various concentrations of Na~03 in deionised water

-

o

--~

f-o ----middot

1m (FInII)

I-=-- = 0 -shy bull

-

(1niIII)

JHGi t--tHt-__-It---L-JI-F~

5shy

i shylto J----__-J

I~ to

o 2 u u bull

~ttllIMHCO9iL

Fig 2variation of Setting times of cement corresponding to various concentrations of NaHC~ in deionised water

Compl888ive Strength Test results of the cubes prepared from water containing different salts are presented in fig 3

As indicated in fig3 the compressive strength of the specimens decrease with increase in concentration of sodium carbonate and sodium bi-carbonate of mixing water But the increase in compressive strength was considerable when the concentration sodium carbonate was 6 gil and 10 giL in mixing water for M20-90day M50-28dy 90day and M20-28day respectively and this

540

0 o~---------------------------

4

f - shy 1121)211__ M2OlaquoI -- - 11150-~ - ~

1= -

I --raquo

0 2 4 bullbull lOnu o Z 4 bull bull W 12 U ~

significant change observed at 10 giL and 15 giL of sodium bi-carbonate in mixing water for M20shy90c1ay M50-90day and M20-28dayM50-90day respectively

CoIlClllb d NIHCO1n ~eod PO1n tp

(a) (b) Fig 3Percentage Variation of compressive strength of concrete corresponding to

various concentrations of (a) Na2CQa (b) NaHC03 in deionised water

Tensile Strength Test results of the cylinders prepared from water containing acids are presented in fig 4

From fig4 the compressive strength of the specimens decreases with increase in concentration of sodium carbonate and sodium bi-carbonate of mixing water But the increase in compressive strength was considerable when the concentration sodium carbonate was 6 giL and 10 giL in mixing water for M20-9Oday M50-28dy 90c1ay and M20-28day respectively and this Significant change observed at 10 giL and 15 giL of sodium bi-carbonate in mixing water for M20-90day M50-90day and M20-28dayM50-90day respectively

I I)0 5middot12

-11fmiddot-11 -raquo

bull 2 4 bull bull ~ n u ~

C-bull _tupO~M~

___21

__ 1InO-IO bull MH-2tMyo

-I-N~

(a)

i middot1-4 t i 5

flO -12

-1-I 2 4 bull bull w u u bull

2

-Nzo21Nyo __an_ - -N50-~ ___ N_

c- olIUHCO MjJIL

(b)

Fig 4Percentage Variation of tensile strength of concrete corresponding to various concentrations of (a) Na2C03 (b) H2S04 in deionised water

5 Conclusions

Based on the present investigation the following conclusions can be drawn a Sodium carbonate when present in mixing water accelerates both the initial and final setting

times b Sodium bi-carbonate when present in mixing water retards both the initial and final setting

times c Sodium carbonate accelerates the initial and final setting times significantly at

concentrations of 6 giL and 4 gil respectively

541

29th

Conference on OUR WORLD IN CONCRETE amp STRUCTURES 25 - 26 August 2004 Singapore

EFFECTS OF ALKALINITY PRESENT IN WATER ON STRENGTH AND SETTING PROPERTIES OF FLY ASH CONCRETE

V Venkateswara Reddy JNT University India H Sudarsana Raomiddot JNT University India

KN Jayaveera JNT University India

Abstract

The effect of alkalinity on setting time and strength development fly ash concrete is assessed under the laboratory conditions The results indicate that the initial and final setting times either retarded or accelerated depending upon the type of alkalinity imparted by Na2C03 or NaHC03 Sodium carbonate when present in water acc~lerated both the initial and final setting time when its content is equal to 6 gIl and 4gl respectively Sodium bi- carbonate when present in water retarded both the initial and final setting time when its content is equal to 4 gl and 6gl respectively The rate of development of compressive strength and tensile strength decreased with increase in concentration of both Na2C03 and NaHC03 when its content was exceeded by 6 gIL and 10 gIL respectively

Keywords cement concrete setting time compressive strength tensile strength alkalinity

1 Introduction Concrete is one of the most durable construction materials available Cement one of the ingredients in concrete is one of the most energy-intensive structural materials to produce however it is the atmospheric pollution released during the production of cement that is cause for great environmental concern The best opportunity to reduce the CO2 attributed to manufacturing cement is to reduce the amount of cement required for concrete mix designs Mineral admixtures such as replacement pozzolonas can be substituted easily for portions of the required cement Fly ash which consists of small glassy spheres that form while the burned coal residue cools rapidly is the most common cement replacement pozzolonas used in concrete Fly ash is the waste by-product resulting from the combustion of coal for electricity generation and it has many benefits beyond CO2 reduction When fly ash is used in concrete it acts like a cement and actually replaces a percentage of the Portland cement Cement and fly ash using in fly ash concrete are mixture of complex compounds The reaction of these with water leads to setting and hardening when it is gauged with water The CA (Tricalcium aluminate) C3S (Tri calcium silicate) and CAF (Tetra calcium alumina ferrite) phases of cement react very rapidly and the gauging water become saturated with Ca(OHh formed in the hydrates rather slowly The initial setting is attributed to hydration reactions The C2S (Dicalcium Silicate) phase the reactions of C3 A C3S and CAF (lea 1956) The aqueous phase is essentially a solution of the hydroxide and sulphates of Ca Na amp K and it is likely that equilibrium sets in among then (Price 1951)

