ACCELERATING ADMIXTURE RAPIDITE -ITS EFFECT ON PROPERTIES OF CONCRETE

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http://www.iaeme.com/IJCIET/issues.asp?JType=IJCIET&VType=6&IType=12 ISSN Print: 0976-6308 and ISSN Online: 0976-6316

ACCELERATING ADMIXTURE

“RAPIDITE”-ITS EFFECT ON PROPERTIES

OF CONCRETE

Dr. Javed Ahmed Naqash

Associate Professor, National Institute of Technology Srinagar, J&K, India

Ifrah Habib Lone, Amir Majid, Bisma Gayas, Itret Hussaini, Mubashir Hassan

Department of Civil Engineering, University of Kashmir, J&K India

ABSTRACT

This paper aims to investigate the effect of use of Rapidite in cold weather

concreting. In order to illustrate such effect, a series of laboratory tests were

conducted. Workability tests, compressive strength tests, flexural tests and

split tensile strength tests were carried out on concrete specimens having

different percentage of Rapidite and the results thus obtained were compared

with those of normal concrete. The results indicated that all the three strength

parameters viz, compressive strength, split tensile strength and flexural tensile

strength of concrete increase when compared with plain one. The increase in

strength reaches the maximum value at the Rapidite percentage of 1.5%,

beyond which it starts decreasing. The increase in 7 day strength is much

higher than increase in 28 day strength. Further adding Rapidte has shown

increase in the workability of mix with respect to the plain mix.

Key words: Rapidite, Workability, Compressive Strength, Flexural Strength

and Split Tensile Strength.

Cite this Article: Dr. Javed Ahmed Naqash, Ifrah Habib Lone, Amir Majid,

Bisma Gayas, Itret Hussaini and Mubashir Hassan, Accelerating Admixture

“Rapidite”-Its Effect on Properties of Concrete. International Journal of Civil

Engineering and Technology, 6(12), 2015, pp. 58-65.

http://www.iaeme.com/IJCIET/issues.asp?JType=IJCIET&VType=6&IType=12

1. INTRODUCTION

Rapidite is a specially developed Concrete Set Accelerator, a ready-to-use, liquid

admixture. It accelerates initial setting time (cement-water chemical reaction

HYDRATION) of normal mortar and concrete and acts as anti-freeze within cement

concrete. It improves workability and strength while fastening the hydration of

cement. It makes the mix easier to place and speeds construction by shortening the

initial set and curing time. Time and labor are saved, because forms and other

protection can be removed earlier and finishing can be started. Rapidite is

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recommended for use during cool and cold weather to accelerate the set time and

reduce the risk of frozen mortar and concrete mixes.

Winter has some peculiarities that affect construction in general and concreting in

particular. Its duration is different in different parts of globe, but cold weather with

white frosts may also happen in spring and autumn not just in winter only. In India

certain regions experience sub-zero temperatures in winter. Concrete structures in

such regions undergo cycles of freezing and thawing and their durability is affected

due to frost action. Fresh concrete contains considerable quantity of fresh water which

gets converted into ice lenses at freezing temperature. The ice formation in fresh

concrete results in about 9% rise in volume and causes permanent damage to concrete

and structural integrity cannot be recovered even if the concrete is made to harden

later at high temperature. Thus, in winters, especially in Kashmir where the

temperatures are below zero degree in winters some admixtures need to be added to

nullify the effects of cold temperature on the strength of concrete. Rapidte is a

commonly used admixture in Kashmir during winter to accelerate the strength gain of

concrete.

2. MATERIALS USED

Cement

Ordinary Portland Cement (OPC) 43 Grade (Khyber cement) confining to IS: 4031[4]

has been used for this Work. The properties of the used cement are shown;

Aggregates:

Fine aggregates used throughout the work comprised of clean river sand with

maximum size of 4.75mm conforming to zone III as per IS:383-1970 [5] Coarse

aggregates used consisted of machine crushed stone angular in shape passing through

20mm I S sieve and retained on 4.75mm I S sieve .

Rapidite

Properties

Color- Lemon-Orange

Appearance-Clear bright Liquid

Relative Density (g/ml)-1g/ml

3. EXPERIMENTAL PROGRAM

Mix Used: Nominal mix M20 (1:1.5: 3) with water to cement ratio of 0.5.