The quality of the water plays an important role in the preparation of concrete Impurities in water may interfere with the setting of the cement and may adversely affect the strength of the concrete (Neville 1970) The chemical constituents present in water may participate in the chemical reactions and thus affect the setting hardening and strength development of concrete A popular yard stick to the suitability of water for making concrete is that if it is fit for drinking it is fit for making concrete The IS

537

456 (2000) code stipulates the water quality standards for mixing and curing of concrete works In some arid areas local drinking water is impure and may contain an excessive amount of acids due to contamination by industrial wastes The effects of acids on setting hardening and strength development of fly ash concrete are not known much Hence an investigation is carried out in order to evaluate the effect of alkalis (sodium carbonate amp sodium bi-carbonate) in setting time and strength of fly ash concrete under laboratory conditions The results of the same are presented in this paper

2 Materials and Methods

Cement The cement used in the present investigation is of 53 grade ordinary Portland cement The percent composition of the major compounds present in cement are presented in Table-1

TABLE 1 Percentage compositions of the major compounds present in the test cement

SLNo Name of the compound Conversion formula

Of

Present 1

Tricalcium silicate (3CaO Si02)

407(CaO)-76(Si02)shy6 72(AI20 J)-1 43(Fez~-285(S03)

5149

2 Dicalcium silicate (2CaO Si02l

287(Si02-0754(3Cao Si02) 2337

3 Tricalcium aluminate (3CaO~02)

265(Ab~)-169(FezOJ) 931

4 Tetracalcium alumino ferrite (4CaO A~02 F~03)

304(Fe20 J) 1170

Fly ash The fly ash used in the present investigation is of low -lime fly ash (CaOlt10) The percent composition of the major compounds present in fly ash is presented in Table-2

TABLE 2 Chemical composition of Fly Ash

SLNo CONSTITUENTS Of Present

1 Si02 49-67

2 A~~ 16-33

3 F~OJ 4-10

4 CaO 1-4

5 MgO 02-20

6 S~ 01-20

7 Na20 01-02

8 K20 01-10

9 LOI 01-16

Fine Aggregate The fine aggregate used in this investigation is the river sand obtained from Pandameru River near Anantapur in Andhra Pradesh The properties of sand are presented in Table -3

T bl 3 P a e ro pel res sanrt of d SLNO Properly Unit Result

1 Specific Gravity - 275 2 Bulk Density KNlm 1554 3 Fineness Modulus - 280 4 Particle size variation Mm 009-20 5 Loss of weight with 0124

concentrated Hydrochloric acid

538

Coarse aggregate Crushed Granite stone aggregate of maximum size 20 mm confirming to IS 383-1970 was used The specific gravity and fineness modulus were found to be 2622 and 665 respectively Test results are shown in Table 4

TABLE 4 Grading analysis for coarse Aggregate Sample-5000 gms

SLNO IS Sieve size

Weight Retained (gms)

Cumulative weight retained (gms)

Cumulative retained

passing

1 80mm - - - 10000 2 40mm - - - 10000 3 20mm 83000 83000 1660 8340 4 10mm 119000 202000 4040 5960 5 630mm 31000 233000 4660 3860 6 475mm 74000 307000 6140 5340 7 236mm 193000 500000 10000 -8 118 mm - - 10000 -9 600 microns - - 10000 -10 300 microns - - 10000 -11 150 microns - - 10000 -

Total 500000 66500

Fineness Modulus=66500100 = 665

Water Deionised water spiked with sodium carbonate and sodium bi-carbonate at different concentration is used in mixing water

3 Experimental System The following equipment is used for casting and testing of the specimens

i Cube and cylinder moulds ii 40T UTM (Universal Testing Machine) for cube compressive strength detennination iii Vicats apparatus including moulds confirming to IS 4031 (part 5)-1988 iv Cement concrete cubes and cylinders of M20 and M50 grade are casted with

water containing sodium carbonate and sodium bi-carbonate in the concentration of 1 2 4 610 and 15 giL in mixing water

Setting Time Vicats apparatus confirming IS 4031 (pant 5) 1988 consists of a frame to which a movable rod

having an indicator is attached which gives the penetration weighing 100gms and having diameter and length of 10 mm and 50 mm respectively Vicatss apparatus included three attachmentsshysquare needle for initial setting time plunger for determining normal consistency and needle with annular collar for final setting time

Compressive Strength The test specimens for the determination of compressive strength of concrete are prepared using the standard metallic cube moulds adopting IS procedure for the rodding and hard compactions

The cubes are demoulded after 24 hours of casting and cured in water having similar quality as used in the preparation of mix the cubes are tested for a compressive strength after 28 days and 90 days The compressive strength is computed as the average value of the three samples

Split Tensile Strength The test specimens for the determination of split tensile strength of concrete are prepared using the standards metallic cylinder moulds adopting IS procedure for the rodding and hard compaction The cylinders are demoulded after 24 hours of casting and cured in water having similar quality as used in the preparation of mix The cylinders are tested for split tensile strength test after 28 days and 90 days The split tensile strength is computed as the average value of the three samples

4 Results and Discussion The interpretation of results obtained in this investigation is based on the guidelines specified by IS 456 (2000)

The average of both the setting times of three cement samples prepared from water under consideration are compared with those of the cement specimens prepared from deionised water If

539

the difference is less than 30 minutes the change is considered to be negligible and if the difference is more than 30 minutes the change is considered to be significant

Average compressive strength and average split tensile strength of at least three specimens prepared with water under consideration is compared with that of three similar cases prepared with deionised water (Control) If the difference in the strength is less than 10 it is considered to be insignificant

Setting Time Test results of setting times of the test block made from different water samples and deionised water are reported in fig (1) amp (2)

From the fig 1 it is observed that both setting times are decreased with the increase in concentration of sodium carbonate of mixing water and from the fig 2 it is observed that both the setting times increased with the increase in concentration of sodium bi-carbonate in water Considerable decrease in both the initial and final setting times is observed when amount of sodium carbonate was 6 gil and 4 giL and the significant increase observed at 4 gil and 6 giL of sodium bishycarbonate in mixing water for both initial and final setting times respectively

o

-r-----------------~~==~

~ -~ (11111) 1-=-----~iIiii1iiltili1iiiiilI~_______~~=_1 0-0 )---- shy - ----shy

-~--shy

(hIHIII)

0

52fO

1shyf11M~t~Ht-t~r---~~~mI

to

o o 2 4 bull bull ~ tl ~ ~

CorwentTeIiOII Of 1iICO In gil

Fig 1Variation of Setting times of cement corresponding to various concentrations of Na~03 in deionised water

-

o

--~

f-o ----middot

1m (FInII)

I-=-- = 0 -shy bull

-

(1niIII)

JHGi t--tHt-__-It---L-JI-F~

5shy

i shylto J----__-J

I~ to

o 2 u u bull

~ttllIMHCO9iL

Fig 2variation of Setting times of cement corresponding to various concentrations of NaHC~ in deionised water

Compl888ive Strength Test results of the cubes prepared from water containing different salts are presented in fig 3

As indicated in fig3 the compressive strength of the specimens decrease with increase in concentration of sodium carbonate and sodium bi-carbonate of mixing water But the increase in compressive strength was considerable when the concentration sodium carbonate was 6 gil and 10 giL in mixing water for M20-90day M50-28dy 90day and M20-28day respectively and this

540

0 o~---------------------------

4

f - shy 1121)211__ M2OlaquoI -- - 11150-~ - ~

1= -

I --raquo

0 2 4 bullbull lOnu o Z 4 bull bull W 12 U ~

significant change observed at 10 giL and 15 giL of sodium bi-carbonate in mixing water for M20shy90c1ay M50-90day and M20-28dayM50-90day respectively

CoIlClllb d NIHCO1n ~eod PO1n tp

(a) (b) Fig 3Percentage Variation of compressive strength of concrete corresponding to

various concentrations of (a) Na2CQa (b) NaHC03 in deionised water

Tensile Strength Test results of the cylinders prepared from water containing acids are presented in fig 4

From fig4 the compressive strength of the specimens decreases with increase in concentration of sodium carbonate and sodium bi-carbonate of mixing water But the increase in compressive strength was considerable when the concentration sodium carbonate was 6 giL and 10 giL in mixing water for M20-9Oday M50-28dy 90c1ay and M20-28day respectively and this Significant change observed at 10 giL and 15 giL of sodium bi-carbonate in mixing water for M20-90day M50-90day and M20-28dayM50-90day respectively

I I)0 5middot12

-11fmiddot-11 -raquo

bull 2 4 bull bull ~ n u ~

C-bull _tupO~M~

___21

__ 1InO-IO bull MH-2tMyo

-I-N~

(a)

i middot1-4 t i 5

flO -12

-1-I 2 4 bull bull w u u bull

2

-Nzo21Nyo __an_ - -N50-~ ___ N_

c- olIUHCO MjJIL

(b)