In total five castings were done at the Rapidite percentage of 0.75, 1.25, 1.5, 1.75

and 2

Fineness % Standard Consistency (%) Initial Setting Time Final Setting Time Soundness (mm) Compressive strength(N/mm2) 2.3 28 1 hr. 22 min 6 hrs.10 min 2 38

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First Casting

Average Temp: 1.3

0

C

Percentage of Rapidite by weight of cement = .75%

Compressive Strength (σ

c

)

Cube size(mm)

7 Days Strength 28 Days Strength

Strength (N/mm2) Average Strength

(N/mm2) Strength (N/mm 2 ) Average Strength (N/mm2) P.C.C C.C with Rapidite P.C.C C.C with Rapidite P.C.C C.C with Rapidite P.C.C C.C with Rapidite 150 15.8 16.8 15.9 16.8 20.4 21.3 20.85 21.85 150 16 16.8 21.3 22.4 100 12.5 13.7 13.3 14.75 21.2 23.5 21.9 23.5 100 14.2 15.8 22.6 23.5

Split Tensile Strength (σ

t

) and Flexural Strength (σ

b

)

Type of concrete (σt) (N/mm2) (σb) (N/mm2) Slump Compaction factor PCC 2.49 3.12 10mm .72 CC with Rapidite 2.57 3.35 20mm .77

Second Casting

Average Temp: 2

0

C

Percentage of Rapidite by weight of cement = 1.25%

Compressive Strength (σ

c

)

(N/mm2) Strength (N/mm 2 ) Average Strength (N/mm2) P.C.C C.C with Rapidite P.C.C C.C with Rapidite P.C.C C.C with Rapidite P.C.C C.C with Rapidite 150 14 15 13.3 15 22.4 24 21.8 23.2 150 12.6 15 21.3 22.4 100 13 18 13.4 16.15 22.2 24.5 22.8 25.7 100 13.7 14.3 23.3 26.9

Split Tensile Strength (σ

t

) and Flexural Strength (σ

b

)

Type of concrete Split tensile strength (N/mm2) Flexural strength (N/mm2) Slump Compaction factor PCC 2.43 3.31 15mm .74 CC with Rapidite 2.67 3.67 26mm .81

Third Casting Average Temp: 1.5

0

C

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Compressive Strength (σ

c

)

(N/mm2) Strength (N/mm 2 ) Average Strength (N/mm2) P.C.C C.C with Rapidite P.C.C C.C with Rapidite P.C.C C.C with Rapidite P.C.C C.C with Rapidite 150 10.3 16.2 10.5 16 20.7 28.69 21.1 29.2 150 10.8 15.8 21.6 29.7 100 11.3 17 11.3 16.7 21.8 26.78 21.15 28.23 100 11.3 16.4 21.2 29.68

Split Tensile Strength (σ

t

) and Flexural Strength (σ

b

)

Type of concrete

σ

t (N/mm2)

σ

b (N/mm2) Slump Compaction factor PCC 2.24 3.02 10mm .77 CC with Rapidite 2.92 3.65 50mm .86

Fourth Casting

Average Temp:-1

0

C

Percentage of Rapidite by weight of cement = 1.75 %

Compressive Strength (σ

c

)

Strength (N/mm2) Average Strength (N/mm2) Strength (N/mm2) Average Strength (N/mm2) P.C.C C.C with Rapidite P.C.C C.C with Rapidite P.C.C C.C with Rapidite P.C.C C.C with Rapidite 150 14.4 11.29 14.6 11.6 26 21.2 26.4 20.72 150 14.8 11.9 26.7 20.24 100 14.2 13.3 14.5 12.65 28 22.8 26.5 22.95 100 14.9 12 25 23.1

Split Tensile Strength (σ

t

) and Flexural Strength (σ

b

)

σ

t (N/mm2)

σ

b

(N/mm2) Slump Compaction factor

PCC 1.91 4.08 20mm .75

CC with Rapidite 1.75 3.84 50mm .88

Fifth Casting

Average Temp:-1.2

0

C

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Compressive Strength (σ

c

)

Strength (N/mm2) Average Strength (N/mm2) Strength (N/mm2) Average Strength (N/mm2) P.C.C C.C with Rapidite P.C.C C.C with Rapidite P.C.C C.C with Rapidite P.C.C C.C with Rapidite 150 12.73 11.35 13.13 11.31 23.5 20.4 23.95 20.05 150 13.53 11.26 24.4 19.7 100 12.3 10.7 12.3 10.85 20.4 22 23.7 21 100 12.3 11 27 20

Split Tensile Strength (σ

t

) and Flexural Strength (σ

b

)

σ

t (N/mm2)

σ

b (N/mm2) Slump Compaction factor PCC 1.86 4.42 12mm .73 CC with Rapidite 1.68 4.02 55mm .88

4. DISCUSSION

In order to study the rate of variation of strength with respect to the Rapidite

percentage, a comparative study of the test results achieved at different Rapidite

percentage is performed.

Following Variations are studied

 Variation of increase in 7 day strength with Rapidite %

 Variation of Increase in 28 day strength with Rapidite %

 Variation of split and flexural tensile strength with Rapidite %

 Comparison of Avg. Increase in 7 and 28 day strength for 150mm cube

 Comparison of Avg. Increase in 7 and 28 day strength for 100mm cube

 Variation of compaction factor on adding Rapidite.