Fig 4Percentage Variation of tensile strength of concrete corresponding to various concentrations of (a) Na2C03 (b) H2S04 in deionised water

5 Conclusions

Based on the present investigation the following conclusions can be drawn a Sodium carbonate when present in mixing water accelerates both the initial and final setting

times b Sodium bi-carbonate when present in mixing water retards both the initial and final setting

times c Sodium carbonate accelerates the initial and final setting times significantly at

concentrations of 6 giL and 4 gil respectively

541

456 (2000) code stipulates the water quality standards for mixing and curing of concrete works In some arid areas local drinking water is impure and may contain an excessive amount of acids due to contamination by industrial wastes The effects of acids on setting hardening and strength development of fly ash concrete are not known much Hence an investigation is carried out in order to evaluate the effect of alkalis (sodium carbonate amp sodium bi-carbonate) in setting time and strength of fly ash concrete under laboratory conditions The results of the same are presented in this paper

2 Materials and Methods

Cement The cement used in the present investigation is of 53 grade ordinary Portland cement The percent composition of the major compounds present in cement are presented in Table-1

TABLE 1 Percentage compositions of the major compounds present in the test cement

SLNo Name of the compound Conversion formula

Of

Present 1

Tricalcium silicate (3CaO Si02)

407(CaO)-76(Si02)shy6 72(AI20 J)-1 43(Fez~-285(S03)

5149

2 Dicalcium silicate (2CaO Si02l

287(Si02-0754(3Cao Si02) 2337

3 Tricalcium aluminate (3CaO~02)

265(Ab~)-169(FezOJ) 931

4 Tetracalcium alumino ferrite (4CaO A~02 F~03)

304(Fe20 J) 1170

Fly ash The fly ash used in the present investigation is of low -lime fly ash (CaOlt10) The percent composition of the major compounds present in fly ash is presented in Table-2

TABLE 2 Chemical composition of Fly Ash

SLNo CONSTITUENTS Of Present

1 Si02 49-67

2 A~~ 16-33

3 F~OJ 4-10

4 CaO 1-4

5 MgO 02-20

6 S~ 01-20

7 Na20 01-02

8 K20 01-10

9 LOI 01-16

Fine Aggregate The fine aggregate used in this investigation is the river sand obtained from Pandameru River near Anantapur in Andhra Pradesh The properties of sand are presented in Table -3

T bl 3 P a e ro pel res sanrt of d SLNO Properly Unit Result

1 Specific Gravity - 275 2 Bulk Density KNlm 1554 3 Fineness Modulus - 280 4 Particle size variation Mm 009-20 5 Loss of weight with 0124

concentrated Hydrochloric acid

538

Coarse aggregate Crushed Granite stone aggregate of maximum size 20 mm confirming to IS 383-1970 was used The specific gravity and fineness modulus were found to be 2622 and 665 respectively Test results are shown in Table 4

TABLE 4 Grading analysis for coarse Aggregate Sample-5000 gms

SLNO IS Sieve size

Weight Retained (gms)

Cumulative weight retained (gms)

Cumulative retained

passing

1 80mm - - - 10000 2 40mm - - - 10000 3 20mm 83000 83000 1660 8340 4 10mm 119000 202000 4040 5960 5 630mm 31000 233000 4660 3860 6 475mm 74000 307000 6140 5340 7 236mm 193000 500000 10000 -8 118 mm - - 10000 -9 600 microns - - 10000 -10 300 microns - - 10000 -11 150 microns - - 10000 -

Total 500000 66500

Fineness Modulus=66500100 = 665

Water Deionised water spiked with sodium carbonate and sodium bi-carbonate at different concentration is used in mixing water

3 Experimental System The following equipment is used for casting and testing of the specimens

i Cube and cylinder moulds ii 40T UTM (Universal Testing Machine) for cube compressive strength detennination iii Vicats apparatus including moulds confirming to IS 4031 (part 5)-1988 iv Cement concrete cubes and cylinders of M20 and M50 grade are casted with

water containing sodium carbonate and sodium bi-carbonate in the concentration of 1 2 4 610 and 15 giL in mixing water

Setting Time Vicats apparatus confirming IS 4031 (pant 5) 1988 consists of a frame to which a movable rod

having an indicator is attached which gives the penetration weighing 100gms and having diameter and length of 10 mm and 50 mm respectively Vicatss apparatus included three attachmentsshysquare needle for initial setting time plunger for determining normal consistency and needle with annular collar for final setting time

Compressive Strength The test specimens for the determination of compressive strength of concrete are prepared using the standard metallic cube moulds adopting IS procedure for the rodding and hard compactions

The cubes are demoulded after 24 hours of casting and cured in water having similar quality as used in the preparation of mix the cubes are tested for a compressive strength after 28 days and 90 days The compressive strength is computed as the average value of the three samples

Split Tensile Strength The test specimens for the determination of split tensile strength of concrete are prepared using the standards metallic cylinder moulds adopting IS procedure for the rodding and hard compaction The cylinders are demoulded after 24 hours of casting and cured in water having similar quality as used in the preparation of mix The cylinders are tested for split tensile strength test after 28 days and 90 days The split tensile strength is computed as the average value of the three samples

4 Results and Discussion The interpretation of results obtained in this investigation is based on the guidelines specified by IS 456 (2000)

The average of both the setting times of three cement samples prepared from water under consideration are compared with those of the cement specimens prepared from deionised water If

539

the difference is less than 30 minutes the change is considered to be negligible and if the difference is more than 30 minutes the change is considered to be significant

Average compressive strength and average split tensile strength of at least three specimens prepared with water under consideration is compared with that of three similar cases prepared with deionised water (Control) If the difference in the strength is less than 10 it is considered to be insignificant

Setting Time Test results of setting times of the test block made from different water samples and deionised water are reported in fig (1) amp (2)

From the fig 1 it is observed that both setting times are decreased with the increase in concentration of sodium carbonate of mixing water and from the fig 2 it is observed that both the setting times increased with the increase in concentration of sodium bi-carbonate in water Considerable decrease in both the initial and final setting times is observed when amount of sodium carbonate was 6 gil and 4 giL and the significant increase observed at 4 gil and 6 giL of sodium bishycarbonate in mixing water for both initial and final setting times respectively

o

-r-----------------~~==~

~ -~ (11111) 1-=-----~iIiii1iiltili1iiiiilI~_______~~=_1 0-0 )---- shy - ----shy

-~--shy

(hIHIII)

0

52fO

1shyf11M~t~Ht-t~r---~~~mI

to

o o 2 4 bull bull ~ tl ~ ~

CorwentTeIiOII Of 1iICO In gil

Fig 1Variation of Setting times of cement corresponding to various concentrations of Na~03 in deionised water

-

o

--~

f-o ----middot

1m (FInII)

I-=-- = 0 -shy bull

-

(1niIII)

JHGi t--tHt-__-It---L-JI-F~

5shy

i shylto J----__-J

I~ to

o 2 u u bull

~ttllIMHCO9iL

Fig 2variation of Setting times of cement corresponding to various concentrations of NaHC~ in deionised water

Compl888ive Strength Test results of the cubes prepared from water containing different salts are presented in fig 3

As indicated in fig3 the compressive strength of the specimens decrease with increase in concentration of sodium carbonate and sodium bi-carbonate of mixing water But the increase in compressive strength was considerable when the concentration sodium carbonate was 6 gil and 10 giL in mixing water for M20-90day M50-28dy 90day and M20-28day respectively and this

540

0 o~---------------------------

4

f - shy 1121)211__ M2OlaquoI -- - 11150-~ - ~

1= -

I --raquo

0 2 4 bullbull lOnu o Z 4 bull bull W 12 U ~

significant change observed at 10 giL and 15 giL of sodium bi-carbonate in mixing water for M20shy90c1ay M50-90day and M20-28dayM50-90day respectively

CoIlClllb d NIHCO1n ~eod PO1n tp

(a) (b) Fig 3Percentage Variation of compressive strength of concrete corresponding to

various concentrations of (a) Na2CQa (b) NaHC03 in deionised water

Tensile Strength Test results of the cylinders prepared from water containing acids are presented in fig 4

From fig4 the compressive strength of the specimens decreases with increase in concentration of sodium carbonate and sodium bi-carbonate of mixing water But the increase in compressive strength was considerable when the concentration sodium carbonate was 6 giL and 10 giL in mixing water for M20-9Oday M50-28dy 90c1ay and M20-28day respectively and this Significant change observed at 10 giL and 15 giL of sodium bi-carbonate in mixing water for M20-90day M50-90day and M20-28dayM50-90day respectively

I I)0 5middot12

-11fmiddot-11 -raquo

bull 2 4 bull bull ~ n u ~

C-bull _tupO~M~

___21

__ 1InO-IO bull MH-2tMyo

-I-N~

(a)

i middot1-4 t i 5

flO -12

-1-I 2 4 bull bull w u u bull

2

-Nzo21Nyo __an_ - -N50-~ ___ N_

c- olIUHCO MjJIL

(b)

Fig 4Percentage Variation of tensile strength of concrete corresponding to various concentrations of (a) Na2C03 (b) H2S04 in deionised water