Average increase in 7 days and 28days strength (%age)

Percentage of Rapidite

Average % increase 7 days strength Average % increase in 28 days strength 150mm cube 100mm cube 150mm cube 100mm cube 0.75 5.66 10.40 5 7.3 1.25 12.78 21 6.17 13 1.5 51.94 47.78 38.26 31 1.75 -20.27 -13.1 -21.46 -13.4 2 -13.86 -11.78 -16.28 -11.4

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G1: Variation of 7 day strength with Rapidite %

G2: Variation of 28 day strength with Rapidite %

The increase in 7 day strength is much higher than increase in 28 day strength, in case

of 150mm cubes former is 180% more increase and in case of 100mm cubes former

shows 214% more increase. Thus increase in early strength is more significant than

increase in lateral strength

Average increase in Split tensile strength (σ

t

) and Flexural strength (σ

b

)

Percentage of Rapidite

Average percentage increase in Split tensile

strength

Average percentage increase in Flexural strength 0.75 3.2 7.37 1.25 9.8 10.87 1.5 30.35 20.86 1.75 -8.3 -5.88 2 -9.69 -9 0 5 10 15 20 0.75 1.25 1.5 1.75 2 C om p re ssi ve S tr e n gt h %age of Rapidite

Avg 7 day strength of P.C.C OF 100mm cube Avg 7 day strength of C.C with rapidite OF 100mm cube Avg 7 day strength of P.C.C OF 150mm cube 0 10 20 30 40 0.75 1.25 1.5 1.75 2 C om p re ssi ve S tr e n gt h %age of Rapidite

Avg 28 day strength of P.C.C OF 100mm cube

Avg 28 day strength of C.C with rapidite OF 100mm cube Avg 28 day strength of P.C.C OF 150mm cube

Avg 28 day strength of C.C with rapidite OF 150mm cube G2:Variation of 28 day strength with Rapidite %

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G3: Variation of split tensile strength with Rapidite %

G4: Variation of Flexural strength with Rapidite %

There is an increase in both split and flexural tensile strengths up to the 1.5% of

rapidite, beyond this value the strength decreases in both the cases.

G5: Variation of Compaction factor with Rapidite %

The compaction factor always increases when compared with the plain concrete, thus

workability increases by the addition of rapidite.

-15 -10 -5 0 5 10 15 20 25 0 0.5 1 1.5 2 2.5

Avg %age increase in flexural strength 0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1 0.75 1.25 1.5 1.75 2 P.C.C. -20 -10 0 10 20 30 40 0 0.5 1 1.5 2 2.5

Avg %age increase in split tensile strength

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5. CONCLUSION

 The use of admixture Rapidite increases the compressive, flexural and split tensile strength of concrete compared to plain concrete. The increase in strength reaches the maximum value at the Rapidite percentage of 1.5%, beyond which it starts decreasing.

 The increase in 7 day strength is much higher than increase in 28 day strength, in case of 150mm cubes former is 180% more increase and in case of 100mm cubes former shows 214% more increase. Thus increase in early strength is more significant than increase in lateral strength

 There was no freezing of water as there is increase in early strength of concrete so whole water was available for complete hydration of cement. The admixture used is an anti freezing agent which depressed the freezing point of water mixed and protected the concrete from freezing in early age.

 The compaction factor always increases when compared with the plain concrete, thus workability increases by the addition of Rapidite.

REFERENCES

[1] Cold weather concreting, reported by ACI committee 306, Nicholas J. Carino, Chairman, p. 306 R-1.

[2] Annual book of ASTM Standards (1979), part 13, ASTM C 191 – 77: Standard test method for time of setting of hydraulic cement. ASTM RaceSt. Philadelphia,pa. 19103.

[3] Concrete Technology, A. M. Neville and J. J. Brooks.

[4] 43 Grade Ordinary Portland Cement – Specification. IS 8112:1989, Bureau of Indian Standards, New Delhi.

[5] Specification for Coarse and Fine Aggregates from Natural Sources for Concrete. IS: 383-1970, Bureau of Indian Standards, New Delhi.

[6] Recommended Guidelines for Concrete Mix Design. IS: 10262-1982, Bureau of Indian Standards, New Delhi.

[7] Sameer Ul Bashir, Younis Majid and Ubair Muzzaffer Rather, Effect of Rapidite on Strength of Concrete in Warm Climates. International Journal of Civil Engineering and Technology, 4(6), 2013, pp. 126 - 133.

[8] Concrete Technology, A. M. Neville and J. J. Brooks. [9] Concrete Technology, A. M. Neville and J. J. Brooks, p. 166

[10] Methods of Sampling and Analysis of Concrete. IS: 1199-1959, Bureau of Indian Standards, New Delhi.

[11] Methods of Tests for Strength of Concrete. IS: 516-1959, Bureau of Indian Standards, New Delhi.

[13] Sameer Ul Bashir, Shabbir Ahmad Parray and Syed Rizwan Shah, Harmful Effects of Rapidite on Strength of Concrete. International Journal of Civil Engineering and Technology, 4(6), 2013, pp. 116 - 125.

[14] Splitting Tensile Strength of concrete – Methods of test. IS 5816:1999.