5 Conclusions

Based on the present investigation the following conclusions can be drawn a Sodium carbonate when present in mixing water accelerates both the initial and final setting

times b Sodium bi-carbonate when present in mixing water retards both the initial and final setting

times c Sodium carbonate accelerates the initial and final setting times significantly at

concentrations of 6 giL and 4 gil respectively

541

Coarse aggregate Crushed Granite stone aggregate of maximum size 20 mm confirming to IS 383-1970 was used The specific gravity and fineness modulus were found to be 2622 and 665 respectively Test results are shown in Table 4

TABLE 4 Grading analysis for coarse Aggregate Sample-5000 gms

SLNO IS Sieve size

Weight Retained (gms)

Cumulative weight retained (gms)

Cumulative retained

passing

1 80mm - - - 10000 2 40mm - - - 10000 3 20mm 83000 83000 1660 8340 4 10mm 119000 202000 4040 5960 5 630mm 31000 233000 4660 3860 6 475mm 74000 307000 6140 5340 7 236mm 193000 500000 10000 -8 118 mm - - 10000 -9 600 microns - - 10000 -10 300 microns - - 10000 -11 150 microns - - 10000 -

Total 500000 66500

Fineness Modulus=66500100 = 665

Water Deionised water spiked with sodium carbonate and sodium bi-carbonate at different concentration is used in mixing water

3 Experimental System The following equipment is used for casting and testing of the specimens

i Cube and cylinder moulds ii 40T UTM (Universal Testing Machine) for cube compressive strength detennination iii Vicats apparatus including moulds confirming to IS 4031 (part 5)-1988 iv Cement concrete cubes and cylinders of M20 and M50 grade are casted with

water containing sodium carbonate and sodium bi-carbonate in the concentration of 1 2 4 610 and 15 giL in mixing water

Setting Time Vicats apparatus confirming IS 4031 (pant 5) 1988 consists of a frame to which a movable rod

having an indicator is attached which gives the penetration weighing 100gms and having diameter and length of 10 mm and 50 mm respectively Vicatss apparatus included three attachmentsshysquare needle for initial setting time plunger for determining normal consistency and needle with annular collar for final setting time

Compressive Strength The test specimens for the determination of compressive strength of concrete are prepared using the standard metallic cube moulds adopting IS procedure for the rodding and hard compactions

The cubes are demoulded after 24 hours of casting and cured in water having similar quality as used in the preparation of mix the cubes are tested for a compressive strength after 28 days and 90 days The compressive strength is computed as the average value of the three samples

Split Tensile Strength The test specimens for the determination of split tensile strength of concrete are prepared using the standards metallic cylinder moulds adopting IS procedure for the rodding and hard compaction The cylinders are demoulded after 24 hours of casting and cured in water having similar quality as used in the preparation of mix The cylinders are tested for split tensile strength test after 28 days and 90 days The split tensile strength is computed as the average value of the three samples

4 Results and Discussion The interpretation of results obtained in this investigation is based on the guidelines specified by IS 456 (2000)

The average of both the setting times of three cement samples prepared from water under consideration are compared with those of the cement specimens prepared from deionised water If

539

the difference is less than 30 minutes the change is considered to be negligible and if the difference is more than 30 minutes the change is considered to be significant

Average compressive strength and average split tensile strength of at least three specimens prepared with water under consideration is compared with that of three similar cases prepared with deionised water (Control) If the difference in the strength is less than 10 it is considered to be insignificant

Setting Time Test results of setting times of the test block made from different water samples and deionised water are reported in fig (1) amp (2)

From the fig 1 it is observed that both setting times are decreased with the increase in concentration of sodium carbonate of mixing water and from the fig 2 it is observed that both the setting times increased with the increase in concentration of sodium bi-carbonate in water Considerable decrease in both the initial and final setting times is observed when amount of sodium carbonate was 6 gil and 4 giL and the significant increase observed at 4 gil and 6 giL of sodium bishycarbonate in mixing water for both initial and final setting times respectively

o

-r-----------------~~==~

~ -~ (11111) 1-=-----~iIiii1iiltili1iiiiilI~_______~~=_1 0-0 )---- shy - ----shy

-~--shy

(hIHIII)

0

52fO

1shyf11M~t~Ht-t~r---~~~mI

to

o o 2 4 bull bull ~ tl ~ ~

CorwentTeIiOII Of 1iICO In gil

Fig 1Variation of Setting times of cement corresponding to various concentrations of Na~03 in deionised water

-

o

--~

f-o ----middot

1m (FInII)

I-=-- = 0 -shy bull

-

(1niIII)

JHGi t--tHt-__-It---L-JI-F~

5shy

i shylto J----__-J

I~ to

o 2 u u bull

~ttllIMHCO9iL

Fig 2variation of Setting times of cement corresponding to various concentrations of NaHC~ in deionised water

Compl888ive Strength Test results of the cubes prepared from water containing different salts are presented in fig 3

As indicated in fig3 the compressive strength of the specimens decrease with increase in concentration of sodium carbonate and sodium bi-carbonate of mixing water But the increase in compressive strength was considerable when the concentration sodium carbonate was 6 gil and 10 giL in mixing water for M20-90day M50-28dy 90day and M20-28day respectively and this

540

0 o~---------------------------

4

f - shy 1121)211__ M2OlaquoI -- - 11150-~ - ~

1= -

I --raquo

0 2 4 bullbull lOnu o Z 4 bull bull W 12 U ~

significant change observed at 10 giL and 15 giL of sodium bi-carbonate in mixing water for M20shy90c1ay M50-90day and M20-28dayM50-90day respectively

CoIlClllb d NIHCO1n ~eod PO1n tp

(a) (b) Fig 3Percentage Variation of compressive strength of concrete corresponding to

various concentrations of (a) Na2CQa (b) NaHC03 in deionised water

Tensile Strength Test results of the cylinders prepared from water containing acids are presented in fig 4

From fig4 the compressive strength of the specimens decreases with increase in concentration of sodium carbonate and sodium bi-carbonate of mixing water But the increase in compressive strength was considerable when the concentration sodium carbonate was 6 giL and 10 giL in mixing water for M20-9Oday M50-28dy 90c1ay and M20-28day respectively and this Significant change observed at 10 giL and 15 giL of sodium bi-carbonate in mixing water for M20-90day M50-90day and M20-28dayM50-90day respectively

I I)0 5middot12

-11fmiddot-11 -raquo

bull 2 4 bull bull ~ n u ~

C-bull _tupO~M~

___21

__ 1InO-IO bull MH-2tMyo

-I-N~

(a)

i middot1-4 t i 5

flO -12

-1-I 2 4 bull bull w u u bull

2

-Nzo21Nyo __an_ - -N50-~ ___ N_

c- olIUHCO MjJIL

(b)

Fig 4Percentage Variation of tensile strength of concrete corresponding to various concentrations of (a) Na2C03 (b) H2S04 in deionised water

5 Conclusions

Based on the present investigation the following conclusions can be drawn a Sodium carbonate when present in mixing water accelerates both the initial and final setting

times b Sodium bi-carbonate when present in mixing water retards both the initial and final setting

times c Sodium carbonate accelerates the initial and final setting times significantly at

concentrations of 6 giL and 4 gil respectively

541

the difference is less than 30 minutes the change is considered to be negligible and if the difference is more than 30 minutes the change is considered to be significant

Average compressive strength and average split tensile strength of at least three specimens prepared with water under consideration is compared with that of three similar cases prepared with deionised water (Control) If the difference in the strength is less than 10 it is considered to be insignificant

Setting Time Test results of setting times of the test block made from different water samples and deionised water are reported in fig (1) amp (2)

From the fig 1 it is observed that both setting times are decreased with the increase in concentration of sodium carbonate of mixing water and from the fig 2 it is observed that both the setting times increased with the increase in concentration of sodium bi-carbonate in water Considerable decrease in both the initial and final setting times is observed when amount of sodium carbonate was 6 gil and 4 giL and the significant increase observed at 4 gil and 6 giL of sodium bishycarbonate in mixing water for both initial and final setting times respectively

o

-r-----------------~~==~

~ -~ (11111) 1-=-----~iIiii1iiltili1iiiiilI~_______~~=_1 0-0 )---- shy - ----shy

-~--shy

(hIHIII)

0

52fO

1shyf11M~t~Ht-t~r---~~~mI

to

o o 2 4 bull bull ~ tl ~ ~

CorwentTeIiOII Of 1iICO In gil

Fig 1Variation of Setting times of cement corresponding to various concentrations of Na~03 in deionised water

-

o

--~

f-o ----middot

1m (FInII)

I-=-- = 0 -shy bull

-

(1niIII)

JHGi t--tHt-__-It---L-JI-F~

5shy

i shylto J----__-J

I~ to

o 2 u u bull

~ttllIMHCO9iL

Fig 2variation of Setting times of cement corresponding to various concentrations of NaHC~ in deionised water

Compl888ive Strength Test results of the cubes prepared from water containing different salts are presented in fig 3

As indicated in fig3 the compressive strength of the specimens decrease with increase in concentration of sodium carbonate and sodium bi-carbonate of mixing water But the increase in compressive strength was considerable when the concentration sodium carbonate was 6 gil and 10 giL in mixing water for M20-90day M50-28dy 90day and M20-28day respectively and this

540

0 o~---------------------------

4

f - shy 1121)211__ M2OlaquoI -- - 11150-~ - ~

1= -

I --raquo

0 2 4 bullbull lOnu o Z 4 bull bull W 12 U ~

significant change observed at 10 giL and 15 giL of sodium bi-carbonate in mixing water for M20shy90c1ay M50-90day and M20-28dayM50-90day respectively

CoIlClllb d NIHCO1n ~eod PO1n tp

(a) (b) Fig 3Percentage Variation of compressive strength of concrete corresponding to

various concentrations of (a) Na2CQa (b) NaHC03 in deionised water

Tensile Strength Test results of the cylinders prepared from water containing acids are presented in fig 4

From fig4 the compressive strength of the specimens decreases with increase in concentration of sodium carbonate and sodium bi-carbonate of mixing water But the increase in compressive strength was considerable when the concentration sodium carbonate was 6 giL and 10 giL in mixing water for M20-9Oday M50-28dy 90c1ay and M20-28day respectively and this Significant change observed at 10 giL and 15 giL of sodium bi-carbonate in mixing water for M20-90day M50-90day and M20-28dayM50-90day respectively

I I)0 5middot12

-11fmiddot-11 -raquo

bull 2 4 bull bull ~ n u ~

C-bull _tupO~M~

___21

__ 1InO-IO bull MH-2tMyo

-I-N~

(a)

i middot1-4 t i 5

flO -12

-1-I 2 4 bull bull w u u bull

2

-Nzo21Nyo __an_ - -N50-~ ___ N_

c- olIUHCO MjJIL

(b)

Fig 4Percentage Variation of tensile strength of concrete corresponding to various concentrations of (a) Na2C03 (b) H2S04 in deionised water

5 Conclusions

Based on the present investigation the following conclusions can be drawn a Sodium carbonate when present in mixing water accelerates both the initial and final setting

times b Sodium bi-carbonate when present in mixing water retards both the initial and final setting

times c Sodium carbonate accelerates the initial and final setting times significantly at

concentrations of 6 giL and 4 gil respectively

541

0 o~---------------------------

4

f - shy 1121)211__ M2OlaquoI -- - 11150-~ - ~

1= -

I --raquo

0 2 4 bullbull lOnu o Z 4 bull bull W 12 U ~

significant change observed at 10 giL and 15 giL of sodium bi-carbonate in mixing water for M20shy90c1ay M50-90day and M20-28dayM50-90day respectively

CoIlClllb d NIHCO1n ~eod PO1n tp

(a) (b) Fig 3Percentage Variation of compressive strength of concrete corresponding to

various concentrations of (a) Na2CQa (b) NaHC03 in deionised water

Tensile Strength Test results of the cylinders prepared from water containing acids are presented in fig 4

From fig4 the compressive strength of the specimens decreases with increase in concentration of sodium carbonate and sodium bi-carbonate of mixing water But the increase in compressive strength was considerable when the concentration sodium carbonate was 6 giL and 10 giL in mixing water for M20-9Oday M50-28dy 90c1ay and M20-28day respectively and this Significant change observed at 10 giL and 15 giL of sodium bi-carbonate in mixing water for M20-90day M50-90day and M20-28dayM50-90day respectively

I I)0 5middot12

-11fmiddot-11 -raquo

bull 2 4 bull bull ~ n u ~

C-bull _tupO~M~

___21

__ 1InO-IO bull MH-2tMyo

-I-N~

(a)

i middot1-4 t i 5

flO -12

-1-I 2 4 bull bull w u u bull

2

-Nzo21Nyo __an_ - -N50-~ ___ N_

c- olIUHCO MjJIL

(b)

Fig 4Percentage Variation of tensile strength of concrete corresponding to various concentrations of (a) Na2C03 (b) H2S04 in deionised water

5 Conclusions

Based on the present investigation the following conclusions can be drawn a Sodium carbonate when present in mixing water accelerates both the initial and final setting

times b Sodium bi-carbonate when present in mixing water retards both the initial and final setting

times c Sodium carbonate accelerates the initial and final setting times significantly at

concentrations of 6 giL and 4 gil respectively

541

d Sodium bi-carbonate retards the initial and final setting times significantly at concentrations of 4 giL and 6 giL respectively

e Sodium carbonate and sodium bi-carbonate when present in mixing water decreases the development of compressive and tensile strength

f Sodium carbonate decreases the compressive and tensile strength significantly at concentrations of 6 giL

g Sodium bi-carbonate decreases the compressive and tensile strength significantly at concentrations of 10 giL

6 References

i IS 4562000 Code of Practice for Plain and Reinforced Concrete ii IS 383 1970 Specification of Coarse and Fine Aggregates from Natural Sources for

Concrete (Second revision) iii IS 4031 968 Methods a Physical Tests for Hydraulic Cement iv Lea FM (1956) The Chemistry of Cement and Concrete Edward Arnold (Publ) Ltd v Neville AM (1970) Properties of Concrete The English Language Book Society Pitaru

Publishers vi Price WH(1951) Factors influencing concrete strength A CI Vol 47 pp 417

542